Motor control and movement disorders Flashcards
Acetylcholine
Contraction of skeletal muscles results from the release of the this neurotransmitter from the terminals of motor neurons.
Where can we find cell bodies of motor neurons?
Spinal cord, which are controlled by a variety of descending neurons from the brain and some ascending neurons in the cord itself.
Brain-spinal cord pathways
Neurons in cortex do not make direct contact with muscles, but Fritsch and Hitzig found that electrical stimulation of the brain can rapidly induce movement.
There are 4 major tracts from the brain:
- the corticospinal tract
- the corticobulbar pathway
- The ventromedial pathway
- The rubrospinal pathway
The corticospinal tract
Consist of neurons whose cell bodies are found in the cortex (primary motors trip, M1), which is the most posterior gyrus of the frontal lobes and immediately forward of the primary somatosensory cortex.
M1 is highly topographically organized.
The axons descend within the brain to the MEDULLA, where they cross to the opposite side before continuing into the spinal cord to synapse with motor neurons.
The pathway consist of two tracts:
- The lateral tract: control distal muscles contralaterally.
- The ventral tract: controls medial muscles on both sides.
The corticobulbar pathway
Origin in primary motor strip, but the axons only descend to the pons where they innervate some of the cranial nerves to control facial, mouth, and tongue muscles.
The ventromedial pathway
Origins in the brainstem or midbrain rather than cortex and projections terminate in proximal muscles in the trunk, shoulders and neck.
The rubrospinal pathway
Origins in the red nucleus of the midbrain, which receives inputs from both the motor cortex and the cerebellum.
It projects mainly to distal limb parts and the primary function is thought to be the movement of limbs independent of movements of trunk.
ipsilateral
to the same side of the body; opposite of contralateral.
Cerebellum
fundamentally involved in the modulation of motor coordination and the acquisition of motor skills, because of its reciprocal connections between the cortex and parts of the cerebellum.
The cerebellum influence motor control on the IPSILATERAL side of the body, so right side damage affects movement on the right side of the body.
Cerebellar structure
size of two walnuts, the structure is bilateral symmetrical.
The cerebellum contains four different types of neurons:
- innermost: vermis (receives somatosensory and kinesthetic information from the spinal cord) affect balance.
- the next: reciprocal information from the red nucleus. intentional tremor.
- The lateral zones (left and right outer sections): receives information from motor and association cortex. affect movement of limbs.
Bilateral
affecting both sides
Three anatomically separate regions of cerebellum
Can be distinguished in terms of inputs and outputs as well.
- Medial region: modulate and smooth out movement
- Lateral regions: coordinate skill movement enacted “in time”.
Damage to the cerebellum does not eliminate movement per se, rather it seems that tasks that were once effortless become a struggle after cerebellar damage.
The basal ganglia
A group of subcritical structure that connect with each other and the cortex in a series of five parallel “closed loops”. Each of the loops originates from, and returns output to, a particular region of cortex.
- Motor loop
- Oculomotor loop
- Dorsolateral prefrontal loop
- Orbitolateral loop
- Limbic loop
Motor loop
Mainfunction: the initiation, maintenance and switching of actions
Oculomotor loop
Main function: the direction of voluntary eye movements
Dorsolateral prefrontal loop
Main function: maintenance of spatiale working memory and other executive functions, shifting sets.
Orbitolateral loop
Main function: switching/inhibiting behaviors, perhaps including the inhibition of inappropriate behaviors in relation to social settings. Possibly also empathy and imitation.
Limbic loop
Main function: remain vague but likely to involve selection of emotional expression or tone, and motivated behavior.
Components of basal ganglia
Caudate, putamen and ventral striatum, the internal and external segments of the globus pallid us, the subthalamic nucleus, and the substantial nigra.
D1 receptors
a class of dopamine receptor found particularly in the frontal lobes and striatum
D2 receptors
Another class of dopamine receptor found particularly in the striatum and pituitary.
Direct and indirect routes
For each oft he major parallel loops, two competing paths through the basal ganglia.
Direct route: path from the striatum > internal regions of the globus pallid us > thalamus > back to cortex.
Basal ganglia functions
Damage to basal ganglia sometimes have writhing-like movements or other postural disturbances, they also sometimes have difficulties in starting movements but are OK once they start.
The motor strip
Predominantly contralateral control.
in cases where the entire left or right primary motor cortex is damages = contralateral hemiplegia.
Hemiplegia
paralysis of one side of the body.
When the entire left or right primary motor cortex is damaged.
what control the activity of pyramidal cells?
Supplementary motor area and premotor cortex. its hierarchical.
Damage to this area: have fine motor control fingers but are impaired on tasks that require the coordination of two hands.
What are the main outputs from supplementary motor area?
Primary motor cortex bilaterally.
involved in movement
What are the main inputs from the supplementary motor area?
Prefrontal cortex and basal ganglia
involved in movements
When does prefrontal region becomes active? (movement)
When individual begin to plan behavior or when acquiring new motor skills.
Damage to prefrontal region?
Difficulties to plan, whether or not movement is involved.
do poor on test such as tower of Hanoi.
When is anterior cingulate active?
when attention must be directed towards novel stimuli that require effortful responses, particularly when there is conflict between response options.
Mirror neurons
A region that becomes active when both engaging in a particular behavior aswell as observe others engage in the same particular behavior.
its a class of sensory-motor neurons, first discovered in premotor cortex.
Suggested that we routinely use this system to understand other people’s action in order to “mind read” and empathize.
Myasthenia gravis
Autoimmune disorder.
The symptoms might vary from mildly disabling to life threatening.
Myasthenia gravis (symptoms)
muscle weakness or fatigue (especially in head-neck region).
Myasthenia gravis (cause)
Its not a damage to the tissue/muscle itself, but from impaired neuromuscular synaptic transmission. In most cases, acetylcholine are released from motor neurons, but this fails to have the expected effect on the target muscles.
It seems that they have reduced number of ACh receptors, which is thought to occur as a result of an inappropriate immune response, where the body attacks the receptors as if they were foreign.
Mysasthenia gravis (treatment)
Mild symptoms: good effect with drugs > boost activity in synapses between motor neurons and muscles.
Sideeffects: sleep disturbance, cognitive impairment, and even hallucinations.
Multiple sclerosis (MS)
Demyelinating disease = progressive loss of myelin. Can occur throughout the nervous system and may affect all myelinated neurons.
Auto-immune disease, but the trigger is unknown.
Two patterns of progression in MS
Relapsing-remitting form (4/5 cases, and most common)
Progressively disabling from (1/5 cases)
In either case, progression is often slow, although eventually white matter in the brain, especially those surrounding the ventricles, will be lost.
Relapsing-remitting form (MS)
involves period of relapse, coinciding with inflammation of regions of CNS white matter, followed by recovery
Progressively disabling form (MS)
Involves a slow but steady deterioration of function.
Early signs of MS
loss or disturbed sensation in hands or lower limbs, and loss/imparied muscle control. Blurred vision is also common.
As the disease progresses, more widespread paralysis (an loss of sensation) will be seen, there might be cognitive change as well.
Motor neuron disease (MND)
One of a group of disorders characterised by progressive destruction of the motor neurons that control voluntary action.
Generally more aggressive, death often within few years of onset. often respiration and swallowing become affected.
ALS
Form of MND
Amyotropihic lateral sclerosis (ALS): motor neurons in spinal cord and cranial nerves dies > progressive loss of muscle function.
Cause of MND
remains a mystery, but less then 5% of the cases = genetic.
Unknown viruses, possible exposure to toxins and even head injury is considered.
It is, however, known to involve the over-expression of genes coding for a particular glutamate receptor, which leads to loss of tissue.
Cause of hemiplegia
interruption of blood supply via mid-cerebral artery due to aneurysm, hemorrhage or clot to the primary motor strip. other causes included head injury, epilepsy and tumor.
Recovery from hemiplegia
usually a modest degree of function over time, because symptoms result not just from cell death, but additionally from temporary loss of function in surrounding neurons.
Diaschisis
effect a short-term reduction in activity levels because of reduced inputs from the now-dead cells. (often in hemiplegia).
Cerebral palsy
May take a variety of form, encompassing many signs and symptoms, depending on extent of damage. however, hallmark is motor disturbance and might involve ataxia, athetoidy.
cause: trauma during late foetal development or birth.
Ataxia
Difficulties in making vulnetary movements
Athetoidy
Unwanted involuntary movements
Apraxia
1 A failure to produce a correct movement in response to a verbal command.
2 A failure to correctly imitate a movement.
3 A failure to correctly perform a movement (or sequence of movements) in
response to an observed object.
4 A failure to even correctly handle an object.
Liepmanns two form for apraxia
- ideo-motor apraxia: cannot repeat/pantomime particular actions. cannot use the relevant tool.
- Ideational apraxia; may be able to make well-formed movements, but they are inappropriate.
He also added “motor apraxia”.
Today: “limb apraxia” is used to encompass both conditions.
unilateral callosal apraxia
Damage with anterior part of the corpus callous, which prevents motor commands from the left hemisphere traveling to the right side which affect the left hand.
Almost always affects te left hand in right-handed individuals.
Buccofacial (oral) apraxia
the most common form and is characterized by an inability to produce particular pro-facial movement, such as sticking out ones tongue or blowing a kiss on demand.
Damage to left frontal lobe (part of brocades area).
Parkinsons disease
Subcortical disorder, affect few people under 50. its progressive disorder, and symptoms may develop quite slowly, and it is in principle a terminal illness (it progress is so slow that most people die of unrelated illness before PD has run its full course, thought to be at least 15 years).
Symptoms of parkinsons
all of them need not to be present for the diagnosis to be appropriate. The severity will become more pronounced over time.
Positive symptoms:
- resting tremor
- muscular rigidity
- involuntary movements
Negative symptoms:
- disordered posture
- loss of spontaneous movement
- Bradykinesia: cannot do the behavior after a command, e.g. clap their hands together even thought they understand what the command is.
- slowness in movement
- disordered locomotion
- disturbed speech
Huntington´s disease
rare, genetically determined ndisorder causing dementia and death due to progressive loss of neurons in the striatum.
Leads to death within 12-15 years of onset of symptoms.
Choreic stage of HD
Marked by the presence of usual and intrusive movements which may appear benign, taking the form of fidgeting or restlessness. but soon, they become apparent in limbs, trunk, head and neck, to the extent that they interfere with “normal” actions including walking, talking, and even swallowing.
psychological and cognitive changes can also occur, and can sometimes lead to misdiagnosis of mental illness.
“end-stage” of HD
Resembles the negative symptoms of PD, the individuall may be immobile, mute, bed-ridden and have difficulty in breathing and swallowing. Memory and attentional impairments.
Death is often due to aspiration pneumonia.
Cause of HD
Early stage HD, the only changes are found in the “caudate” where a progressive loss of “spiny” interneurons is observed.
The presence of a single dominant gene on chromosome 4. If a parent has it, you have 50% chance of develop it.
Symptoms debut of HD
Symptoms does not appear until middle age, around 40 years old, and most people have had children by then. therefor, people still gets the disease.
Tics
Brief, involuntary, unpredictable and purposeless repetitive gesture that often focus on the face and head. Sometimes vocal tics occur (most common in children and often disappear in adolescence). If tics persist into adulthood the condition merges with Tourettes syndroms.
Tourette´s syndrom
severe form of tic disorder.
Often have echolalia, and ins every cases coprolalia (use of language of sexual nature).
They have insight to their condition, but they cannot control action. It get worse by anxiety or stress and can be improved by relaxation and dopamine-blocking drugs.
Corpolalia
Use of foul language often of a sexual nature
Ballism (unilateral hemi-ballism)
Rare movement disorder linked to damage of sub thalamic nucleus, usually from stroke.
Main features: wild fling-like movements of limb, sometimes also neck/head > they can be so pronounced that they can cause severe injuries.
Treatment: dopamine-blocking drugs.
Sydenham´s chorea
May develop from rheumatic fever in 1/5 affected children.
Features: tics, twitches and other motor signs such as sudden aimless movement in the head, trunk, and limbs.
Usually resolves within a few weeks, but there are cases where children have had recurrent episodes over a period of several years.
