Microscopic Anatomy of Skeletal Muscle

Questions and Answers

What is the most common type of muscle tissue in the body?

Cardiac muscle

Epithelial tissue

Smooth muscle

Skeletal muscle (correct)

What are the functions of skeletal muscle?

Shapes the body, 2. Gives the ability to move, 3. Manipulate the environment, 4. Produces heat, 5. Maintain body posture and position, 6. Stabilize joints

What are muscle fibers?

Skeletal muscle cells that are long, cylindrical, and have more than one nucleus.

What is the sarcolemma?

The plasma membrane of a muscle fiber. Signup and view all the answers

What are myofibrils?

Long, rod-shaped organelles that fill the sarcoplasm and have alternating light and dark bands. Signup and view all the answers

What are myofilaments made of?

Actin and myosin. Signup and view all the answers

What slides past each other during muscle contraction?

Actin and myosin. Signup and view all the answers

What are sarcomeres?

Contractile units of muscle made up of the parts between two Z discs. Signup and view all the answers

What are thin filaments primarily composed of?

Actin. Signup and view all the answers

What are thick filaments primarily composed of?

Myosin. Signup and view all the answers

What is a transverse (T) tubule?

A junction of an A band and I band that runs deep into the muscle fiber. Signup and view all the answers

What is a terminal cistern?

Cross channels of the sarcoplasmic reticulum. Signup and view all the answers

What is the sarcoplasmic reticulum?

The muscle endoplasmic reticulum that surrounds muscle fibers. Signup and view all the answers

What makes up a triad?

A T tubule and two terminal cisterns. Signup and view all the answers

What is the endomysium?

The sheath that surrounds each muscle fiber. Signup and view all the answers

What is the perimysium?

The sheath that surrounds several muscle fibers, forming a bundle called a fascicle. Signup and view all the answers

What is a fascicle?

A bundle of muscle fibers surrounded by perimysium. Signup and view all the answers

What is the epimysium?

The sheath that covers an entire muscle. Signup and view all the answers

What are tendons?

Structures that attach muscles to bones or to each other. Signup and view all the answers

What are aponeuroses?

Flattened sheets that attach muscles to each other or to bones. Signup and view all the answers

What is an insertion in muscle anatomy?

The movable part of a muscle. Signup and view all the answers

What is an origin in muscle anatomy?

The immovable part of a muscle. Signup and view all the answers

What functions do tendons serve?

They provide durability and conserve space. Signup and view all the answers

What is a neuromuscular junction?

The junction between an axon of a motor neuron and a muscle fiber. Signup and view all the answers

What is a motor unit?

A neuron and all the muscle fibers it stimulates. Signup and view all the answers

What is the synaptic cleft?

A small fluid-filled gap that separates the neuron and muscle fiber membranes. Signup and view all the answers

What characteristics do all muscles share?

Excitability, contractibility, extensibility, elasticity. Signup and view all the answers

What is the structure of a sarcomere?

The structure consists of the area between two Z discs that contains myofilaments. Signup and view all the answers

What do myosin heads do?

They tug on the thin actin filaments, causing contraction. Signup and view all the answers

What happens as a muscle shortens?

I bands shorten, the distance between Z discs shortens, H zones disappear, and contiguous A bands move closer together. Signup and view all the answers

What sequence of events must occur for a muscle to contract?

<ol> <li>Fiber must be stimulated by a nerve ending. 2. An action potential must be generated in the sarcolemma. 3. The action potential must be propagated along the sarcolemma. 4. Intracellular calcium levels must rise.</li> </ol> Signup and view all the answers

How does a motor neuron stimulate a skeletal muscle fiber?

<ol> <li>Nerve impulse reaches the end of axon, releasing ACh. 2. ACh attaches to receptors on the sarcolemma. 3. ACh binding triggers electrical events that generate an action potential.</li> </ol> Signup and view all the answers

What is the generation of an action potential in a skeletal muscle fiber?

<ol> <li>Generation of end plate potential, ACh binding opens Na channels. 2. Depolarization occurs as more Na enters. 3. Repolarization returns the sarcolemma to its polarized state.</li> </ol> Signup and view all the answers

Study Notes

Skeletal Muscle Overview

Skeletal muscle is the predominant type of muscle tissue in the body.
Key functions include shaping the body, facilitating movement, manipulating the environment, generating heat, maintaining posture, and stabilizing joints.

Muscle Structure

Muscle fibers are long, cylindrical cells that contain multiple nuclei.
The sarcolemma is the plasma membrane surrounding a muscle fiber.
Myofibrils are rod-shaped organelles that occupy the sarcoplasm, recognizable by alternating light (I) and dark (A) bands that create a striped appearance.
Myofilaments, composed of actin (thin) and myosin (thick), are the threadlike structures forming myofibrils.

Muscle Contraction

Myosin heads interact with actin filaments during muscle contraction, allowing them to slide past each other.
Sarcomeres serve as contractile units, defined between two Z discs.
During muscle contraction, I bands shorten, the distance between Z discs decreases, H zones vanish, and A bands remain the same length.

Muscle Fiber Components

Transverse (T) tubules are found at the junction of A and I bands, extending deep into muscle fibers alongside terminal cisterns.
Terminal cisterns are cross channels of the sarcoplasmic reticulum, which is akin to endoplasmic reticulum in muscle fibers.
A triad consists of a T tubule and two terminal cisterns.

Connective Tissue Coverings

Endomysium is the sheath around individual muscle fibers made of areolar connective tissue.
Perimysium surrounds groups of muscle fibers, forming bundles (fascicles), and consists of collagenous tissue.
Epimysium encases the entire muscle, enclosing numerous fascicles with dense irregular connective tissue.

Tendons and Aponeuroses

Tendons connect muscles to bones or other muscles, derived from extensions of the epimysium, having a cord-like structure.
Aponeuroses are sheet-like extensions of epimysium that also connect muscles to each other or to bones.

Muscle Attachments

The insertion refers to the movable part of the muscle, while the origin is the fixed attachment.

Neuromuscular Physiology

Tendons help in durability and conserving space.
The neuromuscular junction is where a motor neuron connects with a muscle fiber.
A motor unit consists of one neuron and all muscle fibers it innervates.
The synaptic cleft is the small gap separating neuron and muscle fiber membranes.

Muscle Characteristics

All muscle types share properties such as excitability, contractility, extensibility, and elasticity.

Action Potential Generation

Muscle contraction initiates when a nerve stimulate occurs, leading to an action potential in the sarcolemma.
The action potential travels along the sarcolemma and requires a rise in intracellular calcium levels for contraction.
ACh (acetylcholine) is released from the axon terminal into the synaptic cleft, binding to receptors on the sarcolemma and triggering electrical events that lead to contraction.
The process includes generation of an end plate potential, depolarization (Na influx), and repolarization (K efflux).

Myosin Functionality

Myosin heads pull on actin filaments, which is crucial for muscle contraction.

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Description

Explore the key concepts of skeletal muscle anatomy with this quiz, focusing on the structure and functions of muscle tissue. Understand how skeletal muscles shape the body, enable movement, and contribute to heat production and posture maintenance.