Download BioH Nervous System PPT 2013

Human Anatomy & Physiology
NERVOUS SYSTEM
BioH
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Nervous System Functions
Control &
coordinate functions
throughout the body
Respond to
internal & external
stimuli
Provides fast
communication
between body
systems and parts
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Nervous system cells
 Neuron
signal
direction

a nerve cell
dendrites
cell body
 Structure fits function
many entry points
for signal
 one path out
 transmits signal

axon
myelin sheath
dendrite  cell body  axon
signal direction
synaptic terminal
synapse
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Neuron Basic Structure
Messages sent by the nervous system are electrochemical signals (impulses) carried by neurons (nervous
system cells)
Impulses always travel from dendrites, through the cell
body to the axon terminal
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Neuron Anatomy
Dendrites – short, branched extensions that receive
impulses from the environment or other neurons toward the
cell body
Cell Body – the largest part of a neuron, containing most of
the cytoplasm and the nucleus
Axon – the long extension that carries an impulse away from
the cell body
Myelin (myelin sheath) – insulating membrane surrounding
most axons (roduced by Schwann cells) separated by small
gaps (Nodes of Ranvier = “nodes”)
Axon terminals – branches at the end of an axon
Neurons may have many dendrites and axon terminals, but
only one axon
Nerve – bundle of axons and dendrites from many neurons
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Fun facts about neurons
• Most specialized cell in
animals
• Longest cell
– blue whale neuron
• 10-30 meters
– giraffe axon
• 5 meters
– human neuron
• 1-2 meters
Nervous system allows for
1 millisecond response time
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Neuron Types
Sensory Neuron – carries impulse from sense organs to brain & spinal
cord
Motor Neuron – carries impulse from brain to muscles & glands
Interneuron – connects sensory and motor neurons
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Nerve Impulse
HOW does a signal travel along an neuron?
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Transmission of a signal
• Think dominoes!
– start the signal
• knock down line of dominoes by tipping 1st one
 trigger the signal
– propagate the signal
• do dominoes move down the line?
 no, just a wave through them!
– re-set the system
• before you can do it again,
have to set up dominoes again
 reset the axon
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Transmission of a nerve signal
• Neuron has similar system
– protein channels are set up
– once first one is opened, the rest open in
succession
• all or nothing response
– a “wave” action travels along neuron
– have to re-set channels so neuron can react
again
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Resting Neuron
When a neuron is resting (NOT transmitting an impulse),
the outside of the cell has a net positive ion charge, while
the inside has a net negative charge.
Na+ ions are pumped out of the cell while K+ ions are
pumped into the cell, using active transport
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Na+ K+ pumps
(active transport)
and leakage
channels
This creates a
difference in charge
between the inside
and the outside of a
neuron = resting
potential
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Measuring cell voltage
unstimulated neuron = resting potential of -70mV
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Moving Impulse
The neuron remains in a
“resting state” until it receives
a stimulus large enough to
start an impulse (“All or
nothing response”) from the
environment or another
neuron.
The electrical imbalance
between the inside and the
outside of the neuron is
reversed as the impulse
travels along the axon toward
the axon terminals =
ACTION POTENTIAL
(nerve impulse)
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What happens at the end of the axon?
Impulse has to jump the synapse!
– junction between neurons
– has to jump quickly from one cell to next
How does
the wave
jump the gap?
Synapse
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The Synapse
The action potential travels along the axon (“jumping” from
node to node) until it reaches an axon terminal and the
gap (synapse) between it and another cell
Chemicals
(neurotransmitters)
travel between the
axon terminal and the
next cell through the
synaptic cleft
(synapse)
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Action potential graph
40 mV
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30 mV
Membrane potential
1. Resting potential
2. Stimulus reaches threshold
potential
3. Depolarization
Na+ channels open;
K+ channels closed
4. Na+ channels close;
K+ channels open
5. Repolarization
reset charge gradient
6. Undershoot
K+ channels close slowly
20 mV
10 mV Depolarization
Na+ flows in
0 mV
–10 mV
3
–20 mV
Repolarization
K+ flows out
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–30 mV
–40 mV
–50 mV
Threshold
–60 mV
2
–70 mV
–80 mV
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Resting potential
Hyperpolarization
(undershoot)
6 Resting
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Divisions of the Nervous System
Central Nervous System (CNS) – brain
and spinal cord
“Coordination/communication center”
Receives most impulses and
determines “next steps”
Sends communication along spinal
cord
Peripheral Nervous System (PNS) – all
the nerve cells not part of the CNS
Receives internal and external
sensory input
Receives and sends impulses to
muscles or glands
Reflex arcs
Autonomic Nervous System – regulates
activities that are involuntary
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CNS and PNS
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Reflex Arc
Impulse pathway travels directly from sensory neuron to
spinal cord, interneuron and back to muscle or gland
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Summary – Brain Basics &
Neuroscience
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