Lecture 12: Cerebellum and Basal Nuclei Control of Motor Function I

Question 1

Anatomically, the cerebellum is divided into ___ lobes by two deep fissure

Answer 1

• 3
• The anterior lobe
• the posterior lobe
• Flocculonodular lobe

Question 2

Functions of the Primary Motor Cotrex (Area 4)

Answer 2

• 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

Question 3

Function of premotor cortex (area 6)

Answer 3

Plans movements based on sensory and visual cues

Question 4

Functions of supplementary motor area (area 6)

Answer 4

Retrieves and corrdinates memorized motor sequences

Question 5

functions of the motor cotex system

Answer 5

• 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”

Question 6

List basic functions of the Cerebellum

Answer 6

• 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

Question 7

Identify the three lobes of the cerebellum (from most anterior to most posterior)

Answer 7

• Anterior lobe
• Posterior lobe
• Flocculonodular lobe (note is associated with vestibular system)

Question 8

Which of the three lobes of the Cerebullum is evolutionarily the oldest

Answer 8

Flocculonodular lobe

Question 9

What are the Folia

Answer 9

Narrow, leaflike gyri of the cerebellar cortex

Question 10

What and where is the vermis; with what functions is it associated

Answer 10

• 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

Question 11

What are the general functions of the intermediate and lateral zones

Answer 11

• 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

Question 12

List the four pairs of deep cerebellar nuclei and relate lesions to their normal function

Answer 12

• 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

Question 13

Lst the cells that make up the cerebellar cortex and describe their circuitry

Answer 13

• 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)

Question 14

Describe the functional unit of the cerebellum

Answer 14

• 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

Question 15

What are pendular movements? How does the cerebellum affect pendular movements?

Answer 15

• 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

Question 16

What are ballistic movements

Answer 16

• rapid movements of the body, such as the movements of the fingers in typing, occur so rapidly that it is not possible to receive feedback information either from the periphery to the cerebellum or from the cerebrum back to the motor cortex befor the movements are over.
• The entire movemnt is preplanned and set into motion to go a specific distance and then to stop

Question 17

How does removal of the cerebellum affect movements of the body

Answer 17

• great effects on ballistic movements
  
  • Movements are slow to develop
  • force developed is weak
  • movements are slow to turn off

Question 18

Dysmetria

Answer 18

in the absence of the cerebellum, the subconscious motor control system cannot predict how far movement will go. Therefore, the movemtns ordinarily overshoot their intedned mark; then the conscious portion of the brain overcompensates in the opposite direction for the succeeding compensatory movement

Question 19

Ataxia

Answer 19

• uncoordinated movements that are a result of dysmetria

Question 20

past pointing

Answer 20

• in the absence of the cerebellum, a person ordinarily moves the hand or some other moving part of the body considerably beyond the point of intention.

Question 21

disdiadochokinesia

Answer 21

• Inability to perform rapid alternating movements
• when the motro control system fials to predict where the different parts of the body will be at a given time, it “loses” perception of the parts during rapid motor movemtns. as a result, the succeeding movement may begin much too early or much too late, so no orderly “progression of movement” can occur
• the patent rapidly “loses” all perception of the instantaneous position fo teh bdoy part (ex. hand) during any portion of movement

Question 22

dysarthria

Answer 22

• Failure of progression in talking
  
  • because the formation of words depends on rapid and orderly succession of individual muscle movements in the larynx, mouth, and respiratory system
  • lack of coordination among these structures and the inability to adjust in advance either the intesntiy of sound ro the duration of each successive sound causes jumbled vocalization, with some syllables loud, some weak, some held for long intervals, and some held for short intervals, with resultant speech that is oftne unintelligible

Question 23

cerebellar nystagmus

Answer 23

• tremor of the eyeballs
• is a tremor of the eyeballs that usually occurs when one attmepts to fixate the eyes on a scene to one side of the head.
• This off-center type of fixation results in rapid, tremulous movements of the eys rather than steady fixation, and it is another manifestation of the failure of damping by the cerebellum
• it occurs especially when the flocculonodular lobes of the cerebelum are damaged

Question 24

hypotonia

Answer 24

• Decreased tone of musculature
• loss of the deep cerebellar nuclei, particularly of the dentate and interposed nuclei, causes decreased tone of the peripheral body musculature on the side of the cerebellar lesion. The hypotonia results from loss of cerebellar facilitation of the motor cortex and brain stem motor nuclei by tonic signals from the deep cerebellar nuclei

Question 25

Describe the functional organization of the cerebellum by listing the composition and functions of the vestibulocerebellum, the spinocerebellum, and the cerebrocerebellum

Answer 25

• Nervous system uses cerebellum ot coordinate motor control functions at three levels
  
  • Vestibulocerebellum
    
    • consists of flocculonodular lobes and vermis
    • functions in control of balance and eye movements
    • Envolved at about the same time as vestibular system
    • Receives fibers from:
      
      • Vestibular system
      • Oculomotor system (pontocerebellar fibers)
    • Sends output primarily to vestibular system
    • Loss of flocculonodular lobes–> extreme disturbance of equilibrium and postural movements
    • Relationship with pendular movements
  • Spinocerebellum
    
    • consists mostly of vermis and intermediate zone
    • functions in synergy: control of rate, force, range and direction of movment
    • Receives:
      
      • information from motor cortex and red nucleus telling cerebellum intended sequential plan of movement for the next few fractions of a second
      • Feedback information from periphery telling cerebellum what actual movements result
    • Compares two sources of information and sends correction to:
      
      • Motor cortex via thalamus
      • Magnocellular portion of red nucleus
  • Cerebrocerebellum
    
    • Consists of lateral parts of hemispheres
    • Mostly associated with the premotor and the primary and association somatosensory areas of the cerebral cortex
    • Receives corticopontocerebellar projections
    • Involved in coordination of skilled movement and speech
    • Plans as much as tenths of a second in advance of actual movements:
      
      • Referred to as “motor imagery”

Question 26

Diagram each of the afferent tracts to the cerebellum and designate which tracks form the mossy fibers and which tracks form the climbing fibers

Answer 26

• Climbing fibers
  
  • Originate from medullary olives
  • Make multiple synapses with Purkinje cells
  • Provide high frequency bursts (complex spikes)
  • “condition” the Purkinje Cells
  • Play a role in motor learning
• Mossy fibers
  
  • Originate from multiple centers in brainstem and spinal cord, including vestibulocerebellar, spinocerebellar, and pontocerebellar tracts
  • Make multiple synapses on Purkinje cells and result in simple spikes
  • synapse on granule cells in glomeruli

Question 27

List the efferent tracks of the cerebellum

Answer 27

• Purkinje cell axons:
  
  • only ouput rom cerebellar cortex
  • Output is always inhibitory
  • GABA is the neurotransmitter used
  • Project to deep cerebellar nuclei and vestibular nucleus
  • Modulates output of cerebellum and provides syndergy (regulates rate, range, and direction of movement)

Question 28

Layers in Cerebellar Cortex

Answer 28

• Granular Layer
  
  • innermost layer
  • made up of granule cells, golgi type II cells, and glomeruli
  • axons of mossy fibers synapse with granular cells and golgi type II cells in the glomeruli
• Purkinje cell layer
  
  • middle layer
  • contains Purkinje cells
• Molecular layer
  
  • outmost layer
  • Contains stellate cells, basket cells, Purkinje dendrites, Golgi type II cells, and axons of granule cells (parallel fibers)

Question 29

What is the only output from the cortex

Answer 29

• Purkinje cells (note this output is always inhibitory)

Question 30

Intention tremor

Answer 30

• also known as an action tremor
• when a person who has lost the cerebellum performs a voluntary act, the movemnts tend to oscillate,especially when they approach the intended mark, first overshooting the mark and then virbating back and forth several times before settling on the mark.
• results form the overshooting and failure of the cerebellar system to “damp” the motor movements