View source for Internal carotid artery

{{Infobox Artery |
  Name        = Internal carotid artery |
  Latin       = arteria carotis interna |
  GraySubject = 146 |
  GrayPage    = 566 |
  Image       = Gray513.png |
  Caption     = Arteries of the neck. The [[internal carotid artery|internal carotid arteries]] arise from the [[common carotid artery|common carotid arteries]] - labeled ''Common caroti'' on the figure. |
  Image2      = |
  Caption2    =  |
  BranchFrom  = [[common carotid artery]] |
  BranchTo    = [[ophthalmic artery]], [[anterior cerebral artery]], [[middle cerebral artery]], [[posterior communicating artery]] |
  Vein        = [[internal jugular vein]] |
  Supplies    = |
  MeshName    = Carotid+Artery,+Internal |
  MeshNumber  = A07.231.114.186.200.230 |
  DorlandsPre = a_61 |
  DorlandsSuf = 12153675  |
}}

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==Overview==

In [[human anatomy]], the '''internal carotid artery''' is a major [[artery]] of the head and neck that helps supply blood to the [[brain]].  

==Classification==
[[Terminologia Anatomica]] currently breaks the artery into four parts: "cervical", "petrous", "cavernous", and "cerebral".<ref>{{LoyolaMedEd|Neuro/neurovasc/navigation/ica.htm}}</ref><ref>{{Dorlands|a_61|12153675}}</ref> However, a more recent classification system of the internal carotid artery follows Bouthillier,<ref name="Bouthillier et al 1996">{{cite journal |last=Bouthillier |first=Alain |coauthors=Harry van Loveren, Jefferey Keller  |year=1996 |month=March |title=Segments of the internal carotid artery: a new classification. |journal=Neurosurgery |volume=38 |issue=3 |pages=425-432 |id=PMID 8837792 }}</ref> and describes seven anatomical segments of the internal carotid artery. The Bouthillier system is often used clinically by neurosurgeons, neuroradiologists and neurologists. This nomenclature system is a clinical one, based on the [[angiographic]] appearance of the artery and its relationship to surrounding anatomy, in contrast to an [[embryologic]] classification system. An older clinical classification is based on work by Fischer in 1938 is also commonly used, as well as classification schemes based on the embryologic anatomy of the carotid artery.

The segments of the internal carotid artery are as follows:

* '''Cervical segment''', or C1, identical to the commonly used [[Cervical part of internal carotid artery|Cervical portion]]
* '''Petrous segment''', or C2
* '''Lacerum segment''', or C3
**C2 and C3 comprise the commonly used [[Petrous portion of the internal carotid artery|Petrous portion]]
* '''Cavernous segment''', or C4, almost identical to the commonly used [[Cavernous part of internal carotid artery|Cavernous portion]]
* '''Clinoid segment''', or C5. This segment is not identified in some earlier classifications, and lies between the commonly used [[Cavernous part of internal carotid artery|Cavernous portion]] and  [[Cerebral portion of internal carotid artery|Cerebral or Supraclinoid portion]]

* '''Ophthalamic''', or supraclinoid segment, or C6
* '''Communicating''', or terminal segment, or C7
** C6 and C7 together comprise the commonly used [[Cerebral portion of internal carotid artery|Cerebral or Supraclinoid portion]]

==Course==
<!-- Editing note: Terminologia Anatomica terms that fall under this article in the hierarchy have been designated with bold type.-->
The internal carotid artery is a terminal branch of the [[common carotid artery]]; it arises around the level of the third cervical [[vertebra]] when the common carotid bifurcates into this artery and its more superficial counterpart, [[external carotid artery]].  

===C1: Cervical segment===
[[Image:Gray384.png|thumb|left|Level of 6th cervical vertebrae -- still at level of common carotid, but relationships are similar to those of cervical segment of internal carotid.]]
The '''cervical segment''', or C1, of the internal carotid extends from the carotid bifurcation until it enters the carotid canal in the skull anterior to the jugular foramen. 

At its origin, the internal carotid artery is somewhat dilated.  This part of the artery is known as the [[carotid sinus]] or the carotid bulb.  The ascending portion of the cervical segment occurs distal to the bulb, when the vessel walls are again parallel.

The internal carotid runs perpendicularly upward in the [[carotid sheath]], and enters the [[skull]] through the [[carotid canal]]. During this part of its course, it lies in front of the transverse processes of the upper three cervical vertebrae. 

It is relatively superficial at its start, where it is contained in the [[carotid triangle]] of the neck, and lies behind and lateral to the external carotid, overlapped by the sternocleidomastoid muscle, and covered by the deep fascia, the [[platysma]], and integument: it then passes beneath the [[parotid gland]], being crossed by the [[hypoglossal nerve]], the [[digastric muscle]] and the [[stylohyoid muscle]], the [[occipital artery]] and the [[posterior auricular artery]]. Higher up, it is separated from the external carotid by the [[styloglossus]] and [[stylopharyngeus]] muscles, the tip of the styloid process and the [[stylohyoid ligament]], the [[glossopharyngeal nerve]] and the pharyngeal branch of the [[vagus nerve]]. It is in relation, behind, with the [[longus capitis]], the [[superior cervical ganglion]] of the [[sympathetic trunk]], and the [[superior laryngeal nerve]]; laterally, with the [[internal jugular vein]] and vagus nerve, the nerve lying on a plane posterior to the artery; medially, with the [[pharynx]], superior laryngeal nerve, and [[ascending pharyngeal artery]]. At the base of the skull the glossopharyngeal, vagus, accessory, and hypoglossal nerves lie between the artery and the internal jugular vein.

Unlike the [[external carotid artery]], the internal carotid normally has no branches in the [[neck]].  

===C2: Petrous segment===
The '''petrous segment''', or C2, of the internal carotid is that which is inside the petrous part of the [[temporal bone]]. This segment extends until the [[foramen lacerum]]. The petrous portion classically has three sections: an ascending, or vertical portion; the genu, or bend; and the horizontal portion.
   
When the internal carotid artery enters the canal in the [[petrous portion of the temporal bone]], it first ascends a short distance, then curves anteriorly and medially. The artery lies at first in front of the [[cochlea]] and [[tympanic cavity]]; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and often partly absorbed in old age. Farther forward it is separated from the [[trigeminal ganglion]] by a thin plate of bone, which forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal. Frequently this bony plate is more or less deficient, and then the ganglion is separated from the artery by fibrous membrane. The artery is separated from the bony wall of the [[carotid canal]] by a prolongation of [[dura mater]], and is surrounded by a number of small veins and by filaments of the [[carotid plexus]], derived from the ascending branch of the [[superior cervical ganglion]] of the sympathetic trunk. 

The named branches of the petrous segment of the internal carotid artery are:
*the [[vidian artery]] or artery of the pterygoid canal
*the [[caroticotympanic artery]]

===C3: Lacerum segment===
The '''lacerum segment''', or C3, is a short segment that begins above the [[foramen lacerum]] and ends at the petrolingual ligament, a reflection of [[periosteum]]  between the lingula and petrous apex (or petrosal process) of the [[sphenoid]]. The lacerum portion is still considered to be 'extra-dural', as it is surrounded by periosteum and fibrocartilage along its course. The lacerum segment normally has no named branches, though the vidian artery may occasionally arise from this segment.

===C4: Cavernous segment===
[[Image:Gray571.png|thumb|left|Oblique section through the cavernous sinus.]]
The '''cavernous segment''', or C4, of the internal carotid artery begins at the petrolingual ligament and extends to the proximal dural ring, which is formed by the medial and inferior periosteum of the anterior clinoid process. The cavernous segment is surrounded by the [[cavernous sinus]].

In this part of its course, the artery is situated between the layers of the dura mater forming the cavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward the [[posterior clinoid process]], then passes forward by the side of the [[body of the sphenoid bone]], and again curves upward on the medial side of the [[anterior clinoid process]], and perforates the dura mater forming the roof of the sinus. This portion of the artery is surrounded by filaments of the sympathetic trunk, and on its lateral side is the [[abducent nerve]], or cranial nerve VI.

The named branches of the cavernous segment are:
* the meningohypophyseal artery
* the inferolateral trunk

The cavernous segment also gives rise to small capsular arteries that supply the wall of the cavernous sinus.

===C5: Clinoid segment===
The '''clinoid segment''', or C5, is another short segment of the internal carotid that begins after the artery exits the [[cavernous sinus]] at the proximal dural ring and extends distally to the distal dural ring, afterwhich the carotid artery is considered 'intra-dural' and has entered the [[subarachnoid space]]. 

The clinoid segment normally has no named branches, though the [[ophthalmic artery]] may arise from the clinoid segment.

===C6: Ophthalmic segment===
[[Image:Gray514.png|thumb|left|The ophthalmic artery and its branches.]]
The '''ophthalmic segment''', or C6, extends from the distal dural ring, which is continuous with the falciform ligament, and extends distally to the origin of the [[posterior communicating artery]].  The ophthalmic segment courses roughly horizontally, parallel to the [[optic nerve]] which runs superomedially to the carotid at this point. 

The named branches of the ophthalmic segment are:
*the [[ophthalmic artery]]
*the [[superior hypophyseal artery]]

===C7: Communicating segment===
The '''communicating segment''', or terminal segment, or C7, of the internal carotid artery passes between the optic and oculomotor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure. Angiographically, this segment extends from the origin of the [[posterior communicating artery]] to the bifurcation of the internal carotid artery.  

The named branches of the communicating segment are:
*the [[posterior communicating artery]]
*the [[anterior choroidal artery]]

The internal carotid then divides to form the [[anterior cerebral artery]] and [[middle cerebral artery]]. The internal carotid artery can receive blood flow via an important [[anastomosis|collateral pathway]] supplying the brain, the cerebral arterial circle, which is more commonly known as the [[Circle of Willis]].

==Branches==

The following are the branches of the internal carotid artery, listed by segment:<ref name="Osborn 1999">{{cite book |last=Osborn |first=Anne |title=Diagnostic Cerebral Angiography |edition=2nd |year=1999 |month= |publisher=Lippincott Williams & Wilkins |location=Philadelphia, PA, USA |language=English |id= ISBN 0-397-58404-0 }}</ref>
* C1: Branches from the cervical portion - none.

* C2: Branches from the petrous portion
** [[Caroticotympanic arteries]]
** [[Artery of pterygoid canal|vidian artery]]

* C3: Branches from the lacerum portion - none

* C4: Branches from the cavernous portion
**Branches of the '''meningohypophyseal trunk''':
*** '''Tentorial basal branch'''
*** '''Tentorial marginal branch'''
*** '''Meningeal branch''' - helps supply blood to the meninges of the anterior cranial fossa 
*** '''Clivus branches''' - tiny branches that supply the [[clivus]]
*** '''[[Inferior hypophyseal artery]]'''
** Capsular branches''' - supplies wall of [[cavernous sinus]]
** '''Branches of the inferolateral trunk''':
*** '''Branches to trigeminal ganglion''' - provide blood to [[trigeminal ganglion]]
*** '''''Artery of the [[foramen rotundum]]'''''
*** '''Branches to nerves'''

* C5: Branches from the clinoid portion - none

* C6: Branches from the ophthalmic portion
** [[Ophthalmic artery]]
** [[Superior hypophysial artery]]

* C7: Branches from the communicating portion
** [[Posterior communicating artery]]
** [[Anterior choroidal artery]]
** [[Anterior cerebral artery]] (a terminal branch)
** [[Middle cerebral artery]] (a terminal branch)

==Carotid plexus==
The [[sympathetic trunk]] forms a plexus of nerves around the artery known as the [[carotid plexus]].  The internal carotid nerve arises from the [[superior cervical ganglion]], and forms this plexus, which follows the internal carotid into the skull.

==Additional images==
<gallery>
 Image:Circle of willis.png|Circle of Willis
 Image:Gray516.png|The arteries of the base of the brain.
 Image:Circle_of_Willis_en_svg.png |Diagram of the arterial circulation at the base of the brain.
 Image:Gray569.png|Tentorium cerebelli from above.
 Image:Gray777.png|Nerves of the orbit, and the ciliary ganglion. Side view.
 Image:Gray908.png|Horizontal section through left ear; upper half of section.
 Image:Gray915.png|Auditory tube, laid open by a cut in its long axis. 
 Image:Gray1031.png|Muscles of the pharynx, viewed from behind, together with the associated vessels and nerves.
 Image:Gray1032.png|The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.
</gallery>

==See also==
* [[External carotid artery]]
* [[Carotid endarterectomy]]
* [[Carotid sinus]]
* [[Carotid body]]
* [[Carotid sheath]]
* [[Carotid triangle]]
* [[Circle of Willis]]

==References==
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<references/>
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==External links==
* {{SUNYAnatomyLabs|28|09|02|12}}
* {{UMichAtlas|n3a8p1}}
* [http://www.anatomywiz.com?Internal%20Carotid0 The Anatomy Wiz.] Internal Carotid Artery
{{Arteries of head and neck}}

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[[Category:Arteries]]
[[Category:Thorax]]
[[Category:Head and neck]]
[[Category:Anatomy]]
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