Cerebellar circuit movement

Cerebellar circuit movement

1. 1. BACKGROUND - CEREBELLUM

   • c. Summary of motor modulation by the cerebellum
     • **MUST LEARN DIAGRAM**
       • The central processing components, the cerebellar cortex, receives multiple inputs from the cerebral cortex
         • It also generates signals that adjust incoming responses of the upper motor neurons
           • Modulatory inputs influence processing the the cerebellar cortex
             • Cerebellar cortex's output signals are relayed to the thalamus and back to the motor cortex, where they modulate commands
               • There are multiple other sensory inputs modulating the circuit
   • b. Interactions
     • The cerebellum is a closed side-loop of the descending motor control system
       • All sensory information from the primary motor cortex is sent to the cerebellum via the pons
         • The number of fires entering it is greater than the fibres leaving it 40:1
           • THEREFORE, IT IS HIGHLY CONVERGENT
             • This convergence of multiple pathways leads to a high degree of processing (contains >50% of the total number of neurons in the CNS)
               • INPUTS - regions projecting into the cerebellum
                 • The cortical projections are mainly from the sensory association cortex of the parietal lobe and motor association areas of the frontal lobe
               • OUTPUTS - targets of the cerebellum
                 • Ascending pathways:
                   • Motor cortex (Via relay in ventral and lateral nuclei of the thalamus)
                   • Red nucleu
                 • Descending pathways:
                   • Vesticular nuclei
                   • Superior coliculus
                   • Reticular formation
   • a.
     • The spinal cord can generate complex motor patterns independently of the brain
       • However, the cerebellum is required for balance during execution
         • Whilst the PERIPHERAL MOTONEURONS and CENTRAL MOTOR PATHWAYS initiate and execute movement
           • The cerebellum is required for coordinated execution of movement and maintenance of balance

2. 3. IMPORTANT ROLES OF THE CEREBELLUM

   • a. Role of the cerebellum in voluntary movement
     • Begins with forming an idea in the brain, which occurs in the prefrontal cortex
       • [rpgramming for preparation of movement occurs in the motor association corticles
         • Execution of the movement mainly occurs at the primary motorcortex
           • The cerebellum plays two roles:
             • Activity of the motor cortex is copied to the cerebellum
               • It is able to modify movement before it finishes even though it is not involved in the generation of movement
             • The feedback mechanism aloows it to gain ifnromation on the outcome of its activity
   • b. Role of the cerebellum in the integration of visual and vestibular information
     • The cerebellar receives strong inputs form both:
       • INFERIOR OLIVE (RETINA)
       • VESTIBULAR NUCLEUS (VESTIBULAR APPARATUS)
     • The vestibulo-ocular reflex:
       • Keeps the eyes directed toward the same point in space as the head rotates
         • They eyes change position in an appropriate way to keep the light from the external world on the same portion of the retina at the back of the eys
       • Adaptive changes in the vestibulo-ocular reflex
         • Normally the reflex operates to move the eyes as the head moves, so that the retinal images remains stable
           • When an animal observes the world through minifying glasses the eyes normally move too far with respect to 'slippage' of the visual image on the retina
             • After practice, the VOR is reset and the yes move an appropriate (shorter) distance in relation to head movement

3. 2. LESIONS TO THE CEREBELLUM

   • a. Pathological changes
     • Pathological changes caused by neurological diseases provide insight into the features of the cerebellum
       • Studies have shown chronic alcohol use leading to degradation to the anterior cerebellum caused difficulties in walking
         • But little impairment of speech and arm movements
   • b. Insights
     • Provides a complete picture of the central role of the cerebellum in motor control systems
       • Initiation and control of goal-directed motor activity:
         • From the cerebral cortex through the direct corticospinal pathways, spinal cord and brainstorm reflex circuits to produce the final motor output
         • Error correction and coordination:
           • From the cerebellum to brain stem nuclei. Then through the reticulospinal or vesticulospinal pathways and the muscles of trunk (key components of balance) or distal muscles and converging at the spinal cord