Transcript The Motor System and Its Disorders

The Motor System and
Its Disorders
Lecture 3
Lecture Outline:
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Overview and major pathways
Cerebellum
 Cerebellar atrophy videos
Basal Ganglia
 Hyperkinetic disorders
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Hypokinetic disorder
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Huntington’s chorea
Tourette’s
Tardive Dyskinesia
Parkinson’s Disease - videos
Cortex
 Primary motor
 Premotor, supplementary motor, prefrontal
 Parietal cortex
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Apraxia(s)
Motor Control
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Behaviour is observable motor
output by the organism
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Sitting, writing, speaking, eating,
typing, running, playing, having
sex etc.
These different behaviours are
executed by different aspects
of the motor system
Some motor functions are
automatic (e.g., breathing,
eating, sex), while others
require a lot of practice and
effort (e.g., playing a piano)
Steps in Motor Action
Muscles
4 Major Motor Pathways
1.
2.
Corticospinal (cortex
to spinal cord)
a) Lateral – distal limb
muscles (fine
manipulations)
b) Ventral – trunk and
upper leg muscles
(posture/locomotion)
Corticobulbar (cortex
to pons, 5th, 7th, 10th
and 12th cranial nerves)
– control of face and
tongue muscles; upper
face both contralateral,
lower face contralateral
Major Motor Pathways
3.
4.
Ventromedial (brain
stem to spinal cord) –
trunk and proximal limb
muscles (posture,
sneezing, breathing,
muscle tone)
Rubrospinal (red
nucleus to spinal cord)
– modulation of motor
movement (limb
movement independent
of trunk movement)
Cerebellum
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Vermis
Intermediate zone
Lateral zone
Within are deep
cerebellar nuclei:
 Fastigial nucleus
 Interpositus
nucleus
 Dentate nucleus
Vermis
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Kinesthetic and
somatosensory inputs
from the spinal cord
projections to fastigial
nucleus
Damage interrupts
posture and walking
In monkeys, unilateral
lesions of the fastigial
nucleus cause the
monkeys to fall
(ipsilateral side)
Intermediate Zone
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Inputs from red nucleus (brain
stem & motor cortex) and
somatosensory info from the
spinal cord
Projects to interpositus
nucleus  red nucleus (loop)
Damage produces rigidity and
difficulty in moving limbs
Action tremor or intention
tremor – a tremor causing
movement to occur in a
staggered manner during
motor act.
Lateral Zone
Inputs from motor and
association cortices
(through pons)
 Projections to dentate
nucleus  primary
motor and premotor
cortex
1. Balistic movement –
movement that occurs
so quickly that it can not
be modified by feedback
 E.g., swinging of a
batter trying to hit a ball
moving 140 km/h
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Lateral Zone
2. Multijoint movements
3. Learning of new movements
4. Timing of motor movements
(and cognitive functions)
Basal Ganglia
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Unlike the cerebellum, which
plays a role in rapid balistic
movements, the basal ganglia
are more important for the
accomplishment of movements
that may take some time to
initiate or stop
Important for internal guiding
(rather then external) of
movement
Dopamine – nigrostriatal
pathway
Basal Ganglia
Damage to the basal ganglia:
 Produces either too much activation
(hyperkinetic) responses= twitches,
movements bursts, jarring, etc.
 Huntington’s Chorea-dominant gene
based, increases glutamate in
striatum which destroys GABA
neurons in BG and loss of inhibition
 No cure
 Tourette’s
OR
 Produces too little force
(hypokinetic)=rigidity
 Parkinson’s disease
Pink=inhibition
Blue=excitation
Hyperkinetic Disorder
Huntington’s Chorea
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Genetic disorder associated with
intellectual deterioration and
abnormal movements
The symptoms appear from 30 to
50 years of age
Initially the person shows small
involuntary movements that look
like fidgeting
These symptoms increase until
they are incessant  usually
involve whole limbs
Eventually the movements
become uncontrollable and affect
the head, face, trunk and limbs
Pink=inhibition
Blue=excitation
Hyperkinetic Disorder
Tourette’s Syndrome
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1.
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Three stages:
Only multiple tics (twitches of the face, limbs or the
whole body)
Inarticulate cries are added to multiple tics
Emission of articulate words with echolalia –
repeating what others have said or done – and
coprolalia – uttering of obscene words – are added
in this stage
Onset is typically 2-15 years of age
Drugs that block dopamine (e.g., haloperidol)
ameliorate the disorder
Hyperkinetic Disorder
Tardive Dyskinesia
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Occurs in 20-40% of individuals who are long time (at least 3
months) users of conventional antipsychotics
Conventional or classic antipsychotics (e.g., haloperidol) block
dopamine receptors
Symptoms include:
 Chorea
 Tics
 Akathisia – compulsive, hyperactive, and fidgeting movements of
the legs
 Dystonia – painful, sustained muscle spasms of the same muscle
groups frequently causing twisting and repetitive movements and
abnormal postures
Possible causes are supersensitivity of dopamine neurons after
prolonged suppression
Atypical antipsychotics are good at suppressing psychoses and
they have fewer motor side effects
Hypokinetic Disorder
Parkinson’s Disease
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0.1-1.0% of the population
Incidence rises in older population
Degeneration of neurons in substantia nigra
and to the loss of the neurotransmitter
dopamine
Symptoms:
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2.
Positive – abnormal behaviours not seen in intact
individuals
Negative – absence of normal behaviours
Hypokinetic Disorder
Parkinson’s Disease
POSITIVE SYMTOMS
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Tremors at rest
Muscular rigidity –
simultaneously increasing the
muscle tone in both extensor
and flexor muscles.
Involuntary movements –
akatheisia –motor
restlessness, ranging from a
feeling of inner disquiet to an
inability to sit or lie quietly
NEGATIVE SYMTOMS
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Abnormal posture
Abnormal righting – difficulties in
achieving a standing position
Abnormal locomotion – difficulty
initiating stepping Festination –
tendency to engage in behavior at
faster and faster speeds.
Aprosodia – Lack of emotional
tone in speech and
comprehension of emotional tone
Akinesia – absence of movement
(e.g., blank facial expressions, lack
of blinking)
Bradykinesia – slowness of
movement
Hypokinetic Disorder
Parkinson’s Disease - Causes
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3.
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Idiopathic – cause not known
Postencephalitic – “sleepy sickness” – 1916-1917
 vanished by 1927  see Oliver Sack in
Awakenings
Drug induced (e.g., major tranquilizers, MPTP –
contaminant in heroin – is toxic to dopamine
neurons)
Treatments: L-dopa  dopamine precursor
video
Cortex
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Externally guided
movements – those
requiring sensory
inputs
Picking up objects,
using tools, moving
eyes to explore
faces, making
gestures etc.
Primary Motor Cortex
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Primary motor cortex executes
motor movements
When the primary motor cortex
is damaged the result is
weakness and imprecise fine
motor movements
Premotor and Supplementary
Motor Areas (SMA)
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Premotor and SMA are
involved in a plan of
action - motor programs
– an abstract
representation of an
intended move
We have the ability to
prepare for the next
movement before it
occurs (we have an
internal program)
Premotor and Supplementary
Motor Areas (SMA)
Premotor cortex – Two-hand
Coordination
THE MONKEY HAS LEARNED THE TASK
PUSH THE OBJECT THROUGH THE HOLE AND CATCH IT WITH THE
OTHER HAND; With damage to premotor cortex, cannot coordinate two hands
to do the task
Anterior Cingulate Cortex
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Cingulate is involved in many
functions
Subject of controversy as it is
rarely damaged in isolation
fMRI data shows that it is
activated in variety of tasks
Cingulate has been implicated
in motor planning of movements
especially when they are novel
or require much cognitive
control
“A”  “B” (well rehearsed)
“A”  “M” (novel) anterior
cingulate activation
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Topography for different motor
functions
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Manual – posterior regions
Speech – middle regions
Ocular – anterior regions
Frontal Eye Fields
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Control of voluntary eye
movements (scanning the
visual field to see a friend…or
someone you like)
Reflexive eye movements are
controlled by brain stem nuclei
(superior colliculi)
Frontal eye fields can inhibit the
activity of superior colliculi
Prefrontal Cortex
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Cortex that receives
projections from the
dorsomedial thalamus
Last to develop in
terms of evolution and
ontogenetically
Involved in highest
level of motor
functions – planning
Damage to Cortex
Alien Limb Syndrome
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A disorder in which person feels unable to control
movements of a body part, believes that the limb is
alien, or believes that the body part has its own
personality
It is typically associated with lesions in the
supplementary motor area or those affecting blood flow
to the anterior regions of the corpus callosum and the
anterior cingulate
Man who simultaneously tried to strangle and save his
wife from himself!!!
Parietal Lobe
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Twofold role:
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Integration between motor
and sensory information
Contributes to the ability to
produce complex, welllearned acts
Proprioceptive
information
Kinesthetic information
Damage to Parietal
Lobe
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Superior region important in visual
guided movements
Damage to superior regions can produce
optic ataxia
Optic ataxia – difficulty in using visual
information to guide actions that cannot
be ascribed to motor, somatosensory, or
visual-field or – acuity deficits.
Afferent paresis – loss of kinesthetic
feedback that results from lesions to the
postcentral gyrus and produces clumsy
movements
Apraxia
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Apraxia – an inability to perform skilled, sequential, purposeful
movement
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This cannot be accounted by disruptions in more basic motor
processes such as muscle weakness, abnormal posture or tone, or
movement disorder (e.g., chorea).
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Two pieces of evidence that apraxia is a higher order disorder:
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2.
Video
It occurs bilaterally (lower level deficits are contralateral to the side of the
injury)
Individuals can perform behaviours spontaneously but not when imitating
someone or on verbal command
Oral (buccofascial) Apraxia
vs. Limb Apraxia
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Oral apraxia is associated
with difficulties performing
voluntary movements
with the muscles of the
tongue, lips, cheek,
larynx
Limb apraxia disrupts the
ability to use limbs to
manipulate items such as
screwdrivers, scissors or
hammers.
Ideational vs. Ideomotor
Apraxia
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Ideational apraxia – difficulty in performing a
movement when the “idea” of the movement is lost
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It occurs when individuals can perform simple one-step
movement but not multistep movement
Ideomotor apraxia – difficulty in performing a
movement when a disconnection occurs between
the idea of movement and its execution
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Simple movements of an abstract nature are most affected
Other Apraxias
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Constructional apraxia –
individuals cannot manipulate
objects correctly with regards to
their spatial relations (e.g., wooden
block arrangement)
Dressing apraxia – individuals
have difficulty manipulating and
orienting clothing and limbs so that
the clothing can be put on correctly
Callosal apraxia – difficulty with
manipulating and using the left
hand after verbal instructions
(language in the left hemisphere)