Transcript Motor System and Disorders

The Motor System and Its
Disorders
Lecture 3
Announcement:
 Thank you for e-mailing me your preference
for a short talk or poster presentation
 I will shortly post a list of presenters for each
Lecture Outline:
 Overview and major pathways
 Cerebellum
– Cerebellar atrophy videos
 Basal Ganglia
– Hyperkinetic disorders
 Huntington’s chorea
 Tourette’s
 Tardive Dyskinesia
– Hypokinetic disorder
 Parkinson’s Disease - videos
 Cortex
– Primary motor
– Premotor, supplementary motor, prefrontal
– Parietal cortex
 Apraxia(s)
Motor Control
 Behaviour is observable
motor output by the organism
– 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
(pons, 5th, 7th, 10th
and 12th cranial
nerve) – control of
face and tongue
muscles
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
 Vermis
 Intermediate zone
 Lateral zone
 Within are deep
cerebellar nuclei:
– Fastigial nucleus
– Interpositus
nucleus
– Dentate nucleus
Vermis
 Input from the spinal
cord and 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
 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
Lateral Zone
2. Also involved in multijoint
movements
3. Learning of new movements
4. Timing of motor movements
(and cognitive functions)
Basal Ganglia
 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
 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
 Three stages:
1. Only multiple tics (twitches of the face, limbs or the
whole body)
2. Inarticulate cries are added to multiple tics
3. 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
 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
 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:
1.Positive – abnormal behaviours not seen in
intact individuals
2.Negative – absence of normal behaviours
Hypokinetic Disorder
Parkinson’s Disease
POSITIVE SYMTOMS
1.
2.
3.
Tremors at rest
Muscular rigidity –
simultaneously increasing the
muscle tone in both extensor
and flexor muscles.
Involuntary movements –
akathesia –motor
restlessness, ranging from a
feeling of inner disquiet to an
inability to sit or lie quietly
NEGATIVE SYMTOMS
1. Disorders of posture.
2. Disorders of righting –
difficulties in achieving a
standing position
3. Disorders of locomotion –
difficulty initiating stepping.
Festination – tendency to
engage in behavior at faster
and faster speeds.
4. Aprosodia – Disturbances of
speech
5. Akinesia – absence of
movement (e.g., blank facial
expressions, lack of blinking)
6. Bradykinesia – slowness of
movement
Hypokinetic Disorder
Parkinson’s Disease - Causes
1. Idiopathic – cause not known
2. Postencephalitic – “sleepy sickness” – 19161917  vanished by 1927  see Oliver Sack in
Awakenings
3. Drug induced (e.g., major tranquilizers, MPTP –
contaminant in heroin – is toxic to dopamine
neurons)
 Treatments: L-dopa  dopamine precursor
 video
Cortex
 Externally guided
movements – those
requiring sensory
inputs
 Picking up objects,
using tools, moving
eyes to explore
faces, making
gestures etc.
Primary Motor Cortex
 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)
 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)
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
 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
 Anterior cingulate is involved in
attention and emotion regulation
 Posterior 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
 Topography for different motor
functions
– Manual – posterior regions
– Speech – middle regions
– Ocular – anterior regions
Frontal Eye Fields
 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
 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
 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
 Twofold role:
– Integration between
motor and sensory
information
– Contributes to the ability
to produce complex,
well-learned acts
 Proprioceptive
information
 Kinesthetic information
Damage to Parietal
Lobe
 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

Apraxia – an inability to perform skilled, sequential, purposeful
movement

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).

Two pieces of evidence that apraxia is a higher order disorder:
1.
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
 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
 Ideational apraxia – difficulty in performing a
movement when the “idea” of the movement is lost
– 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
– Simple movements of an abstract nature are most
affected
Other Apraxias
 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)