Smooth and Cardiac Muscle Flashcards
(32 cards)
describe the appearance, if multi or single nucleated, and what smooth muscle controls
- *- spindle shaped**
- single nucleus
- non-striated
- mechanical control of organ systems
describe cardiac muscle
- *-** cardiac myocytes are organised in branched meshwork of fibres that run in various directions
- centrally located nuclei
- invol. muscle
- causes beating of the heart
describe skeletal muscle
how does it attach to the bone?
- skeletal / voluntary muscle
- anchored to bones via **tendons
- **function: locomotion, posture maintenance and breathing
- striated (made from actin and myosin)
- multinucleated
describe the structure of cardiac muscle fibres
what are: a) sarcolemma b) sarcomere c) sarcoplasmic reticulum
what type of junctions exist?
made of:
i) A bands = thick filaments
ii) I bands = thin filaments
- surroundered by membrane: sarcolemma
- sarcoplasmic reticulum: like ER, contains Ca2+ ions
- sarcomere: functional contractile unit of muscle (made of A&I band and actin and myosin)
gap junctions are in cardiac muscle fibres
what is the role of intercalated discs?
what type of cell-cell junctions do they contain?
connect cardiac myocytes together
- *cell-cell junctions:**
- fascia adherens (anchoring junctions) - attach sarcomeres to cell membrane
- desmosomes - site of adhesion, keep muscle cells connected when they contract
- gap junctions - faciliate electrical communication - passage of ions and AP spread through
which cell-cell junctions permit AP in intercalated discs?
gap junctions
what are the specialised properties of cardiac muscle cells regarding AP?
what does automaticity & rhymthmicity mean re AP?
- DO NOT require depol from nerves
- automaticity: spontaneously generate an electrical impulse (depol)
- rhymthmicity: generate AP in regular and repetitve manner
properties:
- waves of depol propagate between cells via gap junctions on IC disks
- waves of depol propagate to adjacent cells: contract in synchronouse fashion = rapid, synchronous depolarization of the myocardium
myocardium functions as a single contractile unit: important for pumping action of the heart
which are the repolarsing ions and depolarsing ions involved in AP?
many ion channels are involved in the overall make up of the response
* why are there different AP in different regions of the heart *
different ion channels are expressed in different myocytes around the heart
means that the size and shape of AP can differ between cells, depending on function of cells
where do u find pacemaker cells?
how do u describe the AP that pacemaker cells create?
what do AP look like?
pacemaker cells
- depolarise spontanously (automaticity)
- characteristic shaped AP - wandering baseline
- occur in: SA node & AV node (although atrial and v. cells can do this in disease)
what are the AP of non-pacemaker cells like (esp. ventricular cells?)
what does this mean the heart beats like?
- ventricles act in coordinated fashion - contractile works to expell blood into vessels = WHY they have refractory period
- means have to contract AND relax , rhythmically, before in order to go through cardiac cycle.
explain the mechanism of calcium signalling driving muscle contraction
- depol of membrane from Na+, through Na+ channels = opens Ca 2+ channels
- Ca2+ move through calciumc channels into cell membrane
- rise in Ca2+ triggers further calcium release from the sarcoplasmic reticulum, via the ryanodine receptor
- calcium associates with troponin C in the sarcomere, to initate contraction in the cardiac muscle (systole)
- events terminated by release of Ca2+ from sarcomere (relaxation - diastole), and reuptake into sarcoplasmic reticulum
what happens when calcium binds to troponin for striated muscle contraction?
what does ATP hydrolyse provide energy for ?
calcium: binds to troponin in troponin complex, exposes the myosin binding sites on the actin = allows the myosin to bind
ATP hydrolyses: provides the energy to drive filament sliding
what is the effect of sympathetic and parasympathetic on the heart?
what NT and receptor used for each? ^
sympathetic: increaeses HR and force of contraction. secretion of noradrenalin and activation of B1 adrenoreceptor
parasympathetic: decreases HR. secretion of ACh and activation of muscarinin (M2) receptors
for skeletal, cardiac and smooth muscle - what are they striated and vol / invol?
Skeletal muscle is voluntary and striated
cardiac muscle is involuntary and straited
smooth muscle is involuntary and non-striated.
what is structure of smooth muscle like?
what do intermediate filaments do in SM?
what do dense bodies do?
- loose lattice of thick and thin fillaments (actin & myosin) that run obliquely across the muscle
- non striated
- cytoskeletal intermediate filaments assist in the transmission of force generated by contraction
- dense bodies: attachment for thick and thin filaments - (equivelent to z lines of striated muscle)
what are the two types of attachment you get in smooth muscle?
- mechanical attachments: between cells
- gap junctions: provide a pathway for passage of electrical signals
where is smooth muscle found?
function? (4)
- *location:**
- **within walls of organs and strucutres
- **e.g. BV, bronchi, bladder, uterus, gut
- *functions:**
- *primary function is contraction:**
- regulation of diameter of BV
- regulating diameter of airways
- propulsion of food through GI tract
- contraction of uterus (deliver baby :))
what are the different types of AP shape from SMC? (3)
can smooth muscle cells do spontaneous electrical activity?
shape of AP varies depending on where the SMC are
- e.g. simple spike, spike and plateau , spikes on top of slow waves
smooth muscle cells do spontaneous electrical activity
what is AP length in:
a) smooth muscle
b) skeletal muscle?
a) smooth muscle: 10-50ms
b) skeletal muscle: 2ms
smooth muscle is longer !!
in smooth muscle
- which ion-gate causes depolaristion of AP?
- why do we see slower upstroke of AP compared to skeletal muscle?
- smooth muscle: mainly Ca2+ channels (some Na+)
- calcium channels open more slowly than sodium channels - why we see slower upstroke
decribe the mechanism of excitation-contraction coupling happens in SMC
- rise in intracellular calcium can occur by
i) depol of membrane opens Ca2+ channels and calcium enters
OR
ii) agonist induced release of calcium via IP3., through sarcoplasmic reticulum - Calcium binds to calmodulin, which actiavtes an enzyme called myosin light chain kinase (MLCK)
- MLCK activates myosin head by phosphorylating them (ATP -> ADP + Pi, Pi attaches to the head)
- phosphorylation of myosin light chain increase ATP activity and allows myosin head groups to bind to actin & undergo cross-bridge cycling (which initiates contraction)
-
describe the mechansim of SMC contraction
- thin filaments slide past the thick filaments, pulling on the dense bodies (connected to the sarcolemma)
- dense bodies pull on the intermediate filaments’ networks through the sarcoplasm
- causes entire muscle fibre to contract - ends are pulled towards the centre, causing midsecction to bulge
