Clinical Neuroscience Week 10 - The Cerebellum

• The cerebellum, or "little brain," is attached to the pons via cerebellar peduncles.
• It plays a crucial role in maintaining posture, coordination, and other unconscious functions.
• Information processed by the cerebellum remains ipsilateral to its origin.

Topography

• The cerebellum has three lobes: the anterior, posterior, and flocculonodular lobes
• It contains four deep nuclei with flower-like structures on the cortex

General Information Flow

• Afferent signals from the cerebrum travel to the brainstem, cross over, and then reach the cerebellum.
• Proprioceptive information from the periphery ascends through the spinal cord to the cerebellum.
• The cerebellum connects to the brainstem via three cerebellar peduncles:
  • The superior peduncle transmits information mainly to the midbrain.
  • The middle cerebellar peduncle transmits information to the pons.
  • The inferior cerebellar peduncle transmits information to the medulla.

Review of Afferent Pathways

• There are 11 afferent pathways into the cerebellum.
• Key tracts include:
  • Spinocerebellar tracts:
    • Dorsal (posterior) spinocerebellar tract: uncrossed.
    • Ventral (anterior) spinocerebellar tract: double crossed.
  • Olivocerebellar tract:
    • Modulates movements and coordination.
    • Originates in the inferior olive of the medulla and projects directly to the cerebellum.
    • Damage may result in dystonia.
• These pathways mainly carry proprioceptive information.
• Damage to one side of the cerebellum can cause impaired proprioception on the same side of the body.

Cellular Anatomy

• The cerebellum comprises three layers.
• Mossy fibers and climbing fibers release excitatory neurotransmitters.
  • Mossy fibers originate in the brainstem and spinal cord.
  • They carry somatosensory information related to arousal and balance.
  • Climbing fibers originate in the inferior olivary nucleus in the medulla.
  • They provide information about movement errors.
• Purkinje cells:
  • Neurons with many dendrites.
  • Represent the only efferent output of the cerebellum.
  • Relay information to the deep cerebellar nuclei, which then project to the brainstem or thalamus.

Deep Nuclei

• Information from Purkinje cells goes to one of four deep cerebellar nuclei:
  • Dentate nucleus:
    • Largest nucleus.
    • Located in the lateral zone.
    • Responsible for planning, initiating, controlling, and correcting voluntary movements.
  • Emboliform nucleus:
    • Located in the intermediate zone.
    • Involved in motor learning and correcting motor activity.
  • Globose nucleus:
    • Located in the intermediate zone.
    • Involved in motor learning and correcting motor activity.
  • Fastigial nucleus:
    • Located in the medial zone.
    • Responsible for eye movement.
• Damage to the cerebellum can result in:
  • Involuntary movements.
  • Movements that are too large or uncoordinated.
  • Balance issues.
  • Reduced ability to learn new skills.
• Purkinje cells are inhibitory at baseline, consistent with the observation that cerebellar damage often leads to exaggerated movements due to reduced inhibition.

Functional Divisions

• The cerebellum is divided into three functional divisions:
  • Vestibulocerebellum (medial zone).
  • Spinocerebellum (intermediate zone).
  • Cerebrocerebellum (lateral zone).
• These incorporate all three anatomical lobes.
• These divisions are classified by their roles in maintaining equilibrium, gross motor coordination, and fine distal voluntary movements.

Vestibulocerebellum

• Key structures:
  • Flocculonodular lobe.
  • Has relationship with pons and vestibular nuclei
• Receives information from the vestibular nuclei and vestibulocochlear nerve, then sends information back to the vestibular nuclei.
• Important for balance and posture.
• Input: vestibular nuclei and CN VIII (vestibulocochlear nerve).
• Output: vestibular nuclei; vestibulospinal tract.
• Deficits can cause:
  • Imbalance and difficulty maintaining posture.
  • Difficulty maintaining stable gaze, leading to nystagmus.
  • Gait difficulties.

Spinocerebellum

• Responsible for goal-directed movement.
• Key structures:
  • Vermis and intermediate zone.
• Input: spinal cord.
  • Dorsal spinocerebellar tract (DSCT): Ipsilateral, provides information about internal stimuli.
  • Ventral spinocerebellar tract (VSCT): Double crossed, provides information about reflex arcs.
• Output: vestibular nucleus, red nucleus, reticular formation.
• Responsible for goal directed movements
• Proximal and trunk control
• Deficits can cause:
  • Impaired proprioception.
  • Loss of muscle tone (hypotonia).
  • Difficulty reaching, grasping, and performing rapid alternating movements.
  • Oculomotor deficits.
• The cerebellum uses sensory information to adapt motor output during motion, with the current state of motion influencing subsequent commands from the cerebellum.
• Cerebellar issues can result in dysmetria, leading to shaky and uncontrolled movements.

Cerebrocerebellum

• Located in the lateral aspects or hemispheres of the cerebellum.
• Responsible for visually guided movement.
• Input: deep pontine nuclei, with indirect information from all four cortical lobes.
• Output: thalamus, then cortex.
• Deficits can cause:
  • Challenges with rapid alternating movements.
  • Difficulty isolating certain movements, leading to gross movement patterns.
• Information flows from the pontine nuclei to the lateral cerebellar hemisphere, then to the thalamus, cortex, and down the lateral corticospinal tract.
• Role in movement:
  • Feed-forward mechanism to predict and anticipate movements.
  • Receives information from primary motor and sensory areas to modify actions before they occur.
  • Important for planning and timing movements.
  • Involved in cognitive functions.

Lobes and Their Controlled Body Parts

• Floccular nodular lobe: functions of the head and neck & ocular movement
• Medial portion of the vermis: posture and trunk control
• Lateral portions: Helpful for distal limb control

Blood Supply

• Cerebellar arteries:
  • Superior cerebellar artery (SCA).
  • Anterior inferior cerebellar artery (AICA).
  • Posterior inferior cerebellar artery (PICA).
• Other arteries: basilar and vertebral arteries supply the SCA, AICA, and PICA.

Functions of the Cerebellum

• Key theories on the role of the cerebellum:
  • Coordination: feedback and feed-forward control system to produce ideal movement.
  • Timer of movement: encodes precise timing and temporal sequence of muscle activations, and lesions can cause timing deficits.
  • Motor learning:
    • Receives information about body position and muscle action.
    • Outputs to descending motor systems at the brainstem level.
    • Creates an internal model to predict movement control.
• Functions include:
  • Skill acquisition.
  • Implicit (subconscious) motor learning.
  • Automatic skill performance.
  • Monitoring and integrating sensory information into motor planning.
  • Preparing planned voluntary movement and monitoring ongoing movement.
    • Limb and trunk movements.
    • Anticipatory postural control.
    • Speech articulation.
    • Vestibular adaptation: integrates vestibular system input where deficits can result in dizziness and vertigo

Clinical Application

• Cerebellar ataxia: "uncoordinated movement."
  • Truncal ataxia.
  • Appendicular ataxia.
• Causes: various, including degenerative diseases, tumors, etc.
• Signs and symptoms:
  • Impaired balance.
  • Dizziness or vertigo.
  • Difficulties with fine motor skills and coordination.
• Prognosis depends on the cause. Degenerative conditions have poorer prognoses.
• Treatment: physical therapy can improve balance, modulate dizziness, and enhance coordination.