block 2: peripheral nervous system

What is the peripheral nervous system?

All nervous structures outside of the CNS

What are all the sensory and motor nerves that the peripheral nervous system contain?

Spinal nerves, cranial nerves, sensory ganglia, sensory receptors

What are photoreceptors?

Rods and cones in retina detect light

What are chemoreceptors?

Respond to chemicals

What are nociceptors?

Respond to pain

(noci=harm)

What are thermoreceptors?

Respond to temperature

What are nociceptors and thermoreceptors both represented by?

Most common receptor types: free nerve ending

What are mechanoreceptors?

Responds to touch/pressure

What are the 2 types of mechanoreceptors?

Meissner's corpuscle

Pacinian corpuscle

What is meissner's corpuscle?

Responds to light pressure

What is meissner's corpuscle also known as?

Tactile corpuscle

What is pacinian corpuscle?

Responds to deep pressure

What is pacinian corpuscle also known as?

Lamellar corpuscle

What are porprioceptors?

Awareness of position, movement, balance

What is proprioception?

Sense of position in space

Where are proprioceptors found?

In muscles, tendons, ligaments, skin

What do proprioceptors detect change in?

Detect change in length, tension, and position

What are some examples of proprioceptors?

Neuromuscular spindles (stretch)

Golgi tendon organs (tension/muscle force)

Vestibular system of inner ear (balance, whole body position)

What are dermatomes?

"Map" of sensory innervation of skin

What is each strip of dermatome represented by?

Represented by specific spinal cord levels

What is each strip of dermatome associated with?

Associated with a pair of sensory nerves (left and right)

What is the T4 dermatome?

Nipple line

What is the T10 dermatome?

Umbilicus line

Are dermatomes exclusively innervated by a single spinal nerve?

No, there is overlap from levels above and below

What does total sensation loss require of dermatomes?

Requires damage to 3 adjacent spinal nerve levels

What are shingles?

Rash along entire dermatome

What is referred pain?

Pain in organs results in perceived pain elsewhere

What does referred pain involve?

Visceral sensory (from organs)

Somatic sensory (skin)

Why does the brain perceive additional pain in non-organ regions?

Some visceral signals enter spinal cord at the same level as somatic, through same dorsal root ganglion, shared region in spinal cord leads to this perception

What is myocardial ischemia?

Poor or no blood supply to cardiac muscle

Pain in upper left limb

Possible pain radiating to right limb, neck, and jaw

What is the nervous plexus?

Intertwined network of nerves

What does the nervous plexus innervated?

Bones, muscles, skin, etc.

What are the 4 major components of the nervous plexus?

Cervical, brachial, lumbar, sacral

For all nervous plexuses, what do both motor and sensory nerves derive from?

Ventral rami

Where is the cervical plexus?

C1-C4

What does the cervical plexus arise from?

Arises from cervical enlargement

What does the cervical plexus innervate?

Muscles and skin of neck

What is the major component of the cervical plexus?

Phrenic nerve

Where is the phrenic nerve?

C3, C4, C5

What is the importance of the phrenic nerve?

Keeps you alive

What is the motor innervation of the phrenic nerve?

Diaphragm (respiratory)

Where is the brachial plexus?

C5-T1

What is the motor innervation of the brachial plexus?

Muscles of shoulder and upper limb

What is the sensory innervation of the brachial plexus?

Skin of shoulder and upper limb

What plexus is the axillary nerve a part of?

Brachial plexus

What is the motor innervation of the axillary nerve?

Deltoid muscle

What is the sensory innervation of the axillary nerve?

Skin of shoulder

What happens when there is damage to the axillary nerve?

Limited arm abduction and loss of shoulder sensation

What plexus is the musculocutaneous nerve a part of?

Brachial plexus

What is the motor innervation of the musculocutaneous nerve?

Muscles of the anterior arm: biceps brachii, brachialis

What is the sensory innervation of the musculocutaneous nerve?

Lateral skin of forearm

What happens when there is damage to the musculocutaneous nerve?

Reduced arm flexion, forearm supination

Numbness/pain in lateral forearm

What plexus is the radial nerve a part of?

Brachial plexus

What is the motor innervation of the radial nerve?

Extensors of forearm, wrists, and digits

What is the sensory innervation of the radial nerve?

Portions of posterior and lateral arm and forearm

What happens when there is damage to the radial nerve?

Reduced arm, wrist, digit extension

Numbness/pain in posterior arm and forearm

What causes wrist drop?

Radial nerve damage

What is wrist drop?

Inability to extend wrist

How do doctors test for wrist drop?

Patient asked to pronate

If wrist involuntarily drops into flexion, then radial nerve damage

What plexus is the ulnar nerve a part of?

Brachial plexus

What is the motor innervation of the ulnar nerve?

Flexors

Hypothenar muscles

Lumbricals 3 and 4

What is the sensory innervation of the ulnar nerve?

Numbness/pain in medial skin of hand and half of digit 4

What is the funny bone?

Compression or damage to ulnar nerve at elbow

What is the result of hitting the funny bone?

Pain/numbness at site of damage and medial hand

What is the claw hand?

Severe/chronic damage to ulnar nerve

What is the result of claw hand?

Lumbricals effected

Extensor digitorum extends metacarpophalangeal joint

What plexus is the median nerve a part of?

Brachial plexus

What is the motor innervation of the median nerve?

Flexors of the wrist, thenar muscles, lumbricals 1 and 2

What is the sensory innervation of the median nerve?

Numbness/pain in skin of palms, digits, and half of digit 4

What is carpal tunnel syndrome?

Inflammation of tissue in carpal tunnel

Damage/impingement of median nerve

What is the result of carpal tunnel syndrome?

Painful swelling, limited mobility, numbness of skin

What is ape hand?

Median nerve damage

Loss of thumb opposition

What is the lumbosacral plexus?

Combination of lumbar and sacral plexuses

Where is the lumbosacral plexus?

L1-S4

What plexus is the femoral nerve a part of?

Lumbosacral plexus

What is the motor innervation of the femoral nerve?

Quadriceps

What is the sensory innervation of the femoral nerve?

Skin of anterior thigh and leg

What happens when there is damage to the femoral nerve?

Inability to extend knee

Numbness/pain in skin of anterior lower limb

What plexus is the obturator nerve a part of?

Lumbosacral plexus

What is the motor innervation of the obturator nerve?

Adductor muscles

What happens when there is damage to the obturator nerve?

Inability to adduct thigh

What plexus is the sciatic nerve a part of?

Lumbosacral plexus

What is the motor innervation of the sciatic nerve?

Hamstrings

What is the sensory innervation of the sciatic nerve?

Posterior thigh

What happens when there is damage to the sciatic nerve?

Weakened thigh extension

Inability to flex leg

Why are gluteal injections more favorable?

Not many nerves to damage and avoids sciatic nerve

What is sciatica?

Pain resulting from a pinched or compressed sciatic nerve

Posterior lower limb: weak, numb, pain

What plexus is the tibial nerve a part of?

Lumbosacral plexus

What is the motor innervation of the tibial nerve?

All posterior leg muscles: gastrocnemius, soleus, tibialis posterior, flexor hallucis longus

What happens when there is damage to the tibial nerve?

Reduced ability to plantarflex, flex digits, invert

What plexus is the common fibular nerve a part of?

Lumbosacral plexus

What are the 2 branches of the common fibular nerve?

Deep fibular nerve

Superficial fibular nerve

What is the motor innervation of the deep fibular nerve?

Muscles of anterior leg

What happens when there is nerve damage to the deep fibular nerve?

Reduced or absent dorsiflexion, digit flexion, inversion

What is the motor innervation of the superficial fibular nerve?

Muscles of lateral leg

What happens when there is nerve damage to the superficial fibular nerve?

Eversion

What is another way to say fibular?

Peroneal

What is foot drop?

Deep fibular nerve damage

Inability to dorsiflex

What plexus is the pudendal nerve a part of?

Lumbosacral plexus

What is the motor/sensory innervation of the pudendal nerve?

Pelvic floor/diaphragm