Cerebellum, Balance and Coordination

Question 1

What allows for input and output of information into/from the cerebellum?

Answer 1

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)

Question 2

Describe the different anatomical zones and lobes of the cerebellum

Answer 2

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

Question 3

What is the vestibulocerebellum? And its functions

Answer 3

(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)

Question 4

What is the spinocerebellum?

Answer 4

Functional name for the vermis of the anterior and posterior lobes and adjacent intermediate zones.

Question 5

What is the input from the spinocerebellum?

Answer 5

It receives input from spinocerebellar, auditory, visual and vestibular systems and sensorimotor cortex.

Question 6

What is the output of the spinocerebellum?

Answer 6

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.

Question 7

What is the cerebrocerebellum? and its functions

Answer 7

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

Question 8

What are the three main layers of the cerebellum?

Answer 8

outermost - molecular layer,
Middle - Purkinje layer,
Innermost - Granule layer.

Question 9

What are climbing and mossy fibres?

Answer 9

Input fibres. Mossy fibres indirectly stimulate purkinje cells where as the climbing fibres which originate in the olive nucleus directly stimulate purkinje cells

Question 10

Name the nuclei that are involved in cerebellar output

Answer 10

The deep nuclei;

• Dentate nuclei,
• Interposed nuclei (emboliform nucleus, globose nucleus),
• Fastigial nuclei,
• Vestibular Nucleus.

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Question 11

What are the cerebellum functions?

Answer 11

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)

Question 12

What are clinical features of cerebellar damage?

Answer 12

• 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)

Question 13

What is asynergy?

Answer 13

Inability to coordinate contraction of agonist and antagonist muscles

Question 14

What is dysmetria

Answer 14

Inability to terminate movements (intention tremor)

Question 15

What is dysdiadochokinesis

Answer 15

Inability to perform rapidly alternating movements

Question 16

What is the function of auditory and vestibular system?

Answer 16

Auditory - sense of hearing. Vestibular generates out sense of balance.

Question 17

What is the function the middle ear?

Answer 17

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.

Question 18

What is the membranous labyrinth?

Answer 18

Part of the inner ear which is a system of ducts filled with endolymph and encased in the temporal bone.

Question 19

What are the different parts of the membranous labyrinth?

Answer 19

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

Question 20

Describe the hair cells of the saccule

Answer 20

they have mechanoreceptors that respond to minute movement changes. The hair cells consists of one large kinocilium and several stereocilia that are shorter

Question 21

What are otoliths and what do they detect?

Answer 21

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

Question 22

Describe the orientation of the macula in the saccule and utricle

Answer 22

Vertically in the saccule so they detect up and down acceleration and horizontal in the utricle so they detect left to right acceleration ect

Question 23

What occurs when the head moves linearly?

Answer 23

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.

Question 24

What is the function of semicircular canals (ampulla)

Answer 24

They are sensitive to angular acceleration so detect head rotational movement

Question 25

Describe what happens when there is rotational movement of the head

Answer 25

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

Question 26

What happens to axons from otolith organs?

Answer 26

They project onto lateral vestibular nucleus which then projects via the vestibulospinal tract to spinal motor neurons to control posture

Question 27

What happens to the axons from semi-circular canals?

Answer 27

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.

Question 28

What is the vestibulo-ocular reflex?

Answer 28

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.

Question 29

What is Meniere’s disease?

Answer 29

It occurs when there is an excessive accumulation of endolymph which can damage hair cells. This results in vertigo, nausea, tinnitus and hearing loss.

Question 30

What is vertigo?

Answer 30

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.