Cell-Cell Communication Eukaryotes

Question 1

What may have lead to the early steps in development of multicellularity?

Answer 1

Quorum sensing (not enough of it to do anything, if more bacteria - achieve change in behaviour. Early steps in development of multicellularity.

Question 2

What are the two types of ways cells can communicate with eachother?

Answer 2

a) contact

b) secreted molecules

Question 3

What are the four basic categories of chemical signaling found in multicellular organisms:

Answer 3

paracrine signaling
autocrine signaling
endocrine signaling
signaling by direct contact.

Question 4

What are the two types of ways cells can communicate that are contact-dependant

Answer 4

a) Cell junctions

b) Cell-cell recognition

Question 5

What is juxtacrine signalling?

Answer 5

Juxtacrine signaling involves contact between cells, in which a ligand on one cell surface binds to a receptor on the other (juxed opposed, close together - adjacent)

Question 6

What are cardiomyocytes?

Answer 6

They are the heart muscle cells – that contract to make the heart beat.

Question 7

Contractions of the heart (heartbeats) are controlled by what?

Answer 7

Contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate.

Question 8

Intercalated discs are part of the sarcolemma and contain two structures important in cardiac muscle contraction - what are they?

Answer 8

Intercalated discs are part of the sarcolemma and contain two structures important in cardiac muscle contraction: gap junctions and desmosomes.

Question 9

Intercalated discs are part of the sarcolemma in cardiomyctes and contain two structures important in cardiac muscle contraction - what are they and describe their functions

Answer 9

1) gap junctions - 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.
2) desmosomes - 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

Question 10

What is the function of the sarcolemma?

Answer 10

The sarcolemma generally maintains the same function in muscle cells as the plasma membrane does in other eukaryote cells. It acts as a barrier between the extracellular and intracellular compartments, defining the individual muscle fiber from its surrounding

Question 11

What are intercalated discs?

Answer 11

unique structural formations found between the myocardial cells of the heart and are part of the sarcolemma. They contain two structures important in cardiac muscle contraction - gap junctions and desmosomes

Question 12

Describe how cardiomycytes engage in juxtacrine signalling to contract the muscle of the heart to beat

Answer 12

Heart - pacemakers control rhythm so we get 60 beats per min -> communicate to other cardiomyctes bc they are muscle cells that make the heart beat. Wave of depolarisation that has to get to all cardiomyctes so they all get instructions at the same time -> they do it by gap junctions! Conneins - from channel that allows one cell to communicate with the other (selecivitiy for certain cations, not everything can get through! Sodium and calcium can get through - cells change by polarisation and determines whether active or not. Gap junctions - whole network of cardiomucyes that can share change of depolarisation rapidly. On ecelll becomes depolarised, connected by gap junctions becomes depolarised - rapid change is communicated to allow heart synchronise. Allows heart to act as a fnctional syncytium - synchronous “depolarisation” -functioning syncrhonously

Question 13

The joining of two cells by gap junctions in cardiomyctes is known as what? And what is the purpose?

Answer 13

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.

Question 14

The network formed as a result of the joining of two cells (through gap junction) in cardiomyctes is known as what?

Answer 14

This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium.

Question 15

The network of electrically connected cardiac muscle formed as a result of the joining of two cells (through gap junction) in cardiomyctes is known as what?

Answer 15

This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium.

Question 16

What controls the signals from ANS to speed or slow down the heart rate?

Answer 16

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.

Question 17

What is the function of the functional syncytium?

Answer 17

The wave of contraction that allows the heart to work as a unit, called a functional syncytium, begins with the pacemaker cells IN THE SINO-ATRIAL NODE. 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 (BUIT BASICALLY 60-100 times a minute). 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 (opposing K channels allowing positive ions in the other direction). 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 (sarcoplasmic reticulum)

NICE CYCLE for the pacemaker cells – Sodium channels, then calcium channels, THEN potassium channels – so we depolarise, then further, then with K we reploarise. All are voltage gated so open AND close according to the voltage so it constantly cycles (never at resting potential). The myocyte (cardiac muscle) is quite different – as depolarisation starts and calcium wants to come in and potassium wants to move out, they work sort of in opposition the membrane potential plateaus a little above neutral.

Question 18

Through what structure do action potentials propagate along the surface of muscle fiber from the point of synaptic contact

Answer 18

Through intercalated discs.