coordinates and regulates the function of all other body systems 2 major division central nervous...
TRANSCRIPT
Coordinates and regulates the function of all other body systems
2 major divisionCentral Nervous System (CNS)
Brain Spinal Cord
Peripheral Nervous System (PNS) Nerves
carry sensory info to the CNSMotor commands from CNS to muscles
2 types of cellsNeurons
transmit nerve impulses between parts of the nervous system
Neuroglia Support and nourish neurons Maintain homeostasis Form myelin Help in signal transmission
3 types of neuronsSensory neurons
Take messages to the CNS Sensory receptors detect changes in the
environment Interneuron
Receive input from the sensory neurons before communicate to motor neuron
Motor neuron Takes message away from CNS to rest of body
(organ, muscle or gland)
Fig. 17.1b
glands
brain
sensory neuronssensoryreceptors
motor neurons
skeletalmuscles
other motor neuronssmooth muscle
cardiac muscle
Peripheral nervous systemCentral nervous system
Anatomy of a neuronCell bodyDendrites
Receive signals from other neurons and send them to cell body
Axon Conducts nerve impulses away from the cell
body and send them toward other neurons
Myelin SheathFormed by Schwann Cells around the
axonGaps between Schwan Cells are called
nodes of Ranvier
Myelin Sheath gives nerves white colour
Helps protect and insulate the nerve Helps conduct nerve impulse
cell body
dendrites
Sensory neuron
direction ofconduction
axon
node of Ranviersensoryreceptor(in skin)
cell body
dendrites
Motor neuron
node of Ranvier
direction ofconduction
axon
nucleus ofSchwann cell
(neuroglial cell)
effector(muscle)
cell body
cell body
cell body
dendrites
dendrites
dendrites
Motor neuron
node of Ranvier
direction ofconduction
axon
effector(muscle)
Interneuron
axon terminal
Sensory neuron
direction ofconduction axon
node of Ranviersensoryreceptor
(in skin)
Nervous system uses a nerve impulse to send information
When an axon is not conducting a nerve impulse we call it at resting potential More negative inside the axon Positive outside the axon
Difference in polarity is due to ion concentrationMore Na+ ions outside the axonMore K+ ions inside the axon
Sodium-potassium pumps Actively transport Na+ out of axon and K+ into
axon 3 Na+ for every 2 K+
K+
Na+
+
recordingelectrodeInside axon
axonalmembrane
inside axon
outside axon
a. Resting potential: more Na+ outside the axon and more K+ inside the axon causes polarization.
gated K+
channel
referenceelectrodeoutside axon
gated Na+
channel
+ + + + + + + +
+
+
+ + + + + + + +
Action potential Rapid change in polarity across the axon Nerve impulse
During an action potential DEPOLARIZATION
Sodium channels open up Sodium enters the axon Axon becomes more positive
REPOLARIZATION Potassium gates open K+ moves outside of axon Axon returns to original negative charge
open Na+
channel
b. Action potential be gins: depolarization occurs when Na+ gates open and Na+ moves inside the axon.
direction of impulse
+
+ + + + + + + +
+
+
+ + + + + + + +
+
direction of impulse
open K+
channel
c. Action potential ends: repolarization occurs when K+ gates openand K+ moves outside the axon.
+
+ + + + + + + +
+
+
+ + + + + + + +
+
Refractory periodReturns K+ to the inside of cell and Na+
outside through pump returning the neuron to its normal polarized
state
Time (milliseconds)
Vo
ltag
e (m
V)
threshold
+60
+40
+20
0
–20
–40
–60
0
actionpotential
K+ movesto outsideaxon
Na+ movesto insideaxon
restingpotential
1 2 3 4 5 6
dep
ola
riza
tio
n
repo
larization
d. An action potential can be visualized if voltage changes aregraphed over time.