anatomical BULLSHIT

Q: What do tendons connect?

Tendons connect muscles to bones.

Q: What is a tendon made of?

A: A tendon is made of dense regular fibrous connective tissue.

Q: What is the connective tissue sheath around the muscle called?

A: The connective tissue sheath around the muscle is called the epimysium.

Q: What type of fascia is the epimysium?

A: The epimysium is a superficial (external) fascia.

Q: What are bundles of muscle cells called?

A: Bundles of muscle cells are called fascicles or fasciculi.

Q: What fascia surrounds and aligns the fascicles?

A: The fascicles are surrounded and aligned by the perimysium.

Q: What are the individual muscle cells within a fascicle called?

A: The individual muscle cells are called muscle fibers.

What fascia surrounds each muscle fiber?

A: Each muscle fiber is surrounded by the endomysium.

Q: What is the plasma membrane of a muscle fiber called?

A: The plasma membrane of a muscle fiber is called the sarcolemma.

Q: Why are muscle fibers considered multinucleate cells?

A: Muscle fibers contain many nuclei because they derive from embryonic mesodermal stem cells called myoblasts, which fuse together during muscle development.

Q: What is the cytoplasm of a muscle fiber called?

A: The cytoplasm of a muscle fiber is called the sarcoplasm.

Q: What is the cytoplasm?

A: The cytoplasm is the gel-like substance inside a cell, excluding the nucleus, that contains organelles and is the site for most cellular activities. It consists of the cytosol (fluid) and structures like the endoplasmic reticulum, mitochondria, and ribosomes.

Q: What is the endoplasmic reticulum of a muscle fiber called?

A: The endoplasmic reticulum of a muscle fiber is called the sarcoplasmic reticulum.

Q: What is the cytoskeleton of a muscle cell composed of?

A: The cytoskeleton of a muscle cell is composed of myofibrils and myofilaments.

Q: How is skeletal muscle tissue innervated?

A: Skeletal muscle tissue is innervated by motor neurons in the peripheral nervous system (PNS).

Q: What is a motor unit?

A: A motor unit is a single motor neuron and all the muscle fibers it innervates.

Q: What are neuromuscular junctions?

A: Neuromuscular junctions are the points of contact between the motor neuron’s synaptic bulbs and the muscle fibers it stimulates.

Q: What is the synaptic cleft?

A: The synaptic cleft is the microscopic space that separates the synaptic terminal of the motor neuron from the sarcolemma surface of the muscle fiber.

Q: What is the motor end plate?

A: The motor end plate is the postsynaptic surface of the sarcolemma, containing many deep creases (junctional folds) to increase surface area for ACh receptors.

Q: What enzyme breaks down acetylcholine (ACh) at the neuromuscular junction

A: The enzyme acetylcholinesterase (AChE) breaks down ACh and recycles its amino acids back to the motor neuron.

Q: What principle describes muscle fiber contraction in response to ACh?

A: The "All or None" principle describes muscle fiber contraction, meaning there is either enough ACh to change permeability in the sarcolemma or not.

Q: What two types of protein make up myofilaments in muscle fibers?

A: Thick myofilaments are made of myosin, and thin myofilaments are composed of actin.

Q: What is a sarcomere?

A: A sarcomere is the repeating functional (contractile) unit of myofibrils, organized by myofilaments.

Q: What accounts for the "striated" appearance of muscle fibers?

A: Differences in the size, density, and distribution of thick and thin myofilaments result in the banded (striated) appearance of sarcomeres.

Q: What ions are most common in the extracellular fluid (ECF) and sarcoplasm?

A: Sodium ions (Na+) are most common in the ECF, while potassium ions (K+) and protein anions (Pr-) are most common inside the sarcoplasm.

Q: What is a resting membrane potential in a muscle fiber?

A: A resting membrane potential is when a muscle fiber's sarcolemma is polarized, with most Na+ outside the cell and most K+ and Pr- inside.

Q: How does the muscle fiber’s sarcolemma become depolarized?

A: When ACh binds to receptors, Na+ channels open, causing Na+ to flood into the muscle fiber, making the sarcoplasm more positively charged.

Q: What causes muscle fiber repolarization?

A: K+ channels open, allowing K+ to diffuse out of the sarcoplasm, repolarizing the muscle fiber by restoring the proper ion distribution.

Q: How is the resting membrane potential reset in a muscle fiber?

A: The Na+/K+ exchange pump moves 3 Na+ out for every 2 K+ in, resetting the muscle fiber's membrane potential.

Q: How is the change in membrane permeability conducted in muscle fibers?

A: The change is conducted along the T-tubules of the sarcoplasmic reticulum.

Q: What role does calcium (Ca2+) play in muscle contraction?

A: Ca2+ binds to troponin, causing a shape change that moves tropomyosin and exposes myosin binding sites on actin, initiating contraction.

Q: What is the role of ATP in muscle contraction?

A: ATP is needed for myosin heads to engage actin, pivot inward (power stroke), and recock (recovery stroke) for another contraction.

Q: What happens when the action potential ends in muscle contraction?

A: ACh is broken down by AChE, Ca2+ is reabsorbed into the sarcoplasmic reticulum, and the sarcomeres return to their resting length.

Q: What are graded responses in muscle contractions?

A: Graded responses are different degrees of muscle shortening, influenced by the frequency of stimulation and the number of fibers being stimulated.

Q: What are the types of graded response contractions?

A: Types of graded response contractions include twitch contraction, wave summation, incomplete tetanus, complete tetanus, isotonic contraction, and isometric contraction.

Q: What is a twitch contraction?

A: A twitch contraction is a single, rapid contraction and relaxation of a muscle fiber in response to a single action potential.

Q: What is incomplete tetanus?

A: Incomplete tetanus is a state where muscle fibers are stimulated at a frequency that results in partial relaxation between stimuli, leading to a sustained but incomplete contraction.

Q: What is complete tetanus?

A: Complete tetanus (normal scenario) occurs when the muscle is stimulated at a frequency high enough that no relaxation occurs between stimuli, resulting in a smooth, continuous contraction.

Q: What is an isotonic contraction?

A: An isotonic contraction is a type of contraction where the muscle changes length (shortens or lengthens) while maintaining constant tension, such as during lifting a weight.

Q: What is an isometric contraction?

A: An isometric contraction is when the muscle generates tension without changing its length, such as holding a heavy object still without moving it.

Q: What happens to the permeability of a muscle or nerve cell membrane at rest?

A: In a resting muscle or nerve cell, the plasma membrane (sarcolemma or axolemma) is only slightly permeable to sodium (Na+), chloride (Cl-), calcium (Ca2+), and potassium (K+) ions.

Q: Why is there more sodium (Na+) outside the cell and more potassium (K+) inside the cell at rest?

A: This is because the gated channel proteins for Na+, Cl-, Ca2+, and K+ are mostly closed in a resting cell, preventing the passive movement of ions, thus keeping Na+ outside and K+ inside the cell.

Q: What does it mean when a muscle or nerve cell membrane is described as "polarized"?

A: A membrane is polarized when there is a difference in ion concentrations across the membrane, with much more Na+ outside and much more K+ inside, resulting in a resting membrane potential.

Q: What happens when a muscle fiber receives a threshold stimulus

A: When a muscle fiber receives a threshold stimulus, the resting membrane potential changes, and Na+ gated channels open, allowing Na+ to enter the sarcoplasm, causing depolarization.

Q: What occurs after Na+ enters the muscle fiber during depolarization?

A: After Na+ enters, the Na+ gated channels close, and the muscle fiber undergoes an action potential, starting a chain reaction that eventually leads to muscle contraction.

Q: Why do Na+ and K+ tend to repel each other inside the muscle fiber?

A: Na+ and K+ are both cations, so they tend to repel each other, but are attracted to the protein anions inside and outside the muscle fiber, creating a dynamic balance of forces.

Q: How does the muscle fiber resolve the repulsion between Na+ and K+?

A: K+ gated channels open, allowing K+ to leave the muscle fiber, which repolarizes the membrane potential and restores the balance of ions across the membrane.

Q: What happens to the Na+ and K+ concentrations during repolarization?

A: During repolarization, Na+ is inside the cell and K+ is outside, which is the opposite of the resting membrane potential, but this is temporary before the membrane is reset.

Q: How is the sarcolemma reset to its resting state?

A: The Na+/K+ pump restores the resting membrane potential by actively transporting 3 Na+ out of the cell and 2 K+ into the cell, resetting the membrane for the next stimulus.

What is the synaptic cleft?

A: The synaptic cleft is a microscopic space between the axon terminal (synaptic bouton) of a motor neuron and the sarcolemma (cell membrane) of a muscle fiber.

Q: What is the role of the axon terminal in the synaptic cleft?

A: The axon terminal is the presynaptic cell because it is located before the synaptic cleft, sending signals across to the muscle fiber.

Q: What is the role of the muscle fiber in the synaptic cleft?

A: The muscle fiber is the postsynaptic cell because it is located beyond (after) the synaptic cleft, receiving the signal from the motor neuron.

Q: What occurs first when a motor neuron innervates a muscle fiber?

A: A nerve impulse (action potential) travels down the axon of the motor neuron and arrives at the axon terminal (synaptic bouton).

Q: What happens when the action potential reaches the axon terminal?

A: The action potential causes calcium (Ca2+) channels to open in the axon terminal, allowing calcium cations to enter the axoplasm inside the axon terminal.

Q: How is acetylcholine (ACh) released into the synaptic cleft?

A: Calcium (Ca2+) binds to synaptic vesicles containing ACh, enabling the vesicles to merge with the axolemma and secrete ACh into the synaptic cleft via exocytosis.

Q: How does ACh affect the muscle fiber?

A: ACh diffuses across the synaptic cleft and binds to chemically-gated protein receptors on the postsynaptic sarcolemma, opening Na+ ion channels and allowing Na+ to flood into the sarcoplasm, triggering muscle contraction.

Q: What happens if the threshold value of ACh is not reached?

A: If the threshold value of ACh is not achieved, no contraction of the muscle fiber will occur.

Q: How is ACh broken down after muscle contraction?

A: The enzyme acetylcholinesterase (AChE), found at the synaptic cleft, breaks down ACh into choline and acetyl Coenzyme-A, and Na+ channels close, returning the sarcolemma to its original permeability, ending the contraction.