 video will cover part one of the axial skeleton. As we go, we'll cover the following study objective, identify the bones of the cranium, the features of each cranial bone, cranial sutures, cranial fosse, and the fontanelles. There are eight cranial bones that form the brain case surrounding the brain, and you can use a mnemonic device in order to help you remember the names of these bones. And so, past of, and then there are six different names, parietal, ethmoid, sphenoid, temporal, occipital, and frontal. There are two parietal bones, both left and right, and two temporal bones, both left and right, whereas there's only one ethmoid, one sphenoid, one occipital, and one frontal bone. And so there are six names to remember, but only eight bones total. Here we see a lateral view of the skull, and so let's try and pick out the cranial bones here in the image starting with the P is the parietal bone. So parietal forms the superior and lateral walls of the cranium. The word parietal means wall, and so the wall of the cranium is the parietal bone, and there are two left and right parietal bones. Then there's the ethmoid. We can see just a little bit of the ethmoid here. So there's just one ethmoid bone found in the superior nasal cavity and the anterior floor of the cranium. Next would be sphenoid. So here's the sphenoid bone. It's found in the anterior floor of the cranium, and a unique thing about the sphenoid bone is it forms a joint with all other of the cranial bones. All seven of the other cranial bones form joints with this sphenoid bone. So P-E-S-T is next temporal. So there's two temporal bones we can see right here. The temporal bone has this opening, the ear canal, or external acoustic meatus, also known as the external auditory meatus. And so that will help you remember that the temporal bone is found just deep to the ear because the external acoustic meatus is a feature of the temporal bone, the ear canal that allows vibrations of the air to vibrate the eardrum, the tympanic membrane. So that's P-E-S-T passed. Next is O for occipital. Here's the occipital bone. So this is found as the most posterior and the occipital bone forms the posterior floor of the cranium and the posterior wall of the cranium. And last is frontal. The frontal bone forms the anterior wall of the cranium, the forehead and the roof of the cranium on the anterior as well as part of the floor of the cranium on the anterior. So here we can see an anterior view. The frontal bone has a squamous region, the squamous or the flat region. The squamous of the frontal bone is the forehead. Then the supraorbital margin is this region, the superior edge of the orbit. There is a foramen, a supraorbital foramen. We can see the supraorbital foramen here and here. Supraorbital foramen is an opening in the center of the supraorbital margin that contains a nerve and a division of a cranial nerve, the ophthalmic branch of the trigeminal nerve which carries sensory information from the orbital region, travels through this supraorbital foramen. Supraorbital and there's a zygomatic process of the frontal bone. The zygomatic process gets its name from the fact that it's coming down to form a suture, an immobile joint with the zygomatic bone. The zygomatic bone is one of the 14 facial bones. The zygomatic process of the frontal bone extends down from the supraorbital margin forming the superior lateral margin of the orbit and forms a joint with the zygomatic bone. There are two parietal bones and the parietal bones are surrounded by the major cranial sutures. We can see the coronal suture is between the frontal bone and the parietal bone on the anterior of the parietal bone. The coronal suture runs parallel to the coronal plane. The squamous suture is between the parietal bone and the temporal bone on the lateral side of the parietal bone. This name comes from the fact that the temporal bone has a squamous portion. The squamous portion of the temporal bone is the thin flat part of the temporal bone and the squamous portion of the temporal bone articulates with the parietal bone at the squamous suture. Then the lambdoid suture is found between the parietal bone and the occipital bone. This name comes from the shape the lambdoid suture has this shape which resembles the Greek letter lambda. The last suture surrounding the parietal bone is between the left and right parietal bones the sagittal suture. We can't quite see that from this view but we'll see that on the next slide. Another feature of the parietal bone is called the parietal eminence. The parietal eminence is the region with the greatest convex curvature on the outer surface of the parietal bone. Essentially right in the center of the bone is the eminence. The parietal eminence is in the center of the parietal bone and is the most convex curved region. Here we can see with a posterior view the sagittal suture between the left and right parietal bones. We can also see a better view now of the lambda shape from the lambdoid suture between the parietal and occipital bones. Another important feature of the parietal bone is that on the inner surface of the parietal bone there are grooves for meningeal vessels. Meningees are the membranes surrounding the brain and the blood vessels that are running through those membranes have grooves that contour to their surface on the inner surface of the parietal bone. The occipital bone is the most posterior and inferior and a major feature of the occipital bone is foramen magnum. Foramen magnum literally translates to the the large foramen the large hole through a bone that contains nervous tissue and blood vessels and the foramen magnum contains the spinal cord. The spinal cord meets the most inferior part of the brain the medulla oblongata at the foramen magnum. We can also see here the occipital condyle. There's one on either side of foramen magnum. The occipital condyles are smooth articular surfaces that form a joint with the first vertebrae the most superior vertebrae known as C1 first cervical vertebrae or ATLAS. ATLAS is another name for the first cervical vertebrae that articulates with the occipital bone at the occipital condyles. Another feature of the occipital bone here we can see is the external occipital protuberance. External occipital protuberance is a rough projection of bone on the posterior of the occipital bone and there is a ridge of bone that extends from foramen magnum up to the external occipital protuberance. This is the external occipital crest. The external occipital crest extends from foramen magnum up to a more wide rough projection of bone known as the external occipital protuberance and then extending out laterally our nuchal lines. Here we can see the superior nuchal lines are labeled and there's also inferior nuchal lines. These are rough surfaces on the occipital bone on the posterior of the occipital bone that provide points of attachment for tendons and ligaments. There are elastic ligaments known as the nuchal ligaments that attach from the cervical vertebrae to the occipital bone at the nuchal lines and help to stabilize the neck in the extended upright position holding the head upright. Here we have an inferior view. We can see the foramen magnum that contains the spinal cord. It's the major opening in the occipital bone. We can see the occipital condyles. There is a small opening just lateral to foramen magnum adjacent to the occipital condyles that contains one of the spinal nerves. This is the hypoglossal hypoglossal canal which contains the hypoglossal nerve. Glossus means tongue and the hypoglossal nerve is a nerve that excites the muscles of the tongue and the hypoglossal canal is where the hypoglossal nerve travels out of the cranium. With this inferior view we can also see the jugular notch. The jugular notch is the posterior and medial edge of the jugular foramen. The jugular notch is the part of the jugular foramen that is formed by the occipital bone. We can see the more anterior and lateral edges of jugular foramen are formed by the temporal bone illustrated in the pink color here. The jugular foramen is where the jugular vein starts which carries blood draining from the brain. There are also several cranial nerves that travel out of the cranium through the jugular foramen. Another major foramen that we can see here is traveling through the temporal bone. Through the temporal bone is the carotid foramen or also known as the carotid canal. So here's the entrance to the carotid canal just anterior to the jugular foramen is the carotid foramen or carotid canal which contains the largest artery carrying blood into the brain the carotid artery. Carotid literally translates to stupor because if you restrict blood flow through the carotid artery you'll go into a stupor or the the brain will start to shut down and you can lose consciousness you can pass out as a result of loss of blood supply to the brain. So here we have an illustration of the temporal bone. We can see the external acoustic meadus it's a major opening in the temporal bone that allows vibrations of air to reach the tympanic membrane the eardrum. Just posterior to the external acoustic meadus is a mastoid portion or mastoid process. The mastoid process serves as the point of insertion for a major muscle that moves the head in order to flex the head at the neck or rotate the head the neck the sternocleidomastoid muscle inserts onto the mastoid process. Mastoid literally translates as breast shaped and this is a large bump a large process that projects from the temporal bone just posterior to the external acoustic meadus. Just anterior to the external acoustic meadus is a very slender process known as the styloid process. The styloid process is the origin of several muscles. Stylo glossis is one example. Stylo glossis is a muscle that moves the tongue. Stylo hyoid is another. Stylo hyoid is a muscle that moves the hyoid bone. And so the word styloid comes from the same root as stylus. The thin slender process resembles a stylus or the tip of a pen and there is a foramen located in between the mastoid process and the styloid process called the stylo mastoid foramen. And the stylo mastoid foramen contains the facial nerve a nerve that's important for exciting the muscles of facial expression. This region of the temporal bone on the inferior is known as the petrus portion and deep in the petrus portion deep inside of the petrus portion of the temporal bone is where the internal and middle ear is located. There are three small bones in the middle ear the auditory ossicles, malleus, incus, and stapes. And there's also a foramen traveling out of the petrus portion into the brain is a nerve that carries the sense of hearing as well as a sense important for balance known as the equilibrium sense or the vestibular sense. This nerve is the vestibular cochlear nerve the cochlea is the part of the inner ear that contains the receptors for hearing and there's a foramen called the internal acoustic meatus that carries the vestibular cochlear nerve. The petrus portion the word petrus comes from the same root as petrified petrified wood is wood that's become stone. The petrus portion is the heavy portion of the temporal bone in contrast the squamous portion is thin and flat found more superior the squamous portion forms part of the the inferior part of the lateral wall of the cranium we can see it another process that extends out of the temporal bone called the zygomatic process which joins with the zygomatic bone the zygomatic bone has a temporal process together the zygomatic process of the temporal bone and the temporal process of the zygomatic bone form a zygomatic arch of the cheek of the buccal region another major feature of the temporal bone is the mandibular fossa the mandibular fossa is a smooth surface that articulates with the mandible so here's the mandible which is our lower jaw bone the mandible fits into the mandibular fossa a specific part of the mandible known as the condylar process of the mandible articulates articulates with the mandibular fossa of the temporal bone forming the only mobile joint of the skull that allows us to open and close the jaw here we have a superior view of the cranial floor we can see in the purple color here the temporal bone and on either side here is the internal acoustic meatus where the vestibular cochlear nerve carries the sense of hearing and equilibrium from the inner ear into the brain here we have a view of the sphenoid bone the sphenoid bone forms the anterior part of the anterior floor of the cranium along with the ethmoid and frontal bone and the sphenoid bone articulates with all other cranial bones there are two large broad surfaces the greater wing and lesser wing of the sphenoid bone the greater wing is larger more inferior and extends the entire width of the cranium the lesser wing is smaller and more superior the lesser and greater wings to some extent resemble the the wings of an insect that has two pairs of wings and then we see here the pterygoid plates also known as pterygoid processes extend down inferior from the greater wing and resemble the legs of this insect with two pairs of wings the central portion of the sphenoid is the body of the sphenoid and the body of the sphenoid forms a cup shape known as the sella tersica the sella tersica protects the pituitary gland there are several openings through the sphenoid bone we can see in the greater wing there's foramen spinosum foramen ovale and foramen rotundum spinosum ovale rotundum is the order from most posterior and lateral to medial and anterior spinosum is the smallest ovale is the largest and has an oval shape and rotundum has a round shape superior orbital fissure is an elongated opening between the lesser and greater wing and there are several nerves that travel through the superior orbital fissure cranial nerves that excite muscles to move the eye the optic canal is located medial to the superior orbital fissure and contains the optic nerve the nerve that carries the sense of vision into the brain from the eye here we have a view of the ethmoid bone the ethmoid bone forms the superior portion the roof of the nasal cavity and there's a perpendicular plate that extends down along the midline to form the superior part of the nasal septum the septum is separating the left and right portions of the nasal cavity there are scroll shaped projections of bone called nasal concha that function to increase the turbulence of air as it flows through the nasal cavity so that air has more time to become acclimated to the humidity and temperature inside of the body the middle nasal concha is this portion that extends down and then there's another little projection of bone here the superior nasal concha so both of these are scroll shaped projections of bone that extend into the nasal cavity and we can see that they're found on both the left and the right on the superior surface of the ethmoid bone forming the floor of the cranium there's a cribriform plate and the cribriform plate contains many small foramen up many small openings and so the cribriform foramen are the small openings of the cribriform plate and they contain the olfactory nerve a cranial nerve that's carrying the sense of smell along the midline extending up from the cribriform plate is a ridge of bone known as cristagalli cristagalli literally translates to the rooster's comb cristagalli is a point of attachment for the meninges to help stabilize the brain can see there are also air cells or the ethmoid air cells are also known as sinuses these are one of the perin nasal sinuses in the ethmoid bone there are perin nasal sinuses that connect to the nasal cavity here we have a superior view of the floor of the cranium we can see that the anterior portion is formed from the frontal bone ethmoid bone and a small portion of the sphenoid bone you can see there are smooth convex surfaces on the floor of the cranium that contour around the brain these are the cranial fossa so here's the anterior cranial fossa there's left and right and these are contouring around the inferior surface of the frontal lobe of the cerebral cortex then the middle region of the floor of the cranium you can see is formed from the sphenoid bone the temporal bone temporal bone shown in purple the sphenoid bone there shown in the yellow color and a little bit of the parietal bone is also extending down we can see in orange a little bit of parietal bone and so the smooth convex surface here is a fossa the middle cranial fossa and then the posterior portion of the cranium is formed mostly by the occipital bone there's a little bit of the temporal bone and parietal bone as well but mostly occipital bone and there are fossa in the occipital bone close to the foremen magnum these posterior cranial fossa of the occipital bone can be subdivided so here we see what's known as the cerebellar fossa or the fossa for the cerebellum the cerebellum is the most posterior inferior region of the brain located just posterior to the brain stem then there are fossa located further superior from the fossa for the cerebellum these are known as the fossa for the cerebellum and they contour to the surface of the occipital lobe of the cerebral cortex whereas the middle fossa contour to the temporal lobe of the cerebral cortex and the anterior cranial fossa contour to the frontal lobe of the cerebral cortex together the fossa in the occipital bone are known as the posterior cranial fossa so here we can see an illustration with the anterior middle and posterior cranial fossa illustrated here we can see the cerebellum in the posterior cranial fossa in the fossa for the cerebellum whereas up here we see the occipital lobe and there are also fossa of the occipital bone that contour around the occipital lobe of the cerebrum known as the fossa for the cerebrum of the occipital bone the further inferior fossa ones that we're seeing here are the fossa for the cerebellum so that is the cerebellum whereas this region of the brain back here is the occipital lobe of the cerebrum and this region here is a frontal lobe of the cerebrum and this region here is the temporal lobe and so you can see that the learning the names of the cranial bones will help you learn the names of the lobes of the cerebrum the occipital lobe is just deep to the occipital bone the temporal lobe is just deep to the temporal bone frontal lobe deep to the frontal lobe there's also a parietal lobe of the cerebrum just deep to the parietal bone the fontanelles of the cranium are connective tissue that's a fibrous connective tissue that allows some flexibility to the cranium in a newborn during birth the cranium will change shape to fit through the birth canal and then as the brain continues to grow after birth the cranium will continue to expand and then eventually as the brain reaches maturity the cranium will finish ossification and the fontanelles will mature into cranial sutures we can see here the anterior fontanelle which forms at the junction between the sagittal and coronal sutures you can see that there's a frontal suture here in the newborn skull where there would be a left and right frontal bone as the frontal bone matures the frontal suture disappears leaving only one frontal bone in an adult cranium here we can see the posterior fontanelle the posterior fontanelle is found at the junction of the lambdoid and sagittal sutures posterior fontanelle here and then there is also a sphenoidal fontanelle and a mastoid fontanelle on the lateral sphenoid fontanelle forms at the junction of the squamous and coronal sutures and the mastoid fontanelle forms at the junction of the squamous and lambdoid sutures and the sphenoidal and mastoid fontanelles are paired so that there's a right and a left whereas there's only one anterior fontanelle and only one posterior fontanelle here we see an illustration of the perinazle sinuses these are air filled cavities spaces inside of the bone filled with air that function in order to reduce the weight of the skull they also contribute to the character of the voice as we speak our voice resonates through the sinuses and so there are frontal sinuses in the frontal bone sphenoidal sinuses in the sphenoid ethmoidal air cells or sinuses inside of the ethmoid and a facial bone the upper jaw known as the maxillary also contain maxillary sinuses so there are left and right maxillary bones and each contains a maxillary sinus all of the sinuses have openings that connect to the nasal cavity and are lined with a respiratory mucus membrane that has the pseudo stratified ciliated columnar epithelium produces mucus and the cilia can beat back and forth to move the mucus and any particles that get trapped in that mucus and of course a sinus infection is when the passageways to drain the sinuses become blocked as bacteria are growing inside of the mucus of the sinuses