Muscle Types Overview

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Questions and Answers

What shape are smooth muscle fibers?

Spindle shape (correct)

Branched shape

Multi-nucleated shape

Cigar shape

Which statement about cardiac muscle is true?

It is striated and voluntary.

It has intercalated discs. (correct)

It is found in the walls of hollow visceral organs.

It contracts rapidly and can fatigue quickly.

What initiates muscle contraction in muscle fibers?

The activation of myosin's cross bridges (correct)

Intercalated discs signaling adjacent cells

Direct ATP consumption by muscle fibers

Calcium triggering nerve impulses

Which type of muscle is involuntary and does not have striations?

Smooth muscle Signup and view all the answers

What is the primary function of myosin heads during muscle contraction?

To bind to actin and generate tension Signup and view all the answers

How do skeletal muscles often respond to stimulation?

Voluntarily through conscious control Signup and view all the answers

What role does calcium play in muscle contraction?

Calcium initiates the contraction process. Signup and view all the answers

What structure holds adjacent thick filaments together within a sarcomere?

M line Signup and view all the answers

What is the primary function of the iliopsoas muscle group?

Flex the thigh or trunk on thigh Signup and view all the answers

Which muscle type is primarily responsible for propelling blood throughout the body?

Cardiac muscle Signup and view all the answers

What is the function of the endomysium in skeletal muscles?

Surrounds individual muscle fibers Signup and view all the answers

Which muscle assists in flexing the vertebral column laterally in addition to flexing the thigh?

Psoas major Signup and view all the answers

Which muscle is primarily involved in achieving the cross-legged position?

Sartorius Signup and view all the answers

What is a common consequence of straining the muscle group that consists of the adductors?

Pulled groin Signup and view all the answers

Which adductor muscle primarily extends the thigh when working with the hamstrings?

Adductor magnus Signup and view all the answers

Which function is NOT associated with the adductor muscles?

Extending the thigh Signup and view all the answers

What nerve innervates the entire adductor muscle group?

Obturator nerve Signup and view all the answers

What role does the quadriceps femoris play in physical activities?

Important knee extensor Signup and view all the answers

What role do calcium ions play in excitation-contraction coupling?

They bind to troponin, exposing binding sites for myosin. Signup and view all the answers

During the cross bridge cycle, which event occurs immediately after the power stroke?

Detachment of the cross bridge. Signup and view all the answers

What conditions are necessary for the continuation of the cross bridge cycle?

Continuous presence of calcium and sufficient ATP. Signup and view all the answers

What happens to the distance between successive Z discs during muscle contraction?

It decreases. Signup and view all the answers

What is the result of the myosin head pivoting during the power stroke?

The actin filament is pulled toward the M line. Signup and view all the answers

Which ion is critical for triggering muscle contraction?

Calcium ion Signup and view all the answers

What is the role of troponin in skeletal muscles?

It acts as a bonding site for calcium ions. Signup and view all the answers

What primarily occurs at the neuromuscular junction during excitation?

Acetylcholine binds to receptor proteins on the sarcolemma. Signup and view all the answers

During the depolarization phase of action potential, which ion's concentration increases inside the muscle fiber?

Sodium ion Signup and view all the answers

What characterizes isotonic contractions?

Tension remains constant while muscle length changes. Signup and view all the answers

What occurs to the myosin head when ATP is hydrolyzed?

The myosin head returns to a cocked position. Signup and view all the answers

What happens to the A bands during muscle contraction?

Their length does not change. Signup and view all the answers

What is the resting membrane potential for muscle fibers before stimulation?

-95 Signup and view all the answers

Which step follows the action potential propagation along the T tubules?

Calcium ions are released into the cytosol. Signup and view all the answers

What triggers the closing of sodium channels during action potential?

Reaching a threshold of +30mV Signup and view all the answers

What occurs after potassium exits the muscle fiber during repolarization?

Resting membrane potential is restored. Signup and view all the answers

During excitation-contraction coupling, what leads to the sliding of myofilaments?

Transmission of action potential along the sarcolemma Signup and view all the answers

What happens to the H zones during muscle contraction?

They disappear. Signup and view all the answers

Which muscle is primarily responsible for flexing and rotating the lumbar region of the vertebral column?

Rectus Abdominis Signup and view all the answers

What is the primary function of the diaphragm during respiration?

Flattens on contraction Signup and view all the answers

Which of the following muscles acts synergistically with the sternocleidomastoid and aids in rotating the head?

Semispinalis Signup and view all the answers

Which muscle's action would likely result in flexing the vertebral column laterally?

Quadratus Lumborum Signup and view all the answers

Which of the following muscles is primarily responsible for drawing the scapula forward and downward?

Pectoralis Minor Signup and view all the answers

Which of these muscles is involved in forced expiration by drawing the ribs together?

Internal Intercostals Signup and view all the answers

What is the main action of the Iliocostalis muscle?

Extend and laterally flex the vertebral column Signup and view all the answers

Which of the following muscles helps maintain an erection by retarding venous drainage?

Ischiocavernosus Signup and view all the answers

What is the function of the external oblique muscle when acting individually?

Assist in lateral trunk rotation Signup and view all the answers

Which muscle is a prime mover for protracting and holding the scapula against the chest wall?

Serratus Anterior Signup and view all the answers

Which muscle is responsible for stabilizing and depressing the pectoral girdle?

Subclavius Signup and view all the answers

What function does the rectus abdominis muscle perform during activities like sit-ups?

Flexes the vertebral column Signup and view all the answers

Which muscle helps lift the anal canal during defecation?

Levator Ani Signup and view all the answers

What is a primary function of the rhomboids muscle?

Stabilize and retract the scapula Signup and view all the answers

Study Notes

Muscle Types

Three types: skeletal, smooth, and cardiac; all elongated muscle cells.
Myofilaments (myo = muscle, sarco = flesh) enable muscle contraction by shortening.
Muscles are delicate; protected and bundled by connective tissues.

Skeletal Muscle

Smoothly forms the body's contours with huge, cigar-shaped, multi-nucleated cells.
Largest muscle fibers can reach up to 30 cm in length and are striated.
Voluntary activation often occurs through reflexes; fibers are soft and fragile yet bundled to withstand force.
Enclosed in connective tissue: endomysium, perimysium, and epimysium, which blend with tendons for durability.

Smooth Muscle

Involuntary muscle found in hollow visceral organs like the stomach, with no striations.
Characterized by spindle-shaped cells containing a single nucleus.
Arranged in circular and longitudinal layers; they alternate contractions for processes like peristalsis.

Cardiac Muscle

Unique to the heart; striated but involuntary, responsible for pumping blood.
Innervated by the nervous system and cushioned by a small amount of endomysium.
Features branching cells connected by intercalated discs, facilitating coordinated contractions.
Contains a pacemaker that regulates heartbeat.

Muscle Function

The M-line holds adjacent thick filaments together, while myofibrils consist of chains of sarcomeres aligned in a series.
Thick filaments (myosins) have ATPase enzymes essential for contraction; the heads form cross-bridges with thin filaments (actin).
Thin filaments are anchored at Z discs and contribute to the bonding pattern with myosin heads.
Calcium ions trigger contraction by interacting with troponin in skeletal muscles (calmodulin does so in smooth muscles).

Sliding Filament Theory

Myosin heads generate cross-bridge tensions, allowing thin filaments to slide past thick filaments during contraction.
As thin filaments slide, Z discs move toward the M-line, shortening the muscle fiber.
Muscle fibers need to be activated for contraction, stimulated by nerve endings to generate an action potential.

Excitation-Contraction Coupling

Begins at the neuromuscular junction with the release of acetylcholine, triggering action potential propagation along the sarcolemma.
Calcium ions are released from the sarcoplasmic reticulum, binding to troponin and exposing myosin-binding sites on actin.
Myosin forms cross-bridges with actin, initiating contraction.

Cross Bridge Cycle

Formation: Myosin binds to actin, breaking ATP into ADP and phosphate.
Power Stroke: Release of ADP and phosphate allows myosin head to pivot, pulling actin filaments.
Detachment: ATP binding weakens the connection between myosin and actin.
Cocking: ATP hydrolysis returns the myosin head to a high-energy state for further cycles.

Types of Contraction

Isotonic Contraction: Muscle length changes to move a load.
- Example: External and internal intercostals assist in respiration; diaphragm acts as the prime mover for inspiration.

Key Muscle Groups

Abdominal Muscles: Rectus abdominis, external and internal obliques, and transversus abdominis flex and rotate the trunk and stabilize the pelvis.
Pelvic Floor Muscles: Levator ani and coccygeus support pelvic viscera and resist pressure changes.
Urogenital Diaphragm: Deep transverse perineal muscle and external urethral sphincter support pelvic organs and control urination.
Pectoral Muscles: Pectoralis minor and serratus anterior play roles in scapula movement and stabilization.

Key Muscle Functions

Gluteal Muscles: Extend and laterally rotate the thigh; important for walking and posture.
Quadriceps Femoris: Extends the knee; crucial in activities like jumping and running.

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Description

Explore the three types of muscles: skeletal, smooth, and cardiac. Learn about their similarities, structures, and functions in the human body. This quiz will test your knowledge on muscle characteristics and classifications.