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Flashcards in Locomotion and posture Deck (33)
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What observable signs may characterise faulty motor control?

Paralysis or weakness


Increased reactivity

Ticks, twitches and jerks

Fibrillations and fasiculations

Loss of coordination and smoothness

Loss of the effectiveness of movements


Describe the difference between signs, symptoms and syndromes?

Signs: observable or measurable motor abnormalities, the presence of abnormalities, or the absence of normal motor actions

Symptoms: problems of motor functions reported by patients

Syndromes: associated or clustered signs and symptoms


Describe the morphology of motor neurons?

Large, myelinated axons 

Synapse spreads immensely over territory of muscle 


Describe the organisation of motor neurons within the spinal cord?

Located in the ventral/anterior horn

Topographical organisation

Form motor columns 


Describe the relationship between motor neurons and muscle fibres?

One to many relationship

One motor neuron innervates many muscle fibres - MOTOR UNIT


What is a motor unit?

All of the muscle fibres innervated by a single motor neuron

Vary in size (2-100s)



How many motor units are found in each muscle?

Several motor units make up one muscle 


What activates muscles?

How is this level of activation altered?

Activated by action potentials

Change level of activation by number of APs delivered (APs all same intensity)


Describe the way in which muscle fibres are recruited?

Henneman's size principle: recruit smallest motor units first, then larger ones 

So, start with small forces, then increase

Also, recruit slow muscle fibres first, then fast fatigue-resistant, then fast fatigable

So, recruit aerobicaaly active, then anaerobically active 


Describe the synapse of motor neurons?


Very large, spread out over muscle

Secure synpase (aka 1:1): any AP sufficient to cause contraction 


Which neurotransmitters and receptors are involved at the NMJ?

Ach and NicR


Why is the NMJ a secure synapse?

NMJ spreads over large area

Lots of post-junctional folds that increase SA for NicR - lots of Ach can bind, and massive amount of ion channels can open to generate current 


What are the outcomes of muscle inactivation?



Atrophy and degeneration


Describe the general response to muscles remaining un-activated?

Undergo changes that increase their capacity to become excited 


What is a fibrillation?

What are they caused by?

Tiny muscle contraction caused by activity of a single muscle cell

Due to hypersensitivity: after a period of inactivation, muscle cell increases Ach receptor expression to become more excitable 


What is a fasiculation?

What are they caused by?

Group of muscle fibres contracting involuntarily

Probably a motor unit synaptically activating due to spontaneous activation of a degenerating motor neuron/axon 


Are fibrillations and fasiculations measurable?

Fibrillations are not measurable (sub-threshold, no AP generated)

Can measure fasiculations 


Describe the outcome after long term denervation of muscle?

Atrophy and degeneration

Irreversible muscle loss


When are muscles inactive?

Rarely inactive

Have a resting tone

Only inactive during REM sleep


Which types of motor neurons cause involuntary muscle activation?

Lower motor neurons


What is the afferent input to monosynaptic reflexes (e. knee jerk reflex)?

'Muscle sense'

Length detected by intrafusal fibres/muscle spindles

Force detected by Golgi tendon organs 


What are the effectors of the monosynaptic reflexes (eg. knee jerk reflexes)?

Motor neurons

Direclt innervated by afferent input 


Describe the signs of a lower motor neuron lesion?


Which types of motor neurons cause voluntary muscle activation?

Upper motor neurons


Define an upper motor neuron?

A motor neuron that controls the excitability of lower motor neurons


Where does control of excitation of motor neurons arise from?

Some from spidle afferents

A lot from descending fibres from the brain (make connections mostly to interneurons, but some directly to motor neurons)


What are the two pathways for motor information to descend from the brain to the spinal cord?

Lateral pathways

Ventromedial pathways 


Describe the organisation of the spinal cord, with reference to the lateral and ventromedial tracts?

Topographic organisation

Motor neurons closer to midline of spinal cord innervate more proximal muscles

More lateral motor neurons innervate more distal muscles

Lateral tracts innervate more lateral motor neurons

Ventromedial tracts innervate motor neurons closer to midline 


Compare the motor functions controlled by the lateral and ventromedial corticspinal tracts?

Lateral - voluntary, skilled movements (distal muscles)

Ventromedial - postural control (proximal muscles)


Which is the only tract in humans that has direct connections between upper and lower motor neurons (no interneurons)?

Lateral corticospinal tract


List the three parts of the brainstem that give rise the ventromedial pathways?

Briefly describe the function of each?

Lateral and medial vestibulospinal tracts (postural control from vestibular nuclei)

Reticulospinal tract (maintains postural control in midline muscles)

Colliculospinal tract (orienting reflexes and visual looming)


describe the general effect of loss of brain control over the spinal cord (i.e. UMN damage)?

Motor neurons exhibit hyper-excitability (most of the inputs from the brain were inhibitory)


Describe the signs of an upper motor neuron syndrome?