Cerebellum, balance and coordination Flashcards
what are the names of the three pundcles that attach the cerebellum to the brain stem
- Inferior Cerebellar Peduncle (ICP)
- Middle Cerebellar Peduncle (MCP)
- Superior Cerebellar Peduncle (SCP)
Which peduncles deal mainly with input
- Middle Cerebellar Peduncle (MCP)
- Superior Cerebellar Peduncle (SCP)
Which peduncles deal mainly with output
- Inferior Cerebellar Peduncle (ICP)
where does the superior Cerebellar Peduncle (SCP) connect to
the midbrain
where does the - Middle Cerebellar Peduncle (MCP) connect to
the pons and deals mainly with voluntary movements
what are the three lobes of the cerebellum
anterior
posterior
flocculonodular
• Vestibulocerebellum
this is at the very back of the cerebellum
– consists of flocculonodular lobes (white)
– input from vestibular & visual areas
– output to vestibular nucleus – controls equilibrium and eye movements
Spinocerebellum - middle strip
– consists of vermis of posterior and anterior cerebellum + adjacent
intermediate zones on both sides of vermis
– input from spinocerebellar & auditory, visual, vestibular systems & sensorimotor cortex
– output from vermis to fastigial 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
Cerebrocerebellum - outer areas
– consists of lateral zones of the 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 movements
what are the three layers of the cerebellum
molecular layer
purkinje cell layer
Granule cell layer
what are the two main input fibres
- climbing fibres
- mossy fibres
mossy fibres
these indirectly stimulate purkunje fibres
inputs from pontine nuclei and other sources
climbing fibres
these directly stimulate purkunje fibres
inputs from inferior olivary nucleus
cerebellar output occurs via the deep nuclei, from lateral to medial what are they ?
dentate nuclei emboliform nuclei globose nucleus fastigial nuclei vestibular nucelus
alcohol effects on the cerebellum
alcohol intoxication – depression of cerebellar circuits (truncal ataxia)
how does the cerebellum act as a comparator
– Cerebellum compares descending supraspinal motor signals with ascending afferent feedback
information
– Movement smoothly and accurately coordinated
how does the cerebellum act as a timing device
– Pontocerebellum – creates a sequence for motor activation
– Vestibulocerebellum – maintains balance
– Spinocerebellum – maintains posture
how does the cerebellum initiate and store movements
– Modifiable synapse (Purkinje cell)
– So can store motor information and update it
• Primary role of 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)
how is the 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
• Hypotonia / Reduced muscle tone
Due to reduced input from Deep Cerebellar Nuclei neurone (DCNN) via descending
motor pathways to muscle spindle
Incoordination / Ataxia
– Asynergy – inability to coordinate contraction of agonist and antagonist muscles
– Dysmetria – inability to terminate movements (intention tremor/past pointing)
– Dysdiadochokinesis – inability to perform rapidly alternating movements
Dysarthria (scanning speech)
– Inability to articulate words (slurred and delivered slowly) due to incoordinated
oropharyngeal musculature
Nystagmus
– Rapid jerky eye movements – disruption between vestibular nucleus and oculomotor nuclei
• Palatal Tremor / Myoclonus
– Rare condition
– Hypertrophy of inferior olive which causes damage to dentate nucleus of cerebellum and red nucleus in midbrain
which system generates our sense pf balance
vestibular
the role of the pinna
collected and focuses sound waves
Middle ear is
air filled chamber, bounded by tympanic membrane on one side and oval window on the other
Eustachian tube
connects middle ear to nasophyarynx, allows pressure equalisation
Membranous Labyrinth
- Labyrinth filled with endolymph and encased in temporal bone
- Auditory part is cochlea
vestibular part of the ear contains 2 structures known collectively as the otolith organs
- utricle
- saccule
in the saccule there are hairs
- Mechanoreceptors that respond to minute movement changes
- Consists of one large kinocilium and 50 -150 stereocilia
- Hair cells of cochlea lose there kinocilium with age; vestibular hair cells do not
what is the role of the otolith organs
• Detect changes in linear acceleration (i.e. that experienced as a car starts or stops) and head angle
Macula is orientated what way in the saccule and in the utricle when the head is upright
vertically = saccule
horizontally = utricle
each individual hair cells synapses on an axon of what nerve
vestibular nerve (part of cranial nerve VIII)
Otoliths are
particles of calcium carbonate; they are denser than the endolymph
They are pulled by gravity and mock gelatinous cap in the same direction; cilia of hair cells are deflected
Mechanotransduction in Hair Cells
- Hair cells, project hairs into an otolithic (ear stone) containing gelatinous structure.
- Cilia + kinocilium – provide 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 the hair cell cation channels
Semicircular canals (Ampulla)
Sensitive to angular acceleration (head rotation movements)
• Hair cells clustered in sensory epithelium, crista ampullaris
• Hair cells project into gelatinous cupula, all hair cells orientated in same direction
• As head rotates canal moves but endolymph stays put, this bends the hair cells and they either excite or suppress transmitter release depending on direction of movement
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 – keeps head straight as body moves
Semicircular canals control eye movements – Vestibulo-ocular Reflex
- Direct stimulation of ampullary nerves elicits specific eye movements
- Stimulation of afferents from left horizontal canal causes eyes to turn right (vestibulo-ocular reflexes)
- Specific adaption to allow gaze to remain steady during head movement
- Lateral recti – cranial nerve VI (abducens nucleus)
- Medial recti – cranial nerve III (oculomotor nucleus)
Ménière’s Disease
Clinical symptoms - vertigo, nausea, tinnitus and hearing loss
- The vestibular apparatus is bathed in endolymph
- Normally drains to venous sinus
- Meniere’s cause is unknown, but there is an excessive accumulation of endolymph and damage to hair cells
- Accumulation of endolymph is probably due to poor drainage
Why does increased pressure in the endolymph cause both tinnitus/hearing loss and dizziness?
because there is damage to the hair cell sin the vestibular apparatus so they are stimulated when they shouldn’t be causing dizziness, this causes an increase in endolymph in the cochlea and therefore hearing loss/tinnitus
Vertigo
- Sensation of turning or rotation in space in absence of actual rotation
- Clinical symptoms - nausea, vomiting and gait ataxia
- 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
