Voluntary and Involuntary Muscles
Types of Muscle
- Skeletal Muscle: responsible for movement, usually attached to bone, make up bulk of body's muscle tissue.
- Cardiac Muscle: found only in the heart, myogenic meaning they are self stimulating causing a continuous rhythm.
- Involuntary/Smooth Muscle: found in many parts of the body such as walls of hollow organs such as bladder and stomach, and in vessels such as arteries and digestive tract.
Muscle Type |
Skeletal |
Cardiac |
Involuntary/Smooth |
Fibre Appearance |
Striated |
Specialized striated |
Non-striated |
Control |
Voluntary |
Involuntary |
Involuntary |
Arrangement |
Regular for unidirectional contraction |
Cells branch and interconnect for simultaneous contraction |
No regular arrangement |
Contraction Speed |
Fast |
Medium |
Slow |
Length of Contraction |
Short |
Medium |
Long |
Structure of Skeletal Muscle
- Muscle Fibres
- Skeletal muscles are made of bundles of muscle fibres within a plasma membrane known as a sarcolemma.
- Contain multiple nuclei and are longer than normal cells, formed by multiple cells fusing together for strength.
- Shared cytoplasm within muscle cells is known as sarcoplasm.
- Parts of the sarcoplasm fold inwards (T Tubules) to spread electrical impulses throughout the sarcoplasm, ensuring it all contracts simultaneously.
- Muscle fibres have many mitochondria to provide the large quantities of ATP required for muscle contraction.
- Contain a modified version of endoplasmic reticulum known as sarcoplasmic reticulum extending throughout muscle fibre containing calcium ions needed for contraction.
- Myofibrils
- Long cylindrical proteinaceous organelles within muscle fibres specialised for contraction.
- Collectively very powerful, especially when organised parallel to each other.
- Myofibrils can be one of two filament types:
- Actin - the thinner filament consisting of two strands twisted around each other.
- Myosin - the thicker filament consisting of long rod-shaped fibres with bulbous heads that project to one side.
- The light bands of myofibrils are where the filaments do not overlap (isotopic bands)
- The dark bands are a result of thick myosin filaments, with particularly dark edges where it overlaps with actin.
- The Z-line is found at the centre of each light band. The distance between two Z lines are known as sarcomeres. Sarcomeres are the functional unit of the myofibril. The sarcomere shortens when a muscle contracts.
- The H-zone is a light coloured region found in the centre of each dark band, where only myosin is present. The H-zone shortens when the muscle contracts.
- The textbook just cba to put the answers to this section?
- There are two types of muscle fibres in the body with different proportions of each fibre.
- Slow twitch fibres
- Fibres contract slowly
- Less powerful contractions over a longer period
- Used for endurance activities e.g. your mum
- Gain energy from aerobic respiration
- Rich in myoglobin making the fibres appear red.
- Rich supply of blood and many mitochondria.
- Found in many skeletal muscles which are constantly contracted such as the dorsal and calf muscles used for staying upright.
- Fast twitch fibres
- Fibres contract quickly
- More powerful over a shorter period.
- Used for short bursts of power as they tire quickly.
- Gain energy from anaerobic respiration.
- Low levels of myoglobin means they are pale coloured.
- Contain many thick myosin filaments.
- Store creatine phosphate, a molecule able to rapidly generate ADP in anaerobic conditions.
- Found in muscles which only require short bursts of energy such as the iris or bicep.