Cerebellum: Anatomy, Function, and Divisions

• The cerebellum is the "Little Brain" in Latin, located below the cerebrum with many folds, significantly increasing its surface area
• One needs to be able to describe the functional divisions, enumerate their functions, and describe the effects of disorders

Voluntary Movement

• Instructions for voluntary movement start in cortical association areas
• The cortex, basal ganglia, and cerebellum collaborate to plan movements
• Movement from the cortex travels via the corticospinal and corticobulbar tracts to motor neurons in the brainstem and spinal cord
• The basal ganglia aid in voluntary movement
• The cerebellum gives feedback for movement adjustment and smoothness

Cerebellar Zones

• The cerebellum has three zones, divided by two fissures
• The anterior lobe is one of these zones
• The posterior lobe is another zone
• The Flocculonodular lobe makes up the final zone

Cerebellar Cells and Functions

• Purkinje Cells:
  • They are located in the Purkinje cell layer
  • It is a main output to deep cerebellar nuclei, and inhibitory control
  • GABA (inhibitory) is the neurotransmitter
• Granule Cells:
  • Located in the Granular layer
  • Functions as Excitatory interneurons, relay mossy fiber input
  • The neurotransmitter used is Glutamate (excitatory)
• Basket Cells:
  • They are located in the Molecular layer
  • Enhance signal precision
  • Uses GABA (inhibitory) as a neurotransmitter
• Stellate Cells:
  • They are located in the Molecular layer
  • Inhibits Purkinje cells, refine input from parallel fibers
  • Primarily uses GABA (inhibitory)
• Golgi Cells:
  • Location: Granular layer
  • Function: Inhibit granule cells, regulate sensory input processing
  • Neurotransmitter: GABA (inhibitory)
• Deep Cerebellar Nuclei Neurons:
  • Location: Deep Cerebellar nuclei
  • Function: Excitatory output from cerebellum to motor control centers
  • Neurotransmitter: Glutamate (excitatory)

Functional Divisions

• Spinocerebellum:
  • Comprises the vermis and intermediate cerebellar hemisphere zone
  • Receives proprioceptive input from the body
  • Receives plans for proposed movement from the cortex
  • Smoothes and coordinates ongoing movements with error correction
• Cerebrocerebellum:
  • It's formed by the lateral hemispheres
  • Receives input from the cerebral cortex and pontine nuclei, outputting to the thalamus and red nucleus
  • Concerned with planning and programming movements
  • Regulates muscle activation coordination and is important in visually guided movements
• Vestibulocerebellum:
  • Functional equivalent to the flocculonodular lobe
  • Concerned with: equilibrium (balance) and eye movements, especially fixation on a target
  • Receives inputs from the vestibular system and sends outputs back to the vestibular nuclei

Cerebellar Functions

• Processes information from the spinal cord, sensory systems, cerebral cortex, and other brain parts
• It's overall function is to make fine adjustments to motor actions
• Coordination of voluntary movement, balance, posture, and muscle tone
• Cognitive functions like attention, spatial perception, and language are other responsibilities
• Concerned with learned adjustments for easier coordination of tasks

Cerebellar Tracts

• Afferents:
  • Olivocerebellar
  • Vestibulocerebellar
  • Reticulocerebellar
  • Corticopontocerebellar
  • Trigeminocerebellar
• Efferents:
  • Cerebellovestibular
  • Cerebelloreticular
  • Corticonuclear
  • Cerebellothalamic
  • Cerebellorubral

Signal Processing

• The signal process is almost entirely feedforward
• Signals move through the system from input to output with little internal transmission
• The cerebellum receives and transmits output via a limited number of cells

Neurotransmitters within the Cerebellum

• Glutamate:
  • Primary excitatory neurotransmitter in the cerebellum
  • Involved in synaptic transmission and plasticity
• GABA:
  • is an essential inhibitory neurotransmitter
  • Regulates neuronal activity
• Serotonin:
  • Excites granule cells
  • Inhibits Purkinje cells
  • Regulates mood, appetite, and contributes to motor function.
• Dopamine:
  • Modulates synaptic transmission
  • Contributes to motor control

Cerebellar Disorders

• Cerebellar dysfunction results in motor control problems
• Causes for cerebellar dysfunction include:
  • Alcohol poisoning
  • Trauma
  • Multiple sclerosis
  • Tumors
  • Thrombosis of cerebellar arteries
  • Cerebrovascular accidents (stroke)

Characteristics of Cerebellar Disorders

• Diseases are characterized by hypotonia, ataxia, intention tremor, and nystagmus
• Hypotonia = decreased muscle tone causing floppy limbs and posture issues
• Ataxia = loss of coordination, causing errors in the rate, range, force, and direction of movement
• Intention tremor = rhythmic, oscillatory, high-amplitude tremor during purposeful motor movement, worsening before endpoint
• Nystagmus: causes involuntary, rhythmic eye movements, usually in a horizontal direction

Features of Cerebellar Diseases

• Ataxia symptoms:
  • Wide-based, unsteady, “drunken” gait
  • Slurred, scanning speech (pause after every syllable, slow pronunciation) via poor coordination of speech muscles
• Dysmetria symptoms:
  • Overshooting (hypermetria) or undershooting (hypometria)
  • Intention tremor
• Inability to stop movement symptoms:
  • Rebound phenomenon: Inability to stop a movement abruptly when resistance is removed
  • Dysdiadokokinesia - inability to perform rapidly alternating opposite movements
• Decomposition of movement symptoms:
  • Difficulty performing actions that involve simultaneous motion at more than one joint.
  • The patient relies on movements across one joint at a time

Acronym

• Dysdiadokokinesia
• Ataxia
• Nystagmus
• Intention Tremor
• Scanning speech (Dysarthria)
• Hypotonia

Other symptoms related to Cerebellar Disorders

• Impaired Motor Learning which results in difficulty in learning and refining motor tasks
• Cognitive and Affective Changes in some cases. Some patients experience impairments in planning, attention and emotional regulation

Damage to Specific Functional Areas

• Vestibulocerebellum damage leads to ataxia, disequilibrium, and nystagmus (ataxia of ocular muscles, rhythmical oscillation of the eyes)
• Spinocerebellum damage leads to scanning speech, disturbances controlling axial and trunk muscles during antigravity postures
• Cerebrocerebellum damage leads to delayed initiating movements and decomposition of movement