Peter's Physiology 6 - Spinal nerves, upper motor neurones and control of movement Flashcards
Which type of neurones allow communication between sensory and motor neurones in the CNS?
Interneurones
What 4 sources do spinal interneurons receive input from
Primary sensory axons
Descending axons from the brain
Collaterals (branches) of LMNs
Other interneurones
What type of signal can inputs to spinal interneurones be?
Excitatory or inhibitory (interneurones integrate incoming information to generate an output)
What are the 2 types of spinal interneurones?
Excitatory
Inhibitory
What 2 responses do inhibitory interneurones mediate in order to provide co-cordinate control of flexors and extensors in limb movement?
Inverse myotatic response
Reciprocal inhibition between extensor and flexor muscles
What is the inverse myotatic response?
Other name
Glogli tendon reflex
Skeletal muscle contraction causes the antagonist muscle to simultaneously lengthen and relax
What is reciprocal inhibition between extensor and flexor muscles?
Muscles on one side of a muscle real to accommodate contraction on the other side of that joint
What is another name for the myotatic reflex?
Stretch reflex
At a joint, voluntary contraction of an extensor will stretch an antagonist flexor, initiating what?
How is unopposed extension therefore brought about?
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)
What tract do neurones from the motor cortex travel down in reciprocal inhibition?
Corticospinal tract
What pathways do excitatory interneurones mediate?
Flexor reflex
Crossed extensor reflex
How does a noxious stimulus cause a limb to flex?
What is this reflex called?
Contraction of flexor muscles via excitatory interneurones
Relaxation of extensor muscles via excitatory and inhibitory interneurones
Flexor reflex
How does a noxious stimulus cause a limb to extend?
What is this reflex called?
Contraction of extensor muscles via excitatory internueornes
Relaxation of flexor muscles via excitatory and inhibitory interneurones
Crossed extensor reflex
What is the purpose of the crossed extensor reflex?
To enhance postural support during withsrawal of a foot from a painful stimulus (don’t want to fall over)
What are central pattern generators?
biological neural networks that produce rhythmic patterned outputs without sensory feedback
What type of activity can a simple spinal central pattern generator command?
Rhythmic, alternating activity that moves a limb
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?
Oscillatory, or pacemaker, activity
What type of motor function do high level structures control?
What 2 structures are classified as high level?
Strategy
Neocortical association areas
Basal ganglia
What type of motor function do middle level structures control?
What 2 structures are classified as middle level?
Tactics
Motor cortex
Cerebellum
What type of motor function do low level structures control?
What 2 structures are classified as low level?
Execution
Brain stem
Spinal cord
In terms of motor control hierarchy, what is strategy?
Aim of movement?
How can it best be achieved?
In terms of motor control hierarchy, what is tactics?
What sequence of muscle contractions and relaxations in time and space will fulfil the strategic aim?
In terms of motor control hierarchy, what is execution?
Activation of motor pools and interneurone polls that command the desired movement and make essential postural adjustments
From which 2 areas do descending spinal tracts origiante from?
Cerebral cortex
Brain stem
What are the 2 important groups of descending spinal tracts?
Lateral pathways
Ventromedial pathways
What 2 pathways make up the lateral descending pathways?
Lateral corticospinal tract
Rubrospinal tract
What 4 important pathways make up the ventromedial descending pathways?
Pontine reticulospinal tract
Medullary reticulospianl trat
Lateral vestibulospinal tract
Tectospinal tract
What structure control input to the lateral descending spinal tracts?
Cerebral cortex
What actions are the lateral descending spinal tract pathways important for?
Voluntary control of distal musculature, particularly discrete, skilled movements e.g. hands and fingers in a “fractionated” manner
What structure controls input to the ventromedial spinal tract pathways?
Brainstem
What actions are the ventromedial pathways important for?
Control of posture and locomotion
What is another name for the corticospinal tract?
Pyramdial tract
Where are cell bodies of the corticospinal tract located?
About 2/3rds = motor cotetx
About 1/3rd = somatosensory areas of parietal cortex
What does the axons of the corticospinal tract form at the medulla?
Medullary pyramid
Where do most fibres in the corticospinal tract decussate?
At the pyramidal decussation (on medulla)
What do the decussated fibres of the corticospinal tract form at the pyramidal decussation?
What are the remainder of fibres called?
Lateral corticospinal tract
Ventral corticospinal tract (decussate more caudally)
Where do axons of the corticospinal tracts terminate?
In the dorsolateral region of the ventral horn and intermediate grey
In terms of the corticospinal tract, what side of muscualture does the left hemisphere control?
Right musculature
Where are the cell bodies of the rubrospinal tract located?
What does this receive input from?
Red nucleus (midbrain) Motor cortex and cerebellum
Where do axons of the rubrospinal tract decussate?
At the ventral segmental decussation in the midbrain
Where do axons of the rubrospinal tracts terminate?
Ventral horn
What do axons of the rubrospinal tract control?
Limb flexor muscles
What 2 problems can lesions of the lateral descending pathways cause?
Loss of “fractionated” movements i.e. shoulders elbow, wrist and fingers cannot be moved independently
Slowing and imapirment of accuracy of voluntary movements
What difference to the problems caused by a lesion to the lateral descending pathways can occur if the rubospinal tract is spared?
Initially causes same deficits as pronoun lesions although major recovery can occur (due to rubrospinal tracts taking over)
Where do the cell bodies of the vestibulospinal tracts reside?
Vestibular nuclei (lateral and medial) in the pons
What do the vestibulospinal tracts receive input from?
Vestibular larbyrinthys (via CN VIII) Cerebellar input also important
Where do axons from the lateral vestibular nucleus descend to?
How do they do this?
Lumbar spinal cord
Via the lateral vestibulospinal tract
Do inputs to the vestibulospinal tracts control the ipsilateral or contralateral sides of the body?
Ipsilateral
What do outputs from the lateral vestibulospinal tract do?
Helps to hold us upright and balance upright by facilitating extensor MNs of antigravity muscles e.g. of the leg
Where do axons from the medial vestibular nucleus descend to?
How do they do this?
Cervical spinal cord
Via the medial vestibulospinal tract
What do outputs from the medial vestibulospinal tract do?
Activate cervical spinal circuits that control neck and back muscles guiding head movements
Where do the cell bodies of the tectospinal tract reside?
In the superior colliculus of the midbrain
What does the tectospinal tract receive input from?
Retina
Visual cortex
Afferents conveying somatosensory and auditory information
Where do axons of the tectospinal tract decussate?
In the dorsal tegmental decussation of the midbrain
Give an example of an action the tectospinal tract controls?
Orientation of the head and eyes to an important, new, visual stimulus
Which is the medial and which is the lateral reticulospinal tracts?
Medial = pontine Lateral = medullarly
Where do both reticulospinal tracts arise?
Reticular formation
What is the reticular formation?
A diffuse mesh of neurones that are located along the length and at the core of the brainstem
Does the pontine reticulospinal tract descend ispilaterally, contralaterally or bilaterally?
Ipsilaterally
What 2 functions does the pontine reticulospinal tract mediate?
Enhances antigravity reflexes of the spinal cord
Helps to maintain a standing posture by facililitating contraction of the extensors of the lower limbs
Does the medullary reticulospinal tract descend ispilaterally, contralaterally or bilaterally?
Bilaterally
What 2 functions does the medullary reticulospinal tract mediate?
Opposes the action of the medial tract
Releases antibgravity muscles from reflex control
