Muscle Types, Contraction Mechanisms, and Reflexes in Human Physiology

What are the three types of muscle tissue?

Skeletal, cardiac, and smooth muscle.

What are the characteristics of skeletal muscle fibers?

They are large, multinucleate, and appear striated under a microscope.

How do cardiac muscle fibers differ from skeletal muscle fibers?

Cardiac muscle fibers are smaller, branched, uninucleate, and joined by intercalated disks.

What is the primary function of smooth muscle?

To facilitate involuntary movements and allow for expansion and contraction.

What is the role of antagonistic muscle groups?

They move bones in opposite directions.

What is the difference between flexion and extension?

Flexion brings bones closer together, while extension moves them away from each other.

Define the terms 'origin' and 'insertion' in muscle anatomy.

'Origin' is the anchor point of a muscle (less movable), and 'insertion' is the point on the body part that will move.

What is the function of ATP in muscle contraction?

ATP is required for cross-bridge release and resetting the myosin head.

What initiates muscle contraction at the cellular level?

An increase in calcium levels in the cytosol.

What is the role of troponin in muscle contraction?

Troponin binds calcium, causing tropomyosin to move and expose the myosin-binding sites on actin.

What occurs during the power stroke in muscle contraction?

Myosin heads pull actin filaments toward the center of the sarcomere.

What is the function of the sarcoplasmic reticulum in muscle cells?

It stores calcium ions and releases them to initiate contraction.

What happens during rigor mortis?

All ATP is used, causing muscles to remain contracted due to lack of myosin detachment from actin.

What is the difference between peripheral and central fatigue?

Peripheral fatigue occurs in the muscles due to metabolic changes, while central fatigue involves reduced neural drive from the CNS.

What is the role of creatine phosphate in muscle energy metabolism?

It stores energy from ATP and provides it during muscle contraction.

What are the steps of excitation-contraction coupling?

1. ACh release, 2. Muscle action potential, 3. DHP receptor activation, 4. Ca2+ release from SR, 5. Ca2+ binds to troponin.

What are myofibrils composed of?

Thick and thin filaments, primarily actin and myosin.

What is the role of nebulin and titin in muscle contraction?

Nebulin stabilizes thin filaments, while titin connects Z disks to the M line and provides elasticity.

What is a twitch in muscle physiology?

A single contraction of a muscle fiber in response to a stimulus.

What is the significance of the T-tubules in muscle fibers?

They carry action potentials into the interior of the muscle fiber, facilitating contraction.

How does the body regulate calcium levels during muscle relaxation?

Sarcoplasmic Ca2+ transporters pump calcium back into the sarcoplasmic reticulum.

What is the effect of Clostridium tetani toxin on muscles?

It inhibits the release of inhibitory neurotransmitters, causing uncontrollable muscle spasms.

What is the role of sodium-potassium ATPase in muscle cells?

It restores ion balance across the cell membrane after action potentials.

What is the difference between unfused and complete tetanus?

Unfused tetanus allows slight relaxation between stimuli, while complete tetanus maintains steady tension without relaxation.

What are the four main contributors to muscle fatigue?

Calcium depletion/release, creatine phosphate depletion, oxygen deprivation, and ACh depletion.

What are the characteristics of slow oxidative muscle fibers?

They are aerobic, slow, fatigue-resistant, and have a high myoglobin content, giving them a darker red color.

What type of muscle fibers are fast glycolytic?

They are characterized by rapid, maximum contraction, are easily fatigued, have a larger diameter, and a paler color.

What are fast oxidative muscle fibers adapted for?

They are intermediate, fatigue-resistant, and can be glycolytic or oxidative, suitable for activities like walking.

What is a motor unit?

A motor unit consists of a motor neuron and all the muscle fibers it innervates.

How do fine and gross motor control differ in terms of motor units?

Fine motor control (e.g., fingers) has fewer muscle fibers per motor neuron, while gross motor control (e.g., quads) has many.

What are the main characteristics of skeletal muscle?

Skeletal muscle is multinucleate, has large cylindrical fibers, and is controlled by calcium and troponin.

What distinguishes smooth muscle from skeletal muscle?

Smooth muscle is uninucleate, spindle-shaped, and controlled by calcium and calmodulin, with slower contraction speeds.

What is the role of smooth muscle in the body?

It controls blood flow, respiratory passage diameter, urine expulsion, and movement of sperm, eggs, and babies.

What are the two types of smooth muscle organization?

Single-unit smooth muscle cells are connected by gap junctions and contract as a unit, while multi-unit smooth muscle cells are not electrically linked and must be stimulated independently.

What is the process of smooth muscle contraction?

Calcium binds to calmodulin, activating myosin light chain kinase, leading to phosphorylation of myosin and actin binding.

What is required for relaxation of smooth muscle fibers?

Calcium removal and dephosphorylation of myosin, which decreases myosin ATPase activity.

What is the sequence of events in a neural reflex?

1) Arrival of stimulus and activation of receptor, 2) Activation of sensory neuron, 3) Integration in CNS, 4) Activation of motor neuron, 5) Response by effector.

What are proprioceptors, and what do they include?

Proprioceptors respond to muscle stretch and tension and include muscle spindles and Golgi tendon organs.

What is the function of Golgi tendon organs?

They provide sensory information about the level of tendon stretch during muscle contraction.

What is the difference between intrafusal and extrafusal muscle fibers?

Extrafusal fibers maintain muscle tone and are involved in voluntary movement, while intrafusal fibers are specialized and located within muscle spindles.

What is alpha-gamma coactivation?

It is the simultaneous activation of alpha motor neurons and gamma motor neurons to maintain stretch on intrafusal fibers during muscle contraction.

What is the muscle stretch reflex?

A protective reflex that prevents overstretching by reflexively contracting the muscle when it is stretched.

What is the patellar reflex and its significance?

It is a monosynaptic stretch reflex that tests neural function and indicates lower back neural issues.

What is reciprocal inhibition?

A neuromuscular reflex where contraction of one muscle causes simultaneous relaxation of its opposing muscle at the same joint.

What is the crossed-extensor reflex?

A reflex that allows the body to maintain balance while avoiding a painful stimulus, causing extension in the opposite limb.

What are diagnostic reflexes?

Reflexes used to assess neural function, including stretch reflexes (e.g., patellar) and superficial reflexes (e.g., abdominal).

What are the three stages of voluntary movement?

Planning, initiating, and execution, with sensory feedback allowing for corrections.