ANATOMY OF THE CEREBELLUM
The cerebellum, second only to the cerebrum in size, occupies the inferior and posterior parts of the cranial cavity. It has a highly folded surface that increases the surface area of its gray matter cortex, allowing for a greater number of neurons.
Although the cerebellum accounts for only about one-tenth of the brain’s mass, it contains nearly half of the brain’s neurons. It is located posterior to the medulla and pons and inferior to the posterior portion of the cerebrum.
A deep groove known as the transverse fissure, along with the tentorium cerebelli (which supports the posterior cerebrum), separates the cerebellum from the cerebrum.
Structure of the Cerebellum
When viewed from above or below, the cerebellum resembles a butterfly. The central constricted part is called the vermis (meaning “worm”), and the lateral “wings” are known as the cerebellar hemispheres.
- Each hemisphere consists of lobes separated by deep fissures.
- The anterior lobe and posterior lobe control subconscious aspects of skeletal muscle movements.
- The flocculonodular lobe on the inferior surface helps maintain equilibrium and balance.
Cerebellar Layers and Internal Structure
- The superficial layer, called the cerebellar cortex, consists of gray matter arranged in slender, parallel folds called folia (meaning “leaves”).
- Beneath the gray matter lie tracts of white matter known as the arbor vitae, which resemble the branches of a tree.
- Embedded within the white matter are the cerebellar nuclei, regions of gray matter that send impulses from the cerebellum to other brain centers.
CEREBELLAR CONNECTIONS
Three paired bundles of white matter known as cerebellar peduncles attach the cerebellum to the brainstem. These peduncles carry impulses between the cerebellum and other parts of the brain.
Superior Cerebellar Peduncles
Contain axons that extend from the cerebellum to the red nuclei of the midbrain and to several nuclei of the thalamus.
Middle Cerebellar Peduncles
These are the largest peduncles. Their axons carry impulses for voluntary movements from the pontine nuclei (which receive input from the motor areas of the cerebral cortex) into the cerebellum.
Inferior Cerebellar Peduncles
The inferior peduncles consist of several types of axons, including:
- Axons of the spinocerebellar tracts carrying sensory information from proprioceptors in the trunk and limbs.
- Axons from the vestibular apparatus of the inner ear and vestibular nuclei of the medulla and pons, carrying sensory input from the head.
- Axons from the inferior olivary nucleus of the medulla, which regulate cerebellar neuron activity.
- Axons extending from the cerebellum to the vestibular nuclei of the medulla and pons.
- Axons extending from the cerebellum to the reticular formation.
FUNCTIONS OF THE CEREBELLUM
- The cerebellum coordinates voluntary muscular movements, posture, and balance.
- Its activity is not under voluntary control.
- It ensures smooth, precise, and coordinated muscular actions.
- It maintains posture, balance, and equilibrium through constant sensory input.
Sensory Input and Coordination
The cerebellum receives sensory input from:
- Proprioceptors in muscles and joints (indicating body position).
- Eyes and semicircular canals of the ears (providing information about head position and movement).
This information is integrated by the cerebellum to regulate skeletal muscle activity for balance and posture.
Additional Roles
Besides motor coordination, the cerebellum may also play a role in learning and language processing. Damage to the cerebellum results in clumsy, uncoordinated movements, staggering gait, and inability to perform smooth, steady, and precise actions.
Detailed Notes
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