The Motor System and Its Disorders

1
The Motor System and Its Disorders

• Lecture 3

2
Lecture Outline

• Overview and major pathways
• Cerebellum
• Cerebellar atrophy videos
• Basal Ganglia
• Hyperkinetic disorders
• Huntingtons chorea
• Tourettes
• Tardive Dyskinesia
• Hypokinetic disorder
• Parkinsons Disease - videos
• Cortex
• Primary motor
• Premotor, supplementary motor, prefrontal
• Parietal cortex
• Apraxia(s)

3
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)

4
Steps in Motor Action
5
Muscles
6
4 Major Motor Pathways

• 1. Corticospinal (cortex to spinal cord)
• a) Lateral distal limb muscles (fine
  manipulations)
• b) Ventral trunk and upper leg muscles
  (posture/locomotion)
• 2. Corticobulbar (cortex to pons, 5th, 7th, 10th
  and 12th cranial nerves) control of face and
  tongue muscles upper face both contralateral,
  lower face contralateral

7
Major Motor Pathways

• 3. Ventromedial (brain stem to spinal cord)
  trunk and proximal limb muscles (posture,
  sneezing, breathing, muscle tone)
• 4. Rubrospinal (red nucleus to spinal cord)
  modulation of motor movement (limb movement
  independent of trunk movement)

8
Cerebellum

• Vermis
• Intermediate zone
• Lateral zone
• Within are deep cerebellar nuclei
• Fastigial nucleus
• Interpositus nucleus
• Dentate nucleus

9
Vermis

• 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)

10
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.

11
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

12
Lateral Zone

• 2. Multijoint movements
• 3. Learning of new movements
• 4. Timing of motor movements (and cognitive
  functions)

13
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

14
Basal Ganglia

• Damage to the basal ganglia
• Produces either too much activation
  (hyperkinetic) responses twitches, movements
  bursts, jarring, etc.
• Huntingtons Chorea-dominant gene based,
  increases glutamate in striatum which destroys
  GABA neurons in BG and loss of inhibition
• No cure
• Tourettes
• OR
• Produces too little force (hypokinetic)rigidity
• Parkinsons disease

Pinkinhibition Blueexcitation
15
Hyperkinetic DisorderHuntingtons 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

Pinkinhibition Blueexcitation
16
Hyperkinetic DisorderTourettes Syndrome

• 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

17
Hyperkinetic DisorderTardive 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

18
Hypokinetic DisorderParkinsons 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
• Positive abnormal behaviours not seen in intact
  individuals
• Negative absence of normal behaviours

19
Hypokinetic DisorderParkinsons Disease
POSITIVE SYMTOMS
NEGATIVE SYMTOMS

1. Tremors at rest
2. Muscular rigidity simultaneously increasing the
   muscle tone in both extensor and flexor muscles.
3. Involuntary movements akatheisia motor
   restlessness, ranging from a feeling of inner
   disquiet to an inability to sit or lie quietly

• 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

20
Hypokinetic DisorderParkinsons Disease - Causes

• 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

21
Cortex

• Externally guided movements those requiring
  sensory inputs
• Picking up objects, using tools, moving eyes to
  explore faces, making gestures etc.

22
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

23
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)

24
Premotor and Supplementary Motor Areas (SMA)
25
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
26
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
• 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

27
Frontal Eye Fields

• Control of voluntary eye movements (scanning the
  visual field to see a friendor someone you like)
• Reflexive eye movements are controlled by brain
  stem nuclei (superior colliculi)
• Frontal eye fields can inhibit the activity of
  superior colliculi

28
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

29
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!!!

30
Parietal Lobe

• Twofold role
• Integration between motor and sensory information
• Contributes to the ability to produce complex,
  well-learned acts
• Proprioceptive information
• Kinesthetic information

31
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

32
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
• 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
• Video

33
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.

34
(No Transcript)
35
(No Transcript)
36
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

37
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)