Peter's Physiology 6 - Spinal nerves, upper motor neurones and control of movement

Question 1

Which type of neurones allow communication between sensory and motor neurones in the CNS?

Answer 1

Interneurones

Question 2

What 4 sources do spinal interneurons receive input from

Answer 2

Primary sensory axons
Descending axons from the brain
Collaterals (branches) of LMNs
Other interneurones

Question 3

What type of signal can inputs to spinal interneurones be?

Answer 3

Excitatory or inhibitory (interneurones integrate incoming information to generate an output)

Question 4

What are the 2 types of spinal interneurones?

Answer 4

Excitatory

Inhibitory

Question 5

What 2 responses do inhibitory interneurones mediate in order to provide co-cordinate control of flexors and extensors in limb movement?

Answer 5

Inverse myotatic response

Reciprocal inhibition between extensor and flexor muscles

Question 6

What is the inverse myotatic response?

Other name

Answer 6

Glogli tendon reflex

Skeletal muscle contraction causes the antagonist muscle to simultaneously lengthen and relax

Question 7

What is reciprocal inhibition between extensor and flexor muscles?

Answer 7

Muscles on one side of a muscle real to accommodate contraction on the other side of that joint

Question 8

What is another name for the myotatic reflex?

Answer 8

Stretch reflex

Question 9

At a joint, voluntary contraction of an extensor will stretch an antagonist flexor, initiating what?
How is unopposed extension therefore brought about?

Answer 9

The myotatic reflex

Descending pathways that activate the alpha-MN controlling the extensors muscles also, via inhibitory interneurons, inhibit the alpha-MNs supplying the antagonist muscles (reciprocal inhibition)

Question 10

What tract do neurones from the motor cortex travel down in reciprocal inhibition?

Answer 10

Corticospinal tract

Question 11

What pathways do excitatory interneurones mediate?

Answer 11

Flexor reflex

Crossed extensor reflex

Question 12

How does a noxious stimulus cause a limb to flex?

What is this reflex called?

Answer 12

Contraction of flexor muscles via excitatory interneurones
Relaxation of extensor muscles via excitatory and inhibitory interneurones

Flexor reflex

Question 13

How does a noxious stimulus cause a limb to extend?

What is this reflex called?

Answer 13

Contraction of extensor muscles via excitatory internueornes
Relaxation of flexor muscles via excitatory and inhibitory interneurones

Crossed extensor reflex

Question 14

What is the purpose of the crossed extensor reflex?

Answer 14

To enhance postural support during withsrawal of a foot from a painful stimulus (don’t want to fall over)

Question 15

What are central pattern generators?

Answer 15

biological neural networks that produce rhythmic patterned outputs without sensory feedback

Question 16

What type of activity can a simple spinal central pattern generator command?

Answer 16

Rhythmic, alternating activity that moves a limb

Question 17

To produce a simpel spinal central pattern generator that can command rhythmic alternating activity that moves a limb, what must the excitatory interneurone display in terms of activity?

Answer 17

Oscillatory, or pacemaker, activity

Question 18

What type of motor function do high level structures control?
What 2 structures are classified as high level?

Answer 18

Strategy
Neocortical association areas
Basal ganglia

Question 19

What type of motor function do middle level structures control?
What 2 structures are classified as middle level?

Answer 19

Tactics
Motor cortex
Cerebellum

Question 20

What type of motor function do low level structures control?

What 2 structures are classified as low level?

Answer 20

Execution
Brain stem
Spinal cord

Question 21

In terms of motor control hierarchy, what is strategy?

Answer 21

Aim of movement?

How can it best be achieved?

Question 22

In terms of motor control hierarchy, what is tactics?

Answer 22

What sequence of muscle contractions and relaxations in time and space will fulfil the strategic aim?

Question 23

In terms of motor control hierarchy, what is execution?

Answer 23

Activation of motor pools and interneurone polls that command the desired movement and make essential postural adjustments

Question 24

From which 2 areas do descending spinal tracts origiante from?

Answer 24

Cerebral cortex

Brain stem

Question 25

What are the 2 important groups of descending spinal tracts?

Answer 25

Lateral pathways | Ventromedial pathways

Question 26

What 2 pathways make up the lateral descending pathways?

Answer 26

Lateral corticospinal tract | Rubrospinal tract

Question 27

What 4 important pathways make up the ventromedial descending pathways?

Answer 27

Pontine reticulospinal tract Medullary reticulospianl trat Lateral vestibulospinal tract Tectospinal tract

Question 28

What structure control input to the lateral descending spinal tracts?

Answer 28

Cerebral cortex

Question 29

What actions are the lateral descending spinal tract pathways important for?

Answer 29

Voluntary control of distal musculature, particularly discrete, skilled movements e.g. hands and fingers in a "fractionated" manner

Question 30

What structure controls input to the ventromedial spinal tract pathways?

Answer 30

Brainstem

Question 31

What actions are the ventromedial pathways important for?

Answer 31

Control of posture and locomotion

Question 32

What is another name for the corticospinal tract?

Answer 32

Pyramdial tract

Question 33

Where are cell bodies of the corticospinal tract located?

Answer 33

About 2/3rds = motor cotetx | About 1/3rd = somatosensory areas of parietal cortex

Question 34

What does the axons of the corticospinal tract form at the medulla?

Answer 34

Medullary pyramid

Question 35

Where do most fibres in the corticospinal tract decussate?

Answer 35

At the pyramidal decussation (on medulla)

Question 36

What do the decussated fibres of the corticospinal tract form at the pyramidal decussation? What are the remainder of fibres called?

Answer 36

Lateral corticospinal tract | Ventral corticospinal tract (decussate more caudally)

Question 37

Where do axons of the corticospinal tracts terminate?

Answer 37

In the dorsolateral region of the ventral horn and intermediate grey

Question 38

In terms of the corticospinal tract, what side of muscualture does the left hemisphere control?

Answer 38

Right musculature

Question 39

Where are the cell bodies of the rubrospinal tract located? | What does this receive input from?

Answer 39

``` Red nucleus (midbrain) Motor cortex and cerebellum ```

Question 40

Where do axons of the rubrospinal tract decussate?

Answer 40

At the ventral segmental decussation in the midbrain

Question 41

Where do axons of the rubrospinal tracts terminate?

Answer 41

Ventral horn

Question 42

What do axons of the rubrospinal tract control?

Answer 42

Limb flexor muscles

Question 43

What 2 problems can lesions of the lateral descending pathways cause?

Answer 43

Loss of "fractionated" movements i.e. shoulders elbow, wrist and fingers cannot be moved independently Slowing and imapirment of accuracy of voluntary movements

Question 44

What difference to the problems caused by a lesion to the lateral descending pathways can occur if the rubospinal tract is spared?

Answer 44

Initially causes same deficits as pronoun lesions although major recovery can occur (due to rubrospinal tracts taking over)

Question 45

Where do the cell bodies of the vestibulospinal tracts reside?

Answer 45

Vestibular nuclei (lateral and medial) in the pons

Question 46

What do the vestibulospinal tracts receive input from?

Answer 46

``` Vestibular larbyrinthys (via CN VIII) Cerebellar input also important ```

Question 47

Where do axons from the lateral vestibular nucleus descend to? How do they do this?

Answer 47

Lumbar spinal cord | Via the lateral vestibulospinal tract

Question 48

Do inputs to the vestibulospinal tracts control the ipsilateral or contralateral sides of the body?

Answer 48

Ipsilateral

Question 49

What do outputs from the lateral vestibulospinal tract do?

Answer 49

Helps to hold us upright and balance upright by facilitating extensor MNs of antigravity muscles e.g. of the leg

Question 50

Where do axons from the medial vestibular nucleus descend to? How do they do this?

Answer 50

Cervical spinal cord | Via the medial vestibulospinal tract

Question 51

What do outputs from the medial vestibulospinal tract do?

Answer 51

Activate cervical spinal circuits that control neck and back muscles guiding head movements

Question 52

Where do the cell bodies of the tectospinal tract reside?

Answer 52

In the superior colliculus of the midbrain

Question 53

What does the tectospinal tract receive input from?

Answer 53

Retina Visual cortex Afferents conveying somatosensory and auditory information

Question 54

Where do axons of the tectospinal tract decussate?

Answer 54

In the dorsal tegmental decussation of the midbrain

Question 55

Give an example of an action the tectospinal tract controls?

Answer 55

Orientation of the head and eyes to an important, new, visual stimulus

Question 56

Which is the medial and which is the lateral reticulospinal tracts?

Answer 56

``` Medial = pontine Lateral = medullarly ```

Question 57

Where do both reticulospinal tracts arise?

Answer 57

Reticular formation

Question 58

What is the reticular formation?

Answer 58

A diffuse mesh of neurones that are located along the length and at the core of the brainstem

Question 59

Does the pontine reticulospinal tract descend ispilaterally, contralaterally or bilaterally?

Answer 59

Ipsilaterally

Question 60

What 2 functions does the pontine reticulospinal tract mediate?

Answer 60

Enhances antigravity reflexes of the spinal cord | Helps to maintain a standing posture by facililitating contraction of the extensors of the lower limbs

Question 61

Does the medullary reticulospinal tract descend ispilaterally, contralaterally or bilaterally?

Answer 61

Bilaterally

Question 62

What 2 functions does the medullary reticulospinal tract mediate?

Answer 62

Opposes the action of the medial tract | Releases antibgravity muscles from reflex control