PrayerAttendance Homework

Peripheral Nervous System (PNS)

PNS

21 pairs of cranial nerves 31 pairs of spinal nerves

Innervates ( 신경을 분포시키다 ) upper body and head

Innervates entire body

Peripheral Nervous System (PNS)

PNS

Motor Division (efferent)

From CNS to Effectors

Sensory Division (afferent)

From Sensory Receptors to CNS

Somatic Nervous System 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

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.

Example: Reflex Arc for Knee-Jerk

• 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.

Polysynaptic Reflexes

Questions 10

Motor Division (ANS) • The autonomic nervous system (ANS) regulates the internal

environment using involuntary actions and processes. • ANS motor neurons innervate:

• 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

Heart Smooth muscle in blood vessels

Digestive tract

Endocrine system

Excretory system

Respiratory system

Reproductive system

Sympathetic Division • Responsible for fight or flight responses

• 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).

Increased heart rate

vasoconstriction of blood vessels in the skin

Inhibition of digestion

vasodilation of blood vessels in skeletal muscle

Dilation of pupils학생들 의 팽창 piloerection경직

The Parasympathetic Division • Innervates actions that conserve energy and restore the body

to normal activity following exertion (rest and digest) • Parasympathetic neurons stimulate:

• 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.

Decrease in heart rate.

Increase in digestive action.

Vasodilation of blood vessels in the skin

Questions 11