Chapter 13 Structure and Function of the Neurologic

Overview of the Nervous System Central nervous system (CNS) Ø Brain and spinal cord

Overview of the Nervous System (Cont. ) Peripheral nervous system (PNS) (Cont. ) Ø

Cells of the Nervous System Neuron Variable size and structure throughout the nervous system

Neuron Three components Cell body (soma) • Located mainly in the CNS • Densely

Neuron (Cont. ) Axons Carry nerve impulses away from the cell body Ø Axon

Neuron (Cont. ) Axons (Cont. ) Myelin • Segmented layer of lipid material •

Neuron (Cont. ) Axons (Cont. ) Ø Saltatory conduction • The flow of ions

Structural Classification of Neurons Based on the number of processes extending from the cell

Functional Classification of Neurons Sensory Ø Associational (interneurons) Ø Transmit impulses from sensory receptors

Neuroglia Copyright © 2017, Elsevier Inc. All rights reserved. 11

Neuroglia (Cont. ) “Nerve glue” Support the neurons of the CNS: Astrocytes Ø Oligodendroglia

Neuroglia From Patton KT, Thibodeau GA: Anatomy & physiology, ed 8, St Louis, 2013,

Nerve Injury and Regeneration Wallerian degeneration—degeneration of a nerve fiber that has been separated

Nerve Injury and Regeneration (Cont. ) Proximal to the injury Swelling and dispersal of

Nerve Injury and Regeneration (Cont. ) Process limited to myelinated axons • Generally only

Nerve Impulse Neurons generate and conduct electrical and chemical impulses by selectively changing the

1. Which of the following neurons transmit impulses from neuron to neuron? A. B.

Synapses Region between adjacent neurons Impulses are transmitted across the synapse by chemical and

Synapses (Cont. ) Neurotransmitters More than 30 substances Ø Excitatory (excitatory postsynaptic potential) Ø

Synapses (Cont. ) Summation Temporal summation Ø Spatial summation Ø Copyright © 2017, Elsevier

Central Nervous System Forebrain Ø Midbrain Ø Cerebral hemispheres Corpora quadrigemina, tegmentum, and cerebral

Central Nervous System (Cont. ) Reticular formation Network of connected nuclei that regulate vital

Central Nervous System (Cont. ) Copyright © 2017, Elsevier Inc. All rights reserved. 24

Central Nervous System (Cont. ) Forebrain Ø Telencephalon • Cerebrum Gyri, sulci, and fissures

Forebrain From Jarvis C: Physical examination & health assessment, ed 7, St Louis, 2016,

Forebrain (Cont. ) Copyright © 2017, Elsevier Inc. All rights reserved. 27

Central Nervous System Diencephalon Epithalamus Ø Thalamus Ø Hypothalamus Ø Subthalamus Ø Copyright ©

Central Nervous System (Cont. ) Midbrain Corpora quadrigemina (tectum) • Superior and inferior colliculi

Central Nervous System (Cont. ) Hindbrain (metencephalon) Cerebellum: fine motor control, balance and posture

Spinal Cord Lies within the vertebral canal and is protected by the vertebral column

Spinal Cord (Cont. ) Gray matter Posterior/dorsal horn; substantia gelatinosa Ø Lateral horn Ø

Spinal Cord (Cont. ) From Patton KT, Thibodeau GA: Structure and function of the

Spinal Cord (Cont. ) From Crossman AR, Neary D: Neuroanatomy: an illustrated colour text,

Reflex Arc Receptor Afferent (sensory) neuron Efferent neuron Effector Copyright © 2017, Elsevier Inc.

Reflex Arc (Cont. ) From Jarvis C: Physical examination & health assessment, ed 7,

Upper and Lower Motor Neurons Upper motor neurons Completely contained within the CNS Ø

Upper and Lower Motor Neurons (Cont. ) Lower motor neurons Neurons having direct influence

Neuromuscular Junction From Damjanov I: Pathology for the health professions, ed 4, St Louis,

Motor Pathways Lateral corticospinal Corticobulbar Reticulospinal Vestibulospinal Rubrospinal Copyright © 2017, Elsevier Inc. All

Sensory Pathways Posterior column Anterior spinothalamic tract Lateral spinothalamic tract Copyright © 2017, Elsevier

2. Which of the following motor pathways is responsible for rapidly contracting extensor muscles?

Protective Structures Cranium Eight bones Ø Encloses and protects the brain and its associated

Protective Structures (Cont. ) Meninges Ø Protective membranes surrounding the brain and spinal cord

Protective Structures (Cont. ) Cerebrospinal fluid (CSF) and the ventricular system CSF is a

Protective Structures (Cont. ) Vertebral column Ø 33 vertebrae • 7 cervical, 12 thoracic,

Vertebral Column From Solomon E: Introduction to human anatomy and physiology, ed 4, St

Vertebral Column (Cont. ) From Drake R, Vogl AW, Mitchell AWM: Gray’s anatomy for

Blood Supply to the Brain 800 to 1000 ml per minute CO 2 is

Blood Supply to the Brain (Cont. ) From Moses KP, et al: Atlas of

Blood Supply from the Brain The cerebral veins, classified as superficial and deep veins,

Blood-Brain Barrier Cellular structures that selectively inhibit certain potentially harmful substances in the blood

Blood Supply to the Spinal Cord Vertebral arteries Anterior spinal arteries Ø Posterior spinal

Blood Supply to the Spinal Cord (Cont. ) Redrawn from Rudy EB, editor: Advanced

Peripheral Nervous System 31 pairs of spinal nerves Names correlate with the vertebral level

Peripheral Nervous System (Cont. ) Fascicles Ø Bundles of myelinated axons in the PNS

Peripheral Nervous System (Cont. ) From Applegate E: The anatomy and physiology learning system,

Peripheral Nervous System (Cont. ) Copyright © 2017, Elsevier Inc. All rights reserved. 59

Autonomic Nervous System Located in both the CNS and PNS Coordinates and maintains a

Autonomic Nervous System (Cont. ) Two divisions Ø Sympathetic • Thoracolumbar division • Responds

Neurotransmitters and Neuroreceptors of the ANS Sympathetic preganglionic fibers Ø Sympathetic postganglionic fibers Ø

Sympathetic Nervous System Mobilizes energy stores in times of need Ø Receives innervation from

Parasympathetic Nervous System Functions to conserve and restore energy Ø “Rest-and-tranquility” response Receives innervation

Parasympathetic Nervous System (Cont. ) Preganglionic neurons travel to ganglia close to the organs

Function of Autonomic Nervous System Maintains steady state in internal environment Two opposing systems

Aging and the Nervous System Decrease in the number of neurons Ø Decreased brain

Slides: 67

Download presentation

Overview of the Nervous System Central nervous system (CNS) Ø Brain and spinal cord Peripheral nervous system (PNS) Cranial nerves Ø Spinal nerves Ø Pathways: • Afferent (ascending) • Efferent (descending) Ø Copyright © 2017, Elsevier Inc. All rights reserved. 2

Overview of the Nervous System (Cont. ) Peripheral nervous system (PNS) (Cont. ) Ø Somatic nervous system • Motor and sensory pathways regulating voluntary motor control of skeletal muscle Ø Autonomic nervous system • Motor and sensory pathways regulating the body’s internal environment through involuntary control of organ systems Sympathetic Parasympathetic Copyright © 2017, Elsevier Inc. All rights reserved. 3

Cells of the Nervous System Neuron Variable size and structure throughout the nervous system Ø Cellular constituents: • Microtubules • Neurofibrils • Nissl substances • Microfilaments Ø Copyright © 2017, Elsevier Inc. All rights reserved. 4

Neuron Three components Cell body (soma) • Located mainly in the CNS • Densely packed cell bodies in the CNS are nuclei • Densely packed cell bodies in the PNS are ganglia Ø Dendrites • Receptive portion of the neuron Ø Axons Ø Copyright © 2017, Elsevier Inc. All rights reserved. 5

Neuron (Cont. ) Axons Carry nerve impulses away from the cell body Ø Axon hillock • Cone-shaped process where the axon leaves the cell Ø body Ø Initial segment of the axon • Area of the axon having the lowest threshold for stimulation, so the action potentials begin at this point Copyright © 2017, Elsevier Inc. All rights reserved. 6

Neuron (Cont. ) Axons (Cont. ) Myelin • Segmented layer of lipid material • Insulating substance • Formed and maintained by the Schwann cell in the PNS Ø Nodes of Ranvier • Regular interruptions of the myelin sheath Ø Copyright © 2017, Elsevier Inc. All rights reserved. 7

Neuron (Cont. ) Axons (Cont. ) Ø Saltatory conduction • The flow of ions between segments of myelin rather than along the entire length of the axon Divergence • Ability of branching axons to influence many neurons Ø Convergence • Branches of numerous neurons converging on one Ø neuron Copyright © 2017, Elsevier Inc. All rights reserved. 8

Structural Classification of Neurons Based on the number of processes extending from the cell body Unipolar Ø Pseudounipolar Ø Bipolar Ø Multipolar Ø Copyright © 2017, Elsevier Inc. All rights reserved. 9

Functional Classification of Neurons Sensory Ø Associational (interneurons) Ø Transmit impulses from sensory receptors to the CNS Transmit impulses from neuron to neuron Motor Ø Transmit impulses from the CNS to an effector organ Copyright © 2017, Elsevier Inc. All rights reserved. 10

Nerve Injury and Regeneration Wallerian degeneration—degeneration of a nerve fiber that has been separated by injury or disease Ø Distal to the injury • Swelling appears • Neurofilaments hypertrophy • Myelin sheath shrinks and disintegrates • Axon portion degenerates and disappears Copyright © 2017, Elsevier Inc. All rights reserved. 14

Nerve Injury and Regeneration (Cont. ) Proximal to the injury Swelling and dispersal of the Nissl substance Ø Cell increases in metabolic activity, protein synthesis, and mitochondrial activity Ø New terminal sprouts project from the proximal segment Ø Copyright © 2017, Elsevier Inc. All rights reserved. 15

Nerve Injury and Regeneration (Cont. ) Process limited to myelinated axons • Generally only in the PNS Ø Depends on location, type of injury, inflammatory response, and scar tissue formation Ø Copyright © 2017, Elsevier Inc. All rights reserved. 16

Nerve Impulse Neurons generate and conduct electrical and chemical impulses by selectively changing the electrical potential of their plasma membranes and influencing other nearby neurons by the release of neurotransmitters “All or none” response Copyright © 2017, Elsevier Inc. All rights reserved. 17

1. Which of the following neurons transmit impulses from neuron to neuron? A. B. C. D. Interneurons Motor neurons Sensory neurons Unipolar neurons Copyright © 2017, Elsevier Inc. All rights reserved. 18

Synapses Region between adjacent neurons Impulses are transmitted across the synapse by chemical and electrical conduction Presynaptic neurons Ø Proximal to the synapse Postsynaptic neurons Ø Distal to the synapse Copyright © 2017, Elsevier Inc. All rights reserved. 19

Synapses (Cont. ) Neurotransmitters More than 30 substances Ø Excitatory (excitatory postsynaptic potential) Ø Inhibitory (inhibitory postsynaptic potential) Ø Synaptic boutons Synaptic cleft Copyright © 2017, Elsevier Inc. All rights reserved. 20

Central Nervous System Forebrain Ø Midbrain Ø Cerebral hemispheres Corpora quadrigemina, tegmentum, and cerebral peduncles Hindbrain Ø Cerebellum, pons, and medulla Copyright © 2017, Elsevier Inc. All rights reserved. 22

Central Nervous System (Cont. ) Reticular formation Network of connected nuclei that regulate vital reflexes, such as cardiovascular and respiratory function Ø Together with the cerebral cortex is referred to as the reticular activating system Ø Copyright © 2017, Elsevier Inc. All rights reserved. 23

Central Nervous System (Cont. ) Forebrain Ø Telencephalon • Cerebrum Gyri, sulci, and fissures Gray matter and white matter • Brodmann areas • Lobes Frontal: primary motor area, limbic system Parietal: somatic sensory input Occipital: primary visual cortex Temporal: primary auditory cortex, Wernicke • Cerebral nuclei (basal ganglia) Copyright © 2017, Elsevier Inc. All rights reserved. 25

Central Nervous System (Cont. ) Midbrain Corpora quadrigemina (tectum) • Superior and inferior colliculi Ø Tegmentum • Red nucleus and substantia nigra Ø Basis pedunculi Ø Copyright © 2017, Elsevier Inc. All rights reserved. 29

Central Nervous System (Cont. ) Hindbrain (metencephalon) Cerebellum: fine motor control, balance and posture Ø Pons: a bridge Ø Myelencephalon Ø Medulla oblongata Copyright © 2017, Elsevier Inc. All rights reserved. 30

Spinal Cord Lies within the vertebral canal and is protected by the vertebral column Connects the brain and the body Ø Conducts somatic and autonomic reflexes Ø Provides motor pattern control centers Ø Modulates sensory and motor function Ø Copyright © 2017, Elsevier Inc. All rights reserved. 31

Spinal Cord (Cont. ) Gray matter Posterior/dorsal horn; substantia gelatinosa Ø Lateral horn Ø Anterior/ventral horn Ø White matter Ø Spinal tracks Copyright © 2017, Elsevier Inc. All rights reserved. 32

Upper and Lower Motor Neurons Upper motor neurons Completely contained within the CNS Ø Control fine motor movement and influence/modify spinal reflex arcs Ø Synapse with interneurons Ø Copyright © 2017, Elsevier Inc. All rights reserved. 37

Upper and Lower Motor Neurons (Cont. ) Lower motor neurons Neurons having direct influence on muscles Ø Cell bodies originate in the gray matter of the spinal cord, but their axons extend into the PNS Ø Copyright © 2017, Elsevier Inc. All rights reserved. 38

2. Which of the following motor pathways is responsible for rapidly contracting extensor muscles? A. B. C. D. Corticobulbar Reticulospinal Vestibulospinal Lateral corticospinal Copyright © 2017, Elsevier Inc. All rights reserved. 42

Protective Structures Cranium Eight bones Ø Encloses and protects the brain and its associated structures Ø Galea aponeurotica • Thick, fibrous band of tissue overlying the cranium Ø between the frontal and occipital muscles, affords added protection to the skull Copyright © 2017, Elsevier Inc. All rights reserved. 43

Protective Structures (Cont. ) Cerebrospinal fluid (CSF) and the ventricular system CSF is a clear, colorless fluid similar to blood plasma and interstitial fluid 125 to 150 ml in ventricles Ø Produced by the choroid plexuses in the lateral, third, and fourth ventricles Ø Reabsorbed through the arachnoid villi Ø Copyright © 2017, Elsevier Inc. All rights reserved. 45

Protective Structures (Cont. ) Vertebral column Ø 33 vertebrae • 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal Ø Intervertebral disks • Nucleus pulposus Copyright © 2017, Elsevier Inc. All rights reserved. 46

Blood Supply to the Brain 800 to 1000 ml per minute CO 2 is the primary regulator for CNS blood flow Internal carotid and vertebral arteries Arterial circle (circle of Willis) Copyright © 2017, Elsevier Inc. All rights reserved. 49

Blood Supply from the Brain The cerebral veins, classified as superficial and deep veins, drain into venous plexuses and dural sinuses and eventually join the internal jugular veins at the base of the skull Head injury: avoid turning head Copyright © 2017, Elsevier Inc. All rights reserved. 52

Blood-Brain Barrier Cellular structures that selectively inhibit certain potentially harmful substances in the blood from entering the interstitial spaces of the brain or CSF Implications for drug therapy because certain types of antibiotics and chemotherapeutic drugs show a greater propensity than others for crossing this barrier Copyright © 2017, Elsevier Inc. All rights reserved. 53

Peripheral Nervous System 31 pairs of spinal nerves Names correlate with the vertebral level from which they exit Ø Mixed nerves Ø Arise from the anterior and posterior horn cells of the spinal cord Ø 12 pairs of cranial nerves Ø Sensory, motor, and mixed Copyright © 2017, Elsevier Inc. All rights reserved. 56

Peripheral Nervous System (Cont. ) Fascicles Ø Bundles of myelinated axons in the PNS Rami Plexuses Brachial plexus Ø Lumbar plexus Ø Sacral plexus Ø Dermatomes Copyright © 2017, Elsevier Inc. All rights reserved. 57

Autonomic Nervous System Located in both the CNS and PNS Coordinates and maintains a steady state among the visceral (internal) organs Neurons Preganglionic (myelinated) Ø Postganglionic (unmyelinated) Ø Copyright © 2017, Elsevier Inc. All rights reserved. 60

Autonomic Nervous System (Cont. ) Two divisions Ø Sympathetic • Thoracolumbar division • Responds to stress by mobilizing energy stores and prepares the body to defend itself Ø Parasympathetic • Craniosacral division • Conserves energy and the body’s resources Both systems function, more or less, at the same time Copyright © 2017, Elsevier Inc. All rights reserved. 61

Neurotransmitters and Neuroreceptors of the ANS Sympathetic preganglionic fibers Ø Sympathetic postganglionic fibers Ø Acetylcholine and cholinergic receptors Norepinephrine and adrenergic receptors Parasympathetic preganglionic and postganglionic fibers Ø Acetylcholine and cholinergic receptors Copyright © 2017, Elsevier Inc. All rights reserved. 62

Sympathetic Nervous System Mobilizes energy stores in times of need Ø Receives innervation from cell bodies located from the first thoracic (T 1) through the second lumbar (L 2) regions of the spinal cord Ø Fight or flight response Thoracolumbar division Sympathetic (paravertebral) ganglia Copyright © 2017, Elsevier Inc. All rights reserved. 63

Parasympathetic Nervous System Functions to conserve and restore energy Ø “Rest-and-tranquility” response Receives innervation from cell bodies located in the cranial nerve nuclei and sacral region of the spinal cord Ø Craniosacral division Copyright © 2017, Elsevier Inc. All rights reserved. 64

Function of Autonomic Nervous System Maintains steady state in internal environment Two opposing systems Sympathetic responds to stress by mobilizing energy and prepares for defense Ø Parasympathetic conserves energy and resources Ø Copyright © 2017, Elsevier Inc. All rights reserved. 66

Aging and the Nervous System Decrease in the number of neurons Ø Decreased brain weight and size Lipofuscin and neurofibrillary tangles Slowing of neurologic responses Copyright © 2017, Elsevier Inc. All rights reserved. 67