lecture 6 descending tracts and movement control

Question 1

What is an upper motor neuron?

Answer 1

Originates in the cortex or brainstem and ends in the CNS

Question 2

what is a lower motor neuron?

Answer 2

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

Question 3

What is a motor unit?

Answer 3

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

Question 4

what are the 3 types of muscle fibers?

Answer 4

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

Question 5

what is feed forward?

Answer 5

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

Question 6

what is feedback?

Answer 6

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

Question 7

wat is movement decomposition?

Answer 7

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

Question 8

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?

Answer 8

-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)

Question 9

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

Answer 9

• tectospinal
• medial reticulospinal
• medial vestibulospinal
• lateral vestibulospinal
• medial cortiospinal

Question 10

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

Answer 10

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

Question 11

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

Answer 11

• lateral corticospinal
• rubrospinal
• lateral reticulospinal

Question 12

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

Answer 12

• cerulospinal

- raphespinal

Question 13

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

Answer 13

• face
• tongue
• pharynx
• larynx
• trapezius
• SCM

Question 14

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

Answer 14

• lower face: contralateral control

- upper face: bilateral control

Question 15

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

Answer 15

3- occulomotor
4-trochlear
6- abducens

Question 16

What is the order in which motor units are recruited?

Answer 16

They are recruited small to large

• S: slow twitch, fatigue
• FR: fast twitch, fatigue resistant next
• FF: fast twitch, fatiguable last

Question 17

What is a simple reflex arch?

Answer 17

minimal descending input

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

Question 18

What is a reciprocal reflex pattern?

Answer 18

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

Question 19

what is a reciprocal movement pattern?

Answer 19

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

Question 20

Can you have conscious control over a simple reflex?

Answer 20

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

Question 21

what is UMN damage and list 5 examples

Answer 21

UMN damage is damage of neuron leaving the cortex
Examples:
-paresis
-paralysis
-spasticity or hypertonia
-rigidity
-hypotonia

Question 22

what is paresis?

Answer 22

UMN injury causing partial loss of voluntary motor control

-hemiparesis- partial loss of voluntary contraction on one side of the body

Question 23

what is paralysis?

Answer 23

UMN injury causing complete loss of voluntary motor control

Question 24

what is spasticity or hypertonia?

Answer 24

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

Question 25

what is rigidity?

Answer 25

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

Question 26

what is hypotonia?

Answer 26

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

Question 27

what is a LMN injury and what are 5 examples

Answer 27

``` a LMN injury is damage of alpha mn cell body or peripheral axons Examples: -paralysis or flaccidity -atrophy -loss of reflexes -fibrillations -Polio ```

Question 28

what is paralysis or flaccidity?

Answer 28

LMN injury causing there to be no volitional control, atrophy

Question 29

what s atrophy?

Answer 29

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

Question 30

what is polio?

Answer 30

LMN injury; virus destroys alpha motor neurons

Question 31

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

Answer 31

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

Question 32

what is the cause and presentation of amyotrophic lateral sclerosis?

Answer 32

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

Question 33

what is the cause and presentation of cerebral palsy?

Answer 33

Cause: not always clear but includes: -abnormal neuronal development, migration, and maturation -hypoxia -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

Question 34

what is the cause and symptoms of brown sequard syndrome?

Answer 34

Cause: injury- hemisection of the spinal cord Symptoms: -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