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Chapter 8-2
A. INTRO
1. Nervous system communicates by electrical and
chemical signals
2. 3 overlapping functions
a. Sensory input – sense receptors to monitor
change in and out of body
b. Integration – processes and interprets data to
see what to do
c. Motor output – causes response of effector
organs
B. ORGANIZATION OF NERVOUS SYSTEM
1. 2 main parts
a. Central nervous system (CNS)
1) Brain and spinal cord
2) Interprets sensory input
3) Dictates motor responses
b. Peripheral Nervous System (PNS)
1) Nerves (axons)
2) Links all of the body to CNS
2. All parts work together
C. HISTOLOGY OF NERVOUS TISSUE
1. Made of 2 types of cells
a. Supporting cells – small cells that surround
neurons
b. Neurons – transmit electrical signals
1) Conduct messages by nerve impulses
2) Have long lifespan (+100yrs w/proper
nutrition)
3) Amitotic – once in place they don’t divide
4) High metabolic rate
a) Need continuous supply of glucose and O2
b) Can’t survive more than a few minutes w/o O2
2. Neuron structure
a. Cell body
1) Nucleus surrounded by cytoplasm
2) Most located in CNS and protected by skull
3) Normal cellular organelles found here
b. Processes
1) Dendrites
a) Short and branching
b) Input regions – large surface area to pick
up signal
c) Dendritic spines – “thorns” off dendrite
d) Send messages towards the cell body
2) Axons
a) Comes off cell body at the axon hillock
b) Terminal branches – end of axon where it splits
(10,000x not uncommon)
c) Synaptic knob (axon terminals) – end of terminal
branches
d) Generates nerve impulses and transmits them
i. Goes away from the cell body
ii. Impulse originates at axon hillock and travels to
terminal branches
c. Myelin
1) Myelin sheath – whitish, fatty substance that
covers some nerve fibers
a) Increases speed of nerve impulse
b) Protects and insulates fibers
2) White matter – dense collections of myelinated
fibers in brain and spinal cord
3) Gray matter – mostly nerve cell bodies –
unmyelinated
D. NEUROPHYSIOLOGY
1. Neurons highly responsive to stimuli
2. Action potential – response to simuli
3. Graded potential – incoming
signals over short distance
a. Short lived changes
b. Decreases in magnitude
w/distance
c. Stronger stimuli = more volts
= further distance
d. Can be a stimulus of the
senses
4. Resting Potential
a. Nerve cells at rest
b. Higher concentration of Na+ outside and higher
conc. of K+ inside membrane
c. Na+K+ pump works
d. K+ diffuses out quickly causing the outside to be +
and inside to be – in comparison
e. Resting potential = difference in charges
5. Action potential – long distance signals of axons
a. Usually only neurons and muscles generate these
b. Do not decrease in strength w/distance
c. All or nothing – stimulus has to overcome threshold
d. Steps
1) Threshold is reached
2) Channels change
3) Allow Na+ to freely enter cell
4) Electrical charge is lost and becomes depolarized
5) Other channels open and K+ moves out causing it
to polarize
6) Fig 8.3/8.4 pg 143
e. Refractory periods
1) Absolute refractory period – interval that keeps
axon from firing again until brought back to resting
place (1/1000 of a sec)
2) Relative refractory period
a) Time after absolute refractory period
b) Can fire again but needs a larger stimulus
ACTION AND RESTING POTENTIAL
• http://www.youtube.com/watch?v=p0lmlWoEEKY
• http://www.youtube.com/watch?v=U0NpTdge3aw
f. Conduction velocity
1) Axon diameter – wider = faster impulses
2) Myelination
a) More myelin = faster speed
b) No leakage of charge
E. NEURAL PROCESSING
1. Serial processing
a. All or none manner
b. Travels along one pathway to location
c. One neuron stimulates the next, which
stimulates the next, then the next, etc.
d. Reflexes
1) Rapid automatic response to stimuli
2) Help with homeostasis
3) Control heart rate, breathing, blood pressure
4) Loud noise – blink
5) Touch something hot – pull hand away
6) Reflex arc – unconditioned, present at birth
a) Starts w/receptor at end of a nerve
b) Fiber leads to CNS which processes it
c) Communicates w/motor neuron
d) Motor neurons connect with effectors
2. Parallel processing
a. Signal travels along several pathways
b. Each pathway is dealt w/at same time by
different neural circuitry
c. Takes longer
d. Get multiple responses
Stepping on a nail will cause you to do the following
at the same time:
- Withdraw your foot, shift
your weight
- Move your arms, feel
the pain
- Shout “ouchie,
ouchie, ouchie!”
3. Conditioned Reflex – based on experience, learned
response; habits, repetition
https://www.youtube.com/watch?v=WfZfMIHwSkU
Smelling manure could cause you to think of 1 or
more things:
- I have to spread manure on the farm
- That smells like money
- My friend slipped and fell face first in a cow pie
- We can use that to heat stoves