3 - Peripheral Nervous System

PNS

• Consists of 12 CNs and 30 pairs of spinal nerves

• Can regenerate

• Also include motor, somatosensory, and autonomic neurons

Motor neurons

• Found in the ventral horn of the SC

• Aka lower motor neurons

Somatosensory

Cell bodies located in the small ganglia adjacent to the SC

Autonomic neurons

• Within all 30 pairs of spial nerves

• Innervate smooth mm in blood vessels and sweat glands

Do the thoracic spina nerves form a plexus?

Yes

What type of thoracic spinal nerves innervate the back muscles and the skin?

Dorsal rami

What type of thoracic spinal nerves form the intercostal nerves?

Ventral rami

Herpes Zoster

 Viral infection of the sensory ganglia of spinal and cranial nerves

 Caused by varicella virus

 Usually appears along a single dermatomal pathway

 Causes a painful (nerve pain), blistering rash

Lumbar plexus 

Nerves L1 to L4

Sensory portion of lumbar plexus nerves

Genitofemoral, Lateral femoral cutaneous, Saphenous

Motor portion of the lumbar plexus nerves

Iliohypogastric, Ilioinguinal, Obturator, Femoral

Sacral plexus 

Nerves from L5-S3

What is the largest branch of the sacral plexus and the larges nerve in the body? What do it divide into?

• Sciatic nerve

• Divides into tibial and common fibular nerves)

Epineurium

outermost covering; continuous with the dura mater around the spinal cord

Perineurium

groups nerve fibers into bundles (fascicles) . Protects nerves from the blood

Endoneurium 

innermost connective tissue sheath

Why do peripheral nerves need to glide in their sheaths? Why can nerve gliding exercise help?

Because the gliding of nerves promotes both blood flow to the axons and movement of axoplasm (fluid within axons)

What are the fastest types of nerves?

large diameter axons with the thickest myelin sheaths

Alpha motor neurons

innervate muscles to create muscle tension and produce movement. Fast conducting with a thick myelin sheath

Gamma motor neurons

Innervate muscle spindles to maintain and alter muscle tension. Do not cause movement. Slower conducting

Neuropathy

Damage to the peripheral nerves that can impair motor and sensory functions

 Ex: carpal tunnel syndrome, diabetic neuropathy

 Motor impairments may result in loss of sweating, orthostatic hypotension (sympathetic neurons), bowel and bladder incontinence, sexual impotence, blurred vision, etc.

What is the PNS regeneration rate?

1 mm/day.

How long does the motor end plate stay intact after PNS damage?

1 year

When the axon, myelin sheath and all connective tissues are severed, the chance of recovery is less likely.

True

Denervated skeletal muscle will lose about 70% of cross-sectional area within 2 months

True

What are the symptoms of diabetic neuropathy?

 Paresthesias

 Paresis

 Hypotension

 Tachycardia

 Digestive problems

 Bowel and bladder incontinence

 Sexual dysfunction

 Thickening of blood vessels leading to ischemia