 Hello everyone welcome back to another session in dentistry and more so we are continuing our anatomy classes. So today's topic is muscles of mastication. So muscles of mastication are the muscles which involve in the process of chewing or mastication. So they are group of muscles that help in movement of the mantable during the chewing and speech okay. So we need to study these muscles because these muscles control the opening and closing the mouth and the role in the equilibrium which created within the mouth and they also play a role in configuration of face okay. So we have four pairs of muscles in the mantable which make chewing movement possible. So these muscles along with accessory muscles are together known as muscles of mastication. So other important factors of muscles of mastication are these muscles have roles in prosthetic dentistry which defines the borders and peripheral extensions of the dentures. So the primary muscles are temporalis, masseter, lateral chirogoid and medial chirogoid. The accessory muscles we can divide it into two groups that is the muscles which is above the hyoid bone are suprahyoid muscles and the muscles which is below the hyoid bone are infrahyoid muscles. The suprahyoid muscles are digastric, stylohyoid, mylohyoid and geniohyoid. Infrahyoid are sternohyoid, tyrohyoid and omohyoid. So these accessory muscles it's very easy because it's origin and insertion is given in the name itself. Anyway we have another classification that is joe elevators and joe depressor. Joe elevators are masseter, temporalis and medial chirogoid. The lateral chirogoid involves in joe depression. Joe depressors along with lateral chirogoid we have anterior digastric, geniohyoid and mylohyoid. So let's see one by one the primary muscles and accessory muscles of mastication. So we'll start with primary muscles of mastication. So we have masseter, temporalis, lateral and medial chirogoid. So we are studying this under four headings that is its origin, its insertion, its nerve block and glitz supply and the venous drainage and its basic actions in mastication. So we'll start with the muscle, masseter. The word masseter in Greek means a chur. So it is a basic or it is a powerful muscle which helps in mastication or chewing. That is basically it elevates mantable and it helps to occlude teeth in mastication. That is the basic function. So masseter is a muscle which has three layers that is superficial layer, middle layer and deeper layer. And it is a quadrilateral muscle. So quadrilateral means quad means four. So it has four sides exactly. We can make out it as a four side dimension. So it is known as quadrilateral muscle and this three layers that is superficial, middle and deep layers blend anteriorly. So this is anterior part, this is posterior part, superior part, inferior part. So this has superficial, middle and deeper layers. So these three layers are blending at the anterior portion. So you need to visualize it in a three-dimensional format. This is a two-dimensional picture, it is not easy to depict a three layers. So that is why I just drawn a quadrilateral fibers representing the masseter muscle. So let's see the origin of these three layers. So the origin means where this muscle fibers are starting from and insertion means where this muscle fibers are ending up. So the superficial layer which starts from maxillary process of zygomatic bone. So this is a zygomatic bone and this is a zygomatic arch. So it starts from maxillary process of zygomatic bone and the anterior two-third of inferior border of zygomatic arch. So let this be the inferior arch. So it is from the anterior two-third. So anterior two-third and posterior one-third. So it is from the anterior two-third of inferior border of zygomatic arch and the zygomatic bone in specific maxillary process of zygomatic bone. Whereas the middle layer, middle layer is formed from medial aspect of anterior third of zygomatic arch. So this is a zygomatic arch. This will be the lateral side because we are seeing from outside. So that will be the lateral side. So there will be a medial side inside. So the middle layer is originating from medial aspect of anterior two-third of zygomatic arch. So that is middle layer and lower border of posterior third of zygomatic arch and posterior third we have. It is originating from the lower border and also from the medial aspect of zygomatic arch. It is a deeper layer originating from deep surface of zygomatic arch. So we have three layers, superficial, middle and deep layers. So superficial from maxillary process of zygomatic bone and anterior two-third of inferior border of zygomatic arch. Middle portion is from the medial aspect of anterior two-third of zygomatic arch and the lower border of posterior third of zygomatic arch and the deep surface of zygomatic arch giving rise to the deeper layer of masseter muscle. And now it is where it is ending up or it is getting inserted. So layer by layer, superficial layer is inserted in angle of mandible. So this portion is angle of mandible and the posterior half. Lower posterior half of lateral surface of mandibular ramus. So this is the lateral surface of mandibular ramus and the inside will be the medial surface and it is getting inserted into the lower posterior half, lower posterior half. This is upper half, this is lower half and posterior. So this area, so it is inserted into the angle of mandible and lower posterior. This is an anterior portion, posterior portion, upper portion, lower portion. So the lower posterior will be here. So lower posterior border and angle of mandible whereas the middle layer which is the middle part of ramus of mandible. So this is the middle part of ramus of mandible and the deeper layer will be on the coronoid process and upper part of mandibular ramus. This is the coronoid process, we can see this one. This is the contiler process, coronoid process. So it is formed in coronoid process and upper part of mandibular ramus. That is the insertion. Now let us see the nerve supply and blade supply. Nerve supply is by the massotric nerve which is an inter anterior division of mandibular nerve and blade supply by massotric artery which is a branch of maxillary artery and the venous drainage by massotric vein. And as I mentioned the action is to elevate mandible, it is to elevate mandible and occlude the teeth and mastication. That is why it is very important muscle masseter, it is to elevate mandible. So the masseter is over. Now we are into temporal muscle or temporalis muscle. The name itself gives temporalis muscle, it is mainly on the temporal bone. So we know frontal bone which is the front bone, parietal bone, it is the topper bone and the temporal bone on the lateral side and occipital bone on the back side. So this is a temporal bone and it is a particularly a fan-shaped muscle that covers the temporal region. You can see it is a fan-shaped muscle which is on the temporal side of our skull. And it is the largest masticatory muscle but not considered to be the most powerful one. So it has origin from the inferior temporal line or the floor of the temporal fossa and from the overlying temporal fascia. So we have temporal line, temporal fossa and temporal fascia. So inferior temporal line, floor of temporal fossa and overlying temporal fascia. So as I mentioned since it is a two-dimensional picture it is not easy to explain it but you understand the temporal line, temporal fossa and temporal fascia, all our structures which is present in the temporal bone which is giving its origin. So it has basically three areas anterior temporal and the middle temporal and the posterior temporal. This is the posterior part, anterior part and middle part. So the origin is having temporal line, temporal fossa and temporal fascia. So these three giving rise to temporalis muscle which is a fan-shaped muscle. Now let's see the insertion. So you can see it is inserted in the coronoid process and anterior part of ramus. So margins and deep surfaces of coronoid process and anterior border of ramus of mandible. The nerve supply of temporalis is the deep temporal branches which is branch of mandibular nerve from the anterior division and the blood supply is from superficial temporal artery which is a branch of maxillary artery and the venous drainage is from superficial and middle temporal vein. Now let's see the functions of temporalis, the anterior fibres. So the anterior fibres they elevate the mandible and posterior fibres they retract the mandible okay once it is protruded the retraction bringing back the mandible towards the normal position by the posterior fibres and also crushing the foot between mollusks and there will be side to side movements. And all so helps in grinding movements. Now we have lateral teregoid muscle which is also known as external teregoid muscle and it is a muscle of mastication that occupy a horizontal position okay rest all are in a vertical direction this is in a horizontal direction and it is a thick shot conical and triangular muscle with two heads it has superior head and inferior head. So it is origin the superior head originates from the intratemporal surface and intratemporal crest of greater wing of sphenoid bone okay so it is originating from greater wing of sphenoid bone and intratemporal surface whereas the inferior head originating from lateral surface of lateral teregoid plate that is why this name it is originating from lateral surface of lateral teregoid plate and it is getting inserted into these fibres run backwards and laterally and converge into teregoid fovea on anterior surface of neck of mandible. So you can see here it is of teregoid fovea to the neck of mandible and also to the anterior margin of articular disc and capsule of TMJ okay. So TMJ is here so it is also getting inserted into the articular disc and capsule of TMJ so that is lateral teregoid which is getting inserted into the disc articular disc and capsule of TMJ and also to the teregoid fovea on anterior surface of neck of mandible okay. The nerve supply is lateral teregoid nerve which is a branch of anterior trunk of mandible nerve blood supply is via maxillary artery and ascending palatine artery and basic functions are it is when it is acting together these muscles protrude the mandible and depress the chin okay so it is protrude the mandible and depress the chin and when it is acting alone and alternatively they produce side to side movements of mandible okay side to side movements of mandible is when they acting alone and alternatively okay one medial teregoid then the lateral teregoid so alternatively it helps to move the mandible side to side so that is a function of lateral teregoid mainly to protrude the mandible and depress the chin when acting together and the next and the last and primary muscles of massification is medial teregoid muscle which is also known as internal teregoid lateral teregoid is known as external teregoid medial teregoid is known as internal teregoid muscle it is almost a mirror like image of masseter muscle okay so the masseter muscle is on the lateral side this is on the medial side okay it is a mirror like image of masseter muscle and it is a rhomboid shape and practically in same direction of the inner surface of mandible so this is actually inner surface of mandible that is why I am putting dots here so it is rhomboidal in shape and runs through the same direction of the inner surface of mandible it has two heads that is superficial and deeper head so superficial head originating from axillary tuberosity and deep head which is from the medial surface of lateral teregoid plate and part of palatine bone so that is why it is based on the lateral teregoid plate whether it is originating from medial side whether it is origin from the lateral side the name is given okay so it is from the medial surface of lateral teregoid and also a part of palatine bone and it is inserted into the that is these fibers run backwards downwards and laterally to the roughened area of medial surface of the anglof mandible so it's so this area okay so that's why putting dot here it is on the medial side okay so it is originating from medial surface of lateral teregoid plate this is from the lateral side of lateral teregoid plate that is why lateral teregoid and medial teregoid name and its nerve supply is the main trunk of mandibular now blood supply is teregoid branch of the maxillary artery and the functions are it is helps to elevate the mandible and closes the jaw and also acting together they help to protrude the mandible when acting alone it helps to grinding motion on alternative side similar actions such as lateral teregoid but when they alternatively helps in movement from side to side so these are the primary muscles of mastication masseter temporalis lateral teregoid and medial teregoid this is a quadrilateral shape this is a fan shaped and this is a rhomboid shape this is running in horizontal direction and its origin insertion nerve and blood supply venous drainage and its action now we have accessory muscles of mastication and now we have accessory muscles of mastication so principle muscles of mastication we are covered masseter temporalis medial and lateral teregoid this is accessory muscles which helps the mastication process along with the principle muscles okay the first one is digastric muscle so this is a mandible a drawn and this is a upward tilted mandible and this is a hyoid bone okay so hyoid bone and mandible so it is connecting two bellies these are known as anterior bellies and these are the posterior bellies so these are two bellies masses of muscle tissues joined by an intermediate tendon which originate like anterior belly which originate from the digastric fossa of mandible so this is supposed to be the digastric fossa it originate from digastric fossa and lateral to the symphysis mentee so symphysis mentee will be exactly at this position so lateral to the mental symphysis it originates and posterior belly originates from mastoid notch of temporal bone okay so the mastoid notch will be inside anyway it is originating from mastoid notch of temporal bone and it insert both into an intermediate tendon and help by the fibrous pulley to the hyoid bone so this is anyway hyoid bone so both are attached to the hyoid bone by help of a tendon so the digastric muscle origin and insertion and the nerve supply is anterior belly by nerve to myelo hyoid and the posterior belly is by facial nerve and the functions are depression of jaw and it is helping for elevation of hyoid during the swallowing this will pull up the hyoid while swallowing that is about digastric muscle it has anterior belly and posterior belly which originating from the symphysis mentee and the mastoid notch of temporal bone both are inserted into hyoid bone now to myelo hyoid and facial nerve and depression of jaw and elevation of hyoid bone the action the next muscle is myelo hyoid muscle so myelo hyoid muscle is a flat rectangular muscle lying deep to the anterior belly of digastric okay so again this is a poor tilted mantle hyoid bone so it is a flat triangular muscle lying deep to the anterior belly of digastric so this is anterior belly of digastric so it lies deep to these two bellies and it forms the floor of the mouth okay so this is the floor of the mouth this is the upper tilted upper tilted and this forms the floor of the mouth it origin from myelo hyoid line of mantle myelo hyoid line from mandible and inserted into like the middle and anterior fibers into median raffae and posterior fibers into the body of hyoid bone okay and the nerve supply is nerve to myeloid and function is to helps in depression of mantle and elevation of hyoid bone so also it helps to elevate the floor of the mouth to help in deglutination okay and the third muscle we have is genio hyoid genio hyoid is very short and narrow muscle which lies above myelo hyoid and it origin from inferior mantle spine that is genial tubercle and inserted into hyoid bone the body of anterior surface of hyoid bone and the nerve supply is hypoglossal nerve and the artery is facial artery elevation of hyoid bone and also we have stylo hyoid muscle which is a small muscle that lies along the upper border of posterior belly of digastric muscle so this is a posterior belly and the upper border of posterior belly of digastric muscle origin from the lateral and inferior surface of styloid process because it is origin from styloid process ending in hyoid bone it origin from tubercle ending in hyoid bone origin from the myelo hyoid line ending in hyoid bone okay so all these four muscles are above the hyoid bone so it is known as supra hyoid muscles and these two are intra hyoid muscles because it is connecting to sternum to hyoid thyroid to hyoid these are the structures which lies below the hyoid bone which is known as infra hyoid muscles so stylohyoid muscle inserted into the body of hyoid bone nerve supply is branched from facial nerve and function it pulls the hyoid bone upward and backward so we have two infra hyoid muscles they are sternohyroid and tyrohyoid sternohyroid muscle which origin from posterior surface of manobrium deep to sternohyroid and it inserted into oblique line of thyroid cartilage arterial supply superior thyroid artery nerve supply is ancestral vecalis c2 and c3 branches and its action is depression of larynx that is sternohyroid now we have thyroid hyoid it origin from upper part of oblique line on thyroid cartilage inserted into lower border of greater corner of hyoid bone arterial supply is superior thyroid artery nerve supply is hypoglossal nerve c1 and also it's helps to depress the hyoid bone okay so that's all about muscles of mastication we have seen principal muscles diga principal muscles are temporalis masseter medial teregoid lateral teregoid and accessory muscles they are digastric myelohyroid geniohyoid stylohyoid sonoma suprahyoid muscles sternohyroid thyroid and also omohyroid is there so all these are the accessory muscles it's an important question commonly asked in university the muscles of mastication so you need to draw a picture it's not very easy to draw a picture at least if you can draw you need to draw you can write the principal muscles you can draw at least showing the boundaries and its origin and insertion and you need to write in this format it will fetch you more marks because it is easy to understand for the evaluator under these subheadings origin insertion nerve supply or blood supply and action okay rather than writing up like paragraphs so this format you need to write so I'll come up with a new topic in human anatomy thank you