Peripheral Nervous SystemPathophysiology

The Peripheral Nervous System (Boissonnault pg. 1140)

Includes all cranial nerves, spinal nerves and cell bodies located within the brain stem and spinal cord.

Peripheral Nervous System

Peripheral Nervous System

Peripheral Nervous System

PNS Problems(Goodman pg 1595)

May involve the motor or sensorysystems or ANS.

PNS Problems(Goodman pg 1595)

Following sites may be affected:

Cell body of the alpha motor neuron (anterior horn cell) located in the spinal cord or brainstem

The axon that arises from the anterior horn cell (AHC) that form the spinal, cranial or other peripheral nerves

The motor endplate of the axon

Muscle fibers innervated by the motor nerve axon

Anatomy of the Peripheral Nerve

Types of NervesCopstead and Banasik (pg 1069)

Multipolar (Motoneuron)most common, large number of dendrites extending from the cell body and one axon.

Unipolar (Sensory Neuron) prevalent in somatosensory nerves grouped in the dorsal root ganglia have a single process protruding from the cell body and splits into the axon and dendrite.

Bipolar (Interneuron)prevalent in retina, cochlea and olfactory structures, have one dendrite and one axon.

Cross Section of a Nerve

Cross Section of a Nerve

Sensory Afferent, Motor Efferent & Muscle Spindle

Muscle SpindleKandel, Schwartz and Jessell, pg 716

Muscle SpindleKandel, Schwartz and Jessell, pg 718-719

Sensory:Ia primary spindle ending for muscle length and speed changesII secondary spindle ending for muscle stretch/length

Motor: Small diameter gamma fibers (intrafusal). Large alpha fibers (extrafusal)

Muscle SpindleKandel, Schwartz and Jessell, pg 718-719

Muscle SpindleKandel, Schwartz and Jessell, pg 718-719

Injury to a Peripheral Nerve

PNS

Nerve Involvement of Peripheral Nerves (Boissonnault pg 1143)

Mononeuropathy – involvement of one nerve usually a result of trauma

Polyneuropathy – involvement of several nerves

Radiculoneuropathy – involvement of the nerve root as it emerges from the spinal cord

Polyradiculitis – involvement of several nerve roots usually as a result of an infection causing an inflammatory response

Mononeuropathy(Boissonnault pg 1142)

Traumatic injury to a nerve can result from compression, stretching, ischemia, infection, toxins, can be hereditary

Clinical presentation and potential for recovery is directly related to the amount of nerve damage sustained

Mononeuropathy

Clinical presentation and recovery is directly related to the extent of the nerve damage.

Mononeuropathy(Goodman pg 1597)

Three categories:

Neurapraxia

Axonotmesis

Neurotmesis

Mononeuropathy: Neurapraxia(Goodman pg 1597)

Three categories:

Neurapraxia – Segmental demyelination (myelinopathy) leaves the axon intact while the myelin breaks down.

Mononeuropathy: Neurapraxia(Goodman pg 1597)

Slows or blocks the nerve impulse at the point of demyelination. Usually a result of a compression where there is ischemia to a nerve.

Often termed segmental demyelination or myelinopathy

Mononeuropathy:Axonotmesis(Boissonnault pg 1142)

Axonotmesis – Axon has been damaged, but the connective tissue covering (epinerium and perineurium) that supports and protects the nerve remains intact. Usually caused by prolonged compression that creates an area of necrosis.

Axonal degeneration occurs distal to the area of compression

Neurotmesis

Mononeuropathy:Neurotmesis(Boissonnault pg 1142)

Neurotmesis – Most severe type of injury where the entire nerve is completely severed. The axon as well as the connective tissue covering is destroyed. Usually the result of stabbing wounds, lacerations, gun shot wounds or avulsion injuries.

Mononeuropathy

Mononeuropathy: Neurapraxia, Axonotmesis, Neurotmesis(Boissonnault pg 1142)

Response to an Injury

PNS

Response to Injury:Neurapraxia(Boissonnault pg 1142)

In the case of neurapraxia, segmental degeneration occurs by loss of myelin

The repair process occurs rapidly. The Schwann cells divide and remyelinate the bare portion of the nerve.

There is a shorter internodal distance that occurs with remyelination. Nerve conduction does not return to normal even if the muscle can contract normally.

Response to Injury (Boissonnault pg 1142)

Response to Injury:Axonotmesis and Neurotmesis(Boissonnault pg 1142)

In the case of axonotmesis or neurotmesis Wallerian degenerationoccurs, the anterograde (distal) degeneration of the axon.

Wallerian degeneration occurs in any peripheral nerve injury that involves the axon. The difference between the axonotmesis and the neurotmesis is the remaining connective tissue sheath.

Response to Injury:Axonotmesis and Neurotmesis(Boissonnault pg 1142)

Recovery is more complex in the case of Wallerian degeneration than with segmental degeneration

Clinical PresentationPNS

Clinical Presentation

Presence of paresis or paralysis in all of the muscles that are innervated by that nerve distal to the lesion.

Sensory loss will be in the pattern of a peripheral nerve distribution

No signs of CNS involvement

Involvement of Peripheral Nerves: Mononeuropathy

So how do they heal?Nerves

Response to Injury: Clinical Manifestation (Wadsworth,C. The Wrist and Hand: Physical Therapy Patient Management Utilizing Current Evidence).

Sensory nerve cell bodies in the dorsal root ganglia must produce axoplasm to fill in the regenerating endoneurial tubes.

The size of the tube becomes important

The smallest C fibers requires less axoplasm and regenerate the fastest permitting pain perception first.

Response to Injury: Clinical Manifestation (Wadsworth,C. The Wrist and Hand: Physical Therapy Patient Management Utilizing Current Evidence).

The largest A beta and A gamma fibers that transmit touch, pressure and movement sensation regenerate slowest so patients will recover pain and temperature before touch and gnosis.

Motor fibers (A alpha) require longer to regenerate so motor recovery occurs after sensation

Axon Size

Consider

Think about what your patient may experience in terms of return of sensation, and motor response as they heal.

Recovery(Boissonnault pg 1142)

The proximal section of the nerve must grow across the lesion site and re-grow down the connective tissue channel and reestablish a motor end plate or sensory connection before remyelination occurs.

Recovery(Boissonnault pg 1142)

In neurotmesis, projections may enter near by soft tissue and fail to reestablish their connections forming a neuroma.

Average Speed of regeneration is about 1 mm per day or approximately 1 inch per month (Wadsworth)

Nerve Surgery

Nerve Surgery

Surgical Repair of a Nerve

Implications for Rehab for Non Surgical Nerve Injuries1. Maintain joint and soft tissue mobility with gentle pain free ROM

and flexibility exercises. Especially if full motion can not be attainted actively.

2. For weak muscles that can not move against gravity by themselves (less than a 3/5 muscle grade)• Perform isometric and active assisted exercises.• Do not add resistance• Overstressing the nerve and cause further nerve and soft tissue injury

Implications for Rehab for Non Surgical Nerve Injuries3. For weak muscles that can move against gravity by themselves (greater than a 3/5 muscle grade)• Perform active exercises. • Gradually add resistance as tolerated avoiding all pain and

excessive tension• Gradually add eccentric training as tolerated avoiding all pain and

excessive tension• Overstressing the nerve and cause further nerve and soft tissue

injury