Neurophysiology Of Spacticity - 18 & 19 Flashcards
Baclofen
Presynaptic mediated inhibition. Inhibits calcium influx and therefore suppresses release of excitatory neurotransmitter’s binds to GABA-B receptors.
Define spasticity
Overactivity of neuromuscular systems interfering with voluntary motions secondary to upper motor neuron lesion. It is velocity dependent resistance to passive range of motion in one direction, generally antigravity mms
Benzodiazepine or diazepam
GABA agonist increases inhibition in the brain stem and spinal cord. Binds GABA-A receptors to increase infinity for GABA in brain and spinal cord
Tizanidine
Inhibits excitatory neurons throughout central nervous system by increasing inhibitory neurotransmitters and decreasing excitatory neurotransmitters
Dantrolene
Directly inhibits skeletal muscle contraction by blocking calcium release from sarcoplasmic reticulum
How is a temporary nerve block done?
Changing membrane permeability to sodium to stop nerve conduction using local anesthetics effects start quickly and last several hours
How does neurolysis work?
Chemically destroy nerve tissues with alcohol or phenol, creates a lesion then degeneration occurs but the axon can regrow in 2 to 12 months
How does chemodenervation work?
Botulinum toxin is injected directly into the muscle to block muscle contraction. Effects last for 3 to 6 months. Basically like Botox for wrinkles.
Name the two mechanisms that produce neuromuscular overactivity
Absence of corticospinal inhibition onto lower motor neurons. Primarily Alpha and gamma motor neurons or interneurons that control motor neuron pools.
Brainstem upper motor neuron over activity
Name the conditions that generally have spasticity
Cerebral palsy, spinal cord injury, brain injury, stroke, multiple sclerosis
Describe what causes cerebral palsy
Damage to the corticospinal tract in development. Causes excess synapses to not be terminated in adolescence, leading to improper cocontractions of agonist, antagonist and synergistic muscles at the same time. Also causes loss of corticospinal tract inhibition of lower motor neurons and disinhibition of reticulospinal tract producing abnormal synergies
What is the usual outcome after a stroke, what is damaged?
Unilateral corticospinal tract and medullary reticulospinal tract. This leads to reticulospinal tract over activity which leads to decreased cortical inhibition which then increases reticulospinal tract signals causing excessive muscle contraction synergies
What happens after spinal cord injury?
Disinhibition of lower motor neurons below the lesion. Hyperreflexia, enhanced lower motor neuron excitability, therefore interneurons and lower motor neuron’s overreact to somatosensory input and increase sensitivity of muscle spindles
Where does voluntary movement originate?
Motor cortex, basal ganglia, cerebellum, thalamus, brainstem, spinal motor neurons
What is muscle tone?
Muscles are tonically active and have a general resting tension when not actively being used. Also refers to general muscle resting strength