19-09-23 - Cerebellum, balance and coordination Flashcards
Learning outcomes
- Recall the structure of the cerebellum
- Recall the major functions and the associated pathways and nuclei of the cerebellum
- Recall the effects of cerebellar damage
- Know how the vestibular system works and how it connects with other structures to maintain balance and coordination
- Be aware of common causes of vertigo
What is the cerebellum?
Where is it integrated?
What does the cerebellum take part in the control of?
What do lesions to the cerebellum result in?
What is the function of the 3 peduncles?
- The cerebellum (“little brain”) is a central brain structure deeply integrated into major loops with the cerebral cortex, brainstem, and spinal cord.
- The cerebellum takes part in motor control and lesions to it cause a movement incoordination syndrome - ataxia.
- The cerebellum operates as a forward controller learning to predict the precise timing of correlated events.
- The function of the 3 peduncles:
1) Inferior peduncles connect thecerebellum to medulla – sensory information from muscle proprioceptors
2) Middle peduncles connect the cerebellum to pons – voluntary motor activities from motor cortex
3) Superior peduncles connect the cerebellum to midbrain – neurons in deep cerebellar nuclei & communication with motor cortex via thalamus
The Cerebellum Macroscopic Structure.
How is the cerebellum divided sagitally and horizontally?
How is the cerebellum connected to the brainstem?
What are the 3 layers of the cerebellar cortex?
What are the 3 nuclei the outputs of the cerebellum go to?
What are the 2 cerebellar associated syndromes?
Describe the anatomic, phylogenetic, and functional divisions of the cerebellum (in picture)
- The Cerebellum Macroscopic Structure
- The cerebellum is divided sagitally into 3 areas:
1) Vermis
2) Intermediate
3) Lateral) - The cerebellum horizontally consists of 3 lobes:
1) Anterior
2) Posterior
3) Flocculonodular - The cerebellum is connected to brainstem by 3 pairs of peduncles:
1) Superior
2) Middle
3) Inferior - 3 layers of the cerebellar cortex
1) Molecular
2) Purkinje
3) Granular - The 3 nuclei the outputs of the cerebellum go to:
1) Fastigial
2) Interposed
3) Dentate - The 2 cerebellar associated syndromes:
1) Ataxia
* a term for a group of disorders that affect co-ordination, balance and speech
* Any part of the body can be affected, but people with ataxia often have difficulties with:
* Balance and walking
* Speaking
* Swallowing
* Tasks that require a high degree of control, such as writing and eating
* Vision
2) Intention tremor
* a rhythmic, oscillatory, and high amplitude tremor during a directed and purposeful motor movement, worsening before reaching the endpoint
- Anatomic, phylogenetic, and functional divisions of the cerebellum (in picture)
The Cerebellum Macroscopic Structure.
What are the 3 functional divisions of the cerebellum?
What do they each consist of?
What are each of their inputs and outputs?
What do each of their outputs control?
- The Cerebellum Macroscopic Structure
- 3 functional divisions of the cerebellum:
1) Vestibulocerebellum
* Consists of flocculonodular lobes (white)
* Input from vestibular & visual areas
* Output to vestibular nucleus – controls equilibrium and eye movements
2) Spinocerebellum
* Consists of vermis of 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 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
3) Cerebrocerebellum
* 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
The Cerebellum Microscopic Structure.
What are the 2 major parts of the cerebellum?
What are the 3 layers of the cerebellar cortex from outermost to innermost?
- The Cerebellum Microscopic Structure
- The cerebellum consists of two major parts : The cerebellar deep nuclei and the cerebellar cortex
- The cerebellar deep nuclei (or cerebellar nuclei) are the sole output structures of the cerebellum.
- These nuclei are encased by a highly convoluted sheet of tissue called the cerebellar cortex, which contains almost all of the neurons in the cerebellum.
- 3 layers of the cerebellar cortex from outermost to innermost:
1) Molecular layer
2) Purkinje cell layer
3) Granular layer
What are the 2 types of input fibres of the cerebellum?
Where do these fibres originate?
What effect do these fibres have on the Purkinje cells?
Where do Purkinje cells synapse?
Is output of the cerebellar cortex excitatory or inhibitory?
Why is this?
Where is information then passed too?
- 2 types of input fibres of the cerebellum:
1) Climbing fibres
* Climbing fibres originate from inferior olive (nucleus in medulla).
* Climbing fibres are excitatory on purkinje cells
* They stimulate purkinje cells directly, but also synapse with basket, Golgi & stellate interneurons
2) Mossy fibres (bulk of input)
* Mossy fibres originate in cortico-, vestibulo-, reticulo- & spinocerebellar tracts
* Indirectly excite purkinje cells via parallel fibres of granule cells
- Purkinke cells synapse into the molecular layer at the top end of the cerebellar cortex – fibres then come into the deep cerebellar nuclei
- The output of the cerebellar cortex is wholly inhibitory.
- This is because purkinje cells have a large, flat, highly branched dendritic tree and a single long axon that forms an inhibitory projection to the deep cerebellar nuclei
- The deep cerebellar nuclei then feed out to the medullary region of the brainstem
How does cerebellar output occur?
What are the 4 deep nuclei from lateral to medial?
What is a pneumonic for this?
- Cerebellar output occurs via deep nuclei
- 4 deep nuclei from lateral to medial:
1) Dentate nuclei (D)
2) Interposed nuclei (IP) – emboliform nucleus – Globose nucleus
3) Fastigial nuclei (F)
4) Vestibular nucleus (V)
- From lateral to medial: Don’t Eat Greasy Food
What does stimulation of the cerebellum cause?
What does loss of cerebellum lead to?
What are 3 functions of the cerebellum?
Which functional region of the cerebellum is responsible for each function?
- Stimulation of 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 (truncal ataxia)
- 3 functions of the cerebellum:
1) Acts as a comparator
* Cerebellum compares descending supraspinal motor signals with ascending afferent feedback information
* Movement smoothly and accurately coordinated
2) Acts as a timing device
* Cerebro(Ponto)cerebellum – creates a sequence for motor activation –
* Vestibulocerebellum – maintains balance
* Spinocerebellum – maintains posture
3) Initiating and storing movements
* Modifiable synapse (Purkinje cell)
* So can store motor information and update it
Cerebellum & Control of Movement.
How is most of the understanding of the cerebellum gained?
What is the primary roll of the cerebellum?
Describe how the cerebellum does this
- Cerebellum & Control of Movement
- Most understanding of the cerebellum is gained from effects of lesions
- The 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)
- From the motor cortex, there is a collateral from the corticospinal tract which contains information about voluntary movement that goes down the spinal cord
- The cerebellum is primed and compares the information coming back from muscle spindles and joints with the information from the motor cortex to see if the movement has occurred
- If we have to make more changes, the cerebellum will send signals through the red nucleus, through the thalamus, and back to the motor cortex, where movement can be corrected
Input from Muscle Spindles & Golgi Tendon Organs.
What is the secondary and third role of the hypothalamus?
When is the cerebellum informed of movement from the cortex?
What is then generated?
- Input from Muscle Spindles & Golgi Tendon Organs
- The cerebellum has a secondary role in control of postural mechanisms – Exerts control on a moment-by moment basis (e.g rate of contraction, force of contraction)
- Its third role is in maintenance of tone of muscles
- Cerebellum informed of movement by cortex before it occurs
- Then the cerebellum processes sensory information to generate an error signal which is fed back to cortex and movement is adjusted
What are 5 clinical features of cerebellar damage?
- 5 clinical features of cerebellar damage:
1) Hypotonia / Reduced muscle tone
* Due to reduced input from Deep Cerebellar Nuclei neurone (DCNN) via descending motor pathways to muscle spindle
2) 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
3) Dysarthria (scanning speech)
* Inability to articulate words (slurred and delivered slowly) due to incoordinated oropharyngeal musculature
4) Nystagmus
* Rapid jerky eye movements – disruption between vestibular nucleus and oculomotor nuclei
5) Palatal Tremor / Myoclonus
* Rare condition
* Hypertrophy of inferior olive which causes damage to dentate nucleus of cerebellum and red nucleus in midbrain
Overview of Balance and Coordination.
What 3 information sources does equilibrium of balance and coordination depend on?
How many of these information sources are needed to maintain equilibrium?
What are 2 parts of the Romberg sign?
- Overview of Balance and Coordination
- 3 information sources equilibrium of balance and coordination depends on:
1) Visual
2) Proprioceptive
3) Vestibular - Equilibrium can be maintained by any two of these but not by one only
- 2 parts of the Romberg sign:
1) Loss of awareness of position of lower limbs (e.g. degeneration of spinal cord pathways)
2) If you make patient put feet together and close eyes, patient will start to sway and fall, as they only have the vestibular apparatus for maintaining equilibrium due to proprioceptive (neurological) dysfunction
The Ear.
What system provides the sense of hearing?
Which system generates our sense of balance?
What 3 structures does the peripheral vestibular apparatus contain?
How is the ear divided up?
What is the role of the pinna of the ear?
Where does the external auditory canal end?
What is the middle ear filled with?
What is it bounded by?
What does the eustachian tube connect?
What does this allow for?
- The Ear
- The auditory system provides sense of hearing
- The vestibular system generates our sense of balance by detecting the position and movement of our head in space
- 3 structures the peripheral vestibular apparatus contains:
1) Saccule
2) Utricle
3) Semicircular canals - The ear is divided into the outer, middle, and inner ear
- The pinna of the ear collects and focuses sound waves
- The skin lined external auditory canal ends up at tympanic membrane (eardrum)
- The middle ear is air filled chamber, bounded by tympanic membrane on one side and oval window on the other
- The Eustachian tube connects middle ear to nasophyarynx, which allows pressure equalisation
Membranous Labyrinth. What is the labyrinth filled with?
What is the auditory part of the labyrinth?
What are the 2 structures in the vestibular part of the labyrinth?
- Membranous Labyrinth
- The Labyrinth is filled with endolymph and encased in temporal bone
- The auditory part of the labyrinth is the cochlea
- 2 structures in the vestibular part of the labyrinth:
1) Otolith organs (detect gravity & head tilt)
2) Semicircular canals (detect head rotation)
What are the hair cells of the saccule?
What do they consist of?
How are hair cells affected with age?
- Hair cells of the saccule are mechanoreceptors that respond to minute movement changes
- Each hair cell consists of one large kinocilium and 50 -150 stereocilia
- Hair cells of cochlea lose their kinocilium with age; vestibular hair cells do not
Otolithic Organs (Saccule & Utricle).
What is the vestibule?
What does it contain?
How is the macula orientated in the saccule and utricle when upright?
Why are otolithic organs called this?
How dense are otoliths? What do otolithic organs detect changes in?
How is this done?
Where does each hair cell synapse?
- Otolithic Organs (Saccule & Utricle)
- The vestibule (vestibular apparatus) is a region of the inner ear which contains the saccule and the utricle, each of which contain a macula to detect linear acceleration.
- Macula is orientated vertically in saccule and horizontally in utricle when head upright
- Otolith organs are called this because of these specialised calcium carbonate crystals (otoliths / otolith organs) that sit on top of this gelatinous mass, with the hair cells protruding below in this gelatinous mass
- Otoliths are denser than endolymph (a physiological fluid that fills the inner ear’s labyrinth and serves crucial sensory functions)
- Otolithic organs detect changes in linear acceleration (i.e. that experienced as a car starts or stops) and head angle
- This is done by otoliths being pulled by gravity and moving the gelatinous cap in same direction; cilia of hair cells are deflected
- Each hair cell synapses on an axon of vestibular nerve (part of CN VIII)
Mechanotransduction in Hair Cells.
Where do hair cells project into?
What structures of hair cells provide directional information?
How does movement of the otolithic membrane affect the cilia?
How much movement is required to open/close the hair cell cation channels?
- Mechanotransduction in Hair Cells
- Hair cells, project hairs into an otolithic (ear stone) containing gelatinous structure.
- Cilia + kinocilium from hair cells – 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
What side are hair cells found on?
How will the movement of head position affect the hair cell cation gates on each side?
Where do electrical signals s then go?
What do these signals allow the brain to do?
- Hair cells are found on both side of the head in the peripheral vestibular apparatus of the ears
- When the head is tilted, the hair cell cation gates will open, leading to an influx of calcium and depolarization (positive mechanical deformation), while the hair cell cation gates on the other side will close, leading to hyperpolarization due to there not being an influx of calcium (negative mechanical deformation)
- These electrical signals then travel down an axon to the vestibular nuclei of the brain, where it can interpret if we mainly moving forward, back, up or down, and if we are accelerating or not
Semicircular canals (Ampulla).
What are the semicircular canals (ampulla) sensitive to?
Where are hair cells found here?
Where do these hair cells project into?
How do the semicircular canals detect head rotation?
- Semicircular canals (Ampulla)
- Semicircular canals (Ampulla) are sensitive to angular acceleration (head rotation movements)
- Hair cells are found clustered in sensory epithelium of the crista ampullaris
- Hair cells project into gelatinous cupula, all hair cells orientated in same direction
- As the head rotates, the semicircular canal moves but endolymph stays put, this bends the hair cells and they either excite or suppress transmitter release depending on direction of movement
- In the same manner as in the otolithic organs, hair cells on one side will depolarize, while the other side hyperpolarizes, leading to information being fed to the vestibular nuclei of the brain via the vestibular nerve and analysed
Where do Vestibular axons from CN VIII make direct connections to?
Where do axons from the otolith organs and semicircular canals project to?
What do these projections aid in?
- 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.
What does direct stimulation of ampullary nerves elicit?
What does Stimulation of afferents from left horizontal canal cause?
What 2 adaptations do we have that allow gaze to remain steady during head movement?
- Semicircular canals control eye movements – Vestibulo-ocular Reflex
- Stimulation of afferents from left horizontal canal causes eyes to turn right (vestibulo-ocular reflexes)
- 2 adaptations do we have that allow gaze to remain steady during head movement:
1) Lateral recti – cranial nerve VI (abducens nucleus)
2) Medial recti – cranial nerve III (oculomotor nucleus)
