Motor and neuromuscular control Flashcards
what is the 2 broad ways motor systems are organised
1) Hierarchical organisation: high order neurons are involved in more complex functions (programme and decide on movements, coordinate muscle activity), lower order neurons are tasked with execution of movement (lower level tasks)
2) Functional segregation: different areas of the motor system control different aspects of movement
what does the PMC do and where is it found in the brain
in precentral cyrus, anterior to central sulcus
Fine discrete and precise voluntary movements
Descending signals
what does the supplementary area to the PMC do and where is it found in the brain
*Supplementary area: anterior and medial to the PMC
planning complex movements (Internally cued, speech) → becomes active prior to voluntary movement
where is the premotor area found in the brain and what is it’s function
anterior to the PMC
movement planning + regulation of externally cued movements (seeing an apple and reaching out for it)
What are the 2 pyramidal tracts
1) Corticospinal
2) Corticobulbar
What are pyramidal tracts and describe how they travel down from the brain
Pass through medulla pyramids
Motor cortex to spinal cord or brainstem cranial nerve nuclei
Voluntary movements of body and face
Major descending tract
What are the 2 corticospinal tracts and what do they innervate + where do they decussate
85-90% of nerves decussate at medulla →these form the lateral corticospinal that supply limb muscles
10-15% uncrossed fibres → anterior corticospinal: trunk muscles
What does the corticobulbar tract control?
Voluntary movements of face and neck: eye movements, jaw muscles, muscles of facial expression and mastication, tongue
What are extrapyramidal tracts and describe how they travel down from the brain
Brainstem nuclei to spinal cord
Don’t pass through pyramids of medulla
Involuntary (automatic) movements for balance, posture and locomotion
Major descending tract
What are the 4 types of extrapyramidal tracts
1) vestibulospinal
2) tectospinal
3) reticulospinal
4) rubrospinal
what is the function of the vestibulospinal tract
Stabilizing the head as it moves or as the body moves
Coordinate head movements with eye movements
Mediate postural adjustments
what is the function of the tectospinal tract and where does it originate
From superior colliculus ( visual system) of midbrain - orients head and neck during eye movements
what is the function of the reticulospinal tract
+ where does it originate
Most primitive descending tract (from medulla and pons)
Changes in muscle tone associated with voluntary movement
Postural stability
what is the function of the rubrospinal tract and where does it originate
From midbrain red nucleus - mostly taken over by corticospinal tract in humans ( important in legions of the CNS)
Innervate lower motor neurons of upper limb flexors
Where can you find upper motor neurons
Upper motor neurons: extend from the PMC in the cortex via the pyramids of the medulla and down the corticospinal tract.
What are teh 2 types of symptoms that you can see in an UMN lesion
-ve signs : There is loss of voluntary motor function.
+ve signs : Increased abnormal motor function due to loss of inhibitory descending inputs.
What are the -ve signs of an UMN lesion
-ve signs : There is loss of voluntary motor function.
Paresis: Graded weakness of movements
Paralysis (plegia): Complete loss of voluntary muscle activity.
What are the +ve signs of an UMN lesion
+ve signs : Increased abnormal motor function due to loss of inhibitory descending inputs.
Spasticity: Increased muscle tone
Hyperreflexia: Exaggerated reflexes
Clonus: Abnormal oscillatory muscle contractions
Babinski’s sign
Where can LWN be found
within cranial nerve nuclei to corticobulbar tracts/ spinal cord for innervating limb muscles
What are the symptoms of a LMN lesion
Weakness
Hypotonia (reduced muscle tone) Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: Damaged motor units produce spontaneous action potentials, resulting in a visible twitch of muscles
Fibrillations: Spontaneous twitching of individual muscle fibres; recorded during electromyography examination.
Fibrillations = not visible to eye , fasciculation = visible to eye
What is aprixia and what is it caused by?
Usually caused due to a UMN legions
patients are not paretic however have lost information regarding how to perform skilled movements
Lesion of inferior parietal lobe, the frontal lobe (Premotor cortex, supplementary motor area-SMA).
Stroke and dementia are the most common causes of apraxia
What is motor neuron disease amyotrophic lateral sclerosis
progressive neurodegenerative disorder of motor system - it is a spectrum of disorders
What does MND effect
As it effects both UMN and LMN it has signs of both
what are the upper motor neuron signs of MND
Spasticity (Increased tone of limbs and tongue).
Brisk limbs and jaw reflexes
Babinski’s sign:
Shows upper motor neuron lesion affecting the corticospinal tract
Normal response induces plantar flexion but in MND, there is dorsiflexion (Extension) of the large toe
loss of inhibitory function on the extensor hallucis longus.
Loss of dexterity
Dysarthria (Difficulty speaking)
Dysphagia (Difficulty swallowing).
What are the lower motor neuron signs of motor neuron disease
Lower motor neuron signs: Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia
What is the function of the basal ganglia
decision to move
elaborated associated movements (e.g Swinging arms when walking, changing facial expression to match emotions)
Moderating and coordinating movement - suppressing unwanted movement
Performing movements in order
What are teh structures that can be found in the basal ganglia
( see pic on docs)
Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus)
Caudate + putamen = striatum
Nucleus accumbens
Subthalamic nuclei
Substantia nigra ( midbrain)
Ventral pallidum, claustrum, nucleus basalis (of meynert)
What causes parkinsons
degeneration of substantia nigara
What is the substantia nigra
dopaminergic nucleus residing within the midbrain - project to striatum
What are they symptoms of parkinson’s
1) Bradykinesia: 2) Slowness of small movements ( ie doing up buttons)
3) Hypomimic face: 4) Expressionless, mask-like (absence of movements that normally animate the face).
5) Akinesia: Difficult in initiation of movements
6) Rigidity: Muscle tone increases, causing resistance to externally impose joint movements.
7) Tremor at rest: 4-7Hz, starts in one hand (‘pill-rolling tremor’)- with time spread to other areas of the body.
What is the cause of huntingtons
degeneration of GABAergic neurons in the striatum, caudate and putamen.
Genetic disorder : Autosomal dominant trinucleotide repeats disorder (CAG) on chromosome 4.
CAG repeats generate elongated polyglutamine tail of the huntingtin protein Interferes with normal cellular function.
Symptoms of huntington’s
Symptoms :
Chorea (Rapid jerky involuntary movements of the body, hands and face (affected first legs)
Speech impairment (aphasia)
Dysphagia
Unsteady gait
Cognitive decline and dementia manifesting at later stages of the disease.
What is ballism and what is it normally caused by
Sudden uncontrolled flinging of extremities- contralateral symptoms ( flinging occurs on the opposite side of the body to symptoms
From stroke affecting subthalamalic nucleus
Usually one sided
were is the cerebellum
Inside posterior cranial fossa and separated from cerebrum above by tentorium cerebelli
