The Cerebellum, Balance and Coordination Flashcards
What connects the cerebellum to the medulla? And what is the function of this pathway?
- Inferior peduncles connect cerebellum to medulla – sensory information from muscle proprioceptors
What connects the cerebellum to the pons? And what is the action of this pathway?
- Middle peduncles connect cerebellum to pons – voluntary motor activities by motor cortex
What connects the cerebellum to the midbrain? And what is the action of this pathway?
- Superior peduncles connect cerebellum to midbrain – neurons in deep cerebellar nuclei and communication with motor cortex via thalamus
What is the cerebellar output?
occurs via deep nuclei - tonically activated by climbing and mossy fibres
From lateral to medial:
- Dentate nucleus
- Emboliform nucleus
- Globose nucleus
- Fastigial nucleus
**Emboliform + globose nucleus = interposed
What is the action of climbing and mossy fibres in the cerebellum?
integrate sensory information (excitatory)
What is the action of the golgi and purkinje cells of the cerebellum?
inhibitory output
Describe the function of the cerebellum
Stimulation of the cerebellum causes neither sensation nor significant movement. However, loss of cerebellum leads to severe abnormalities of motor function
Describe the function of the cerebellum as a comparator
- Cerebellum compares descending supraspinal motor signals with ascending afferent feedback information
- Movement smoothly and accurately coordinated
Describe the function of the cerebellum as a timing device
- Pontocerebellum – creates a sequence for motor activation
- Vestibulocerebellum – maintains balance
- Spinocerebellum – maintains posture
Describe the action of the cerebellum in initiating and storing movements
- Modifiable synapse (Purkinje cell)
- So can store motor information and update it
Give an overview of the motor regulatory function of the cerebellum
- Modulates motor output based on integration of:
- Activity in the pre-motor & motor areas as well as spinal motor circuits (information about potential motor output)
- Sensory feedback from vestibular system, visual system, and ascending proprioceptive information (about real motor input)
- Modulation by the cerebellum is affected at the motor cortex and brainstem
What is thought to be the primary role of the cerebellum?
- Primary role of cerebellum thought to be a supplement and correlate activities of other motor areas e.g. correction of rapid muscular movement initiated by cortex (typing, musical instrument)
What is the action of the cerebellum due to inputs from muscle spindles and golgi tendon organs
- Secondary role in control of postural mechanisms
- Exerts control on a moment-by-moment basis
- Third role in maintenance of tone of muscles
- 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 the main clinical features of cerebellar damage?
- Hypotonia/Reduced muscle tone
- Incoordination/Ataxia
- Dysarthria (scanning speech)
- Nystagmus
- Palatal Tremor/Myoclonus
Why does hypotonia/reduced muscle tone occur in cerebellar damage?
- Due to reduced input from Deep Cerebellar Nuclei neurone (DCNN) via descending motor pathways to muscle spindle
Asynergy
- inability to coordinate contraction of agonist and antagonist muscles
Dysmetria
inability to terminate movements (intention tremor/past pointing)
Describe the inputs and outputs that control balance and co-ordination
- Inputs
- eye
- joint position, proprioception, superifical sensation
- Labyrinthine activity
- cortex cerebellum, reticular formation, extra-pyramidal system
- Outputs
- cortical awareness of head/body/motion
- Eye movement/control of oculomotor activity
- control of posture
- control of motor skills
What is the function of different aspects of the 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 to nasopharynx, allows pressure equalisation
What is the membranius labyrnith filled with?
- Labyrinth filled with endolymph and encased in temporal bone
What is the auditory part of the membranous labyrinth?
cochlea
What is the vestibular part of the membranous labyrinth?
- Vestibular part contains 2 structures:
- Otolith organs (detect gravity and head tilt)
- Semi-circular canals (detect head rotation)
Describe the actions of the hair cells of the saccule?
- 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 function and action of the otolithic organs?
(Saccule and Utricle)
- Detect changes in linear acceleration (i.e. that experienced as a car starts or stops) and angle
- Macula is orientated vertically in saccule and horizontally in utricle when head upright
- Each hair cell synapses on an axon of vestibular nerve (part of CN VIII)
- Otoliths are particles of calcium carbonate; they are denser than the endolymph
- Otoliths are pulled by gravity and move the gelatinous cap in the same direction; cilia of hair cells are deflated
Describe the mechanotransuduction in hair cells
- Hair cells, project 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
How do the semi-circular canals function?
- 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 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, which project via vestibulospinal tract to spinal motor neurons – posture
- Axons from semi-circular canals project to medial vestibular nucleus, which project via medial longitudinal fasciculus to motor nerves of trunk and neck muscles – keeps head straight as body moves
Describe the vestibulo-ocular reflex
semi-circular canals control eye movements
- Direct stimulation of ampullary nerves elicits specific eye movements
- Stimulation of afferents from left horizontal canal causes eye to turn right (vestibulo-ocular reflexes)
- Specific adaption to allow gaze to remain steady during head movements
- Lateral recti – cranial nerve VI (abducens nucleus)
- Medial recti – cranial nerve III (oculomotor nucleus)
Draw a diagram of the pathways in the brain
