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Cardiac Muscle Cheat Sheet

Cardiacmuscle
1,614 views 192 downloads 27 May 2025 History
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Cardiac Muscle

Structure 1
1) striated
2) thin filaments have tropom­yosin (belt) and troponin (3 spheres)
3) contains an abundance of mitoch­ondria and myoglobin
4) possess T-tubles and sarcop­lasmic reticulum
5) Ca++ enters the cytosol from voltag­e-gated Ca++ channels (small amount) in the plasma membrane and triggers internal release of Ca++

AP in contra­ctile cardiac muscle cells (P 1)

 
1) AP in cardiac contra­ctile cells differs consid­erably from the AP in cardiac autorhymic cells
2) -90mV resting potential
3) rapid rising phase of AP result of Na+ entry on opening of fast Na+ channels at threshold (-70mV)
4) Brief repola­riz­ation after potential reaches its peak bc of limited K+ efflux on opening of transient K+ channels, coupled w/ inacti­vation ofNa+ channels

Anatomy of the heart

 
dual-pump system includes 4 chambers:
- left and right Atria, Ventricles
- chambers on right pump = oxygen­-poor blood through pulmonary circul­ation -> lungs
- chambers on left pump = oxygen­-rich blood through systempic circul­ation -> body tissues

Path of the blood (based on valves)

 
1) right AV valve/­tri­cuspid (r.a.-­>r.v)
2) pulmon­ary­/se­milunar valve (r.v.-­>pu­lmonary artery)
3) left AV valve/­bic­usp­id/­mitral (l.a.-­>l.v.)
4) aprtic­/se­milunar valve (l.v.-­>aorta)

Purkinje Fibers

 
- small terminal fibers of specia­lized, cardiac pacemaker cells that extend from Bundle of His and spread throughout the ventri­cular myocardium
- 30 A.P./min
- In normal condit­iona, follow SA node (and AV node) at 70 AP/min

Nodes

 
Sinoatrial (SA) Node:
- right atrium near the opening of the superior vena cava
- exhibits an autorh­yth­micity of 70 action potentials per min and leads the activity of the other pacemaker structures int he heart

Atriov­ent­ricular (AV) Node:
- Cardiac pacemaker cells located at the base of the right atrium
- exhibits an autorh­yth­micity of 50 action potentials per min
- Under normal condit­ions, this node follows faster SA node at 70 A.P./min

Affect of Pressure on Valve

 
Structure of Heart Valve = ensure a one-way flow of blood (no backflow)

- When pressure is greater behind the valve, it opens
- When pressure is greater in front of the valve, it closes

Heart Walls

 
Endoca­rdium: thin layer of endoth­elial tissue lining the interior of each chamber

Myocar­dium: middle later of heart wall, composed of cardiac muscle
- cardiac muscle cells are connected end-to-end by interc­alated disks (formed desmosomes and gap-ju­nct­ions)

Epicar­dium: thin external membrane covering the heart and is filled with a small volume of perica­rdial fluid

Excita­tio­n-C­ont­raction Coupling

 
- mechanism of Ca++ entry into the cytosol is different from that in skeletal muscle cells

- T-tubule membranes have dehydr­opy­ridine receptors (volta­ge-­gated Ca++ channels). open and allow Ca++ to flow into cytosol

- Ca++ entry triggers further release of Ca++ from sarcop­lasmic reticulum. these 2 sources of Ca++ activate power stroke of contrs­tra­ction

- # of activated crossb­ridges is propor­tional to the cytosolic Ca++ conc.

Cardiac Muscle

Structure 2
6) it displays pacemaker activity intiating its own actions potential
7) connected by gap junctions
8) innervated by atonomic neuronal fibers
9) action potentials are longer ind uration than both smooth and skeletal muscle
- longer duration to prevent fatigue but requires a lot of energy

Intera­trial Pathway

 
cardiac cells that conducts pacemaker acitivty fromt he right atrium to the left atrium
- from SA node to AV node

Pacemaker activity of cardiac autorh­ythmic cells

Pacemaker activity of cardiac autorhythmic cells

Pacemaker Activity

 
99% of cardiac muscle cells are contra­ctile and don't initiate their own action potentials

1% are autorh­ythmic and intrin­sically initiate their own action potentials at a regular frequency

Myocardium

 
- interc­alated discs
1)desm­osomes = mechan­ically hold cells together
2)gap-­jun­ctions = provide paths of low resistance to the flow of electrical current between muscle cells

- gap-ju­nctions enable the cardiac muscle to form a functional syncytium (a group of cells that act as a single functional unit despite mainta­ining their individual identi­ties)

Valves of the Heart

Right Atrium - Receives oxygen­-poor blood from systemic venous circul­ation (inferior and superior vena cava veins)
- pumps blood into the right ventricle through the right atriov­ent­ricular (AV) (tricuspus valve)
Right Ventricle - receives oxygen­-poor blood from right atrium and pumps blood through the pulmonary (semil­unar) valve into the pulmonary artery

Picture of the heart

Picture of the heart

AP in contra­ctile cardiac muscle cells 1

 
1) AP in cardiac contra­ctile cells differs consid­erably from the AP in cardiac autorhymic cells
2) -90mV resting potential
3) rapid rising phase of AP result of Na+ entry on opening of fast Na+ channels at threshold (-70mV)
4) Brief repola­riz­ation after potential reaches its peak bc of limited K+ efflux on opening of transient K+ channels, coupled w/ inacti­vation ofNa+ channels

Relati­onship of AP and Refractory Period

Relationship of AP and Refractory Period

Electrical Activity of the Heart

 
- heart muscle generates its own rhythmic electricla activity (autor­hyt­hmi­city)
- occurs due to pacemaker activity
- nodes: pacemaker cells grouped together in specia­lized regions
- 2 nodes
- control rate and coordi­nation of cardiac contra­ctions

Connective Tissue

 
- separates atria from ventricles and provides a rigid base for attachment of heart valves and cardiac muscle
- a ring of dense fibrous connective tissue surrounds each of the valves of the heart

Valves of the Heart

 
Left Atrium - receives oxygen­-rich blood from left and right pulmonary veins
- pumps blood through the left atriov­ent­ricular (AV) (biscuspid or mitral) valve into the left ventricle
Left Ventricle - Receives oxygen­-rich blood from left atrium and pumps blood through aortic (semil­unar) valve into the aorta

Nodes

 
Sinoatrial (SA) Node:
- wall of the right atrium near opening of superior vena cava
- 70 action potentials per min

Atriov­ent­ricular (AV) Node:
- base of right atrium
- exhibits an autorh­yth­micity of 50 action potentials per min
- Under normal condit­ions, this node follow faster SA node at 70 A.P./min

bundle of his

 
tract of specia­lized, cardiac pacemaker cells that originate sa tthe AV node and divides and projects into the left and right ventricles

AV Nodal Delay

 
- PA conducted relatively slowly through the AV node resulting in a delay of approx. 100ms
- to ensures that ventricles contract after atrial contra­ction

System Overview

 
Circul­atory stsmtems include:
1) heart (pump)
2) blood vessels (pipes)
3) blood (fluid)

This system function is impacted by nervous system and kidneys (endocrine system)

Functions:
- supply oxygen and nutrients
- remove "­was­tes­"
- temper­ature regulation
- distribute hormones
- immuno­-vi­gilance

Definition

 
found only in the heart and shares charac­ter­istics of both skeletal and smooth muscle

AP contra­ctile cardiac muscle cells 2

 
1) Prolonged plateau phase is result of slow Ca2+ entry on opening of :-type Ca2+ channels, coupled w/ reduced K+ efflux on closure of several types of K+ channels
2) rapid falling phase is result of K+ efflux on opening of ordinary voltag­e-gated K+ channels, as in other excitable cells
3) Resting potential is maintained by opening of leaky K+ channels

Picture of AP in cardiac cell

Picture of AP in cardiac cell

Electr­oca­rdi­ogram (ECG)

Electrocardiogram (ECG)
- electrical currents generated by coodinated action potentials of the heart muscle can reach the surface of the body and detected as voltage differ­ences between 2 points on the body surface

- can detect distur­bances in heart function

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