Module 4: Section 4 - Skeletal Muscle metabolism

what are the two major classifications of fatigue

central and muscle

what is central fatigue

a slowing down and cessation of activity even though the muscle fibres themselves are not fatigued due to the central nervous system decreasing its activation of motor neurons

why does central fatigue happen

can be because the person is bored with the activity, they are tired, or just lack motivation to continue to exercise

what is muscle fatigue

reduced contractile activity before the ATP supply runs out

how does muscle fatigue happen

1. accumulation of ADP and phosphate groups

2. accumulation of lactic acid

3. accumulation of extracellular potassium

4. depletion of glycogen

how does an accumulation of ADP and phosphate groups cause muscle fatigue

an excess of ATP metabolite concentrations can interfere with cross-bridge cycling

how does an accumulation of lactic acid cause muscle fatigue

by inhibiting the enzymes of glycolysis which reduces ATP production and interfering with excitation-contraction coupling

how does an accumulation of extracellular potassium cause muscle fatigue

since there is no ATP, the sodium-potassium pump cannot function correctly making concentration gradients form and with extra potassium, the muscle fibres are less excitable

how does a depletion of glycogen cause muscle fatigue

there is nothing to make glucose from so no ATP is being made, no energy source present

types of muscle fibres

slow twitch (type I)

fast twitch (type II)

what are the properties of slow and fast twitch muscle fibres

1. speed of contraction

2. innervation

3. metabolic properties

what does speed of contraction mean regarding slow twitch fibres

they contract and relax at slower rates than the other type of twitch fibres

what does innervation mean in regards to slow twitch fibres

what type of motor neuron supplies them, these types of fibres are supplied by alpha 2 motor neurons meaning they have a lower activation threshold and slower conduction speeds

what does metabolic properties mean regarding slow twitch fibres

they produce their ATP via aerobic processess (oxidative)

what does speed of contraction mean regarding fast twitch fibres

they contract and relax at a quicker rate

what does innervation mean in regards to fast twitch fibres

are supplied by alpha 1 motor neurons and since they are the larger type, they have a higher activation threshold and faster conduction speed

what does metabolic properties mean regarding fast twitch fibres

split into two types, fast oxidative glycolytic fibres and fast glycolytic fibres

how do fast oxidative glycolytic fibres work

they make ATP by both aerobic and anaerobic metabolism

how do fast glycolytic fibres work

makes ATP by anaerobic means

how does the colour of muscle fibres change

by how they produce their energy

what are red fibres

slow oxidative and fast oxidative glycolytic fibres, they have numerous mitochondria and are highly vascularized (lots of blood vessels), have lots of myoglobin to support the high use of oxygen

what does the myoglobin do in highly vascularized red fibres

gives the red fibres their red look

what are white firbes

fibres that mostly use anaerobic metabolism and have few mitochondria, no myoglobin; fast glycolytic fibres

so what are the types of muscle fibres?

slow oxidative

fast oxidative glycolytic

fast glycolytic

overview