Cerebellum

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)

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"

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

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.

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

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

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

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

Cerebellar Double Crossings (Important)

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

Three Parts of Cerebellum (In Terms of Phylogenesis)

Archicerebellum Paleocerebellum Neocerebellum

PICA & Cerebellum

Arises form the Vertebral Arteries SUPPLIES: Dorsolateral Medulla, Inferior Vermis and Caudal Hemispheres and Tonsils

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

AICA & Cerebellum

Arises from Proximal Basilar Artery and gives out Internal Auditory Arteries to the Inner Ears SUPPLIES: Flocculus and Adjacent Area

Fastigial Nuclei

Associated with the Vestibular Cerebellum and Spinocerebellum FUNCTION: Antigravity & postural maintenance in standing & walking (axial muscles), modulation of saccade & smooth pursuit

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

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

Vermis

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

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)

Feedback Loops of Cerebellum

Cerebellum-Cerebellum Loop (Triangle of Guillian-Mollaret, Cerebellum-SC Loop) & Cerebrum-Cerebellum Loop ALL HAVE DOUBLE DECUSSATIONS

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

Interposed Nuclei

Consists of Globose and Emoliform Nuclei Associated with Spinocerebellum FUNCTION: Modulation of stretch reflex (distal muscles)

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 Lesion Symptoms

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

Cerebellar Functions

Equilibrium Muscle Tone Stretch Reflex Motor Planning Execution of Movement

Nystagmus

Eye jerks- many different types Many show fast & slow beating phases (direction of fast phase is used to name direction of nystagmus)

Dorsal Spinovestibular Tracts

Fastest conducting system in the entire CNS that concerns inputs from Muscle Spindles From Clarke's Nucleus & Accessary Cuneate Nucleus

Deep, Paired Nuclei of Cerebellum

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

Cerebrocerebellum Signs and Symptoms

Functions - Functions - Signs & Symptoms

Spinocerebellum Signs and Symptoms

Functions - Functions - Signs & Symptoms

Vestibulocerebellum Signs and Symptoms

Functions - Functions - Signs & Symptoms

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

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

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

Vestibulocerebellum Territory

Includes Nodulus and Bilateral Flocculi

Spinocerebellum Territory

Includes Vermis and Intermediate Hemispheres

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.

Cerebellar Output (Important)

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

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*

Purkinje Cell Layer - Layer, Cell Types

LAYER: Middle CELL TYPES: One layer of Purkinje Cells

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

Dentate Nuclei

Largest Cerebellar Nuclei Associated with Cereberocerebellum FUNCTION: Initiation & control (fine toning) of volitional motor activities (programming & planning)

Cerebrocerebellum Territory

Lateral Cerebellar Hemispheres

Vestibular Nuclei

Located in the Medulla but descendant from the Cerebellum Associated with Vestibulocerebellum FUNCTION: Static & dynamic stabilization of gaze & posture

White Matter of Cerebellar Folium

Located underneath the Granule Cell Layer

Aminergic Afferents

Modulatory fibers from: RAPHE NUCLEI - Use Serotonin (5-HT) LOCUS CERULEUS - Use Norepinephrine (NE) Both have terminations in almost all layers

Layers of Cerebellar Folium (Cortex)

Molecular Layer Purkinje Cell Layer Granule Cell Layer

Cerebellar Lesion Signs

Nystagmus Ataxia Dysequilibrium Abnormal Stance

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)

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

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

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)

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

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-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

Tonsils

Rounded structures on the Inferior Surface Cerebellum flanking the Nodulus

Cerebellar Peduncles

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

Folia

Small Gyri on the tips of each Lobule

Blood Supply to the Cerebellum

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

Lobules

There are 10 (I-X)

Functional Parts of the Cerebellum

Vestibulocerebellum Spinocerebellum Cerebrocerebellum