B3. Muscle Structure Flashcards
Types of muscle
There are three different types of muscle in the body…
Smooth muscle
Cardiac muscle
Skeletal muscle
Smooth muscle contracts without _________control. It’s found in walls of ________ _______(apart from the heart), e.g. _________, _________and _________ _______.
Smooth muscle contracts without conscious control. It’s found in walls of internal organs (apart from the heart), e.g. stomach, intestine and blood vessels.
Cardiac muscle contracts without __________control (like smooth
muscle) but it’s only found in the __________.
Cardiac muscle contracts without conscious control (like smooth muscle) but it’s only found in the heart.
Skeletal muscle (also called striated, striped or voluntary muscle) is the type of muscle you use to _____, eg, the biceps and triceps move the lower arm.
Skeletal muscle (also called striated, striped or voluntary muscle) is the type of muscle you use to move, eg, the biceps and triceps move the lower arm.
Role of skeletal muscle
Skeletal muscles are attached to bones by __________. _____________attach bones to other bones, to hold them together. Pairs of skeletal muscles contract and relax to move bones at a joint - the bones of the skeleton are incompressible (rigid) so they act as levers, giving the muscles something to pull against.
Skeletal muscles are attached to bones by tendons. Ligaments attach bones to other bones, to hold them together. Pairs of skeletal muscles contract and relax to move bones at a joint - the bones of the skeleton are incompressible (rigid) so they act as levers, giving the muscles something to pull against.
Antagonistic pairs
Muscles that work together to move a bone are called antagonistic pairs.
The contracting muscle is called the _________and the relaxing muscle is called the ___________.
Example - Biceps and triceps
Muscles that work together to move a bone are called antagonistic pairs.
The contracting muscle is called the agonist and the relaxing muscle is
called the antagonist.
Structure of skeletal muscle
Skeletal muscle is made up of large bundles of long cells, called ________ _______. The ____ _____________of muscle fibre cells is called the ______________. Bits of the ______________-fold ________across the _______ ________and stick into the ___________(a muscle cell’s cytoplasm). These folds are called __________(T) ___________and they help to spread electrical impulses throughout the _______________so they reach all parts of the muscle fibre
Skeletal muscle is made up of large bundles of long cells, called muscle fibres. The cell membrane of muscle fibre cells is called the sarcolemma. Bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm (a muscle cell’s cytoplasm). These folds are called transverse (T) tubules and they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
Structure of skeletal muscle
A network of internal membranes called the _______________ ____________runs through the ___________. The _______________ ___________stores and releases ________ ___that are needed for _________ ____________. Muscle fibres have lots of _______________to provide the ____that’s needed for ________ _____________. They are multinucleate (contain many nuclei) and have lots of long, cylindrical organelles called _________. ____________are made up of ________and are highly ___________for contraction
A network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm. The sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction. Muscle fibres have lots of mitochondria to provide the ATP that’s needed for muscle contraction. They are multinucleate (contain many nuclei) and have lots of long, cylindrical organelles called myofibrils. Myofibrils are made up of proteins and are highly specialised for contraction
Tip: ____________ are organelles within the cell (muscle fibre).
Tip: Myofibrils are organelles within the cell (muscle fibre).
Figure 4: Diagram showing the structure of skeletal muscle and a muscle fibre.
Examination under an optical microscope
You could look at skeletal muscle under an optical microscope. What you see will depend on how the sample has been stained and whether you’re looking at a longitudinal or transverse cross-section.
-Example
This photomicrograph shows a longitudinal cross-section of skeletal muscle.
You can see six muscle fibres. The blue parts are nuclei there are many in each muscle fibre. The cross-striations (alternating darker and lighter pink stripes) are the _-bands and _-bands of the myofibril
This photomicrograph shows a longitudinal cross-section of skeletal muscle.
You can see six muscle fibres. The blue parts are nuclei there are many in each muscle fibre. The cross-striations (alternating darker and lighter pink stripes) are the A-bands and I-bands of the myofibril
Myofibrils
Myofibrils contain bundles of thick and thin myofilaments that move past each other to make muscles contract. The thick myofilaments are made of the protein _________and the thin myofilaments are made of the protein _______.
If you look at a myofibril under an electron microscope, you’ll see a pattern of alternating dark and light bands (see Figures 5 and 6). Dark bands contain the thick ________filaments and some overlapping thin _____filaments - these are called _-bands. Light bands contain thin ______filaments only- these are called _-bands.
A myofibril is made up of many short units called ______________. The ends of each sarcomere are marked with a _-line. In the middle of each sarcomere is an _-line. The _-line is the middle of the ________filaments. Around the M-line is the _-zone. The _-zone only contains _________filaments.
Myofibrils contain bundles of thick and thin myofilaments that move past each other to make muscles contract. The thick myofilaments are made of the protein myosin and the thin myofilaments are made of the protein actin.
If you look at a myofibril under an electron microscope, you’ll see a pattern of alternating dark and light bands (see Figures 5 and 6). Dark bands contain the thick myosin filaments and some overlapping thin actin filaments - these are called A-bands. Light bands contain thin actin filaments only- these are called l-bands.
A myofibril is made up of many short units called sarcomeres. The ends of each sarcomere are marked with a Z-line. In the middle of each sarcomere is an M-line. The M-line is the middle of the myosin filaments. Around the M-line is the H-zone. The H-zone only contains myosin filaments.
Tip: To remember which band is which, think: dark = _-bands and light = _-bands.
Figure 6: A transmission electron microscope (TEM) of myofibrils showing the banding of myosin (red) and actin (yellow).
Tip: To remember which band is which, think: dark = A-bands and light = I-bands.
Figure 5: The structure of a sarcomere - a unit of a myofibril.
The sliding filament theory-
Muscle contraction is explained by the sliding filament theory. This is where ________and _______filaments slide over one another to make the __________contract-the myofilaments themselves don’t contract. The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract. Sarcomeres return to their original length as the muscle relaxes.
Muscle contraction is explained by the sliding filament theory. This is where myosin and actin filaments slide over one another to make the sarcomeres contract-the myofilaments themselves don’t contract. The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract. Sarcomeres return to their original length as the muscle relaxes.
Figure 7: Sarcomeres during relaxation (top) and contraction (bottom).
