 sternocleidomastoid. This is a supangate ever, we are talking the right side and the gambler person is also the right side. So this is the sternocleidomastoid that we see in front of us. The sternocleidomastoid was covered by deep fascia of the neck, part of which we have retained here. This is the investing layer of cervical fascia. An investing layer of cervical fascia forms the roof of the natural cervical region. It splits to include the sternocleidomastoid and the outer leaf of that we can see here. The origin of the sternocleidomastoid is from two places. One is from the merubrium sterni which we can see here and this is the clavicular head. The fibers then converge and they go in a spiral fashion on the lateral side of the neck and they go up and they get inserted onto the mastoid process and to the lateral part of the supianuclele. Another sublime the sternocleidomastoid is the accessory nerve which I'm going to show you just a little later when I reflect the sternocleidomastoid. The action of the sternocleidomastoid when it is acting on one side the sternocleidomastoid is responsible for tilting the head to the same side and turning the chin to the opposite side. When it is acting on both the sides then it touches the chin to the chest wall. The third action is the sternocleidomastoid again when it acts on both the sides it extends the neck at the lantox a little joint. In this connection I would like to mention something very unique which is of neurological significance. The sternocleidomastoid is perhaps the only skeletal muscle of the human body which is controlled by the same side of the cerebral cortex. So in other words the right sternocleidomastoid is not controlled by the left motor cortex but it is controlled by the right cerebral cortex. Now why is this so? Let's say for example the person is doing something with his or her left hand. What controls the left hand? The right cerebral cortex, motor cortex and in order to do something with the left hand the person has to turn his head to the left to see what the hand is doing and what turns the head to the left the sternocleidomastoid on the right side. So therefore it is the right motor cortex which controls the left hand and also the right sternocleidomastoid. The corticospinal tracts which come down they cross over and they recross inside the spinal cord to supply the motor nucleus of the spinal accessory nerve on the same side. So that is the reason why the sternocleidomastoid gets controlled by the same side motor cortex. So that is a unique feature about the sternocleidomastoid. Now let's come to some important relationships of the sternocleidomastoid that we can see here. We can imagine the sternocleidomastoid as a diagonal. If the chin were turned that side then we can consider the side of the neck as one big quadrangle formed by the chin, the midline of the neck, the clavicle and a line joining the lateral and the clavicle to the mastoid process. Considering this quadrangle the sternocleidomastoid is like a diagonal which goes from one angle to the opposite angle and therefore it divides the whole right side or one side of the neck into an anterior cervical region and lateral cervical region. The sternocleidomastoid forms the lateral boundary of the anterior cervical region and therefore it also by default forms the lateral boundary of all the triangles in the anterior cervical region and it also forms the middle boundary of the lateral cervical region and therefore it also forms the middle boundary of the triangles in the lateral cervical region. The most notable structure which travels on the surface of the sternocleidomastoid is the one which is visible here. This is the external jugular vein. In fact this is called the external jugular vein because it runs on the surface of the sternocleidomastoid. There can be a lymph node in relation to that which is a part of the superficial cervical lymph nodes. This external jugular vein is visible and it's also used clinically for many puncture purposes on the lateral surface of the sternocleidomastoid. The other structures are all deep to the sternocleidomastoid and for that we have split the sternocleidomastoid along here and we are going to reflect it. So now I'm reflecting the proximal part of the sternocleidomastoid and the distal part of the sternocleidomastoid to see the structures which are deep inside. We have completely separated the sternocleidomastoid. This is the upper half of the sternocleidomastoid and this is the lower half and so we are seeing the deep aspect and we can see this is the internal jugular vein which we have reflected. We can see the floor of the lateral cervical region. So let's take a look at these nodes which are coming out. This one which I've lifted up is the C1 root of the cervical plexus. This is the C2 root. This is the C3 root. This is the C4 root and down below this is the C5 and further below is the C6. So these are the roots of the cervical plexus and they're forming the primary loops and from the loops we are having the branches of the cervical plexus coming out. This is the transverse cervical and the grader of the auricular and the lesser occipital and these branches which I have lifted up here these are the supraclavicular nerves and this nerve that we have picked up here this is the phrenic nerve and this is the scallionous anterior. This is the scallionous media so therefore this is the scallion triangle and finally this nerve which is coming in front of the internal jugular vein and going to the deep surface of the sternocular mastoid. This is the accessory nerve and we can see it is giving a branch which is running across the lateral cervical region and entering into the deep surface of the trapezius. So these are the structures that are in relation to the deep surface of the sternocular mastoid which I wanted to show you. In this context I can give a surface correlation. If I were to put the sternocular mastoid back in its normal location the spinal accessory nerve emerges from the deep aspect of the sternocular mastoid and the lateral cervical region at the junction of the lower two-thirds and upper one-third and then it runs down the lateral cervical region and it enters the deep surface of the descending fibers of the trapezius at the junction of the lower one-third and upper two-third. That brings me to yet another important correlation pertaining to the nerves emerging from the posterior border of the sternocular mastoid and we can see some of those nerves here. These are the branches of the cervical plexus which I showed you just a little while back which are on the deep surface. These nerves they emerge from approximately a position which is midway along the posterior border of the sternocular mastoid and that point is referred to as the nerve point. The four important cutaneous nerves which come out from this region are the great auricular, lesser occipital, transversal cervical and supraclavicular and this region is referred to as the nerve point of the neck. So if we were to inject a local anesthetic at a point roughly midway between the lower and the upper ends of the posterior border of the sternocular mastoid then we can anesthetize a huge area of the side of the neck and upper part of the chest. This same nerve point can also be denoted by yet one more line. With the chin turned to the opposite side we can drop an imaginary vertical line from the mastoid process to the middle of the clavicle and the midpoint of that line will correspond to the nerve point of the neck. So that is yet one more relationship which I wanted to bring your attention to. The sternocular mastoid is responsible for one clinical condition which is referred to as tauticalis. There are two types of tauticalis. One is called spasmodic tauticalis also called cervical distonia which is seen in adults those who are taking anti psychotic drugs also called neuroleptics. As a manifestation of an adverse reaction of these neuroleptics they get what is known as cervical distonia where the patient has spasmodic contractions of the sternocular mastoid and the trapezius alternately or simultaneously on one or both the sides and therefore the head and the chin tilt and turn to one side of the other side that is called cervical distonia. The other condition of tauticalis is seen in children and that is called congenital tauticalis. When there can be tear of a few fibres of the sternocular mastoid and that can lead to hematoma formation and later on it leads to scar formation. There can be yet another condition in children called fibrometosis coli where the sternocular mastoid undergoes fibrosis. That occurs during breach delivery and these children also develop tilting of the head to one side and the chin is turned to the other side so that is called congenital tauticalis. Between the sternocular mastoid and the clavicular head of the sternocular mastoid this small depression that we see here this is called the lesser supraclavicular fossa and this lesser supraclavicular fossa can sometimes be the site of a lymph node enlargement. If it is seen on the left side which we have not decided out here and such a lymph node is significantly positive then that lymph node is referred to as furcos lymph node and the presence of such a lymph node is a sign of gastrointestinal pregnancy and that is called schroaziase sign but that is applicable only to the left side though we are showing the right side. So these are some of the salient points which I wanted to mention about the sternocular mastoid thank you very much for watching Dr. Sanjay Sanyal signing out Anderson is the camera person if you have any questions or comments please put them in the comment section below have a nice day