1. Chapter 8 The Nervous System

2. - Central Nervous System (CNS) - Peripheral Nervous System (PNS)
Three Branches
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
- Autonomic Nervous System (ANS)
Nervous System Physiology & Anatomy
CNS
PNS
ANS
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4. ORGANS AND DIVISIONS OF THE NERVOUS SYSTEM (Figure 8-1)
Central nervous system (CNS)—brain and spinal cord
Peripheral nervous system (PNS)—all nerves
Autonomic nervous system (ANS) – Parasympathetic/Sympathetic NS
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6. CELLS OF THE NERVOUS SYSTEM
Neurons
Consist of three main parts—dendrites; cell body of neuron; and axon (Figure 8-2)
Dendrites conduct impulses to cell body of neuron
Axons conduct impulses away from cell body of neuron
Neurons classified according to function
Sensory (afferent) neurons: conduct impulses to the spinal cord and brain
Motor (efferent) neurons: conduct impulses away from brain and spinal cord to muscles and glands
Interneurons: conduct impulses from sensory neurons to motor neurons
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8. CELLS OF THE NERVOUS SYSTEM
Glia (neuroglia)
Support cells, bringing the cells of nervous tissue together structurally and functionally
Three main types of glial cells of the CNS (Figure 8-3)
Astrocytes—star-shaped cells that anchor small blood vessels to neurons
Microglia—small cells that move in inflamed brain tissue carrying on phagocytosis
Oligodendrocytes—form myelin sheaths on axons in the CNS
Schwann cells form myelin sheaths on axons of the PNS (Figure 8-2)
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10. NERVES AND TRACTS (Figure 8-4)
Nerve—bundle of peripheral axons
Tract—bundle of central axons
White matter—tissue composed primarily of myelinated axons (nerves or tracts)
Gray matter—tissue composed primarily of cell bodies and unmyelinated fibers
Nerve coverings—fibrous connective tissue
Endoneurium—surrounds individual fibers within a nerve
Perineurium—surrounds a group (fascicle) of nerve fibers
Epineurium—surrounds the entire nervea
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12. REFLEX ARCS
Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs; conduction by a reflex arc results in a reflex (that is, contraction by a muscle or secretion by a gland)
The simplest reflex arcs are two-neuron arcs—consisting of sensory neurons synapsing in the spinal cord with motor neurons
Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons (Figure 8-5)
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14. NERVE IMPULSES
Definition—self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane
Mechanism
A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron
Inward movement of positive sodium ions leaves a slight excess of negative ions outside at a stimulated point; marks the beginning of a nerve impulse
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15. THE SYNAPSE
Definition—chemical compounds released from axon terminals (of a presynaptic neuron) into a synaptic cleft
Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane
Names of neurotransmitters—acetylcholine, catecholamines (norepinephrine, dopamine, and serotonin), and other compounds
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16. CENTRAL NERVOUS SYSTEM
Divisions of the brain (Figure 8-9 and Table 8-1)
Brainstem
Consists of three parts of brain; named in ascending order: the medulla oblongata, pons, and midbrain
Structure—white matter with bits of gray matter scattered through it
Function—gray matter in the brainstem functions as reflex centers (e.g., for heartbeat, respirations, and blood vessel diameter)
Sensory tracts in the brainstem conduct impulses to the higher parts of the brain
Motor tracts conduct from the higher parts of the brain to the spinal cord
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18. CENTRAL NERVOUS SYSTEM
Divisions of the brain (cont.)
Diencephalon
Structure and function of the hypothalamus
Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter
Acts as the major center for controlling the ANS; therefore, it helps control the functioning of most internal organs
Controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands
Contains centers for controlling body temperature, appetite, wakefulness, and pleasure
Structure and function of the thalamus
Dumbbell-shaped mass of gray matter in each cerebral hemisphere
Relays sensory impulses to cerebral cortex sensory areas
In some way produces the emotions of pleasantness or unpleasantness associated with sensations
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19. CENTRAL NERVOUS SYSTEM
Divisions of the brain (cont.)
Cerebellum
Second largest part of the human brain
Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures
Cerebrum
Largest part of the human brain
Outer layer of gray matter is the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons
Interior of the cerebrum composed mainly of white matter (that is, nerve fibers arranged in bundles called tracts)
Functions of the cerebrum—mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements
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20. CENTRAL NERVOUS SYSTEM
Spinal cord (Figure 8-11)
Outer part is composed of white matter made up of many bundles of axons called tracts; interior composed of gray matter made up mainly of neuron dendrites and cell bodies
Functions as the center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain
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22. CENTRAL NERVOUS SYSTEM
Coverings and fluid spaces of the brain and spinal cord
Coverings
Cranial bones and vertebrae
Cerebral and spinal meninges—the dura mater, the pia mater, and the arachnoid mater (Figure 8-13)
Fluid spaces—subarachnoid spaces of meninges, central canal inside cord, and ventricles in brain (Figure 8-14)
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25. PERIPHERAL NERVOUS SYSTEM
Cranial nerves (Figure 8-16 and Table 8-2)
Twelve pairs—attached to undersurface of the brain
Connect brain with the neck and structures in the thorax and abdomen
Spinal nerves
Structure—contain dendrites of sensory neurons and axons of motor neurons
Functions—conduct impulses necessary for sensations and voluntary movements
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27. AUTONOMIC NERVOUS SYSTEM
Autonomic nervous system—motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue; regulates the body’s automatic or involuntary functions (Figure 8-18)
Autonomic neurons—preganglionic autonomic neurons conduct from spinal cord or brainstem to an autonomic ganglion; postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue
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