Power Point Lecture Slides prepared by Meg Flemming

Chapter 8 Learning Outcomes • 8 -1 • Describe the anatomical and functional divisions of the nervous system. • 8 -2 • Distinguish between neurons and neuroglia on the basis of structure and function. • 8 -3 • Describe the events involved in the generation and propagation of an action potential. • 8 -4 • Describe the structure of a synapse, and explain the mechanism of nerve impulse transmission at a synapse. • 8 -5 • Describe three meningeal layers that surround the central nervous system. © 2013 Pearson Education, Inc.

Chapter 8 Learning Outcomes • 8 -6 • Discuss the roles of gray matter and white matter in the spinal cord. • 8 -7 • Name the major regions of the brain, and describe the locations and functions of each. • 8 -8 • Name the cranial nerves, relate each pair of cranial nerves to its principal functions, and relate the distribution pattern of spinal nerves to the regions they innervate. • 8 -9 • Describe the steps in a reflex arc. • 8 -10 • Identify the principal sensory and motor pathways, and explain how it is possible to distinguish among sensations that originate in different areas of the body. © 2013 Pearson Education, Inc.

Chapter 8 Learning Outcomes • 8 -11 • Describe the structures and functions of the sympathetic and parasympathetic divisions of the autonomic nervous system. • 8 -12 • Summarize the effects of aging on the nervous system. • 8 -13 • Give examples of interactions between the nervous system and other organ systems. © 2013 Pearson Education, Inc.

The Nervous System and the Endocrine System (Introduction) • The nervous system and endocrine system coordinate other organ systems to maintain homeostasis • The nervous system is fast, short acting • The endocrine system is slower, but longer lasting • The nervous system is the most complex system in the body © 2013 Pearson Education, Inc.

Functions of the Nervous System (8 -1) • Monitors the body's internal and external environments • Integrates sensory information • Coordinates voluntary and involuntary responses © 2013 Pearson Education, Inc.

Divisions of the Nervous System (8 -1) • Anatomical divisions are: • The central nervous system (CNS) • Made up of the brain and spinal cord • Integrates and coordinates input and output • The peripheral nervous system (PNS) • All the neural tissues outside of the CNS • The connection between the CNS and the organs © 2013 Pearson Education, Inc.

Divisions of the Nervous System (8 -1) • Functional divisions are: • The afferent division • Includes sensory receptors and neurons that send information to the CNS • The efferent division • Includes neurons that send information to the effectors, which are the muscles and glands © 2013 Pearson Education, Inc.

Efferent Division of the Nervous System (8 -1) • Further divided into: • The somatic nervous system (SNS) • Controls skeletal muscle • The autonomic nervous system (ANS) • Controls smooth and cardiac muscle, and glands • Has two parts 1. Sympathetic division 2. Parasympathetic division © 2013 Pearson Education, Inc.

Figure 8 -1 A Functional Overview of the Nervous System. CENTRAL NERVOUS SYSTEM Information processing PERIPHERAL Sensory information NERVOUS within SYSTEM afferent division Motor commands within efferent division includes Somatic nervous system Autonomic nervous system Parasympathetic Sympathetic division Receptors Somatic sensory Visceral sensory receptors (monitor internal conditions the outside world and the status and our position in it) of other organ systems) © 2013 Pearson Education, Inc. Effectors Skeletal muscle Smooth muscle Cardiac muscle Glands

Checkpoint (8 -1) 1. Identify the two anatomical divisions of the nervous system. 2. Identify the two functional divisions of the peripheral nervous system, and describe their primary functions. 3. What would be the effect of damage to the afferent division of the PNS? © 2013 Pearson Education, Inc.

Neurons (8 -2) • Cells that communicate with one another and other cells • Basic structure of a neuron includes: • Cell body • Dendrites • Which receive signals • Axons • Which carry signals to the next cell • Axon terminals • Bulb-shaped endings that form a synapse with the next cell © 2013 Pearson Education, Inc.

Neurons (8 -2) • Have a very limited ability to regenerate when damaged or destroyed • Cell bodies contain: • Mitochondria, free and fixed ribosomes, and rough endoplasmic reticulum • Free ribosomes and RER form Nissl bodies and give the tissue a gray color (gray matter) • The axon hillock • Where electrical signal begins © 2013 Pearson Education, Inc.

Figure 8 -2 The Anatomy of a Representative Neuron. Cell body Mitochondrion Golgi apparatus Axon hillock Dendrite Axon terminals Collateral Nucleus Axon (may be myelinated) Nucleolus Nerve cell body Nucleolus Nucleus Axon hillock Nissl bodies Nerve cell body LM x 1500 © 2013 Pearson Education, Inc.

Structural Classification of Neurons (8 -2) • Based on the relationship of the dendrites to the cell body • Multipolar neurons • Are the most common in the CNS and have two or more dendrites and one axon • Unipolar neurons • Have the cell body off to one side, most abundant in the afferent division • Bipolar neurons • Have one dendrite and one axon with the cell body in the middle, and are rare © 2013 Pearson Education, Inc.

Figure 8 -3 A Structural Classification of Neurons. Multipolar neuron Unipolar neuron Bipolar neuron

Sensory Neurons (8 -2) • Also called afferent neurons • Total 10 million or more • Receive information from sensory receptors • Somatic sensory receptors • Detect stimuli concerning the outside world, in the form of external receptors • And our position in it, in the form of proprioceptors • Visceral or internal receptors • Monitor the internal organs © 2013 Pearson Education, Inc.

Motor Neurons (8 -2) • Also called efferent neurons • Total about half a million in number • Carry information to peripheral targets called effectors • Somatic motor neurons • Innervate skeletal muscle • Visceral motor neurons • Innervate cardiac muscle, smooth muscle, and glands © 2013 Pearson Education, Inc.

Interneurons (8 -2) • Also called association neurons • By far the most numerous type at about 20 billion • Are located in the CNS • Function as links between sensory and motor processes • Have higher functions • Such as memory, planning, and learning © 2013 Pearson Education, Inc.

Neuroglial Cells (8 -2) • Are supportive cells and make up about half of all neural tissue • Four types are found in the CNS 1. Astrocytes 2. Oligodendrocytes 3. Microglia 4. Ependymal cells • Two types in the PNS 1. Satellite cells 2. Schwann cells © 2013 Pearson Education, Inc.

Astrocytes (8 -2) • Large and numerous neuroglia in the CNS • Maintain the

Oligodendrocytes (8 -2) • Found in the CNS • Produce an insulating membranous wrapping around axons called myelin • Small gaps between the wrappings called nodes of Ranvier • Myelinated axons constitute the white matter of the CNS • Where cell bodies are gray matter • Some axons are unmyelinated © 2013 Pearson Education, Inc.

Microglia (8 -2) • The smallest and least numerous • Phagocytic cells derived from white blood cells • Perform essential protective functions such as engulfing pathogens and cellular waste © 2013 Pearson Education, Inc.

Ependymal Cells (8 -2) • Line the fluid-filled central canal of the spinal cord and the ventricles of the brain • The endothelial lining is called the ependyma • It is involved in producing and circulating cerebrospinal fluid around the CNS © 2013 Pearson Education, Inc.

Figure 8 -4 Neuroglia in the CNS. Gray matter White matter CENTRAL CANAL Ependymal cells Gray matter Neurons Myelinated axons Microglial cell Internode White matter Myelin (cut) Axon Node Astrocyte Oligodendrocyte Capillary © 2013 Pearson Education, Inc. Basement membrane

Neuroglial Cells in PNS (8 -2) • Satellite cells • Surround and support neuron cell bodies • Similar in function to the astrocytes in the CNS • Schwann cells • Cover every axon in PNS • The surface is the neurilemma • Produce myelin © 2013 Pearson Education, Inc.

Figure 8 -5 Schwann Cells and Peripheral Axons. Nodes Schwann cell nucleus Myelin covering internode Neurilemma Axons Schwann cell nucleus Myelinated axon TEM x 14, 048 A myelinated axon in the PNS is covered by several Schwann cells, each of which forms a myelin sheath around a portion of the axon. This arrangement differs from the way myelin forms in the CNS; compare with Figure 8 -4. © 2013 Pearson Education, Inc. Unmyelinated TEM x 14, 048 axon A single Schwann cell can encircle several unmyelinated axons. Every axon in the PNS is completely enclosed by Schwann cells.

Organization of the Nervous System (8 -2) • In the PNS: • Collections of nerve cell bodies are ganglia • Bundled axons are nerves • Including spinal nerves and cranial nerves • Can have both sensory and motor components © 2013 Pearson Education, Inc.

Organization of the Nervous System (8 -2) • In the CNS: • Collections of neuron cell bodies are found in centers, or nuclei • Neural cortex is a thick layer of gray matter • White matter in the CNS is formed by bundles of axons called tracts, and in the spinal cord, form columns • Pathways are either sensory or ascending tracts, or motor or descending tracts © 2013 Pearson Education, Inc.

Figure 8 -6 The Anatomical Organization of the Nervous System. CENTRAL NERVOUS SYSTEM GRAY MATTER ORGANIZATION PERIPHERAL NERVOUS SYSTEM GRAY MATTER Ganglia Collections of neuron cell bodies in the PNS WHITE MATTER Nerves Bundles of axons in the PNS RECEPTORS Neural Cortex Gray matter on the surface of the brain Nuclei Collections of Higher Centers neuron cell The most complex bodies in the centers in the interior of the brain CNS WHITE MATTER ORGANIZATION Tracts Columns Bundles of CNS axons that share a common origin, destination, and function Several tracts that form an anatomically distinct mass PATHWAYS Centers and tracts that connect the brain with other organs and EFFECTORS systems in the body Ascending (sensory) pathway Descending (motor) pathway © 2013 Pearson Education, Inc. Centers Collections of neuron cell bodies in the CNS; each center has specific processing functions

Checkpoint (8 -2) 4. Name the structural components of a typical neuron. 5. Examination of a tissue sample reveals unipolar neurons. Are these more likely to be sensory neurons or motor neurons? 6. Identify the neuroglia of the central nervous system. 7. Which type of glial cell would increase in number in the brain tissue of a person with a CNS infection? 8. In the PNS, neuron cell bodies are located in ____ and surrounded by neuroglial cells called ____ cells. © 2013 Pearson Education, Inc.

The Membrane Potential (8 -3) • A membrane potential exists because of: • Excessive positive ionic charges on the outside of the cell • Excessive negative charges on the inside, creating a polarized membrane • An undisturbed cell has a resting membrane potential measured in the inside of the cell in millivolts • The resting membrane potential of neurons is – 70 m. V © 2013 Pearson Education, Inc.

Factors Determining Membrane Potential (8 -3) • Extracellular fluid (ECF) is high in Na+ and CI– • Intracellular fluid (ICF) is high in K+ and negatively charged proteins (Pr –) • Proteins are non-permeating, staying in the ICF • Some ion channels are always open • Called leak channels • Some are open or closed • Called gated channels © 2013 Pearson Education, Inc.

Factors Determining Membrane Potential (8 -3) • Na+ can leak in • But the membrane is more permeable to K+ • Allowing K+ to leak out faster • Na+/K+ exchange pump exchanges 3 Na+ for every 2 K+ • Moving Na+ out as fast as it leaks in • Cell experiences a net loss of positive ions • Resulting in a resting membrane charge of – 70 m. V © 2013 Pearson Education, Inc.

Figure 8 -7 The Resting Potential Is the Membrane Potential of an Undisturbed Cell. EXTRACELLULAR FLUID – 70 – 30 0 +30 m. V Na+ leak channel K+ leak channel Sodium– potassium exchange pump Plasma membrane CYTOSOL Protein KEY Sodium ion (Na+) Protein Potassium ion (K+) Chloride ion (Cl–) © 2013 Pearson Education, Inc.

Changes in Membrane Potential (8 -3) • Stimuli alter membrane permeability to Na+ or K+ • Or alter activity of the exchange pump • Types include: • Cellular exposure to chemicals • Mechanical pressure • Temperature changes • Changes in the ECF ion concentration • Result is opening of a gated channel • Increasing the movement of ions across the membrane © 2013 Pearson Education, Inc.

Changes in Membrane Potential (8 -3) • Opening of Na+ channels results in an influx of Na+ • Moving the membrane toward 0 m. V, a shift called depolarization • Opening of K+ channels results in an efflux of K+ • Moving the membrane further away from 0 m. V, a shift called hyperpolarization • Return to resting from depolarization: repolarizing © 2013 Pearson Education, Inc.

Graded Potentials (8 -3) • Local changes in the membrane that fade over distance • All cells experience graded potentials when stimulated • And can result in the activation of smaller cells • Graded potentials by themselves cannot trigger activation of large neurons and muscle fibers • Referred to as having excitable membranes © 2013 Pearson Education, Inc.

Action Potentials (8 -3) • A change in the membrane that travels the entire length of neurons • A nerve impulse • If a combination of graded potentials causes the membrane to reach a critical point of depolarization, it is called the threshold • Then an action potential will occur © 2013 Pearson Education, Inc.

Action Potentials (8 -3) • Are all-or-none and will propagate down the length of the neuron • From the time the voltage-gated channels open until repolarization is finished: • The membrane cannot respond to further stimulation • This period of time is the refractory period • And limits the rate of response by neurons © 2013 Pearson Education, Inc.

Figure 8 -8 The Generation of an Action Potential SPOTLIGHT FIGURE 8 -8 The Generation of an Action Potential Sodium channels close, voltage-gated potassium channels open, and potassium ions move out of the cell. Repolarization begins. 3 +30 Axon hillock First part of axon to reach threshold Membrane potential (m. V) DEPOLARIZATION 0 Potassium channels close, and both sodium and potassium channels return to their Voltage-gated sodium normal states. channels open and sodium ions move into the cell. The 4 membrane potential rises to +30 m. V. 2 Resting potential – 40 Threshold – 60 – 70 1 A graded depolarization brings an area of excitable membrane to threshold (– 60 m. V). REFRACTORY PERIOD During the refractory period, the membrane cannot respond to further stimulation. 0 Resting Potential 1 – 70 m. V Depolarization to Threshold – 60 m. V 2 Activation of Sodium Channels and Rapid Depolarization 3 REPOLARIZATION Inactivation of Sodium Channels and Activation of Potassium Channels +10 m. V Time (msec) 4 1 Closing of Potassium Channels – 90 m. V 2 Resting Potential – 70 m. V +30 m. V Local current The axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential. = Sodium ion = Potassium ion © 2013 Pearson Education, Inc. The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold. When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from – 60 m. V to a positive value. As the membrane potential approaches +30 m. V, voltage-gated sodium channels close. This step coincides with the opening of voltagegated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolarization now begins. The voltage-gated sodium channels remain inactivated until the membrane has repolarized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about – 70 m. V). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization. As the voltage-gated potassium channels close, the membrane potential returns to normal resting levels. The action potential is now over, and the membrane is once again at the resting potential.

Figure 8 -8 The Generation of an Action Potential Sodium channels close, voltagegated potassium channels open, and potassium ions move out of the cell. Repolarization begins. 3 +30 Membrane potential (m. V) D E P O L A R I Z AT I O N R E P O L A R I Z AT I O N 0 2 Resting potential – 40 – 60 – 70 Potassium channels close, and both sodium and potassium channels return to their normal states. Voltage-gated sodium channels open and sodium ions move into the cell. The membrane potential rises to +30 m. V. Threshold 1 A graded depolarization brings an area of excitable membrane to threshold (– 60 m. V). 4 REFRACTORY PERIOD During the refractory period, the membrane cannot respond to further stimulation. 0 © 2013 Pearson Education, Inc. Time (msec) 1 2

Figure 8 -8 The Generation of an Action Potential Resting Potential – 70 m. V Depolarization to Threshold – 60 m. V The axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential. = Sodium ion = Potassium ion © 2013 Pearson Education, Inc. Activation of Sodium Channels and Rapid Depolarization +10 m. V Local current The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold. When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from – 60 m. V to a positive value.

Figure 8 -8 The Generation of an Action Potential Inactivation of Sodium Channels and Activation of Potassium Channels Closing of Potassium Channels – 90 m. V Resting Potential – 70 m. V +30 m. V As the membrane potential approaches +30 m. V, voltage-gated sodium channels close. This step coincides with the opening of voltagegated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolarization now begins. © 2013 Pearson Education, Inc. The voltage-gated sodium channels remain inactivated until the membrane has repolarized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about – 70 m. V). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization. As the voltage-gated potassium channels close, the membrane potential returns to normal resting levels. The action potential is now over, and the membrane is once again at the resting potential.

Propagation of an Action Potential (8 -3) • Occurs when local changes in the membrane in one site: • Result in the activation of voltage-gated channels in the next adjacent site of the membrane • This causes a wave of membrane potential changes • Continuous propagation • Occurs in unmyelinated fibers and is relatively slow • Saltatory propagation • Is in myelinated axons and is faster © 2013 Pearson Education, Inc.

Figure 8 -9 The Propagation of Action Potentials over Unmyelinated and Myelinated Axons. Action potential propagation along an unmyelinated axon Stimulus depolarizes membrane to threshold EXTRACELLULAR FLUID Action potential propagation along a myelinated axon Stimulus depolarizes membrane to threshold EXTRACELLULAR FLUID Myelinated Internode Plasma membrane CYTOSOL Myelinated Internode Plasma membrane Myelinated Internode CYTOSOL Myelinated Internode Local current Myelinated Internode Repolarization (refractory period) © 2013 Pearson Education, Inc. Repolarization (refractory period) Local current

Checkpoint (8 -3) 9. What effect would a chemical that blocks the voltage-gated sodium channels in a neuron's plasma membrane have on the neuron's ability to depolarize? 10. What effect would decreasing the concentration of extracellular potassium have on the membrane potential of a neuron? 11. List the steps involved in the generation and propagation of an action potential. 12. Two axons are tested for propagation velocities. One carries action potentials at 50 meters per second, the other at 1 meter per second. Which axon is myelinated? © 2013 Pearson Education, Inc.

The Synapse (8 -4) • A junction between a neuron and another cell • Occurs because of chemical messengers called neurotransmitters • Communication happens in one direction only • Between a neuron and another cell type is a neuroeffector junction • Such as the neuromuscular junction or neuroglandular junction © 2013 Pearson Education, Inc.

A Synapse between Two Neurons (8 -4) • Occurs: • Between the axon terminals of the presynaptic neuron • Across the synaptic cleft • To the dendrite or cell body of the postsynaptic neuron • Neurotransmitters • Stored in vesicles of the axon terminals • Released into the cleft and bind to receptors on the postsynaptic membrane PLAY ANIMATION Neurophysiology: Synapse © 2013 Pearson Education, Inc.

Figure 8 -10 The Structure of a Typical Synapse. Axon of presynaptic cell Axon terminal Mitochondrion Synaptic vesicles Presynaptic membrane Postsynaptic Synaptic membrane cleft © 2013 Pearson Education, Inc.

The Neurotransmitter ACh (8 -4) • Activates cholinergic synapses in four steps 1. Action potential arrives at the axon terminal 2. ACh is released and diffuses across synaptic cleft 3. ACh binds to receptors and triggers depolarization of the postsynaptic membrane 4. ACh is removed by ACh. E (acetylcholinesterase) © 2013 Pearson Education, Inc.

Figure 8 -11 The Events at a Cholinergic Synapse. An action potential arrives and depolarizes the axon terminal Presynaptic neuron Synaptic vesicles Action potential EXTRACELLULAR FLUID Axon terminal ACh. E POSTSYNAPTIC NEURON Extracellular Ca 2+ enters the axon terminal, triggering the exocytosis of ACh Ca 2+ Synaptic cleft Chemically regulated sodium ion channels © 2013 Pearson Education, Inc.

Figure 8 -11 The Events at a Cholinergic Synapse. ACh binds to receptors and depolarizes the postsynaptic membrane Initiation of action potential if threshold is reached ACh is removed by ACh. E Propagation of action potential (if generated) © 2013 Pearson Education, Inc.

Table 8 -1 The Sequence of Events at a Typical Cholinergic Synapse © 2013

Other Important Neurotransmitters (8 -4) • Norepinephrine (NE) • In the brain and part of the ANS, is found in adrenergic synapses • Dopamine, GABA, and serotonin • Are CNS neurotransmitters • At least 50 less-understood neurotransmitters • NO and CO • Are gases that act as neurotransmitters © 2013 Pearson Education, Inc.

Excitatory vs. Inhibitory Synapses (8 -4) • Usually, ACh and NE trigger depolarization • An excitatory response • With the potential of reaching threshold • Usually, dopamine, GABA, and serotonin trigger hyperpolarization • An inhibitory response • Making it farther from threshold © 2013 Pearson Education, Inc.

Neuronal Pools (8 -4) • Multiple presynaptic neurons can synapse with one postsynaptic neuron • If they all release excitatory neurotransmitters: • Then an action potential can be triggered • If they all release an inhibitory neurotransmitter: • Then no action potential can occur • If half release excitatory and half inhibitory neurotransmitters: • They cancel, resulting in no action © 2013 Pearson Education, Inc.

Neuronal Pools (8 -4) • A term that describes the complex grouping of neural pathways or circuits • Divergence • Is a pathway that spreads information from one neuron to multiple neurons • Convergence • Is when several neurons synapse with a single postsynaptic neuron © 2013 Pearson Education, Inc.

Figure 8 -12 Two Common Types of Neuronal Pools. Divergence A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS © 2013 Pearson Education, Inc. Convergence A mechanism for providing input to a single neuron from multiple sources

Checkpoint (8 -4) 13. Describe the general structure of a synapse. 14. What effect would blocking calcium channels at a cholinergic synapse have on synapse function? 15. What type of neural circuit permits both conscious and subconscious control of the same motor neurons? © 2013 Pearson Education, Inc.

The Meninges (8 -5) • The neural tissue in the CNS is protected by

The Dura Mater (8 -5) • Is the outer, very tough covering • The dura mater has two layers, with the outer layer fused to the periosteum of the skull • Dural folds contain large veins, the dural sinuses • In the spinal cord the dura mater is separated from the bone by the epidural space © 2013 Pearson Education, Inc.

The Arachnoid • Is separated from the dura mater by the subdural space • That contains a little lymphatic fluid • Below the epithelial layer is arachnoid space • Created by a web of collagen fibers • Contains cerebrospinal fluid © 2013 Pearson Education, Inc.

The Pia Mater • Is the innermost layer • Firmly bound to the neural

Checkpoint (8 -5) 16. Identify the three meninges surrounding the CNS. © 2013 Pearson

Spinal Cord Structure (8 -6) • The major neural pathway between the brain and the PNS • Can also act as an integrator in the spinal reflexes • Involving the 31 pairs of spinal nerves • Consistent in diameter except for the cervical enlargement and lumbar enlargement • Where numerous nerves supply upper and lower limbs © 2013 Pearson Education, Inc.

Spinal Cord Structure (8 -6) • Central canal • A narrow passage containing cerebrospinal fluid • Surface of the spinal cord is indented by the: • Posterior median sulcus • Deeper anterior median fissure © 2013 Pearson Education, Inc.

31 Spinal Segments (8 -6) • Identified by a letter and number relating to the nearby vertebrae • Each has a pair of dorsal root ganglia • Containing the cell bodies of sensory neurons with axons in dorsal root • Ventral roots contain motor neuron axons • Roots are contained in one spinal nerve © 2013 Pearson Education, Inc.

Figure 8 -14 a Gross Anatomy of the Spinal Cord. Cervical spinal nerves Thoracic spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 Lumbar spinal nerves Cervical enlargement Posterior median sulcus Lumbar enlargement Inferior tip of spinal cord L 3 L 4 Cauda equina L 5 Sacral spinal nerves Coccygeal nerve (Co 1) © 2013 Pearson Education, Inc. S S 11 S S 22 S S 33 S S 44 S S 55 In this superficial view of the adult spinal cord, the designations to the left identify the spiral nerves.

Figure 8 -14 b Gross Anatomy of the Spinal Cord. Posterior median sulcus Dorsal root ganglion Gray matter Central canal White matter Spinal Ventral nerve root © 2013 Pearson Education, Inc. Anterior median fissure C 3 This cross section through the cervical region of the spinal cord shows some prominent features and the arrangement of gray matter and white matter.

Sectional Anatomy of the Spinal Cord (8 -6) • The central gray matter is made up of glial cells and nerve cell bodies • Projections of gray matter are called horns • Which extend out into the white matter • White matter is myelinated and unmyelinated axons • The location of cell bodies in specific nuclei of the gray matter relate to their function © 2013 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord (8 -6) • Posterior gray horns are somatic and visceral sensory nuclei • Lateral gray horns are visceral (ANS) motor nuclei • The anterior gray horns are somatic motor nuclei • White matter can be organized into three columns • Which contain either ascending tracts to the brain, or descending tracts from the brain to the PNS © 2013 Pearson Education, Inc.

Figure 8 -15 Sectional Anatomy of the Spinal Cord. Posterior white column Dorsal root ganglion Posterior gray horn Lateral white gray horn column Anterior gray horn Posterior median sulcus Posterior gray commissure Functional Organization of Gray Matter The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Somatic Visceral Somatic Sensory nuclei Motor nuclei Ventral root Anterior gray commissure Anterior white column Anterior median fissure The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. POSTERIOR Structural Organization of Gray Matter The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray horn Posterior median sulcus Posterior gray commissure Dura mater Arachnoid mater (broken) Central canal Anterior gray commissure Anterior median fissure Pia mater © 2013 Pearson Education, Inc. Lateral gray horn Dorsal root ANTERIOR Anterior gray horn Dorsal root ganglion Ventral root A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord.

Figure 8 -15 a Sectional Anatomy of the Spinal Cord. Posterior white column Dorsal root ganglion Lateral white column Posterior gray horn Lateral gray horn Anterior gray horn Posterior median sulcus Posterior gray commissure Somatic Visceral Somatic Functional Organization of Gray Matter The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Sensory nuclei Motor nuclei Ventral root Anterior white column Anterior gray commissure Anterior white commissure Anterior median fissure The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. © 2013 Pearson Education, Inc.

Figure 8 -15 b Sectional Anatomy of the Spinal Cord. POSTERIOR Posterior median sulcus Posterior gray commissure Dura mater Arachnoid mater (broken) Central canal Anterior gray commissure Anterior median fissure Pia mater Structural Organization of Gray Matter The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray horn Lateral gray horn Dorsal root ANTERIOR Anterior gray horn Dorsal root ganglion Ventral root A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. © 2013 Pearson Education, Inc.

Checkpoint (8 -6) 17. Damage to which root of a spinal nerve would interfere with motor function? 18. A person with polio has lost the use of his leg muscles. In which areas of his spinal cord could you locate virus-infected neurons? 19. Why are spinal nerves also called mixed nerves? © 2013 Pearson Education, Inc.

Six Major Regions of the Brain (8 -7) 1. The cerebrum 2. The diencephalon

Major Structures of the Brain (8 -7) • The cerebrum • Is divided into paired cerebral hemispheres • Deep to the cerebrum is the diencephalon • Which is divided into the thalamus, the hypothalamus, and the epithalamus • The brain stem • Contains the midbrain, pons, and medulla oblongata • The cerebellum • Is the most inferior/posterior part © 2013 Pearson Education, Inc.

Figure 8 -16 a The Brain. Right cerebral hemisphere CEREBRUM Left cerebral hemisphere Longitudinal fissure A N T E R I O R Cerebral veins and arteries below arachnoid mater © 2013 Pearson Education, Inc. CEREBELLUM Superior view P O S T E R I O R

Figure 8 -16 b The Brain. Central sulcus Precentral gyrus Postcentral gyrus Parietal lobe Frontal lobe of left cerebral hemisphere Lateral sulcus Occipital lobe Temporal lobe CEREBELLUM PONS Lateral view © 2013 Pearson Education, Inc. MEDULLA OBLONGATA

Figure 8 -16 c The Brain. Corpus Precentral Central sulcus callosum gyrus Fornix Frontal lobe Postcentral gyrus Thalamus Hypothalamus DIENCEPHALON Pineal gland (part of epithalamus) Parieto-occipital sulcus Optic chiasm Mamillary body Temporal lobe MIDBRAIN Brain stem PONS MEDULLA OBLONGATA © 2013 Pearson Education, Inc. CEREBELLUM Sagittal section

The Ventricles of the Brain (8 -7) • Filled with cerebrospinal fluid and lined with ependymal cells • The two lateral ventricles within each cerebral hemisphere drain through the: • Interventricular foramen into the: • Third ventricle in the diencephalon, which drains through the cerebral aqueduct into the: • Fourth ventricle, which drains into the central canal © 2013 Pearson Education, Inc.

Figure 8 -17 The Ventricles of the Brain. Cerebral hemispheres Ventricles of the Brain Cerebral hemispheres Lateral ventricles Interventricular foramen Third ventricle Cerebral aqueduct Pons Medulla oblongata Spinal cord Fourth ventricle Central canal A lateral view of the ventricles © 2013 Pearson Education, Inc. Central canal Cerebellum An anterior view of the ventricles

Cerebrospinal Fluid (8 -7) • CSF • Surrounds and bathes the exposed surfaces of the CNS • Floats the brain • Transports nutrients, chemicals, and wastes • Is produced by the choroid plexus • Continually secreted and replaced three times per day • Circulation from the fourth ventricle into the subarachnoid space into the dural sinuses © 2013 Pearson Education, Inc.

Figure 8 -18 a The Formation and Circulation of Cerebrospinal Fluid. Extension of choroid plexus into lateral ventricle Choroid plexus of third ventricle Cerebral aqueduct Lateral aperture Choroid plexus of fourth ventricle Median aperture Arachnoid mater Subarachnoid space Dura mater © 2013 Pearson Education, Inc. A sagittal section of the CNS. Cerebrospinal fluid, formed in the choroid plexus, circulates along the routes indicated by the red arrows. Arachnoid granulations Superior sagittal sinus Central canal Spinal cord

Figure 8 -18 b The Formation and Circulation of Cerebrospinal Fluid. Superior sagittal sinus Cranium Dura mater (outer layer) Arachnoid granulation Fluid movement Dura mater (inner layer) Cerebral cortex The relationship of the arachnoid granulations and dura mater. © 2013 Pearson Education, Inc. Subdural space Arachnoid mater Pia mater Subarachnoid space

The Cerebrum (8 -7) • Contains an outer gray matter called the cerebral cortex • Deep gray matter in the cerebral nuclei and white matter of myelinated axons beneath the cortex and around the nuclei • The surface of the cerebrum • Folds into gyri • Separated by depressions called sulci or deeper grooves called fissures © 2013 Pearson Education, Inc.

The Cerebral Hemispheres (8 -7) • Are separated by the longitudinal fissure • The central sulcus • Extends laterally from the longitudinal fissure • The frontal lobe • Is anterior to the central sulcus • Is bordered inferiorly by the lateral sulcus © 2013 Pearson Education, Inc.

The Cerebral Hemispheres (8 -7) • The temporal lobe • Inferior to the lateral sulcus • Overlaps the insula • The parietal lobe • Extends between the central sulcus and the parietooccipital sulcus © 2013 Pearson Education, Inc.

The Cerebral Hemispheres (8 -7) • The occipital lobe • Located most posteriorly • The lobes are named for the cranial bone above it • Each lobe has sensory regions and motor regions • Each hemisphere sends and receives information from the opposite side of the body © 2013 Pearson Education, Inc.

Motor and Sensory Areas of the Cortex (8 -7) • Are divided by the central sulcus • The precentral gyrus of the frontal lobe • Contains the primary motor cortex • The postcentral gyrus of the parietal lobe • Contains the primary sensory cortex © 2013 Pearson Education, Inc.

Motor and Sensory Areas of Cortex (8 -7) • The visual cortex is in

Association Areas (8 -7) • Interpret incoming information • Coordinate a motor response, integrating the sensory and motor cortexes • The somatic sensory association area • Helps to recognize touch • The somatic motor association area • Is responsible for coordinating movement © 2013 Pearson Education, Inc.

Figure 8 -19 The Surface of the Cerebral Hemispheres. Primary motor cortex (precentral gyrus) Somatic motor association area (premotor cortex) Central sulcus Primary sensory cortex (postcentral gyrus) PARIETAL LOBE Somatic sensory association area FRONTAL LOBE Visual association area OCCIPITAL LOBE Visual cortex Auditory association area Prefrontal cortex Gustatory cortex Insula Lateral sulcus Auditory cortex Olfactory cortex TEMPORAL LOBE © 2013 Pearson Education, Inc.

Cortical Connections (8 -7) • Regions of the cortex are linked by the deeper white matter • The left and right hemispheres are linked across the corpus callosum • Other axons link the cortex with: • The diencephalon, brain stem, cerebellum, and spinal cord © 2013 Pearson Education, Inc.

Higher-Order Centers (8 -7) • Integrative areas, usually only in the left hemisphere • The general interpretive area or Wernicke's area • Integrates sensory information to form visual and auditory memory • The speech center or Broca's area • Regulates breathing and vocalization, the motor skills needed for speaking © 2013 Pearson Education, Inc.

The Prefrontal Cortex (8 -7) • In the frontal lobe • Coordinates information from the entire cortex • Skills such as: • Predicting time lines • Making judgments • Feelings such as: • Frustration, tension, and anxiety © 2013 Pearson Education, Inc.

Hemispheric Lateralization (8 -7) • The concept that different brain functions can and do occur on one side of the brain • The left hemisphere tends to be involved in language skills, analytical tasks, and logic • The right hemisphere tends to be involved in analyzing sensory input and relating it to the body, as well as analyzing emotional content © 2013 Pearson Education, Inc.

Figure 8 -20 Hemispheric Lateralization. RIGHT HAND LEFT HAND Prefrontal cortex Speech center Anterior commissure C O R P U S C A L L O S U M Writing Auditory cortex (right ear) General interpretive center (language and mathematical calculation) Analysis by touch Auditory cortex (left ear) Spatial visualization and analysis Visual cortex (right visual field) Visual cortex (left visual field) LEFT HEMISPHERE © 2013 Pearson Education, Inc. RIGHT HEMISPHERE

The Electroencephalogram (8 -7) • EEG • A printed record of brain wave activity • Can be interpreted to diagnose brain disorders • More modern techniques • Brain imaging, using the PET scan and MRIs, has allowed extensive "mapping" of the brain's functional areas © 2013 Pearson Education, Inc.

Figure 8 -21 Brain Waves. Patient being wired for EEG monitoring Alpha waves are characteristic of normal resting adults Beta waves typically accompany intense concentration Theta waves are seen in children and in frustrated adults Delta waves occur in deep sleep and in certain pathological conditions 0 Seconds 1 © 2013 Pearson Education, Inc. 2 3 4

Memory (8 -7) • Fact memory • The recall of bits of information • Skill memory • Learned motor skill that can become incorporated into unconscious memory • Short-term memory • Doesn't last long unless rehearsed • Converting into long-term memory through memory consolidation • Long-term memory • Remains for long periods, sometimes an entire lifetime • Amnesia • Memory loss as a result of disease or trauma © 2013 Pearson Education, Inc.

The Basal Nuclei (8 -7) • Masses of gray matter • Caudate nucleus • Lies anterior to the lentiform nucleus • Which contains the medial globus pallidus and the lateral putamen • Inferior to the caudate and lentiform nuclei is the amygdaloid body or amygdala • Basal nuclei • Subconscious control of skeletal muscle tone © 2013 Pearson Education, Inc.

Figure 8 -22 The Basal Nuclei. Head of caudate nucleus Lentiform nucleus Thalamus Tail of caudate nucleus Amygdaloid body Head of caudate nucleus Lateral view of a transparent brain, showing the relative positions of the basal nuclei Corpus callosum Lateral ventricle Insula Amygdaloid Lentiform Putamen Globus pallidus nucleus body Frontal section © 2013 Pearson Education, Inc. Tip of lateral ventricle

The Limbic System (8 -7) • Includes the olfactory cortex, basal nuclei, gyri, and tracts between the cerebrum and diencephalon • A functional grouping, rather than an anatomical one • Establishes the emotional states • Links the conscious with the unconscious • Aids in long-term memory with help of the hippocampus © 2013 Pearson Education, Inc.

Figure 8 -23 The Limbic System. Cingulate gyrus Corpus callosum Thalamic nuclei Hypothalamic nuclei

The Diencephalon (8 -7) • Contains switching and relay centers • Centers integrate conscious and unconscious sensory information and motor commands • Surround third ventricle • Three components 1. Epithalamus 2. Thalamus 3. Hypothalamus © 2013 Pearson Education, Inc.

The Epithalamus (8 -7) • Lies superior to the third ventricle and forms the roof of the diencephalon • The anterior part contains choroid plexus • The posterior part contains the pineal gland that is endocrine and secretes melatonin © 2013 Pearson Education, Inc.

The Thalamus (8 -7) • The left and right thalamus are separated by the third ventricle • The final relay point for sensory information • Only a small part of this input is sent on to the primary sensory cortex © 2013 Pearson Education, Inc.

The Hypothalamus (8 -7) • Lies inferior to the third ventricle • The subconscious control of skeletal muscle contractions is associated with strong emotion • Adjusts the pons and medulla functions • Coordinates the nervous and endocrine systems © 2013 Pearson Education, Inc.

The Hypothalamus (8 -7) • Secretes hormones • Produces sensations of thirst and hunger • Coordinates voluntary and ANS function • Regulates body temperature • Coordinates daily cycles © 2013 Pearson Education, Inc.

The Midbrain (8 -7) • Contains various nuclei • Two pairs involved in visual and auditory processing, the colliculi • Contains motor nuclei for cranial nerves III and IV • Cerebral peduncles contain descending fibers • Reticular formation is a network of nuclei related to the state of wakefulness • The substantia nigra influence muscle tone © 2013 Pearson Education, Inc.

The Pons (8 -7) • Links the cerebellum with the midbrain, diencephalon, cerebrum, and spinal cord • Contains sensory and motor nuclei for cranial nerves V, VII, and VIII • Other nuclei influence rate and depth of respiration © 2013 Pearson Education, Inc.

The Cerebellum (8 -7) • An automatic processing center • Which adjusts postural muscles to maintain balance • Programs and fine-tunes movements • The cerebellar peduncles • Are tracts that link the cerebral cortex, basal nuclei, and brain stem • Ataxia • Is disturbance of coordination • Can be caused by damage to the cerebellum © 2013 Pearson Education, Inc.

The Medulla Oblongata (8 -7) • Connects the brain with the spinal cord • Contains sensory and motor nuclei for cranial nerves VIII, IX, X, XI, and XII • Contains reflex centers • Cardiovascular centers • Adjust heart rate and arteriolar diameter • Respiratory rhythmicity centers • Regulate respiratory rate © 2013 Pearson Education, Inc.

Figure 8 -24 a The Diencephalon and Brain Stem. Cerebral peduncle Optic tract Cranial nerves N III N IV Thalamus Diencephalon Thalamic nuclei Midbrain Superior colliculus Inferior colliculus NV N VI Pons N VIII N IX NX N XII Spinal nerve C 1 Spinal nerve C 2 © 2013 Pearson Education, Inc. Cerebellar peduncles Medulla oblongata Spinal cord Lateral view

Figure 8 -24 b The Diencephalon and Brain Stem. N IV Choroid plexus Thalamus Third ventricle Pineal gland Corpora quadrigemina Superior colliculi Inferior colliculi Cerebral peduncle Cerebellar peduncles Choroid plexus in roof of fourth ventricle Dorsal roots of spinal nerves C 1 and C 2 © 2013 Pearson Education, Inc. Posterior view

Checkpoint (8 -7) 20. Describe one major function of each of the six regions of the brain. 21. The pituitary gland links the nervous and endocrine systems. To which portion of the diencephalon is it attached? 22. How would decreased diffusion across the arachnoid granulations affect the volume of cerebrospinal fluid in the ventricles? 23. Mary suffers a head injury that damages her primary motor cortex. Where is this area located? © 2013 Pearson Education, Inc.

Checkpoint (8 -7) 24. What senses would be affected by damage to the temporal lobes of the cerebrum? 25. The thalamus acts as a relay point for all but what type of sensory information? 26. Changes in body temperature stimulate which area of the diencephalon? 27. The medulla oblongata is one of the smallest sections of the brain. Why can damage to it cause death, whereas similar damage in the cerebrum might go unnoticed? © 2013 Pearson Education, Inc.

Peripheral Nervous System (8 -8) • Links the CNS to the rest of the body through peripheral nerves • They include the cranial nerves and the spinal nerves • The cell bodies of sensory and motor neurons are contained in the ganglia © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • 12 pairs, noted as Roman numerals I through XII • Some are: • Only motor pathways • Only sensory pathways • Mixed having both sensory and motor neurons • Often remembered with a mnemonic • "Oh, Once One Takes The Anatomy Final, Very Good Vacations Are Heavenly" © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • The olfactory nerves (N I) • Are connected to the cerebrum • Carry information concerning the sense of smell • The optic nerves (N II) • Carry visual information from the eyes, through the optic foramina of the orbits to the optic chiasm • Continue as the optic tracts to the nuclei of the thalamus © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • The oculomotor nerves (N III) • Motor only, arising in the midbrain • Innervate four of six extrinsic eye muscles and the intrinsic eye muscles that control the size of the pupil • The trochlear nerves (N IV) • Smallest, also arise in the midbrain • Innervate the superior oblique extrinsic muscles of the eyes © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • The trigeminal nerves (N V) • Have nuclei in the pons, are the largest cranial nerves • Have three branches 1. The ophthalmic • From the orbit, sinuses, nasal cavity, skin of forehead, nose, and eyes 2. The maxillary • From the lower eyelid, upper lip, cheek, nose, upper gums, and teeth 3. The mandibular • © 2013 Pearson Education, Inc. From salivary glands and tongue

The Cranial Nerves (8 -8) • The abducens nerves (N VI) • Innervate only the lateral rectus extrinsic eye muscle, with the nucleus in the pons • The facial nerves (N VII) • Mixed, and emerge from the pons • Sensory fibers monitor proprioception in the face • Motor fibers provide facial expressions; control tear and salivary glands © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • The vestibulocochlear nerves (N VIII) • Respond to sensory receptors in the inner ear • There are two components 1. The vestibular nerve • Conveys information about balance and position 2. The cochlear nerve • • © 2013 Pearson Education, Inc. Responds to sound waves for the sense of hearing Their nuclei are in the pons and medulla oblongata

The Cranial Nerves (8 -8) • The glossopharyngeal nerves (N IX) • Mixed nerves innervating the tongue and pharynx • Their nuclei are in the medulla oblongata • The sensory portion monitors taste on the posterior third of the tongue and monitors BP and blood gases • The motor portion controls pharyngeal muscles used in swallowing, and fibers to salivary glands © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • The vagus nerves (N X) • Have sensory input vital to autonomic control of the viscera • Motor control includes the soft palate, pharynx, and esophagus • Are a major pathway for ANS output to cardiac muscle, smooth muscle, and digestive glands © 2013 Pearson Education, Inc.

The Cranial Nerves (8 -8) • The accessory nerves (N XI) • Have fibers that originate in the medulla oblongata • Also in the lateral gray horns of the first five cervical segments of the spinal cord • The hypoglossal nerves (N XII) • Provide voluntary motor control over the tongue © 2013 Pearson Education, Inc.

Figure 8 -25 The Cranial Nerves. Olfactory bulb, termination of olfactory nerve (I) Olfactory tract Optic chiasm Optic nerve (II) Mamillary body Basilar artery Infundibulum Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Hypoglossal nerve (XII) Accessory nerve (XI) Pons Vertebral artery Cerebellum Medulla oblongata Spinal cord Inferior view of the brain © 2013 Pearson Education, Inc. Diagrammatic view showing the attachment of the 12 pairs of cranial nerves

Table 8 -2 The Cranial Nerves © 2013 Pearson Education, Inc.

The Spinal Nerves (8 -8) • Found in 31 pairs grouped according to the region of the vertebral column • 8 pairs of cervical nerves, C 1–C 8 • 12 pairs of thoracic nerves, T 1–T 12 • 5 pairs of lumbar nerves, L 1–L 5 • 5 pairs of sacral nerves, S 1–S 5 • 1 pair of coccygeal nerves, Co 1 © 2013 Pearson Education, Inc.

Nerve Plexuses (8 -8) • The origin of major nerve trunks of the PNS • The cervical plexus • Innervates the muscles of the head and neck and the diaphragm • The brachial plexus • Innervates the shoulder girdle and upper limb • The lumbar plexus and the sacral plexus • Innervate the pelvic girdle and lower limb © 2013 Pearson Education, Inc.

Figure 8 -26 Peripheral Nerves and Nerve Plexuses. Cervical plexus Brachial plexus Lumbar plexus Sacral plexus C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 3 L 4 L 5 S 1 Phrenic nerve (extends to the diaphragm) Axillary nerve Musculocutaneous nerve Radial nerve Ulnar nerve Median nerve S 2 S 3 S 4 S 5 Co 1 Femoral nerve Obturator nerve Gluteal nerves © 2013 Pearson Education, Inc. Saphenous nerve Sciatic nerve

Dermatome (8 -8) • A clinically important area monitored by a specific spinal nerve

Figure 8 -27 Dermatomes. C 2–C 3 NV C 2–C 3 C 2 C 3 T 2 C 6 L 1 L 2 C 8 C 7 T 1 L 3 L 4 L 5 C 4 C 5 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 C 3 C 4 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 4 L 3 L 5 C 5 T 2 C 6 T 1 C 7 SS S 2 4 3 L 1 S 1 L 5 S 5 C 8 L 2 S 2 L 3 S 1 L 4 ANTERIOR © 2013 Pearson Education, Inc. POSTERIOR

Table 8 -3 Nerve Plexuses and Major Nerves © 2013 Pearson Education, Inc.

Checkpoint (8 -8) 28. What signs would you associate with damage to the abducens nerve (N VI)? 29. John is having trouble moving his tongue. His physician tells him it is due to pressure on a cranial nerve. Which cranial nerve is involved? 30. Injury to which nerve plexus would interfere with the ability to breathe? © 2013 Pearson Education, Inc.

Reflexes (8 -9) • Rapid, automatic, unlearned motor response to a stimulus • Usually removes or opposes the original stimulus • Monosynaptic reflexes • For example, the stretch reflex • Which responds to muscle spindles, is the simplest with only one synapse • The best known stretch reflex is probably the knee jerk reflex © 2013 Pearson Education, Inc.

Simple Reflexes (8 -9) • Are wired in a reflex arc • A stimulus activates a sensory receptor • An action potential travels down an afferent neuron • Information processing occurs with the interneuron • An action potential travels down an efferent neuron • The effector organ responds © 2013 Pearson Education, Inc.

Figure 8 -28 The Components of a Reflex Arc. Arrival of stimulus and activation of receptor Stimulus Response by effector Activation of a sensory neuron Receptor Dorsal root Sensation relayed to the brain by axon collaterals Information processing in the CNS REFLEX ARC Effector Ventral root Activation of a motor neuron © 2013 Pearson Education, Inc. KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

Figure 8 -29 A Stretch Reflex. Stretching of muscle tendon stimulates muscle spindles Stretch Muscle spindle (stretch receptor) REFLEX ARC Spinal Cord Contraction Activation of motor neuron produces reflex muscle contraction © 2013 Pearson Education, Inc.

Complex Reflexes (8 -9) • Polysynaptic reflexes • With at least one interneuron • Are slower than monosynaptic reflexes, but can activate more than one effector • Withdrawal reflexes • Like the flexor reflex, move a body part away from the stimulation • Like touching a hot stove • Reciprocal inhibition • Blocks the flexor's antagonist • To ensure that flexion is in no way interfered with © 2013 Pearson Education, Inc.

Figure 8 -30 The Flexor Reflex, a Type of Withdrawal Reflex. Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors inhibited © 2013 Pearson Education, Inc. KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) Motor neuron (inhibited) Inhibitory interneuron

Input to Modify Reflexes (8 -9) • Reflexes are automatic, but higher brain centers can influence or modify them • The Babinski sign • Triggered by stroking an infant's sole, resulting in a fanning of the toes • As descending inhibitory synapses develop, an adult will respond by curling the toes instead, called the plantar reflex © 2013 Pearson Education, Inc.

Checkpoint (8 -9) 31. Define reflex. 32. Which common reflex do physicians use to test the general condition of the spinal cord, peripheral nerves, and muscles? 33. Why can polysynaptic reflexes produce more involved responses than can monosynaptic reflexes? 34. After injuring his back lifting a sofa, Tom exhibits a positive Babinski reflex. What does this imply about Tom's injury? © 2013 Pearson Education, Inc.

Sensory Pathways (8 -10) • Are ascending pathways • Posterior column pathway • Spinothalamic pathway • Spinocerebellar pathway • A sensory homunculus • A mapping of the area of the cortex dedicated to the number of sensory receptors, not the size of the body area © 2013 Pearson Education, Inc.

Figure 8 -31 The Posterior Column Pathway. KEY Axon of firstorder neuron Second-order neuron Third-order neuron Sensory homunculus of left cerebral hemisphere Nuclei in thalamus MIDBRAIN Nucleus in medulla oblongata MEDULLA OBLONGATA SPINAL CORD Dorsal root ganglion © 2013 Pearson Education, Inc. Fine-touch, pressure, vibration, and proprioception sensations from right side of body

Motor Pathways (8 -10) • Are descending pathways • Corticospinal pathway • Also called pyramidal system • Medial and lateral pathways • Also called extrapyramidal system • A motor homunculus • Represents the distribution of somatic and ANS motor innervation © 2013 Pearson Education, Inc.

Figure 8 -32 The Corticospinal Pathway. KEY Axon of upper motor neuron Lower motor neuron Motor homunculus on primary motor cortex of left cerebral hemisphere To skeletal muscles Motor nuclei of cranial nerves Lateral corticospinal tract To skeletal muscles © 2013 Pearson Education, Inc. MIDBRAIN MEDULLA OBLONGATA Anterior corticospinal tract SPINAL CORD Motor neuron in anterior gray horn

Table 8 -4 Sensory and Motor Pathways © 2013 Pearson Education, Inc.

Checkpoint (8 -10) 35. As a result of pressure on her spinal cord, Jill cannot feel touch or pressure on her legs. What sensory pathway is being compressed? 36. The primary motor cortex of the right cerebral hemisphere controls motor function on which side of the body? 37. An injury to the superior portion of the motor cortex would affect the ability to control muscles of which parts of the body? © 2013 Pearson Education, Inc.

The Autonomic Nervous System (8 -11) • Unconscious adjustment of homeostatically essential visceral responses • Sympathetic division • Parasympathetic division • The somatic NS and ANS are anatomically different • SNS: one neuron to skeletal muscle • ANS: two neurons to cardiac and smooth muscle, glands, and fat cells © 2013 Pearson Education, Inc.

Two Neuron Pathways of the ANS (8 -11) • Preganglionic neuron • Has cell body in spinal cord, synapses at the ganglion with the postganglionic neuron • In sympathetic division • Preganglionic fibers are short • Postganglionic fibers are long • In parasympathetic division • Preganglionic fibers are long • Postganglionic fibers are "short" © 2013 Pearson Education, Inc.

Figure 8 -33 The Organization of the Somatic and Autonomic Nervous Systems. Upper motor neurons in Primary motor cortex Visceral motor nuclei in hypothalamus BRAIN Somatic motor nuclei of brain stem BRAIN Preganglionic neuron Visceral Effectors Smooth muscle Skeletal muscle Lower motor neurons SPINAL CORD Glands Cardiac muscle Somatic motor nuclei of spinal cord Skeletal muscle Somatic nervous system © 2013 Pearson Education, Inc. Adipocytes Autonomic ganglia Ganglionic neurons Preganglionic neuron Autonomic nuclei in brain stem SPINAL CORD Autonomic nuclei in spinal cord Autonomic nervous system

Neurotransmitters at Specific Synapses (8 -11) • All synapses between pre- and postganglionic fibers: • Are cholinergic (ACh) and excitatory • Postganglionic parasympathetic synapses • Are cholinergic • Some are excitatory, some inhibitory, depending on the receptor • Most postganglionic sympathetic synapses: • Are adrenergic (NE) and usually excitatory © 2013 Pearson Education, Inc.

The Sympathetic Division (8 -11) • Sympathetic chain • Arises from spinal segments T 1–L 2 • The preganglionic fibers enter the sympathetic chain ganglia just outside the spinal column • Collateral ganglia are unpaired ganglia that receive splanchnic nerves from the lower thoracic and upper lumbar segments • Postganglionic neurons innervate abdominopelvic cavity © 2013 Pearson Education, Inc.

The Sympathetic Division (8 -11) • The adrenal medullae • Are innervated by preganglionic fibers • Are modified neural tissue that secrete E and NE into capillaries, functioning like an endocrine gland • The effect is nearly identical to that of the sympathetic postganglionic stimulation of adrenergic synapses © 2013 Pearson Education, Inc.

Figure 8 -34 The Sympathetic Division. Eye PONS Salivary glands Sympathetic nerves Cervical sympathetic ganglia Spinal nerves Heart T 1 Cardiac and Splanchnic pulmonary nerve plexuses Collateral ganglion Splanchnic nerves Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) L 2 Collateral ganglion L 2 Lung Liver and gallbladder Stomach Spleen Pancreas Large intestine Small intestine Adrenal medulla Kidney Sympathetic chain ganglia KEY Preganglionic neurons Ganglionic neurons © 2013 Pearson Education, Inc. Spinal cord Uterus Ovary Penis Scrotum Urinary bladder

The Sympathetic Division (8 -11) • Also called the "fight-or-flight" division • Effects • Increase in alertness, metabolic rate, sweating, heart rate, blood flow to skeletal muscle • Dilates the respiratory bronchioles and the pupils • Blood flow to the digestive organs is decreased • E and NE from the adrenal medullae support and prolong the effect © 2013 Pearson Education, Inc.

The Parasympathetic Division (8 -11) • Preganglionic neurons arise from the brain stem and sacral spinal cord • Include cranial nerves III, VII, IX, and X, the vagus, a major parasympathetic nerve • Ganglia very close to or within the target organ • Preganglionic fibers of the sacral areas form the pelvic nerves © 2013 Pearson Education, Inc.

The Parasympathetic Division (8 -11) • Less divergence than in the sympathetic division, so effects are more localized • Also called "rest-and digest" division • Effects • Constriction of the pupils, increase in digestive secretions, increase in digestive tract smooth muscle activity • Stimulates urination and defecation • Constricts bronchioles, decreases heart rate © 2013 Pearson Education, Inc.

Figure 8 -35 The Parasympathetic Division. Terminal ganglion N III Terminal ganglion PONS N VII Terminal ganglion N IX N X (Vagus) Lacrimal gland Eye Salivary glands Terminal ganglion Heart Cardiac and pulmonary plexuses Lungs Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic nerves Small intestine Rectum Spinal cord Kidney S 2 S 3 S 4 KEY Preganglionic neurons Ganglionic neurons © 2013 Pearson Education, Inc. Urinary bladder Uterus Ovary Penis Scrotum

Dual Innervation (8 -11) • Refers to both divisions affecting the same organs •

Table 8 -5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS

Checkpoint (8 -11) 38. While out for a brisk walk, Megan is suddenly confronted by an angry dog. Which division of the ANS is responsible for the physiological changes that occur as she turns and runs from the animal? 39. Why is the parasympathetic division of the ANS sometimes referred to as the anabolic system? 40. What effect would loss of sympathetic stimulation have on the flow of air into the lungs? 41. What physiological changes would you expect in a patient who is about to undergo a root canal procedure and is quite anxious about it? © 2013 Pearson Education, Inc.

Aging and the Nervous System (8 -12) • Common changes • Reduction in brain size and weight and reduction in number of neurons • Reduction in blood flow to the brain • Change in synaptic organization of the brain • Increase in intracellular deposits and extracellular plaques • Senility can be a result of all these changes © 2013 Pearson Education, Inc.

Checkpoint (8 -12) 42. What is the major cause of age-related shrinkage of the

Figure 8 -36 Body System Provides sensations of touch, pressure, pain, vibration, and temperature; hair provides some protection and insulation for skull and brain; protects peripheral nerves Controls contraction of arrector pili muscles and secretion of sweat glands Provides calcium for neural function; protects brain and spinal cord Controls skeletal muscle contractions that results in bone thickening and maintenance and determine bone position Facial muscles express emotional state; intrinsic laryngeal muscles permit communication; muscle spindles provide proprioceptive sensations Controls skeletal muscle contractions; coordinates respiratory and cardiovascular activities Integumentary (Page 138) Nervous System Skeletal (Page 188) SYSTEM INTEGRATOR Nervous System Muscular (Page 241) Muscular Skeletal Integumentary Body System © 2013 Pearson Education, Inc. Cardiovascular (Page 467) Lymphatic (Page 500) Respiratory (Page 532) Digestive (Page 572) Urinary (Page 637) Reproductive (Page 671) The nervous system is closely integrated with other body systems. Every moment of your life, billions of neurons in your nervous system are exchanging information across trillions of synapses and performing the most complex integrative functions in the body. As part of this process, the nervous system monitors all other systems and issues commands that adjust their activities. However, the impact of these commands varies greatly from one system to another. The normal functions of the muscular system, for example, simply cannot be performed without instructions from the nervous system. By contrast, the cardiovascular system is relatively independent—the nervous system merely coordinates and adjusts cardiovascular activities to meet the circulatory demands of other systems. In the final analysis, the nervous system is like the conductor of an orchestra, directing the rhythm and balancing the performances of each section to produce a symphony, instead of simply a very loud noise. Endocrine (Page 376) The NERVOUS System