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Unformatted text preview: ntations possible ! Video-47-04.mpg! Gap Junctions • Cardiac and smooth muscle cells are arranged
in sheets. • Cells in the sheet are in electrical contact via
gap junctions. • An action potential in one cell can spread to all
others in the sheet. ! Figure 5.7 Junctions Link Animal Cells Together (C)! GAP GAP junctions:
• Connect the cytoplasm of two neighboring cells.
• Allows direct electrical communication between cells.
• Allows direct chemical communication between cells
(small second messengers, such as IP3 and Ca2+)
• Allows passage of molecules smaller than ~1,000
• Allow cardiac and smooth muscle cells to contract
! Gap junctions allow communication ! calcium-waves.mov Video-47-04.mpg! ! Tissue Layers of the Vertebrate Gut! Smooth Muscle Smooth muscle: • Are the simplest muscle cells structurally.
• Single nucleus/cell.
• “Smooth” because actin/myosin are not as
regularly arranged. • Present in most internal organs (e.g. GI-tract,
bladder, blood vessels) • Under autonomic nervous system control. ! Smooth muscle cell and endothelial cell surrounding blood vessel and
smooth muscle cell
! Jejunum ! 47.1 How Do Muscles Contract? What is a “twitch”?
Skeletal muscle: minimum unit of contraction = a
A twitch is measured in terms of tension, or force
A single action potential generates a single
! 47.1 How Do Muscles Contract? Single twitch: if action potentials are close
together in time, the twitches are summed,
Twitches sum because Ca2+ pumps can not clear
Ca2+ from sarcoplasm before the next action
Tetanus: when action potentials are so frequent
there is always Ca2+ in the sarcoplasm.
! Twitches and Tetanus How Do Muscles Contract? How long muscle fiber can sustain tetanic
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This note was uploaded on 02/13/2014 for the course MCDB 1B taught by Professor Weimbs during the Winter '08 term at UCSB.
- Winter '08