CNS, Neuromuscular and Musculoskeletal Function Flashcards
What is the function of the cerebellum?
Coordination of planned, voluntary multi-joint movements, balance and muscle tone
Comparator function - detects difference in ‘motor error’ i.e. between intended movement and actual movement. Correction of ongoing movements
Error reduced via projections from cerebellum to upper motor neurones
Motor memory - stores learned movement. Consciousness to unconsciousness, e.g. riding a bicycle, driving a car, professional sportsperson
What is the function of the basal ganglia?
Control of movement - Motor cortex produces commands (excitatory) - basal ganglia exerts inhibitory influence to modulate the initiation and termination of motor commands
Selection and maintenance of voluntary movements
Inhibitory influence on motor systems suppresses inappropriate movements
Modulates movements through complex feedback circuitry
Also involved in non-motor functions, e.g. cognition, working memory, attention
What is the function of both the cerebellum and basal ganglia?
Improve the accuracy of movements by providing feedback loops with motor and sensory areas in cortex
Modify signal of upper motor neurones only - no direct connection to lower motor neurones
What are the effects of damage to the cerebellum?
Disrupts the modulation and coordination of ongoing movements - movements in patients become jerky, imprecise, slow and uncoordinated
Movement errors are always on the same side of the body as the damage to the cerebellum (sensory and motor information are represented ipsilaterally)
What are the effects of damage to the basal ganglia?
Uncontrolled movements at rest, e.g. Parkinson’s, Huntington’s, Hemiballism
Describe the cerebellum.
‘Little brain’
Located in the hindbrain
Dorsal surface is folded - folia (ridges) and divided into lobules, has two hemispheres and lots of lobules
Cerebellum constitutes about one tenth of total volume of brain, but contains approximately 50% of total number of neurones in the CNS (high surface area)
White matter - arbor vitae (interior)
Grey matter - highly convoluted with lots of surface area (exterior)
Deep cerebellar nuclei (deep within)
What are the divisions of the cerebellum?
Based on sources of input
Cerebrocerebullum - Large in humans. Inputs from cerebral cortex. Involved in the regulation of highly skilled movements (complex sequences of movements including speech), two - one on either side (medial)
Spinocerebellum - Direct input from spinal cord. Lateral part involved in movements of distal muscles. Central part (vermis) concerned with movements of proximal muscles
Vestibulocerebellum - |Includes nodules and flocculus. Inputs from vestibular nuclei in brainstem. Involved in movements underlying posture and balance
What are the cerebellar peduncles?
Stalks which attach the cerebellum to the brainstem (pons)
What is the structure of the cerebellar peduncles?
Superior cerebellar peduncle - almost entirely an efferent pathway from cerebellum
Middle cerebellar peduncle - Afferent pathway to the cerebellum via pons (largest)
Inferior cerebellar peduncle - Both afferent and efferent pathways
Main white matter tracts
What are the inputs to the cerebellum?
Motor inputs from cerebral cortex via relay neurones in pons cross over to the opposite cerebellar hemisphere (middle cerebellar peduncle)
Sensory inputs (muscle proprioceptors, vestibular, visual, auditory) on same side convey position and motion information (inferior cerebellar peduncle)
Inferior olive - modulatory inputs - timing, learning, memory
What are the outputs from the cerebellum?
Deep cerebellar nuclei - major output structures
Cerebellar cortex -> deep cerebellar nuclei -> superior cerebellar peduncle -> VL complex (thalamus) -> primary motor and premotor cortex
What are the deep cerebellar nuclei?
Major output structures
Embedded in deep white matter
Relay cortical cerebellar information to motor cortex and brainstem to make corrections in movement
Dentate nucleus, two interposed nuclei, fastigial nucleus (lateral to medial)
What nucleus is each cerebellar division paired with?
Vestibulocerebellum - Fastigial nucleus or direct (vestibular nuclei) (balance and eye movement)
Spinocerebellum - Interposed (+ fastigial) nucleus (motor execution)
Cerebrocerebellum - Dentate nucleus (motor planning)
What are the main cell types of the cerebellar cortex?
Inputs:
- Climbing fibres (from inferior olive)
- Mossy fibres (all other inputs)
Outputs:
- Purkinje fibres
Interneurons:
- Granule
- Stellate
- Golgi
- Basket cells
What are the layers of the cerebellar cortex?
Molecular layer
Purkinje layer (contains purkinje cell bodies)
Granule cell layer
White matter
What is a simplified view of the microcircuitry of the cerebellar cortex?
Mossy fibres (input from cerebral cortex, spinal cord, vestibular system) synapse with granule cell in granule layer Granule cell leads into molecular layer and branches into a parallel fibre which purkinje cell dendrites synapse with Purkinje cell body in purkinje layer and then output down axon through granule layer Climbing fibres surround purkinje cells (input from inferior olive) and synapse
What are climbing fibres?
Carry error signals when movement has failed to meet target/expectations
Make corrections by alternating effectiveness of the parallel inputs to Purkinje cell
Inputs from inferior olive and twist around dendrites of Purkinje cells
Each Purkinje cell receives input from only one inferior olive neurone, BUT input is very strong (generated large depolarisation in Purkinje cell)
What are Purkinje cells?
Purkinje axons synapse onto neurones in deep cerebellar nuclei
Use neurotransmitter GABA (inhibitory)
Although a Purkinje cell receives only one synapse from each passing parallel fibre it does so from ~100000 parallel fibres
What are granule cells?
Receive input from mossy fibres
Numerous, small, tightly packed. Half the total number of neurones in the brain
Outputs branch like a ‘T’ in molecular layer. Each branch is called a parallel fibre
What arteries supply the cerebellum?
Superior portion including deep nuclei - superior cerebellar artery
- Damage would result in postural and gait ataxia, upper limb ataxia and dysarthria
Inferior portion - posterior inferior cerebellar artery
- Damage would result in trunk ataxia, oculomotor problems
What is the outcome of damage to the vestibulocerebellum?
Disturbances of balance and eye movements
What is the outcome of damage to the spinocerebellum?
Impaired gait, e.g. wide-based gait with small shuffling movements (no sensory feedback to produce smooth actions)
What is the outcome of damage to the cerebrocerebellum?
Impairments in highly skilled sequences of learned movements
What is cerebellar ataxia?
Movements become jerky, imprecise and uncoordinated
