The Motor System and Its Disorders

Lecture 3

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 Pathways1. 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

Major Motor Pathways3. 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)

Cerebellum Vermis Intermediate zone Lateral zone

Within are deep cerebellar nuclei: Fastigial nucleus Interpositus

nucleus Dentate nucleus

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)

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. 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 GangliaDamage 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=inhibitionBlue=excitation

Hyperkinetic DisorderHuntington’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=inhibitionBlue=excitation

Hyperkinetic DisorderTourette’s Syndrome

Three stages:1. Only multiple tics (twitches of the face, limbs or the

whole body)2. Inarticulate cries are added to multiple tics3. 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 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

Hypokinetic DisorderParkinson’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

individuals2. Negative – absence of normal behaviours

Hypokinetic DisorderParkinson’s Disease

1. Tremors at rest2. 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

1. Abnormal posture 2. Abnormal righting – difficulties in

achieving a standing position3. Abnormal locomotion – difficulty

initiating stepping Festination – tendency to engage in behavior at faster and faster speeds.

4. Aprosodia – Lack of emotional tone in speech and comprehension of emotional tone

5. Akinesia – absence of movement (e.g., blank facial expressions, lack of blinking)

6. Bradykinesia – slowness of movement

POSITIVE SYMTOMS NEGATIVE SYMTOMS

Hypokinetic DisorderParkinson’s Disease - Causes

1. Idiopathic – cause not known

2. Postencephalitic – “sleepy sickness” – 1916-1917 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)

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 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

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. It occurs bilaterally (lower level deficits are contralateral to the side of the

injury)2. Individuals can perform behaviours spontaneously but not when imitating

someone or on verbal command

Video

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)