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By the end of this section, you will be able to:
  • Describe intercalated discs and gap junctions
  • Describe a desmosome

Cardiac muscle tissue is only found in the heart. Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Similar to skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle ( [link] ). However, cardiac muscle fibers are shorter than skeletal muscle fibers and usually contain only one nucleus, which is located in the central region of the cell. Cardiac muscle fibers also possess many mitochondria and myoglobin, as ATP is produced primarily through aerobic metabolism. Cardiac muscle fibers cells also are extensively branched and are connected to one another at their ends by intercalated discs. An intercalated disc    allows the cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump.

Cardiac muscle tissue

This image is a micrograph of cardiac muscle cells.
Cardiac muscle tissue is only found in the heart. LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

View the University of Michigan WebScope at (External Link) to explore the tissue sample in greater detail.

Intercalated discs are part of the sarcolemma and contain two structures important in cardiac muscle contraction: gap junctions and desmosomes. A gap junction forms channels between adjacent cardiac muscle fibers that allow the depolarizing current produced by cations to flow from one cardiac muscle cell to the next. This joining is called electric coupling, and in cardiac muscle it allows the quick transmission of action potentials and the coordinated contraction of the entire heart. This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium. The remainder of the intercalated disc is composed of desmosomes. A desmosome    is a cell structure that anchors the ends of cardiac muscle fibers together so the cells do not pull apart during the stress of individual fibers contracting ( [link] ).

Cardiac muscle

This image shows the structure of the cardiac muscle. A small image of the heart is shown on the top left of the figure and then a magnified view of the cardiac muscle is shown, with the nucleus and the cardiac muscle fiber labeled. A further magnification shows the structure of the intercalated discs with the desmosome and gap junction.
Intercalated discs are part of the cardiac muscle sarcolemma and they contain gap junctions and desmosomes.

Contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate. Although cardiac muscle cannot be consciously controlled, the pacemaker cells respond to signals from the autonomic nervous system (ANS) to speed up or slow down the heart rate. The pacemaker cells can also respond to various hormones that modulate heart rate to control blood pressure.

The wave of contraction that allows the heart to work as a unit, called a functional syncytium, begins with the pacemaker cells. This group of cells is self-excitable and able to depolarize to threshold and fire action potentials on their own, a feature called autorhythmicity    ; they do this at set intervals which determine heart rate. Because they are connected with gap junctions to surrounding muscle fibers and the specialized fibers of the heart’s conduction system, the pacemaker cells are able to transfer the depolarization to the other cardiac muscle fibers in a manner that allows the heart to contract in a coordinated manner.

Another feature of cardiac muscle is its relatively long action potentials in its fibers, having a sustained depolarization “plateau.” The plateau is produced by Ca ++ entry though voltage-gated calcium channels in the sarcolemma of cardiac muscle fibers. This sustained depolarization (and Ca ++ entry) provides for a longer contraction than is produced by an action potential in skeletal muscle. Unlike skeletal muscle, a large percentage of the Ca ++ that initiates contraction in cardiac muscles comes from outside the cell rather than from the SR.

Chapter review

Cardiac muscle is striated muscle that is present only in the heart. Cardiac muscle fibers have a single nucleus, are branched, and joined to one another by intercalated discs that contain gap junctions for depolarization between cells and desmosomes to hold the fibers together when the heart contracts. Contraction in each cardiac muscle fiber is triggered by Ca ++ ions in a similar manner as skeletal muscle, but here the Ca ++ ions come from SR and through voltage-gated calcium channels in the sarcolemma. Pacemaker cells stimulate the spontaneous contraction of cardiac muscle as a functional unit, called a syncytium.

Questions & Answers

type 2 is controled by diet
Chloe Reply
Diet and life style
Paias
Diet how? maybe eating food containing less sugar?
BTS
what is hypotension
regina Reply
hypotension is when the blood pressure is less than 60/50
Mursal
hypo means low so it implies low blood pressure
Isaac
ok
Mursal
what is mild DKA
Mursal
mild diabetic ketoacidosis is when there is high level of sugar in the blood and the ketone bodies build up in the body ,is a type 1 which can lead to type 2
Isaac
what is the normal range for blood pressure?
BTS
120 over 80
Danielle
low blood pressure; opposite of high blood pressure which is hypertension
Regina
what if your a type 2 diabetic and you have no way to get meds due to no insurance what is some good over the counter medications to take?
Ashley
type 2 diabets is controlled by diet not meds.type 1 is contolled by insulin.
Chloe
type 1 diabets cant be controlled type 2 can be controlled.type 1 is worse than type 2 diabets.
Chloe
type 2 is purely a lifestyle disease, eat healthy, fresh, natural unprocessed real foods.
Danielle
sometime , we already eat diabetic diet than the results of blood sugar level not turn good , what is the reason ?
Muhammad
What is a "diabetic diet" though? Be specific. Juvenile diabetes and/or Type 1 diabetes is something that one can be born with, this needs medical diagnosis and intervention.
Danielle
what i mean by diabetic diet is we take fiber-rich food like vegetables,nut and also fish.
Muhammad
ok, no cause a doctor told me I needed metformin and my suger won't go under 300
Ashley
what is the difference between plasma and serum
Gloria Reply
Plasma contains fibrinogen while serum doesn't
Kateregga
plasma ----- fibrinogen = serum
Sneha
In what time stomach empty it's content in to doudemun? what is chyme?
Sneha Reply
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Chemical digestion---Mixtures of the food with the gastric acid Mechanical digestion--- churning of the food in the stomach making it become more involved into chyme
Mercy
absorption takes place in the small intestine because of the presence of the villi
Enada
name the muscles supplied redina nerve
Appu Reply
mechanism of hormone releasing by gland
said Reply
why is muscle tissue not considered to be a type of connective tissue?
Ezel Reply
A Skeletal muscles consist of numerous muscles cells called Muscle Fibers . Three layers of connective tissues surrounded these fibers to make the muscles tissues
Manisha
that's wny connective tissues is not considered as muscles fibers
Manisha
there are 4 types of tissues : epithelial, connective tissue, nervous tissue and muscle tissue, each one has its own properties. The main function of connective tissue is nutrition, it supplies nutrientes to epithelial tissues that are responsible for protection.
Ariete
Muscle tissue has properties that allow movement, the function here is movement and not nutrition like connective tissue.
Ariete
In what time stomach empty it's content in to doudemun?
Sneha
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Does absorption take place in stomach? what are the absorption in the stomach by which cell?
Sneha
mechanism of hormone controlling releasing by gland
said
please can someone explain renin angiotensin aldosteron system for me
okolie
name the joint present between epichysif and diachysif
JAYKISHAN Reply
what is arteries
JAYKISHAN
oxygenated blood carrying vessels
Karanpreet
I think oxygenated blood carrying pulmonary vein
Omaryare
ya this stetment is right 4 pulmonary vein carrying the oxygenated blood
Sneha
What is the relation between cold and clammy skin and disorders that cause poor perfusion?
Tyrone Reply
name the instruments used to measure the gas volume and flow in pulmonary function test
Preethi Reply
Spirometer
Ravi
In a spirometry test, While you are sitting, you breath into a mouthpiece that is connected to an instrument called a spirometer . The spirometer records the amount and the rate of air that you breath in and out over a period of time. When standing, Some numbers might be slightly different.
Ravi
tq soo much
Preethi
u most wlcm
Ravi
what is signal transduction?
Bahle
Signal Transduction (Also know as cell signaling) is the transmission of molecular signal from a cell exterior to its interior.Signals receive by cells must be transmitted effectively into the cell to ensure an appropriate response. This step is initiated by cell - surface receptors.
Ravi
i know now didn't know
Cypline
that's great respond
Feng
what is histological anatomy?
Thelma Reply
what is histological anatomy?
Thelma
the study of form of structure seen under the microscope
Metinah
is the branch of biology which studies the microscopic anatomy of biological tissues.
Jeffrey
it's the study of the microscopic anatomy of cells and tissues in the plants and it's carried out by examining a thin slice of tissues under a microscope light / or an electronic microscope
Manisha
is the study of anatomy in a microscopic level
simon
thank you
Thelma
what are the significance differrences can be donated between the female and male skeleton..
charles
What is Ions and Ionic bonds
Ravi Reply
2 less stable atoms
Hope
Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively
Hope
what is osmosis
Brown Reply
it's out Body Fluid.
Sa
high pressure to low pressure flow
Sneha
Osmosis is the movement of solvent from a region of lower solute concentration to a region of higher solute concentration through a semi- permeable membrane.
Ravi
how many types of tissue
ABBAKARR Reply
4, that is muscle tissue, connective, nerve and epithelial tissue
Mapesho
We have four types of tissue these are ,epithelial tissue,nerve tissue,muscle tissue and connective tissue
Samboat
function of labia minora
temba
why is a graph of plasma [glucose] superimposed
Sefai Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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