Myology: Anatomy and Functions of Muscles

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Questions and Answers

Which of the following is NOT one of the four characteristics of muscle tissue?

Elasticity

Contractibility

Rigidity (correct)

Excitability

What is the primary function of muscle tissue related to temperature?

Fluid regulation

Nutrient storage

Body temperature maintenance (correct)

Protection

Which layer of connective tissue surrounds the entire skeletal muscle?

Perimysium

Fascia

Epimysium (correct)

Endomysium

What structure is found at the site of chemical communication between a neuron and a muscle fiber?

Neuromuscular junction Signup and view all the answers

Which of the following is a thick filament found within myofibrils?

Myosin Signup and view all the answers

What is the main characteristic of red muscle fibers?

High myoglobin content Signup and view all the answers

What distinguishes Type 2A muscle fibers from Type 2 fibers?

Higher myoglobin content Signup and view all the answers

What is the main role of satellite cells in muscle tissue?

Repair damaged muscle fibers Signup and view all the answers

What do Z discs define in a sarcomere?

The boundaries of the sarcomere Signup and view all the answers

What is the significance of the synaptic cleft in muscle contraction?

It contains synaptic vesicles with neurotransmitters. Signup and view all the answers

Which type of muscle contraction is characterized by brief, involuntary twitches not visible under the skin?

Fibrillation Signup and view all the answers

Which component is responsible for holding calcium ions in muscle cells?

Sarcoplasmic reticulum Signup and view all the answers

Which organization pattern of muscle fibers is characterized by fibers running parallel to the muscle's longitudinal axis?

Parallel Signup and view all the answers

What happens when a threshold stimulus is reached according to the all-or-none principle?

Muscle fibers will contract fully or not at all. Signup and view all the answers

What type of muscle fibers produce ATP anaerobically and are characterized as fast-twitch?

Type 2 fibers Signup and view all the answers

Which type of atrophy occurs due to loss of nerve supply?

Denervation atrophy Signup and view all the answers

What is the primary action of synergist muscles?

To assist prime movers and stabilize joints Signup and view all the answers

Which muscle shape is represented by the term 'deltoid'?

Triangular Signup and view all the answers

Which of the following describes the function of fixators?

They stabilize the origin of the prime mover Signup and view all the answers

Which prefix indicates a muscle with two tendons of origin?

biceps Signup and view all the answers

What distinguishes intrinsic muscles from extrinsic muscles?

Intrinsic muscles operate within an organ Signup and view all the answers

Which term describes skeletal muscles whose actions oppose the actions of agonists?

Antagonist Signup and view all the answers

What term refers to muscle fibers running at an angle to the long axis of the body?

Obliques Signup and view all the answers

Which muscle group does 'maximus' denote?

Biggest Signup and view all the answers

Study Notes

Myology

Study of muscles.
Four key characteristics: excitability, contractibility, extensibility, and elasticity.

Main Muscle Functions

Movement: Muscles contract to produce motion.
Support: Muscles help maintain posture and stability.
Body temperature maintenance: Muscle contraction generates heat.
Guarding orifices: Muscles control openings in the body.

Muscle Types

Smooth: Involuntary muscle found in internal organs.
Cardiac: Involuntary muscle found in the heart.
Skeletal: Voluntary muscle attached to bones, responsible for movement.

Gross Anatomy of Skeletal Muscle

Three layers of connective tissue:
- Epimysium: Surrounds the entire muscle.
- Perimysium: Divides muscle into compartments (fascicles).
- Endomysium: Surrounds individual muscle fibers.
Satellite cells: Located between the endomysium and muscle fibers, responsible for muscle repair.
Tendon: Connective tissue that attaches muscle to bone.
Neuromuscular junction: Site where a motor neuron communicates with a muscle fiber.

Microanatomy of Muscle Fibers

Sarcolemma: Plasma membrane of muscle fiber.
Sarcoplasm: Cytoplasm of muscle fiber.
Muscle fibers: Long, multinucleated cells formed by fusion of myoblasts.
Transverse tubules (T-tubules): Invaginations of the sarcolemma that conduct electrical impulses.
Myofibrils: Contractile units within muscle fibers, composed of myofilaments.
Mitochondria: Abundant in muscle fibers to provide energy.
Glycogen: Stored energy source in muscle fibers.

Structure of Myofibrils

Composed of thin filaments and thick filaments.
Thin filaments: Primarily made of actin.
Thick filaments: Primarily made of myosin.
Troponin and Tropomyosin: Regulatory proteins associated with actin.
Titin: Large protein that helps maintain structure and elasticity.

Sarcomere: The Functional Unit of Muscle

Z-disks/lines: Separate adjacent sarcomeres.
A-band: Dark band, where thick and thin filaments overlap.
M-line: Center of the A-band, where thick filaments connect.
H-zone: Light zone in the center of the A-band, containing only thick filaments.
I-band: Light band, containing only thin filaments.

Motor Neurons and Muscle Contraction

Motor neurons: Stimulate muscle fibers.
Synaptic vesicles: Contain acetylcholine, a neurotransmitter.
Synaptic cleft: Space between the axon terminal and sarcolemma.

All-or-None Principle

Muscle fibers within a motor unit contract maximally or not at all, depending on the strength of the stimulus.

Muscle Atrophy and Hypertrophy

Disuse atrophy: Muscle wasting due to lack of use.
Denervation atrophy: Muscle wasting due to nerve damage.
Hypertrophy: Muscle growth due to increased workload.

Types of Skeletal Muscle Fibers

Red muscle fibers (Type I): Slow-twitch, oxidative, fatigue-resistant. High myoglobin content, rich in mitochondria and blood supply.
White muscle fibers (Type II): Fast-twitch, glycolytic, fatigable. Low myoglobin content, fewer mitochondria and blood supply.
Type IIA fibers (Intermediate): Fast-twitch, oxidative and fatigue-resistant.

Abnormal Muscle Contractions

Spasm: Involuntary contraction of a large group of muscles.
Tremor: Rhythmic, involuntary contractions of opposing muscle groups.
Fasciculation: Brief, involuntary twitch of a muscle visible under the skin.
Fibrillation: Brief, involuntary twitch of a muscle not visible under the skin.

Organization of Muscle Fibers

Four patterns of fascicle arrangement:
- Parallel: Fibers run parallel to the long axis of the muscle.
- Convergent: Fibers converge from a broad origin to a single insertion.
- Pennate: One or more tendons run through the muscle.
  - Unipennate: Muscle fibers on one side of the tendon.
  - Bipennate: Muscle fibers on both sides of the tendon.
- Circular or sphincter: Concentrically arranged around an opening.

Muscle Attachments, Actions, and Naming

Origin: Fixed point of attachment.
Insertion: Movable point of attachment.
Action: Movement produced by muscle contraction.

Muscle Action Types

Prime movers (agonists): Muscles primarily responsible for a specific movement.
Synergists: Muscles that assist prime movers.
Antagonists: Muscles that oppose the action of prime movers.
Fixators: Muscles that stabilize the origin of prime movers.

Skeletal Muscle Naming Conventions

Directional:
- Rectus: Straight fibers.
- Transversus: Fibers run across.
- Obliques: Fibers run at an angle.
Unusual structure features:
- Biceps: Two tendons of origin.
- Triceps: Three tendons of origin.
- Quadriceps: Four tendons of origin.
Shape:
- Trapezius: Trapezoid.
- Deltoid: Triangular.
- Rhomboideus: Rhomboid.
- Orbicularis: Circular.
- Longus: Long.
- Longissimus: Longest.
- Teres: Long and round.
- Brevis: Short.
- Magnus: Big.
- Major: Bigger.
- Maximus: Biggest.
- Minor: Small.
- Minimus: Smallest.
Location
- Externus or superficial: Visible at body surface.
- Internus or profundus: Internal.
- Extrinsic: Muscles that position or stabilize an organ.
- Intrinsic: Muscles that operate within an organ.
Origin and Insertion:
- Genioglossus: Originates at the chin (genio) and inserts on the tongue (glossus).
Function:
- Flexor: Muscle that decreases joint angle.
- Extensor: Muscle that increases joint angle.
- Retractor: Muscle that draws a structure backwards.
General:
- Most skeletal muscles have "muscle" in their names, except for the platysma and diaphragm.

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Description

Learn about myology, the study of muscles, including their key characteristics and functions. This quiz covers the types of muscles, their anatomical structure, and the important roles they play in the body. Test your knowledge on smooth, cardiac, and skeletal muscles, along with their connective tissues.