Motor Function Flashcards
three areas of motor cortex
primary motor cortex, premotor area, and supplementary motor area
how much of the motor cortex is devoted to the hands and speech?
1/2
what occurs in primary motor cortex damage if the caudate nucleus and adjacent premotor and supplementary areas remain intact?
- loss of voluntary control of discrete movements of the hand and finger
- can contract but loss of fine control
Where does the intention to contract a muscle begin?
-motor assocaition (premotor) area of frontal lobes
What occurs in premotor area of frontal lobes?
- plan our behavior
- neurons compile a program for degree and sequence of muscle contraction
- program transmitted to neurons of the precentral gyrus (primary motor area)
What are the upper motor neurons?
pyramidal cells of the precentral gyrus
What determines the onset and cessation of intentional movements?
basal nuclei
What is the feedback circuit that the basal nuclei is invovled in?
cerebrum–> basal nuclei–> thalamus–> cerebrum
what controls highly practiced, learned behaviors that one carries out with little thought?
basal nuclei
Dyskinesias are movement disorders caused by what?
lesions in the basal nuclei
cerebellum controls what factors of motro control?
Highly important in motor coordination Aids in learning motor skills Maintains muscle tone and posture Smooths muscle contraction Coordinates eye and body movements Coordinates the motions of different joints with each other
What part of the brain is effected in ataxia and what are the symptoms?
cerebellum
clumsy, awkward gait
What does the supplementary motor cortex do? What effect does excitation usually have?
- positions body and head for the fine motor control movements of the arms and hands
- excitation causes bilateral contraction
What are the characteristics of the lateral corticospinal tract?
- crosses in the medulla
- terminates on interneurons in spinal cord
- gross motor movements
What are the characteristics of the ventral corticospinal tract?
- cross in spinal cord throughout neck and upper thoracic
- bilat control of postural muscles
What do the alpha motor neurons innervate?
large skeletal msucle fibers
What is th emotor unit of the alpha motor neurons?
several to several hundred individual skeletal muscle fibers
What do the gamma motor neurons innervate?
intrafusal fibers
maintain basic muscle tone
What are interneurons responsible for?
intergration of information
-make up many different circuits within the spinal cord
Dynamic vs, static neruons in the excitation of spinal cord motor neurons
dynamic: initial neuron excitation–> very high rate and intitiates a rapid development of force
static: fire much slower but maintain the force of contraction
muscle spindles give information about…
muscle length and rate of change in length
golgi tendon organs (GTOs) give information about…
tendon tension and rate of change in tension
What are the two ways that the sensory fibers of the muscle spindle can be excited?
- lengthening the muscle will stretch the spindle
- contraction of the end portion of th emuscle spindle fiber
What are the sensory fibers (group IA) of the muscle spindle?
primary ending- connects to both bag and chain fibers
secondary ending- excited only by chain fibers
Does the center of the muscle spindle have contractile proteins?
no
thats why it sensory
What is the static response of the muscle spindle?
during slow stretch the number of impulses transmitted is directly proportional to the degree of stretch
What sensory fibers of the muscle spindle are activated in static response?
both primary and secondary
What is the dynamic response of the muscle spindle?
during rapid stretch the primary ending is stimulated powerfully, transmits a tremendous excess of impulses
What is the stretch (myotatic) reflex?
- when a msucle is stretched, it contracts and maintains increased tonus (stretch reflex)
- very sudden muscle stretch causes tendon reflex
- reciprocal inhibition prevents muscles from working against each other
When a muscle is stretched by tapping its tendon with a reflex hammer, that information is carried to where?
the spinal cord by a 1a afferent axon
Where does the 1a fibers synapse in deep tendon reflexes?
directly on alpha motor neurons that innervate the muscle
the alpha motor neurons fire and muscle contracts
When does the golgi tendon reflex occur?
excessive tension on tendon inhibits motor neuron
also functions when muscle contacts unevenly
what is the tendon reflex and an example?
reflexive contraction of a muscle when its tendon is tapped
-knee-jerk reflex is a monosynaptic reflex
What is the reciprocal inhibition?
reflex phenomenon that prevents muscles from working against each other by inhibiting the antagonist
What are the 8 parts of the patellar tendon reflex arc?
- extensor muscle stretched
- muscle spindle stimulated
- primary afferent neuron excited
- primary afferent neuron stimulates alpha motor neuron to extensor muscle
- alpha motor neuron stimulates extensor muscle to contract
- primary afferent neuron stimulates inhibitory interneuron
- interneuron inhibits alpha motor neuron to flexor muscle
- flexor muscle (antagonist) relaxes
When does flexor withdrawal reflexes occur?
during withdrawl of foot from pain
What are the 6 steps of flexor withdrawl reflexes?
- stepping on glass stimulates ppain receptors in right foot
- sensory neuron activates multiple interneurons
- Ipsilateral motor neurons to flexor excited
- Ipsilateral flexor contracts
- contralateral motor neurons to extensor excited
- contralateral extensor contracts
How are movement patterns performed? What are some examples?
- performed by initiation in cortex and maintained with pattern generation centers within the spinal cord
- walking, scratching, posture
What do lesions of the pyramidal tract do?
abolishes fine grasping movement
Motor control pathways have a high level of convergence in order to provide high level of muscle control. What are the motor control pathways?
Propriospinal Corticospinal Rubrospinal Reticulospinal Tectospinal Vestibulospinal
What special functions does the brainstem control?
Respiration Cardiovascular Partial GI Stereotyped movements Equilibrium Eye movements
What does the pontine reticular nuclei of the brainstem control?
excite the axial muscles of the boyd
vertebral column and extensor muscles of the limbs
What does the medullary reticular nuclei of the brainstem control?
counterbalance signals from the pontine reticular nuclei
What does the vestibular nuclei of the brainstem control?
function in association with the pontine reticular nuclei to control antigravity muscles
What are main functions of the cerebellum?
responsible for coordination of rapid movement activities, sequence motor activation, makes correctvie adjustments while activities are being executed
What portion of the cerebellum controls motor execution?
spinocerebellum
What portion of the cerebellum controls motor planning?
cerebrocerebellum
What portion of the cerebellum controls balance and eye movement?
vestibulocerebellum
What do the topographical sections of the cerebellum control?
vermis–> axial muscles
intermediate zone–> upper/lower limbs
lateral zone–> higher order planning/coordination
What connect the motor cortex with the lateral zones of the cerebellum?
corticopontocerebellar
What is the feedback system of the ventral spinocerebellar?
the ventral spinocerebellar is excited by motor signals arrivings in the sminal cord
the feedback systen tells the cerebellum what signals have arrived
used to compare what is happening with what is supposed to happen
Deep nuclei receive information from where?
cerebellar cortex & deep sensory afferent tracts to the cerebellum
What are the 2 efferent pathways from the cerebellum (beginning with vermis and intermediate zone)?
- vermis–> fastigial nucleus–> pontine brainstem(equilibrium)
- intermediate zone –> interposed nuclei–> thalamus–> cortex–> thalamus–> basal ganglia–> red nucleus and reticular formation (coordination of reciprocal contraction of agonist and antagonist muscles of the limbs)
What are the climbing fibers in the cerebellar cortex?
they are what always produces a single, prolonged AP in each purkinje cell they contact
What are the mossy fibers in the cerebellar cortex?
very weak synaptic connections with purkinje cells
therefore requires a lot of mossy fibers to excite a purkinje cell
Damage to the vestibulocerebellum
equilibrium is disturbed during the performance of rapid motions and during change in direction
spinocerebellum is responsible for
coordination of the movement of the limbs
intermediate zone of the spinocerebellum
compares the intended sequential plan of movement with the actual movements
interposed nuclei of the spinocerebellum
send corrective signals to the cortex thru the thalamus
send corrective signals to the red nucleus
how does the planning of sequential movement from the cerebrocerebellum work?
communicates with premotor and sensory cortices
dentate nuclei coordinate this information
how does timing of sequential movements from the cerebrocerebellum work?
loss of dentate nuclei–> failure of smooth progression of movements
cerebellar disorder ataxia
uncoordinated, clumsy gait
cerebellar disorder dysmetria
abnormal overshoot or undershoot
cerebellar disorder dysrhythmia
abnormal rhythm and timing of movements
cerebellar disorder dysdiadochokinesia
patient cannot perform rapidly alternating movements
What is the basal nuclei?
masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus
What are the functions of the basal nuclei?
- recevies input from the substantia nigra of the midbrain and the motor areas of the cortex
- sends signals back to both these locations
- involved in motor control
Basal ganglia
accessory motor system
-receive most input from the cerebral cortex and return most output to the cerebral cortex
what are the components of the basal ganglia circuitry?
Caudate nucleus Globus pallidus Putamen Substantia nigra Subthalamic nucleus
Putamen circuit of the basal ganglia
- execution of learned patterns of movement
- inputs mainly from the premotor and supplemental motor cortex
- outputs back to the primary motor cortex
What 3 things can be caused by damage to the putamen circuit of the basal ganglia?
- athetosis–> spntaneous often continuous writhing movements
- hemiballismus–> flailing movements
- chorea–> flicking movements
Caudate circuit of the basal ganglia
cognitive control of motor acitvity
output from the caudate circuit of the basal ganglia
premotor and supplemental motor cortex
input from the caudate circuit of the basal ganglia
association areas of the cerebral cortex
What is responsible for planning which patterns of movement will accomplish the complex goal of fleeing from a lion?
caudate circuit of the basal ganglia– puts together sequential patterns of activity lasting 5 or more seconds
What causes parkinsonism?
loss of dopamine which decreases thalamocortical excitation
what are 5 characteristics of parkinson’s?
- bradykinesis
- rigidity
- gait instability
- resting tremor
- masked face
Why is Parkinson’s treated with L-dopa and not just dopamine?
L-dopa crosses the BBB
Loss of pigmentation in the substantia nigra is indicative of….
a loss of dopaminergic neurons (Parkinson’s)
L-Deprenyl is also a treatment for Parkinson’s; what does it do?
inhibtis MAO, dopamine remains in the synaptic cleft longer
