Neuromuscular System Flashcards
What are the four components of a neurone?
Soma (cell body) - contains the nucleus and structures that support chemical processing of the neurone e.g. neurotransmitter production.
Axon - tail, carries nerve impulses away from cell body to other tissues or neurones.
Dendrites - tree-like structures that receive info from other neurones.
Myelin Sheath - insulates axons and enhances transmission speed.
How would you describe a synapse (neuromuscular junction)?
Junction between two neurones where the nerve impulse is carried across. Neurotransmitters are released into the synapse and bind to the receptors on the other neurone allowing transaction of the excitation.
What do neurones communicate with?
Other neurones and other tissues in the sympathetic nervous system.
What is the resting membrane potential?
Intra and extracellular fluid have different ions. The outside has mostly sodium which gives it a more positive charge, and the inside has mostly potassium, giving it a less positive charge. The differences in charge render the neurone polarised. Resting potential is -70mV. Making the cell more polarised (negative) is called hyperpolarisation, making the cell less polar (positive) is depolarisation.
Why do ions not pass freely through the cell?
If they could, the concentration gradient would not be equal. The plasma membrane is impermeable to prevent this. Sodium and potassium channels allow a tunnel for ions to pass through. Some channels are ‘leak’ channels meaning they’re open in resting neurones, others remain closed and only open in response to a signal. The polarisation of the cell depends mostly on potassium moving through potassium leak channels.
Where do potassium ions and sodium ions lie around the cell membrane?
Potassium is intracellular and sodium is extracellular. When potassium channels open, potassium moves down its concentration gradient and diffuses out of the cell. This causes charge imbalance. A sodium-potassium pump is integral to maintain -70mV.
How is an action potential generated?
(1) - 70mV = voltage gated iron channels remain closed and the movement of ions happens only through the sodium potassium pump.
(2) Dendrites receive a stimulus, usually the neurotransmitter binding to the post-synaptic membrane receptor.
(3) If the threshold has been met, the channels open creating an influx o sodium, depolarising the cell. Crossing the threshold initiates an active potential, all or nothing.
(4) The cell becomes more positive and the sodium gates close, potassium gates open and cause potassium to leave the cell, returning the cell to its negative value through repolarisation.
(5)After the potential returns to resting, this causes hyperpolarisation ‘refractory period’ and another AP cannot be generated.
How and where does an action potential spread accross?
Along the axon to another neurone or tissue. The wave of depolarisation spreads along the uncovered areas of the axon - Nodes of Ranvier.
What is the somatic nervous system?
This controls voluntary movement. When muscles contract, APs are initiated in the brains motor cortex, in the frontal lobe. The right side of the brain controls the left side of the body. The corticospinal tract is the primary descending pathway controlling voluntary movements of contractual limb muscles.
What are the types of neurones in the spinal cord?
Motor neurones (efferent) - in the ventral horn and exit through ventral roots and supply skeletal-smooth muscle.
Sensory neurones (afferent) - enter the spinal cord from the peripheral through the dorsal horn.
Interneurons - signal each other.
What are alpha-motor neurones?
receive signals and send them to the muscle fibres that they innervate. One MN can innervate 6000 muscle fibres. The MN and the muscle fibres that they innervate are termed the motor unit.
What are the types of motor unit? (twitch)
Slow twitch (S) - smaller number of type 1 fatigue resistant muscle fibres, recruited first.
Fast twitch (fatigue resistant FR) - larger number of type 2a muscle fibres, recruited second like for moderate forces.
Fast twitch (fatigable FF) recruit a large number of 2x muscle fibres, recruited last at high forces.
How does temperature affect action potentials?
Cold temp slows the sodium and potassium channel activation required to generate an AP initiation (depolarisation), reducing nerve conduction and velocity.
What is electromyography?
2 electrodes attached to the skin, bipolar ECG its called. This is because it measures difference in charge between the first and second electrode, there are many motor units underneath.
What are afferent pathways?
From muscles to the nervous system. Muscle proprioceptors (location, movement, tension - mechanoreceptors) and nociceptors (chemical changes (chemoreceptors). Together they protect the muscle from harm like excessive stretching.
