lecture 6 descending tracts and movement control Flashcards Preview

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What is an upper motor neuron?

Originates in the cortex or brainstem and ends in the CNS


what is a lower motor neuron?

alpha motor neuron or a final common pathway; leaves the CNS to go out to the periphery


What is a motor unit?

1mn and the muscle fibers it innervates; ranges from 1:3 in the stapedius to 1:1000 fibers in gastric


what are the 3 types of muscle fibers?

Type I- red, slow twitch
Type IIa- white, fast twitch fatigue resistant
Type IIb- white, fast twitch fatiguable


what is feed forward?

anticipatory use of sensory information to prepare for movement; example: checking out the competition in order to make up a strategy of how you will start the hot dog eating competition


what is feedback?

use of sensory information during or after movement to make corrections; example: you choke on a dry hot dog bun


wat is movement decomposition?

loss of synchronization of skilled movements; segmented movement by single joints rather than coordinated movement of multiple joints; example: when you start to speed up or slow down from your normal pace you start to forget the order of events and become uncoordinated


Automatic movement routines triggered by the pre motor and motor cortex are ruled by subconscious feed forward- feedback loops are dependent on what 3 things?

-visual input (sometime auditory input)
-somatosensory input
-proprioceptive input
(loss of one will cause movement decomposition and the movement routine will then rise to conscious control)


What 5 descending tracts are for postural and gross movement whose nuclei are located in the medial spinal cord?

-medial reticulospinal
-medial vestibulospinal
-lateral vestibulospinal
-medial cortiospinal


what are 2 major differences between the sensory and motor homunculus?

In the motor homunculus the hip ins at the bend and the neck is between the hand and face


what 3 tracts are for fine movement and limb flexion whose nuclei are located in the lateral spinal cord?

-lateral corticospinal
-lateral reticulospinal


what 2 tracts are non specific upper motor neurons tracts whose nuclei are located in the ventral horn?



The corticobulbar tract supplies cranial nuclei for the motor control of what 6 structures?



does the cortiocbulbar tract for contralateral, ipsilateral, or bilateral control?

-lower face: contralateral control
-upper face: bilateral control


what 3 cranial nerve nuclei are NOT supplied by the corticobulbar tract?

3- occulomotor
6- abducens


What is the order in which motor units are recruited?

They are recruited small to large
-S: slow twitch, fatigue
-FR: fast twitch, fatigue resistant next
-FF: fast twitch, fatiguable last


What is a simple reflex arch?

minimal descending input
- stimulate afferent> efferent loop>ascending input for cortical awareness
-interneuronal connection to cause you to immediately contract and pull back


What is a reciprocal reflex pattern?

stimulate afferent>efferent loop and reciprocal innervation of opposite muscle contralaterally (flexion withdrawal and extensor patterns) with ascending input for cortical awareness


what is a reciprocal movement pattern?

subcortical control unless disrupted
-central/ stepping pattern generator for complex intralimb movements
-CPGs are linked contralaterally between UEs and Les
-examples: walking, arm swing, running, free style swimming; NOT skipping


Can you have conscious control over a simple reflex?

yes, when you are going to get a shot you know it will be painful but you prepare yourself for it and instead of pulling away you remain still


what is UMN damage and list 5 examples

UMN damage is damage of neuron leaving the cortex
-spasticity or hypertonia


what is paresis?

UMN injury causing partial loss of voluntary motor control
-hemiparesis- partial loss of voluntary contraction on one side of the body


what is paralysis?

UMN injury causing complete loss of voluntary motor control


what is spasticity or hypertonia?

UMN injury causing velocity dependent increase in stretch reflex with increased resting tone


what is rigidity?

UMN injury causing resistance to passive stretch regardless of speed of force
-decerebrate rigidity- midbrain damage resulting in UE and LE extension
-decorticate rigidity- damage above the midbrain level resulting in UE flexion and LE extension


what is hypotonia?

UMN injury causing low tone due to pervasive brain damage, genetic disorders, or developmental delays


what is a LMN injury and what are 5 examples

a LMN injury is damage of alpha mn cell body or peripheral axons
-paralysis or flaccidity
-loss of reflexes


what is paralysis or flaccidity?

LMN injury causing there to be no volitional control, atrophy


what s atrophy?

LMN injury causing loss of muscle bulk
-neurogenic atrophy- due to nerve damage
-disuse atrophy- due to lack of use


what is polio?

LMN injury; virus destroys alpha motor neurons


what is the cause of a stroke/ CVA and what will be lost?

Cause- interrupted blood supple to motor cortex
- there will be sensory and motor losses mostly contralateral to the lesion


what is the cause and presentation of amyotrophic lateral sclerosis?

cause: usually unknown, with a small percent having a genetic component; bilateral destruction of UMNs, brainstem, and spinal cord LMNs
-hyper- reflexia
-Babinski's sign
-difficulty stallion, breathing, and speaking due to CN involvement


what is the cause and presentation of cerebral palsy?

Cause: not always clear but includes:
-abnormal neuronal development, migration, and maturation
-abnormal supra spinal development of spinal MNs
-intra or periventricular hemorrhages, cerebral infarcts, periventricular leukomalacia
Presentation: motor disorders: hyper or hypotonia, postural imbalances, hyper reflexia, abnormal muscle recruitment patterns, and muscle co- contraction


what is the cause and symptoms of brown sequard syndrome?

Cause: injury- hemisection of the spinal cord
-ipsilateral spastic paralysis below the level of the lesion
-ipsilateral disruption of tactile, vibration and position sense
-contralateral disruption of pain and temperature 1-2 levels below the lesion