Neuro: Lecture 7 (peripheral nervous system)

Fascicles

Another name for a bundle of nerve fibers is

Somatic

Nerves carrying both sensory and motor fibers are called

Efferent

Nerves carrying just sensory fibers are referred to as sensory, or _______

Posterior rami

Innervate paravertebral muscles, posterior parts of vertebrae & overlying cutaneous areas

Anterior rami

Innervate the skeletal, muscular, and cutaneous areas of the limbs and the anterior and lateral trunk

Spinal lesions

Deficits in sensory, autonomic, and motor show a myotomal and/or dermatomal distribution

Peripheral lesions

Deficits in sensory, autonomic, and motor in a peripheral nerve distribution

General signs of Peripheral nerve injury

• paresis or paralysis

• Sensory loss

• Abnormal sensations

• Muscle atrophy

• Reduced or absent deep tendon reflexes

Endoneurium

Separates individual axons

Perineurium

Surrounds bundles of axons called fascicles

Epineurium

Encloses the entire nerve trunk

Mesoneurium

Surrounds the epineurium

Cervical plexus

• formed by anterior rami of C1-C4

• Sensory (posterior scalp to the clavicle bone)

• Motor (neck muscles and the diaphragm)

• Phrenic nerve: most important nerve of this plexus

  • Cell bodies are in the cervical spinal cord C3-C5. Only motor supply and is the main sensory nerve for the diaphragm.

Brachial plexus

• formed by anterior rami of C5-T1

• Gives rise to nerves that innervate upper limb

Brachial plexus nerves

• Axillary Nerve: important for shoulder movement and stability

• Musculocutaneous nerve: activates muscles in upper arm (like the biceps) and allowed for elbow flexion and forearm rotation

• Ulnar nerve: controls hand muscles for fine movement and provides sensation to he ring finger and the little finger

• Median nerve: controls many of the forearm muscles involved in wrist and finger flexion, provides sensation to the palm of the hand, thumb, index and middle and half the ring finger

• Radial nerve: extensor muscles of the arm such as triceps. Provides sensation for the back of the hand, thumb, index, middle, and half of the ring finger.

Lumbar plexus

• arises from L1-L4

• Innervates anterior and medial leg

• Saphenous nerve: cutaneous branch that innervates medial leg and foot

Sacral plexus

• arises from S1-S4

• Innervates posterior thigh, most of leg and foot

• Contains parasympathetic axons

• Sciatic nerve: longest and thickest nerve of the body

Movement and nerve health

• promotes blood flow

• Promotes axoplasm flow by thinning it to facilitate retrograde and anterograde transport

Axon wrinkling

Folding or buckling of axons that occurs as the brain develops and expands

Neuromuscular junction

Synapse of motor axons with muscle fibers

Signs of peripheral nerve damage

• sensory changes- decreased or lost sensations

  • Possible abnormal sensations of hyperalgesia, dysesthesia, paresthesia, alloy is

• Autonomic changes- completely severed single nerve= lack of sweating and loss of sympathetic control to arterial walls —> edema

• Motor changes- paresis or paralysis

• Denervation tropic changes

Mononeuropathy

• traumatic myelinopathy: loss of myelin limited to the site of injury

  • Demyelination

  • Typical recovery is complete and RAPID, by remyelination

• Traumatic axonopathy: disrupts axons but leaves myelin intact

  • Wallerian degeneration occurs distal to the lesion

  • Axonal damage

  • Recovery: slow by regrowth of axons but good recovery since Schwann and connective tissue sheaths intact

• Severance: nerves are physically divided by excessive stretch or laceration

  • Axon and myelin degeneration.

  • Recovery is slow, with poor results owing to inappropriate reintervention and traumatic neuroma

Multiple mononeuropathy

• individual nerves are affected, producing random asymmetric presentations of signs

• Ischemia of neuron complication of diabetes or blood vessel inflammation

• Involvement of 2 or more nerves in different parts of the body

Polyneuropathy

• symmetric involvement of sensory, motor, and autonomic fibers often progressing

• Complication of diabetes or autoimmune disorder

• Metabolic or inflammatory

Polyneuropathy disorders

• diabetic polyneuropathy

• Idiopathic polyneuropathy

• Guillain-Barré syndrome

• Charcot-Marie-tooth disease (hereditary motor and sensory neuropathy)