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| shorter than skeletal muscle with centrally located nucleus. The ends of neighboring cardiac fibers connect by intercoralated disk. The intercoralated disk contain gap junctions, which allow action potentials to conduct to neighboring fibers. This structure coordinates atrial and ventricular contraction. Many more mitochondria in cardiac muscle than skeletal muscle |
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| self excitable fibers that repeatedly generate action potentials that trigger heart contractions. They do not need the brain to send a signal. About 1% of cardiac muscle fibers become autorythmic fibers. 2 main functions: 1. Act as a pace maker (setting the rhythm of heart contractions) 2. Form a conductions system(coordinate chamber contractions |
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· sequence that occurs for a heart beat
sinotrial (SA) node
Atrioventricular (AV) node
Purkinje fibers
Sa node is known as the natural pace maker of the heart. starting the contraction action potential |
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o located in the wall of the right atrium and it initiates cardiac contraction when depolarized. The SA node send it’s action potential through each atria causing coordinated contraction |
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| Atrioventricular (AV) node |
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| the action potential from the sa noted reaches the AV node in the inter atrial septum. Which sends and action potential to the atrioventricular bundle which branches and travels down the interventricular septum to the heart |
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| they conduct the action potential upward from the apex to the rest of the myocardium of the ventricles causing contraction and pushing blood out of the heart. |
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| action potential and contraction of contractile fibers |
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Definition
Action potentials produced by the sa nodes spread to contractile fibers of the heart
- depolarization
- plateau
- repolarization
contraction occurs the same as skeletal muscle with regulatory proteins binding to troponin and activating actin and mysoin. cardiac muscle relies almost entriely on arobic cellular resporation for atp production
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| contractile fibers resting membrane potential is -90mv. When brought to threshold sodium channels are open and contraction occurs. |
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1. the period of maintained depolarization due to the opening of calcium channels and potassium channels. |
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| recovery to the resting membrane potential. Closure of calcium channels more opening of potassium channels. |
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| electrocardiogram (EKG) (ECG) |
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Definition
· records action potential during each heart beat for 4 reasons
1. It determines whether the conduction pathway is normal or abnormal
2. Determines if The heart is enlarged
3. Determine if the heart is damaged
4. Determines the cause of chest pain |
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all events associated with one heart beats. It consist of systole and diastole of both atrias and ventricles.
- atrial systole
- ventricular systole
- pause
- relaxation
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| pressure and volume changes in cardiac cycle |
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| the atrius and ventricles alternate contractions forcing blood from high concentration to a low concentration. |
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| It last about 0.1 seconds and is the time that the atrias are contracting and ventricles are relaxed. Typically at rest 25ml goes to the atria to the ventricles. |
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| last about 0.3 seconds. And is the time that the ventricles are contracting and the atria are relaxed. Typically about 70 ml of blood are injected from the ventricles. |
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o There is a 0.5 second pause between atrial systole and ventricular sytole |
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o last about 0.4 seconds where the atrias and ventricles are relaxed. When your heart has to beat faster the relaxation period gets shortened. |
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· technically 4 sounds but only the 1st 2 can be heard because smooth blood flowing through the artery is silent. |
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o act of listening to the sounds in the body, usually done with a stethoscope. |
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| first heart sound and its called lub. It is louder and longer than the 2nd sound. The sound is paused by closer of the av valves after ventricular systole. |
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o second heart sound called dub. Shorter and softer sound. Caused by closure of semi lunar valves at ventricular diastole(when ventricles relax) |
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volume of blood injected from the left ventricle into the aorta each minute. |
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| volume of blood injected by the ventricle |
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| regulation of heart rate (2) |
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- autonomic regulation
- chemical regulation
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| controlled by the cardiovascular center of the medulla oblongata this area regulates heart rate by receiving input from various sensory receptors. It regulates by either increasing or decreasing autonomic stimulation and increasing is done by sympathetic autonomic nervous system specifically the cardiac accelerator nerves. Decreasing heart rate is done by parasympathetic autonomic system specifically vagus nerve. |
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| receptors that monitor limb position and muscle nerve impulses. When these receptors are stimulated they increase their signal to the cardiovascular center. |
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| receptors that monitor chemical changes in the blood, such as oxygen levels, ph, and cations. |
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§ monitor the stretching of arteries and veins due to pressure from the blood flowing through them. their rule is to regulate blood pressure. They are found in the aorta and carotid artery. |
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| epinephrine and norepinephrine enhance the hearts pumping by increasing heart rate and contractions. Thyroid hormone increases cardiac contraction and heart rate, hyperthyroidism symptom is a racing heart. |
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| potassium, calcium, and sodium effect heart function. |
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| any activity that works large muscles for at least 20 minutes Elevating cardiac output |
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§ Exercise increases oxygen demand this requires the heart to increase its rate of oxygen delivery to the tissues. Stroke volume increases while heart rate decreases when you are a trained athlete |
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