Download Central Nervous System

Transmitting
an impulse
How a nerve impulse is transmitted
1) At Rest - The neuron is POLARIZED (-70mV)
There is a slightly negative charge on the inside, and a
positive charge on the outside….. Why?
Resting Potential
sodium-potassium pump maintains balance
Pumps Na+ (sodium) outside & Pumps K+
(potassium) inside by active transport
Membrane is more leaky to K+ and more K+ goes
back out than Na+ leak back inside
Some large negatively charged ions stuck inside
Resting Potential= -70mV because overall more
positive charges outside and negative charges
inside
Sodium-potassium pumps
(3 Na+ out /2 K+ in)
Na+/K+ channels (always open)
12-8
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ECF
Figure 12.11
Na+ 145 m Eq/L
K+
Na+
channel
4 m Eq/L
K+
channel
Na+ 12 m Eq/L
K+ 150 m Eq/L
ICF
 Na+ concentrated outside of cell (ECF)
 K+ concentrated inside cell (ICF)
Large anions
that cannot
escape cell
How a nerve impulse is transmitted
2)
Depolarization:
 When neuron is stimulated by chemicals, light, heat,
or mechanical disturbance it causes opening of Na+
channels, allowing Na+ to rush in and de-polarize
membrane
 If Axon Hillock reaches threshold (-55mV), an action
potential is created
How a nerve impulse is transmitted
2) Depolarization
 This is all-or-none (stimulus must exceed a
threshold for the action potential to occur, and once
it starts, it will continue all the way down axon
toward axon endings)
The positive charges inside axon triggers
neighboring Na+ gates to open (Na+ gates only
inactivated once rising membrane potential passes 0 mV)
How a nerve impulse is transmitted
3) Repolarization
 After inside flooded with Na+, K+ gates open (they are
slower to respond) and let K+ out which are repelled by +
inside
 Na+ gates remain closed
 The inside becomes negative while outside become
positive and this repolarizes membrane
How a nerve impulse is transmitted
4) Refractory period
 Na+/K+ pumps work to create original
concentration (K+ on inside and Na+ outside)
 During this time the neuron will not respond to
new impulses
Refractory Period
Refractory period – short period of time
after an action potential when a
threshold stimulus will NOT trigger
another action potential.
a.Limits frequency
b.Ensures the impulse is only transmitted in
one direction – down the axon.
Fig 9.15
20
Fig 9.16
21
Signal Conduction in Nerve Fibers
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12-22
Dendrites
Cell body
Axon
Signal
Action potential
in progress
Refractory
membrane
Excitable
membrane
++++–––++ ++++ +++++
––––+++–––––– –––– –
––––+++–––––– –––– –
++++–––++ ++++ +++++
+++++++++ –––+ +++ ++
–––––––––+++– –––– –
–––––––––+++– –––– –
+++++++++ –––+ +++ ++
+++++++++ ++++ ––– ++
––––––––––––– +++– –
––––––––––––– +++– –
+++++++++ ++++ ––– ++
Figure 12.16
Impulse Conduction Rate
Myelinated neurons faster than unmyelinated
Myelinated fibers conduct impulses from one
Node of Ranvier to the next, a phenomenon
called saltatory conduction.
Speed of impulse conduction is proportional
to the diameter of the axon
a.Thick, myelinated motor axons conduct at 120
m/s
b.Thin, unmyelinated sensory axons conduct at 0.5
m/s
All-or-None Response
If a nerve fiber responds at all to a stimulus
of threshold or above, it responds
completely by conducting an impulse (allor-none response).
All action potentials are of the same
strength.
Greater intensity of stimulation triggers
more impulses per second, not stronger
impulses.
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The Synapse
• Neurons DON’T touch
• The gap between the axon of one neuron, and
the dendrites of another is called the SYNAPSE
1. Action potential happens
2. Neurotransmitter is released by axon ending
 Neurotransmitter is a chemical that sends a signal
3. Neurotransmitter binds to dendrite
membrane of next neuron
4. Excitation or inhibition of the membrane
occurs
5. Neurotransmitter is ‘recycled’
The Synapse
Divisions of the Nervous System:
1. Central Nervous
System (CNS)
1. Peripheral Nervous
system (PNS)
1. The Central Nervous System (CNS)
Relays messages, processes information
and analyzes information.
Includes:
Brain
Spinal Cord
Parts of the Brain
Cerebrum’s Purpose:
Controls voluntary activities of the body
Cite of intelligence, learning, and judgment
Made up of frontal, parietal, occipital, and
temporal lobes
Phineus Gage
Parts of the brain
Cerebellum: coordination and balance
Brain stem: regulates blood pressure,
heart rate, breathing, and swallowing
Parts of Brain
Thalamus: relays sensory input to proper region
of cerebrum
Hypothalamus: control center for recognition
and analysis of hunger, thirst, fatigue, anger, and
body temperature
2. Peripheral Nervous System:
everything outside of CNS
1. Sensory Division:
transmits impulses from
sense organs to central
nervous system
What are sense organs?
Organs designed to pick
up stimuli (name 5 sense
organs)
2. Motor Division: Transmits
impulses from CNS to the
muscles or glands
Quick Quiz: Which is
sensory which is motor?
Seeing Sensory
Raising your hand Motor
Tasting Sensory
Blinking when a ball is thrown
past your face
Sensory when you see the ball,
motor when you blink
Motor Division of PNS
2 parts
1. Somatic Nervous system
 Regulates activities under conscious control (ex.
Moving skeletal muscles)
 Some involved with reflexes and can act without
conscious control (see next slide)
2. Autonomic Nervous System
 Regulates activities that are automatic or involuntary
 Example: when running, speeds up heart and blood
flow, stimulates sweat glands and slows down digestion
 Divided into sympathetic and parasympathetic
 Sensory neuron
interneuron
 Without brain processing
Reflex Arc
motor neuron
Reflex Arc
Parkinson’s Disease
Cause
Parkinson's disease is a disorder of the brain that
leads to shaking (tremors) and difficulty with
walking, movement, and coordination.
Caused by loss of dopamine producing cells in
brain (substantia niagra)
Dopamine helps control muscle movement by
releasing inhibitory function of substantia niagra so
things are not moving when not specifically told to
do so
Without dopamine, it takes more effort for each
motion and movements are shaky
Helpful Links
Why we have pain and how we kill it
Nerve Impulse Molecular Mechanism
Action potential
Nervous System and Neuron overview