L9: Functional Anatomy of the PNS

what kind of neurons carry SENSORY information from receptors in the skin and organs TO the CNS?

Afferent Neurons

Where are the cell bodies of afferent neurons located?

Outside of the spinal cord and brainstem

What kind of neurons carry MOTOR information FROM the brain to the PNS?

Efferent neurons

Where are the cell bodies of efferent neurons located?

In the ventral horn of the spinal cord

What are the 4 types of somatosensory receptors?

1- Mechanoreceptors

2- proprioceptors

3- Thermoreceptors

4- Nociceptors

Which kind of somatosensory receptor detects touch, pressure, stretchings, and vibration?

Mechanoreceptors

What kind of somatosensory receptor provides continuous information about the body and limb position?

Proprioceptors (spacial awareness)

What kind of somatosensory receptor consists of free nerve endings that respond to temperature?

Thermoreceptors

What kind of somatosensory receptors consists of free nerve endings that respond to extreme mechanical, thermal, or chemical stimuli and initiate the sensation of pain?

Nociceptors

Sensory receptors convert stimuli into ____ impulses that are transmitted by _____ neurons from the ______ to the brainstem or ____ ____.

• electrical

• Sensory

• PNS

• Spinal cord

What 2 factors of a neuron influence the conduction velocity of action potentials?

1- neuron diameter

2- myelination

Is conduction velocity of a neuron faster or slower when myelination is present?

FASTER

Is conduction velocity of neurons faster or slower with a smaller neuron diameter?

SLOWER

What is a spinal reflex?

A rapid, predictable, involuntary response to a stimulus involving the spinal cord

What is a stretch reflex?

Quick stretch of a muscle (activated muscle spindles) that causes contraction of the muscle being stretched

What is a withdrawal reflex?

Protective reflex that withdraws a body part from a painful stimulus

If a lower limb is involved in a withdrawal reflex, what happens to the lower limb on the opposite side?

Opposite side extensors contract to support the body

_____ ______ give rise to spinal nerves that branch into posterior (dorsal) rami and anterior (ventral) rami

Spinal segments

Posterior (dorsal) rami innervate?

Deep back muscles and skin over the back

Anterior rami innervate?

Muscles and skin in the extremities, front and sides of the neck, thorax, and abdomen

What is the area of skin supplied by a spinal cord segment/spinal nerve called?

Dermatome

is there overlap between adjacent dermatomes?

YES

What are the regional dermatome ranges discussed in class?

• C2-C4: neck

• C5-T2: upper extremity

• C4-L1: trunk

• L1-S4: lower extremity

• S3-coccygeal nerve: perineum

What are the spinal segment innervations of muscle called?

Myotomes

What are the two major myotomes discussed in class?

• upper extremity: C5-T1

• Lower extremity: L1-S3

What spinal segments make up the cervical plexus?

C1-C4

What does the cervical plexus innervate?

Skin of the anterior and lateral neck, some anterior neck muscles, and the phrenic nerve

What spinal segments make up the brachial plexus?

C5-T4

What does the brachial nerve innervate/what are its branches?

• provides motor and sensory to the upper limb

• Major nerves: axillary, radial, musculocutaneous, median, and ulnar

What spinal segments make up the lumbosacral plexus?

L1-S4

Where does the lumbosacral plexus supply innervation to?

The lower extremity and perineum

What is the function of connective tissue in nerves?

Protection and support

Does the connective tissue in nerves contain blood vessels?

YES

What are the layers, from superficial to deep, of the connective tissue in nerves?

Epineurium → perineurium → endoneurium