1. An air-filled cavity in a dense portion of a skull bone: The sinuses are formed in four right and left pairs: The frontal sinuses are positioned behind the forehead, while the maxillary sinuses are behind the cheeks.

The sphenoid and ethmoid sinuses are deeper in the skull behind the eyes and maxillary sinuses.

The sinuses are lined by mucous-secreting cells. Air enters the sinuses through small opening in bone called ostia. If an ostium is blocked, air cannot pass into the sinus and also the mucous cannot drain out.

2. A channel permitting the passage of blood or lymph fluid that is not a blood or lymphatic vessel; such as, the sinuses of the placenta.
3. Etymology: "abscess, sore", from Middle Latin sinus, from Latin sinus, "bend, fold, curve".

A dilation of the arterial wall at the bifurcation of the common carotid artery which contains sensory nerve endings from the glossopharyngeal (tongue and throat) nerve which respond to changes in blood pressure.

Caroti sinus stimulation by intermittent finger pressure, designed to enhance vagal tone and slow the heart rate or to terminate an arrythmia (abnormality in the rhythm of the heartbeat).

A neural mechanism in which an increase in blood pressure in the carotid artery at the level of its bifurcation results in a decrease in heart beat.

1. A temporary loss of consciousness which sometimes causes provoked convulsive seizures as a result of the intensity of the carotid sinus reflex when pressure increases in one or both carotid sinuses.
2. Intense hypotension (low blood pressure) and bradycardia (abnormally slow heartbeat) following carotid sinus stimulation, resulting in dizziness, fainting or convulsions, and occasionally other neurologic symptoms.

An intracardiac electrogram which records electrical potentials within the coronary sinus: A coronary sinus electrogram is used for the indirect monitoring of the left ventricular hollow parts or cavities in an organ or in each of the two main chambers of the heart, left and right.

An air cavity or space within the ethmoid bone, opening into the nasal cavity.

A slow sinus rhythm with an atrial rate below 60 beats per minute in an adult and 70 beats per minute in a child.

In sinus endoscopy, an endoscope is inserted into the nose, and the interior of the nasal passages, the sinuses, and the throat are examined.

This procedure can be done in a physician's office. The endoscope is inserted into a nostril and is threaded through the sinus passages to the throat.

To make viewing of these areas easier, and to record the areas being examined, a camera, monitor, or other similar viewing device is connected to the endoscope.

An intracardiac electrogram obtained by placing electrodes near the sinus node or the cardiac muscle fibers located in the posterior wall of the right atrium of the heart which acts as a pacemaker by generating at regular intervals the electric impulses of the heartbeat.

The purpose is to examine the time for impulse conductions from the node to the atrium, one of the upper chambers on either side of the heart, which receive blood from the body and transmit it to the ventricles.