Peripheral Nervous System
and
Reflex Physiology
PNS Components:
► All
Nerves
extending from the brain and
spinal cord (CNS).
► Reminder:
What’s a nerve?
A bundle of axons (fibers)!
Categories of Nerves
► Motor
(efferent) nerves
conduct impulses from CNS
► Sensory
(afferent) nerves
conduct impulses toward CNS
► Mixed
nerves
have both motor and sensory fibers
* the most common type of nerve!!!
The Cranial Nerves
connect directly with the BRAIN
► 12 pairs
►
 1st 2 pairs connect to cerebrum
 All others connect to brain stem
 Extend to areas in the head/neck only
(with one exception!)
Cranial Nerve Names
I.
OLFACTORY
SMELL
(SENSORY)
II.
OPTIC
VISION /
SIGHT
SENSORY
III.
OCULOMOTOR
IV.
TROCHLEAR
Moves
eyeballs
MOTOR
Moves
eyeballs
MOTOR
V.
TRIGEMINAL
SENSORY (face)
MOTOR (chewing)
VI.
ABDUCENS
Moves
Eye
MOTOR
VII
FACIAL
Facial
MOTOR
Expression
Taste
SENSORY
VIII.
AUDITORY
Hearing/
balance
SENSORY
IX
GLOSSOPHARYNGEAL
Tongue/
Pharynx
SENSORY
MOTOR
X.
VAGUS
Organs of
Chest/
abdomen
SENSORY
MOTOR
XI.
ACCESSORY
Head / Neck
Muscles
MOTOR
XII.
HYPOGLOSSAL
Tongue
movement
MOTOR
REFLEXES
► Definition:
 rapid, involuntary response to
stimulus
►Reflexes can be :
 Pre-programmed for survival!
 Learned / Acquired
►Reflex
Arcs:
 Neuron pathways that carry
impulses involved in generating a
reflex
Reflex Arc
Components
►Receptor
► A sensory
(afferent) neuron
►Integration center
►Synapse
► interneuron(s)
►A motor (efferent neuron)
►Effector of some sort (usually muscle)
Two Major Reflex Categories
1. SOMATIC REFLEXES:
Result in activation of skeletal muscles
2. VISCERAL REFLEXES:
Result in activation of internal
organs/effectors
Reflex Examples
► Stretch
Reflex:
 Muscle contracts to counteract stretch stimulus
► Withdrawal
Reflex
 Stimulus (Pain or Perceived threat) leads to
withdrawal of threatened body part!
► Plantar
Reflex
 normal
► Babinski
 infants
Reflex
others
Abdominal Reflexes
Blink Reflexes
Reaction-time Reflexes
Pupillary Reflexes