Nerves, MUs, planes, axes Flashcards
Function of the spinal cord
To transmit signals from the brain to the peripheral nervous system and from the peripheral nervous system to the brain
What is the role of the nervous system
The nervous system collects information from external and internal stimuli,
processes the information, and initiates and controls the response of the
musculoskeletal system to the stimuli
Cranial and spinal nerves
12 pairs of cranial nerves that pass from the brain through openings in the skull to the head, chest, neck and abdomen
31 pairs of spinal nerves that orignate from the SC, which pass through openings between the vertebrae on each side and then form different plexuses
5 plexi of the spinal nerves
Cervical
Branchial
Lumbar
Sacral
Pudendal
Motor neurons consist of
Cell body
Dendrites
Axon
Nodes of Ranvier
Terminal branches
Where is the cell body located
Located within the spinal cord (CNS)
What do dendrites do
transmit impulses from the CNS to the cell body
The dendrites of motor neurons synapse with thousands of other neurons. Some may be inhibitory, others excitatory
Role of the axon
Transmits impulses away from the cell body, towards the muscle
How does an impulse travel from the cell body to the terminal brances
Dendrites receive information from surrounding tissue within the CNS and conduct nerve impulses to the cell body
If the impulse exceeds the threshold of the cell body, an AP is sent from the cell body down to the muscle fibres that the motor neuron innervates with
What is a motor unit
A single motor neuron and all the muscle fibres that it innervates
If a movement needs greater precision, what size of motor units will there be?
Small motor units
Motor units with motor neurons that innervate fewer muscle fibres are associated with greater precision
If a movement needs greater force generation, what size of motor units will there be?
Large motor units
Motor units with motor neurons that innervate many muscle fibres are associated with greater force generation
How does the impulse travel across the NMJ?
ACh is released and binds to receptors on sarcolemma, causing it to depolarise
This initiates muscle contraction
What does an influx of sodium ions do?
An influx of sodium ions through sodium channels associated with the ACh receptors causes depolarization of the muscle fibre (end plate potential), which creates an action potential within the muscle fiber
What do T tubules do?
Following depolarisation of the sarcolemma, the AP travels to the interior of the MF through T tubules
The action potential then triggers the release of calcium ions from its storage in the ________.
Sarcoplasmic reticulum
The calcium ions diffuse out of the sarcoplasmic reticulum and into the_____
Sarcoplasm
What initiates contraction of the muscle fibre by its sarcomeres?
The arrival of calcium into the saroplasm
What is the sliding filament theory?
Thick myosin filaments attach and pull on thin actin filaments so they slide over one another. This sliding pulls the Z lines of the sarcomere closer together, thus shortening the sarcomere and an increase in tension in the muscle
How does calcium open the binding sites?
Calcium arrives and bonds to troponin, displacing tropomyosin, opening binding sites
Phases of a single muscle contraction in response to a single depolarisation (a twitch)
Stimulus
Latent period - 5 milliseconds following stimulus
Contraction phase - muscle fibres begin shortening, lasts about 40ms
Relaxation phase - lasts 50ms
What is the motor unit All or None theory
When an AP is initiated in a motor neuron, it causes depolarisation of all the muscle fibres innervated by the motor neurone
2 ways in which muscle tension can be graded
- Number of motor units recruited
- Frequency of motor unit stimulation
For a task requiring great strength, would motor units be stimulated more or less frequently
More
What is summation
When successive stimuli are provided before relaxation phase of first twitch has completed, subsequent twitches combine with the first to produce a sustained contraction
This generates a greater amount of tension than single contraction would produce individually
What is tetanus
As frequency of stimuli increase, the resultant summation increases
accordingly producing increasingly greater total muscle tension
* This is true up to a point, once the muscle is receiving impulses at a rate that
it cannot relax, it reaches a state of continuous contraction (tetanus)
3 axes of roation and the plane of movement that works around this axis
Mediolateral axis (sagittal)
Anteroposterior axis (frontal)
Vertical/longitudinal axis (transverse)
What is internal rotation
The anterior surface of the moving segment rotates medially
