Nervous System
Nervous System
Functions
Neurons
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Receptors:
Interpret:
Response:
Afferent
Efferent
Organization of Nervous System
Central Nervous System
Peripheral Nervous System
Motor (Efferent)
Sensory(Afferent)
ANS
Somatic
Sympathetic
Parasympathetic
“Fight or Flight”
“Resting and Digesting”
Cellular Organization: 2 types of Cells
Neurons

Responsible for
conducting electrical
impulses
Characterisitics
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Long Life Span
Amitotic
High Metabolic Rate
Dendrite, Cell Body and Axon
Dendrites: Receive stimuli from receptors
Cell Body: Contains nucleus and organelles; lacks
centrioles
Axon: Generate and transmit nerve impulses
Secreting output
Input
conducting
Sensory Neurons
(Afferent)
Exteroceptors
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Provide information of about
external environment
I.e.
Proprioceptors
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Monitor the position of
skeletal muscles and joints
Interoceptors
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Monitor the activities of
internal systems and organs
I.e.
Motor Neurons
(Efferent)
Carry Instructions
from CNS to
muscles, tissues
and organs
Called Effectors
because they cause
a response
Interneurons
Located in brain and
spinal cord
Analyze sensory input
(afferent) and
coordinate motor
output (efferent)
Neuroglia/Glial Cells
Supporting cells to neurons
Act as phagocytes
Outnumber Neurons
Mitotic
Astrocytes
Secretes chemicals
important for the
maintenance of the
Blood Brain Barrier
o Feeds neurons
o Repairs damaged
neural tissues
Ependymal Cells
Produce CSF
(cerebrospinal fluid)
Line central cavities of
brain and spinal cord
These ciliated cells
circulate CSF
Microglia
Phagocytic
cells
Produced by
leukocytes
(WBCs)
Fight infection
Schwann Cells/Oligodendrocytes
Produce myelin sheath
-increases the speed of impulses,
insulator
Myelin=lipid components
Nodes of Ranvier-gaps in myelin
sheath, axon contacts its external
environment
Schwann cells-glial cells in PNS that
produce myelin sheath
Mylenated vs. Unmyelinated axons
Demylinated (multiple sclerosis)
Unmyleninated vs. Myleninated Axon
Ion transport occurs along the length of
the axon in an unmyleninated axon.
Ion transport occurs only where the
Nodes of Ranvier are located in a
myleninated axon.
Na+-K+ Pump
Active Transport – requires ATP
Resting Membrane Potential
Measured as voltage difference across the
membrane
Inside of membrane is -70 mV (.07 V) C
battery = 1.5 V
Maintained by Na+K+ pump
3 Na ions are pumped out for every
 2 K ions that are pumped in
 Requires ATP; maintaining a concentration
gradient

More Na+ leave the cell than K+ enter.
Charge
difference of
-70mv across
membrane
Inside of
axon is
negative
compared to
the outside.
Na ions and K ions are actively pumped out and in the cell.
Maintain a concentration gradient (difference) Ions do not
reach equilibrium.
Depolarization
Axon hillock is where impulse will begin
Na diffuses into axon
Reach -55mV = threshold
At threshold Na gates open; Na ions diffuse
into axon
Reach +30 mV; Na gates close
Graded Potential – depolarization occurs but
you never reach threshold.
Not enough Na+ moves into cell, impulse is
not sent.
Action Potential/Impulse
Enough
neurons fire so
red neuron
reaches
threshold
Impulse is sent
to next neuron
(green)
Enough Na+ diffuses into the cell reaching
threshold
Na+ continues to diffuse into cell until voltage
rises to +30 mV.
Repolarization – Na gates close, K
gates open. K+ diffuse out of cell
Repolarization
K+ ions
diffuse out
of the cell
Returning
the inside
of the cell
to its
negative
charge.
Charge inside the axon
goes below -70mV.
Caused by K+ leaving
the cell and Na+ not able
to enter the cell.
Increase in negative
charge since + ions are
leaving axon with no +
ions being able to enter
the neuron.
Change in Ion permeability with
Impulse.
Why would Na+ enter the
cell before K+?
What is happening when
Na+ enter the cell?
What is happening when
K+ leave the cell?
Absolute Refractory Period
•time needed to return the
neuron’s membrane to Resting
Membrane Potential
•Limits the number of
impulses that can be sent
Intensity of Impulse
Number of
times impulse is
sent

More impulses;
higher intensity
Speed of Impulse
Presence of Myelin
Sheath
Size of Neuron
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Large neurons =
less resistance;
impulse travels
faster through
neurons larger in
diameter
Axon Bud
-Responsible for
sending chemical
messengers
(neurotransmitter)
across the synapse.
-Synaptic vesicles
release NT by
exocytosis
-Receptor cells on
the dendrites receive
the NT.
Axon Bud
Exocytosis requires ATP
Axon Bud Animation
Impulse travels to axon bud
Ca ions enter through gated channels of axon bud.
Ca attaches to vesicles; NT released by exocytosis.
NT attaches to receptor cells on dendrite
Na gates open in dendrite and Na ions begin to enter the
dendrite. Reach Threshold = Action Potential
How is the impulse stopped?
As long as the NT remains attached to a
receptor, it will continue to send impulses.
NT is stopped by:
Reuptake of NT into vesicles; begin as soon as
impulse begins in postsynaptic neuron
 NT diffuses away from postsynaptic synapse
 Enzymes break down NT.
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I.e. neurotransmitter acetylcholine is broken down by
acetylcholinerase
 Acetylcholine → acetate + choline
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What happens at the Axon Bud!
Antidepressants