17-01-22 - Structure of Skeletal, Cardiac, and Smooth Muscle Flashcards
Learning Outcomes
- Describe the structural hierarchy of skeletal muscles
- Classify muscles according to their different physiological function - skeletal, cardiac and smooth
- Compare and contrast the major histological features of skeletal, cardiac and smooth muscle
What are the 7 functions of skeletal muscle?
What type of muscle are responsible for each function?
• 7 functions of skeletal muscle:
1) Body movement
• Skeletal muscle contraction
2) Body posture
• Continual adjustment of skeletal muscles
3) Support and protection
• Skeletal muscles e.g surrounding joints and within the abdominal wall
4) Sphincter control
• Skeletal and smooth muscle e.g cardiac sphincter in the stomach, bladder and anus
• Mixture of voluntary and involuntary muscles e.g internal sphincter of bladder is under involuntary control and outer sphincter is under voluntary control
5) Movement along the GIT
• Smooth muscle generates peristalsis
6) Regulation of blood flow
• Cardiac muscle pumps blood
• Smooth muscle in the vessel walls regulates blood flow
7) Temperature regulation
• Skeletal muscle generates friction via shivering
• Smooth muscle is responsible for the erecting of hairs
What are the 4 characteristics of all muscles?
When does isometric contraction occur?
When does concentric contraction occur?
What is an example of concentric contraction?
When does eccentric contraction occur?
What is an example of eccentric contraction?
• 4 characteristics of all muscles:
1) Excitability
• Responsive to stimuli e.g a chemical signal such as a neurotransmitter
2) Contractibility
• Ability to shorten forcibly when adequately stimulated
3) Extensibility
• Can extend beyond their resting/relaxed length
• Can happen if 1 muscle is contracting, another has to relax in order to allow that muscle to contract, which may stretch it further
4) Elasticity – Recoil and resume is resting length after stretching
- Isometric contraction occurs when the muscle length remains fairly constant as tension is produced
- Concentric contraction occurs when the total length of the muscle shortens as tension Is produced e.g during a bicep curl
- Eccentric contraction occurs when the total length of the muscle increases as tension is produced e.g the lowering phase of the bicep curl
What are 4 common features of all muscles?
• 4 common features of all muscles:
1) Actin and myosin proteins
• Generate force for contraction
2) Use of ATP
• Needed for contraction and generated via respiration
• Aerobic oxidative respiration
• Anaerobic glycolytic respiration
3) Calcium ions (Ca2+)
• Needed for activation of contraction
4) Stimulation
• Need an action potential from a neuron
What percentage of muscle protein is made from actin and myosin?
What do actin and myosin have in common?
How does actin form a thin filament?
How is the structure of the thin filament stabilised?
What does this stability factor also cover?
What is this associated with?
What are the three different parts of troponin?
What is the function of each part?
- Actin and myosin make up approximately 90% of muscle protein
- Actin and myosin are both ATPases (enzymes) that can hydrolyse ATP to ADP and Pi
- Actin forms a thin filament through 2 filaments of actin intertwined in an alpha helix with some other proteins
- The structure of the thin filament is stabilised by a filament of tropomyosin, which covers the individual actin monomers
- In resting muscle, the tropomyosin filament also covers the active site where myosin binds with actin when contraction takes place
- The active site is associated with troponin complex, which is the regulatory aspect of contraction
- There are 3 parts to troponin: Troponin I, C, and T
- Troponin T connects o the tropomyosin
- Troponin C binds calcium that moves into the cell in order to initiate contraction
- Troponin I is the inhibiting aspect that binds to the actin, and prevents binding sites for myosin being revealed when there is currently no Calcium, ATP and neuronal stimulus
How does myosin form a thick filament?
What is found around the myosin filament?
What happens to actin and myosin when calcium floods into the muscle cell?
- Myosin forms a thick filament, which is a rod like structure composed of 300-400 individual myosin which have a rod-like chain that intertwines
- Around the thick filament, there are globular heads that jut out at very angle around the myosin filament, so it can interact with actin
- When calcium floods into the muscle cell, and there is ATP around following neuronal stimulation, the tropomyosin moves out of the way, and enables the globular heads to bind to the active sites on the actin
What is a myocyte?
What is the cell membrane referred to as in muscle cells?
What is the cytoplasm referred to as?
How many nuclei do they have?
What are muscle cells full of?
What are they composed of?
How many mitochondria are required in muscle cells?
Why is this?
What is the sarcoplasmic reticulum?
What is its role?
What are t-tubules (transverse tubules)?
What is their role?
What do they allow for in the heart?
What gives rise to striations?
What does the sarcolemma undergo?
- A myocyte is a single muscle cell
- The cell membrane in a muscle cell is called the sarcolemma
- The cytoplasm is called the sarcoplasm
- Muscle cells can have 1 or multiple nuclei, depending on the type
- Muscle cells are full of myofibrils, which are made from thick and thin myofilaments composed of actin and myosin respectively
- Muscle cells have many mitochondria, as they are very metabolically active cells, and constantly require energy for contraction
- The sarcoplasmic reticulum is extensive endoplasmic reticulum
- The sarcoplasmic reticulum stores Ca2+ ions until the initiation of muscle contraction
- T -tubules (transverse) tubules are extensions of the cell membrane
- T-tubules penetrate into the centre of skeletal and cardiac muscles, which allows for rapid transmission of action potentials into the cell, and also play a part in the regulating calcium concentration
- T-tubules allow heart muscle cells to contract more forcefully by synchronising calcium release from the sarcoplasmic reticulum of the cell
- The layout of actin and myosin gives rise to striations
- The sarcolemma undergoes depolarisation by receiving excitation from a neurotransmitter that transmits the electrical signal to the muscle cell
How many skeletal muscles are there in the body?
What % of body mass do they account for?
What is the main thing they allow for?
How do skeletal muscles attach to the skeleton?
How big are skeletal muscle cells?
How many nuclei do they contain?
Are skeletal muscles under voluntary or reflexive control?
Is skeletal muscle contraction sporadic or continual?
- There are approximately 640 skeletal muscles in the body, which accounts for about 40% of the bodies mass
- Skeletal muscles allow for body movement
- Skeletal muscles attach to the skeleton via tendons
- Skeletal muscle cells are large multinucleated cells (can be as big as 100µm - 600mm)
- They are under voluntary and reflexive control
- Skeletal muscle contraction can be both sporadic (occurring at irregular intervals) and continual e.g certain muscles contract every second to correct posture
How is muscle attached to bone?
What is the role of connective tissue in muscles?
What is a fascicle?
Why is so much connective tissue required in muscles?
What are the 3 layers of connective tissue in muscles from inside to out?
What do they exist between?
What do all of these connective tissues form?
- Muscle is attached to one via tendons
- Connective tissue covers, supports and maintains structural integrity of muscles
- A fascicle is a grouping of elongated bundles of muscle fibres (muscle cells)
- So much connective tissue is required in muscles in order to allow for allow distribution of force across the entire muscle to avoid damage/straining
• 3 layers of connective tissue in muscles from inside to out:
1) Endomysium – between individual muscle fibres
2) Perimysium – loose collagenous tissue between individual muscle fibres
3) Epimysium – dense collagenous sheath that surrounds gross muscle
• All of these connective tissues form tendons
Label this histological diagram with: • Blood vessels (B/C) • Epimysium (E) • Endomysium (barely visible) • Centre of fascicle (F) • Nuclei (N) • Perimysium (P)
How are striations formed?
What is a myofibre/myocyte?
What is a sarcomere?
What does Each sarcomere contain?
- Striations are formed by the overlapping actin and myosin myofilaments
- A myofiber/myocyte is a muscle cell containing myofilaments
- A sarcomere is the basic contractile unit of muscle fibre
- Each sarcomere contains two types of myofilaments: thin filaments made from actin and thick myofilaments made from myosin
How is the cardiac muscle able to contract?
Is the cardiac muscle voluntary or involuntary?
What is it regulated by?
What are cardiomyocytes?
Are they striated or non-striated?
How big are they?
How many nuclei do they have?
Describe the histological appearance of cardiomyocytes?
How are they joined together?
What are the roles of gap junctions and desmosomes?
What are 2 ways synchronous contraction is ensured in cardiomyocytes?
How are boundaries of sarcomeres denoted in the heart?
How many mitochondria is there in cardiomyocytes?
Why is this?
What kind of respiration does cardiac muscle use?
- The cardiac muscle can contract without stimulation (auto-arrhythmic)
- The cardiac muscle is an involuntary muscle
- It is regulated by the autonomic nervous system (ANS)
- Cardiomyocytes are the cells responsible for generating contractile force in the intact heart
- Cardiomyocytes are striated and small (about 100µm in length)
- They are typically uni-nucleated, but can be bi-nucleated
- Cardiomyocytes appear as branches interdigitations jointed together by intercalated disks formed from gap junctions and desmosomes
- The gap junctions allow for ions and small molecules to pass between the cardiomyocytes, which plays an important role in impulse conduction along the surface of cardiomyocytes (transmitting wave of excitation)
• Synchronous contraction is ensured in cardiomyocytes through:
1) Desmosomes – couples cells together to maintain structural integrity so they can contract in unison
2) Sarcoplasmic reticulum – arranged around the actin and myosin, enabling excitation and synchronous and contraction
• Boundaries of sarcomeres are denoted in the heart through t-tubules, which are at the intercalated disks
• Cardiomyocytes have a large number of mitochondria (25-35% of cell volume) so the heart can resist fatigue
• Cardiac muscle uses aerobic respiration
What is the pericardium?
What are 2 parts of the pericardium?
What are they for?
What are visceral and parietal layers?
• The pericardium is the fibrous sac that surrounds the heart
• The fibrous pericardium is the outermost layer
• It is a tough, dense connective tissue responsible for:
1) Protection
2) Anchoring to surrounding structures
3) Prevents build-up of fluid
4) Prevents heart from overextending
- The inner serous pericardium is continuous with the epicardium (outermost) layer of the heart
- It has a layer of serous fluid, which allows for friction free movement of the heart
- Visceral layer of cavity touches organ
- Parietal layer of cavity is away from organ
What are gap junctions formed from?
What do they form?
What is electrical resistance like at gap junctions?
How do cells of the myocardium contract?
- Gap junctions are formed from 6 connexons from each cell
- Gap junctions form a pore that ions can pass through
- The gap junctions allow for ions and small molecules to pass between the cardiomyocytes, which plays an important role in impulse conduction along the surface of cardiomyocytes
- Gap junctions are the sites of low electrical resistance
- Cells of the myocardium contract as a unit – all or nothing
What are the 7 places where smooth muscle is found?
• Smooth muscle is found in:
1) Blood vessels
• Regulates lumen diameter
• Contributes to the maintenance of blood pressure
2) Digestive tract
• Rhythmic peristalsis propels food
3) Bladder wall/urinary tract
4) Respiratory tract
5) Reproductive tract
6) Eyes
7) Skin
How large are smooth muscle cells?
How are they organised?
Do they have striations?
How many nuclei do they have?
Are they under voluntary or involuntary control?
What 3 things can they be controlled by?
How is smooth muscle organised in the intestinal tract?
- Smooth muscle cells are small – about 100-200µm in length
- They are spindle shaped cells arranged in sheets that are perpendicular to each other, and are less regularly organised
- Smooth muscle cells do not have striations
- They have a single nucleus
- They are under involuntary control
• Smooth muscle cells can be controlled by:
1) Autonomic Nervous System
2) Hormones
3) Stretch
• Smooth muscle in the intestinal tract is arranged in longitudinal and circular layers
What are dense bodies?
What is their role?
How are smooth muscle cells electrically connected?
How are smooth muscle cells structurally connected?
How does contraction rate of smooth muscles compare with that of skeletal and cardiac muscles?
What control are smooth muscles under?
What occurs when smooth muscle contracts?
What does this allow?
What is this due to tin the intestines?
- Dense bodies are non-contractile, but tether actin and myosin within the cell, and transmit mechanical forces within its tissues
- Smooth muscle cells are electrically connected via gap junctions, so a wave of excitation can be passed from one muscle cell to another (impulse conduction)
- Smooth muscle cells are structurally connected by focal adhesions, which transmit forces so the smooth muscle can contract in unison
- Contraction rate of smooth muscle is slow, but also longer than that of cardiac or smooth muscle
- Smooth muscles are under control from the Autonomic Nervous System (ANS)
- When smooth muscle undergoes contraction, it shortens longitudinally like skeletal muscles, but is also squeezed sideways
- This allow something to be pushed through in an organised manner, which is down to the organisation of the longitudinal and transverse circular muscles around the intestines
Skeletal, Cardiac and Smooth Visceral Muscle: • Size • Shape • Striations • Nuclear content • Intercalated discs • Gap junctions • Control • Metabolism
