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Transcript
http://www.cogsci.bme.hu/~ktkuser/KURZUSOK/BMETE47MC23/2015_2016_2/
Kognitív idegtudomány
Introduction to neurosciences for MSs.
Motor system 3
Cerebellum
Organization of the motor system
Level 3
Cerebral cortex
motor areas
Basal
Ganglia
Level 2
Thalamus
Brain Stem
Cerebellum
Spinal Cord
Sensory
receptors
Muscles
Contraction
Level 1
Cerebellum
Anatomy

Two major fissures running
mediolaterally divide the cerebellar
cortex into three primary
subdivisions:



posterolateral fissure separates
the flocculonodular lobe from the
corpus cerebelli
primary fissure separates the corpus
cerebelli into a posterior lobe and
an anterior lobe
The cerebellum is also divided
sagittally into three zones that run
from medial to lateral:



The vermis is located along the
midsagittal plane of the cerebellum.
Directly lateral to the vermis is the
intermediate zone.
lateral hemispheres are located
lateral to the intermediate zone
Cerebellar nuclei
All outputs from the cerebellum originate
from the cerebellar deep nuclei
1. fastigial nucleus: medially located.

receives input from the vermis and from cerebellar
afferents that carry vestibularproximal somatosensory,
auditory, and visual information.
projects to the vestibular nuclei and the reticular formation.
2.
interposed nuclei:
3.
dentate nucleus:
4.
vestibular nuclei:
emboliform nucleus and the globose nucleus.
Situated lateral to the fastigial nucleus.
receives input from the intermediate zone and from cerebellar afferents that carry
spinal, proximal somatosensory, auditory, and visual information.
project to the contralateral red nucleus.
lateral to the interposed nuclei.
receives input from the lateral hemisphere and from cerebellar afferents that carry information from the
cerebral cortex.
projects to the contralateral red nucleus and the ventrolateral (VL) thalamic nucleus.
in the medulla.
receive input from the flocculonodular lobe and from the vestibular labyrinth.
project to various motor nuclei and originate the vestibulospinal tracts.
Functional Subdivisions of the Cerebellum

Vestibulocerebellum:




Spinocerebellum:





flocculonodular lobe
oldest part of the cerebellum.
vestibular reflexes and in postural maintenance.
vermis and the intermediate zones
major inputs from the spinocerebellar tract.
output to rubrospinal, vestibulospinal, and reticulospinal tracts.
integration of sensory input with motor commands to produce adaptive motor
coordination.
Cerebrocerebellum:



largest functional subdivision, comprising the lateral hemispheres and the dentate
nuclei.
connections with the cortex.
planning and timing of movements, cognitive functions of the cerebellum.
Functions of cerebellum
1.
Maintenance of balance and posture:
1.
2.
Coordination of voluntary movements:
1.
3.
coordinate the timing and force of muscles groups.
Motor learning:
1.
2.
4.
postural adjustments to maintain balance.
adapting and fine-tuning motor programs
to make accurate movements through a trial-and-error process (e.g.,
learning to hit a baseball).
Cognitive functions:
1.
language.
2.
http://www.dailymotion.com/video/x1j0an_cerebellar-disease_news
Citology

Granule cells:


Purkinje cells.


receive input from mossy fibers and project to the Purkinje
cells.
the dendritic tree is flat, oriented in parallel.
Golgi cell, the basket cell, and the
stellate cell.
Cerebellar Inputs and Outputs

The cerebellum operates in 3’s:




there are 3 routes in and out of the cerebellum
there are 3 main inputs
there are 3 main outputs from 3 deep nuclei.
The 3 routes are the peduncles, or “stalks” - the rostral,
middle and caudal cerebellar peduncles.
Cerebellar Inputs and Outputs

The 3 inputs are:



mossy fibers from the spinocerebellar pathways and
mossy fibers from the pons, carrying information from the
contralateral cortex
climbing fibers from the inferior olive
Connectivity

Mossy fibers:




originate in the pontine nuclei, the spinal cord, the brainstem reticular formation, and the
vestibular nuclei,
excitatory projections onto the cerebellar nuclei and onto granule cells,
each mossy fiber innervates hundreds of granule cells.
Climbing fibers



originate in the inferior olive
make excitatory projections onto the cerebellar nuclei and onto the Purkinje cells
Each Purkinje cell receives input from a single climbing fiber,extremely powerful, excitatory
input onto Purkinje cells.
Cerebellar Efferent Pathways



To medullary and pontine regions of the brain stem –
posture and equilibrium
To thalamus (VL & VA), to cortex, to thalamus (midline),
to basal ganglia, red nucleus, & reticular formation –
coordination between agonists and antagonists
To thalamus (VL & VA) to cortex – coordination of
sequential motor actions
Cerebellar Circuits





Inputs to the cerebellar cortex (mossy and
climbing fibers) excite the deep nuclei cells as they
enter.
The output of the CBL cortex (Purkinje cell
axons) inhibits the deep nuclei cells.
Climbing fibers excite Purkinje cell dendrites.
Mossy fibers excite granule cells, whose axons
(parallel fibers) excite Purkinje cell dendrites.
Deep nuclei cells and Purkinje cells fire tonically.
Cerebellar Circuits
Cerebellar circuits
Basket cell
Stellate cell
4.
Paralell fibers
Golgi cell
3.
6.
5.
Purkinje cell
2.
Granulate cell
Deep
cerebellar
nuclei cells
Mossy fibers
Climbing fibers
1.
Spinal ch.,Vest. nuclei, cerebrum
Motor output
nucl. olivaris inferior
kollaterals
The Cerebellum - Claude Ghez W. Thomas Thach
SZENTÁGOTHAI JÁNOS ÉS A KISAGYKUTATÁS
Hámori József
Cerebellum anatomy
The Cerebellum - Claude Ghez W. Thomas Thach
SZENTÁGOTHAI JÁNOS ÉS A KISAGYKUTATÁS Hámori József
Diseases of the motor system




Lower syndrome
Upper motor syndrome
Damages of the Basal ganglia
Cerebellar damages
Lower motor syndrome


1.
2.
3.
4.
5.
6.
lower motor neurons refer to alpha motor neurons in the spinal cord and
brain stem
arises from certain diseases that selectively affect alpha motor neurons
(such as polio)
Muscle atrophy. (decrease in the mass of the muscle)
Weakness.
Fasciculation. spontaneous action potentials, visible twitch (called a
fasciculation)
Fibrillation. generate spontaneous action potentials; causing individual
muscle fibers to contract, called a fibrillation.
Hypotonia. (low muscle tone)
Hyporeflexia. (below normal reflexes)
Upper syndrome


1.
2.
3.
4.
above the level of alpha motor neurons
stroke, tumors, and blunt trauma
Weakness. graded weakness of movement (paresis), which differs from the
complete loss of muscle activity caused by paralysis (plegia).
Hypertonia:. increased firing rate of alpha and/or gamma motor neurons.
Hyperreflexia:
Clonus: stretch reflex is so strong that the muscle contracts a number of
times in a 5-7 Hz oscillation when the muscle is rapidly stretched and then
held at a constant length.
5.
Initial contralateral flaccid paralysis:
contralateral side of the body shows a flaccid paralysis.
6.
Spasticity:
velocity dependent resistance to passive movement of the limb,
7.
Babinski sign.
normal in infants for the first 2 years of life.
Paralysis: damage occurs at the cervical level,
 all four limbs will be paralyzed (quadriplegia).
 If the damage occurs below the cervical enlargement, then only the legs
are paralyzed (paraplegia).
 Other terms used to describe patterns of paralysis are hemiplegia
(paralysis to one side of the body)
 monoplegia (paralysis of a single limb).
Disorders of the basal ganglia

Dyskinesias
1.
Resting tremors:
Parkinson’s disease.
4-7 Hz tremor “pill-rolling tremor.”
The tremor stops when the body part engages in active movement.
https://www.youtube.com/watch?v=0-t4RTQ0EsM
2.
Athetosis:
is characterized by involuntary, writhing movements, especially of the hands and face.
https://www.youtube.com/watch?v=J_wIDm1_ax4
3.
Chorea:
continuous, writhing movements of the entire body
Huntington’s disease.
4.
Ballismus:
involuntary, ballistic movements of the extremities.
http://www.dailymotion.com/video/x1j0an_cerebellar-disease_news
5.
Tardive dyskinesia:
involuntary movements of the tongue, face, arms, lips, and other body parts;
https://teddybrain.wordpress.com/2013/01/18/differences-between-choreaathetosis-and-ballismus/
Disorders of the basal ganglia II.

Akinesias
1.
Rigidity:
resistance to passive movement of the limb,
does not depend on the speed of the passive movement.
2.
Dystonia:
involuntary adoption of abnormal postures, as agonist and antagonist muscles both
contract and become so rigid that the patient cannot maintain normal posture.
3.
Bradykinesia:
slowness, or poverty of movement.
Direct and indirect pathways
The direct pathway travels from the striatum (GABA) directly
to the internal segment of the globus pallidus or the substantia
nigra pars reticulata.The isgp and the snpr project inhibitory
(GABA) synapses to the thalamus. Result: Excitation of the
thalamus -> excitation of the motor cortex -> movement
excitation
((-1)+(-1)=+1))
 The indirect pathway takes a detour from the striatum,
(GABA) first to the external segment of the globus pallidus
(GABA) and then to the subthalamic nucleus (Glu), before
finally reaching the internal segment of the globus pallidus or
the substantia nigra pars reticulata. The isgp and the snpr
project inhibitory (GABA) synapses to the thalamus. Result:
Inhibition of the thalamus -> inhibition of the motor cortex ->
movement inhibition.
((–1)(–1) (+1) (–1) = –1).

Direct- and indirect pathways
Disorders of the basal ganglia






Parkinson disease:
1.
Slowness or absence of movement (bradykinesia or akinesia)
2.
Difficulty in initiating a movement
3.
Rigidity
4.
Resting tremor
Loss of dopaminerg neurons in the substantia nigra pars compacta
projects to both direct pathway and indirect pathways neurons in the
striatum;
excites the direct pathway - to excite motor cortex,
inhibits the indirect pathway- to inhibit motor cortex.
The loss of the nigrostriatal dopaminergic pathway upsets the fine balance
of excitation and inhibition in the basal ganglia and reduces the excitation
of motor cortex.

Treatement:
 L-dopa: precursor of dopamin; temporary, and typically symptoms return
after a number of years
 lesions to the globus pallidus internal segment (pallidotomy)
 deep brain stimulation of the subthalamic nucleus
 https://www.youtube.com/watch?v=_L_WF6gv5BI

Huntington disease:
genetic disorder that is caused by an abnormally large number of repeats of the
nucleotide sequence CAG on chromosome 4
effect of the mutation: loss of the indirect pathway neurons in the striatum,
particularly in those of the caudate nucleus. Removal of inhibition from the
external segment of the globus pallidus, allowing it to inhibit the subthalamic
nucleus. Inhibition of the subthalamic nucleus produces a situation similar to a
lesion of the subthalamic nucleus.
Symptoms:
1. Choreidoform movements (involuntary, continous movements)
2. advanced stages is associated degeneration of both pathways and with
dementia



the excitatory effect of the direct pathway is no longer kept in check by the
inhibition of the indirect pathway.
 Motor cortex gets too much excitatory input from the thalamus, sending
involuntary movement commands to the brain stem and spinal cord.
 Inappropriate motor programs are not inhibited normally.
 No treatment
https://www.youtube.com/watch?v=HOalYWvVLU8
 Hemiballismus:
 unilateral lesion to the subthalamic nucleus, usually caused by a stroke
(problems just on the contralateral side)
 Symptoms:
 involuntary, ballistic movements
 Treatment: surgical
https://www.youtube.com/watch?v=hqg2GTUq1k4

Cerebellar syndrome
1.
Ataxia: general impairments in movement coordination and accuracy
Disturbances of posture: lesions to the vestibulocerebellum.
difficulty in maintaining posture.
Decomposition of movement: loss of the cerebellum’s ability to coordinate the activity and
timing of many muscle groups to produce smooth, fluid movements.
2.
Dysmetria:
inappropriate force and distance that characterizes target-directed movements.
3.
Dysdiadochokinesia:
inability to perform rapidly alternating movements, such as rapidly pronating and supinating
the hands and forearms.
4.
Scanning speech:
staccato nature of speech, difficulty in coordinating these muscle groups appropriately,
speech is slow and disjointed.
5.
Hypotonia:
Cerebellar syndrome II.
1.
Intention tremor:
increasingly oscillatory trajectory of the limb in a target-directed movement
Note that this tremor contrasts with the resting tremor of Parkinson’s disease.
2.
Nystagmus:
Vestibulocerebellum damage
https://www.youtube.com/watch?v=phpe_RVGqcA
3.
Delay in initiating movements:
take longer to initiate movements,
often because they must actively plan sequences of movements that are performed
effortlessly by normal individuals.
4.
Cognitive deficits:
impaired ability to estimate time intervals.
Born without cerebellum
- The woman’s (24) condition was discovered after she
sought medical attention due to nausea and vertigo. CT
scans and MRI images revealed the missing cerebellum,
which readily explains why those symptoms would be
present.
- wasn’t able to speak until she was six
- wasn’t able to walk until age seven. She had never been
able to play and jump like normal kids due to this
defect.
- had been unable to walk steadily without support
- No trouble understanding vocabulary, but the missing
cerebellum caused her to have difficulties with
pronunciation. Her voice trembles, words are slurred,
and the doctors described her voice tone as “harsh.
- pons appeared underdeveloped
http://brain.oxfordjournals.org/content/early/2014/08/22/brain.awu239
Over-Simplified Summary




Motor cortex – initiation of movements
Brain stem centers – balance of excitation and
inhibition of antigravity muscles; integration of
vestibular information
Basal ganglia – posture and planning and coordination
of motor action
Cerebellum – equilibrium; coordination of motor
action based on sensory information and feedback
Literature



Fonyó: Élettan orvosoknak
Ádám – Fehér szerk.: Élettan biológusoknak
James Knierim’s notes, Johns Hopkins University