Cerebellum, Balance and Coordination Flashcards
What allows for input and output of information into/from the cerebellum?
Input occurs mainly via the inferior and middle cerebellar peduncle. Output will mainly occur via the superior cerebellar peduncle (goes to the vestibular nuclei and the red nucleus)
Describe the different anatomical zones and lobes of the cerebellum
There is an anterior lobe, posterior lobe (which makes up the majority of the cerebellum) and most inferiorly is the flocculonodular lobe. In the middle, is the vermis. On either side of the vermis is the intermediate zone and the most lateral sides of the cerebellum are called the lateral zones
What is the vestibulocerebellum? And its functions
(its a the name for the functional flocculonodular lobe) It receives input from the vestibular and visual areas and sends output to the vestibular nucleus to control eye movement and equilibrium (balance)
What is the spinocerebellum?
Functional name for the vermis of the anterior and posterior lobes and adjacent intermediate zones.
What is the input from the spinocerebellum?
It receives input from spinocerebellar, auditory, visual and vestibular systems and sensorimotor cortex.
What is the output of the spinocerebellum?
Output from vermis to fastigial nuclei then to vestibular and reticular formation of pons and medulla to control antigravity muscles in posture and locomotion.
Output from intermediate zone to interposed nuclei to red nucleus to thalamus then cortex. This is to act on stretch reflexes and other somatosensory reflexes.
What is the cerebrocerebellum? and its functions
It consists of the lateral zones. It receives input from cerebral motor cortex, premotor cortex and somatosensory cortex.
It then sends output to dentate nucleus, then to thalamus and then back to motor and premotor cortices. Thus creates a feedback with the cortical sensorimotor system to plan sequential voluntary body and limb movements
What are the three main layers of the cerebellum?
outermost - molecular layer,
Middle - Purkinje layer,
Innermost - Granule layer.
What are climbing and mossy fibres?
Input fibres. Mossy fibres indirectly stimulate purkinje cells where as the climbing fibres which originate in the olive nucleus directly stimulate purkinje cells
Name the nuclei that are involved in cerebellar output
The deep nuclei;
- Dentate nuclei,
- Interposed nuclei (emboliform nucleus, globose nucleus),
- Fastigial nuclei,
- Vestibular Nucleus.
Don’t eat greasy food violently
What are the cerebellum functions?
Acts as comparator - compares descending supraspinal motor signals with ascending afferent feedback to ensure smooth movement which is accurately coordinated.
Acts as a timing device - (pontocerebellum creates a sequence for motor activation, vestibulocerebellum which maintains balance and spinocerebellum which maintains posture)
Initiating and storing movements (modifiable synapses of purkinje cells)
What are clinical features of cerebellar damage?
- Hypotonia which occurs due to reduced input from deep cerebellar nuclei neurone via descending motor pathway to muscle spindles.
- Incoordination (ataxia),
- Dysarthria (inability to articulate words.
- Nystagmus (rapid jerky eye movements, occurs due to disruption between vestibular nucleus and oculomotor nuclei)
- Myoclonus (hypertrophy of inferior olive nuclei)
What is asynergy?
Inability to coordinate contraction of agonist and antagonist muscles
What is dysmetria
Inability to terminate movements (intention tremor)
What is dysdiadochokinesis
Inability to perform rapidly alternating movements
What is the function of auditory and vestibular system?
Auditory - sense of hearing. Vestibular generates out sense of balance.
What is the function the middle ear?
It is an air filled chamber bounded by the tympanic membrane on one side and the oval window on the other. It is connected to the nasopharynx by the eustachian tube which allows the middle ear to equalise the pressure in-between inner and outer ear.
What is the membranous labyrinth?
Part of the inner ear which is a system of ducts filled with endolymph and encased in the temporal bone.
What are the different parts of the membranous labyrinth?
Cochlea - Auditory part
Vestibular part consists of two structures, the otolith organs (utricle and saccule) which detects gravity and head tilt and the semicircular canals which detects head rotation
Describe the hair cells of the saccule
they have mechanoreceptors that respond to minute movement changes. The hair cells consists of one large kinocilium and several stereocilia that are shorter
What are otoliths and what do they detect?
Small particles of calcium carbonate which are more dense than endolymph. They sit on top of the otolithic membrane which is a gelatinous membrane which coats the hair cells, and separates them from the otolithic organs. They detect changes in linear acceleration and head angle
Describe the orientation of the macula in the saccule and utricle
Vertically in the saccule so they detect up and down acceleration and horizontal in the utricle so they detect left to right acceleration ect
What occurs when the head moves linearly?
The change in gravity causes the otoliths to move, in doing so they pull the gelatinous cap in the same directions which causes a movement of the cillia. If the cilia move towards to kinocilium then the rate of action potential firing will increase and if the cilia move away from the kinocilium then if causes a decrease in the rate of firing of the action potentials.
What is the function of semicircular canals (ampulla)
They are sensitive to angular acceleration so detect head rotational movement
Describe what happens when there is rotational movement of the head
It causes the semi-circular canal to move which deflects the cupula, which is a gelatinous substance the hair cells project into, it is found in the ampulla of the semi-circular canal. Therefore since the cupula is deflected, it bends the hair cells which causes an excitatory or supressing effect on transmitter release depending on the movement of the hair. The endolymph starts still
What happens to axons from otolith organs?
They project onto lateral vestibular nucleus which then projects via the vestibulospinal tract to spinal motor neurons to control posture
What happens to the axons from semi-circular canals?
They project onto medial vestibular nucleus which projects via the medial longitudinal fasciculus to motor nerves to trunk and neck. This keeps head straight as body moves.
What is the vestibulo-ocular reflex?
Occurs when there is direct stimulation of the ampullary nerves which elicits specific eye movements. For example, stimulation of afferents from the left horizontal canal causes eyes to turn right. Thus allowing gaze to remain steady during head movement.
What is Meniere’s disease?
It occurs when there is an excessive accumulation of endolymph which can damage hair cells. This results in vertigo, nausea, tinnitus and hearing loss.
What is vertigo?
The sensation of turning or rotation in space in absence of actual rotation. It is caused by debris from otolithic membrane adhering to cupula in ampulla of posterior semi-circular canal. Causes symptoms of nausea, vomiting and gait ataxia.
