Heart Rate Report: Physiology and Cardiac Contraction

This report explores the concept of heart rate, explaining its significance as the number of heart beats per minute and its importance in pumping blood to meet the body's metabolic needs. It details the normal heart rate ranges for adults and children, and highlights the role of the SA node, AV node, Purkinje fibers, and His bundle in cardiac muscle contraction. The report further outlines the four steps involved in cardiac muscle contraction: rapid depolarization, initial rapid repolarization, the plateau phase, and complete repolarization. It describes how the SA node acts as the natural pacemaker, generating contractions at a rate of 100 beats/min, and how the AV node and Purkinje fibers also contribute to action potential generation. The contraction of cardiomyocytes is discussed in detail, along with the influence of the parasympathetic and sympathetic nervous systems on heart rate regulation. The report concludes by referencing sources that support the information provided.

Running head: Heart Rate
Heart Rate
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Author Note

1Heart Rate
Heart rate refers to the number of heart beats per minute for ejecting blood to the
various portion of the body through arteries. The main purpose of beating heart is to pump
bloods so that the metabolic needs of body can be attained. In every minute, the amount of
blood ejected by heart is referred to as cardiac output. In a resting condition, the heart rate of
normal adults (age more than 10years), is ranging from 60 beats to 100 beats/ minute. In case
of highly trained person, this resting heart rate is within the range between 40-60 beats/ min.
This normal range of heart rate differs in case of children. In case of children of 1 to 2 years,
this normal heart rate ranges from 80 to 130 beats/ min. For 3 to 4 years children, this heart
rate range is 80 to 120 beats/ min ( Hall , 2015).
Heart rate is the functionality of cardiac muscles that involves a set of activities and
this function is the collaborative action of SA node (sinoatrial node), AV node (atrioventrical
node), purkinje fibres and His bundle. The contraction of cardiac muscles is responsible for
beating of heart that is heart rate. SA node is located on the walls of right atrium ( Hall,
2015).
The contraction of cardiac muscles take place due to the generation of electrical
impulse that is known as action potentials Heart rate is completely dependent on this action
potential generation and the pacemaker cells such as SA node, AV node, purkinje fibres and
His bundle. SA node is the natural pace maker of human body. The causative factors of heart
rate that is the cardiac contraction is completed through four steps. The cells of SA nodes are
generally modified cardiomyocytes and they are connected to the neighbouring cells through
gap junctions so that they can depolarize the cardiomyocytes locally. The first step of cardiac
muscle contraction is characterized by rapid depolarization and in this phase voltage gated
sodium channels are opened and sodium ions enter into the cells resulting potential of cells
reach to +20 mv to +30 mv ( Khurana, 2018). This step is followed by initial rapid
repolarization due to closure of fast sodium channels and opening of a few K+ channels

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causing transient outward current. Next, plateaue phase takes place in which membrane
potential slowly falls to -40 mv due to opening of L-type Ca+2 channels and inward
rectifying K+ channels. During the third step of repolarization, complete repolarization
happens due to closing of Ca+2 channels and opening of delayed outward rectifying K+
channels. In the last phase, resting membrane potential is achieved and the membrane
potential becomes -90 mv. This contraction of cardiomyocytes is transferred from one cell to
another and contraction take place. SA nodes can generate contraction 100 beats/ min and
this contraction is controlled by parasympathetic and sympathetic nervous system. AV nodes
can generate action potential at the rate of 40-60 beats/ min and on the other hand purkinje
fibre can produce action potentials at a rate of 30-40 beats/ min ( Khurana, 2018).

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References
Hall, J. E. (2015). Pocket Companion to Guyton & Hall Textbook of Medical Physiology E-
Book. Elsevier Health Sciences.
Khurana, I. (2018). Medical physiology for undergraduate students-E-book. Elsevier Health
Sciences.

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