Zsuzsanna ArányiDept. of Neurology

Semmelweis University

The peripheral nervous system

The peripheral nerve

Anatomy of the peripheral nerve

Elements of the peripheral nerve:– Axons and Schwann cells– Connective tissue elements– Blood vessels

Internal structure of the peripheral nerve

– Axons are organized into fascicles

– Fascicles are organized into fasciclegroups

– Continuous interchange of axonsbetween the fascicles: plexiformstructure

The ratio of fascicles versus connective tissue elements ranges between 25 and 75%

Internal architecture of peripheral nerves

▪ Plexiform structure

▪ Fibers to a specifictarget run together fromproximal to distal

▪ Plexiform structure is less evident distally

Myelin sheath and nerve conduction

Saltatory conduction of a myelinated nerve fiber

Myelin sheath:▪ Provides insulation to the nerve fiber▪ Increases fiber diameter▪ Allows for saltatory conduction▪ Dramatic increase of conduction velocity

▪ Myelinated fibers: 35-75 m/s▪ Unmyelinated fibers: 1-5 m/s

Node of Ranvier

Main types of peripheral nerve damage

Conduction block(neurapraxia, focaldemyelination)

Axonal damage(axonotmesis,neuronotmesis)

Symptoms: sensoryloss, weakness

Symptoms: sensoryloss, weakness, muscleatrophy

Wallerian degeneration

Connective tissue elements of the peripheral nerve

– Mesoneurium - paraneurium

– Epineurium

– Perineurium

– Interfascicular fat

– Endoneurium

– Basal lamina

EpineuriumOuter layer surrounding the whole nerve (outerepineurium) and separating the fascicles / fascicle groups (inner epineurium)

Az ideg proximo-distalis tengelye

– Mainly consists of collagen fibers

– Wavy collagen fibers are diagonally organisedwith respect to the longitudinal axis of thenerve

– Contains elastin fibers as well

– Few cellular components

Relatively resistant to stretch!

outer

inner

group

Perineurium

Layer sorrounding individual fascicles

– Mainly consists of cellular components

– 8-18 alternating concentric layers of cellularlaminae and connective tissue (longitudinalcollagen)

– Tight junctions between flat, polygonal cells

Barrier function: blood-nerve barrier

Less resistant against resistant

Endoneurium

Layer surrounding individual axons (axon + Schwanncells + basal lamina)

Consists of two layers of collagen:

– Outer, longitudinally oriented layer

– Inner, looser layer connected to the basal lamina

Endoneural tubes (axons and Schwann cells removed)

Important role in axon regeneration

Basal lamina

Extracellular matrix surrounding the axon + Schwanncell complex

Non-myelinated axons

Crucial role in axon regeneration: guides theregenerating axon

– Produced by Schwann cells

– Matrix structure: laminin 2 + collagen IV polymers

– Non –myelinated axons: the basal laimnaproduced by one Schwann cell surrounds severalaxons

„Bands of Fontana”

Bands of Fontana: dark circular shadows seenon normal nerves under the microscope

– Cause: optical phenomenon caused by theundulating, spiral course of the axons

– Disappears under stretch

Peripheral nerves resist some degree of stretch

(15-20%?) without damage

„Elasticity” of nerves:

– Undulating, spiral course of axons

– Connective tissue elements, elasticity of the epineurium

Before stretch

Under stretch

Main types of peripheral nerve damage

Conduction block(neurapraxia, focaldemyelination)

Axonal damage(axonotmesis,neuronotmesis)

Symptom: loss of sensation, muscle weakness

Symptom: loss of sensation, muscle weakness and atrophy

Waller-f. degeneration

Symptoms and signs of peripheral nerve damage

Sensory fibers: sensory loss in the innervation area of theaffected nerve

Motor fibers: weakness / wasting of the muscles innervatedby the affected nerve

Autonomic: loss of sweating, dry skin, vasodilatation

Localization within the peripheral nervous system

Root / spinal segment?

Plexus?

Peripheral nerve?

Peripheral nerve – at what levelis the nerve damaged?

Localization within the peripheral nervous system

Root / spinal segment?

Plexus?

Peripheral nerve?

Peripheral nerve – at what levelis the nerve damaged?

Distribution of weakness / muscle atrophy and sensory loss

Requires mainly anatomicalknowledge

1. dorsal interosseous (FDI) brachioradial muscle

Check contraction (change in bulk) of the muscle tested: other muscleswith the same function may mask weakness of the muscle tested

Physical examination of muscle power▪ Spontaneous movements, gait▪ Contraction against resistance of the examiner

Median nerve

forearm flexors

thenar

motor innervation sensory innervation

Level of lesion within a peripheral nerve

Median nerve

▪ Motor and sensory branches branching distal tothe lesion are affected

▪ Innervation area proximal to the lesion is normal

▪ All muscles supplied by the given nerve shouldbe tested

Distal median nerve damage: carpal tunnel syndrome

Causes:▪ idiopathic▪ overuse (housewife, athletes, carpenters)▪ change of tunnel anatomy (arthritis, edema, fractures, etc.)▪ diabetes

Carpal tunnel syndrome

thenar atrophy

Loss of sensation: 1-4th fingers; superficial palmar branch (skin above the thenar) spared

Motor deficit: thenar; finger flexion spared

RadLun

Cap

PL

Flexorín

Thenar

Dist Prox

PQ

Normal median nerve in the carpal tunnel in longitudinal section

Carpal tunnel syndrome: nerve ultrasound

Rad

Lun

Flexor tendon

Median nerve in the carpal tunnel

CSA: 23.6 mm2 CSA: 6 mm2 CSA: 23.5 mm2

longitudinal

axial

Palm Carpal tunnel Wrist

Normal CSA: < 13 mm2

Video: from proximal to distal at the wrist

Carpal tunnel syndrome

Proximal median nerve lesion

▪ All muscles supplied by the median nerve are weak:‘oath hand’ when making a fist

▪ Loss of sensation in the whole innervation area

Median nerve lesion on the upper arm

Proximal median nerve lesion

▪ Loss of flexion in the distal phalanx of 1-2. fingers: FPL, FDP2 and PQ weakness

▪ No sensory loss

Anterior interosseous nerve (AIN) lesion

Pitfalls in the localization of focal nerve lesions

Fascicular lesion: proximal selective involvement of onenerve fascicle▪ clinically the lesion appears more distal

Length-dependent damage of axons▪ distal symptoms are more pronounced

PThu

PTuln

Brach

DistProx

Segmental enlargement of the AIN fascicle within the median nerve atthe elbow

PTPT

PT: pronator teres muscle

PTPT

axial

longitudinal

Sudden onset of AIN lesion (inflammatory neuropathy): selective involvement of AIN fascicle within themedian nerve at the elbow

Video: axial scanning of the median nerve at the elbow from distal to proximal

Segmental innervation

Dermatome: skin area innervated by a single posterior spinal nerve root

Myotome: muscles innervated by a single anterior spinal nerve root

Sensory innervation

Dermatomes Peripheral nerves

Myotomes

Segmental versus peripheral nerve damage

C8-Th1 segmental damage (e.g. spinal nerve root compression by discalherniation) versus ulnar nerve damage (e.g. cubital tunnel syndrome)

❑ Weakness and atrophy of smallhand muscles

❑ The atrophy of the first dorsalinterosseus muscle is the most conspicuous

❑ Claw hand

❑ Sensory loss on the 4-5th finger

Segmental versus peripheral nerve damage

C8-Th1 segmental damage (e.g. spinal nerve root compression by discalherniation) versus ulnar nerve damage (e.g. cubital tunnel syndrome)

Segmental versus peripheral nerve damage

C8-Th1 segmental damage versus Ulnar nerve damage

❑ Weakness / atrophy of ulnar innervatedsmall hand muscles: C8-Th1

❑ Sensory loss on the 4-5th finger

❑ Weakness / atrophy of ulnar innervatedsmall hand muscles: C8-Th1

❑ Sensory loss on the 4-5th finger (half of 4th finger)

❑ Weakness / atrophy of the thenar:median nerve – Th1

❑ Weakness / atrophy of extensorindicis proprius muscle:radial nerve – C8

❑ Sensory loss on the medial aspect of the forearm – Th1

Segmental versus peripheral nerve damage

L5 segmental damage (e.g. root compression caused by discal herniation) versus common peroneal nerve damage (e.g. compression at the fibular head)

❑ Weakness of dorsiflexion of the foot and toes(foot drop)

❑ Weakness of foot pronation

❑ Sensory loss: foot, great toe, lower leg

Segmental versus peripheral nerve damage

L5 segmental damage versus Common peroneal nerve damage

❑ Weakness / atrophy of peronealnerve innervated leg muscles(extensor and peroneal musclegroups: L5)

❑ Sensory loss: hallux (lower leg)

❑ Weakness / atrophy of peroneal nerveinnervated leg muscles (extensor and peroneal muscle groups:

❑ Sensory loss: dorsum of the foot, lateral aspect of the leg

❑ Weakness of tibial posterior muscle(supination of the foot): posteriortibial nerve, L5

❑ Weakness of gluteus medius muscle(hip abduction): superior glutealnerve, L5

L5 indicator muscle: extensor hallucis longus (90% L5)

Thank you for your attention!