Motor Control Flashcards
what are the features of type I muscle fibres?
slow red muscle fibres - specialised for slow, sustained, aerobic exercise. Rich capillary supply, many mitochondria, high levels of myoglobin. Generate ATP by aerobic (oxidative phosphorylation) metabolism. Metabolism gives slow twitch
What are the features of type 2b muscle fibres?
fast, white fibres - specialised for rapid, short duration, anaerobic exercise. Fewer capillaries but rich stores of glycogen. Generate ATP by anaerobic (glycolytic) metabolism. Metabolism gives fast twitch, but they fatigue quickly. Few mitochondria.
What are the features of type 2a muscle fibres?
Fast, pale red fibres - combine properties of Type 1
and Type 2b. Good capillary supply, oxidative and glycolytic metabolism. Fast twitch, fatigue resistant.
What is the histochemistry of type I muscle fibres?
ATPase activity -neutral pH
Stained darkly
What is the histochemistry of type 2 muscle fibres?
ATPase activity - acidic pH
Stained darkly
How many muscle fibres might a single motor neuron contact in a small motor unit?
10- 20
How long does a single motor unit AP last?
7 -13 ms
What is tension summation?
If a second MU action potentials occurs within the relaxation time, higher tension generated
What type of motor units do large MNs with low resistance supply?
FF 2b
What type of motor units do small MNs with low resistance supply?
S type 1
Which motor neurons are first activated with low level activation?
small, high resistance motor neurons of small motor
units.
What is the gain of the mn pool?
Relationship between output of the motoneuron pool and synaptic input
What types of fibre does a muscle spindle contain?
A muscle spindle contains two types of intrafusal fibre, nuclear bag fibres and nuclear chain fibres. Bag fibres are innervated by Ia spindle afferents while chain fibres are innervated by group II muscle afferents.
What happens to muscle spindle in passive stretch?
Both intrafusal and extrafusal fibres stretched, spindles activated
Reflex via 1a fibres causes secondary contraction
Golgi organ not activated
what happens to muscle spindle in active stretch?
central excitation of alpha mns causes contraction of extrafusal fibres, relaxation of intrafusal fibres
Spindles not activated
Tension is low
Golgi tendon organ activated, causing relaxation
How is spindle sensitivity maintained?
alpha-gamma coactivation
Intrafusal and extrafusal fibres contract; spindles activate, reinforcing contraction stimulus via 1a fibres
Tendon organ activated causing relaxation when load is too great
Golgi tendon organ
Contains capsule of axons surrounded by collagen fibres
not all collagen bundles innervated
Is there conscious perception of proprioceptive information?
Yes
Vibration stimulation of biceps 1a afferents leads to misjudgements of perceived arm position
Explain convergence in the 1a
inhibitory pathway.
Ia inhibitory interneurons receive many inputs: corticospinal, FRAs, cutaneous afferents, Ia
afferents and other 1a inhibitory interneurons.
linked alpha and gamma mns and 1a inhib interneurons form functional unit
- inputs produce a-g coac in reciprocal inhibition
What do Ib interneurons do in SC?
Ib interneurons facilitated by low-threshold cutaneous and joint afferents. May provide a “braking” effect if
obstacles or delicate objects are encountered.
Descending systems can modulate the effects of these
inputs.
What is Flexor Reflex afferent system?
Group II muscle afferents form part of a much wider
group of afferents, including joint and cutaneous that form the Flexor Reflex Afferent (FRA) system - activating
the flexion and crossedextension reflex.
When do you see Babinski sign?
babies before 6 months, or after CST injury
sole of foot stroked, big toe moves upwards
What is renshaw cell?
Inhibitory interneuron
May regulate gain of motor neurons
Contrast enhancement
What is the H-reflex?
Hoffman
While recording muscle EMG, stimulation of a motor nerve first activates largest diameter (Ia) fibres which initiate a monosynaptic reflex -H wave
Increasing stimulus strength activates motor fibres - shorter latency M wave
M wave then predominates and H decreases
What are the lateral descending pathways?
rubrospinal
CST
fine movements
What are the ventromedial descending pathways?
Vestibulospinal, tectospinal - postural control of head and neck
pontine, medullary reticulospinal tracts control posture of trunk / antigravity limb muscles
What are muscle spindles?
length receptors
specialised intrafusal muscle fibres in parallel with extrafusal fibres of main muscle
What fibres do muscle spindles contain?
2 or 3 bag fibres
3-5 chain fibres
Which axons branch to spindles and extrafusal fibres?
beta axons
Which receptors are vibration sensitive?
Paciniform corpuscles - in musculo-tendinous junction - group II fibres - vibration sensitive
What are the 4 types of joint receptors?
Type 1 - ruffini
Type 2 - paciniform
Type 3 - Golgi endings
Type 4 - free nerve endings
What are the types and features of cutaneous receptors?
Merkel discs: dynamic and static vertical touch
Meissner corpuscles: dynamic pressure
Ruffini endings: long lasting response to skin stretch
Pacinian: dynamic, vibration
What is Romberg’s sign?
Unable to stand with feet together with eyes closed
peripheral neuropathies
Is Movement direction coded by populations of cortical neurons?
Motor cortex neurons are broadly coded for direction of movement. If large numbers of cells
are recorded during reaching in different directions, the direction is seen to be coded by the
vector sum of the activity
What did Graziano find about purposeful movements?
500 ms trains of microstimulation in M1 –> purposeful, directed movements elicited
showing control of purposeful/functional movements from M1 neurons
What is PMDc suggested to be responsible for?
planning, prep of movement
Complex movements evoked from microstimulation trains in caudal or rostral premotor cortex?
caudal
What is the large-scale organisation of motor cortex?
large-scale organization of motor cortex is somatotopic. Most studies describe a rough body map with some overlap between the representations of different body parts, some fractures in the representations, and some rerepresentations
Can motor maps and circuitry change?
The connectivity between motor cortex and muscles is not fixed but fluid, changing constantly on the basis of feedback from the periphery. This feedback remapping may underlie the ability of the network to regulate almost any high-level or low-level movement parameter, flexibility needed to encode behaviorally relevant actions.
Which lesion causes disruption of visual conditioning learning?
PMd (not PMv) permanent and reversible lesions
What does lesion to PMv result in?
impaired directly cued action
eg objects to be grasped, observed actions (mirror neurons)
