descending pathways

Question 1

what is a ‘tract’ in the brain?

Answer 1

a large number of axons travelling in parallel within the CNS

Question 2

what is a pathway?

Answer 2

the route taken along tracts by either a sensory signal or a motor signal - can cross tracts or travel along just a portion of them

Question 3

what is a system in the brain?

Answer 3

this is the name usually given to a complex group of tracts found in a particular portion of the spinal cord or a group of tracts serving a similar function

Question 4

where do UMNs arise from (upper motor neurones)?

Answer 4

found in the cortex and brainstem nuclei, restricted to the CNS (can have a control over other UMNs or LMNs)

Question 5

where do you find lower motor neurones?

Answer 5

arise from the spinal cord/braainstem and synapse on muscles to stimulate contraction

Question 6

what type of movements are controlled by descending VENTROMEDIAL pathways?

Answer 6

involuntary (e.g. posture, balance, muscle tone, head orientation and breathing)

Question 7

whereabouts in the brain is POSTURE mediated?

Answer 7

in the brainstem

Question 8

which sensory inputs are integrated in the brainstem and used to adjust balance to maintain posture in the VESTIBULOSPINAL PATHWAY (3)?

Answer 8

muscle proprioceptions - information from muscle spindles which give information about muscle length and tension)

2. balance from the vestibular apparatus in the ear
3. visual inputs (detection of movements in visual field representing movement of the body

Question 9

which part of the brainstem is information collected in?

Answer 9

the reticulum

Question 10

which are of the brainstem is the vestibular nucleus found in and what type of motor neurones are found in here?

Answer 10

the medulla - upper motor neurones

Question 11

what information is given to the vestibular nucleus?

Answer 11

information from the vestibular apparatus of the inner ear about balance

Question 12

where do all of the venture medial pathways originate?

Answer 12

brainstem (primarily the reticulum)

Question 13

which ventromedial pathway is balance involved in?

Answer 13

the vestibulospinal pathway

Question 14

what are the two pathways of the vestibulospinal system?

Answer 14

lateral and medial

Question 15

what is the principle effect of the lateral vestibulospinal pathway?

Answer 15

to facilitate extensor motor neurones and relax antagonist muscles
also activates gamma motor neurones which causes enhanced muscle kindle mediates stretch reflexes to increase the tone in antigravity muscles

Question 16

what is the principle effect of the medial vestibulospinal pathway?

Answer 16

controls head and eye movements usually in response to a moving target - head and eye movements remain fixed despite movements of the rest of the body. medial pathway links with lateral which receives information from the vestibular apparatus.

Question 17

what does the reticulospinal pathway control?

Answer 17

co-ordinates movement and posture by receiving information from many different sources

Question 18

where does the reticulospinal pathway receive sensory information from?

Answer 18

1. vestibular nuclei
2. comical areas for voluntary movement
3. proprioception, vision etc

Question 19

what are the main effects of the reticulospinal pathway?

Answer 19

coordinates truncal and proximal muscle activity to orientate body towards or away from a stimulus
also affects muscle tone in response to planned motor activity and overall coordinated distal and proximal muscle activity

Question 20

where is the primary motor cortex located?

Answer 20

just anterior to the central sulcus on the frontal lobe

Question 21

how can you tell if an area of the body is under finer motor control?

Answer 21

takes up a larger area in the primary motor cortex

Question 22

what are the two devisions of the corticobulbar tract?

Answer 22

tract in the brainstem to facial and cranial muscles and influence over unconscious motor output (i.e. override reflexes to make yourself fall over)

Question 23

what are the two divisions of the corticospinal tract?

Answer 23

the lateral contralateral tract and the anterior ipsilateral tract

Question 24

what percentage of motor output is controlled by the lateral contralateral tract?

Answer 24

90-95%

Question 25

what is the purpose of the anterior ipsilateral tract?

Answer 25

to contract antagonist muscles on the opposite side of the body to carry out movements (provides postural compensation for movements contra laterally)

Question 26

where does the anterior ipsilateral tract terminate?

Answer 26

L2

Question 27

how does each tract innervate at the segment?

Answer 27

anterior ipsilateral - bilaterally

lateral contralateral - unilaterally

Question 28

Somatotopic organisation to alpha motor neurons in the ventral horn of the spinal cord - are flexor motor neurons more anterior/posterior?

Answer 28

more posterior than extensors

Question 29

Somatotopic organisation to alpha motor neurons in the ventral horn of the spinal cord - are more distal muscles more lateral/medial?

Answer 29

lateral

Question 30

what can a positive babinski response indicate?

Answer 30

corticospinal lesions - upper motor neurone syndrome

Question 31

what are signs of a lower motor neurone lesion

Answer 31

muscle paralysis
reduced motor tone
reduced stretch reflex
fasciculation
atrophy

Question 32

what are signs of an upper motor neurone lesion?

Answer 32

no atrophy or fasciculation but muscle tone often increase leading to painful spasticity