Marathon runner Flashcards
What are the 2 sources of oxygen for muscle cells?
- Direct diffusion from blood
- Myoglobin stores of O2
Outline the structure of myoglobin. What makes it efficient at storing O2?
Myoglobin is a single polypeptide with a single heme group - therefore only binds one oxygen molecule.
It is found within the sarcoplasm of muscle + cardiac cells.
It has a higher affinity for oxygen than hemoglobin due to its lower affinity for 2,3-BPG.
-> makes it good at taking up O2 from blood stream
-> makes it good at storing O2, only releasing it when needed (low pO2/ high pCO2)
What type of muscle fibres are best for endurance exercise and why?
Type 1, slow oxidative fibres.
These are good for endurance exercise because:
- They produce lots of ATP via aerobic respiration (oxidative phosphorylation).
- Lots of ATP means they are resistant to fatigue.
-They can therefore work for longer.
- They have low Myosin-ATPase activity meaning contractions can be sustained for longer.
-They have a large concentration of capillaries making for efficient access to oxygenated blood required for oxidative phosphorylation.
-Its high myoglobin count allows for binding of oxygen for storage, the oxygen can then be released when required for contraction.
-Its main energy storage is in the form of Triglycerides.
What type of muscles fibres are best for sprinting and why?
Type IIx, Fast Glycolytic fibres
High glycogen stores allows for rapid breakdown of glycogen -> glucose which can then undergo anaerobic glycolysis to produce ATP.
Its high Myosin ATPase activity allows for rapid contractions
However these fibres fatigue quickly because glycogen stores will be depleted and sparse mitochondria, capillary and myoglobin count means it has limited capacity to produce ATP aerobically.
What muscle fibres are best for less taxing exercise such as walking?
Type IIa Fast oxidative-glycolytic fibres
These are a mixture of Type I and Type IIx fibres.
They are fairly resistant to fatigue because they have capacity to produce ATP aerobically via oxidative phosphorylation - have lots of mitochondria, capillaries and myoglobin content.
They have moderate Myosin ATPase activity allowing for fairly quick contractions.
They also have moderate glyocogen storage content for conversion to glucose when required.
Describe a skeletal muscle structure
Epimysium (connective tissue) surrounds the entire muscle.
Muscle organised into Fascicles: Each fascicle surrounded by perimysium (CT) containing blood vessels and nerves.
Each fascicle is made of multiple muscle cells called muscle fibres.
Each muscle fibre surrounded by endomysium.
The muscle fibres plasma membrane is called the sarcolemma, surrounding the sarcoplasm.
Each fibre is arranged into myofibrils running in parallel which are further organised into sarcomeres.
The sarcomeres contain myofilaments which are contractile proteins actin + myosin which give skeletal muscle its striated appearance.
Describe the structure of a tendon
- Tendons are dense fibrous connective tissue.
- 70% collagen type 1, some type 3 and elastin.
-Tendon arranged into fascicles which are composed of:
-> collagen fibres (primary and secondary bundles)
-> Tenocytes (elongated fibroblasts)
Layers of tendon:
Paratenon: surrounds entire tendon.
Epitenon: under paratenon
Endotenon: surrounding fascicles; loose connective tissue containing lymphatics, nerves and blood vessels.
Outline the process of tendon healing
Day 3-5
-Inflammatory reaction, leukocyte migration
-growth factors
-Fibrin clot produced
Weeks 1-6
-Reparative/proliferative phase
-increased vascularity of paratenon
-Phagocytosis of debris
-Growth factors
-Proliferation of fibroblasts.
-Callus formation: this is a disorganised tendon made of Collagen and ECM
6wks - 9months
-Collagen is cross-linked into more organised structure.
Recovery time dependant on:
-Age.
-Severity of damage.
outline four causes of muscle fatigue during exercise
- Conduction failure
-Constant depolarisation of muscle cells results in build up of K+ ions in the T-Tubules.
-This leads to persistent hyperpolarisation meaning it is difficult to reach threshold potential to propagate another AP.
-This means there is reduced calcium release from sarcoplasmic reticulum and so reduced capacity to perform a contraction. - Reduced cross bridge cycling
- Excess accumulation of ADP + Pi in muscle cell during intense activity can inhibit cross-bridge cycling
-This delays detachment of myosin from actin - Lactic acid build up
- During intense exercise, the body turns to break down glucose for energy.
- Glucose broken down to pyruvate, which, if anaerobic conditions will be converted to lactate/ lactic acid.
-When lactic acid is produced at a rate faster then it can be metabolised it begins to accumulate.
-Excess lactic acid will reduce the pH of muscle cell which can hinder normal function of actin, myosin and myosin ATPase activity.
-As Type 1 fibres become fatigued, there will be more reliance on Type II fibres which produce more lactic acid due to reduced oxygen content. - Fuel depletion
-Glycogen stores will eventually become depleted.
-Glucose will be reserved for brain.
-Muscles will turn to triglyceride storage for ATP production however energy production through this route is much slower than via carbs and so intensity of exercise will have to drop.
