Control of Movement Flashcards
define proprioception
knowledge of body position in space
what are the proprioceptors found in the muscles?
muscle spindles - detect length and rate of length change –> spinocerebellar pathway (unconscious)
what are the proprioceptors found in the tendons?
golgi tendon organs - detect tension in muscles –> spinocerebellar pathway (unconscious)
what are the proprioceptors found in skin?
pacinian corpuscles - detect pressure and vibration –> dorsal column pathway (conscious proprioception)
or
ruffini endings - detect tension and stretch –> dorsal column pathway (conscious proprioception)
what are the proprioceptors found in joints?
pacinian corpuscles, ruffini endings and other kinaesthetic receptors - detect position and rate of position change –> dorsal column pathway (conscious proprioception)
what are some of the targets for proprioceptive information?
- somatosensory cortex and association areas - early cognition
- primary motor cortex - initiation of motor control
- pre-motor cortex - develops patterns of movement
- basal ganglia - scaling and action selection
- cerebellum - refinement of motor control
- brain stem nuclei - refinement of motor control
- spinal cord - spinal reflex loops
what is proprioceptive deafferentation?
lack of afferent proprioceptive signals from the body to the brain
what are the possible effects of damage to the proprioceptive system?
- poor balance, difficulty standing and walking
- uncoordinated movement
- clumsiness
- poor postural control
a complete loss of proprioceptive abilities can lead to a complete inability to move.
what structures in the ear make up the vestibular system?
semi circular canals (and the ampullae found at the bottom of each) detect rotation within any plane
otolith organs, the utricle and saccule contain macula which detect forward and backward acceleration.
describe the structure of otolith organs in the inner ear
hair cells, embedded in a layer of support cells, each have a series of microvillae. these consist of shorter stereocillia and one long kinocilium. on top of the hair cells there is a gelatinous layer containing otoliths, which are small calcium carbonate stones which have inertia. hair cells are each connected to a vestibular nerve fibre.
how to otolith organs detect horizontal acceleration?
the otolith stones in the macula have inertia. when the head moves, the stones and gel that they are embedded in lags behind, causing the gel to deform the microvilla of the hair cells. when stereocilia bend towards the kinocilium, the hair cell depolarises and action potentials are sent down the nerve ending. when stereocilia bend away from kinocilium, the hair cell does not depolarise and fewer action potentials are sent.
describe the structure of ampullae in the vestibular system
at the base of each semi-circular canal there is an ampulla. this contains a structure called the cristae ampullare which is a raised section of hair cells with microvilla. these are structured the same as within otolith organs (one kinocilium and many shorter stereocilia). covering these hair cells is the ampullary cupula (a kind of weird membrane). filling the cavity of the ampulla is endolymph (inner ear fluid)
describe how ampullae can detect rotational acceleration
when the head moves, endolymph in the ampulla moves across the ampullary cupula. the movement of the ampullary cupula displaces the microvilla of the hair cells and either depolarises or hyperpolarises the cells. vestibular nerve fibres then send this signal back to the brain via the vestibular nerve.
what are the vestibular nuclei?
a series of nuclei found in the brain stem which collect information from visual, proprioceptive and vestibular receptors and redistribute it to other parts of the body
where does information about proprioception go from the vestibular nuclei?
- the cerebellum (integrates other sensory information to control balance
- visual systems (via the oculomotor complex to control eye movements to follow the movement of the head)
- lower extensors (motor neurons to extensors in the lower limb are activated to maintain balance when moving the body)
- cervical spine (motor neurons in neck to control head movements to follow the body)
what are some possible effects of damage to the vestibular system?
- dizziness or vertigo
- balance disorders
- lack of coordination
- ‘bouncing vision’ (objects appear to bounce as they do not hit the same spot on the retina - occurs due to disrupted vestibuloocular reflex)
what are the two streams of visual information in the brain?
ventral stream = visual information carried to insula and memory areas from primary visual cortex. mostly associated with assigning meaning to visual information
dorsal stream = visual information is carried from the primary visual cortex to the occipital lobe (motor areas) and sensory association areas.
how can loss of visual input effect proprioception and control of movement?
- loss of visual input doesn’t actually effect proprioception that much as long as other proprioceptive systems are functioning. these compensate quite well for loss of visual information.
how do the basal ganglia and cerebellum impact control of movement?
they act as managers in that they have no direct link to lower motor neurons but they enact movement control through the motor cortex and the brainstem.
what is the basal ganglia?
a structure within the brain made up of many component parts. it is part of the motor feedback circuit whereby it receives information from several locations and feeds information back to the cerebral cortex via the thalamus. generally, the basal ganglia work together to control scaling and action selection but each component of the basal ganglia performs its own role.
list the parts of the basal ganglia and their roles in movement control
caudate nucleus = integrates information
putamen = regulates movement, movement sequencing and learning of repetitive movements
globus pallidus = smoothing out movement and initiating movement
subthalamic nucleus = stimulates the basal ganglia to inhibit movement
substantia nigra = facilitates movement by selecting appropriate commands and inhibiting inappropriate commands. also involved in scaling
what are the two pathways in the basal ganglia?
(its actually super complicated but these are the two main ones that are good to know)
direct pathway = sustains or promotes desired behaviours
indirect pathway = inhibits undesired behaviours.
how does the basal ganglia communicate with the rest of the brain?
via the thalamus
what happens to the substantia nigra in parkinsons disease?
it loses it’s dark colour as the dopamine producing cells are lost. this causes many of the motor symptoms associated with parkinsons such as tremors, rigidity and a festinating gait.
it is also why the motor symptoms of parkinsons can be treated with the drug L-Dopa which replaces lost dopamine
