7- peripheral nervous system anatomy

Question 1

Describe the main features of the somatic nervous system

Answer 1

• Voluntary effectors (e.g., striated muscle)
• Single motor neuron from spinal cord to target organ • Always stimulatory
• ACh released at the synapse
• Do not fire at rest

Question 2

Describe the main features of the autonomic nervous system

Answer 2

• Involuntary effectors (e.g., cardiac muscle, glands)
• Usually two neurons from spinal cord to target organ
• Stimulatory or inhibitory
• ACh and/or NE released at the synapse
Have a baseline firing

Question 3

How are the dorsal and ventral roots different

Answer 3

• Dorsal (posterior) root - brings afferent (sensory) signals from the periphery to the CNS
• Ventral (anterior) root - takes efferent (motor) signals from the CNS to the periphery (motor neurons)

Question 4

Describe a rami

Answer 4

• Rami-lateralbranchesofthe spinal nerves

Ramicarrybothmotorand sensory fibres

Question 5

What 3 components make up the structure of a PNS nerve

Answer 5

Epineurium - connective tissue surrounding a nerve

Perineurium - connective tissue surrounding each fascicle Endoneurium - connective tissue surrounding each axon

Question 6

How do the 3 types of PNS neurone differ

Answer 6

• Agroup:largediameter,high conduction velocity, and are myelinated - alpha, beta, delta, gamma types
• Bgroup:myelinated,small diameter, low conduction velocity - conduct autonomic information
• Cgroup:unmyelinated,small diameter, low conduction velocity - dull, aching, burning pain and temperature sensation

Question 7

What is a nerve plexus

Answer 7

• Spinal nerves exit the intervertebral foramina to form nerve plexuses
• Nerve plexuses: networks of intersecting spinal nerves

There is a plexus which goes to EACH of
the four limbs
• Brachial Plexus = goes to the upper limb
• There are FIVE spinal nerves
contributing to the brachial plexus = C5
- T1
• As these spinal nerves leave the spinal
cord, some of them merge together
then later on they'll diverge
• This means that you get mixing up of
the individual spinal nerves so by the

Question 8

What is a dermatome

Answer 8

Areas of skin supplied by a single sensory spinal nerve

Stacked along the thorax and abdomen; longitudinally along the limbs

Question 9

What are the 12 cranial nerves and their functions

Answer 9

I Olfactory (Smell)
II Optic (Sight)
III Oculomotor (Moves eyelid and eyeball and adjusts the pupil and lens of the eye)
IV Trochlear (Moves eyeballs)
V Trigeminal (Facial muscles incl. chewing; Facial sensations)
VI Abducens (Moves eyeballs)
VII Facial (Taste, tears, saliva, facial expressions)
VIII Vestibulocochlear (Auditory)
IX Glossopharyngeal (Swallowing, saliva, taste)
X Vagus (Control of PNS e.g. smooth muscles of GI tract)
XI Accessory (Moving head & shoulders, swallowing)
XII Hypoglossal (Tongue muscles - speech & swallowing)

Question 10

What is neuropraxia, axonotmesis and neurotmesis

Answer 10

• Neuropraxia:involvesareversibleconductionblockcharacterizedby selective demyelination of the axon sheath - endoneurium and axon still intact - e.g., nerve compression
• Axonotmesis:demylinationandaxonloss-epineuriumandperineurium remain intact - still some continuity within the nerve - degeneration occurs below and slightly proximal to the site of injury
• Neurotmesis:mostsevereformofnerveinjury-associatedwithcomplete nerve division and disruption - e.g., commonly seen after lacerations or ischemic injuries

Question 11

What is the difference between dorsal and ventral rami

Answer 11

o DORSAL RAMI innervate muscle and skin of back

o VENTRAL RAMI innervate muscles and skin of rest of body, including limbs

Question 12

What happens when a peripheral nerve is damaged

Answer 12

A – The normal axon is contained by the endoneurium; a compression injury occurs which breaks the continuity of the AXOPLASM, therefore action potentials cannot be propagated
 B - The distal part of the nerve degenerates, but the PROXIMAL STUMP remains intact (unless injury is close to soma) and macrophages phagocytose the axonal and myelin debris (WALLERIAN DEGENERATION)
 C - The proximal part of the axon and cell body usually survive but undergo metabolic changes (CHROMATOLYSIS) – outgrowth of AXONAL SPROUTS from the proximal stump occurs; these are guided down by a scaffold of proliferating Schwann cells
 D – When the first axonal sprout makes contact with target organ, growth and myelination occurs; the other axonal sprouts then draw back into the proximal stump
o Successful regeneration mainly depends on how badly the axons and connective tissue sheaths are damaged and the distance from the target organ
o Failure to reconnect leads to formation of a NEUROMA containing trapped axons
 E – the nodes of Ranvier in the regenerated axon will be closer together than initially

Question 13

What is peripheral neuropathy and what are 2 types

Answer 13

 Progressive degeneration of peripheral nerves
 AXONAL DEGERATION – leads to a complete conduction block; may be the result of prolonged and increase segmental demyelination
SEGMENTAL DEMYELINATION – Schwann cells
eventually die therefore continuous conduction
replaces saltatory which affects the conduction speed

Question 14

Which nerves make up the sympathetic and parasympathetic division

Answer 14

Sympathetic: Formed by neurons from spinal nerves T1 to L2

Formed by neurons from cranial (III,XII,IX,X) and sacral (S2-S4) nerves

Question 15

What are the 5 types of spinal nerve

Answer 15

Cervical, thoracic, lumbar, sacral, coccygeal

Question 16

What happens when function is impaired in sensory, autonomic and motor nerves

Answer 16

• Sensory nerves (sensation): cause tingling, pain, numbness
• Motor nerves (movement): cause weakness to hands and feet
• Autonomic nerves (involuntary functions): cause changes in heart rate or blood pressure

Question 17

What is a EMG

Answer 17

• EMG - technique for evaluating and recording electrical activity produced by muscles. Electromyogram produced

Can be surface or intramuscular emg

Question 18

What is a SEP

Answer 18

• SEP are measured to assess whether sensations (pain, temperature and touch) in the periphery are being transmitted to the brain
Stimulating electrode on limb and recording electrode on head or neck

Question 19

What is a nerve conduction study

Answer 19

Determines conduction velocity
One electrode stimulates nerves and another nerve defects this impulse further along nerve
• Slower than normal speed could indicate nerve damage from direct trauma, diabetic or peripheral neuropathy, viral nerve infection or nerve entrapment diseases like the Carpal Tunnel Syndrome among other conditions