Muscle Flashcards
What are the 4 major functional characteristics of muscle?
Contractility, excitability, extensibility, elasticity.
Describe the initial processes of muscle contraction, that cause calcium ions to be released into the cytoplasm.
- Action potential travels across the sarcolemma and down the T-tubules that fold in towards the cytoplasm.
- Activation of dihydropyridine receptors that connect the T-tubules to the sarcoplasmic reticulum.
- Activate ryanodine receptors which also act as Calcium ion channels allowing Calcium ions to flow down their concentration gradient into cytoplasm.
What are the 7 main functions of muscle?
“My Cat Stretches Out Paws Regularly To Relax”
M – Movement
C – Control of Posture
S – Support and Protection
O – Control of Orifices
P – Peristalsis
R – Regulation of Blood Flow
T – Regulation of Temperature
What is the epimysium?
Connective tissue surrounding an entire skeletal muscle.
What are the principles of sliding filament theory?
Proteins don’t change length, simply slide over each other, shortening the complex. Z-Discs are the protein discs that hold filaments in this shape. Measuring distance between Z-Discs (a sarcomere: small part of muscle that would be functional) allows us to measure contraction.
What are the characteristics of tonic smooth muscle contraction? Give 2 example of smooth muscle that contract in this way.
More or less continuous smooth muscle activity, maintaining tension. Examples: vasculature (maintaining blood pressure), sphincters.
What property determines tension of muscle?
Number of cross-bridges formed. The determines the length of the sarcomeres.
What are the characteristics of phasic smooth muscle contraction? Give 2 example of smooth muscle that contract in this way.
Smooth muscle is quiescent for prolonged periods - examples of bladder and intestinal smooth muscle.
Approximately what percentage of total body mass do muscles make up?
50%
What type of smooth muscle units can have spontaneous activity?
Single-Unit Smooth Muscle (cells are connection by gap junctions). Unit is autorhythmic and tonic - example of spincter muscles.
What is the purpose of an electromyogram (EMG)?
To measure the level of activation in skeletal muscles by recording the electrical activity (action potentials) of muscle fibres during contraction.
Intercalated discs are only found in cardiac muscle, what is their function?
To enable co-ordinated contraction of cardiac muscle.
Contain
- Desmosomes (physical connections) that ensure contraction of 1 cell does not tear it from their neighbouring cells.
- Gap Junctions (electrical connections) for co-ordinated contraction.
How does the regulation of contraction differ between skeletal and smooth muscle?
Skeletal muscle contraction is regulated by Calcium ion-troponin interactions, whereas smooth muscle contraction is regulated by calcium ion-calmodulin interactions. Also in skeletal muscle, the Calcium ions are released from the sarcoplasmic reticulum, whereas in smooth muscle, most of the calcium ions come from the extracellular fluid.
How are calcium ions returned to the sarcoplasmic reticulum after muscle contraction, ready for future contraction?
Calcium ions are actively pumped back into the sarcoplasmic reticulum from the cytoplasm, using ATP.
What can force of muscle tension can be graded by?
Recruitment – the number of motor units activated.
Rate modulation – the rate of firing of action potentials from the motor neurones.
Length-tension relationship – the number of cross-bridges formed.
Describe the contraction mechanism of smooth muscle.
Action potential causes opening of voltage-gated Calcium ion channels: Calcium ions enter cell and binds to calmodulin forming a complex with myosin light-chain kinase. This complex uses ATP to phosphorylate myosin-actin cross-bridges. Without phosphorylation, the cross-bridges would not be strong enough.
Describe the structure of a myosin filament.
Larger diameter than actin filaments, heads attach to myosin binding sites on actin filaments. Contain a hinge region allowing heads to bend, shortening the muscle structure. This process requires energy from ATP.
What is a single muscle fibre bundle (a bundle of muscle cells) contained within the muscle called? What is the connective tissue called that covers this unit?
A fasciculus. Covered by the perimysium.
How do calcium ions trigger muscle contraction in skeletal muscle?
Calcium ions bind to troponin proteins at their C-site. Each troponin molecule can bind 4 Ca2+ in a co-operative fashion. This binding moves tropomyosin (bound to troponin at site T) exposing myosin-binding sites, allowing myosin heads to bind to actin filaments forming cross bridges.
How does multi-unit smooth muscle differ from single-unit smooth muscle?
Each fibre contracts independently, there are few or no gap junctions between cells, must be stimulated by automic neurones - no spontaneous activity.
Describe the structure of an actin filament.
Smaller diameter than myosin filament. Comprised of G-actin monomer units that are strung together to form an F-actin chain. 2 F-actin chains form double helix structure. Tropomyosin proteins are bound to the actin filament roughly every 7 G-actin units. Troponin proteins are bound to the actin filament roughly every 7 G-actin units. Collectively, these components form an actin filament.
What is the cell membrane of an individual muscle cell/fibre known as?
Sarcolemma.
What are the proteins found in muscle cells that enable contraction called and what 2 types of filament are they made up of?
Myofibrils, made up of actin and myosin filaments.
What is the difference between isometric and isotonic contraction?
Isometric: muscle develops tension without changing length.
Isotonic: muscle shortens while tension remains constant.
In cardiac muscle, how does release of calcium ions cause further release of calcium ions?
Action potential causes opening of voltage-gated Calcium ion channels: 25% of the required calcium ions enter from the extracellular fluid. This initial influx of calcium ions stimulates the sarcoplasmic reticulum to release the remaining 75% of calcium ions required.
What does an EMG signal represent in skeletal muscle activity?
The summed action potentials of motor units activated by nerves, indicating nerve stimulation and the level of motor unit recruitment before contraction occurs.
