Cerebellum, balance and coordination Flashcards
What does the vestibular apparatus do?
Sensory system that is responsible for providing our brain with information about motion, head position, and spatial orientation; it also is involved with motor functions that allow us to keep our balance, stabilize our head and body during movement, and maintain posture
What is the cerebellum shaped like?
A curled up woodlouse
What are peduncles?
Connections between cerebellum and brainstem
What do inferior peduncles connect?
Cerebellum to medulla
WHat info do inferior peduncles carry?
Sensory info from muscle proprioceptors
What do middle peduncles connect?
Cerebellum to pons
What fibres do middle peduncles carry?
Voluntary motor activities by motor cortex
What fibres to superior peduncles connect?
Neurons in deep cerebelar nuclei and communication with motor cortex via thalamus
Whta do the superior peduncles connect?
Cerebellum to midbrain
What tract along with the cerebellum allow for movement to be modified?
Rubrospinal
What is the cerebellum essentially?
Sensory integrating system
What does the molecular layer contain?
Lots of paralel fibres axons, sensory information
What does the purkinje cell layers contain?
Purkinje cells - all straight line
What does the granular cell layer contain?
Granular cells - also inputs from other cells i.e golgi cells
Where do climbing fibres synapse?
With paralel fibres in cortical regions
What do mossy fibres synapse with?
Paralel fibres in cortex and integrating sensory information
Are mossy and climbing fibres excitatory or inhibitory?
Excitatory
What cells produce inhibitory signals?
Golgi cells and purkinje cells
What are the cell layers of the cerebellum?
- Molecular layer
- Purkinje cell layer
- Granule cell layer
What do granular cells do?
Interperts different inhibitory and positive signals.
What are the single output from the cerebellum?
Deep cerebellar nuclei (will send signals to red nuclei and then to thalamus )
What fibres are cerebellar inputs?
Mossy fibres and climbing fibres
What are the deep nuclei from lateral to medial?
- Dentate nucleus
- Emboliform nucleus (interposed nucleus)
- Globose nucleus (interposed nucleus)
- Fastigial nucleus
Dont Eat Greasy Food
What are the functions of the cerebellum?
- Act as a comparator
- Acts as a timing device
- Initiating and storing movements
How does the cerebellum act as a comparator?
- Cerebellum compares descending supraspinal motor signals with ascending afferent feedback information
- Movement smoothly and acuurately coordinated
What part of the cerebellum creates a sequence for motor activation?
Pontocerebellum
What part of the cerebellum maintains balance?
Vestibulocerebellum
What part of the cerebellum maintains posture?
Spinocerebellum
What allows for initiating and storing movements in the cerebellum?
Modifiable synapses (purkinje cells) - So can store information and update it
What does alcohol cause?
Depression of cerebellar circuits
What does the cerebellum integrate in order to modulate motor output?
- Activity in the pre-motor and motor areas as well as spinal motor circuits (information about potential motor output)
- Sensory feedback from vestibular system, visual system, and ascending proprioceptive info (about real motor output)
- Modulation by the cerebellum is effected at the motor cortex and brainstem
Where has most of our understanding of the cerebellum’s control of movement come from?
Effects of lesions
What is the primary role of the cerebellum?
Thought to be to supplement and correlate activities of other motor areas e.g. correction of rapid muscular movement initiated by cortex (typing, musical instrument)
What types of neurons help to maintain posture?
Golgi tendon organs and muscle spindle
What do the golgi tendon organs and muscle spindles reach the cerebellum via?
- Nucleus dorsalis of Clarke
- Post. spinocerebellar tract
- Inf. cerebellar peduncle (restiform body)
- Cerebellum
What are the clinical features of cerebellar damage?
- Hypotonia
- Incoordination / ataxia
- Dysarthria (scanning speech), inability to articulate words
- Nystagmus
- Palatal tremor / myoclonus
How can cerebellar damage cause hypotonia?
Reduced inout from Deep Nuclei neurone (DCNN) via descending motor pathways to muscle spindle
What is asynergy?
Inability to coordinate contraction of agonist and antagonist muscles
What is dysmetria?
Inability to terminate movements (intention tremor/ past pointing
What is Dysdiadochokinesis?
Inability to perform rapidly alternating movements
How can cerebellar damage cause dysarthria?
Incoordinated oropharyngeal musculature
What is nystagmus?
Rapid jerky eye movements
How does cerebellar damage cause nystagmus?
Disruption between vestibular nucleus and oculomotor nuclei
What is a palatal tremor / myoclonus?
Hypertrophy of inferior olive which causes damage to dentate nucleus of cerebellum and red nucleus in midbrain
What system generates our sense of balance?
Vestibular system
What can the ear be divided into?
Outer, middle and inner ear
What structure collects and focuses sound waves?
Pinna
What is the middle ear bound by?
Air filled chamber bounded by tympatic membrane on one side and oval window on the other
What does the eustachian tube connect?
Middle ear to nasopharynx, allows pressure equalisation
What do semi-circular canals give us information about?
Move,ent of the head
What do sacular organs give info about?
Accelaration
What bone is the labyrinth elcased in?
Temporal bone
What is the labyrinth filled with?
Endolymph
What is the auditory part of the labyrinth?
Cochlea
What are the 2 structures contained in the vestibular part of the membranous labyrinth?
- Otolith organs (detect gravity and head tilt)
- Semicircular canals (detect head rotation)
What are the hair cells of the saccule?
- Mechanoreceptors that respond to minute movement changes
- Consist of one large kinocillium and 50-150 sterocilia
What hair cells lose there kinocillium with age?
Coclea
What are the hair cells contained in?
Gelatinous cap
What sits on top of the gelatinous cap?
Otoliths (particles of calcium carbonate, denser than the endolymph cause hair cells to move in same direction))
What are the otolithic organs?
Saccule and utricle
What do the otolithic organs detect?
Changes in linear acceleration
What way are the macula orientated?
Vertically in saccule and horizontally in utricle when head is upright
Where do the hair cells synapse?
Axon of vestibular nerve (CN VIII)
What provide directional information?
Cilia and kinocilium
What opens/closes the hair cell cation channels?
0.5-micron movement of the kinocilium
What causes K+ channels to open in the stereocilia?
Mechanical deformation towards the kinocilium
- Ca2+ enters the cell, allowing vesicle fusion and the release of transmitter
- Away causes K+ channels to close
Where are hair cells clustered?
In sensory epithelium - crista ampullaris
What are semicircular canals sensitive to?
Angular acceleartion (head rotation movements)
What happens to the semicircular canals when the head rotates?
Canal moves but endolymph stays put, this bends the hair cells and they either excite or suppress transmitter releases depending on direction of movement
Describe the vestibular nervous pathway?
- Vestibular axons from CN VIII make direct connections to vestibular nucleus and cerebellum
- Axons from otolith organs project to lateral vestibular nucleus, which project via vestibulospinal tract to spinal motor neurons - posture
- Axons from semicircular cnanals project to medial vestibular nucleus, which project via medial longitudinal fasiculus to motor nerves of trunk and neck muscles - keeops head straight as body moves
What is the semicircular canals which control eye movements reflex called?
Vestibulo-ocular reflex
Direct stimulation of what nerve elicits specific eye movements?
Ampullary nerves
Stimulation of afferents from left horizontal canal causes eyes to turn in wht direction?
Right (vestibulo-ocular reflex)
What does the vestibulo-ocular reflex allow for?
Allows gaze to remain steady during head moveemnt s
What nerve stimulates the lateral recti?
Cranial nerve VI - Abducens via abducens nucleus
What nerve stimulates the medial recti?
Cranial nerve 3 - oculomotor via oculomotor nucleus
What is menieres disease?
- Vestibular appartus bathed in endolymph - excessive accumulation of endolymph and damage to hair cells due to poor draniage (probably)
- Normally drains to venous sinus
- Excessive stimulation
- Symptoms of vertigo, nausea, tinnitus and hearing loss
What is vertigo?
- Sensation of turning or raotation in space in absence of actual rotation
- Nausea, vomitting and gait ataxia
What can vertigo be caused by?
- Debris from otolithic membrane adhering to cupula in ampulla of posterior semicircular canal
- Can be due to lesions of vestibular aspect of CNVIII or central lesions affecting brainstem vestibular nuclei
- Inappropriate activation of hair cells
