Test 2 Material Flashcards
How many muscles does each motor neuron innervate?
Only one but many muscle fibers
What is a motor neuron pool?
A group of neurons that innervate a specific muscle
How are motor neuron pools organized?
In columns
For motor neurons, how is the ventral horn organized?
Topographically, medial to lateral does proximal to distal respectively
What muscles do the medial portions of the ventral horn innervate?
Proximal, close to body
Which part of the ventral horn innervates more distal muscles?
the lateral portion
Where on the ventral horn is innervation for finger and toe muscles?
The most lateral portion to of the midline.
Which pathways in the spinal cord control posture?
the medial part
Which pathways in the spinal cord control fine movement in extremities?
the lateral pathways
Where do local circuit neurons in the medial portion of the spinal cord terminate?
bilaterally
Where do local circuit neurons in the lateral part terminate?
ipsilateral
What do alpha motor neurons innervate?
the extrafusal muscle fibers
What are extrafusal muscle fibers?
force producing fibers
What do the extrafusal muscle fibers control?
posture and movement
What do gamma motor neurons innervate?
intrafusal muscle fibers
What do intrafusal muscle fibers control?
muscle tension
How many muscle fibers does an alpha motor neuron innervate?
Many but all in the same muscle
How does the force apply to a muscle when innervated by an alpha motor neuron?
Evenly
What is the benefit to alpha motor neurons innervating so many muscle fibers?
This reduces the chance that losing a single alpha motor neuron will create a big impact.
What generates the contraction?
the action potential
What is a motor unit?
the alpha motor neuron and the muscle fibers it innervates
What do group 1A afferents respond to?
phasically small stretches
What do Group IIA afferent respond to?
they fire to signal degree of sustained stretch
What does striking the patellar tendon stimulate?
stretch sensory receptors (i.e. muscle spindles)
Where does striking the patellar tendon trigger an impulse?
Ia afferent nerve fiber
The sensory neuron synapses directly with a(n) ______ ______ _______ in the spinal cord that conducts an efferent impulse to the quadriceps triggering _______.
alpha motor neuron; contraction
What is feed forward inhibition?
activation of the inhibitory interneurons that ensures only the appropriate muscle get acitvated
How does feed forward inhibition enhance the effect of the active pathway?
By suppressing the activity of other opposing pathways
What is feed-back inhibition?
self regulating mechanism that prevents over-excitation
What specifies the muscle length in feed back inhibition?
descending upper motor neuron controls
What do gamma motor neurons regulate?
excitability of muscle spindles
What is change the gain?
the amount of muscle force generated in response to a given stretch of the intrafusal fiber
While muscle spindles detect changes in muscle _______, mechanoreceptors in tendons predominantly signal changes in ______ _______.
length, muscle tension
Ib afferents contact the inhibitory local circuit neurons to provide ______ ______ to same muscle’s motor unit.
negative feedback
What leads to flexion reflex?
painful sensory stimulation
What happens with flexion reflex?
inhibition of extensor and activation of flexor on affected side
What accompanies flexion reflex?
crossed extension reflex
What does opposite activation do?
serves to maintain posture
Where do motor cortex neurons descend?
via lateral columsn
What do motor cortex neurons control?
voluntary precise movements of distal parts of limbs
Where do brainstem neurons descend?
via anterior medial columsn
What plans and initiates the voluntary movements?
premotor cortex for planning and primary motor cortex for movements
Where do premotor and primary motor cortices receive input from?
cerebellum and basal ganglia via the ventrolateral thalamus
What are the pyramidal cells of cotrical layer 5?
upper motor neurons, can be Betz and non-Betz cells
Where does the corticobulbar tract go?
to brainstem nuclei
where does the corticospinal tract go?
spinal cord lower motor neurons
What are the largest cells in the human nervous system?
Betz cells
Pyramidal tract upper motor neuron axons descend through the ______ ______ (forebrain).
internal capsule
after going through the internal capsule, pyramidal tract then goes trough… ____ _____ and _____ _____ ______
cerebral peduncle, pontine fiber bundles
What forms the medullary pyramids?
pyramidal tract after leaving the pons
What does the pyramidal tract innervate?
brainstem nuclei, reticular formation and red nucleus
What does pyramidal tract decussate?
the medulla
Once the pyramidal tract decussates, what is it called?
corticospinal tract
the latercal corticospinal tract forms a direct pathway from _____ _____ to ____ ______.
cortex neurons; ventral horn (local circuitry)
What type of animal is the lateral corticospinal tract more prevalent in?
verterbates that are skilled with their hands
Who found that electrical stimulation elicits contralateral muscle contraction?
Fritsch and Hitzig
Who found spatial representation of body’s muscles in great apes?
Charles Sherrington
Who had 400 neurosurgical patients which led to motor homunculus discovery?
Wilder Penfield
Corticobulbar tract controls…
upper motor neurons of the cranial nerves terminates on motor neuron within the brain stem motor nuclei (muscles of face, head, and neck)
Corticospinal tract controls….
controls spinal motor neurons (movement of upper torso, upper and lower limbs)
Which corticospinal tract controls distal extremities?
lateral
What controls proximal limbs?
Ventral (anterior) corticospinal tract
How are maps organized for muscles?
not like homunculus, they are put into groups
___% of axons in corticospinal tract arise directly from premotor cortex
30
What happens in Parkinson’s disease?
there is a loss of nigrostriatal dopaminergic neurons
What happens to the direct and indirect pathways in Parkinson’s?
direct: sustained inhibition
indirect: augments direct pathway’s inhibition
What happens to the outflow of basal ganglia in Parkinson’s?
it is abnormally high
How is Parkinson’s treated?
L DOPA
Symptoms of Parkinson’s
tremor, muscle rigidity, akinesia, slowness in movement, instability, lowered facial expressions
What is the treatment for Huntington’s?
a drug that blocks DA transmission
What happens when the inhibitory outflow of the basal ganglia is reduced?
Upper motor neurons become activated by inappropriate signals
What is the result of loss of GABAnergic MSNs?
the GP cells become abnormally active which recudes the excitatory output of the indirect pathway
What causes Huntington’s?
Loss of GABAnergic MSNs
What happens when the striatum is activated?
the thalamus is disinhibited and can signal to the upper motor neurons
What do you do to the thalamus to prevent unwanted movement at rest?
tonically inhibit it
The basal ganglia-thalmocortical motor circuit is organized in _____.
loops
Putamen —-> ____ ____ —-> thalamus —–> ___ ____
globus pallidus, motor cortex
MSNs send _____ inhibitory GABAnergic projections
converging
What is the main output of the basal ganglia?
Inhibitory
What is the firing of MSNs associated with?
decision to move
What do medium spiny neurons do?
they receive excitatory glutaminergice synapses from cortical neurons
What is a physical characteristic of medium spiny neurons?
they have large dendritic trees which indicates a divergence of cortical input
How is the straitum organized?
topographically
What is the putamen responsible for?
somatosensory, visual, auditory, premotor and primary motor inputs (ALL OVER)
What is the caudate responsible for?
eye motor and multimodal association of cortical inputs (MOSTLY FROM FRONTAL CORTEX)
The corticostraital pathway synapses at…
the caudate and putamen
What are two subdivisions of the striatum?
caudate and putamen
What is the function of the straitum of the basal ganglia?
input zone
What is the major role of the basal ganglia?
permission for the intitation of movement by the upper motor neurons
What are the four motor nuclei of the basal ganglia?
- corpus straitum
- globus pallidus
- substantia nigra
- subthalamic nucleus
Hyperkinesia is common to what disease?
Huntington’s disease
Hyperkinesia is what?
excessive movement
Hypokinesia is common in what disease?
Parkinson’s
Hypokinesia is…
diminished movement
What are the three characteristics of motor disturbances of the basal ganglia?
- tremor and other involuntary movement
- changes in posture and muscle tone
- rapid jerky movements or slowness of movement without paralysis
What first suggested that the basal ganglia is involved in the control of movement?
clinical observations… aks diseases
What is the Babinski sign?
it indicates a loss of descending control of the reflex arc…. toes will point up instead of down when foot has stimuli run across it
What is upper motor neuron syndrome?
loss of reflexes or brainstem control
How does the reticulospinal pathway work in anticipatory maintenance of body posture?
- it predicts the disturbance and generates stabilizing response
- it then uses an anticipatory feed-forward mechanism to make a postural adjustment
What is the reticulospinal tract responsible for? detailed list (3 things)
- integrates info from motor systems to coordinate automatic movements of posture and locomotion
- facilitates and inhibits voluntaray movement, influences muscle tone
- mediates autonomic functions
What is the colliculospinal tract responsible for?
orienting head and eye movements (mostly in response to auditory/visual stimuli)
What is the reticulospinal tract responsible for? basic list
temporal and spatial coordination of limb and trunk movements (and balance)
Where does the lateral vestibulospinal tract receive its input from?
otoliths (cranial nerve VIII)
What is the lateral vestibulospinal tract responsible for?
proximal limbs, posture/balance and gaze fixation
Where does the medial vestibulospinal tract receive its input from?
semicircular canals (cranial nerve VIII)
What is the medial vestibulospinal tract responsible for?
reflex control of neck muscles
What are the two divisions of the vestibulospinal tract?
medial and lateral
What are the three tracts in the brain stem?
Vestibulospinal, reticulospinal, colliculospinal
What “governs” the extrapyramidal tract?
neurons in vestibular nuclei, reticular formation and superior colliculus
What is the function of the extrapyradmidal tract?
involuntary reflexes and movement and modulation of movement
What does the brainstem control? (major and three sub items)
Motor control (some of): 1 balance 2 posture 3 gaze
upper motor neurons synapse on ____ circuit neurons and/or _____ motor neurons in the spinal cord.
local, lower
The tectospinal (colliculospinal) system does….
1- receives visual input
2- projects from superior colliculus to the spinal cord
3-helps transform visual inputs into motor commands
4- helps coordinate head movements with eye movements
What are the two gray matter structures of the cerebellum?
laminated cerebellar cortex and deep cerebellar nuclei
The cerebellum does not initiate movement, but it contributes to _______, precision, and _____ _______.
coordination, accurate timing
Where does the cerebellum receive input from?
sensory systems of the spinal cord (and other parts of brain)
What does the cerebellum do?
integrates sensory input to fine tune motor activity
What does damage to the cerebellum cause?
disorders in fine movement, equilibrium, posture, and motor learning
What are three subdivisions of the cerebellum?
1-cerebrocerebellum
2- spinocerebellum
3- vestibulocerebellum
Where does the cerebrocerebellum receive input from?
indirectly from the cortex
What does the cerebrocerebellum do?
it regulates highly skilled movements and executes complex spatial and temporal sequences
Where does the spinocerebellum receive input from?
direct input from the spinal cord
What does the spinocerebellum do?
acts on distal (Lateral) and proximal (medical) muscles
Where does the vestibulocerebellum receive input from?
vestibular nuclei
What does the vestibulocerebellum do?
regulates posture and equilibrium
What are the three cerebellar pathways?
1- middle cerebellar peduncle
2-superior cerebellar peduncle
3- inferior cerebellar peduncle
Is there middle cerebellar peduncle afferent/efferent?
afferent
Is there superior cerebellar peduncle afferent/efferent?
efferent
Is there inferior cerebellar peduncle afferent/efferent?
efferent
Which cerebellar pathway plays a role in the sleep/wake cycle?
inferior cerebellar pathway
What is the role of the inferior olive?
it participates in memory and learning
In cerebellar ataxia, do problems arise contralateral or ipsilateral?
ipsilateral
What is error correction mediated by in the cerebellum?
climbing fibers from inferior olive into Purkinjie neurons
