Motor control in health and disease (8.6) Flashcards
Describe the organisation of the motor system
The motor system has several layers of control.
Main ‘layers of control’:
- Spinal cord
- Brainstem
- Cerebral cortex
2 side-loops: Basal ganglia and cerebellum
NOTE: Functioning of these components relies on sensory information (interneurones, muscle spindle, UMNs in the brain)
Explain the role of sensory feedback in guiding movement
Sensory feedback:
- Sensory input from muscle: Feedback via the stretch and golgi tendon reflexes.
Acts to protect muscles from excessive stretch.
HOWEVER, reflexes are unconscious movements and hence information does not travel back to the cerebrum.
- Sensory feedback aids the coordination of movement, allows awareness of our position in space and the amount of force required to perform a particular movement
- Visual input guides movement
Outline the role of the cerebral cortex in guiding movement
Primary motor cortex = 4
Pre-motor and supplementary motor areas = 6
Acts to plan and initiate complex voluntary movement through issuing commands to the contralateral musculature.
Has various inputs and connections. Different regions of the brain act to provide regulation and an ‘initiation plan’ for the motor cortex, prior to the discharge of motor neurones.
Cerebellum + basal ganglia → thalamus → supplementary motor cortex → primary motor cortex
Identify key regions and functions of the cerebellum
*Has no direct connections with LMN - acts through modulating UMN firing*
*Supervisor of the motor system - operates at an unconscious level*
- Deep nuclei act as the output of the cerebellum
Function:
- Controls balance - influences posture and muscle tone
- Coordinates movement
- Compares intended and actual movement - allows for the detection of error
- Motor learning - roles in attention and planning
3 main functional regions:
Spinocerebellum: Regulates axial muscle tone and posture
Neocerebellum: Controls muscle co-ordination, trajectory, force and speed
Vestibulocerebellum: Maintains balance and equilibrium. Controls the status of head and eye position
Key anatomical areas: 2 hemispheres joined by the vermis; 2 lobes (anterior and posterior) divided by the primary fissure; floculonodular and cerebellar tonsil are seen on the inferior surface of the cerebellum
Outline the main afferent and efferent connections of the cerebellum
(main connections, cerebellar peduncles, deep cerebellar nuclei)
The connections of the cerebellum aid the coordination of movement.
Describe the organisation of neural circuits within the cerebellum
Cerebral cortex → Deep pontine nuclei → Contralateral cerebellar cortex via mossy fibres → Granule cells → Purkinje fibres via parallel fibres → Deep cerebellar nuclei
☆ The deep cerebellar nuclei (DIF) are the only output of the cerebellum. Since the Purkinje fibres are GABAergic the output of the cerebellar cortex is inhibitory. (Purkinje fibres act to modulate the excitatory input of the mossy and climbing fibres upon the deep cerebellar nuclei)
Local circuits acting upon Purkinje cells
Main inputs and outputs of the cerebellum
Draw diagram
State the possible consequences of a cerebellar lesion(/ deduce the location, given a set of symptoms)
CEREBELLAR LESIONS ⇒ IPSILATERAL SYMPTOMS
DANISH - Dysdiadochokinesis Ataxia Nystagmus Intention tremor Slurred/staccato speech Hypotonia
PLUS gait ataxia, poor coordination
Midline lesion (spinocerebellum): Loss of postural control - unable to sit or stand, but limb coordination is preserved
Unilateral cerebellar lesion: Ipsilateral incoordination of limbs WITHOUT weakness of sensory loss
Describe the neural circuitry in the basal ganglia
Nigrostriatal pathway - Projections from the Substantic Nigra (pars compacta) to the caudate nucleus and putamen (striatum)
Corticostriatal fibres - Cerebral cortex to the striatum
Describe the direct and indirect pathways of the basal ganglia
Clinical link: How may these pathways be affected in disease?
Basal ganglia disorder ⇒ CONTRALATERAL symptoms
Parkinsons: Loss of a dopaminergic neurons of the nigrostriatal pathway and accumulation of Lewy bodies.
Signs/symptoms: TRAMP (resting Tremor, Rigidity, Ataxia, Masking, Postural instability)
Describe the role of the cerebellum and basal ganglia in the control of movement
Cerebellum: Involved in timing and controlling precise motor movements. Balance, maintenance of posture, control of muscle power/trajectory and coordination. Motor learning
Basal ganglia: Motor control - facilitating movement, motor learning
