The peripheral nervous system is a collection of nerves that connect the brain and spinal cord to other body parts (peripheral system).

Definitions

Somatic nervous system: Innervate the skin and muscle of voluntary control
Autonomic nervous system: Innervate the visceral organs such as heart, stomach, liver; control is involuntary
Lower motor neuron lesion: Nerve damage to nerve fibers that connect the spinal cord to the peripheral muscles; common symptoms will be muscle weakness, muscle atrophy, fasciculations, hypotonia, and hyporeflexia
Fasciculations: Involuntary muscle twitching that occurs when peripheral nerve is overactive and damaged

Components of peripheral nervous system

There are four (4) major components of the peripheral nervous system– cranial nerves, spinal nerves, peripheral nerves, and the nerves that comprise the autonomic nervous system.

Cranial nerves
- 12 pairs of nerves arising from the brainstem responsible for sensory and motor functions of the head and neck
- List of cranial nerves
  - Olfactory neve-I:
    - Sensory only
      - Function: smell
  - Optic nerve - II:
    - Sensory only
      - Function: visual acuity
  - Oculomotor nerve- III:
    - Motor only
      - Function: move eye up, down, and in (medially)
  - Trochlear nerve -IV:
    - Motor only
      - Function: move adducted eye down (torsional movement)
  - Trigeminal nerve - V:
    - Sensory and motor
      - Function: sensory -touch, pain and temperature to face; motor - muscles of mastication
  - Abducens nerve - VI:
    - Motor only
      - Function: moves out out (laterally)
  - Facial nerve - VII:
    - Sensory and motor
      - Function: sensory- taste to anterior two-thirds of tongue; motor- facial expressions
  - Vestibulocochlear nerve- VIII:
    - Sensory only
      - Function: balance and hearing acuity
  - Glossopharyngeal nerve - IX:
    - Sensory and motor
      - Function: sensory- taste to posterior one-third of tongue; motor- gag reflex, pharynx and larynx control
  - Vagus nerve- X:
    - Sensory and motor
      - Function: sensory- autonomic nervous system; motor- pharynx and larynx control, assist with digestion, aids in slowing heart rate, and bronchial constriction
  - Accessory nerve- XI:
    - Motor only
      - Function: control trapezius and sternocleidomastoid muscle
  - Hypoglossal nerve - XII:
    - Motor only
      - Function: controls tongue movements

Spinal nerves

Thirty-one (31) pairs of nerves exiting the varying vertebral areas- divided into dorsal (sensory) and ventral (motor) roots
- Each spinal nerve corresponds with a segment of the spinal cord (i.e. 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal)

Structure of peripheral nerves

Consists of the following:

Nerve fibers
- Axons send electrical signals from dendrites to cell body
Connective tissue
- The endoneurium, perineurium, and epineurium surrounding and binding the nerves providing protection from injury
Blood vessels
- Aid in vascularizing nerve
Myelin
- Fatty tissue surrounding and protecting the nerve

Definitions

Axon: Projection that conducts electrical impulses away from the nerve cell body
Dendrite: Receiving connection of the nerves
Nerve fascicle: Bundle of nerve fibers that are targeting the same anatomical location- located inside of dendrite
Perineirium: Innermost layer of connective tissue that surrounds a nerve fascicle
Endoneurium: Layer of connective tissue associated with the peripheral nerve composed of collagen, fibroblasts, macrophages, or mast cells that provinces protection to nerve fiber
Epineurium: Outermost layer of connective tissue that surrounds a nerve fascicle

Autonomic nervous system

Provides motor innervation to smooth muscle, cardiac muscle, and glands to provide unconscious control
Further divided into sympathetic, parasympathetic, and enteric divisions- each division works to maintain homeostasis within the body
- Sympathetic nervous system
  - Works to manage individual’s response to anxiety, stress
- Parasympathetic
  - Works to manage individual at rest
- Enteric system
  - Management of gastrointestinal system

Dermatomes and myotomes

A dermatome is an area on the skin associated with a specific spinal nerve root (31 spinal nerve roots) in which sensory information is carried. A myotome is the link between a group of peripheral muscles and a specific spinal nerve root (31 spinal nerve roots) in which motor information is carried. Dermatomes and myotomes are used to diagnose the potential damage of a spinal nerve root. Review the below dermatome map and myotome chart.

Myotomes

Upper extremity
- C1- cervical rotation
- C2-C4- shoulder elevation
- C5- shoulder abduction/elbow flexion
- C6- wrist extension
- C7- elbow extension/wrist flexion
- C8-digit flexion/thumb extension
- T1- finger adduction
Lower extremity
- L1-L2: hip flexion
- L3: knee extension
- L4: knee extension/ankle dorsiflexion
- L5: ankle dorsiflexion/great toe extension
- S1: ankle eversion/ankle plantar flexion
- S2: ankle plantar flexion

Spinal reflexes

Spinal reflexes (also called deep tendon reflexes) are automatic, involuntary responses of the motor system in response to sensory stimuli. Spina reflexes occur in the spinal cord and thus allow the body to respond quickly without conscious thought. Review the spinal reflexes below.

Spinal reflexes
- C5: biceps reflex
- C6: brachioradialis reflex
- C7: triceps reflex
- L3-L4: patellar reflex
- L5: semitendinosus reflex
- S1-S2: achilles reflex

Example of reflexes work in spinal cord below:

Brachial, lumbar, and sacral plexuses

The brachial, lumbar, and sacral plexuses are a network of nerves that form a connection between the peripheral nerves and central nervous system. The peripheral nerves innervating all muscles are derived from the brachial, lumbar, and sacral plexuses.

The brachial plexus provides innervation to the chest and upper limbs.

The lumbar plexus provides innervation to the abdomen, groin, anterior thigh and leg, and feet.

The sacral plexus provides innervation to the pelvis, buttocks, feet, and genitals.

Brachial plexus

Muscles Innervated by the Brachial Plexus

Roots (C5–T1)

Dorsal scapular nerve (C5):
- Rhomboid major
- Rhomboid minor
- Levator scapulae
Long thoracic nerve (C5–C7):
- Serratus anterior

Trunks

Suprascapular nerve (Upper trunk: C5–C6):
- Supraspinatus
- Infraspinatus
Nerve to subclavius (Upper trunk: C5–C6):
- Subclavius

Divisions

No direct muscle innervations from divisions.

Lateral Cord

Lateral pectoral nerve (C5–C7):
- Pectoralis major (clavicular head)
Musculocutaneous nerve (C5–C7):
- Biceps brachii
- Brachialis
- Coracobrachialis

Medial Cord

Medial pectoral nerve (C8–T1):
- Pectoralis major (sternal head)
- Pectoralis minor
Medial cutaneous nerves (arm & forearm):
- No motor function (sensory only)
Ulnar nerve (C8–T1):
- Flexor carpi ulnaris
- Medial half of flexor digitorum profundus
- Most intrinsic hand muscles:
  - Hypothenar muscles (abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi)
  - Adductor pollicis
  - 3rd and 4th lumbricals
  - Palmar and dorsal interossei

Posterior Cord

Upper subscapular nerve (C5–C6):
- Subscapularis
Thoracodorsal nerve (C6–C8):
- Latissimus dorsi
Lower subscapular nerve (C5–C6):
- Subscapularis
- Teres major
Axillary nerve (C5–C6):
- Deltoid
- Teres minor
Radial nerve (C5–T1):
- All muscles in the posterior arm and forearm:
  - Triceps brachii
  - Anconeus
  - Brachioradialis
  - Extensor muscles of wrist and fingers (e.g., extensor carpi radialis longus/brevis, extensor digitorum, extensor carpi ulnaris, extensor pollicis muscles)
  - Supinator
Posterior interosseous nerve (C7-C8):
- Majority of muscles in the posterior (extensor) compartment of the forearm:
  - Extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus.

Median Nerve (from both Lateral and Medial Cords)

Most anterior forearm muscles:
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
- Flexor digitorum superficialis
- Lateral half of flexor digitorum profundus
- Flexor pollicis longus
- Pronator quadratus
Thenar muscles:
- Abductor pollicis brevis
- Flexor pollicis brevis (superficial head)
- Opponens pollicis
1st and 2nd lumbricals
Anterior Interosseous Nerve (AIN) (C7-T1):
- Motor nerve branching from the median nerve:
  - Flexor pollicis longus, flexor digitorum profundus, and pronator quadratus.

Lumbar plexus

Muscles Innervated by the Lumbar Plexus (L1–L4)

Iliohypogastric Nerve (L1)

Internal oblique
Transversus abdominis

Genitofemoral Nerve (L1–L2)

Cremaster muscle (in males; part of spermatic cord)

Lateral Femoral Cutaneous Nerve (L2–L3)

No motor innervation – sensory only

Femoral Nerve (L2–L4)

Iliacus
Pectineus (also sometimes by the obturator nerve)
Sartorius
Quadriceps femoris group:
- Rectus femoris
- Vastus lateralis
- Vastus medialis
- Vastus intermedius

Obturator Nerve (L2–L4)

Obturator externus
Adductor longus
Adductor brevis
Adductor magnus (adductor portion)
Gracilis
Pectineus (occasionally – (occasionally shared with femoral nerve)

Sensory nerves of lumbar plexus

Lateral Femoral Cutaneous Nerve (L2–L3)

No motor innervation – sensory only lateral aspect of the thigh

Saphenous Nerve (L3–L4)

No motor innervation – sensory only medial aspect of the lower leg

Sacral plexus

Muscles Innervated by the Sacral Plexus (L4–S3)

Superior gluteal nerve (L4-S1)

Gluteus medius and minimus
Tensor fasciae latae

Inferior gluteal nerve (L5–S2)

Gluteus maximus

Sciatic Nerve (L4–S3)

Tibial and Common Peroneal (Fibular) divisions
2 joint Hamstring group (Tibial division):
- Biceps femoris long head semimembranosus
- Semitendinosus
- Semimembranosus
1 joint Hamstring muscle (Common Peroneal/Fibular division):
- Biceps femoris short head

Upper limb tension tests

Definitions

Assists with identifying peripheral nerve injury by placing the upper limb in positions of that will stress nerve

Upper limb tension test 1 (ULTT1)- median and anterior interosseous nerve
- Cervical spine: contralateral lateral flexion
- Shoulder: depression and abduction to 110 degrees
- Elbow: extension
- Forearm: supination
- Wrist: extension
- Fingers and thumb: extension
Upper limb tension test 2 (ULTT 2)- median, axillary, and musculocutaneous nerve
- Cervical spine: contralateral lateral flexion
- Shoulder: depression and abduction to 10 degrees, lateral rotation
- Elbow: extension
- Forearm: supination
- Wrist: extension
Upper limb tension test 3 (ULTT 3)- radial nerve** * Cervical spine: contralateral lateral flexion * Shoulder: depression and abduction to 10 degrees; internal rotation * Elbow: extension * Forearm: pronation * Wrist: flexion with ulnar deviation * Fingers and thumb: flexion
Upper limb tension test 4 (ULTT 4)- ulnar nerve * Cervical spine: contralateral lateral flexion * Shoulder: depression and abduction (10 - 90 degrees) with hand to ear * Elbow: flexion * Forearm: pronation * Wrist: extension and radial deviation * Fingers and thumb: extension

Thoracic outlet syndrome

Definitions

Assess for structural damage of nerves and arteries that pass through the thoracic inlet

Adson’s test (compression of the subclavian artery and/or nerves as it passes through the interscalene space)
- Patient sitting with radial nerve palpated; head rotated toward extremity being tested with shoulder extended and externally rotated; extend head
  - Positive: reproduction neurological (pain, weakness, numbness, and loss of hand coordination) and vascular symptoms (loss of radial pulse)
Roos elevated arm test (nerves and/or blood vessels in the space between the collarbone and the first rib are compressed)
- Patient standing with shoulders fully externally rotated, 90 degrees abducted, elbows flexed to 90 degrees- patient then rapidly opens and closes hand for 3 minutes
  - Positive: reproduction neurological (pain, weakness, numbness, and loss of hand coordination) and vascular symptoms (loss of radial pulse)
Wright test (compression at the space behind the pectoralis minor muscle)
- Patient seated with passive movement of arm into abduction and external rotation
  - Positive: reproduction neurological (pain, weakness, numbness, and loss of hand coordination) and vascular symptoms (loss of radial pulse)
Costoclavicular test (compression of the neurovascular bundle between the clavicle and first rib)
- To perform the test the patient sitting, the therapist assists the patient in performing the following 4 movements: scapula retraction, scapula depression, elevation, and protraction- the patient holds each position for up to 30 seconds, while the patient rests his or her forearms on his thighs
  - Positive: reproduction neurological (pain, weakness, numbness, and loss of hand coordination) and vascular symptoms (loss of radial pulse)

Peripheral nervous system

Components of peripheral nervous system

Spinal nerves

Structure of peripheral nerves

Autonomic nervous system

Dermatomes and myotomes

Spinal reflexes

Brachial, lumbar, and sacral plexuses

Brachial plexus

Muscles Innervated by the Brachial Plexus

Trunks

Divisions

Lateral Cord

Medial Cord

Posterior Cord

Median Nerve (from both Lateral and Medial Cords)

Lumbar plexus

Muscles Innervated by the Lumbar Plexus (L1–L4)

Iliohypogastric Nerve (L1)

Genitofemoral Nerve (L1–L2)

Lateral Femoral Cutaneous Nerve (L2–L3)

Femoral Nerve (L2–L4)

Obturator Nerve (L2–L4)

Sensory nerves of lumbar plexus

Lateral Femoral Cutaneous Nerve (L2–L3)

Saphenous Nerve (L3–L4)

Sacral plexus

Muscles Innervated by the Sacral Plexus (L4–S3)

Superior gluteal nerve (L4-S1)

Inferior gluteal nerve (L5–S2)

Sciatic Nerve (L4–S3)

Upper limb tension tests

Thoracic outlet syndrome