BIO310 Test 2 Muscle Tissue

Describe the fascia adheren component of the intercalated disc

A transverse structural component similar to zonula adherens. It is primarily made up of alpha-actinin because it is associated with the z line. This is an adhering junction that holds the cardiac muscle cells at their ends to form the functional cardiac muscle fiber. It also serves as an attachment site for thin filaments

How does Ach trigger the release of calcium?

Ach binds to ligand-gated ion channels of the sarcolemma causing them to open and allow extracellular Na to enter the cell. This changes the polarity of the membrane-- causing it to depolarize. The t tubules propagate this depolarization signal. The voltage-gated ion channels along the t tubule respond and cause the sarcoplasmic reticulum to release its stored calcium. The calcium is then able to diffuse down its concentration gradient into the sarcoplasm where it binds to troponin and initiates contraction. After the stimulus is removed, calcium is actively transported back into the SR

Describe atrial fibers of cardiac muscle

Atrial fibers are usually much smaller and contain granules (with hormones such as the precursor to the hormone atrial natriuretic peptide) within their cytoplasm

Describe the five basic steps of the contraction cycle

Attachment (myosin head is attached to actin) Release (ATP binds and induces a conformational change that breaks the myosin-actin bond) Bending (Hydrolysis of ATP causes myosin head to bend and stretch) Power stroke (the myosin head attaches to a new actin molecule, causing the head to straighten and pull) Reattachment (like the first stage, the myosin head is tightly bound to a new actin molecule and the cycle can repeat)

Compare the general characteristics of cardiac muscle to skeletal muscle

Cardiac muscle is very similar to skeletal muscle in that is has the same method of contraction, same arrangement of proteins, and is striated. It is different from skeletal muscle in that its fibers are branched and usually containing one central nucleus. Also, the SR is less organized and has a slightly different arrangement. The key feature is the presence of intercalated discs. Cardiac muscle cells contain a significant amount of mitochondria due to higher energetics requirements. Purkinje fibers are also present.

Describe the gap junctions of intercalated discs

Gap junctions are made up of a series of proteins called connexins and they allow for communication between cells. This allows cardiac muscle cells to behave as a syncytium and efficiently communicate the signal to contract from cell to cell. This communication is important since the heart requires simultaneous contraction to perform correctly and regulate blood pressure

What are purkinje fibers?

Highly specialized conducting fibers that generate and rapidly transmit the contractile impulse to various parts of the myocardium in a precise sequence. They are found at the end of the conduction system.

What are the general features of muscle tissue?

Muscle tissue is responsible for the movement of the body and its parts. It is made up of a group of cells organized by connective tissue. These cells are generally longer than than wide and are called muscle fibers. Muscle tissue has four main characteristics: elastic (go back to original shape), excitable (generates electrical impluse), extensible (stretch without damage), and contractile (able to shorten)

What is rigor mortis?

Rigor mortis describes the rigidity of muscles that occurs after death. Calcium is released due to cell lysis encouraging the myosin-actin bond. Since no ATP being produced by the body, there is no ATP to break the myosin-actin bond of muscles.

Describe the general characteristics of skeletal muscle cells

Skeletal muscle cells are elongated, unbranched, cylindrical, and multinucleated. Their nuclei are peripherally located. Skeletal muscle has a striated appearance. Each skeletal muscle cell is connected to a nerve.

Describe the myofilaments of skeletal muscle

Skeletal muscle contains thick and thin myofilaments. Thin myofilaments are primarily made up of filamentous actin (a polymer of globular actin), a contractile protein. It also contains regulatory proteins tropomyosin and troponin Thick myofilaments are made up of myosin which aggregate tail to tail to form a bipolar arrangement

Describe the skeletal muscle structure

Skeletal muscle is composed of fasicles which are composed of a bundle of muscle fibers. Each muscle fiber contains myofibrils which are made up of filaments.

Describe the general characteristics of Smooth Muscle tissue

Smooth muscle tissue looks significantly different than the other two types. It is not striated and It has spindle-shaped fibers with a single, large nucleus. It contains a number of mitochondria and a large Golgi complex. Each fiber produces its own basal lamina which contains type III collagen. It also contains gap junctions that regulates contraction of the entire sheet of smooth muscle. It's myofilaments also have a different arrangement. Smooth muscle cells overlap and form prominent layers. CT is still associated with each individual cell

Describe the contraction process of smooth muscle

The SR releases calcium when prompted by a mechanical, electrical, or chemical stimuli-- not always a nervous signal. Once calcium enters the cell, it binds to calmodulin causing it to activate myosin light chain kinase. MLCK phosphorylates the light chain of myosin using ATP. The phosphorylation changes the conformation of the light chain of myosin and allows the myosin head to bind to actin. When the stimulus is gone, a phophatase cleaves the phosphate groups off of myosin which causes it to resume its inactive conformation

Describe the Sarcoplasmic Reticulum of smooth muscle

The Sarcoplasmic reticulum of smooth muscle stores calcium. Instead of T tubules, it has a well-developed sER, many invaginations, and viscles similaar to caveolae.

How does the nerve impulse travel from the neuron to the muscle cell to begin the contraction cycle?

The contraction cycle begins with a signal from the CNS and is regulated by the release of calcium. The nerve impulse is coming from motor neurons. The impulse travels down the axon, comes to the end of the nerve, and is collected as a chemical signal into synaptic vesicles that bind to the membrane. The contents (usually the neurotransmitter, Ach) of these vesicles are released via exocytosis and travel across the synapse (space between synaptic end bulb and muscle cell) to bind with ligand-gated ion channels of the sarcolemma. After the initial stimulus is removed, Ach is enzymatically broken down

Describe the visceral type of smooth muscle

The most common type of smooth muscle. It is found in hollow walls of various organs, thoracic cavity, abdominal cavity, digestive tract, and is especially prominent in the smaller parts of the respiratory system. It contains thick, thin, and intermediate filaments (primarily desmin). It has relatively poor nerve supply so it depends on gap junctions to spread the contraction signal from cell to cell. This type of smooth muscle behaves as a syncytium. A subunit of this type is vascular muscle tissue which is found in the walls of blood vessels. Its intermediate filaments contain vimentin, but it has the same function

Describe the structure of the sarcomere and its regions

The sarcomere is the basic contractile unit of striated muscle and it contains interacting thin / thick filaments and proteins. It is the region in between one z line and another z line. An "M" line exists in the middle of each sarcomere. The A band represents the overlap of tick and thin filaments. The I band represents the thin filament region (shortens when muscle contracts). The H band is in the middle of the A band and represent the exclusively thick filament region. (narrows during contraction)

Describe the macula adheren component of intercalated discs

These desmosomes are present in both transverse and lateral components. They function as a "spot weld" between two cardiac cells and strengthens the cells to withstand constant contractions

Identify the different types of smooth muscle

Visceral (subunit vascular) and Multiunit

define "syncytium"

a group of muscle fibers that are stimulated to contract together

Describe the role dystrophin plays in the sarcomere

a protein that is responsible for linking thin filaments and the alpha-actinin to the sarcolmma and ties them together

Descrone the role of troponin in skeletal muscle

a regulatory protein of the thin filament that is made up of three subunits. TnT attaches to tropomyosin, TnC binds calcium, and TnI binds to actin to inhibit actin-myosin interaction.

Describe the role of tropomyosin in skeletal muscle

a regulatory protein of the thin filament. It lies in the groove of the two f actin polymers' double helix and blocks the myosin binding site of actin.

Describe the role alpha-actinin plays in the sarcomere

alpha-actinin is an actin-binding protein that bundles thin filaments and anchors them at the z line. It is the primary protein component of the z line and helps attach titin and actin.

Name the protein components of the sarcomere

alpha-actinin, c protein, desmin, dystrophin, myomesin, nebulin, titin, and tropomodulin

What are the two types of cardiac muscle fibers?

atrial and ventricular

Identify the three components of intercalated discs

fascia adherens, macula adherens, gap junctions

Describe the role desmin plays in the sarcomere

intermediate filament that surrounds the sarcomere and attaches them to one another

what is the role of the calmodulin protein in smooth muscle?

it binds calcium (similar to skeletal muscle's TnC) then activates myosin light chain kinase

What is the role of the hormone, atrial natriuretic peptide, whose precursor is secreted by the heart?

it opposes the action of the hormone aldostirone of the kidneys and lowers blood volume. It promps the excretion of sodium by the kidneys. Loss of sodium leads to loss of water which lowers blood volume. A high blood volume causes the heart to stretch, which prompts their granules to release this hormone

what is the role of the myosin light chain kinase protein in smooth muscle?

it phosphorylates the light chain of myosin which allows the myosin head to bind to an actin filament

describe the multiunit type of smooth muscle

located in the iris of the eye and functions to control the size of the pupil. It has a very rich nerve supply. Each cell has the ability to contract independently - greater control of contraction

Describe the role myomesin plays in the sarcomere

primary protein component of the M line. It binds to titin and stabilizes structure. It also holds thick filaments at the M line.

Briefly describe the sarcoplasmic reticulum of skeletal muscle cells

rough equivalent to the endoplasmic reticulum. It is arranged around the myofibrils and has invaginations called T tubules that penetrate / extend to all levels of the muscle fiber. It serves as a reservoir for calcium ions. Along the SR, there are a number of ligand and voltage gated ion channels

Describe the role c protein plays in the sarcomere

similar role as myomesin

Where are the three types of muscle fibers located?

skeletal muscle is found externally and is associated with bone cardiac muscle is found exclusively in the heart smooth muscle is found in virtually every other organ and is especially important in the walls of hollow organs (blood vessels, digestive tracts)

What are the three types of muscle fibers?

skeletal, cardiac, smooth

What is the neuromuscular junction?

the contact made by the terminal branches of the axon with the muscle fiber's motor end plate

Describe the structure of the contractile unit of smooth muscle

thin filaments contain actin that is bound to alpha-actinin. The alpha-actinin is located in part of a dense body that is anchored to the cell membrane thick filamets contain myosin in a side polar arrangment that maximizes arrangement between thick and thin filaments. intermediate filament (containing desmin and vimentin) is present and is tied to the dense bodies. Proteins unique to smooth muscle include myosin light chain kinase and calmodulin. As the actin and myosin slide across each other, they pull on the dense bodies and have a type of "drawstring effect' that causes the whole cell to shorten and widen in the middle

Describe the role tropomodulin plays in the sarcomere

this actin-binding protein is attached to thin filaments and is responsible for regulating the length of the actin thin filament

Describe the role nebulin plays in the sarcomere

this inelastic structural protein wraps around the entire length of the thin filament and helps anchor it to the z disk

Describe the role titin plays in the sarcomere

titin is a coiled, spring-like molecule that anchors thick filaments to the z line. It connects the z line to the m line to stabilize the position of the thick filament. Largely accountable for the elasticity and extensibility of the myofibril

Describe ventricular fibers of cardiac muscle

ventricular fibers are usually larger because they are required to do more work. They generate much more pressure than the atria because they are responsible for pumping blood throughout the body.