Transcript 3cf1482f14bbaf7x

MOTOR AREAS
EXTRAPYRAMIDAL SYSTEM
Definition:
Tracts other than corticospinal tract are
Known as extrapyramidal tracts.
The word extrapyramidal is slowly being
replaced by Corticonuclear &
corticobulbar tracts.
Components of extrapyramidal system
1. Basal Ganglia
2. Midbrain giving rise to following bulbospinal tracts:
A.
B.
C.
D.
E.
Rubrospinal tract.
Vestibulospinal Tract.
Reticulospinal Tract
Tectspinal Tract.
Olivospinal Tract.
Descending Spinal Pathways
extrapyramidal system
- Coordination of head &
eye movements,
- Coordinated function of
trunk & extremity
musculature to maintaining
posture and balance
- Synapse in some
intermediate nucleus rather
than directly with lower
motor neurons
Reticulospinal Tract
The reticular formation makes up a central core
through much of the brainstem. It contains many
different nuclear groups.
Pontine and medullary nuclei projects to the anterior
horn of the spinal cord.
Functions: influence motor functions as for example
voluntary & reflex movement and is also responsible
for the muscle tone.
Olivospinal Tract
It arises in the cells of inferior olive of the
medulla and is found only in the cervical region
of the spinal cord.
Function is unknown.
Role of the brain stem
Support of the Body Against Gravity.
Roles of the Reticular and Vestibular
nuclei.
1- The vestibular nuclei:
Selectively control the excitatory signals to the different
antigravity muscles (the muscles of vertebral column and
the extensor muscles of the limbs).
to maintain equilibrium in response to signals from the
vestibular apparatus.
2- The medullary reticular system:
Transmit inhibitory signals to the same antigravity anterior
motor neurons (medullary reticulospinal tract).
So that under normal conditions, the body muscles are
normally tense.
Functions of the Cerebellum
Anterior and posterior lobes govern subconscious aspects
of skeletal muscle movements.
Flocculondular lobe on inferior surface contributes to
equilibrium and balance.
Main functions:
Cerebellum evaluates movements
•
smoothes movements
•
corrects errors
•
coordinates sequence
•
regulates posture and balance
•
makes possible all skilled muscular activities
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Table 13.2 part 3
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BASAL GANGLIA AND CONTROL OF MOTOR
FUNCTIONS
BASAL GANGLIA
THE BASAL GANGLIA ARE MASSES OF GREY MATTER
MADE OF CELL BODIES LYING DEEP INSIDE THE WHITE
MATTER OF THE CEREBRUM, AND MAKES UP PART
OFTHE MIDBRAIN.
An upper mass is called the caudate nucleus, is
separated from a lower mass, the lentiform
nucleus. The lentiform nucleus consists of the
putamen and the globus pallidus.
Other nuclei include the substantia
nigra and subthalamic nucleus.
Basal
Nuclei
Caudate
Nucleus
Lenticular
Nucleus
Corpus
Striatum
Putamen
Globus Pallidus
Subthalamic Nucleus
Substantia Nigra
Connections for Motor Control
Functions of Basal Ganglia
• Control of movements
• Planning and programming of movements
• Cognition
The Putamen Circuit
Executes Learned Patterns of Motor Activity
Basal ganglia function in association with the corticospinal
system to control complex patterns of motor activity.
Examples are:
– writing of letters of the alphabet.
– cutting paper with scissors,
– hammering nails,
– shooting a basketball through a hoop,
– passing a football,
– throwing a baseball,
– the movements of shoveling,
– most aspects of vocalization,
– controlled movements of the eyes
– virtually any other of our skilled movements, most of them
performed subconsciously.
The Caudate Circuit
Cognitive Control of Sequences of Motor Patterns:
Cognition means the thinking processes of the brain, using both
sensory input to the brain plus information already stored in memory.
Thoughts are generated in the mind by a process called cognitive
control of motor activity.
Example:
A person seeing a lion approach and then responding instantaneously
and automatically by:
(1) turning away from the lion,
(2) beginning to run, and
(3) even attempting to climb a tree.
Thus, cognitive control of motor activity determines subconsciously,
and within seconds, which patterns of movement will be used together
to achieve a complex goal.
The Caudate Circuit
Change the Timing and to Scale the Intensity of Movements.
Two important capabilities of the brain in controlling
movement are:
(1) to determine how rapidly the movement is to be
performed and
(2) to control how large the movement will be.
For instance, a person may write the letter "a" slowly or
rapidly. Also, he or she may write a small "a" on a piece of
paper or a large "a" on a chalkboard. Regardless of the choice,
the proportional characteristics of the letter remain nearly the
same.
Movement Disorders
Hyperkinetic
•Hemiballismus
•Huntington’s
Disease
•Athetosis
Hypokinetic
•Parkinson’s Disease
•Drug Induced (Neuroleptics, MPTP)
Parkinson’s Disease
PD
Loss of dopamine-generating
cells
normal
Parkinson’s Disease
Substantia Nigra,
Loss of DOPAminergic
Neurons
Clinical Feature (1)
Slowness of Movement
- Difficulty in Initiation and Cessation
of Movement
Parkinson’s Disease
Clinical Feature (2)
Resting Tremor
Parkinsonian Posture
Rigidity-Cogwheel Rigidity
Parkinson’s Disease
• Described by James Parkinson
• Degeneration of dopamine-generating cells in the
substantia nigra (60-80 %).
• Five cardinal features
– Tremor
– Rigidity
– Akinesia & Bradykinesia
– Postural Changes
– Speech Changes
Huntington’s Disease
•
•
•
•
Hereditory , autosomal dominant
Rare onset at 30-40s as early as 20s
Disease of caudate & putamen.
Early, Jerky movement of hands toward end of
reaching an object
• Later, hyperkinetic choreiform movements appear
and gradually increase until they incapacitate the
patient
• Slurred speech and incomprehensive
• Progressive Dementia