Lecture 12: Cerebellum and Basal Nuclei Control of Motor Function I Flashcards
Anatomically, the cerebellum is divided into ___ lobes by two deep fissure
- 3
- The anterior lobe
- the posterior lobe
- Flocculonodular lobe
Functions of the Primary Motor Cotrex (Area 4)
- Signals motor neurons to contract skeletal muscle fibers
- Signals via the corticospinal (pyramidal tract)
- Execution of commands is preceded by extensive processing by cerebellum and basal nuclei
Function of premotor cortex (area 6)
Plans movements based on sensory and visual cues
Functions of supplementary motor area (area 6)
Retrieves and corrdinates memorized motor sequences
functions of the motor cotex system
- Provides most of activating signals to spinal cord
- Issues sequential and parallel commands that initiate various cord patterns
- Cortical patterns are usually complex and can be learned
- Cord patterns are mainly determined by heredity and are “hard-wired”
List basic functions of the Cerebellum
- The cerebellum plays major roles in the timing of motor activities and in rapid, smooth progression from one muscle movement to the next.
- not essential for locomotion
- helps sequence motor activities
- Monitors and makes corrective adjustments to motor activities while they are being executed
- Compares actual movements with intended movments
- Aids cortex in planning next sequential movement
- Learns by its mistakes
- Functions with spinal cord to enhance the stretch reflex
- functions with brain stem to make postural movements
- functions with cerebral cortex to provide accessory motor functions
- Turns on antagonist at appropriate time
- Helps program muscle contraction in advance
- Functions mainly when muscle movements have to be rapid
Identify the three lobes of the cerebellum (from most anterior to most posterior)
- Anterior lobe
- Posterior lobe
- Flocculonodular lobe (note is associated with vestibular system)
Which of the three lobes of the Cerebullum is evolutionarily the oldest
Flocculonodular lobe
What are the Folia
Narrow, leaflike gyri of the cerebellar cortex
What and where is the vermis; with what functions is it associated
- down the center of the cerebellum is a narrow band called the vermis
- fxn: location for control functions for muscle movements of the axial body, neck, shoulders, and hips
What are the general functions of the intermediate and lateral zones
- Intermediate zone: concerned with controlling muscle contractions in the distal potions of the upper and lower limbs, especially the hands, fingers, feet, and toes
- Lateral zone: associated with cerbral cortex with planning sequential motor movements
- without the lateral zone, most discrete motor activites of the body lose their appropriate timing and sequencing and therefore become uncoordinated
List the four pairs of deep cerebellar nuclei and relate lesions to their normal function
- Inracerebellar nuclei
- Dentate
- Emboliform
- Globose
- Fastigial
- Dentate, Emboliform, and Globose nuclei
- Fibers project to the red nucleus
- Related to limb musculature and fine manipulative movement
- Lesions in these nuclei:
- lead to extremity ataxia
- Fastigial nuclei:
- Fibers project to reticular formation and vestibular nuclei
- Related to postural activity and limb movements via reticulospinal and vestibulospinal tracts
- Lesions in this nucleus
- lead to trunk ataxia
Lst the cells that make up the cerebellar cortex and describe their circuitry
- Granular cells
- Axons form parallel fibers in cortex (+)
- Golgi cells
- Project from parallel fibers to granular cell bodies (-)
- Basket cells
- Project from parallel fibers to Purkinje axon hillock (-)
- Stellate cells
- Project from parallel fibers to Purkinje dendrites (-)
- (note that the basket and stellate cells provide lateral inhibition on adjacent Purkinje cells to provide damping)
Describe the functional unit of the cerebellum
- 30 million fucntional units in cerebellar cortex
- each functional unit is centered on a Purkinje cell and a corresponding deep nuclear cell
- Output from a functional unit is from a deep nuclear cell
- Afferent inputs to the cerebellum are mainly from the climbing and mossy fibers
- All climbing fibers originate from the inferior olives
- Mossy fibers enter cerebellum from a variety of sources
- Send excitatory to deep nuclear cells and then synapse in granular layer with thousands of granular cells
- Granule cells send axons to outer cerebellar surface; axons branch in two directions parallel to folia
- Dendrites of Purkinje cells project to these parallel fibers
- Direct stimulation by climbing and mossy fibers excites deep nuclear cells. Purkinje cell signals inhibit deep nuclear cells
- Basket cells and stellate cells also function as inhibitory cells
What are pendular movements? How does the cerebellum affect pendular movements?
- Most body movements are pendular (swing back and forth)
- all pendular movements have tendency to overshoot (this is due to momentum)
- Appropriate learned subconscious signals from intact cerebellum can stop movement precisely at intended point (=damping system)
- if overshooting occurs in a person whose cerebellum has been destroyed, the conscious centers of the cerebrum eventually recognize this occurrence and initiate a movement in the reverse direction to attempt to bring the arm to its intended position. However, the arm, by virtue of its momentum, overshoots once more in the opposite direction.
- thus the arm oscillates back and forth past its mark. This effect is called an action tremor or intention tremor