Prayer
Attendance
Homework
Peripheral Nervous System (PNS)
PNS
21 pairs of cranial nerves
31 pairs of spinal nerves
Innervates (신경을 분포시
키다) upper body
and head
Innervates entire body
Peripheral Nervous System (PNS)
PNS
Motor Division
(efferent)
From CNS to Effectors
Somatic Nervous System
Sensory Division
(afferent)
From Sensory Receptors to CNS
Autonomic Nervous System
Sympathetic Division
Parasympathetic Division
Questions 9
Motor Division (SNS)
• The somatic nervous system (SNS) moves
muscles when there is external stimuli.
• Somatic pathways:
– Most are under voluntary control (자발적 통제)
– Some are involuntary (무의식적) monosynaptic or
polysynaptic reflexes.
• Very simple somatic pathway:
– Has one sensory neuron and one motor neuron
Monosynaptic Reflexes
• Has only 1 synapse between the sensory
neuron and the motor neuron.
• The pathway, or reflex arc, travels from the
sensory receptor to the sensory neuron, which
synapses directly with the motor neuron in
the spinal cord.
• The reflex arc is involuntary and occurs in the
spinal cord.
• Example: Reflex Arc for Knee-Jerk
Example: Reflex Arc for Knee-Jerk
1. The tendon covering the patella
(knee) is hit.
2. Stretch receptors fire.
3. An action potential is sent along
the sensory neuron and into the
spinal cord.
4. The sensory neuron synapses
with a motor neuron in the
spinal cord.
5. This simulates the quadriceps
muscle to contract.
6. The knee jerks forward.
Polysynaptic Reflexes
• The sensory neurons synapse with one or
more interneurons.
• The withdrawal reflex is an example of a
postsynaptic reflex.
– When a person steps on a nail, the injured leg
withdraws in pain, while the opposite leg extends
to offer support.
Questions 10
Motor Division (ANS)
• The autonomic nervous system (ANS) regulates the
internal environment using involuntary actions and
processes.
• ANS motor neurons innervate:
Heart
Smooth
muscle in
blood vessels
Digestive tract
Endocrine
system
Excretory
system
Respiratory
system
Reproductive
system
• Most ANS pathways have 2 motor neurons.
• One motor neuron has its cell body within the CNS, then
synapses outside the CNS with another motor neuron,
which innervates the effector.
• Two divisions: sympathetic and parasympathetic
Sympathetic Division
• Responsible for fight or flight responses
Increased heart
rate
vasoconstriction of Inhibition of
blood vessels in the digestion
skin
vasodilation of
blood vessels in
skeletal muscle
Dilation of pupils
학생들 의 팽창
piloerection
경직
• Sympathetic neurons start in the thoracic and lumbar parts of
the spinal cord.
• The presynaptic axon is short
• The postsynaptic axon is long.
• The presynaptic membrane secretes acetylcholine
• The postsynaptic membrane (effector) secretes
norepinephrine (adrenaline).
The Parasympathetic Division
• Innervates actions that conserve energy and restore the
body to normal activity following exertion (rest and digest)
• Parasympathetic neurons stimulate:
Decrease in heart
rate.
Increase in
digestive action.
Vasodilation of
blood vessels in the
skin
• Vagus nerve is one of the most important parasympathetic
nerves.
• Parasympathetic neurons start in the cranial and sacral
parts of the spinal cord.
• The presynaptic axon is long
• The postsynaptic axon is short.
• The neurotransmitter secreted in both the presynaptic
synapse and the postsynaptic synapse is acetylcholine.
Questions 11