MUSCULAR SYSTEM:

Cardiac Muscle

Only found in the HEART. Involuntary (Autonomic Nervous System) Moderate Contraction Striated Nuclei is centrally located (Size of nucleus is 10-15um) Branched Abundant in mitochondria (40% of its cell’s weight) Each cell have and average length of 50-100um and, 15um width Each fiber is envelope with ENDOMYSIUM The fascicle is surrounded by PERIMYSIUM Intercalated Discs – connects one fiber tissue to another. It also allows action potential

to flow through the heart like a wave allowing the heart to pump blood.3 keys to recognize :

ADHERENT JUNCTION – anchors/actin fibers of the sarcomere to the end of each cardiac fiber.

DESMOSOMES – proteins mechanically linked one cardiac fiber to another. GAP JUNCTIONS – Type of synapse, Electrical synapse which facilitates

passage of membrane excitation quickly from the fiber to another. PURKINJE FIBERS are non-contractile but are specialized to initiate and conduct the

electrical impulse that controls cardiac contraction. The chain of events that occurs during contraction of cardiac muscle cells is identical to

the skeletal muscle cells. Unlike skeletal muscle cells, cardiac muscle cells contract without neural impulse. WEIGHT: 250-300g

It is approximately the size of your fist. PUMPS: 70ml/beat WORKS: 70 beats/minute SINOATRIAL NODES – are cluster of specialize cells found in right atrium, pacemaker

cells, that generates spontaneous action potential spread across the cardiac muscle through its own intrinsic conduction system to create a heartbeat pushing the blood around the body. It fires 100x heartbeats per minute.

AUTONOMIC NERVOUS SYSTEM regulates the electrical excitation made by Sinoatrial nodes, reducing the heartbeat of the cardiac muscle from 100x to 70x per minute.

Layers of the Heart:

PERICARDIUM – a double-walled sac around the heart.

Composed of:

• A superficial FIBROUS PERICARDIUM.

• A deep two-layer SEROUS PERICARDIUM.

• The PARIETAL LAYER lines the internal surface of the fibrous pericardium.

• The VISCERAL LAYER or EPICARDIUM lines the surface of the heart.

• They are separated by the fluid-filled pericardial cavity called the PERICARDIAL CAVITY or PERICARDIAL FLUID.

MYOCARDIUM Thickest layer of the heart Thickest in left ventricle because must pump hard to overcome high pressure of

systemic circulation Right atrium the thinnest because of low resistance to back flow Consist of cardiac muscle cells = MYOCYTES Different from smooth or skeletal muscle cells due to placement of nuclei, cross

striations, and intercalated disks ENDOCARDIUM

The myocardium‘s smooth inner lining, Innermost layer Composed of simple squamous epithelium (ENDOTHELIUM)

2 Divisions of the Heart

RIGHT HEART – receives venous blood from systemic circulation via superior vena cava and inferior vena cava into right atrium.

LEFT HEART – receives oxygenated blood from the pulmonary vein pumps blood into systemic circulation.

Parts of the Heart

SEPTUM – a thin partition or membrane that divides two cavities or soft masses of tissue in an organism.

INTER-ATRIAL SEPTUM

Located between right and left atria.

Contains:

FOSSA OVALIS – remnant of the foramen ovale

FORAMEN OVALE – opening of interartrial septum in fetus

INTERVENTRICULAR SEPTUM

Located between right and left ventricles

Upper membranous part

Thick lower muscular part

SULCUS – a long narrow slit or groove that divides an organ into lobes. 4 SULCUS/GROOVES OF THE HEART

CORONARY SULCUS (CIRCULAR SULCUS) – marks the division between atria and ventricles, contains the trunks of the coronary vessels and completely encircles the heart

INTERATRIAL GROOVE －separates the two atria and is hidden by pulmonary trunk and aorta in front

INTERVENTRICULAR GROOVES －ANTERIOR AND POSTERIOR, mark the division between ventricles (which separates the RV from the LV), the two grooves extend from the base of the ventricular portion to a notch called: the cardiac apical incisure

VENA CAVA SUPERIOR VENA CAVA – one of the two main veins that bring deoxygenated blood

from the body to the heart. INFERIOR VENA CAVA – carries blood from the lower part of the body to the heart.

CORONARY SINUS Opens into the right atrium Returns deoxygenated blood from heart muscle (coronary veins)

RIGHT AND LEFT PULMONARY VEINS Open into the left atrium Return oxygenated blood from lungs

PULMONARY TRUNK

Carries deoxygenated blood from right ventricle to lungs Splits into right and left pulmonary arteries

ASCENDING AORTA Carries oxygenated blood away from left atrium to body organs Three major branches

Brachiocephalic Left common carotid, Left subclavian artery

ATRIA – receiving chambers of the heart RIGHT ATRIUM

The right upper chamber of the heart. The right atrium receives deoxygenated blood from the body through the

vena cava and pumps it into the right ventricle which then sends it to the lungs to be oxygenated.

LEFT ATRIUM Left atrium receive oxygenated blood through the pulmonary vein. The blood is then pumped into the left ventricle chamber of the heart

through the mitral valve. VENTRICLES – discharging chambers of the heart

RIGHT VENTRICLE The right ventricle is the chamber within the heart that is responsible for

pumping oxygen-depleted blood to the lungs. It is located in the lower right portion of the heart below the right atrium and

opposite the left ventricle. LEFT VENTRICLE

The left ventricle receives oxygenated blood from the left atrium via the mitral valve and pumps it through the aorta via the aortic valve, into the systemic circulation.

VALVES Also known as HEARTSTRINGS Ensures unidirectional blood flow through the heart “LUB-DUP” – heart sound due to closing of valves

LUB – closing of Atrioventricular Valves DUP – closing of Semilunar Valves

ATRIOVENTRICULAR Lies in atrium and ventricles Prevents backflow into the atria when the ventricles contract Has CHORDAE TENDINAE – anchors atrioventricular valve to papillary

muscle of the ventricular wall TRICUSPID – found between Right Atrium and Right Ventricle MITRAL – found between Left Atrium and Left Ventricle

SEMI-LUNAR Prevents backflow into the ventricles No chordae tendinae

PULMONIC – located between the right ventricle and the pulmonary artery. AORTIC

How Does Blood Travel Through the Heart?