Lecture 27: Disease of Motor Units Flashcards
_________ are the most common symptoms in patients with neurological diseases.
Movement disorders are the most common symptoms in patients with neurological diseases.
What is Paralysis What are some types of paralysis?
Paralysis is the loss of the ability to move some or all of the body. • Monoplegia (one limb) • Hemiplegia (one side of the body) • Paraplegia (two legs) • Quadriplegia (or tetraplegia) (whole body)
What is Paresis? What are somet yes of Paresis?
Weakness a condition of muscular weakness caused by nerve damage or disease; partial paralysis. • Monoparesis, hemiparesis etc.
What are some abnormalities of muscle tone?
• Hypertonia (↑ muscle tone) o Spasticity (e.g. in stroke or MS) (velocity and amplitude dependent) o Rigidity (e.g. in PD) (non-velocity and amplitude dependent)
What is Ataxia?
What are some types of ataxia?
(= incoordination)
- ‘Decomposition’ of movement (jerky),
- Dysmetria (cf. the finger-nose test with closed eyes)
What are some involuntary movements that are seen in some neurological diseases?
- Muscle spasm (cramp)
- Epileptic fit
- Tremor (e.g. ‘tremor at rest’ in PD, or ‘intention tremor’ in cerebellar ataxia)
- Dyskinesia (e.g. Levodopa-induced dyskinesia in PD after prolonged L-DOPA)
- Category of movement disorders that are characterized by involuntary muscle movements, including movements similar to tics or chorea and diminished voluntary movements.
What are some frequent symptoms in people with Neurological Diseases?
Paralysis
- Monoplegia (one limb)
- Hemiplegia (one side of the body)
- Paraplegia (two legs)
- Quadriplegia (or tetraplegia) (whole body)
Paresis (= weakness)
- Monoparesis, hemiparesis etc.
Abnormalities of muscle tone
- Hypertonia (↑ muscle tone)
- Spasticity (e.g. in stroke or MS) (velocity and amplitude dependent)
- Rigidity (e.g. in PD) (non-velocity and amplitude dependent)
Ataxia (= incoordination)
- ‘Decomposition’ of movement (jerky),
- Dysmetria (cf. the finger-nose test with closed eyes)
Involuntary movements / muscle contractions
- Muscle spasm (cramp)
- Epileptic fit
- Tremor (e.g. ‘tremor at rest’ in PD, or ‘intention tremor’ in cerebellar ataxia)
- Dyskinesia (e.g. Levodopa-induced dyskinesia in PD after prolonged L-DOPA)-hyper-activity.
- Category of movement disorders that are characterized by involuntary muscle movements, including movements similar to tics or chorea and diminished voluntary movements.
What are 4 groups/types of lesion/motor(and sensory) CAUSES
Acute vs Chronic
Focal vs Diffuse (neuro-degeneration = e.g. parkinsons disease)
Describe the location of motoneurons
Location of Motoneurons (Figure Above)
- Motor nuclei in the spinal cord (‘anterior/ventral horn cells’)
- Motor nuclei in the brainstem (III, IV, V, VI, VII, IX, X, XI and XII)
What are some types of Motoneurons
Types
- α motoneurons (innervate extrafusal muscle fibres, directly responsible for the generation of force by muscles)
- ɣ motoneurons (innervate intrafusal muscle fibres, control excitability of stretch receptors in _muscle spindle_s, located near α motoneurons)
Defie Motoneurons
(=Motor neurons =’Lower’ Motor Neurons)
Location of Motoneurons (Figure Above)
- Motor nuclei in the spinal cord (‘anterior/ventral horn cells’)
- Motor nuclei in the brainstem (III, IV, V, VI, VII, IX, X, XI and XII)
Types
- α motoneurons (innervate extrafusal muscle fibres, directly responsible for the generation of force by muscles)
- ɣ motoneurons (innervate intrafusal muscle fibres, control excitability of stretch receptors in _muscle spindle_s, located near α motoneurons)
What are the types of motor units?
Motor units are functional elements of the motor system. They vary not only in size (large vs small innervation ratio), but also according to physiological and biochemical properties. Two major types are:
- ‘FF’ type (fast twitch, fatigable)
- ‘S’ type (slow twitch)
Where do the a Motoneurons get their synaptic inputs from?
- Descending tracts (converging on α motoneurons)
- Cortico-spinal (pyramidal) tract
- Rubro-spinal tract
- Vestibule-spinal tract (coordination)
- Reticuolo-spinal tract (basic muscle tone)
- Tecto-spinal tract
- Spinal (or brainstem) interneurons (making synapses with α motoneurons)
- la inhibitory interneurones
- Renshaw cells
-
Peripheral receptors
* la afferent fibres from muscle spindles
Where are some locations of lesions in ‘motor units’?
- Disorders of muscles (myopathies)
- Disorders of motoneurons (neuropathies)
What is muscular dystrophy and
What are some types of muscular dystrophy? (A Familiar Form Of Myopathy)
A group of inherited disorders characterized by deficits in muscle proteins and progressive muscle wasting and weakness (without primary structural abnormality in motoneurons).
Examples include:
- Duchenne muscular dystrophy (DMD)
- The most common form of muscular dystrophy in children.
- Mutation of gene coding for dystrophin (muscle ‘cytosceletal’ protein)
- Myotonic muscular dystrophy (MMD)
- The most common form of muscular dystrophy in adults; Males and females equally affected in early adult life
- Onset usually in the 3rd decade of life
- Wasting and weakness of muscles (include heart!)
- Myotonia (muscle stiffness, hypertonia_):_ delayed relaxation of a muscle after a strong contraction
- Inherited (dominant!): up to 2000 ‘triple’ CTG repeats in chromosome 19 coding for a protein kinase (myotonin)
Describe Myasthenia gravis
An example of a dsiease affecting neuromuscular junction (End plate)
- Myasthenia gravis (‘generalized’ [most muscles] and/or ‘ocular’ [eye muscles] form)
- Muscle weakness (without wasting!) which is often exaggerated after exercise
-
Autoimmune disease:
- ↓ ACh binding sites for receptors
- ↓amplitude of EPPs (end plate potential)
- ↓‘safety factor’ for synaptic transmission (immune system targets its own tissue)
- Example of ocular form of myasthenia gravis:
- Facial appearance before and after injection of edrophonium (Tensilon), a blocker of ACh esterase
- (Patients often pre-treated with atropine to reduce gastrointestinal side-effects due to ↑ACh in autonomic synapses [symp.])
- Another diagnostic test is detection of antibodies against ACh receptors in serum (in ~85% of patients)
Describe what may happen with various Injury Of Axons (Axotomy)
After i_njury of axons_ resulting from d_isc protrusion_ or plexus lesion:
- Changes in distal segment of axon: Wallerian degeneration
- Loss of synaptic transmission (on electrical stimulation of the axon) within ~24hrs
- Degeneration within days (due to loss of ‘axon survival factor’ NMNAT2)
- Changes in proximal segment of axon (motoneuron cell body): chromatolysis**
- Central chromatolysis is a histopathologic change seen in the cell body of a neuron, where the chromatin and cell nucleus are pushed to the cell periphery, in response to axonal injury.
- Axon regeneration (1-2mm/day) facilitated by arrays of Schwann cells → re-innervation of muscles → (partial) re-myelination of axons → functional recovery?(sometimes)
- Note that Wallerian degeneration of axons can occur also in CNS but is not followed by regeneration.
What is this?
How is this diagnosed?
Myasthenia Gravis
- Facial appearance before and after injection of edrophonium (Tensilon), a blocker of ACh esterase ( which increases time at which the neurotransmitter acts on the receptor)
- (Patients often pre-treated with atropine to reduce gastrointestinal side-effects due to ↑ACh in autonomic synapses [symp.])
- Another diagnostic test is detection of antibodies against ACh receptors in serum (in ~85% of patients)
