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
What is the function of the cerebellum
coordinator and protector of movement
What are the 3 parts of the cerebellum
vestibulocerebellum
spinocerebellum
cerebrocerebellum
what is the vestibulocerebellum responsible for
Regulation of gait, posture, and equilibrium
Coordination of head movements with eye movements
what is the spinocerebellum responsible for
Speech coordination
Adjusting muscle tone
Coordination of limb movement
what is the cerebrocerebellum responsible for
Coordination of skilled movements
Cognitive function, attention, language processing
Emotional control
what would damage vestibulocerebellum and what are the symptoms of damage ?
Damage (tumour): syndrome similar to vestibular disease leading to gait ataxia and tendency to fall - even when sitting with eyes open
what would damage the spinocerebellum and what are the symptoms of damage?
Damage (degeneration and trophy associated chronic alcoholism) affected mainly legs: abnormal gait and wide based stance
what are the symptoms of cerebrocerebellum damage?
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What are the sifgns of cerebellar dysfunction
note these are only apparent on movement
Dysdiadochokinesia: Inability to perform repeated, alternating movements.
Ataxia: Broad-based gait / impairment sin movement coordination + accuracy ( ie drunken gait)
Nystagmus: Rapid involuntary movements of the eyes
Intention tremor: Tremor, usually of the hands, that gets worsened with purposeful movements.
Staccato Speech: Interrupted and non-fluent speech
Hypotonia: Reduced muscle tone
Dysmetria: Inappropriate force and distance for target-directed movements.
What are the 2 types of muscle fibres and what do they do
Extrafusal : muscle fibres that can contract
Intrafusal : muscle fibres that can’t contract
contain sensory organs that responds to stretch and tension in the muscle
convey sensory info to CNS about the status of the muscle ( ie is muscle contracted or not) → helps with reflex activity
What are the lower motor neurons of teh brainstem and spinal cord called
alpha motor neurons
Where are alpha motor neurons found , what do they innervate and what is their function
Occupy grey matter of ventral horn of spinal cord
Innervate extrafusal muscles fibres of skeletal muscles
Activation causes muscle contraction
What is a motor neuron pool
all alpha motor neurons innervating a single muscle
what is a motor unit and what does it do
Motor unit : a single motor neuron together with all the muscle fibres that it innervates
It is the smallest functional unit with which to produce force
On average each motor neuron supplies about 600 muscle fibres.
Stimulation of one motor unit causes contraction of all the muscle fibres in the unit
What is an innervation ratio and what does a small innervation ratio mean ?
how many muscle fibres are supplied by one motor neuron
A small innervation ratio allows for fine precise muscle control as there are small increases of muscle force generation compared to a huge muscle all contracting at once producing large amounts of force
What are the 3 different ways to classify different motor units
Amount of tension generated
Speed of contraction
Fatigability
What are the 3 types of motor units
Slow ( S type 1) Fast fatigue resistant ( FR, type IIa) Fast fatigable ( FF, type IIb)
Which of the motor unit has the smallest diamete cell bodies + axon
slow
What of the motor units have the largest dendritic tress
Type II muscles
What of the motor units have the fasts conduction velocity
1) Fast fatigable
2) fast fatigue resistant
3) slow
which type of motor unit produces the most force
1) FF
2) FR
3) S
which types of muscle unit can contract for teh longest amount of time
1) S
2) FR
3) FF
why do different muscles have different ratios of muscle types
for function
ie muscles used for postural stability have a greater proportion of slow type muscle fibres ( ie soleus muscle of the calf) which allows us to walk and stand up.
Muscles used for activity ( ie gastrocnemius muscle of calf) generate much more force and are made up of more fast fibres but are more prone to fatigue
what are the 2 ways that the CNS can regulate the force of musles
Recruitment
rate coding
what is recruitment
( aka how many muscle fibres are used)
CNS determines which motor units are switched on and off
What principle governs recruitment?
Size principle
What is the size principle
Size principle:
Tells the order to which muscle fibres are switch on
Small units are required first
generally slow twitch fibres
As more force is required more units are recruited
This allows fine control ( ie when writing) under which low force levels are required)
What is rate coding
( aka how many times are muscle fibres contracting)
A motor unit can fire at a range of frequencies
As firing rate increases , force produced by the muscle increases
Slow units fires at a lower frequency
What is ment by plasticity of motor units
Fibre types can change properties under many different conditions
What are the 3 scenarios where muscle fibres can change type?
Type IIB → Type IIA common under training
Type I → II in cases of severe deconditioning or spinal cord injury
Microgravity in space results in shift from slow to fast muscle fibre types
Loss of type I and II due to ageing
Preferential loss of type II fibres. This results in a large probation of type I fibres in aged muscle ( evidenced from slowe contraction time)
what are neurotophic factors
Neurotrophic factors
Muscles will waste if nerve supply is cut even if arteries remain in tact ( aka this shows muscle cells need more than glucose and O2 )
Motor neurons produce growth factors ( neurotrophic factors) to:
prevent neuronal death
promote growth of neurons after injury
Control recruitment and rate firing ( check this statement pls) ! ( aka provide Action potentials to muscles)
Why do muscles produce neurotrophic factors
prevent neuronal death
promote growth of neurons after injury
Control recruitment and rate firing ( check this statement pls) ! ( aka provide Action potentials to muscles)
What is a reflex
Automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre then outward to an effect ( ie muscle / gland) without reaching the level of consciousness
Involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
The magnitude and timing of which are determined respectively by the intensity and onset of the stimulus
Reflexes differ from voluntary movement in that once they are released , they can’t be stopped
Describe the process of a monosynaptic / stretch reflex
Tendon hammer strikes thigh
Sensory ( stretch receptor ) in thigh senses the stimulus and delivers AP to CNS via the sensory nerve that goes through the dorsal root ganglion to the sc .
Sensory neuron synapses onto a LMN which causes movement of muscle → excitatory movement of muscle and inhibitory muscle to the muscle antagonist to cause the knee jerk reaction
Reflex contraction via monosynaptic reflex .
This is just one example of a reflex there are many other reflexes
What is the effect of the CNS on reflexes
Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex
Inhibitory control of reflexed by CNS is dominated in normal conditions
What is Jendrassik’s manoeuvre
Ie Jendrassik’ s maneuver : reduces the amount of inhibition that the brain / CNS exert under the reflex making the reflex stronger
when clenching , making a fist or pulling against locked fingers when having the patellar tendon tapped ( in knee jerk reaction) the reflex becomes larger
What 2 experiments show that the CNS has a control over reflexes
Decerebration
Jendrassik manoeuvre
How do descending tracts control reflexes ( 5 ways)
Activate:
1) Alpha motor neurons → muscle to cause voluntary contraction
2) Inhibitory neurons → reduce reflex reactions
3) Propriospinal neurons → interneurons that go up + down sc to activate nearby muscles
4) Gamma motor neurons → lower motor neurons supply intrafusal muscle fibres
This will tell the SC the state of a muscle ie stretched / unstretched
ie when the organs are stretched they cause a signal to go back to the sc and generate a reflex contraction of a muscle
5) Activating terminals of afferent fibres
What is hyperreflexia and what is it caused by
overactive / brisk reflexes caused by UMN lesions
what are the symptoms of hyperreflexia
Clonus
Babinski’s sign
What is clonus
Involuntary and rhythmic muscle contraction → stretching the muscle will start a reflex rhythmic contraction of muscles until someone forcibly stops the muscle from moving .
What is babinski’s sign
When sole of foot and balls of feet are stimulated with blunt instrument:
the big toe curls downwards → normal
Big toe circles upwards and other toes will fan out → abnormal associated with upper motor neuron lesion
Note toes curl upward in infants ( this is normal) ( and hence wouldn’t be called babinski’s sign as this would be normal)
What is hyporeflexia
Blow normal or absent relaxed → associated with lower motor neuron diseases ( problem with the lower motor neurons) ->
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