A report on Sinoatrial node

Sinoatrial node shown at 1. The rest of the conduction system of the heart is shown in blue.

Figure 2: Low magnification stained image of the SA node (center-right on image) and its surrounding tissue. The SA node surrounds the sinoatrial nodal artery, seen as the open lumen. Cardiac muscle cells of the right atrium can be seen to the left of the node, and fat tissue to the right.

Figure 3: Sinoatrial node action potential waveform, outlining major ion currents involved (downward deflection indicates ions moving into the cell, upwards deflection indicates ions flowing out of the cell).

Schematic representation of the atrioventricular bundle

Group of cells known as pacemaker cells, located in the wall of the right atrium of the heart.

- Sinoatrial node

29 related topics with Alpha

Heart

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Muscular organ in most animals.

Computer-generated animation of a beating human heart

The human heart is in the middle of the thorax, with its apex pointing to the left.

Heart being dissected showing right and left ventricles, from above

Frontal section showing papillary muscles attached to the tricuspid valve on the right and to the mitral valve on the left via chordae tendineae.

Layers of the heart wall, including visceral and parietal pericardium

The swirling pattern of myocardium helps the heart pump effectively

Arterial supply to the heart (red), with other areas labelled (blue).

Development of the human heart during the first eight weeks (top) and the formation of the heart chambers (bottom). In this figure, the blue and red colors represent blood inflow and outflow (not venous and arterial blood). Initially, all venous blood flows from the tail/atria to the ventricles/head, a very different pattern from that of an adult.

The cardiac cycle as correlated to the ECG

The x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.

Transmission of a cardiac action potential through the heart's conduction system

The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarization and repolarization. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell; there is no resting potential.

3D echocardiogram showing the mitral valve (right), tricuspid and mitral valves (top left) and aortic valve (top right).
The closure of the heart valves causes the heart sounds.

Heart and its blood vessels, by Leonardo da Vinci, 15th century

Elize Ryd making a heart sign at a concert in 2018

The tube-like heart (green) of the mosquito Anopheles gambiae extends horizontally across the body, interlinked with the diamond-shaped wing muscles (also green) and surrounded by pericardial cells (red). Blue depicts cell nuclei.

Basic arthropod body structure – heart shown in red

The human heart viewed from the front and from behind

Heart illustration with circulatory system

Animated Heart 3d Model Rendered in Computer

The heart pumps blood with a rhythm determined by a group of pacemaker cells in the sinoatrial node.

Cardiac pacemaker

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Initiated by electrical impulses known as action potentials.

Schematic representation of the sinoatrial node and the atrioventricular bundle of His. The location of the SA node is shown in blue. The bundle, represented in red, originates near the orifice of the coronary sinus, undergoes slight enlargement to form the AV node. The AV node tapers down into the bundle of HIS, which passes into the ventricular septum and divides into two bundle branches, the left and right bundles. The ultimate distribution cannot be completely shown in this diagram.

In most humans, the concentration of pacemaker cells in the sinoatrial (SA) node is the natural pacemaker, and the resultant rhythm is a sinus rhythm.

Heart; conduction system. 1. SA node. 2. AV node. 3. Bundle of His. 8. Septum

Electrical conduction system of the heart

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Overview of the system of electrical conduction which maintains the rhythmical contraction of the heart

Principle of ECG formation. Note that the red lines represent the depolarization wave, not bloodflow.

Different wave shapes generated by different parts of the heart's action potential

The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node in the heart to cause contraction of the heart muscle.

Cardiac muscle

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One of three types of vertebrate muscle tissue, with the other two being skeletal muscle and smooth muscle.

3D rendering showing thick myocardium within the heart wall.

The swirling musculature of the heart ensures effective pumping of blood.

Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.

They are located in the sinoatrial node positioned on the wall of the right atrium, near the entrance of the superior vena cava.

Action potential

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Action potential occurs when the membrane potential of a specific cell location rapidly rises and falls.

Shape of a typical action potential. The membrane potential remains near a baseline level until at some point in time, it abruptly spikes upward and then rapidly falls.

Approximate plot of a typical action potential shows its various phases as the action potential passes a point on a cell membrane. The membrane potential starts out at approximately −70 mV at time zero. A stimulus is applied at time = 1 ms, which raises the membrane potential above −55 mV (the threshold potential). After the stimulus is applied, the membrane potential rapidly rises to a peak potential of +40 mV at time = 2 ms. Just as quickly, the potential then drops and overshoots to −90 mV at time = 3 ms, and finally the resting potential of −70 mV is reestablished at time = 5 ms.

Action potential propagation along an axon

$Ion movement during an action potential. Key: a) Sodium (Na+) ion. b) Potassium (K+) ion. c) Sodium channel. d) Potassium channel. e) Sodium-potassium pump. In the stages of an action potential, the permeability of the membrane of the neuron changes. At the resting state (1), sodium and potassium ions have limited ability to pass through the membrane, and the neuron has a net negative charge inside. Once the action potential is triggered, the depolarization (2) of the neuron activates sodium channels, allowing sodium ions to pass through the cell membrane into the cell, resulting in a net positive charge in the neuron relative to the extracellular fluid. After the action potential peak is reached, the neuron begins repolarization (3), where the sodium channels close and potassium channels open, allowing potassium ions to cross the membrane into the extracellular fluid, returning the membrane potential to a negative value. Finally, there is a refractory period (4), during which the voltage-dependent ion channels are inactivated while the Na+ and K+ ions return to their resting state distributions across the membrane (1), and the neuron is ready to repeat the process for the next action potential.$

When an action potential arrives at the end of the pre-synaptic axon (top), it causes the release of neurotransmitter molecules that open ion channels in the post-synaptic neuron (bottom). The combined excitatory and inhibitory postsynaptic potentials of such inputs can begin a new action potential in the post-synaptic neuron.

In pacemaker potentials, the cell spontaneously depolarizes (straight line with upward slope) until it fires an action potential.

In saltatory conduction, an action potential at one node of Ranvier causes inwards currents that depolarize the membrane at the next node, provoking a new action potential there; the action potential appears to "hop" from node to node.

Comparison of the conduction velocities of myelinated and unmyelinated axons in the cat. The conduction velocity v of myelinated neurons varies roughly linearly with axon diameter d (that is, v ∝ d), whereas the speed of unmyelinated neurons varies roughly as the square root (v ∝√d). The red and blue curves are fits of experimental data, whereas the dotted lines are their theoretical extrapolations.

Cable theory's simplified view of a neuronal fiber. The connected RC circuits correspond to adjacent segments of a passive neurite. The extracellular resistances re (the counterparts of the intracellular resistances ri) are not shown, since they are usually negligibly small; the extracellular medium may be assumed to have the same voltage everywhere.

Electrical synapses between excitable cells allow ions to pass directly from one cell to another, and are much faster than chemical synapses.

Phases of a cardiac action potential. The sharp rise in voltage ("0") corresponds to the influx of sodium ions, whereas the two decays ("1" and "3", respectively) correspond to the sodium-channel inactivation and the repolarizing eflux of potassium ions. The characteristic plateau ("2") results from the opening of voltage-sensitive calcium channels.

Giant axons of the longfin inshore squid (Doryteuthis pealeii) were crucial for scientists to understand the action potential.

As revealed by a patch clamp electrode, an ion channel has two states: open (high conductance) and closed (low conductance).

Tetrodotoxin is a lethal toxin found in pufferfish that inhibits the voltage-sensitive sodium channel, halting action potentials.

Image of two Purkinje cells (labeled as A) drawn by Santiago Ramón y Cajal in 1899. Large trees of dendrites feed into the soma, from which a single axon emerges and moves generally downwards with a few branch points. The smaller cells labeled B are granule cells.

Ribbon diagram of the sodium–potassium pump in its E2-Pi state. The estimated boundaries of the lipid bilayer are shown as blue (intracellular) and red (extracellular) planes.

Equivalent electrical circuit for the Hodgkin–Huxley model of the action potential. Im and Vm represent the current through, and the voltage across, a small patch of membrane, respectively. The Cm represents the capacitance of the membrane patch, whereas the four g's represent the conductances of four types of ions. The two conductances on the left, for potassium (K) and sodium (Na), are shown with arrows to indicate that they can vary with the applied voltage, corresponding to the voltage-sensitive ion channels. The two conductances on the right help determine the resting membrane potential.

The cardiac pacemaker cells of the sinoatrial node in the heart provide a good example.

Purkinje fibers

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The Purkinje fibers (often incorrectly ; Purkinje tissue or subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium.

Purkinje fiber just beneath the endocardium.

The electrical origin of atrial Purkinje fibers arrives from the sinoatrial node.

Heart rate

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Speed of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm).

Autonomic Innervation of the Heart – Cardioaccelerator and cardioinhibitory areas are components of the paired cardiac centers located in the medulla oblongata of the brain. They innervate the heart via sympathetic cardiac nerves that increase cardiac activity and vagus (parasympathetic) nerves that slow cardiac activity.

Effects of Parasympathetic and Sympathetic Stimulation on Normal Sinus Rhythm – The wave of depolarization in a normal sinus rhythm shows a stable resting HR. Following parasympathetic stimulation, HR slows. Following sympathetic stimulation, HR increases.

Heart rate (HR) (top trace) and tidal volume (Vt) (lung volume, second trace) plotted on the same chart, showing how heart rate increases with inspiration and decreases with expiration.

The various formulae provide slightly different numbers for the maximum heart rates by age.

At 21 days after conception, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating.

Heart rate monitor with a wrist receiver

In obstetrics, heart rate can be measured by ultrasonography, such as in this embryo (at bottom left in the sac) of 6 weeks with a heart rate of approximately 90 per minute.

Pulsatile retinal blood flow in the optic nerve head region revealed by laser Doppler imaging

While heart rhythm is regulated entirely by the sinoatrial node under normal conditions, heart rate is regulated by sympathetic and parasympathetic input to the sinoatrial node.