Motor Control in mammals II

Question 1

What is proprioception?

Answer 1

Spatial awareness of the body’s position and movement

Question 2

What happens if you have lost your proprioception?

Answer 2

Have a loss of sense of joint position, vibration and fine tactile sensations including tendon reflexes

Question 3

What is locomotion?

Answer 3

Using rhythmic or alternating movements of body r appendages

Question 4

At which level of the CNS is locomotion automatically controlled?

Answer 4

Low levels of the CNS

Question 5

What were 2 major experiments carried out in the 60s to explore locomotion?

Answer 5

1. Rhythmic patterns of motor activity elicited in spinal animals by application of adrenergic drugs
2. Walking evoked in decerebrate cats by electrical stimulation of a small region of he brain stem

Question 6

What do flexors and extensors do to each other?

Answer 6

Inhibit each other reciprocally

Question 7

What does supraspinal mean?

Answer 7

Above the spine

Question 8

What were the 4 conclusions that Thomas Brown work came to?

Answer 8

1. Supraspinal commands not necessary for basic motor pattern
2. Rhythmically stepping produced by neural circuits entirely within spinal cord
3. Spinal circuits can be modulated by tonic descending signals from the brain
4. Spinal pattern - generating networks do not require sensory input but are strongly regulated by input from limb proprioceptors

Question 9

What does proprioception ‘do’ in regard to stepping?

Answer 9

Regulates timing and amplitude stepping

Question 10

What are the 4 phases that the swing and stance phase are divided into?

Answer 10

Flexion (F)
First extension (E1)
Second Extension (E2)
Third Extension (E3)

Question 11

Where is the foot in the swing and stance phase?

Answer 11

Swing - foot off ground

Stance - foot on ground

Question 12

What does proprioceptive information in extensor muscles do?

Answer 12

Prolong stance phase, often delaying onset of swing until stimulus has ended

Question 13

What affect do Golgi tendon organs have on ankle extensor motor neurons and what does this mean? How is this information signalled?

Answer 13

Excitatory action in walking but inhibitory in rest.
Means no swing phase until extensor muscles unloaded and forces exerted by these muscles are low. This is signalled by a decreased in activity from Golgi tendon organs

Question 14

What phases are in swing phase and which ones are in stance phase?

Answer 14

F & E1 - in swing phase

E2 & E3 - in stance phase - foot makes contact in ground

Question 15

What happens when a cat comes across an object on the floor? What is this called?

Answer 15

Excitation of flexor motor neurons and inhibition of extensor motor neurons. Causes rapid flexion of paw away from stimulus and elevation of leg to step over the object. AKA Stumbling corrective reaction

Question 16

What are the 3 pathways that transmit excitatory information from extensor muscles to extensor motor neurons?

Answer 16

1. Monosynaptic pathway - from primary muscle spindles
2. Disynaptic pathway - from primary muscle spindles and Golgi tendon organs
3. Polysynaptic pathway - from primary muscle spindles and Golgi tendon organs that include interneurons in central pattern generators

Question 17

At which phase can the corrective flexion movement only be produced?

Answer 17

Only if paw is stimulated in swing phase. If flexion reflex were produced during stance phase animal might fall over because its being supported by the limb

Question 18

What is spinal preparation?

Answer 18

Where the spinal cord is transected at the lower thoracic level

Question 19

Why are spinal preparations performed?

Answer 19

To study rhythmic motor output that’s similar to locomotion after suppression of all afferent inflow and isolating segments that control hind limb musculature (study neuronal control of stepping)

Question 20

What happens in acute spinal preparations?

Answer 20

1. Adrenergic drugs i.e. L-DOPA/ nialamide - administered immediately after transection
2. Elevation of norepinephrine in spinal cord
3. Spontaneous generation of locomotor activity 30 mins after administration (movement due to administration of drug)

Question 21

What happens in chronic spinal preparations?

Answer 21

1. Tran-section of spinal cord studied for weeks/ months
2. Locomotor activity can take weeks to come back
3. Locomotor function returns spontaneously in kittens
4. Daily training required to restore function in adult cats

Question 22

What was found from decerebrate preparations?

Answer 22

Tonic electrical stimulation of mesencephalic locomotor region initiates stepping when decerebrate animals are placed on a treadmill.

Question 23

What are decerebrate preparations and what is their purpose?

Answer 23

Brainstem is transected at midbrain level so it removes communication between rostral brain centres and spinal cord.
Purpose is to be able to investigate the roles of the cerebellum and brain stem in controlling locomotion

Question 24

What happens in the the decerebrate preparation: pre-mammillary body preparation? What does this lead to?

Answer 24

Brainstem transected from rostral margin of superior colliculi to a point immediately rostral to mammillary bodies.

Brainstem centres remain connected to spinal cord and causes spontaneous stepping

Question 25

What happens in the the decerebrate preparation: post-mammillary body preparation? What does this lead to?

Answer 25

Transection made caudal to mammillary bodies. No spontaneous stepping. Electrical stimulation of mesencephalic locomotor region is required to evoke walking. Used to show how spontaneous stepping occurs and how the brain and spinal cord communicate

Question 26

What information is carried down the descending spinal tracts?

(5 marks)

Answer 26

Control of movement
Muscle tone
Spinal reflexes
Spinal autonomic functions
Modulation of sensory information to higher centres

Question 27

What is the function of the corticospinal tract?

Answer 27

Control of voluntary, discrete and skilled movement of distal limb

Question 28

What is the pathway of the corticospinal tract?

Answer 28

Goes down from motor and sensory cortices
Pass through internal capsule
Enter crus cerebri of midbrain
Goes down ventral portion of pons
To medulla oblongata (down pyramidal tracts)
Fibres decussate into lateral corticospinal cord (75%-90%)
and anterior corticospinal tract (10%-25%)

Question 29

What percentage of the corticospinal tract terminate at different levels?

Answer 29

55% cervical
20% thoracic
25% lumbosacral

Question 30

What is hereditary spastic paraparesis?

Answer 30

Inherited degenerative disorder. Autosomal dominant and causes progressive weakness of the legs, increased muscle tone and marked stiffness in gait

Question 31

What are the causes of hereditary spastic paraperesis?

Answer 31

Degeneration of lateral corticospinal tract. Chiefly affects thoracic cord, spastic paraparesis.

Question 32

What is an acute lesion of the spinal cord?

Answer 32

Occlusion of anterior spinal artery.

Trauma = fracture of the spine

Question 33

What is chronic compression of spinal cord and emerging nerve roots?

Answer 33

Injection and tumours of spine, meninges and nerve roots. Prolapsed intervertebral discs - presses on nerve root and causes pain

Question 34

What are focal lesions of spinal cord and root nerves?

Answer 34

Lesions that destroy function at segmental level. Lesion disrupts descending motor tracts

Question 35

What can an injury to the spinal cord result in?

Answer 35

Loss of sensation, movements and, autonomic function

Question 36

What is the focus right now in terms of curing spinal lesions?

Answer 36

Promoting regeneration of injury sites of axons

Question 37

How can you improve walking for a spinal cord injury?

Answer 37

Repetitive weight supported stepping on a treadmill. Practical support of bodyweight essential as reduces requirements for supraspinal control of posture and balance

Question 38

What is a benefit to repetitive supported weight training?

Answer 38

Facilitates training of spinal cord circuits