Muscle Control Flashcards
What are the subdivisions of the nervous system?
- Topographical subdivisions
- Functional subdivisions
- Directional subdivisions
What is included in the topographical subdivisions?
- central NS - brain and spinal cord
- peripheral NS - cranial and spinal nerves
What’s included in functional subdivisions?
- somatic (voluntary)
- visceral (involuntary) also includes the sympathetic and parasympathetic subdivisions
What’s included in the directional subdivisions?
- Afferent = towards brain and spinal cord
- Efferent = away from the brain and spinal cord
what is a neuron?
- A type of nerve cell that transmits information quickly
What do dendrites do?
-Synapse with other neurones to receive information
What does and axon do?
- axon rapidly conduct action potential to distant site
- myelination enhances conduction speed
What is a motor neuron?
- Efferent nerve cell transmitting information from CNS to muscle to elicit contraction
- they are excitatory
Complete the sentence … each skeletal muscle fibre is innervated by …
- one motor neurone
- but each neurone can innervate few or many fibres
Skeletal muscle requires innervation from what to contract?
- motor neurons
The pattern of muscle contraction (strength, speed, duration) is determined by what?
- the pattern of activity in motor neurons
what is a motor unit?
- A motor neurone plus all the muscle fibres it innervates
Ratio of neurone to muscle fibres depends on what?
- the muscle function
If a muscle has fine control and low force what size motor unit would it have?
- small motor unit
If a muscle has less control and a large force what size motor unit would it have
- large motor units
What can muscle force be controlled by?
- number of motor units recruited
- altering pattern of activity within a motor unit
What is a neuromuscular junction?
- A specialised chemical synapse between motor neurone and muscle
Synaptic vesicles contain what neurotransmitter? and what does it do?
- acetylcholine which enforces one-way messaging
why is the sarcolemma folded at the neuromuscular junction
- to increase surface area
How do we ensure that there is only one action potential per nerve?
- Acetylcholinesterase rapidly degrades Ach left in the cleft
How can you detect muscle action potentials?
- electromyography can be used to detect electrical activity in muscles
What is the function of T-tubules?
- T-tubules conduct an action potential deep into the muscle fibre
- T-tubules surrounded by sarcoplasmic reticulum
What is the function of the sarcoplasmic reticulum?
- Store of calcium ions
What are coupled receptors?
- voltage-sensitive proteins in the T-tubules which are linked to calcium channels in the sarcoplasmic reticulum
What is the name for the calcium ion channels in the sarcoplasmic reticulum?
- Ryanodine receptors
What causes Ryanodine receptors to open?
- when an action potential arrives at a ryanodine receptor, it causes a change in shape of the voltage sensor meaning that protein channels open and calcium ions move from the sarcoplasmic reticulum into the cytosol
What happens after muscle control?
calcium ions in the cytosol are pumped back into the sarcoplasmic reticulum ( the pump required ATP). This stops contraction.
Increasing the frequency of nerve impulses means what?
- contraction force doesn’t have time to fully subside before a new action potential arrives
- greater force can be developed
- more stretching of elastic components in muscle
If action potentials are frequent enough muscles will undergo what?
- tetanic contraction
What is tetanic contraction?
- Sustained, constant high force
- useful
- normal contraction type for most skeletal muscles
How does depolarisation of the postsynaptic membrane result in muscle contraction?
- The sarcolemma has thin, tube-like
extensions into the cell (T-tubules),
surrounding Z-discs of myofibrils - T-tubules conduct AP deep into muscle fibre
- Sarcoplasmic reticulum expanded and well-developed near to T-tubules
- AP travel in T-tubule stimulates Ca2+ release
from SR
