Controlling movements and autonomic outputs-contributions of the brain Flashcards
Why do the cervical and lumbar regions of the spinal cord have larger ventral horns?
packed with mainly motor neurones innervating muscle
whereas the thoracic spinal cord has a smaller ventral horn because it only controls muscles of the trunk which are involved in less fine control
What is the intermediate horn also called?
laminae 7- intermediolateral cell column
What is the ventral horn also called?
laminae 9- motor nucleus
What inputs do alpha motor neurones receive?
it is complex as they receive triple influences
- sensory inputs
- spinal interneurones
- descending tracts
Why are interneurones so important ?
They are important for integrating information
What is the high level of motor control hierarchy?
its function is strategy and the structures involved are association areas of neocortex and basal ganglia
What is the middle level of motor control hierarchy?
its function is tactics and the structures involved are the motor cortex and cerebellum
What is the low level of motor control hierarchy?
its function is execution and the structures involved are the brainstem and spinal cord
What are the 2 major groups of descending pathways that enable communication between the brain and motoneurons in the spinal cord?
1) LATERAL PATHWAYS
2) VENTROMEDIAL PATHWAYS
What are the lateral pathways like?
involved in voluntary movements of distal musculature
direct cortical control
fine control of distal musculature
What are the ventromedial pathways like?
posture and locomotion
brainstem control
posture and balance
What is meant by species differences in pathways ?
the location of pathways is different in different species, therefore it is important to consider this when using animal models
- in humans the corticospinal tract (important for dexterity) is present laterally whereas in rats/mice it is present in the dorsal column
What are the impairments induced by corticospinal tract injuries?
the deterioration of motor impairments are dependent upon the extent of CST damage
What occurred in a complete unilateral hemisection of the CST?
eliminated grip causing sever impairments in food retrieval by the forepaw ipsilateral to the lesion
What does a hemisection mean ?
if the damage crosses onto the other side, damage will occur on both sides whereas hemisection is only on one side
What can happen if not all pathways are damaged?
the pathways that remain may undergo plasticity and therefore slight recovery may occur
How was it tested to see if the rubrospinal tract could compensate for CST loss?
they lesioned the pyramidal tract and then the dorsalateral funicular and compared motor function to animals that has lesions to both tracts simultaneously
Can the rubrospinal tract compensate for CST loss?
it can only compensate for skilled reaching and there was only a degree of compensation
How can recovery occur in incomplete injuries?
due to sprouting of undamaged fibres
- in mice there is little ipsilateral labeling initially however after 4 weeks the ipsilateral side started to be labelled
sprouting is important for recovering function
How can forelimb and hindlimb movements be improved after CST damage?
stimualtion of spared CST fibres improves locomotor function- it suggested pathways are crossing and sending new pathways across to the impaired side to try and recover some function
What is the link between the ventromedial (MLF) and corticospinal tracts onto single interneurones thought to be ?
thought there may be plasticity within the system because when recording from single interneurones in monkeys when they were reaching to grasp food
they expected CST simulation to cause the interneurone to fire but they were surprised that it also occurred when the ventromedial pathway was stimulated
What happens to dextrous movements in macaque monkeys overtime?
1 day after the CST lesion there is a loss of ability to grasp a sugar cube= loss of dextrous activity
7 days after the CST lesion, there are improvements in grasping suggesting compensation has occurred
What was determined about the reticulospinal pathway in terms of compensation?
7 days after a lesion, grasping was a struggle
whereas 4 weeks after the injury recovery of grasping action had occurred - this and the previous experiment indicate that the ventromedial pathways can compensate for the loss and therefore we should exploit this
Why is the RVLM so important?
it has a major role in sympathetic control
- important for controlling BP
- injecting glutamate cases increases in bp, hr and sympathetic activity
also important in temperature regulation
What is the role of the raphe nuclei?
if you inject NMDA or KA into it then it increases HR, BAT activity and expiration of carbon dioxide
What are organs that are also very important for sympathetic control, particularly for SCI patients?
bladder, bowel and sex organs - there receive complex autonomic and motor control
- the bladder receives somatic, parasympathetic and sympathetic inputs
What is the barrington’s nuclues?
it provides inputs to autonomic neurones innervating both bladder and colon
- injecting psuedorabies virus into bladder or colon and it goes back into spinal cord labelling SPNS into BN and LC
What is important about the development of the descending pathways involved in bladder and bowel control?
when you are young you have no supra spinal control- sometimes in males this doesn’t develop until 7/8 years old
What are the symptoms of autonomic dysfunction?
severe postural hypotension- loss of consciousness
incontinence
impotence
