Peripheral Nerves Flashcards
Sensory and motor innervation of the face is accomplished via
cranial nerves V and VII, the trigeminal and facial nerves.
The facial nerve (cranial nerve VII)
supplies motor innervation to muscles of facial expression
The trigeminal nerve (cranial nerve V)
supplies sensory innervation to the entire face via three major divisions:
- Ophthalmic division supplies forehead, orbits, and superior nasal cavity.
- Maxillary division supplies cheeks, the upper jaw and lip, and the inferior portion of nasal cavity.
- Mandibular division supplies area anterior to ear, area over parotid, lower jaw and oral cavity.
* The mandibular division also supplies MOTOR innervation to muscles used in chewing (muscles of mastication).
All spinal nerves participate in the formation of one of four nerve plexuses:
Cervical, Brachial, Lumbar, or Sacral
After leaving the vertebral column, each spinal nerve is divided into:
a ventral and a dorsal ramus. The dorsal ramus innervates the medial portion of the back, while the ventral ramus contributes to the formation of a nerve plexus or forms an intercostal nerve.
Cervical Plexus
A. Formed by ventral rami of C-1 to C-4 (contribution from C-5).
B. Sensory component of cervical nerves supplies superficial or cutaneous innervation to the posterior regions of the head and neck (actually from dorsal rami), the anterior and lateral neck and side of the posterior portions of the jaw and ear, and the upper parts of the shoulders and upper thorax (from ventral rami of plexus).
C. Phrenic Nerve - Diaphragm
Most important contribution of cervical plexus is from C-3, C-4, and C-5, which send fibers which unite and form the phrenic nerve. This is the nerve which controls the diaphragm. Therefore, they must be intact for breathing. A broken neck above C-3,4, and 5 will cause death. A broken neck below this level will cause total paralysis.
D. Motor component - Major portion = Ansa cervicalis - this supplies the “strap muscles” of the neck.
E. Cutaneous nerves:
1. Ventral Rami
a. Lesser occipital - posterior lateral side of the head behind ear
b. Greater auricular - area around the ear
c. Transverse cervical - front of the neck
d. Supraclavicular - upper shoulder and thorax (chest)
2. Dorsal Rami
a. Back of the neck is innervated by branches of dorsal rami.
b. Greater occipital- back of the head
c. Dorsal rami of spinal nerves 3 - 8
Brachial Plexus
A. Formed by ventral rami of C-5 through T-1 (some contribution from C-4 and T-2).
B. Supplies entire innervation of upper extremities.
C. Ventral rami of spinal nerves form the “roots” of the brachial plexus.
1. These then unite to form 3 “trunks”
a. upper
b. middle
c. lower
2. Then each trunk divides into an anterior and posterior division.
3. These divisions then unite to form 3 cords in the axillary region:
a. posterior cord
b. medial cord
c. lateral cord
4. These cords then form branches which are the named peripheral nerves of the upper extremity.
roots trunks divisions cords branches
R T D C B
“Robert Taylor Drinks Cold Beer”
Nerves (Median Nerve)
(innervates structures in forearm and hand only)
a. Formed by contributions from medial and lateral cords.
b. Innervates:
- motor supply to flexors of the wrist and lateral fingers in the forearm and hand, also pronator muscles in forearm,
- sensations of the lateral 2/3’s of the palm and fingertips.
c. Loops from medial side of the humerus across the anterior forearm to the lateral palm.
d. This is the nerve that becomes compressed in carpal tunnel syndrome.
Nerves (Ulnar Nerve)
(innervates structures in forearm and hand only)
a. Arises from the medial cord.
b. Innervates: - motor supply to the medial anterior flexors of the wrist and digits in the forearm, most of the muscles in the palm of the hand, - sensation over the medial forearm and medial hand.
c. Loops posterior to the medial epicondyle of the humerus ("funny bone" sensation) and then courses along medial forearm to the medial palm.
Nerves (Radial Nerve)
(innervates dorsal arm, forearm and hand)
a. Arises from the posterior cord.
(The other branch of the posterior cord is in the axillary region and supplies motor to the deltoid and teres minor. Less important nerve = Axillary Nerve)
b. Innervates:
- motor to the extensors located in the arm and forearm
- sensation to posterior lateral surface of arm, forearm and hand.
Nerves (Musculocutaneous Nerve)
a. Arises from the lateral cord.
b. Innervates:
- motor to the flexors in the arm (Biceps, etc.).
- sensation over lateral forearm
Clinical Diagnosis in upper extremity
A. Radial nerve damage - “wrist drop” - inability to extend the hand at the wrist - also unable to extend fingers. (sensory loss in posterior arm or forearm and lateral hand)
B. Median nerve damage - difficulty in flexing wrist, lateral fingers, or thumb - inability to pronate the forearm. Most frequently damaged at wrist causing tingling or numbness in lateral hand
C. Ulnar nerve damage - difficulty in flexing wrist or spreading fingers - inability to adduct the wrist.
Lumbar Plexus
A. Formed by ventral rami of nerves L-1 through L-4.
B. Gives rise to nerves which supply:
- motor input to anteriolateral abdominal wall and anterior thigh
- sensation from inferior lateral and anterior abdominal wall, external genitalia, and anterior and medial thigh. (also a small saphenous nerve brings sensory info from the medial leg)
C. Nerves:
1. Obturator nerve - passes through obturator foramen. Sensation to medial portion of the thigh, and motor input to adductors of the leg.
2. Femoral nerve = Most important nerve from the lumbar plexus - supplies the quadriceps (motor) and sensation from anterior thigh and medial leg and foot.
3. Iliohyogastric, Ilioinguinal, and Genitofemoral Nerves - (T-12 to L-2) supply motor to anterolateral abdominal muscles, and sensation from lower anterolateral abdomen, genitals, and medial thigh.
Sacral Plexus
- (Often the Lumbar Plexus and the Sacral Plexus are considered together as one plexus = the Lumbosacral Plexus)
A. The Sacral Plexus is from ventral rami of L-4 through S-4 and is located within pelvic cavity.
B. Supplies sensory and motor innervation from the buttocks.
C. Pudendal nerve which is major sensory innervation of the genitals.- Pudendal Block - is often done during child birth for control of pain.
- Nerve leaves through greater sciatic foramen with sciatic nerve and then returns through the lesser sciatic foramen on the medial side of the ischium to genitalia
D. Sciatic Nerve = Largest nerve from sacral plexus = largest nerve of the body . - Supplies motor innervation to the hamstrings in posterior thigh.
- Also carries sensory fibers from gluteal region and posterior thigh
- Splits into 2 nerves at the knee.
a. Tibial - supplies muscles on posterior leg and plantar side of the foot (plantar flexors). Also supplies sensation from skin over these areas.
b. Common Peroneal - divides into a superficial and a deep branch which supply both sensory and motor information for lateral and anterior portions of the leg and the dorsal portion of the foot (abductors and dorsiflexors) - Clinical test for damage to the sciatic nerve is an inability to dorsiflex the foot (condition called “foot drop”) - evidenced when walking.
Intercostal Nerves
A. Spinal nerves from levels T-2 through T-12 do not form nerve plexuses, but instead exit (enter) the vertebral column and are distributed circumferentially around the trunk.
B. Ventral Rami:
1. Found within the costal grooves on the inferior side of each rib along with a vein and an artery.
2. Give motor innervation to intercostal muscles and bring sensory information from anterior and lateral chest and abdominal wall.
C. Dorsal rami of thoracic spinal nerves supply deep muscles and skin of the back.
