Cerebellum, balance and coordination Flashcards
What segments are the cerebellum broken up into ?
- Vestibulocrbellum
- Spinocerebellum
- Cerebrocerebellum
What are the features of the Vestibulocerebellum?
- consists of flocculonodular lobes (white)
- inputs from vestibular and visual areas
- output to vestibular nucleus - controls equilibrium and eye movements and equally brings more balance
What are the features of the Spinocerebellum?
- consists of vermis or posterior and anterior cerebellum (green) + adjacent intermediate zones on both sides of vermis (purple)
- Input from spinocerebellar & auditory, visual, vestibular systems & sensorimotor cortex
- Output from vermis to fastgial nuclei to vestibular & reticular formation of pons and medulla (control antigravity muscles in posture and locomotion)
- Output from intermediate zone to interposed nuclei to red nucleus to thalamus then cortex (act on stretch reflexes & other somatosensory reflexes)
What are the features of the Cerebrocerebellum?
Consists of lateral zone of cerebellar hemispheres (pink/flesh)
Input from cerebral motor cortex & adjacent premotor & somatosensory cortices
Output to dentate nucleus to thalamus to motor and premotor cortices
Creates a feedback with the cortical sensorimotor system to plan sequential voluntary body and limb movement
What 4 layers make up the cerebellum microscopic structure?
Molecular layer
Purkinje cell layer
Granular cell layer
White matter
What do Mossy fibres in the cerebellum do ?
They are inputs which synapse with granular cells in cerebellum and interact with molecular layer. Axons that makes up the integration of information that comes in and they effect the purkiinje cells
(from pontine nuclei and other sources)
What are climbing fibres?
Inputs from the olivary nucleus
How do the 2 inputs (mossy and climbing fibres) affect cerebral outputs?
They positively inhibit the deep cerebellar nuclei and vestibular nuclei which the cerebellar cortex usually negatively inhibits. Then this will encourage a positive cerebellar output
What are the cerebellar outputs?
Dentate nuclei (D)
Interposed nuclei (IP)
- Emboliform nucleus
- Globose nucelus
Fastigial nuclei (F)
Vestibular nucleus (V)
Remember nemonic from medial to lateral;
Dont
Eat
Greasy
Food
What are the general function software the cerebellum?
Stimulating the cerebellum causes neither sensation nor significant movement, however loss of cerebellum leads to severe abnormalities of motor function (e.g alcohol intoxication - depression of cerebellar circuits known as truncal ataxia)
Acts as a comparator;
- Compares descending supra-spinal motor signals with ascending afferent feedback information
- Movement smoothly and accurately co-ordinated
Acts as a timing device;
Pontocerebellum - creates a sequence for motor activation
Vestibulocerebellum - maintains balance
Spinocerebellum - maintains posture
Initiating and storing movements;
- Modifiable synapses (purkinje cell)
- So can store motor information and update it
How does the cerebellum control movement?
Most understanding of what we know about the cerebellum is gained from effected lesions and alcohol.
Primary role of cerebellum though to be supplement and correlate activities of other motor areas (e.g - correction of rapid muscular movement initiated by cortex - typing, musical instrument)
Secondary role in control of postural mechanisms;
- exerts control on a movement-by-movement basis
Third role in maintenance of tone and muscle
What pathways does thee cerebellum use? can you draw these ?
Cerebellum informed of movement by cortex before it occurs, then cerebellum processes sensory information to generate an error signal which is fed back to cortex and movement is adjusted
What are some clinical features you can see in cerebellar damage?
Hypotonia / Reduced muscle tone;
- Due to reduced input from Deep Cerebellar Nuclei neurone (DCNN) via descending motor pathways to muscle spindle
Incoordination / Ataxia (one of the most major issues of cerebellar damage);
- Asynergy - inability to coordinate contraction of agonist and antagonist muscles
- Dysmetria - inability to terminate movement (intention tremor / past pointing)
- Dysdiadochokinesis - inability to perform rapidly alternating movements
Dysarthria (scanning speech);
- Inability to articulate words (slurred and delivered slowly) due to uncoordinated oropharyngeal musculature
Nystagmus;
- Rapid jerky eye movements - disruption between vestibular nucleus and oculomotor nuclei
Palatal Tremor / Myoclonus;
- Rare condition
- Hypertrophy of inferior olive which cause damage to dentate nucleus or cerebellum and reed nucleus in midbrain
How does balance and coordination work ?
Information from the eye, joint position, proprioception, superficial sensation, labyrinthine activity, cortex cerebellum, reticular formation and the extra-pyramidal system comes in
It comes into the integrating / data storage system
Then the information is put out to control of motor skills, control of posture, eye movement / control of oculomotor activity, cortical awareness of head / body / motion
How does the ear work?
- Auditory system provides sense of hearing
- Vestibular system generated our sense off balance
- Divided into outer, middle and inner ear
- Pinna collects and focuses sound waves
- External auditory canal also skin lined ends up at tympanic membrane (eardrum)
- Middle ear is air filled chamber, bounded by tympanic membrane on one side and oval window on the other
- Eustachian tube connects middle ear too nasopharynx, allows pressure equalisation
What its the membranous Labyrinth?
- Labyrinth filled with endolymph and encased in temporal bone
- Auditory part is cochlea
Vestibular part contains 2 structures;
- Otoloth organs (detect gravity & head tilt)
- Semicircular canals (detect head rotation)
What is the function of the Otholithic organs (saccule & utricle) ?
- Detect changes in near acceleration (i.e that experienced as a car starts or stops) and head angle
- Macula is orientated vertically in saccule and horizontally in utricle when head upright
- Each hair cell synapse on an axon of vestibular nerve (part of CN VIII)
- Otoliths are particles of calcium carbonate; they are denser than endolymph
- Otoliths are pulled by gravity and move gelatinous cap in the same direction; cilia of hair cells are deflected
How does mechanotransduction in hair cells occur?
- Hair cells project hairs into an otolithic (ear stone) containing gelatinous structure
- Cilia + kinocilium - proviide directional information
- Movement of otolithic membrane (from tilting or translational movement) bends the cilia / kinocilium in a very direction specific way
- A 0.5-micron movement of the kinocilium opens / closes hair cll cation channels
Neurotransmitter is transported down vestibular nerve to tell brain we have movement
How do hair cells tell us the position of our heads?
Image ->
How do semicircular canals (ampulla) work?
- Sensitive to angular acceleration (head rotation movements)
- Hair cells clustered in sensory epithelium, crest ampullaris
- Hair cells project into gelatinous cupula, all hair cells orientated in same direction
- As head rotates canal moves but emndolymph stays put, behind this bends the hair cells and they either excite or suppress transmitter release depending on direction of movement
What is the vestibular nervous pathway?
Vestibular axons from CN VIII make direct connections to vestibular nucleus & cerebellum
Axons from otolith organs project to lateral vestibular nucleus, which project via vestibulospinal tract to spinal motor neurons - posture
- Axons from semicircular canals project to medial vestibular nucleus, which project via medial longitudinal fasiculus to motor nerves of trunk and neck muscles - keep head straight as body moves
How do the semicircular canals control eye movements - Vestibulo-ocular Reflex
Semicircular canals control eye movements - Vestibulo-ocular Reflex
- Direct stimulation of ampullarf nerves elicits specific eye movements
- Stimulation of afferents from left horizontal canal causes eyes to turn right (vestibulo-ocular reflexes)
- Specific adaptation to allow gaze to remain steady during head movement
- Lateral recti - cranial nerve VI (abducens nucelus)
- Medial recti - cranial nerve III (oculomotor nucleus)
