9. Excitable Tissue (2) Flashcards
What is Cardiac muscle? (2)
- Fibres are much smaller than skeletal muscle and usually have a single nucleus per fibre
- signal for myocardial contraction are not from the nervous system but from specialised cardiac muscles
What are the features of cardiac muscle tissue? (5)
- Contain myofibrils = striated
- Cells contact each other at intercalated discs
- Myogenic
- Cells generate action potentials by themselves without any nerve stimulation
- involuntary
Action potential: Cardiac muscle
* Auto-rhythmic cells (1%) : (3)
- Do not contract
- Display a pacemaker activity (INITIATE THEIR OWN A.P.).
- Have no resting membrane potential. e.g. Membranes of SA (sino-atrial) node are leaky to ions therefore they have no stable resting membrane potential
When do “Funny channels” open?
“Funny channels” open when membrane is hyperpolarised because they are permeable to both Na+ and K+
Why do cardiac muscles have a much longer action potential? (2)
- Cardiac muscles have a much longer action potential due to the plateau phase which is a result of calcium entry
- This is to prevent tetanus because the heart must fully relax between each beat
Action potential: Cardiac muscle
Process -
Cardiac muscle: neurotransmitters and receptors
Cardiac muscle contraction:
- The cardiac muscle has a long refractory period ~____ _____due to the long plateau phase of the AP
- Th cardiac muscle AP is almost as long as the contraction it ______
- Cardiac muscle can’t be stimulated until contraction is over; precludes summation of contractions & protects muscle against _____ ______
250 mescal
initiates
tetanus contractions
B,D,E
What is smooth muscle? (2)
- Primary muscle of internal organs and tubes such as stomach, bladder, and blood vessels
- primary function is to influence movement of material into and out of the body e.g. movement of food through the GIT
What are the features of smooth muscle? (4)
- Lacks visible cross striations.
- Actin & myosin present BUT not arranged
in sarcomeres. - Cytoplasmic dense bodies replace Z lines
- Doesn’t contain troponin, instead Calmodulin
Smooth muscle
Two types:
- Single-unit
- Multiunit
Smooth muscle:
Single-unit: (3)
- form a sheet or bundle of tissue
- Myogenic Generate own AP
- Muscles of visceral organs e.g. GIT, uterus, ureters & some smaller blood vessels
Smooth muscle:
Multi-unit: (3)
- Showing discrete, individual smooth muscle fibres Fibres function independently
- Neurogenic —-> Rely on nerve stimulation
- Iris and ciliary body of the eye, large arteries
Action potential: Smooth muscle
- No true resting membrane potential; averages _____
- Spontaneous slow waves – BER: _________________
-50/-60mV
BER: basic electrical rhyth
Action potential: Smooth muscle
As smooth muscle has no troponin, how is cross-bridge activity activated by excitation?
Smooth muscle contraction process: (5)
Study the following table:
Contractility and Excitability:
- Skeletal muscle contractility (strength of the contraction) : (2)
- Not affected by ECF calcium concentrations
- Stronger stimulus will result in increased neurotransmitter release and thus increased action potentials in T-tubules and in turn increased calcium release from the SR (resulting in increased cross-bridge formation and a stronger contraction
Contractility and Excitability:
- Cardiac Muscle contractility:
- Increased ECF calcium concentrations result in increased contractility, since there will be increased calcium-induced calcium release
Contractility and Excitability:
- Neurone, skeletal muscle & cardiac muscle excitability: (2)
- ECF Ca2+ concentrations = blockage of voltage gated Na+ channels
- less Na+ enters the cell —> decreased chance of AP occurring
