More on Motor Pathways Flashcards
When does degeneration happen?
After an injury
What is orthograde degeneration?
Axon is severed
Distal portion loses its source of nourishment an soon dies
Liberated calcium facilitates disintegration of the axon
Can there be regeneration following orthograde degeneration?
Yes
Schwann cells reorganize into schwann tubes for the regrowing nerve to follow
What is retrograde degeneration?
Cell body changes after the axon is severed
Loss of neurotrophic factors coming from the axon to the cell body
Soma becomes swollen
Nucleus moves to the periphery
Reorganization of the rough endoplasmic reticulum
What ultimately happens after retrograde degeneration?
Cell death
What are denervated muscles?
Muscles that are not getting stimulation
What are the 3 stages of denervated muscles?
Fasciculations
Fibrillations
denervation atrophy
What are fasciculations?
Twitches
Not connected to command center so cannot carry out full movement
What are fibrillations?
Small contractions that are unable to be seen from the surface
If the soma is not damaged, does the injured neuron begin to produce materials necessary for the reconstruction of the distal axon?
Yes
What happens during regeneration?
Increased protein synthesis
A growth cone forms on the proximal portion of the injured neuron
Neurites sprout from the cone and elongate
Neurite can follow schwann tube and grow to reach target
Regenerating neuron is attracted to the acetylcholine receptors on the muscle
T/F: Regeneration is more likely with a crushed axon than a severed one
True
What are the cortical motor areas?
Primary motor area, supplementary motor area, and premotor area
Where do the motor areas receive info from?
Cerebellum, basal ganglia, and peripheral sensory systems
What kind of info does the primary motor area give?
Gives most direct cortical control of the motor neurons
What kind of info does the premotor area give?
Gives what you need to know before the movement happens
What kind of info does the supplementary motor area give?
Facilitates coordinated motor acts
Only needed for complex movements
What structure forms a loop for completion of motor acts between movement, cognition, and emotion?
Basal ganglia (nuclei)
What does the loop consist of?
Projections from the cortex to basal ganglia , then projections from basal ganglia to thalamus and back to cortex
Some limbic connections to striatum (caudate nucleus, nucleus accumbens, and putamen)
What is hyperkinetic?
Too much movement
What is hypokinetic?
Too little movement
What is chorea?
Series of nearly continuous, rapid, involuntary movements of face, tongue, and limbs that may resemble choreography
What is athetosis?
“Without position”; slow, writhing movements, difficulty holding limb in fixed position
What is ballismus?
“Jumping about”; wild flailing movements of one arm and leg
What is dystonia?
Increased or abnormal tone in muscles resulting in fixed posture
What is hypotonia?
Loss of muscle tone
What is rigidity?
Tone increase in flexors and extensors
What is bradykinesia?
Decreased or slow movements
What was huntington’s disease formerly called?
Huntington’s chorea because the movements resembled dancing
What causes huntington’s disease?
Neuronal degeneration that is severe in the striatum and especially the caudate nucleus
Controls to motor movement is damaged
When does huntington’s symptoms show up?
30-50 years old
What changes due to huntington’s?
Involuntary movements (chorea) and alteration of mood or cognitive function
Do movements become more pronounced with worsening dementia during huntington’s?
Yes
Is huntington’s disease genetic?
Yes
Autosomal dominant inheritance
Chromosome 4 short arm identified
Many patients have started families before knowing they have the disease
Can do genetic testing
Is parkinson’s disease hypokinetic or hyperkinetic?
Hypokinetic
What is parkinson’s disease?
Biochemical disease of basal ganglia (evident in the substantia nigra cells that should produce dopamine and transport it to the striatum)
What types of movement result from parkinson’s?
Bradykinesia - decreased spontaneity of movement
Resting tremor, goes away with voluntary movement
Rigidity or cog-wheel rigidity (tremor or brief relaxations and rigidity)
What are treatments for parkinson’s disease?
L-dopa (chemical needed to produce dopamine)
Given in hopes that patients will make dopamine on their own
Is there surgical treatment for parkinson’s?
Surgery to disrupt loop (last resort) and implantation of electrodes in the globus pallidus
What type of cells does the cerebellum have?
Purkinje cells
Is the cerebellum ipsilateral or contalateral?
Ipsilateral
What does the cerebellum do?
Involved in equilibrium, control of muscle tone, posture, and coordination of voluntary movements
What inputs does that cerebellum receive?
Vestibular, spinal, and cortical
Where does vestibular information go?
It goes through the juxtarestiform body to the nodulus
What can damage to the cerebellum result in?
Changes in gait
Incoordination
Changes in muscle tone, reflexes, and coordination of voluntary movements ipsi to the site of lesion
Do voluntary movements take longer to initiate with damage to the cerebellum?
Yes
Do people with cerebellum damage have problems stopping or changing the direction of movement?
Yes
Do corrective movements appear at intention tremor during voluntary movements?
Yes
What is dysdiadochokinesia?
Difficulty with rapid alternating movements
