Download Neuronal Organization of the Cerebellar Cortex

Nervous System
Physiology
By
Dr. SHAHAB SHAIKH
PhD MD MBBS
Lecture – 8: Cerebellum
••••••••••••••••••••••••••••••••••
Faculty of Medicine
Al Maarefa Colleges of Science & Technology
CEREBELLUM
• Cerebellum - Latin for "little brain"
• Neurons found in cerebellum are approximately four times
more than that are present in the rest of brain.
2
CEREBELLAR FUNCTIONS
1) Maintenance of balance
2) Enhancement of muscle tone
3) Coordination and planning of skilled voluntary
muscle activity
4) Sequences the motor activities= also function of
premotor area= cerebrum
5) Monitors and makes corrective adjustments in the
activities initiated by other parts of the brain
6) Compares the actual motor movements with the
intended movements and makes corrective
changes.
7) The cerebellum does not initiate movement, but it
contributes to coordination, precision, and accurate
timing.= like the fun of Basal Ganglia
3
Functional Organization of the Cerebellum
Functionally cerebellum can be divided into . . .
• The Floculonodular lobe – Vestibulocerebellum
– participates mainly in balance and spatial orientation
• Intermediate zone - Spinocerebellum
– Enhances muscle tone and coordinates skilled voluntary
movements
• Lateral zone - Cerebrocerebellum
– controls sequencing movements of the muscle. Important
for timing and coordination of movement.
– Plays role in planning and initiating voluntary activity
– Stores procedural memories= learned movement
4
Neuronal Organization of the Cerebellar Cortex
Cerebellar Cortex is organized in three layers
– Molecular layer
– Purkinje cell layer
– Granular cell layer
5
Neuronal Organization of the Cerebellar Cortex
Cerebellar Cortex is organized in three layers
I. Granular layer
–
It is thick inner most layer and contains Granule cells, Golgi type II
cells and other interneurons( largest # on neuron , max neurons)
II. Purkinje cell layer (lots of dendrites, one axon)
–
–
–
It is middle layer
Contains Purkinje cells
Output is always Inhibitory(secret GABA)
III. Molecular layer
–
–
It is outermost layer
Contains stellate and basket cells, dendrites of Purkinje and Golgi
type II cells and parallel fibers (axons of granule cells)
6
Neuronal Organization of the Cerebellar Cortex
Purkinje cell:
• Purkinje cells are among the most distinctive
neurons in the brain
• The dendrites branch very profusely. The dendrites
are covered with dendritic spines which receives
synaptic input from a parallel fiber.
• Their axons travel into the
deep cerebellar nuclei.
• Purkinje cells use GABA as
their neurotransmitter, and
therefore exert inhibitory
effects on their targets.
7
Neuronal Organization of the Cerebellar Cortex
Granule cell:
• Granule cells are among the smallest neurons
in the brain.
• They are the most numerous neurons in the
brain; about 3/4 of the brain's neurons are
cerebellar granule cells.
• A granule cell receives excitatory input from
mossy fibers and inhibitory input from Golgi
cells on its ‘Dendritic Claw’.
• The axons of granule cells rise vertically to the
molecular layer, where they form parallel
fibers, synapsing with Purkinje dendrites.
• The neurotransmitter is Glutamate and is
excitatory.
8
Neuronal Organization of the Cerebellar Cortex
Three types of axons play dominant roles:
I. Mossy fibers input –
– enter the cerebellum from outside
II. Climbing fibers input – Inf Olivary nucleus
– enter the cerebellum from outside
– project to Purkinje cells and also
collaterals directly to the deep nuclei
send
III.Parallel fibers
– are the axons of granule cells present in
molevular layer
9
Neuronal Organization of the Cerebellar Cortex
Mossy fibers:
– Originate from brain
stem and spinal cord
Includes
Vestibulocerebellar,
Spinocerebellar and Pontocerebellar afferents.
– Form
excitatory
synapses
with
the
Granule cells and the
cells of the deep
cerebellar nuclei.
10
Neuronal Organization of the Cerebellar Cortex
Climbing Fibers:
– Originate from inferior olivary
nucleus of contralateral side in the
medulla.
– Gives
Collaterals
to
Deep
Cerebellar Nuclei and make
multiple synapses on Purkinje cells.
– Each Purkinje cell receives input
from exactly one climbing fiber; but
this single fiber "climbs" the
dendrites of the Purkinje cell,
winding around them and making
multiple synapses.
– Play role in cerebellar motor
learning.
11
Circuit of the Cerebellum
Thus in Summary ….
Output of the Cerebellar cortex
• Purkinje cells are the only output of the cerebellar cortex
which goes to Deep cerebellar Nuclei
• Output of the Purkinje cells is always inhibitory. the
neurotransmitter is γ- aminobutyrie acid (GABA)
• Output of the cerebellum regulates rate, range and
direction of movement.
Input to the Cerebellar cortex
• From Mossy fibers originating from brain stem and
spinal cord
• From Climbing fibers originating from Inferior Olivary
Nucleus in Medulla
12
Circuit of the Cerebellum
Explanation will be in the next slide
Deep nuclear cells receive excitatory and inhibitory inputs
Inhibitory from
Purkinje cells
Excitatory afferent
inputs from climbing
fibers and mossy
fibers
13
Circuit of the Cerebellum
What ever info is coming in (climbing or mossy)
One copy goes to nucleus of cerebellum
One copy goes to molecular layer to form parallel
fiber (analyze the info)
The result will be sending info back to nucleus will
be inhibitory
**( increase or decrease inhibition)
14
Deep Cerebellar Nuclei
• These are clusters of gray matter lying within the white
matter at the core of the cerebellum.
• These nuclei receive collateral projections from mossy
fibers and climbing fibers as well as inhibitory input from
the Purkinje cells of the cerebellar cortex.
• There are four nuclei …
1.
2.
3.
4.
Dentate: communicates exclusively with the lateral parts of the cerebellar cortex.
Globose:
Emboliform
Fastigial
• These nuclei are the sole sources of output from the
cerebellum except for the Floculonodular lobe which does
not project to the deep nuclei—its output goes to the
vestibular nuclei instead.(works like cerebellum nuclei)
15
Afferent Pathways to the Cerebellum
from the periphery …
• Dorsal spinocerebellar tract fastest neruons
in body
• transmits information mostly from muscles
spindle but also from Golgi tendon organs,
tactile, and joint receptors
• apprises the brain of the momentary status of
muscle contraction, muscle tension and limb
position and forces acting on the body surface
• Ventral spinocerebellar tract
• signals from anterior horn, and interneurons
• transmits information about which signals have
arrived at the cord
16
Peduncle
Description
SUPERIOR
The superior cerebellar peduncle is the major output = Efferent pathway of the
cerebellum. Most of the efferent fibers originate within the dentate nucleus which
in turn project to
MIDDLE
Input
This is composed entirely of afferent fibers.
INFERIOR
Output
Clinical Signs In Cerebellar Disease
**U have to know the def of each one**
• Ipsilateral control
• Drunken gait – wide based, unsteady gait
•
‫يمشي كأه سكران‬
• Nystagmus – Rhythmic, oscillating eye movements
•
‫ عيونه تتحرك بسرعة‬rapid jerky eye movement
• Hypotonia - Reduced muscle tone but no paralysis
• Dysdiadokokinesia - Inability to perform rapid
alternate
movements smoothly
‫ هنا مارح يقدر‬, ‫مثل تشوفي صرصور وتتحركي بسرعة‬
‫لما ً ا‬
• Intention tremor – tremors on activity
• Dysmetria - patients overshoots intended target
•
‫ما يقدر يحسب المسافة بين رجله واالرض‬
• Dysarthria - Scanning, slurred speech
•
‫كلم متلعثم مو مفهوم‬
18
Clinical Signs
T – ANDDD
•
•
•
•
•
•
T – Tremor (intention)
A – Ataxia
N – Nystagmus
D – Dysarthria
D – Dysdiadokokinesia
D – Dysmetria
19