The carotid canal is the name given to a passageway present in the temporal bone via which the carotid artery occurring internally in the neck passes into middle cranial fossa. The canal commences at the outer opening of the carotid foramen or the carotid canal on the temporal bone’s inferior surface and climbs vertically at first, then curves into a bend, finally moving forward horizontally and medialward. The internal opening of the canal is called the foramen lacerum.
The term carotid refers to the internal carotid artery which passes across the groove. The term has its origins in the Greek work ‘karoun’ or ‘karos’ which means to stupefy or a deep slumber/sleep. It is associated with the vital flow of oxygen carried by the canal to the brain. If this oxygen flow is disrupted then the person may fall into a stupor or may faint. The term canal is derived from the Latin word ‘canalis’ which means a channel or a tube.
The carotid canal transmits the carotid plexus of the nerves and the internal carotid artery into the head. It also acts as a passageway for the sympathetics of the superior cervical ganglion into the cranium. The sympathetics have many motor functions like dilation of the pupil, raising of eyelids, constriction of blood vessels present in the head, and innervation of sweat glands present in the scalp and face.
Contents and functions of the carotid canal
The carotid canal is a curved passageway which acts as a channel for the internal carotid artery across the petrous temporal bone. One end of the canal opens as the carotid foramen on the inferior surface area of the temporal bone. The oval opening continues its path superiorly for about 1 cm into the bone before antero-medially bending through the petrous bone. The antero-medially directed channel runs within the bone for about 2 cm before exiting into the foramen lacerum at the apex of the petrous bone. The carotid artery will then turn superiorly once again and enter the skull vault. The carotid sympathetic nerve plexus also follows the carotid artery across this canal.
The internal carotid artery passes through the carotid canal, enters the cranium, and transmits via cerebral branches to the anterior section of the brain. It also supplies to the eye and the ocular appendages as well as pass branches to the nose and forehead. The artery has many curves in varied sections of its pathway. When it goes across the sphenoid bone’s side section and the carotid canal, it elicits a double curvature thereby giving it the shape of an italic ‘S’ letter.
The carotid artery will then go upwards to the pharynx at right angle and later continue moving towards the base of the cranium. It is now that the artery enters into the carotid canal situated at the petrous section of the temporal bone. Initially, the internal part of the carotid artery will rest in the outer side of the external carotid artery before going posterior to it.
The commencement point of the internal carotid artery is in the superior carotid pyramid. As it moves upwards, it lays deeper, below the parotid gland, the stylohyoid and stylopharyngeus muscles, the back belly of the digastric muscle, and the styloid process. The occipital and posterior auricular arteries and the hypoglossal and glossopharyngeal nerves cross it.
On the outside, the carotid artery is next to the internal jugular veins and the pneumogastric nerve, and around the base of the cranium with the glossopharyngeal, hypoglossal, and spinal accessory nerve. From the back, the artery is next to the sympathetic nerve’s superior ganglion, the major muscle rectus capitis anticus, and the superior laryngeal nerve.
The size of the internal carotid artery in an adult is almost the same as the external carotid. However, it is bigger than the channel in children. Branches of the 2 internal carotid arteries and the basilar artery combine at the bottom of the brain to create a ring of tiny blood vessels which is referred to as the circle of Willis. The carotid arteries consist of 2 sensory areas in the neck, the carotid body and the carotid sinus. The former performs the function of regulating breathing and managing the blood oxygen content, while the latter maintains the blood pressure.
Carotid canalin the skull – pictures (location)
In this demo of the skull, you can see the carotid canal in the form of a passageway.