Download Nervous System

Nervous System
Basic Structure & Function
I.
Introduction – organs of the nervous system are divided into
A. Central Nervous System (CNS) – brain, spinal cord
B. Peripheral Nervous System (PNS) – Cranial & spinal nerves –
connect CNS with other parts of the body
II.
General Functions of the Nervous System
A. Sensory Function
1.
2. External Internal 3.
B. Integrative Functions –
C. Motor Functions
1. Employ peripheral nerves that carry impulses from CNS to
responsive parts called effectors
2. Effectors are outside the NS and include
a.
b.
III.
Nervous Tissue – neurons (nerve cells) are the functional unit;
neuroglia support physiological needs of neurons
A. Neurons – specialized to react to physical & chemical changes in
their surroundings and conduct nerve impulses
1. Functional differences
a. motor neurons –
b. sensory neurons –
c. interneurons –
2. Structural differences – see handout
a. bipoloar –
b. unipolar/monopolar –
c. multipolar –
3. Anatomy
a. dendrite –
b. cell body –
c. axon –
B. Neuroglia cells
1. Accessory cells
2. Fill spaces, support neurons, hold nervous tissue together;
play a role in the metabolism of glucose, help regulate K+
concentration, produce myelin, and carry on phagocytosis
C. Regeneration of nerve fibers
1.
2.
3.
IV. Structure of Peripheral Nerves – consists of bundles of nerve fibers
surrounded by connective tissue
A. Epineurium –
B. Fasicicle –
C. Perineurium –
D. Endoneurium –
V.
Cell Membrane Potential and Nerve Impulses
A cell membrane is usually electrically charges or polarized so
That outside is + and inside is A. Resting Potential (-70 mvolts)
1. Nerve cell is not conducting impulses
2.
3. There is a large number of negatively charged ions inside the
cell which can’t diffuse out
4.
5.
B. Local Potential changes
1. Stimulation of a membrane affects its resting potential in a
local region (light, temp., other neurons)
2.
3.
C. Action Potential – 1/1000 sec. or less
1. At threshold, Na+ channels open and Na+ diffuse inward
causing depolarization
2. About the same time K+ channels open and K+ diffuses
outward, causing repolarization
3.
4.
5.
D. Refractory Period
1. A brief time (10-30 msec.) following the passage of a nerve
impulse when the membrane is unresponsive to ordinary
stimuli
2.
E. All – or – None Response
1. If a nerve fiber responds at all, it responds completely
2. All impulses carried on that fiber will be of the same
strength
F. Coding & Interpretation of Messages
1. Frequency of action potentials –
2. Duration of a burst of action potentials –
3. Number & kinds of neurons firing – The threshold needed to
initiate a nerve impulse varies from one neuron to another.
Thus a weak stimulus will cause only a few neurons to fire,
strong will fire all of these neurons, plus others with higher
thresholds.
G. Impulse Conduction
1. Unmyelinated fibers conduct impulses that travel over their
entire surface
2. Myelinated –
3.
VI. The Synapse – The junction between 2 neurons. A synaptic cleft is the
gap between parts of two neurons at a synapse.
A. Impulses usually travel from a dendrite or cell body, then along the
axon to a synapse
B.
C.
D. When the neurotransmitter reaches the nerve fiber on the distal side
of the cleft, a nerve impulse is triggered.
VII. Nerve Pathways – the route followed by an impulse as it travels
through the nervous system
A. Reflex Arc – simplest nerve pathway
1.
2.
B. Reflex Behavior
1.
2.
3.
4.