1.4 Muscle fibre characteristics and functions Flashcards
(12 cards)
Common features of muscles (7)
Nervous control: nerve stimuli control muscle action
Excitability: muscles receive and respond to a stimulus to initiate movement
Contractility: muscles contract and become thicker
Extensibility: muscles have the capacity to stretch when a force is applied
Elasticity: muscles can return to their original size and shape once stretched
Atrophy: muscles can decrease in size (waste) as a result of injury, illness or lack of exercise
Hypertrophy: muscles can increase in size (growth) with an increase in activity.
Fusiform muscles
Fibres run the length of the muscle belly in the same direction as the tendon.
Designed for mobility as they produce contractions over a large range, yet they produce low force
Pennate muscles
Fibres run at angles to the tendons. Designed for strength and power. The three categories include:
Unipennate muscles: fibres are only found on one side of a central tendon (e.g. the semimembranosus in the hamstrings)
Bipennate muscles: fibres run off either side of a central tendon (e.g. the rectus femoris in the quadriceps)
Multipennate muscles: fibres branch out from several tendons (e.g. the deltoid). Generates the greatest force
Convergent muscles
Fibres radiate from the main tendon.
Compromise between fusiform and pennate as they are capable of producing strength and power while retaining mobility
Structure of skeletal muscles
Covered with a layer of connective tissue called epimysium. It thickens as it reaches the ends of the muscle to form tendons
Consists of thousands of muscle fibres that run the length of the muscle. Arranged in bundles called fasciculi, a single bundle is fasciculus.
Each individual muscle fibre is surrounded by connective tissue called the endomysium, binds the fibres together to form the bundles.
The fasciculi are surrounded by a layer of connective tissue called the perimysium, helps bind the fasciculi together
The muscle fibre
Surrounded by sarcolemma cell membrane
Sarcolemma contains sarcoplasm, containing mitochondria, myoglobin, energy nutrients, ATP, enzymes, and contractile proteins.
Muscle fibres consist of myofibrils, each containing sarcomeres for muscle contraction.
Sarcomeres
Sarcomeres are contractile units with a Z line at either end
Composed of two protein myofilaments: actin and myosin
Actin is a thin filament attached to the Z line
Myosin is a thick filament between each actin filament
Myosin filaments have cross bridges attracted to the actin filaments.
Bands and zones define sarcomeres: I band (only actin), A band (both actin and myosin), H zone (only myosin)
Sliding filament theory
Myofilaments (actin and myosin) slide across each other during muscle contraction
Calcium release at the neuromuscular junction allows myosin filaments to attach to actin
ATP breakdown allows myosin cross bridges to attach to actin filaments, causing a ‘rowing’ action and sarcomere contraction
Cross bridges detach and reattach from actin filaments, shortening the sarcomere
Structural rearrangement changes, causing Z lines to move closer together, I band to reduce width, A band to remain the same length, and H zone to disappear.
Muscle contraction occurs when actin and myosin filaments lose contact, causing muscle relaxation.
Muscle tone
Myosin filaments and actin remain in contact, causing muscle tone
Advantages: Actin and myosin are partially connected, enabling quick muscle contraction activation
Helps maintain good posture
Type 1 muscle fibres
Slow-twitch oxidative
Contain large amounts of myoglobin, and large numbers of mitochondria and blood capillaries
Red in colour, split ATP at a slow rate and have a slow contraction velocity
resistant to fatigue, and have a high capacity to generate ATP by oxidative metabolic processes
Suited to low-intensity, longer duration, aerobic work.
Example: events such as marathons, triathlons and long-distance cycling
Type 2A muscle fibres
Fast-twitch oxidative
Contain an large amount of myoglobin, and large numbers of mitochondria and blood capillaries
Pinkish in colour and have a very high capacity for generating ATP by oxidative metabolic processes
Split ATP at a very rapid rate and have a fast contraction velocity
Relatively resistant to fatigue
Classed as partially aerobic and are suited to events that require both aerobic and anaerobic elements.
Example: events such as middle-distance running and swimming
Type 2B muscle fibres
Fast-twitch glycolytic
Contain a low myoglobin content, relatively few mitochondria and blood capillaries, and large amounts of glycogen
White in colour and geared to generate ATP by anaerobic metabolic processes
Fatigue easily
Split ATP at a fast rate, and have a fast contraction velocity
Suited to high-intensity, short-duration, anaerobic work.
Example: events that require explosive actions, such as sprinting, throwing and weight-lifting
