The Motor Unit - Neurological Consideration for Movement (week 7) Flashcards
muscles are responsible for…
muscles are responsible for producing force and absorbing energy during locomotion
state 3 introductory facts about the neuromuscular basic for human movement
- MVMT = combined effort of several muscles under the control of the CNS
- CNS distributes signals to appropriate motor nerves with specific timing and in the appropriate number
- to accomplish this, the CNS needs constant feedback from a variety of sensory receptors
state the anatomical differences between the CNS PNS
- CNS - brain + spinal chord
2. PNS - cranial nerves (12 pairs) and spinal nerves (31 pairs)
what’s the main function of cranial nerves (12 pairs)
mostly used in relation to human senses. do not relate to the control of movement
state how many pairs of nerves are located at each section of the vertebrae
- cervicle - 8 pairs
- thoracic - 12 pairs
- lumbar - 5 pairs
- sarcal - 5 pairs
- coccygeal - 1 pair
state the function of the cervicle nerves
control head, neck, and upper extremities
state the function of the thoracic nerves
control the upper extremities + trunk
state the function of the lumbar nerves
control the lower extremities + pelvis
state the function of the sarcal nerves
control the lower extremities + pelvis
state the function of the coccygeal nerves
control the coccyx
state what it is meant by the key term - nerve
a nerve is a bundle of fibres within a connective tissue sheath
state 2 facts about nerves
- nerves may consist of only efferent or afferent neurones
2. however, a typical spinal nerve contains both in the same sheath
state what it is meant by the key term - neurone
a neurone is a single nerve cell
state the 3 types, and functions, of neurones
- motor neurones = efferent, signals exit spinal chord (ventral/front)
- sensory neurones = afferent, signals enter the spinal chord (dorsal/back)
- interneurones = only within the CNS, can elicit excitatory and inhibitory responses in other neurones
state what it is meant by the key term - alpha motor neurones
responsible for initiating the muscle contractions by innervating extrafusal muscle fibres
state what it is meant by the key term - gamma motor neurones
innervate intrafusal muscle fibres of the muscle receptors (muscle spindles)
state the names of the two types of motor neurones
- alpha motor neurones
2. gamma motor neurones
state the 6 main structures you need to know in motor neurones
- cell body/soma
- dendrites
- axon
- terminal branches
- myelin sheath
- nodes of ranvier
state 2 facts about the cell body/soma
- contains the nucleus
- usually contained within the grey matter of the spinal chord, or in bundles of cells just outside the spinal body called ganglia
state 2 facts about dendrites
- projections of the cell body
2. receive signals from other neurones
state 3 facts about axons
- the nerve fibre
- exits spinal chord via ventral (front) root where it’s bundled together with axons from other cells
- axons of motor neurones are large
state 2 facts about terminal branches
- un-myelinated branches at the end of motor neurones known as the motor end planes
- form neuromuscular junction with muscle fibres
state 2 facts about myelin sheaths
- axon is insulated to aid with transmission of the signals
- Schwann cells form the myelin sheaths in sections around the axon
state 2 facts about the nodes of ranvier
- the gaps between the Schwann cells
2. AP jumps between nodes via a process called saltatory conduction
state 3 facts about neuromuscular synapses
- uni-directional
- influenced by use and disuse
- all or nothing principle
- may be thousands of synapses at the end of a neurone
- no physical union between cells
state what it is meant by the key term - motor unit
a motor unit is the motor neurone plus all the muscle fibres it innervates
how many muscle fibres can there be within a motor unit, and what is the effect of this?
- between 10 and 2000 muscle fibres per motor neurone
2. the ratio directly determines the precision of the movement of the muscle
muscle fibres innervated by an axon…
muscle fibres innervated by an axon are not necessarily in the same fascicle, they are spread across the belly of the muscle
state the metabolism, size, contraction time, conduction velocity, and examples of… type 1 MU’s
- oxidative
- small
- > 70 ms
- 80 m/s
- endurance activities
state the metabolism, size, contraction time, conduction velocity, and examples of… type 2a MU’s
- oxidative
- medium
- 30-50 ms
- 80-100 m/s
- sustained power required
state the metabolism, size, contraction time, conduction velocity, and examples of… type 2x MU’s
- glycolytic
- large
- 30-40 ms
- 100 m/s
- explosive power required
state the 4 steps to the experiment to how they determined what determines motor unit type
- isolated a type 1 and type 2b motor unit from a cat
- cut axons in half on each motor neurone sand swapped them over to the other muscle fibre
- came back in a couple weeks and saw muscle fibres had adapted to the new motor neurone
- proves motor neurone determines MU type
state the 2 ways you can increase the force of a muscle contraction
- increase the number of MU’s recruited
- increase the frequency of stimulation (frequency/rate coding)
generally happens in that order
state 2 things fibre type influences
- the contraction force and velocity
2. time to develop force
order of MU recruitment (3 points)
- MU recruitment starts with smallest MU as has lowest threshold
- followed progressively by larger MU’s if more force is required
- principle reversed with release of tension (first on = last off)
state 3 facts about the frequency of MU stimulation
- if frequency low, muscle fibres can partially relax
- at higher frequency stimulation, there is no relaxation - max contraction
- combination of max MU’s and high frequency stimulation = max strength
state the 2 types of electromyography
- indwelling EMG
2. surface EMG
what is EMG used for
EMG can be used to measure muscle activation
state the 3 principles that EMG sticks to:
- brain sends signals via motor neurones
- motor neurones innervate their associated muscle fibres
- the AP in the muscle fibres initiates excitation-contraction coupling
state the 3 determinants of EMG signal size
- the number of MU’s activated
- MU AP firing rate
- types of MU’s activated
state 2 uses of EMG
- can tell you when a muscle is turned on and off
2. can tell you if a muscle is active or passive during a movement
state 1 thing you can’t use EMG for
can’t tell you muscle force (force is determined by activation, fibre length and conduction velocity)
