ANATOMY AND PHYSIOLOGY CHAPTER 5: THE SKELETON (SKULL) ANATOMY AND PHYSIOLOGY

WORMIAN BONES (small sutural bones) are often seen along sagittal and lambdoid sutures – like little islands of bone with the suture lines passing around them. Internal areas of the parietal and frontal bones have markings that look like river tributaries, which are bone that has been molded around blood vessels of the meninges.

Sometimes a PARIETAL FORAMEN occurs near corner of lambdoid and sagittal sutures. A pair of slight thickenings of the skull form across the parietal and frontal bones. They mark the attachment of the large, TEMPORALIS MUSCLE, a chewing muscle that passes between the zygomatic arch and temporal bone and inserts on the mandible.

TEMPORAL BONES (2) Located just above and anterior to the ear “temporal region” (inferior to parietal bones) – forms much of lower wall and part of floor of cranial cavity. Very complex shape.

Temporal bone is divided into 4 regions SQUAMOUS PART (flat, vertical, enclosed by squamous suture, right above ear near temporal region). Squamous part bears 2 prominent features ZYGOMATIC PROCESS (extends anteriorly to form part of the zygomatic arch or “cheekbone”) MANDIBULAR FOSSA (depression where the mandible articulates with cranium)

TYMPANIC PART – small ring of bone bordering the external acoustic meatus (opening into ear canal). It has a pointed spine on its inferior surface called the STYLOID PROCESS. The styloid process gives attachment for muscles of the tongue, pharynx, and hyoid bone. MASTOID PART – lies posterior to tympanic part. It contains MASTOID PROCESS, which you can feel as a lump behind your earlobe. Its filled with air sinuses that communicate with the middle-ear cavity. These sinuses are subject to infection “mastoiditis” and can erode the bone and spread to the brain. A groove called the MASTOID NOTCH lies medial to the mastoid process. The DIGASTRIC MUSCLE is attached here to open the mouth. The notch is perforated by the STYLOMASTOID FORAMEN at its anterior end and MASTOID FORAMEN at its posterior end.

Mastoid Foramen

PETROUS PART – found in cranial floor, resembles little mountain ranges separating the middle cranial fossa and the posterior fossa. It houses the middle- and inner-ear cavities. The INTERNAL ACOUSTIC MEATUS, an opening on its inner surface, allows passage of the vestibulocochlear nerve which carries sensations of hearing and balance from inner ear to brain. Also on petrous part you find the CAROTID CANAL which is a passageway for the carotid artery which supplies blood to the brain. It is so close to inner ear you can sometimes hear the pulsing of your blood. The JUGULAR FORAMEN is large, irregular opening just medial to styloid process between temporal and occipital bones. Blood drains from brain through this foramen into internal jugular vein of neck. 3 cranial nerves also pass through this foramen.

Mastoid Foramen

OCCIPITAL BONE: (1) Rear of skull and much of its base. It is bordered by the lambdoindal suture and the OCCIPITOMASTOID SUTURE. The foramen magnum is here, admits spinal cord to cranial cavity and provides a point of attachment for dura mater. BASILAR PART is a thick medial plate anterior to foramen magnum. OCCIPITAL CONDYLES are 2 smooth knobs on either side of foramen magnum where skull rests on vertebral column. Next to the condyles you find the HYPOGLOSSAL CANAL – hypoglossal nerve passes through it to supply muscles to tongue.

The EXTERNAL OCCIPITAL PROTUBERANCE is a prominent bump used for attachment of the NUCHAL LIGAMENT, which binds the skull to the vertebral column. SUPERIOR NUCHAL LINE provides attachment to the skull for several neck and back muscles. By pulling down on the occipital bone, some of these muscles help to keep the head erect. The INFERIOR NUCHAL LINE gives attachment for some deep neck muscles.

SPHENOID BONE (1) Complex shape, thick medial BODY, outstretched GREATER WINGS and LESSER WINGS THAT GIVE THE BONE A SOMEWHAT RAGGED MOTHLIKE SHAPE. Best to see this bone from superior perspective. These form about half of the middle cranial fossa (with the temporal bone forming the rest).

The greater wing forms part of the lateral surface of cranium just anterior to the temporal bone. The lesser wing forms the posterior wall of the orbit and contains the OPTIC CANAL, which allows passage of the optic nerve and ophthalmic artery. The body of the sphenoid has a “saddlelike” prominence named the SELLA TERCICA. It consists of a deep pit called the HYPOPHYSEAL FOSSA, which houses the pituitary gland; a raised anterior margin called the TUBERCULUM SELLA; and a posterior margin called the DORSUM SELLAE.

Sphenoid Bone Tuburculum sella Dorsum sella

Lateral to the sella turcica, the sphenoid is perforated by several foramina. The FORAMEN ROTUNDUM and FORAMEN OVALE are passages for 2 branches of the trigeminal nerve. The FORAMEN SPINOSUM, about the diameter of a pencil lead, provides passage for an artery of the meninges. The gash called the FORAMEN LACERUM occurs at the junction of the sphenoid, temporal, and occipital bones.

In an inferior view, the sphenoid can be seen just anterior to the occipital bone. The internal openings of the nasal cavity seen here are called the INTERNAL NARES. Lateral to these, the sphenoid bone exhibits a pair of parallel plates: the MEDIAL PTERYGOID PLATE and LATERAL PTERYGOID PLATE. These plates provide attachment for some of the jaw muscles. The SPHENOID SINUS occurs within the body of the sphenoid bone.