1. Central nervous system (CNS)
Peripheral nervous system (PNS)
Brain and spinal cord
Cranial nerves and spinal nerves
Integrative and control centers
Communication lines between the
CNS and the rest of the body
Sensory (afferent) division
Motor (efferent) division
Somatic and visceral sensory
nerve fibers
Motor nerve fibers
Conducts impulses from the CNS
to effectors (muscles and glands)
Conducts impulses from
receptors to the CNS
Somatic sensory
fiber
Somatic nervous
system
Autonomic nervous
system (ANS)
Skin
Somatic motor
(voluntary)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
skeletal muscles
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Visceral sensory fiber
Stomach
Skeletal
muscle
Motor fiber of somatic nervous system
Sympathetic division
Parasympathetic
division
Mobilizes body
systems during activity
Conserves energy
Promotes house-
keeping functions
during rest
Sympathetic motor fiber of ANS
Heart
Structure
Function
Sensory (afferent)
division of PNS
Parasympathetic motor fiber of ANS
Bladder
Motor (efferent)
division of PNS

2. Capillary
Neuron
Astrocyte

3. Myelin sheath
Process of
oligodendrocyte
Nerve
fibers

4. Neuron
Microglial
cell

5. Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue

6. Satellite
cells
Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber

7. Dendrites
Cell body
Neuron cell body
(receptive
regions)
(biosynthetic center
and receptive region)
Nucleolus
Axon
(a)
Dendritic
spine
(impulse
generating
and conducting
region)
Nucleus
Impulse
direction
Nissl bodies
Node of Ranvier
Axon terminals
(secretory
region)
Axon hillock
Schwann cell
(one inter-
node)
Neurilemma
Terminal
branches

8. rotates around the axon, wrapping its plasma membrane loosely around
Schwann cell
plasma membrane
Schwann cell
cytoplasm
A Schwann cell
envelopes an axon. 1
Axon
Schwann cell
nucleus
The Schwann cell then
rotates around the axon,
wrapping its plasma
membrane loosely around
it in successive layers. 2
Neurilemma
The Schwann cell
cytoplasm is forced from
between the membranes.
The tight membrane
wrappings surrounding
the axon form the myelin
sheath. 3
Myelin sheath
(a) Myelination of a nerve fiber (axon)

10. Receptor
Neurotransmitter chemical
attached to receptor
Na+
Na+
Chemical
binds K+ K+
Closed
Open
(a) Chemically (ligand) gated ion channels open when the appropriate neurotransmitter binds to the receptor, allowing (in this case) simultaneous movement of Na+ and K+.

11. Na+
Na+
Membrane
voltage
changes
Closed
Open
(b) Voltage-gated ion channels open and close in response to changes in membrane voltage.

12. Voltmeter
Plasma
membrane
Ground electrode
outside cell
Microelectrode
inside cell
Axon
Neuron

13. Na+-K+ ATPases (pumps) maintain the concentration
The concentrations of Na+ and K+ on each side of the membrane are different.
Outside cell
The Na+ concentration
is higher outside the
cell.
Na+
(140 mM ) K+
(5 mM )
The K+ concentration
is higher inside the
cell. K+
(140 mM )
Na+
(15 mM )
Na+-K+ ATPases (pumps)
maintain the concentration
gradients of Na+ and K+
across the membrane.
Inside cell
The permeabilities of Na+ and K+ across the
membrane are different.
Suppose a cell has only K+ channels...
K+ loss through abundant leakage
channels establishes a negative
membrane potential.
K+ leakage channels K+ K+ K+ K+
Cell interior
–90 mV
Now, let’s add some Na+ channels to our cell...
Na+ entry through leakage channels reduces
the negative membrane potential slightly. K+ K+
Na+ K K+
Na+
Cell interior
–70 mV
Finally, let’s add a pump to compensate
for leaking ions.
Na+-K+ ATPases (pumps) maintain the
concentration gradients, resulting in the
resting membrane potential.
Na+-K+ pump K+ K+
Na+ K+ K+
Na+
Cell interior
–70 mV

14. The concentrations of Na+ and K+ on each side
of the membrane are different.
Outside cell
The Na+
concentration
is higher
outside the
cell.
Na+
(140 mM ) K+
(5 mM )
The K+
concentration
is higher
inside the
cell. K+
(140 mM )
Na+
(15 mM )
Inside cell
Na+-K+ ATPases (pumps) maintain
the concentration gradients of Na+
and K+ across the membrane.

15. K+ K+ The permeabilities of Na+ and K+ across the
membrane are different.
Suppose a cell has only K+ channels...
K+ loss through
abundant leakage
channels establishes
a negative membrane
potential.
K+ leakage channels K+ K+
Cell interior
–90 mV K+ K+

16. Stimulus
Depolarized region
Plasma
membrane
(a) Depolarization: A small patch of the
membrane (red area) has become depolarized.

17. Spread of depolarization: The local currents
(black arrows) that are created depolarize
adjacent membrane areas and allow the wave of
depolarization to spread.

18. SHINGLES