Control of Movement

Question 1

define proprioception

Answer 1

knowledge of body position in space

Question 2

what are the proprioceptors found in the muscles?

Answer 2

muscle spindles - detect length and rate of length change –> spinocerebellar pathway (unconscious)

Question 3

what are the proprioceptors found in the tendons?

Answer 3

golgi tendon organs - detect tension in muscles –> spinocerebellar pathway (unconscious)

Question 4

what are the proprioceptors found in skin?

Answer 4

pacinian corpuscles - detect pressure and vibration –> dorsal column pathway (conscious proprioception)
or
ruffini endings - detect tension and stretch –> dorsal column pathway (conscious proprioception)

Question 5

what are the proprioceptors found in joints?

Answer 5

pacinian corpuscles, ruffini endings and other kinaesthetic receptors - detect position and rate of position change –> dorsal column pathway (conscious proprioception)

Question 6

what are some of the targets for proprioceptive information?

Answer 6

• 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

Question 7

what is proprioceptive deafferentation?

Answer 7

lack of afferent proprioceptive signals from the body to the brain

Question 8

what are the possible effects of damage to the proprioceptive system?

Answer 8

• 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.

Question 9

what structures in the ear make up the vestibular system?

Answer 9

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.

Question 10

describe the structure of otolith organs in the inner ear

Answer 10

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.

Question 11

how to otolith organs detect horizontal acceleration?

Answer 11

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.

Question 12

describe the structure of ampullae in the vestibular system

Answer 12

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)

Question 13

describe how ampullae can detect rotational acceleration

Answer 13

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.

Question 14

what are the vestibular nuclei?

Answer 14

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

Question 15

where does information about proprioception go from the vestibular nuclei?

Answer 15

• 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)

Question 16

what are some possible effects of damage to the vestibular system?

Answer 16

• 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)

Question 17

what are the two streams of visual information in the brain?

Answer 17

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.

Question 18

how can loss of visual input effect proprioception and control of movement?

Answer 18

• 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.

Question 19

how do the basal ganglia and cerebellum impact control of movement?

Answer 19

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.

Question 20

what is the basal ganglia?

Answer 20

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.

Question 21

list the parts of the basal ganglia and their roles in movement control

Answer 21

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

Question 22

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)

Answer 22

direct pathway = sustains or promotes desired behaviours
indirect pathway = inhibits undesired behaviours.

Question 23

how does the basal ganglia communicate with the rest of the brain?

Answer 23

via the thalamus

Question 24

what happens to the substantia nigra in parkinsons disease?

Answer 24

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

Question 25

what are the functional divisions of the cerebellum and what elements of movement do they control?

Answer 25

vestibulocerebellum = balance, connections with the vestibular system via the vestibular nuclei
spinocerebellum = posture and muscle tone, receives input from proprioceptors via the spinocerebellar tract and outputs to the motor centres in the brainstem
corticocerebellum = coordination and motor learning, receives input from motor cortex and outputs to the motor cortex via the thalamus

Question 26

what is the role of the cerebellum in movement control?

Answer 26

• balance
• posture and muscle tone
• coordination and motor learning
• acts as a comparator between intended and actual performed movement

Question 27

what are some potential effects of cerebellar lesions?

Answer 27

• problems with balance or posture
• ataxia (abnormal, uncoordinated movements)
• asynergia (difficulty creating fluid movements)
• dysmetria (lack of ability to judge distance or scale)
• scanning speech (uncoordinated development of speech)
• decomposition of movement (component movements rather than one smooth action)