Lec 16: Cardiac Muscle Flashcards
Cardiovascular system is comprised of: (2)
heart
blood vessels
Cardiovascular System Functions: (5)
- ) Deliver blood to all organs and tissues of the body
- ) Provide nutrients & oxygen to the tissues
- ) Remove wastes
- ) Deliver hormones
- ) Deliver immune system cells to sites of infection
Memorize Pulmonary/Systemic Circuit pressure system (screenshot)
plzzzzzzzzz
(Cardiac Muscle)
Only in…
- Cells =
- like skeletal, they are…
- …but…
- the heart
= cardiac myocytes
- they are striated,
- involuntary (autonomic NS control)
(Cardiac Muscle)
- Cardiac myocytes are…
- Ultrastructure is
- Lots of…
- short, irregular in shape, and sometimes branched with a central nucleus
~10 mm in diameter - very similar to skeletal muscle (i.e., sarcomere, myofibrils, t-tubules, SR)
- capillaries & mitochondria
Heart Function =
= Pump blood throughout the cardiovascular system – pulmonary & systemic circulation
Blood vessels are…
highly specialized tubes
3 kinds of Blood vessels:
arteries
capillaries
veins
NEVERMIND
(Arteries)
- Handle…
- Regulate: (2)
- high blood pressures & pulse pressure (= SP-DP) (physical exertion)
- mean arterial pressure (70-110 mm Hg) (Resistance vessels) & tissue perfusion
NEVERMIND
(Capillaries)
Facilitate the Transfer of: (4)
- ) O2 and nutrient molecules to the tissues from blood
- ) wastes from the tissues to the blood
- ) hormones to the tissues from blood
- ) immune system cells to the tissues from blood
NEVERMIND
(Veins)
- Require…
- May have…
- low pressures (in order for blood to flow through capillaries)
- valves to insure one-way flow to the heart
The cardiac myocytes are connected…
Allows for…
…in series via intercalated discs
Intercalated disc = combination of gap junctions and desmosomes
… electrical coupling (“functional syncitium”), passing of AP from cell to cell
Heart functions as a
‘pump’
Diastole =
Systole =
= the phase of the heartbeat when the heart muscle is relaxed
= the phase of the heartbeat when the heart muscle contracts.
Heart pumping steps: (3)
& Thus…
(use pic screenshot for visualization)
- ) Both atria and ventricles are relaxed and both fill with returning blood.
- ) Atria contract (atrial systole)– pumping blood into the ventricle.
- ) Ventricle contracts second (ventricular systole)-pumping blood out of the heart.
…the heart has a system to control the order and rhythm of myocyte contraction
S-A Node =
A-V Node =
= sinoatrial node (sets rhythm of the heartbeat)
= atrioventricular node
(Conducting System of Heart)
- Heart contains a specialized conduction system for: (2)
Note =
- ) Setting the rhythm of the heart beat – autorhythmicity
- ) Transferring the electrical signal to various parts of the heart musculature
= These are all cardiac muscle cells NOT nerve cells
(Conducting System of Heart) Steps: (6)
- ) S-A node fires AP first
- ) AP spreads throughout the Atria (Atria contract – blood flows from atria to ventricles)
- ) AP conduction is delayed at the A-V node
- ) AP is carried to the apex of the ventricles via conducting fibers (Bundle of His)
- ) AP is carried to the ventricular muscle via Purkinje fibers
- ) AP spreads throughout the ventricles (ventricles contract – blood flows out of ventricles to systemic and pulmonary circuits
APs are…
different at various regions
(S-A Node)
- Cells in the SA node set…
- since they…
- They are:
- SA node cells are aka
- NOTE =
- the rhythm of the heart beat,
- fire (AP) first and all other cells will follow in succession.
- Autorhythmic – fire an AP spontaneously
- “Pacemaker cells”
= other cells in the heart are also auto- rhythmic, but the activity of the S-A node normally sets their pace and the pace of the heart rate.
(Pacemaker cells of S-A Node_
- Have…
- Other cardiac myocytes are at
- Leaky to…
- and have…
- Also have very few…
- a high resting potential (Vm) = ~ -60 to -65 mV
- ~ -90 mV
- Na+
- a lower K+ permeabilty, thus Vm is a little closer to ENa+
- voltage-gated Na+ channels
(Pacemaker Cell AP (autorhythmicity))
Steps: (5)
- ) The pacemaker cells “spontaneously” depolarize (Pacemaker Potential)
- Due to Na+ leaking in (called If for “funny” current) through “pacemaker channels”.
- Some Ca2+ leaks in too.
- ) Once threshold is reached → fire AP
- ) AP is due to Ca2+ entering through voltage gated Ca2+ channels (L- & T-type)
- ) Repolarization is due to opening of voltage-gated K+ channels
- ) The L & T-type Ca2+ channels become inactivated leading to a refractory period
(Atrial & Ventricular Contractile Myocytes)
- Have…
- Highest permeability at rest is to…
- Also have many: (2)
- a low resting potential (Vm) = ~ -90 mV
- K+, thus Vm is close to EK+
- voltage-gated Na+ and Ca2+ channels
(Atrial & Ventricular APs)
- Both are…
- ______ __ is shorter in duration than _____ __
- Both have…
- prolonged 200 – 400 mSec (neuron AP lasts
- Atrial AP is shorter in duration than ventricular AP
- a plateau at the top
(AP duration)
Nerve =
Skeletal Muscle =
Atrial & Ventricular Myocyte =
S-A Node =
= 1 - 2 mSec
= 2 – 5 mSec
= 200 – 400 mSec
= 200 mSec
Review Atrial & Ventricular AP phase graph (screenshot)
plzzzzz don’t you want an AAAAAA
Phase 4 =
Highest permeability =
Vm is…
= Rest
= K+
- …close to EK+
Phase 0 =
Highest permeability =
What opens?
Influx of
Causes…
= Depolarization (initiated by preceding myocyte)
= Na+
= Voltage-gated Na+ channels
- Na+
- the large depolarization (-90 to +30)
Phase 1 =
Inactivation of…
Activation of…
The relatively gradual activation of
Note =
= Short small repolarization (+30 to +10)
- Na+ channels
- K+ channels accounts for the repolarization (slow)
- L-type Ca2+ channels opposes repolarization and leads to the plateau (phase 2)
= The initial depolarization causes all of these changes
Phase 2 =
What’s open?
Requires…
Cell remains…
K+ channels are…
K+ efflux is…
= Plateau
L-type Ca2+ channels are
- several hundred mSec to completely inactivate
- depolarized for several hundred mSec
- open, but balanced by L-type Ca2+ channels
- balanced by Ca2+ influx
(stay at -10 to +10 mV)
Phase 3 =
- Complete inactivation of…
Returns __ towards…
= Repolarization
- L-type Ca2+ channels
Open K+ channels (they eventually close) - Vm towards EK+
ECG =
Electrocardiogram
P Wave =
QRS Complex =
T Wave =
& draw diagram (screenshot)
= Activation of the atria
= Activation of the ventricles
= Recovery Wave
(Cardiac Myocyte contraction)
Similar to…
- skeletal muscle (thick and Thin Filaments, sarcomeres, etc)
(Cardiac Myocyte contraction)
The AP Causes: (2)
- ) Causes an influx of Ca2+
2. ) Causes release of Ca2+ from the SR
(Cardiac Myocyte contraction)
2 sources of Ca2+ for cardiac muscle:
Extracellular
Sarcoplasmic reticulum
E-C Coupling =
Ca2+ induced Ca2+ release
(E-C Coupling)
Important Components: (2)
Contraction follows…
Relaxation due to…
- ) Ryanodine receptor
- ) L-type Ca2+ Channels.
- the rise in free Ca2+.
- Ca2+ removal: Ca2+ pumps at sarcolemma & SR and Na+/Ca2+ exchanger
VICR –>
CICR –>
(skeletal muscle)
cardiac muscle
How can heart rate be changed?
Modify the Pacemaker Potential
2 ways to Modify the Pacemaker Potential:
- ) Epinephrine & Autonomic Sympathetic stimulation speeds up the pacemaker potential. Fight or flight response. (Top Panel on slide)
- ) Autonomic Parasympathetic stimulation slows down the pacemaker potential. Resting state. (Bottom Panel on slide)
(Modifying the Pacemaker Potential/#1: Flight or flight)
- Increases…
- Opens…
- Reach…
- Due to…
- Faster…
- If
- pacemaker channels.
- threshold quicker.
- cAMP
- HR
(Modifying the Pacemaker Potential/#2: Autonomic…)
- Decreases…
- Increases…
- Reach…
- Due to
- Slower
- If
- IK+ (opening K+ channels)
- threshold slower
- muscarinic AchR
- HR
