By the name of Allah

Our lectures of this week will cover the neck and part of the face ,today well talk about posterior triangle of the neck, next lecture about anterior triangle and well leave the lecture of Thursday for what we call superficial anatomy of the face . Now the idea is how we defined anatomically the region of the neck ,its region between the head and the trunk , in this position it has multiple anatomical structures and functions , so the neck itself is a large region whish localized using 2 upper and lower boundaries so we can separate the neck from the region of the head using the mandible, if we do a line passing along the inferior border of the body of the mandible back to the angle of it then up to the mastoid process then along the superior nuchal line reaching external structure behind the midline whish is called occipital protuberance.

This line separate the region of the head from the neck .so the superior boundary for us is a line whish is mentioned above . Now the inferior border of the neck is the line separating it from the chest, this line runs from superior border of manubrium of sternum along the clavicles ,now if we go laterally along the clavicles we'll reach acromion of scapula , now we draw a line posteriorly joining the 2 acromial processes with the 7th cervical vertebra. The neck region is further divided into what we call nuchal region whish is the posterior region of the neck and consist of muscles whish belong actually to the back muscles with contribution to the trapezius muscle .these muscles are related to the vertebral column in the neck. The anterior and lateral parts of the neck are very large regions so we have to divide it using our landmark whish is the sternocleidomastoid muscle, cleido is another Greek name for clavicle.

It originate down by 2 heads ,sternal head is rounded tendon originating from manubrium & clavicular head is originating from medial third of clavicle , these 2 heads ascending up and posterior so it isn't a straight muscle and reach 2 regions up whish are the mastoid process of temporal bone & superior nuchal line . We talked that sternocleidomastoid has origin from the clavicle and clavicle itself is attached to the 1st rib in this regard if it contract ,it will rise the 1st rib & sternum so it will be an inspiratory muscle but this is an additional function, now the primary function is rotation the whole head to the opposite site , and the axis of rotation is actually the atlantoaxial joint ,it is inserted behind the axis of rotation so if it contract ,it will pull the whole head to the opposite side and rise the chin ,this is the unilateral action .

P.S : u should differentiate between ipsilateral or unilateral action if one muscle contracts & bilaterally action if 2 muscles contract

Now when this muscle contract bilaterally it will elevate the chin and the whole head will be pushed anteriorly, this is called feeding movement. Innervation Sternocleidomastoid is innervated by 1- accessory cranial nerve just like trapezius this is motor contribution and from 2- cervical plexus anterior rami actually from c2_c3 whish is proprioseptive contribution. So the two nerves sensory and motor combined to make reflex loop. Trapezius also innervated from cervical plexus but from different segment whish is c3_c4. In this regard we should know what we call torticollis whish is caused by spam of sternocleidomastoid or injury of it that happen in false delivery . Now we can divide the neck into 2 large triangles and the sternocleidomastoid is our landmark, there is region in front of it and region behind it. Sternocleidomastoid posteriorly , the midline anteriorly and the mandible superiorly this is what we call anterior triangle of the neck with it's base superiorly and apex inferiorly.

Now just the same in opposite term, sternocleidomastoid anteriorly , clavicle inferiorly and anterior border of trapezius posteriorly this is posterior triangle of the neck.

We use another muscle for further divide whish is called omohyoid muscle (omo is scapula in Greek ) it is very gracile muscle and related to hyoid bone whish is belonging to the axial skeleton situated anteriorly below the mandible ,from this bone the muscle originate and descend down and posterior obliquely unlike sternocleidomastoid then disappear behind sternocleidomastoid . Now what we dont see behind sternocleidomastoid that omohyoid has a tendon anchored to no bone ,from this intermedius tendon arises another part of the muscle whish passes again obliquely behind to disappear deep to the trapezius reaching the superior margin of scapula. So omohyoid is related to what we call infrahyoid muscles and it has 2 superior & inferior bellies joining together at

an angle at intermedius tendon behind sternocleidomastoid.

Posterior triangle now is divided into 2 triangles ,the 1st one is , relatively anterior and inferior, it is called omoclavicular or subclavian triangle , the 2nd one is large, relatively superior and posterior and called occipital triangle because it is closer to occipital bone ,this triangle is clinically not important as subclavian triangle because it's floor consist of multiple muscles if we go through them posteriorly and superiorly we find back muscles whish are splenius capitis & semispinalis capitis . now going more anteriorly we have muscle related to the upper limb called levator scapulae whish is originate from upper cervical vertebrae c1_c4 passing down to insert in medial angle of scapula so it elevate the scapulae. So we have splenius and semispinalis capitis from behind then levator scapulae and if we go most anteriorly we have scalene muscles whish are anterior, medius and posterior (very small) .

We have normaly space between anterior and medius scalene whish is called scalenus gap . also the floor of occipital triangle contains nerves related to it's muscles , one very important nerve whish we have always to remember in relation to the levator scapula whish is accessory nerve , but levator scapulae is innervated by dorsal scapular nerve branch of brachial plexus so why we combined the accessory nerve with levator scapulae ? the answer is some muscles are leader muscles it means according to it's origin and insertion they define a road this road can be used by nerves to reach their destination, so accessory nerve will innervate the trapezius by running similar to the levator scapulae and accompanied with branch of cervical plexus c3_c4 then reach to the deep surface of trapezius muscle . the posterior margin of sternocleidomastoid is the region where sensory branches of cervical plexus emerge , these sensory branches are : most cranial one called lesser occipital nerve ,it originate from c2 and ascend up reaching occipital region. just below it we find great auricular nerve originate from c2_c3 and ascend up to reach ear once it reaches, it will divide into 2 anterior and posterior branches if we go below it we find transverse nerve whish originate from c2_c3 running transversely across the neck and divides into multiple branches whish are responsible for the sensory innervation of whole anterior

and lateral parts the neck , now if we go below it , we'll find the only nerve whish is coming down called supraclavicular nerve originate from c3_c4 and divided into 3 branches , this nerve will supply the skin anteriorly in the chest and shoulder region. All of these 4 nerves emerge approximately at a midpoint of the posterior margin of sternocleidomastoid, it means if u anesthetized this region u will end up having blocking all sensory supply of your neck ,so this point called punctum nervosum of the neck .

We mentioned previously that the great auricular nerve divided into anterior branch in front of the ear and

posterior branch , now the anterior branch will innervate the angle of the mandible and the parotid so trigeminal nerve supply the face except the region of angle and parotid .

Forgive me if I made any mistakes

Your Colleague Ala'a Orabi