Overview of the heart

[iRzilla]

Hello, I am 9th grade biology student working on a presentation on the heart. I was wondering if you guys could help me understand the basic mechnics of the heart. I also have to talk about what happens when an arterial valve fails and what arythmia is. I am trying to find resources online, so if you guys have any good websites it would be awesome if you could post them here! And last thing, could you guys just describe in your own simple words? Thanks so much!

[SMF]

IRzilla. Here is a short bit on how the muscle contractions of the heart are organized to make it an effective pump. I presume you already know about how the heart is actually two separate pumps, but both pumps (left and right sides) are controlled together. There are no neurons in the heart for initiating and controlling muscle contraction. The components that act like neurons, the sino-atrial (S-A) node, the atrio-ventricular (A-V) node, and the atrio-ventricular bundle are made of modified muscle cells that can conduct electrical activity (action potentials) between them by electrical synapses in a manner similar to some neural circuits. These control mechanisms and all of the heart muscle cells have a natural repetitive rhythm of action potentials that will occur without any neural input, and how they all are connected together results in well-organized heart contractions. The S-A node rate of action potentials is the fastest, so it is the initiator of contraction and its activity can be regulated by the nervous system.

 

A in the illustration- A contraction cycle starts when the S-A node cells produce a coordinated action potential (the little spark in the drawing). The stippling indicates that this electrical activity is spreading from the node into the muscle of the Right Atrium and progressing across it.

B-The contraction spreads onto the Left Atrium as well

 

C- When the contraction reaches the A-V node there is a slight pause while all the cells become active, then its activity spreads to down the A-V bundle.

 

D- When the activity reaches the ends of the bundle at the bottom of the heart it starts contraction in both ventricles.

 

E- The contraction spreads up both ventricles.

 

F- Contraction has been completed and the S-A node begins another cycle.

 

Note that the way that the contraction spreads from cell to cell in the atria and ventricles makes for the unique wringing action of the muscle of the pumps that, in turn, make for an efficient pump. Also note that this well organized and complicated behavior is simply due to how all the muscle cells of the heart are connected together. Many heart contraction problems involve disruptions of this organization. SM