Lecture 11: PNS Disorders Flashcards
PNS Structure
- Epineurium
- dense CT
- binds fascicles together - Perineurium
- surrounds bunches of axons -> fascicle - Endoneurium
- delicate CT
- surrounds each fibre
Motor Unit Composition
Basic unit of motor function
- A motor neuron
- Group of muscle fibres that it innervates
Diseases of the MU: Cell Body
- MN diseases
- CNS and PNS disorder
- UMN: cell bodies in the cerebral cortex that issue commands to the LMNs
- LMNs: cell bodies in the SC and BS that directly innervate skeletal muscle
UMN disorders
UMN (+):
- spasticity
- overactive tendon reflexes
- abnormal babinski sign
LMN disorders
LMN (-):
- flaccidity
- atrophy
- fasciculations (muscle twitches)
- decreased muscle tone
- loss of tendon reflexes
Diseases of the MU: Axon
- peripheral neuropathies
- both sensory and motor axons are bundled together, so both sensory and motor functions are affected
Peripheral Neuropathy Symptoms
+ symptoms:
- numbness, tingling, burning, pins and needs, hyper excitability of nerves
(-) symptoms:
- Motor: weakness and loss of tendon reflexes
- Sensory: loss os sensation eg. pain and temp - mosre prominent distally (glove and stocking)
Acute Neuropathy - Guillain Barre Syndrome
- disease of the axon
- often follows resp infection or infectious diarrhea
- mild to severe
- can result in spreading paralysis and can cause death if not treated
- Autoimmune attack on peripheral nerved by circulating antibodies
Pathogenesis: Guillain Barre
- pathogens trigger humoral immune and autoimmune response through molecular mimicry
- activates ‘membrane attack complex’
- results in: myelin detachment, disappearance of Na channels -> nerve dysfunction and symptoms
Diseases of the axon: demyelinating vs axonal
Demyelinating:
- conduction velocity slows and conduction synchrony between diff axons of a nerve is lots
- linked to genetic mutations in genes that code for myelin proteins
Axonal:
- Linked to variety of cellular proteins, including neurofilaments, MT motors eg. kinase
PNS Nerve Injury: Repair
- proximal axon sprouts
- axon sprouts find their way to endoneurium tube with schwann cells
- tube guides axonal growth
- complete recovery possible
Disease of NMJ
- block NT action eg. myasthenia gravis
2. block NT release eg. botulism
Myaesthenia gravis
- weakness, fatiguing of muscle groups
- due to autoimmune block ACh receptors at NMJ (autoimmune attack reduces no of functional receptors)
- treat with ACh inhibitors
Botulism
- Botulinum toxin produced by bacteria
- Block Ach release at eh NMJ
- Therapeutic use: spasticity, painful muscle spasms, wrinkles, reduce sweating
