Musculoskeletal system

What components make up the musculoskeletal system?

Muscles, bones, joints, and connective tissues

What is the primary function of muscle cells?

Specializing in contracting (actively shortening) and relaxing (lengthening by being stretched)

What type of energy do muscles convert into mechanical energy?

Chemical energy (ATP)

What are the three main types of muscle in the body?

Skeletal muscle, Cardiac muscle, and Smooth muscle

Where does skeletal muscle attach?

To bone, skin, or fascia

What are the three main functions of skeletal muscle?

Movement, posture/muscle tone, and heat production

During skeletal muscle movement, which bone generally moves?

The insertion bone

In a team of contracting muscles, what is the muscle actively contracting called?

The agonist (prime mover)

In a team of contracting muscles, what is the muscle relaxing and lengthening called?

The antagonist

What are synergist muscles?

Muscles that help the prime mover during contraction

What is an isotonic muscle contraction?

Occurs when a muscle changes length whilst generating tension

What is a concentric muscle contraction?

Occurs when the length of a muscle shortens as tension is generated

What is an eccentric muscle contraction?

Occurs when a muscle lengthens as tension is generated (acting as brakes, e.g., running downhill)

What is an isometric muscle contraction?

Occurs when a muscle's length does not change when generating tension

What type of contractions do postural muscles use to maintain body position?

Tonic contractions

What are Type I muscle fibres?

Slow-twitch fibres that resist fatigue, are oxidative/aerobic, and contain lots of myoglobin (red) and mitochondria (used in postural muscles)

What are Type IIb muscle fibres?

Fast-twitch fibres with larger diameters, highly glycolytic/anaerobic, fatigue quickly, and contain little myoglobin (white) or mitochondria (used in sprinting and jumping)

What are Type Ila muscle fibres?

Fast oxidative fibres that are intermediate, have many mitochondria but low myoglobin, do not fatigue as quickly as Type IIb, but generate less explosive energy

How do skeletal muscles help maintain body temperature when cold?

Through shivering, where heat generated by contractions is absorbed by passing blood and distributed around the body

What are the structural features of cardiac muscle?

Striated, uninucleate, branching cells joining together at intercalated discs; autorhythmic and involuntary

Where is smooth muscle found?

In the GI tract, walls of arteries, arterioles, venules and veins, attached to hair follicles, in hollow organs, and forming sphincters; non-striated and involuntary

What are the five key properties of muscles?

Excitability, Conductivity, Contractility, Extensibility, and Elasticity

What is the sarcolemma?

The plasma membrane of a muscle fiber

What is the sarcoplasm?

The cytoplasm of a muscle cell, filled with myofibrils, myoglobin, and stored glycogen

What is the function of the sarcoplasmic reticulum (SR)?

To regulate calcium ions ($[Ca^{2+}]$) by storing them at rest and releasing them when stimulated to contract

What are T tubules (transverse tubules)?

Hollow tubes formed from the sarcolemma that penetrate into the cell near terminal cisternae, conducting action potentials deep into the cell and aiding delivery of $O_2$ and glucose

What is a triad in skeletal muscle?

Successive groupings of three membranous structures: terminal cisternae, T tubule, and terminal cisternae

What are myofibrils?

Densely packed, rodlike contractile parts of muscle cells that run parallel and extend the length of the cell

What is a sarcomere?

The smallest contractile unit of a myofibril, located between two Z discs/lines

What are A bands and I bands in skeletal muscle?

A bands are dark, anisotropic (polarizing light) bands; I bands are light, isotropic (non-polarizing) bands

What is the H zone?

A slightly lighter zone in the middle of each A band where thin filaments do not overlap thick ones

What proteins make up thick filaments?

Myosin, consisting of a rodlike tail and two globular heads (crossbridges) with ATPase activity

What protein makes up thin filaments?

Actin, arranged in a helical structure with myosin-binding sites

What is the function of tropomyosin?

A regulatory protein that spirals around thin filament cores to block actin's attachment sites for myosin when the muscle is relaxed

What is the function of troponin?

A regulatory protein that binds to actin, tropomyosin, and $Ca^{2+}$ ions to control contraction

What is the function of titin?

A stretchy protein that attaches thick filaments to the Z disc, can stretch to 4x resting length, and helps stabilize sarcomeres

What is the function of myomesin?

Connects titin to adjacent thick filaments

What is the function of nebulin?

An inelastic protein that aligns thin filaments

What is the function of dystrophin?

Links thin filaments to the sarcolemma and transmits tension generated to tendons

What happens to sarcomeres during muscle contraction according to the sliding mechanism?

Myosin cross-bridges pull thin filaments inward, Z discs come closer together, and sarcomeres and muscle fibres shorten while filament lengths do not change

What neurotransmitter is released by motor neurons at the neuromuscular junction (NMJ)?

Acetylcholine (ACh)

How does ACh trigger a muscle action potential?

It binds to nicotinic ACh receptors (nAChR) on the motor end plate, opening channels that allow $Na^+$ ions to diffuse in, causing depolarization

What role does calcium play in excitation-contraction coupling?

$Ca^{2+}$ released from the SR binds to troponin, changing its conformation to shift tropomyosin and uncover myosin-binding sites on actin

What powers the power stroke during the contraction cycle?

Hydrolysis of ATP by myosin heads

How does muscle relaxation occur?

ACh is hydrolyzed by acetylcholinesterase (AChE), $Ca^{2+}$ active transport pumps clear calcium back into the SR, and tropomyosin-troponin complexes re-shield binding sites

What are circular muscle fibre arrangements (sphincters)?

Concentric rings that surround external body openings to close them upon contraction (e.g., mouth, eyes)

What are convergent muscle fibres?

Muscles with a wide origin that converge towards a single tendon (e.g., pectoralis major)

What are parallel muscle fibres?

Muscle bundles running parallel to the long axis of the muscle (e.g., biceps brachii, sartorius)

What are pennate muscle fibres?

Short bundles attaching obliquely to a central tendon like a feather (unipennate or bipennate like rectus femoris)

How many named bones make up the human skeleton?

206 named bones

How many bones make up the axial skeleton and what regions does it include?

80 bones; includes the skull, vertebral column, and bony thorax

What does the appendicular skeleton consist of?

The bones of the upper/lower limbs and their pectoral/pelvic girdles

What are the functional classifications of joints?

Synarthroses (immovable), Amphiarthroses (slightly movable), and Diarthroses (freely movable)

What are the structural classifications of joints?

Fibrous, Cartilaginous, and Synovial

What are examples of fibrous joints?

Sutures (skull), Syndesmoses (distal tibiofibular joint), and Gomphoses (tooth in socket)

What are examples of cartilaginous joints?

Synchondroses (epiphyseal plates) and Symphyses (intervertebral joints)

What are the key structural features of a synovial joint?

Articular cartilage, joint cavity filled with synovial fluid, and a double-layered articular capsule (fibrous capsule and synovial membrane)

What are the three main types of synovial joint movements?

Gliding, Angular (flexion, extension, abduction, adduction, circumduction), and Rotation

What is a lever in the musculoskeletal system?

A rigid bar (bone) that moves on a fixed point (fulcrum/joint) when a force (effort/muscle) is applied to move a resistance (load)

What is muscular dystrophy?

A group of genetic conditions causing progressive weakness and degeneration of skeletal muscles due to sarcolemma tearing during contraction

What is myasthenia gravis?

A progressive autoimmune condition where nAChRs are destroyed in the NMJ, causing muscle weakness

What is rheumatoid arthritis?

An autoimmune and inflammatory condition affecting joints in a symmetrical pattern

What is osteoporosis?

Loss of bony tissue resulting in bones at a higher risk of fracture