Topic 9: Muscle Tissue

Practice flashcards covering Topic 9: Muscle Tissue, including tissue types, structural organization, neuromuscular junctions, sliding filament mechanism, muscle metabolism, contraction types, fiber types, and homeostatic imbalances.

What are the five primary functions of muscular tissue?

Producing movement for the body, stabilizing body positions, heat production, respiration, and moving substances through the body.

How is skeletal muscle tissue classified regarding voluntary control and striation?

It is voluntary and striated.

How is smooth muscle tissue classified regarding voluntary control and striation?

It is involuntary and non-striated.

How is cardiac muscle tissue classified regarding voluntary control and striation?

It is involuntary and striated.

What are the four special properties of muscular tissue?

Electrical excitability, contractility, extensibility, and elasticity.

What is the epimysium?

The outer layer of connective tissue that encircles the entire muscle.

What is the structural role of the perimysium?

It surrounds groups of $10$ to $100$ muscle fibers, creating muscle fascicles.

What is the endomysium?

A layer of connective tissue that separates each individual muscle fiber inside the fascicles.

What is fascia and what is its function?

A layer of connective tissue that lines the body walls and limbs to support and surround muscle groups, holding muscles with similar functions together.

How do tendons connect muscles to bones?

They are continuous with the epimysium, perimysium, and endomysium, and attach directly to the periosteum of bone.

What is the sarcolemma?

The plasma membrane of a muscle fiber.

What are T tubules?

Tunnels leading into the muscle fiber from the sarcoplasm.

What is the sarcoplasm?

The cytoplasm of a muscle fiber.

What is the function of the sarcoplasmic reticulum?

It consists of fluid-filled sacs that surround myofibrils and store $Ca^{2+}$ needed for muscle contractions.

What are myofibrils?

The contractile units of skeletal muscle composed of bundles of protein filaments.

What are the two types of protein filaments found inside myofibrils?

Actin (thin filaments) and myosin (thick filaments).

What is a sarcomere?

The functional unit of skeletal muscles.

What is the function of the Z disc in a sarcomere?

It separates adjacent sarcomeres.

What makes up the A band of a sarcomere?

Thick filaments (myosin) completely and some of the thin filaments (actin).

What is contained within the I band of a sarcomere?

Thin filaments (actin) only.

What is contained within the H band of a sarcomere?

Thick filaments (myosin) only.

What is the M line of a sarcomere?

The structural line located in the middle of the sarcomere.

What are the three main functional categories of muscle proteins?

Contractile proteins (generate contraction), regulatory proteins (switch contraction on and off), and structural proteins (keep things aligned properly).

Which muscle proteins act as contractile proteins and which act as regulatory proteins?

Actin and myosin are contractile proteins; tropomyosin and troponin are regulatory proteins.

What nerve stimulates skeletal muscle contraction, and how many neuromuscular junctions does each muscle fiber have?

A motor (somatic) nerve stimulates contraction, and every muscle fiber has one neuromuscular junction.

What happens during Step 1 (Release of Acetylcholine) at the neuromuscular junction?

Stimulation of the nerve sends an electrical signal to the nerve ending, causing vesicles to release acetylcholine (ACh).

What occurs during Step 2 (Activation of ACh Receptors) at the neuromuscular junction?

ACh fills the space between the nerve ending and receptors, binding to receptor sites on the motor end plate and opening ligand-gated $Na^+$ channels.

What occurs during Step 3 (Action Potential Production) at the neuromuscular junction?

The influx of $Na^+$ triggers an action potential along the sarcolemma to the T tubules, causing the sarcoplasmic reticulum to release $Ca^{2+}$.

What occurs during Step 4 (Termination of ACh activity) at the neuromuscular junction?

Acetylcholinesterase (AChE) breaks down ACh, inactivating the receptors.

What two binding sites are located on the myosin head?

An ATP-binding site that hydrolyzes ATP into ADP to store energy, and a binding site for actin filaments to pull them toward the midline.

What are the four steps of the sliding filament mechanism?

1) ATP hydrolysis positions the myosin head in the cocked position; 2) $Ca^{2+}$ binds to troponin, removing tropomyosin so myosin binds to actin; 3) The power stroke occurs using energy from ATP; 4) Actin detaches from myosin, and tropomyosin reattaches.

What are the three pathways used by muscle tissue to produce ATP?

Creatine phosphate, glycolysis/Krebs cycle, and the electron transport chain.

How does creatine phosphate generate ATP, and how long does its energy last?

Excess ATP transfers high-energy phosphate groups to creatine; when needed, phosphate quickly transfers back to ADP, providing energy for $15\,\text{seconds}$.

What are the key characteristics and products of anaerobic glycolysis in muscle metabolism?

It occurs in the cytosol without $O_2$, catabolizing glucose into $2\,\text{pyruvic acid}$ molecules and producing $2\,\text{ATP}$; pyruvic acid converts to lactic acid without $O_2$, providing energy for $2\,\text{minutes}$.

Where does the electron transport chain occur, and what is its ATP yield per glucose molecule?

It occurs aerobically in the mitochondria, yielding $30\text{ to }32\,\text{ATP}$ per glucose for endurance activities lasting several minutes to hours.

What is a twitch contraction?

A brief contraction of all muscle fibers in a motor unit elicited by a single stimulus, which is not very useful for accomplishing work.

How do tetanus and muscle tone differ?

Tetanus is a sustained muscle contraction without relaxation that plays a role in posture, whereas muscle tone is a normal state of partial muscle contraction.

What is the difference between isotonic and isometric muscle contractions?

Isotonic contractions maintain equal tension as the muscle length changes, whereas isometric contractions maintain equal length with no movement.

What is the difference between concentric and eccentric isotonic contractions?

In concentric contractions, the muscle shortens while contracting; in eccentric contractions, the muscle lengthens while contracting.

What are the functional characteristics of slow oxidative muscle fibers?

They are slow-twitch and highly resistant to fatigue.

What are the functional characteristics of fast oxidative-glycolytic muscle fibers?

They contract faster than slow oxidative fibers and have mild resistance to fatigue (used in walking and sprinting).

What are the functional characteristics of fast glycolytic muscle fibers?

They produce strong, quick contractions with very little endurance (used in weight lifting).

How do muscle hypertrophy and muscle atrophy differ?

Hypertrophy is an increase in muscle size resulting from overuse (beneficial for all muscles except the heart), while atrophy is muscle wasting or decrease in size from lack of use.

What causes Myasthenia Gravis and what are its symptoms?

An autoimmune disease causing damage to NMJ receptor sites on muscles, impairing contraction and resulting in extreme weakness and fatigue in skeletal and respiratory muscles.

What is Duchenne Muscular Dystrophy, what causes it, and what is its progression?

An inherited muscle-destroying disease caused by a mutated gene on the X chromosome in boys; it causes running/jumping difficulties by age $2\text{ to }5\,\text{years}$, inability to walk by age $12$, and death around age $20$ from respiratory and cardiac failure.