Essentials of Human Anatomy Physiology Elaine N Marieb
Essentials of Human Anatomy & Physiology Elaine N. Marieb Seventh Edition Chapter 9 The Nervous System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Functions of the Nervous System • Maintain homeostasis with electrical signals • Provide for sensation • Provide for higher mental functions and emotions • Activate muscles and glands
Roles of the Nervous System 1. Sensory input – gathering information · To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration – · to process and interpret sensory input and decide if action is needed. 3. Motor output · A response to integrated stimuli · The response activates muscles or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 1 a
Structural Classification of the Nervous System · Central nervous system (CNS) · Brain & spinal cord · Dorsal cavity · Command center · Takes in info & give instruction · Peripheral nervous system (PNS) · Nerves outside the brain and spinal cord · Communication lines Slide 7. 2
Functional Classification of the Peripheral Nervous System · Sensory (afferent) division · Nerve fibers that carry information to the central nervous system Figure 7. 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 3 a
Functional Classification of the Peripheral Nervous System · Motor (efferent) division · Nerve fibers that carry impulses away from the central nervous system Figure 7. 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 3 b
Functional Classification of the Peripheral Nervous System · Motor (efferent) division · Two subdivisions · Somatic nervous system = voluntary · Autonomic nervous system = involuntary Figure 7. 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 3 c
Organization of the Nervous System Figure 7. 2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 4
Neuroglia vs. Neurons • • Neuroglia divide. Neurons do not. Most brain tumors are “gliomas. ” Most brain tumors involve the neuroglia cells, not the neurons. • Consider the role of cell division in cancer!
Support Cells of the PNS · Schwann cells · Form myelin sheath in the peripheral nervous system Figure 7. 3 e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 7 b
Nervous Tissue: Neurons · Neurons = nerve cells · Cells specialized to transmit messages · Major regions of neurons · Cell body – nucleus and metabolic center of the cell · Processes – fibers that extend from the cell body (dendrites and axons) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 8
Neuron Anatomy · Cell body · Nucleus · Large nucleolus Figure 7. 4 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 9 b
Neuron Anatomy · Extensions outside the cell body · Dendrites – conduct impulses toward the cell body · Axons – conduct impulses away from the cell body (only 1!) Figure 7. 4 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 10
Axons and Nerve Impulses · Axons end in axonal terminals · Axonal terminals contain vesicles with neurotransmitters · Axonal terminals are separated from the next neuron by a gap · Synaptic cleft – gap between adjacent neurons · Synapse – junction between nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 11
Nerve Fiber Coverings · Schwann cells – produce myelin sheaths in jelly-roll like fashion · Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7. 5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 12
Application • In Multiple Scleroses the myelin sheath is destroyed. • The myelin sheath hardens to a tissue called the scleroses. • This is considered an autoimmune disease. • Why does MS appear to affect the muscles?
Neuron Cell Body Location · Most are found in the central nervous system · Gray matter – cell bodies and unmylenated fibers · Nuclei – clusters of cell bodies within the white matter of the central nervous system · Ganglia – collections of cell bodies outside the central nervous system Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 13
Classification of Neurons (based on fxn. · Sensory (afferent) neurons · Carry impulses from the sensory receptors · Motor (efferent) neurons · Carry impulses from the central nervous system to muscles and glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Functional Classification of Neurons · Interneurons (association neurons) · Found in neural pathways in the central nervous system · Connect sensory and motor neurons Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Neuron Classification Figure 7. 6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 15
How Neurons Function (Physiology) · Irritability – ability to respond to stimuli · Conductivity – ability to transmit an impulse · The plasma membrane at rest is polarized · Fewer positive ions are inside the cell than outside the cell Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 17
Starting a Nerve Impulse · Depolarization – a stimulus depolarizes the neuron’s membrane · A depolarized membrane allows sodium (Na+) to flow inside the membrane · The exchange of ions initiates an action potential in the neuron Figure 7. 9 a–c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 18
The Action Potential · If the action potential (nerve impulse) starts, it is propagated over the entire axon · Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane · The sodium-potassium pump restores the original configuration · This action requires ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 19
Nerve Impulse Propagation · The impulse continues to move toward the cell body · Impulses travel faster when fibers have a myelin sheath Figure 7. 9 c–e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 20
All-or-None Response • Greater intensity of the stimulation does not produce a stronger impulse but rather more impulses are sent • Remember this from the muscular system? ?
Continuation of the Nerve Impulse btwn. Neurons (Conductivity) · Impulses are able to cross the synapse to another nerve (electrochemical event) · Neurotransmitter is released from a nerve’s axon terminal · The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter · An action potential is started in the dendrite Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 21
How Neurons Communicate at Synapses Figure 7. 10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 22
Ways to slow conduction • • • Alcohol Sedatives Anesthetics Cold Continuous pressure
The Reflex Arc · Reflex – rapid, predictable, and involuntary responses to stimuli · Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Figure 7. 11 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 23
Simple Reflex Arc Figure 7. 11 b, c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 24
• The knee-jerk reflex is an example of a 2 neuron reflex arc (sensory receptor, afferent neuron, efferent organ) • What would be the componeets of a 3 neuron reflex arc?
Types of Reflexes and Regulation · Autonomic reflexes · Smooth muscle regulation · Heart and blood pressure regulation · Regulation of glands · Digestive system regulation · Somatic reflexes · Activation of skeletal muscles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 25
Central Nervous System (CNS) · CNS develops from the embryonic neural tube · The neural tube becomes the brain and spinal cord · The opening of the neural tube becomes the ventricles · Four chambers within the brain · Filled with cerebrospinal fluid Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 26
Regions of the Brain · Cerebral hemispheres · Diencephalon · Brain stem · Cerebellum Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7. 12 Slide 7. 27
Cerebral Hemispheres (Cerebrum) · Paired (lf & rt) superior parts of the brain= hemispheres · Include more than half of the brain mass · Largest & most complex area of the brain Figure 7. 13 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Cerebral Hemispheres (Cerebrum) · The surface is made of ridges (gyri) and grooves (sulci) Figure 7. 13 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Lobes of the Cerebrum · Fissures (deep grooves) divide the cerebrum into lobes · Longitudinal fissure – separates hemispheres · Lobes of the cerebrum · Frontal lobe · Parietal lobe · Occipital lobe · Temporal lobe Slide
Lobes of the Cerebrum Figure 7. 15 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Lobes of the brain · Frontal Lobe · Primary motor area – sends impulses to skeletal muscles · Broca’s area – involved in our ability to speak · Intellectual and psychic functions Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 30
Sensory and Motor Areas of the Cerebral Cortex Figure 7. 14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 31
· Temporal Lobe · Gustatory, auditory, olfactory area · Occipital Lobe · Visual areas · Parietal Lobe · Sensations; pain; hot & cold; touch; speech & reading Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Specialized Area of the Cerebrum · Interpretation areas of the cerebrum · Speech/language region · Language comprehension region · General interpretation area Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Specialized Area of the Cerebrum Figure 7. 13 c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Layers of the Cerebrum · Gray matter · Outer layer · Composed mostly of neuron cell bodies · Initiates thoughts & voluntary actions Figure 7. 13 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Layers of the Cerebrum · White matter · Fiber tracts inside the gray matter · Example: corpus callosum connects hemispheres Figure 7. 13 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Diencephalon · Sits on top of the brain stem · Enclosed by the cerebral heispheres · Made of three parts · Thalamus · Hypothalamus · Epithalamus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Thalamus · The relay station for sensory impulses · Transfers impulses to the correct part of the cortex for localization and interpretation · Ability to concentrate · Degree of wakefulness · Pleasantness & unpleasantness Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 35
Hypothalamus · Helps regulate body temperature · Controls water balance · Regulates metabolism · Appetite and thirst · An important part of the limbic system (emotions) · The pituitary gland is attached to the hypothalamus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Epithalamus · Houses the pineal body (an endocrine gland) – sexual maturity and growth · Includes the choroid plexus – forms cerebrospinal fluid Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 37
Brain Stem · Attaches to the spinal cord · Parts of the brain stem · Midbrain · Pons · Medulla oblongata · Size your thumb (~ 3 inches) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Midbrain · Mostly composed of tracts of nerve fibers · Reflex centers for vision and hearing Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 39
Pons · The bulging center part of the brain stem · Mostly composed of fiber tracts · Includes nuclei involved in the control of breathing Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 40
Medulla Oblongata · The lowest part of the brain stem · Merges into the spinal cord · Contains important control centers · Heart rate control · Blood pressure regulation · Breathing · Swallowing · Vomiting Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 41
Cerebellum · Two hemispheres with convoluted surfaces · Functions in balance and coordination · Provides involuntary coordination of body movements Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Cerebellum Figure 7. 15 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Protection of the Central Nervous System · Scalp and skin · Skull and vertebral column · Meninges Figure 7. 16 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Protection of the Central Nervous System · Cerebrospinal fluid · Blood brain barrier Figure 7. 16 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Meninges · Dura mater · Double-layered external covering · Periosteum – attached to surface of the skull · Meningeal layer – outer covering of the brain · Folds inward in several areas Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Meninges · Arachnoid layer · Middle layer · Web-like · Pia mater · Internal layer · Clings to the surface of the brain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Cerebrospinal Fluid · Similar to blood plasma composition · Forms a watery cushion to protect the brain · Circulated in arachnoid space, ventricles, and central canal of the spinal cord · Changes in composition help diagnose disorders Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 46
Nervous System disorders • Meningitis – inflammation of the meninges; serious threat to the brain b/c of bacterial or viral types may spread into central nervous tissue • Encephalitis – inflammation of the brain • Hydrocephalus – “water on the brain; ” CSF cannot drain and pressure is exerted on the brain
Blood Brain Barrier · Includes the least permeable capillaries of the body · Excludes many potentially harmful substances · Useless against some substances · Fats and fat soluble molecules · Respiratory gases · Alcohol · Nicotine · Anesthesia Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 48
Traumatic Brain Injuries (TBI) · Concussion · Slight or mild brain injury · Bleeding & tearing of nerve fibers happened · Recovery likely with some memory loss · Contusion · A more severe TBI · Nervous tissue destruction occurs · Nervous tissue does not regenerate · Cerebral edema · Swelling from the inflammatory response · May compress and kill brain tissue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 49
Cerebrovascular Accident (CVA) · Commonly called a stroke · The result of a ruptured blood vessel supplying a region of the brain · Brain tissue supplied with oxygen from that blood source dies · Loss of some functions or death may result Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 50
Alzheimer’s Disease · Progressive degenerative brain disease · Mostly seen in the elderly, but may begin in middle age · Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons · Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 51
Spinal Cord · Extends from medulla oblongata to T 12 region · 31 pairs of nerves · Fxn is to conduct nerve impulses& serve for spinal reflex centers · Spinal tap – withdrawal of CSF (2 -3 ml); decreases pressure and can diagnose problems
Peripheral Nervous System · Nerves and ganglia outside the central nervous system · Nerve = bundle of neuron fibers · Neuron fibers are bundled by connective tissue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 55
Classification of Nerves (PNS) · Mixed nerves – both sensory and motor fibers · Afferent (sensory) nerves – carry impulses toward the CNS · Efferent (motor) nerves – carry impulses away from the CNS Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 57
PNS Structure 1. Sensory (afferent) division – nerve fibers that convey impulses to the CNS from sensory receptors a. Somatic sensory fibers – impulses from skin, skeletal muscles, and joints b. Visceral sensory fibers – impulses from visceral organs
PNS structure (cont. ) 2. Motor (efferent) division – caries impulses from the CNS to organs, muscles and glands; causes a response a. (somatic ( voluntary) nervous system – allows voluntary contraction of skeletal muscles b. Autonomic ( involuntary ) nervous system – regulates involuntary actions, such as glands, cardiac, and muscles
Autonomic Nervous System · The involuntary branch of the nervous system · Consists of only motor nerves · Divided into two divisions · Sympathetic division · Parasympathetic division Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 67
Comparison of Somatic and Autonomic Nervous Systems Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7. 24 Slide 7. 69
Anatomy of the Autonomic Nervous System Figure 7. 25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 73
Autonomic Functioning · Sympathetic – “fight-or-flight” · Response to unusual stimulus · Takes over to increase activities · Remember as the “E” division = exercise, excitement, emergency, and embarrassment Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Autonomic Functioning · Parasympathetic – housekeeping activities · Conserves energy · Maintains daily necessary body functions · Remember as the “D” division - digestion, defecation, and diuresis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Development Aspects of the Nervous System · The nervous system is formed during the first month of embryonic development · Any maternal infection can have extremely harmful effects · The hypothalamus is one of the last areas of the brain to develop Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Development Aspects of the Nervous System · No more neurons are formed after birth, but growth and maturation continues for several years (new evidence!) · The brain reaches maximum weight as a young adult · However, we can always grow dendrites! Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide
Nervous System Disorders 1. Cerebral palsy – neuromuscular disability where voluntary muscles are poorly controlled; causes by a temporary lack of oxygen to motor areas of the brain during delivery 2. Spina bifada – results when vertebrae from incompletely; part of the spinal cord is functionless 3. Parkinson’s disease – disorder in the ganglia characterized by shaking
Nervous System Disorders 4. Orthostatic hypertension – type of low blood pressure resulting from changes in body position (sympathetic) 5. Brain shrinkage – common but sped up in boxers and alcoholics (both groups exhibit signs of dementia unrelated to aging) 6. Epilepsy – characterized by seizures – caused by sudden bursts of irregular electrical activity in the brain
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