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Cerebellum Overview

Coordination and stability of body parts in both static & dynamic conditions

Comparison of intention with performance of motor actions

Toning (adjusts status of muscles to ensure sufficient accuracy & stability for accomplishing discrete/skilled motor tasks)

Cerebellar Functions

Equilibrium
Muscle Tone
Stretch Reflex
Motor Planning
Execution of Movement

Lobes of the Cerebellar Cortex

ANTERIOR - Rostral to the Primary Fissure
POSTERIOR - Region between the Primary and Posterolateral Fissures
FLOCCULONODULAR - Structures Ventral to the Posterolateral Fissures

Lobules

There are 10 (I-X)

Folia

Small Gyri on the tips of each Lobule

Tonsils

Rounded structures on the Inferior Surface Cerebellum flanking the Nodulus

Vermis

C-shaped Midline structure of the Cerebellum that separates the Hemispheres

Surroundings of the Cerebellum

BRAINSTEM - Connected Ventrally via Cerebellar Peduncles
4TH VENTRICLE - Forms the Dorsal Roof of the 4th Ventricle and Cerebral Aqueduct
SUBARACHNOID SPACE- Filled with CSF and surrounds the rest of the Cerebellum

Cerebellar Peduncles

SUPERIOR - Connects Cerebellum to the Midbrain
MIDDLE - Connects Cerebellum to the Pons
INFERIOR - Connects Cerebellum to the Medulla

Blood Supply to the Cerebellum

Supplied by Three Pairs of Arteries arising from the Basilar/Vertebral Artery: PICA, AICA and SCA

PICA & Cerebellum

Arises form the Vertebral Arteries

SUPPLIES: Dorsolateral Medulla, Inferior Vermis and Caudal Hemispheres and Tonsils

AICA & Cerebellum

Arises from Proximal Basilar Artery and gives out Internal Auditory Arteries to the Inner Ears

SUPPLIES: Flocculus and Adjacent Area

SCA & Cerebellum

Arises from Distal Basilar Artery

SUPPLIES: Rostroventral and Dorsolateral Hemispheres, Rostral and Ventral Vermis, Deep Nuclei, Paravermis, Peduncles and Tectum of Lower Midbrain

Three Parts of Cerebellum (In Terms of Phylogenesis)

Archicerebellum
Paleocerebellum
Neocerebellum

Archicerebellum - Parts, Development and Functions

INCLUDES: Flocculus, Nodulus and Lingula
DEVELOPMENT: Developed in parallel to the Vestibular Organs
FUNCTIONS: Equilibrium, Stance and Gaze Control

Turtle

Paleocerebellum - Parts, Development and Functions

INCLUDES - Anterior Vermis, Pyramids and Uvula
DEVELOPMENT: Developed in parallel to the Vertebral Spine
FUNCTION: Propulsive and Trunk and Limb Movements

Fish

Neocerebellum - Parts, Development and Functions

INCLUDES - Hemispheres and Middle Vermis
DEVELOPMENT: Developed in parallel to the Cerebral Neocortex
FUNCTION: Fining tuning and coordination of movement, including fingers and toes

Higher Animals

Layers of Cerebellar Folium (Cortex)

Molecular Layer
Purkinje Cell Layer
Granule Cell Layer

Molecular Layer - Layer, Cell Types

LAYER: Outer
CELL TYPES: Stellate and Basket Cells (Inhibitory), Purkinje Cell and Golgi Cell Dendrites, Parallel Fibers of Granule Cells

Purkinje Cell Layer - Layer, Cell Types

LAYER: Middle
CELL TYPES: One layer of Purkinje Cells

Granule Cell Layer - Layer, Cell Types

LAYER: Inner
CELL TYPES: Granule Cells (Excitatory), Golgi Cells (Inhibitory) and Glomeruli

This layer contains more neurons than the entire Cerebral Cortex

White Matter of Cerebellar Folium

Located underneath the Granule Cell Layer

Cell Types of Cerebellar Cortex (Just a Hot Pic)

Purkinje Cells

DENDRITES - Molecular Layer, receive input from Climbing Fibers and Parallel Fibers
CELL BODY - Purkinje Cell Layer
AXONS - Only cell type to project through the Granule Cell Layer and act as Efferent signals from the Cerebellum (IMPORTANT)

Cerebellar Output (Important)

Is composed completely of Purkinje Cell Axons that use GABA as transmitter; therefore Cerebellar Output is Inhibitory

Granule Cells

Project axons from the Granule Layer to the Molecular Layer which then form the PARALLEL FIBERS.

Receive excitatory inputs from Mossy Fibers

They are excitatory neurons (Glutamate)

Golgi Cells

Cell bodies are located in the Granule Cell Layer and Dendrites in the Molecular Layer. These Dendrites are excited by Granule Cells, and resulting Axonal projection functions to INHIBIT the Granule Cells within the Molecular Layer.

(Feedback Inhibition, GABA)

Stellate and Basket Cells

Interneurons within the Moelcular Layer.

Excited by Parallel fibers and form Inhibitory Synpases on the Dendrites of Purkinje Cells within the Molecular Layer.

Mossy Fibers

90% of Afferent Fibers to the Cerebellum, ALL ARE EXCITATORY

Spinal Cord, Vestibular Nerve, Pontine Nuclei → Form Glomeruli that synapse on Granule Cell Bodies/Dendrites of Granular Layer

Climbing Fibers

10% of Afferent Fibers to the Cerebellum

Contralateral Inferior Olivary Nucleus → 10 Purkinje Cell Dendrites of Molecular Layer

ALL FIBERS ARE EXCITATORY, but have stronger power than Mossy Fibers.

Involved in "Error Detection & Correction"

Parallel Fibers

Axons of the Granule Cells that are in the Molecular Layer. They receive Excitatory Input from Mossy Fibers and have several outputs:

PURKINJE CELLS - Each fiber activates several
STELLATE AND BASKET - Inhibitory Interneurons activated by Parallel Fibers

*This means that of all the Purkinje Cell activated by Parallel Fibers, only some remain activated, while the rest are inhibited by Stellate/Basket

Aminergic Afferents

Modulatory fibers from:

RAPHE NUCLEI - Use Serotonin (5-HT)
LOCUS CERULEUS - Use Norepinephrine (NE)

Both have terminations in almost all layers

Glomerulus

A bulbous expansion of distal Mossy Fibers that form Excitatory synapses on Granule Cell Dendrites within the Granular Layer.

These Dendrites are also under Inhibitory influences from Golgi Cells, however, that curb the excitement.

Deep, Paired Nuclei of Cerebellum

Fastigial, Interposed (Globose & Eboliform), Dentate, Vestibular

Fastigial Nuclei

Associated with the Vestibular Cerebellum and Spinocerebellum

FUNCTION: Antigravity & postural maintenance in standing & walking (axial muscles), modulation of saccade & smooth pursuit

Interposed Nuclei

Consists of Globose and Emoliform Nuclei

Associated with Spinocerebellum

FUNCTION: Modulation of stretch reflex (distal muscles)

Dentate Nuclei

Largest Cerebellar Nuclei

Associated with Cereberocerebellum

FUNCTION: Initiation & control (fine toning) of volitional motor activities (programming & planning)

Vestibular Nuclei

Located in the Medulla but descendant from the Cerebellum

Associated with Vestibulocerebellum

FUNCTION: Static & dynamic stabilization of gaze & posture

Inferior Cerebellar Peduncle (ICP)

All fibers are incoming EXCEPT the Cerebellobulbar Tract, which are output fibers from the Cerebellum to the ipsilateral Vestibular Nuclei

Incoming Fibers:
-Primary Vestibular Afferents
-Vestibulocerebellar Projection
-Olivocerebellar Tract
-Dorsal Spinovestibular Tracts
-Afferents from Brainstem Reticular Formation

Dorsal Spinovestibular Tracts

Fastest conducting system in the entire CNS that concerns inputs from Muscle Spindles

From Clarke's Nucleus & Accessary Cuneate Nucleus

Middle Cerebellar Peduncle (MCP)

All fibers are incoming from Contralateral Pontine Nuclei to Neocerebellar Cortices

Superior Cerebellar Peduncle (SCP)

All fibers are outgoing EXCEPT the Spinocerebellar Tract carrying information from Golgi Tendon Organs to Vermis
-ONLY tract that enters cerebellum via SCP

Contains all Cerebellar output fibers except Cerebellobulbar Tract

Feedback Loops of Cerebellum

Cerebellum-Cerebellum Loop (Triangle of Guillian-Mollaret, Cerebellum-SC Loop) & Cerebrum-Cerebellum Loop

ALL HAVE DOUBLE DECUSSATIONS

Triangle of Guillian-Mollaret Loop

Purkinje Cells of Cerebellum → Dentate Nucleus → Decussation to Contralateral Red Nucleus of Midbrain → Inferior Olivary Complex (via Central Tegmental Tract) → Decussation of Climbing Fibers (Back to Purkinje Fibers)

Feedback Loop terminates in the same portion of the Cerebellum as where it began

Cerebellum-Spinal Cord Loop

Purkinje Cells of Cerebellum → Dentate Nucleus → Decussation to Contralateral Red Nucleus of Midbrain → Brainstem (via Rubrospinal Tract) → Decussation to the Contralateral Spinal Cord → Cerebellum

Feedback Loop terminates in the same portion of the Cerebellum as where it began

Cerebellum-Cerebrum

Purkinje Cells of the Cerebellum → Dentate Nucleus → Decussation to Contralateral Thalamus → Cerebral Cortex → Pons via Cerebrobulbar Tract → Decussation to Cerebellum

Feedback Loop terminates in the same portion of the Cerebellum as where it began

Cerebellar Double Crossings (Important)

All loops have Double Decussations, so that when you have a Cerebellar Lesion, all symptoms will be localized IPSILATERALLY.

Functional Parts of the Cerebellum

Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum

Vestibulocerebellum Territory

Includes Nodulus and Bilateral Flocculi

Vestibulocerebellum Phylogenesis, Inputs, Outputs, Functions and Lesion

PHYLOGENESIS: Archicerebellum

INPUTS: Primary & secondary vestibular inbuts

OUTPUTS: Purkinje Cells → Bilateral vestibular nuclei, contralateral cerebellum, brainstem reticular formation

FUNCTIONS: Maintenance of equilibrium, gaze stabilization, posture control

LESION: Distorted equilibrium (astasia, abasia, ataxia, nystagmus, tendency of falling)

Spinocerebellum Territory

Includes Vermis and Intermediate Hemispheres

Spinocerebellum Phylogenesis, Inputs, Outputs, Functions and Lesion

PHYLOGENESIS: Paleocerebellum

INPUTS: Dorsal & ventral spinocerebellar tracts, cuneocerebellar tracts (Ia fibers from Golgi organs & muscle spindles)
-Others: auditory, visual, vestibular, cerebral

OUTPUTS:
-Purkinje Cells (Vermis) → Fastigial Nucleus → Lateral vestibular nucleus, contralateral ventrolateral thalamus & brainstem reticular formation
-Purkinje Cells (Paravermian Hemispheres) → Interposed Nuclei → Contralateral red nucleus & Contralateral ventrolateral thalamus

FUNCTIONS: Axial & proximal muscle tone; control stretch reflexes

LESION: IPSILATERAL truncal & limb ataxia, gait disturbance, scanning speech

Cerebrocerebellum Territory

Lateral Cerebellar Hemispheres

Cerebrocerebellum Phylogenesis, Inputs, Outputs, Functions and Lesion

PHYLOGENESIS: Neocerebellum

INPUTS: Corticopontocerebellar Tract, Olivocerebellar Tract (climbing fibers)

OUTPUTS: Dentatorubrothalamic Tract

FUNCTIONS: Receives cerebral planning about voluntary movement in advance, compares planned * actual motion, and modulates pyramidal & extrapyramidal actions to ensure the precision & smoothness of complex motion

LESION: DISTAL ataxia, dysmetria, asynergia, dysdiadochokinesia, intention tremor, hypotonia, delay in initiation of motor task, inability to estimate weight

Cerebellar Lesion Symptoms

Dizziness (Vertiginous or Non-Vertiginous)
Vertigo
Impiared Eye Control
Gait Disturbance
Difficulty in Coordination

Vertigo

Illusive Perception of Motion. Results from a mismatch of predicted pattern of movement to the real status

Mismatch may occur at any level of the peripheral & central vestibular systems, while the vestibular nucleus is the fundamental structure involved

Cerebellar Lesion Signs

Nystagmus
Ataxia
Dysequilibrium
Abnormal Stance

Nystagmus

Eye jerks- many different types

Many show fast & slow beating phases (direction of fast phase is used to name direction of nystagmus)

Ataxia

A difficulty in performing a voluntary/involuntary motor task in a coordinated manner

Caused by defected execution of intended motor action with abnormalities in direction, speed, stability & accuracy

Vestibulocerebellum Signs and Symptoms

Functions - Functions - Signs & Symptoms

Spinocerebellum Signs and Symptoms

Functions - Functions - Signs & Symptoms

Cerebrocerebellum Signs and Symptoms

Functions - Functions - Signs & Symptoms

Causes of Cerebellar Lesions

Congenital Malformations
Idiopathic and Hereditary Diseases
Trauma and Vascular Lesions
Tumors
Infections
Paroxysmals
Neurotoxicity
Metabolic, Endocrine, and Nutritional Disorders
Inflammatory and Autoimmune Diseases
Non-neurological Causes

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