Cardiac Muscle/Smooth Muscle Flashcards
What are muscle spindles?
- small tapered structures located in midst of myofibers
- responsive to mechanical pressure
- send information re: movement and position to CNS
- facilitates degree of contraction and number of motorneurons involved
- proprioception
How do muscle spindles respond to stretch?
by reflexive contraction
Spindle stretch opens a…
mechanically sensitive channel
What are golgi tendon organs?
- located in the muscle tendon (attachment point to bone)
- its role is to prevent damage to muscle through excessive stretching
- XS stimulation produces an inhibitory reflex of the same muscle
________ and _______ modulate our skeletal muscle system via reflexes.
Muscle spindles and GTOs (they monitor muscle stretch and tension, respectively)
Describe vertebrate cardiac muscle.
- striated
- branch-like
- uninucleated
- intercalated disks
- occur at z-line
- fascia adherens (actin binding)
- macula adherens (desmosome, join cells)
- gap junctions (electrical continuity)
- = synctium
Hearts are innervated by ____, but this serves for…
ANS, modulatory function only
________ cells initiate myogenic contractions in the heart.
Sinoatrial
Do sinoatrial cells have a stable RMP?
No.
- Starts at ~60mV
- they have cation channels (funny channel) activated by hyperpolarization
- Na+ enters and initiates AP+
- Leakage through the Na+ channel (If) depolarizaes the cell until it gets to ~40mV
- Depolarization is mediated by VGCC not Na channels
- Connected by gap junctions to other cells in the heart
Where is the AV node located?
In the right atrium
What serves as the conduit between the atrium and ventricle?
AV node (+fibres)
Why does the AV node help difficult conduction from atria to ventricles?
Allows temporally separate contractions for each.
What structure carries electrical impulses from the AV node into the ventricles?
The bundle of his
Describe the AV node action potential.
- There is a delay in the conduction of the AP from the SA node to the AV node
- enables the ventricles to fill with blood before contraction
- AV node cells will function as pacemaker cells themselves, just at a slower rate.
What is the heart contraction sequence?
- contraction initiated in SA
- L and R atria contract
- AV node conducts depolarization from atria to heart apex
- ventricular contraction starts at apex and moves superiorly
RMP in cardiac myocytes is dominated by…
K+
Why is the cardiac AP much longer in duration than a neuronal skeletal muscle AP?
Because of a long duration Ca2+ current.
What does an electrocardioram (ECG) allow us to do?
Record electrical activity through electrodes placed on the skin. The waves of depolarization and hyperpolarization experienced by the atrie and ventricels can be recorded with extracellular electrodes.
What are the 5 major deflections of voltage on the ECG?
- P - atrial depolarization
- QRS complex - ventricular depolarizatio
- T - ventricualr repolarization
Are VGCC and RyR coupled in cardiac cells?
No. RyR opening is mediated by Ca2+influx
What are the key differences of smooth muscle from skeletal muscle?
- no sarcomeres (no striations)
- thick and thin filaments are scattered in cells
- attached to cell membrane at adhesion plaques
- no t0tubules and minimal SR
- often connected by gap junctions
- typically function as a single unit (synctium)
- contracts in all dimensions
- different mechanism of EC coupling
- spontaneous contractions
- stimulated by exogenous substances (hormones, NT etc)
- pacemaker contractions
At rest, what protein is bound to acin and blocks myosin binding in smooth muscle?
Calesmon (smooth musle DOES NOT have troponin)
Stimulation of smooth muscle cell increases intracelluar Ca2+…
- Ca2+ binds to calmodulin (CaM)
- CaM binds to caldesmon and removes it from actin
- cross-bridges form and contraction ocurs
- CaM also causes phosphorylation of myosin
- increase in myosin ATPase activity
- CaM binds to caldesmon and removes it from actin
Epiniephrine mediates ________ of smooth muscle contraction.
inhibition
