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4. Cardiac Muscle Logo



Longitudinal section Top

  • Central Nuclei (often football-shaped with relatively large ring of cytoplasm surrounding it)
  • Striations
  • Branching
  • Intercalated Discs
  • numerous capillaries


Tranverse section Top

  • Central Nuclei
  • Cytoplasm to Nucleus area ratio is high
  • Nuclei are visible in many ventricular cells in transverse section (compared to very few nuclei in TS of smooth muscle)

Cardiac muscle in longitudinal section (bright field illumination). Bar is 30 microns

Figure 6 - Cardiac muscle in longitudinal section (bright field illumination). Bar is 30 microns


Cardiac muscle in longitudinal section can be identified by centrally placed round to oblong nuclei, striations, branching, and intercalated discs (arrow)

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Cardiac Muscle in longitudinal section (phase-contrast optics). Bar is 30 microns

Figure 7 - Cardiac Muscle in longitudinal section (phase-contrast optics). Bar is 30 microns


Compare this photomicrograph of the same slide as above (6), this time taken using phase-contrast optics. Notice how prominent the striations and intercalated disks (arrows) are when viewed using phase-contrast optics.

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Cardiac muscle in transverse section. Bar is 50 microns

Figure 8 - Cardiac muscle in transverse section. Bar is 50 microns


In transverse section, cardiac muscle is identified by central nuclei and a large ring of surrounding cytoplasm. You may notice a high density of blood vessels and a relatively high proportion of cells that have been sectioned through the nucleus. These features would enable you to distinguish between cardiac and smooth muscle.


Specialised cardiac tissue (pacemaker tissue) Top

Pacemaking activity in cardiac tissue relies not on neuronal tissue but on modified cardiac tissue. Usually these pacemaker regions are electrically isolated from the surrounding myocardium by connective tissue. The properties of cardiac cells isolated from the AV and SA nodes are keenly studied in Bristol by the groups led by Drs. Allan Levi and Jules Hancox
Sino-atrial Node. Cell sectioned approximately transversely. Bar is 250 microns

Figure 9 - Sino-atrial Node. Cell sectioned approximately transversely. Bar is 250 microns


The SA Node surrounds the nodal artery from which it receives a rich blood supply. These smaller, modified muscle cells generate the electrical signal that controls the heart.

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AV Node. Bar is 1 mM

Figure 10 - AV Node. Bar is 1 mM


The Atrio-ventricular Node insulated by extracellular material (like the SA Node) is also composed of smaller modified muscle cells that are capable of generating electrical signals.

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Nodal cells. Bar is 250 microns

Figure 11 - Nodal cells. Bar is 250 microns


This closer look more clearly shows the smaller nodal cells to the right and the larger cardiac cells to the left.

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Copyright � 1998 University of Bristol. All rights reserved.
Author: Phil Langton 		Last modified: 9 Jun 1999 20:33
Authored in CALnet