Nerve activates contraction, Exercises of Anatomy

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CHAPTER 7

THE NERVOUS SYSTEM

The nervous system is the master controlling

& communicating system of the body

Functions of the Nervous System

 Maintains body homeostasis with electrical

signals, provides for sensation, higher

mental functioning, emotional response, and

activates muscles and glands

 Works with the endocrine system

(hormones)

 The nervous system has 3 overlapping

functions:

 Sensory Input

 Integration

 Motor Output 2

Structural Classification: Nervous System

 Includes all the organs of NS, 2 subdivisions:

 Central Nervous System (CNS)

 Brain & Spinal cord, dorsal body cavity

 Act as integrating and command centers of NS

 Peripheral Nervous System (PNS)

 Nerves that extend from the brain & spinal cord

 Serve as communication lines & provide links

 Spinal Nerves- 31 pairs

 Cranial Nerves -12 pairs 4

Functional Classification:

Peripheral Nervous System

 Two Divisions: Sensory (afferent) & Motor

(efferent)

 Sensory (Afferent) Division

 Nerve fibers that carry information to the central nervous system from sensory receptors (constant info. to CNS)

 Somatic sensory fibers – (soma=body) – deliver impulses from skin, skeletal muscles, & joints

 Visceral sensory fibers – deliver impulses from the visceral organs 5

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Organization of the Nervous System

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Nervous Tissue: Support Cells of CNS

 Astrocytes – account for ½ neural tissue

 Abundant, star-shaped cells

 Many swollen projection ends that cling to neurons to brace them and anchor them to nutrient supply lines, blood capillaries

 Form living barrier between capillaries and neurons, to make exchanges between the 2

 Control the chemical environment of the brain (pick up excess ions & recapture neurotransmitters) 10

Nervous Tissue: Support Cells of CNS

 Microglia

 Spider-like phagocytes

 Dispose of debris (dead brain cells, bacteria)

 Ependymal cells

 Line cavities of the brain and spinal cord

 Circulate cerebrospinal fluid by beating their cilia, that fills cavities to give a protective cushion around CNS (^11)

 Satellite cells

 Protect neuron cell bodies, provide cushioning

 Schwann cells

 Form myelin sheath around nerve fibers in the peripheral nervous system

Nervous Tissue: Support Cells PNS

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Nervous Tissue: Neurons

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Neuron Anatomy

 Cell Body

 Nissl Substance – specialized rough endoplasmic reticulum

 Neurofibrils – intermediate cytoskeleton that maintains cell shape

 Nucleus

 Large nucleolus 16

Neuron Anatomy

 Extensions outside

the cell body:

processes- longest

from lumbar region

to the big toe

 Dendrites – conduct impulses toward the cell body  Axons – conduct impulses away from the cell body

 Nerve – bundle of nerve fibers 17

 Axonal terminals are separated from the

next neuron by a gap

 Synaptic cleft – tiny gap between adjacent neurons

 Synapse – functional junction between nerves,

 Although they get close, neurons never actually touch other neurons

 Nerve fibers are covered with a whitish fatty material called myelin, has a waxy appereance

 Myelin protects & insulates and increases transmission rate of nerve impulses

Nerve Fiber Coverings

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Nerve Fiber Coverings

 Axons outside CNS are

myelinated by Schwann

cells – produce myelin

sheaths in jelly-roll like

fashion

 Neurilemma - part of

Schwann cell external to

myelin sheath “neuron husk”

 Nodes of Ranvier – gaps in

myelin sheath along the axon

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