D4 The heart Flashcards
what is cardiac muscle?
striated muscle found in the wall of the heart
what is the structure of the cardiac muscle
- thick and thin muscle fibres with myofibrils
- cell nuclei in centre
- rich in mitochondria and glycogen granules
- “all or none” effect – once activated, max contraction
- long refractory period (cannot contract again)
- intercalated discs
how does the cardiac muscle structure ensure that the contraction/systole of the heart is seperated by a rest/diastole
long refractory period of cardiac muscle = cannot contract for a second time
in cardiac muscle structure: what are intercalated discs?
- transverse cross-bands
- attachment site between cardiac muscle cells
- contain adhering junctions (gap junctions – arrays of densely packed protein channels that permit intercellular passage of ions and small molecules)
what do intercalated discs do? (cardiac muscle)
- allows communication between cells
- allows electrical impulses to pass rapidly from cell to cell, so the linked cells contract almost simultaneously
what are gap junctions (cardiac muscle)
- arrays of densely packed protein channels that permit intercellular passage of ions and small molecules
- electrical activation of the heart requires cell-cell transfer of current thru these
4 similarities between cardiac muscle and skeletal muscle
- SARCOLEMMA (a membrane that surrounds and encloses muscle fibres) + from which transverse tubules tunnel in and around sarcomeres
- SARCOPLASMIC RECTICULUM – modified form of ER
- STRIATED in appearance + similar arrangement of actin and myosin filaments
- all muscle tissue consists of FIBRES that can SHORTEN by a HALF to a THIRD of their length
differences between cardiac muscles and skeletal muscle 7
- C much shorter and wider than S
*2. C have a single nucleus, S multicellular - C are branching and joined end to end in a complex 3D network, ?
*4.C many mitochondria, makes up more of cell vol vs S - C have transverse tubular system consistings of wider invaginations of the cell surface than S (C more abundant branching sarcoplasmic recticulum)
*6. C contract even in absence of stimulation by a nerve, not voluntary (unlike S) - C is unique to heart (unlike S)
how does the structure of cardiac muslce cells (CMC) allow for propogation of stimuli throughout the heart wall 4
- intercalated discs at junctions between CMC
- direct electrical coupling between cells – allows waves of depolarisation to pass thru – syncing contraction of the muscle (As if in a single cell)
- cardiac muscle fibres form an interconnected network
- CSC network of walls of atria – seperate from that of ventricles = transmission delay
define the cardiac cycle
The sequence of events of a heartbeat, by which blood is pumped around the body.
two stages of cardiac cycle
- systole – contraction of heart muscle
- diastole – relaxation of heart muscle
what is a myogenic activity, and how is the heart an example
- no need for nerve stimulus
- heart beats rhythmically throughout life without need to be stimulated by and external nerve
what triggers heartbeats in hearts (they are myogenic!) and how
the sinoatrial node/’pacemaker’
- a network of specialised, self-excitable cardiac muscle fibres
- located in the right atrial wall
- each elec charge is propped thru the network of muscle fibres in both atria walls (via gap junctions in the intercalated discs)
- muscle of both atrial walls contract simultaneously (atrial systole)
what is the function of the atrioventricular node
picks up the signal originating from the SAN (it cannot pass directly from the atria to the ventricles)
- at the base of right atrium
why is there a delay at the atriovetricular node (Essentially AV node structure vs SA node structure)
- cells of AV node take longer to get excited than the SA node
- smaller diameter of AV cells = slowing conduction results
- fewer sodium ion channels in membranes of AV + more negative resting potential
- fewer gap junctions in intercalated discs in AV
