motor units and muscle fibres Flashcards
what is a motor neurone
a nerve cell that conducts a nerve impulse to a group of muscle fibers
what is a motor unit
A motor neuron and the muscle fibres stimulated by its axon
what is a neurotransmitter
a chemical produced and secreted by a neuron which transmits the nerve impulse across the synaptic cleft to the muscle fiber
what is the neurotransmitter in motor units called?
acetylcholine
what is the all or none law
all muscle fibres within a motor unit are stimulated or none are
what does muscle contraction depend on
-number of motor units recruited
-the frequency of which the impulse arrives
what is a neuromuscular junction
where an axon terminal meets at muscle fibre
what is a synaptic cleft
a gap across which acetylcholine is secreted after an electrical impulse has reached the motor endplate and stimulated the vesicle to release it.
function of dendrites
receive incoming signals from other neurons
function of nodes of ranvier
allow an action potential to propagate quickly down an axon - allows the impulse to jump from node to node
function of the myelin sheath
Protect and electrically insulate the axon
Increase speed of nerve impulse transmission
what is a neuromuscular system
This is composed of all the motor units, muscles, and nerves that work together.
what is the motor end plate
location where an action potential can travel to to stimulate a muscle fibre - specialised synapses at the end of axon branches of a motor neuron
How does an eletrical impulse stimulate a muscle cell?
- dendrites of the motor neuron recieve impulses from other neurones + pass them on to the cell body where a nerve impulse is then initiated
- the nerve impulse is conducted down the axon of the motor neuron by a nerve action potential to the synaptic cleft
- the neurotransmitter (acetylcholine) is secreted into the synaptic cleft to conduct the nerve impulse across the gap
- if the electrical charge is above a threshold, the muscle fibre will contract
- this happens on an ‘all or none’ basis
what is the protein that carries the oxygen from the blood to the haemoglobin
myoglobin
what are structural characteristics of slow oxidative muscle fibres
-many mitochondria
-high capillary density
-high myoglobin content
what are structural characteristics of fast glycolytic muscle fibres
-large neurone size
-large amount of fibres per neurone
-high phosphocreatine store
what are structural characteristics of Fast Oxidative Glycolytic Muscle Fibres
-large neurone size
-large fibres per neurone
-high mitochondria density
-high phosphocreatine store
what are functional characteristics of slow oxidative muscle fibres
-fatigue resistant
-aerobic respiration
-low force and strength of contraction
what are functional characteristics of fast glycolytic muscle fibres
-high strength and force of contraction
-fatigues easily
-high anaerobic capacity
what are functional characteristics of Fast Oxidative Glycolytic Muscle Fibres
-moderate strength and force of contraction
-moderate fatigue resistance
-moderate aerobic and anaerobic capacity
Sporting example of slow oxidative muscle fibres
Marathon runner
Sporting example of fast oxidative glycolytic muscle fibres
800m-1500m runner
A sporting example of a fast glycolytic muscle fibre
100m sprinter
What does high capillary density mean for an athlete
More O2 can be transported to muscles
What does high mitochondria density mean for an athlete
More anaerobic respiration can take place-more energy
What does high myoglobin store mean for an athlete
More O2 in muscle to mitochondria
What is phosphocreatine
High energy compound that can be broken down without oxygen
What happens during the first stage of action potential (polarisation)
Sodium ions are extra cellular and potassium ions are intercellular.
The voltage is -70mvolts which creates an imbalance
What happens during the second stage of action potential (depolarisation)
Sodium ions move into intercellular space through sodium gates
The voltage is -55mvolts
This is called the threshold of excitation
What happens during the third stage of action potential (repolarisation/hyperpolarisation)
Potassium ions move to extra cellular space through potassium gates
Charge then becomes too negative (-80mvolts)
This means it is hyperpolarised
What happens on the fourth stage of action potential (polarisation)
It returns back to resting potential
Potassium ions are in intracellular space and sodium ions are in extra cellular space
-70mvolts
What happens when impulses travel through synapses
-calcium ions rush into axon terminals
-acetylcholine (a neuronetransmitter) is released and the impule travels across the synapse
What is resting potential
Where there is a lower charge inside the neurone than outside the neurone
What is action potential
The electrical impulse carried down the axon
