Module 3 Chapters 15 & 16 Disorders of Motor and Brain Function and Disorders of Brain Function Flashcards
What is the motor unit?
A motor unit consists of a motor neuron and all the muscle fibers it innervates.
How does a motor unit control skeletal muscle movement?
Whenever the motor neuron develops an action potential, all the muscle fibers that the motor neuron innervates develop action potentials. This leads all the muscle fibers contracting at once, working to move the bones they are attached to.
Describe the hierarchy of the motor control system
The frontal lobe houses the premotor cortex, this is where planning and purpose of movement originates. Considered the highest level of motor functioning.
Where is the premotor cortex? What does it do?
The premotor cortex is located in the frontal lobe. Planning and purpose of movements originates here. It is considered the highest level of motor function.
Controls complex patterns of movements
Where is the motor cortex? What does it do?
Also located in the frontal lobe. Has a close relationship with the premotor cortex. Controls body movement.
What is the somatosensory cortex/association area? Where is it?
This is located in the parietal lobe, at the top of the brain. It is right next to the motor cortex in the frontal lobe. The somatosensory cortex/ association area receives sensory information from the periphery, processes it and sends that information to the motor and premotor cortex.
What areas of the body take up the most primary motor cortex space?
The hands, face, and speech take up over half of the primary motor cortexes SA.
What is the pyramidal motor system? Why is it called this? What does it control? Where do each of these originate?
The pyramidal motor system is a pyramid shaped network of neurons with the apex located in the motor cortex. These motor tracts are further subdivided into the
1. Pyramidal - controls delicate muscle movement. Voluntary movement. Called pyramidal because they pass through the pyramids of the medulla.
2. Extrapyramidal - crude, supportive movement patterns.
based on the location of their decussation. Involuntary movement.
The P system originates in the motor cortex while the EP system originates in the basal ganglia (brainstem).
How do disorders of the pyramidal tract present? What about the extrapyramidal?
P - spasticity and paralysis. Think of stroke.
EP - involuntary movements, rigidity, immobility.
What does the cerebellum do in regard to movement?
Primary role is controlling balance and coordination.
How do muscles and nerves communicate?
The motor unit - neuron and the muscles fibers it innervates.
Each of those contact points between the neuron and the muscle have a neuromuscular junction.
The neuron communicates by sending out neurotransmitters which the muscle receptors pick up and respond to.
What is an axon terminal?
The portion of the neuron that makes the closest contact with the muscle at the neuromuscular junction. This is where neurotransmitters are released from so the two can communicate.
What neurotransmitter is used at the neuromuscular junction? How does this affect the muscles?
Acetylcholine. Ach binding at the site of the neuromuscular junction results in muscle contraction.
Muscular atrophy. What is it? What causes it?
Shrinking of muscle cells due to reduced use or reduced nutrition. The body wants to be as efficient as possible. Cells that are too big for their current job expend more energy. The body adapts to this and reduces energy expenditure.
Muscular dystrophy
Genetic disorder that results in the progressive deterioration of skeletal muscle. Considered a disorder of mixed muscle deterioration due to a combination of hypertrophy, atrophy, and necrosis of muscle cells.
What happens to damaged peripheral nerves? What are common causes?
Damaged peripheral nerves undergo degenerative changes followed by degradation of the myelin sheath fibers.
Common causes include trauma and poorly controlled DM (neuropathy).
Can peripheral nerves regenerate?
Yes, depends on the proximity to the soma (cell body).
Curare
A naturally found neuromuscular junction blocking agent. Collected from dart frogs. Many drugs have been developed from it.
Roc is one of them. Vec.
How does clostridium botulinum affect Ach? What is this?
Blocks ACH resulting in paralysis. A type of food poisoning.
Myasthenia Gravis
1. What is it?
2. Patho
3. Thymus
4. Who is affected most often?
- An autoimmune disorder that affects the neuromuscular junction.
- A reduction in the number of Ach receptors at the neuromuscular junction. This reduction in number is caused by host antibodies destroying these receptors.
- Enlarged in these patients
- Young women and older men are most commonly affected
What is the thymus? Where is it? What happens to it as we age? How is this observed for with MG?
Large role in immunity in early childhood. Teaches the developing body immunocompetence. Located high up near the sternum. Shrinks as we age, and the immune system starts to know what to do. CT or MRI of the chest can locate enlarged thymus gland and help dx the disease.
Clinical manifestations of myasthenia gravis? What causes these symptoms?
- Muscle weakness with exercise or repetitive muscle movement. This is caused by the limited number of ACH receptors being occupied.
- Difficulty with eye movement, swallowing, talking, handling oral secretions. All of these tasks require ach to maintain. Over time ach gets used up.
How is MG diagnosed?
- Neurological exam
- Blood studies looking for the AChR antibodies - the antibodies responsible for destroying the receptors at the neuromuscular junction site.
- Repetitive nerve conduction studies - EMG
- Tensilon or edrophonium test for classic dx.
- CT or MRI of the chest - looking for enlarged thymus (thymoma)
- Thyroid function test - mainly a RO exam
How is MG managed?
- Immunosuppression - stop the body from attacking the Ach receptors.
- Steroids - reduce inflammation and reduce the body’s immune response.
- Anticholinesterases - prevent the breakdown of Ach allowing more of the neurotransmitter to be present in the body.
- Plasmapheresis - clears the body of antibodies
- IVIG
- Thymectomy
Myasthenic crisis
1. Main concern?
Not enough medications - not enough Ach in the body. Exacerbation of the body weakness secondary to repetitive muscle use.
1. Main concern - respiratory status.
Cholinergic crisis
Too much medications - too much Ach
Lots of secretions, perspiration, abdominal cramping, diarrhea.
Mononeuropathies
Peripheral neuropathy that affects one nerve.
Polyneuropathy
Peripheral neuropathy, typically involves demyelination. If the demyelination occurs in a higher up part of the motor/sensory system. The higher up it occurs, the more downstream effects will be experienced.
How does neuropathy present in the beginning?
Distal moving proximal
What causes polyneuropathy?
- Immune mechanisms (GBS) - the immune system mistaking attacks the myelin sheaths resulting in demyelination. Occurs distal to proximal.
- Toxic agents (lead. alcohol, arsenic)
- Metabolic diseases (DM, uremia)
What are the basal ganglia? Roles?
A group of deep, interrelated subcortical nuclei that control movement. Receives input from cerebellum, sensory systems, and motor cortex.
Plays a role in motor movements, habit forming, procedural learning, eye movements and others. “Muscle memory”.
Located deep in the center of the brain
Basal Ganglia disorders, what will be seen?
Think of extrapyramidal - because they are the highest part of the EP system where decussation occurs.
- Involuntary movements
- Alterations in muscle tones - rigid/stiff/flaccid at inappropriate times
Tremor
involuntary, oscillating contractions of opposing muscle groups around a joint
Tic
involuntary twitch
Chorea
irregular wriggling and writhing movements
athetosis
continuous wormlike, twisting, and turning movements
Ballismus
violent, sweeping, flinging movements
Dystonia
simulataneous contraction of agonist and antagoinst muscles, contortion
Dyskinesias
Frequent involuntary movement of muscles typically face.
Parkinson’s Disease
1. What is it?
2. Patho
3. What problems are seen with PD?
- Degenerative disorder of basal ganglia function that results in variable combinations of tremor, rigidity, and bradykinesia. EP.
- Caused by the destruction of nigrostriatal pathway leading to a reduction in striatal concentrations of dopamine.
- Fatigue, slight tremor, decrease in manual dexterity. Muscle rigidity. Changes in facial expression. Uncontrolled drooling. Dementia. Excessive sweating. Orthostatic hypotension.
What neurotransmitter is deficient in Parkinson’s disease?
Dopamine is deficient in Parkinson’s disease. This is a widely used neurotransmitter in the extrapyramidal pathway.
How is Parkinson’s disease treated?
- Dopamine agonists - pramipexole (mirapex) and Ropiniole (Requip) are commonly used ones. These increase the amount of dopamine avaliable for the basal ganglia.
- Dopamine receptor antagonists
- COMTs
- Deep brain stimulator
- Sterotactic palliotomy
Where are the upper motor neurons (UMN) and the lower motor neurons (LMN)? What is their function?
The UMN originate in the cerebral cortex and travel down to the brain stem or the spinal cord. Here they connect with the LMN to send along impulses of voluntary movement.
The LMN are located in the spinal cord and brainstem and travel throughout the spinal cord, innervating glands and muscles. They send the voluntary muscle impulse along that results in movement or release.
Motor neuron disease
1. What is affected?
2. Examples
- Progressive degeneration of the upper or lower motor neurons.
- ALS, Polio, progressive spinal muscular atrophy