Electrical impulses from the heart muscle cause your heart to beat (contract). This electrical signal begins in the sinoatrial (SA) node, located at the top of the heart's upper-right chamber (the right atrium). The SA node is sometimes called the heart's“natural pacemaker.”

Purkinje tissue is influenced by electrical discharge from the sinoatrial node. During the ventricular contraction portion of the cardiac cycle, the Purkinje fibres carry the contraction impulse from both the left and right bundle branch to the myocardium of the ventricles. In this way these fibres control and initiate heart beat.

• Sino-atrial node (SA node) is located the right upper corner of the right atrium and AVN(AV node) is located in the lower-left corner of the right atrium close to the atrioventricular septum.
• The SAN can generate the maximum number of action potentials, i.e., $70-75 min^{–1}$, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker. From the SA node, the action potential is conducted from the atria to ventricles by AVN.
  
• Hence the action potential is conducted from the atria to ventricles via SA node and AVN.
• So, the correct answer is 'SA node and AVN'.

The sinoatrial node is present at the right upper corner of the right atrium. The node is present below the Vena Cava. It initiates the autonomous contraction of the heart muscles.

The correct series is 

• Heart's sinus node (SA node) is our natural pacemaker (located in the upper right chamber of the heart).
• It sends an electrical impulse to produce the heartbeat.
• The job of a pacemaker is to artificially take over the role of your sinus node if it isn't working properly.
  
• So, the correct answer is 'SA node'.

The heart muscle's electrical impulses cause the heart to beat. This electrical signal starts at the Sinoatrial (SA) node at the top of the upper-right chamber of the heart. Sometimes the SA node is called the "natural pacemaker" of the heart.The SA node sends electrical impulses at some level, but depending on physical requirements, stress, or hormonal variables, heart rate may still alter.  It causes the upper chambers of the heart (the atria) to contract when an electrical impulse is released from this natural pacemaker. Then the signal travels to AV node and then to the bundle of HIs resulting in ventricular contraction.

Sino-atrial node is the natural pacemaker of the heart. These are a group of small, flattened and ellipsoid strip cardiac muscle fiber situated in the upper lateral wall of the right atrium near the Eustachian valve (valve of the inferior vena cava).

A specialised cardiac musculature, called as the nodal tissue is distributed in the heart. A patch of this tissue is present in the right upper corner of the right atrium, called as the sino-atrial node (SAN). 

A small node of specialized tissue is located int he upper right corner of right ventricle called as SA node. It is known as natural pacemaker of heart as it is responsible for initiation and regulation of heart beat. 

In amphibians, such as the frog, the pacemaker is the sinus venosus, an enlarged region between the vena cava and the right atrium. The venae cavae do not open directly into the auricles but into another chamber, the sinus venosus, which drains into the right auricle. 

Malleus is hammer like bone of the middle ear. 

Sinoatrial node is known as pacemaker of the heart. It helps in the generation and conduction of heart beat. It is located in the walls of the right atria just below the opening of superior venacva. The sympathetic nerves release the neurotransmitters and activates the SA node and generates electric impulse which is conducted as heart beat through out the heart. 

The entire heart is made of cardiac muscles. A specialized cardiac musculature called the nodal tissue is also distributed in the heart i.e sino-atrial node (SAN- A patch of this tissue is present in the right upper corner of the right atrium ). The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable. Hence function of the SA node is to ensure heartbeat.

A pacemaker is a tiny battery run instrument placed near to the heart of a patient for generation impulses similar to the SA node for the rhythmic functioning of the heart

Cardiac impulse generates from SA node then it reaches to AV node, then to bundle of HIS and finally to Purkinje fibers, this is how the cardiac impulse is generated.

Pacemaker serves to produce rhythmic impulses for the heart beat. The sinoatrial node (SA) node serves as a pacemaker and is a small mass of specialized cardiac muscle. It is present in the posterior wall of the right atrium near the opening of superior vena cava.