NM and spinal cord control of movement Flashcards Preview

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Flashcards in NM and spinal cord control of movement Deck (46)
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What is an EPSP

excitatory post synaptic potential


What is an IPSP

inhibitory post synaptic potentials


What determines whether a post synaptic cell fires?

Summation of EPSP's and IPSP's and the time they arrive


How can action potenitails be measured

neuography - small potentials

electro muography - large potenitails


What happens to the end plate at rest?

At rest, individual vesicles release ACh at a very low rate causing miniature end-plate potentials (mEPP)


What is an alpha motor neurone?

These are the lower motor neurons of the brainstem and the spinal cord

They innervate the (extrafusal) muscle fibres of the skeletal muscles


What do alpha motor neurones do?

They innervate the (extrafusal) muscle fibres of the skeletal muscles

Their activation causes extrafusal muscle contraction


What are extrafusal muscle fibres?

The skeletal muscle fibres containing actin and myosin

Involved in muscle contraction


What is the motor neurone pool?

The motor neuron pool contains all alpha motor neurons innervating a single muscle


What determines the ability of a muscle to exatct fine control?

The number of different motor neurones that innervate the muscle

The more neurones innervating the mucle = more control


How does alpha motor innervation change from neonate to birth

Before birth several motor neurones can innervate one muscle fibre. In develpoment one wins out and so the others die off

Leaves only one motor neurone's braches innervating the muscle fibre


what is a motor unit?

This is the name given to a single motor neuron together with all the muscle fibres that it innervates.

It is the smallest functional unit with which to produce force.


What happens when you stimulate a motor unit?

Stimulation of one motor unit causes contraction of all the muscle fibres in that unit.


Describe a Type I motor unit

smallest diameter cell bodies

small dendritic trees

thinnest axons

slowest conduction velocity


How are the different types of motor unit distrubuted in a muscle?

Randomly distrubuted throught the muscle so one area of the muscle isnt weaker than another


What are the types of motor unit?

Slow - type I (S)
Fast - type IIA (FR)
type IIB (FF)


Describe a IIA motor unit properties

Fast twitch
Moderate tension/force
Fatigue resistant


Describe a type IIB motor unit properties

Fast twitch
High tension/force
High fatigue


Describe the structure of a type II motor unit

larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity


How is muscle force regulated?

Recruitment and rate coding


Descibe muscle recuirtment

Motor units are not randomly recruited. There is an order to this.
Governed by the “Size Principle”.

Smaller units are recruited first (these are generally the slow twitch units).

As more force is required, more units are recruited.

This allows fine control (e.g. when writing), under which low force levels are required.


Describe muslce rate coding

A motor unit can fire at a range of frequencies.

Slow units fire at a lower frequency.

As the firing rate increases, the force produced by the unit increases.

Summation (tetanus) occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.


Which order is re-recruitment in?

The opposite order to recruitment, fastest switched off first


What are Neurotrophic factors?

Are a type of growth factor
Prevent neuronal death
Promote growth of neurons after injury


Can muscle firbre change type?

Type IIB to IIA most common following training

Type I to II possible in cases of severe deconditioning or spinal cord injury. Microgravity during spaceflight results in shift from slow to fast muscle fibre types


What happends to mucsle firbre types in age?

Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).


What are the pyramidal tracts?

Lateral corticospinal tarct
Anterior corticospinal tract


What are the extra pyramidal tracts?

Vestibulobulbar tract
Oliviospinal tract
Reticulospinal tract
Rubrospinal tract


How are the pyramidal tracks crossed?

Limb neurones crossed
Trunk neurones largely uncrossed


Define reflex

An automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness.

An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli, whose magnitude and timing are determined respectively by the intensity and onset of the stimulus