6. Smooth & Cardiac Muscle Flashcards
What is this muscle?
Skeletal
What is this muscle?
Cardiac
What is this muscle?
Smooth
What are the characteristics of
a) skeletal muscle
b) cardiac muscle
c) smooth muscle
a) striated, multinuclear and peripheral, for locomotion, sarcomeres, Ca2+ binding=troponin
b) striated, meshwork, central nucleus, intrinsic myogenic activity, sarcomeres, Ca2+ binding=troponin
c) involuntary, non-striated, 1 nucleus per fibre, spindle shape, mechanical organ control, no sarcomeres, Ca2+=calmodulin
Do skeletal, cardiac and smooth have cellular junctions?
skeletal - none
cardiac - intercalated discs, gap junctions
smooth - gap junctions
What is an intercalated disc and where are they found?
Thickenning of sarcolemma, connects adjoining cardiac myocetes e.g desmosomes and gap junctions. Found in cardiac muscle only
Label A-F
A: gap junction
B: intercalated disc
C: sarcoplasmic reticulum
D: A band (thick)
E: I band (thin)
F: Z disc
Cardiac cells have automaticity and rhythmicity - what does this mean?
Can spontaneously generate electrical impulses (depolarise) in a regular and repetitive manner
(pacemaker cells in SAN and AVN)
Cardiac myocetes from an electical/functional syncytium - what does this mean?
Electrical impulses propagate between cells via gap junctions on intercalated discs, waves of depol. propagate to adjacent cells which contract in a synchronous fashion
NB: diff size/shape of APs in heart and many ion channels involved in response. Na+ Ca2+ depol, and K+ repol
What two types of cells are found in the heart?
Pacemaker cells (SAN, AVN, have automacity)
Ventricular cells (have refractory periods)
Describe the process of Ca2+ signalling during cardiac contraction.
- Na+ in, membrane depolarises, VGCa2+ channels open (L type)
- Ca2+ influx, intracellular Ca2+ increases triggering Ca2+ release from sarcoplasmic reticulum
- Ca2+ associates with troponin C in sarcomere and stimulates contraction (systole) (unmasks binding site for M to bind with A)
- Ca2+ released from sarcomere causes diastole and its reuptake into sarcoplasmic reticulum
NB: ATP hydrolosis provides energy to drive filament sliding
What happens to the heart under sympathetic and parasympathetic modulation?
Sympathetic: increased heart rate and contraction force, NA secretion and activation of beta1 adrenoreceptor
Parasympathetic: decreased heart rate, ACh secretion and activation of muscarinic receptors (M2)
Label A-D
What is this structure?
A: intermediate filament
B: dense body
C: mechanical junction coupling cells
D: gap junction for electrical and chemical communication
Smooth muscle
Describe smooth muscle.
What do intermediate filaments do?
What do dense bodies do?
What are the 2 types of attachments between cells?
Loose lattice of thick and thin filaments running obliquely across muscle.
Assist in transmission of contraction force
Attachements for thick and thin filaments
Mechanical and gap junctions (electical signals)
List the structures where smooth muscle is found
- Bladder
- Gut (oseophagus, stomach, intestines) (propel food through GI tract)
- Uterus (deliver baby)
- BVs (regulate BV diameter)
- Bronchi (regulate airway diameter)
- Urethra, bladder
- Errector pili in skin