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The Nervous System
I. Introduction
A. Function
1. Monitor changes (sensory input)
a. Inside body
b. Outside body
2. Interpret changes (integration in CNS)
3. Initiate response (motor function or output)
a. Muscle contraction (musculoskeletal system)
b. Glandular secretion (endocrine system)
B. Organization
1. Central Nervous System (CNS)
a. Brain
b. Spinal Cord
2. Peripheral Nervous System (PNS)
a. Cranial Nerves
b. Spinal Nerves
II. The cells of the nervous system
A. The Neuron (The nerve cell)
1. Lose ability to divide and form new cells after birth (amitotic)
a. Can live (under optimal conditions) for a lifetime (>100 years)
b. If cell body is destroyed, cell dies
c. Neuron cannot be replaced
2. Able to conduct nerve impulses
3. Number in body = n x 109, where n >1
4. High metabolic rates
a. need for continuous supply of
(1) glucose
(2) oxygen
b. die if deprived of these for more than a few minutes
B. Functional Classification
1. Sensory (Afferent) Neurons
a. Carry information from detectors (receptors) to CNS
b. Types of sensory detectors
i. Special sense organs (complex receptors)
(A) Vision (eye)
(B) Hearing (ear)
(C) Equilibrium (inner ear)
(D) Taste (tongue)
(E) Smell (nose)
ii. Cutaneous sense organs (skin)
(A) Pain receptor
(B) Touch receptor
(C) Deep pressure receptor
(D) Heat receptor
(E) Cold receptor
iii. Proprioceptors (muscles and tendons)
(A) Detect stretch or tension
2. Motor (Efferent) Neurons
a. Carry impulses from the CNS to
(1) muscles
(2) glands
b. Types
(1) Somatic Nervous System (Voluntary)
(a) carry impulses to skeletal muscles
(2) Autonomic Nervous System (ANS) (Involuntary)
(a) Carry impulses to
i) cardiac muscle
ii) smooth muscles
iii) glands
(b) Functional Subdivisions
i) Sympathetic
ii) Parasympathetic
3. Association (Interneuron) Neurons
a. Located in the CNS
b. Connect motor and sensory neurons
c. Comprise >99% of the neurons of the body
4. Cell body
5. Neuron processes (or fibers)
a. Dendrites
(1) variable number
(2) conduct impulses toward cell body
(3) never myelinated
b. Axon
(1) only one per neuron
(2) conduct impulses away from cell body
(3) release neurotransmitters
6. Synaptic cleft (tiny gap between axon terminal and next axon)
7. Myelin
a. Nature
(1) Structure
(a) whitish, fatty material
(b) part of cell wall from supporting cell
(c) waxy appearance
ii. Function
(A) protects and insulates nerve fibers
(B) increases speed of nerves pulses
b. Source
i. Schwann cells (PNS)
ii. Oligodendrocytes (CNS)
C. Neuroglia (Glial cells) = Supporting Cells
0. General Comments
a. 5-50X more numerous than neurons (80-98% of nervous tissue)
b. Nearly 1/2 of neural tissue volume in CNS
c. Mitotic throughout life
d. Most brain tumors are gliomas
D. Additional Terminology
1. Gray matter
a. tissue formed from neuron cell bodies and unmyelinated nerve fibers
b. refers to color of nerve cells
2. White matter
a. tissue formed from myelinated nerve fibers
b. referes to color of myelin sheath
III. Central Nervous System
A. The Brain
1. Cerebrum
a. Function
(1) involved with
(a) thinking and consciousness
(b) willed movements
(c) memory
(d) vision
(e) hearing
(f) sensory perception
(g) emotions
(h) speech
2. Diencephalon
a. Thalamus
(1) "Gateway of the cerebral cortex" for afferent (sensory) fibers
(2) Relay station for both sensory and motor impulses
b. Hypothalamus
(1) Autonomic control center
(2) Involved with regulation of
(a) Body temperature
(b) Water balance and thirst (via ADH)
(c) Food intake and metabolism
(d) Sleep-wake cycles
(e) Endocrine functioning
c. Epithalamus
(1) Choroid plexus
(a) forms cerebral spinal fluid (CSF)
3. Brain Stem
a. Conduction pathway between higher and lower brain centers
b. Respiratory centers (help maintain normal rhythm of breathing)
c. An autonomic reflex center for mainenance of body homeostasis
(1) Controls (examples)
(a) Heart rate
(b) Blood pressure
(c) Breathing
(d) Swallowing
(e) Vomiting
(f) Hiccuping
(g) Coughing
(h) Sneezing
4. Cerebellum
a. assists the maintenance of proper equilibrium, balance, and normal posture
b. coordinates skeletal muscle movements for the production of normal, smooth coordinated movements
B. Spinal Cord
1. involved with
a. sensory pathways to brain
b. motor pathways to body
IV. Peripheral Nervous System (PNS)
A. Includes all neural structures outside the brain and spinal cord
1. Sensory receptors
2. Peripheral nerves
V. Autonomic Nervous System (ANS)
A. General Comments
1. ANS is a motor subdivision of PNS
2. Autonomic implies "self governing"
2. ANS controls involuntary muscles
a. Cardiac muscle tissue
b. Smooth muscle tissue
i. walls of visceral organs
ii. walls of blood vessels
c. Glandular epithelial tissue
3. (Somatic Nervous System controls voluntary muscles)
B. Sympathetic Nervous System
1. An emergency nervous system
2. Prepare us for the "fight-or-flight" response
3. Gives instantaneous response
4. Sx:
a. pounding heart
b. rapid, deept breathing
c. cold, sweaty skin
d. dilated eye pupils
C. Parasympathetic Nervous System
1. Takes care of normal, everyday conditions
2. The "resting and digesting" system
3. Conserves body energy
4. Gives slower response
5. Sx:
a. low blood pressure
b. low heart rate
c. low respiratory rate
d. the gi tract is actively digesting food
e. skin is warm
f. eye pupils are constricted
g. the lenses of the eye are accommodated for close vision
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