GEN ANA PRELIM EXAM

• The head is mainly formed by the skull with the brain and its covering meninges enclosed in the cranial cavity
• Important landmarks of the skull include:

  • Nasion: depression in the midline on the root of the nose
  • External occipital protuberance: bony prominence at the back of the head
  • Vertex: highest point on the skull in the sagittal plane
  • Superciliary ridge: two prominent ridges on the frontal bones of the upper margin of the orbit
  • Mastoid Process: projects downward and forward from behind the ear
  • Zygomatic Arch: extends forward in front of the ear and ends in front of the zygomatic bone
  • Pterion: point where the greater wing of the sphenoid meets the inferior angle of the parietal bone
• The skull's role is to protect the brain and is made up of 8 cranial bones and 14 facial bones
• The skull bones are united by 4 major sutures:

  • Sagittal Suture
  • Coronal Suture
  • Lambdoidal Suture
  • Squamosal Suture
• The regions of the head include frontal, parietal, occipital, temporal, auricular, orbital, nasal, infraorbital, zygomatic, buccal, oral, and mental regions
• The cranium consists of:

  • Frontal Bone: 1
  • Parietal bones: 2
  • Occipital bone: 1
  • Temporal bones: 2
  • Sphenoid bone: 1
  • Ethmoid bone: 1
• The facial bones consist of:

  • Zygomatic bones: 2
  • Maxillae: 2
  • Nasal bones: 2
  • Lacrimal bones: 2
  • Vomer: 1
  • Palatine bones: 2
  • Inferior conchae: 2
  • Mandible: 1
• The cranial cavity contains the brain and its surrounding meninges, portions of the cranial nerves, arteries, veins, and venous sinuses
• The meninges surrounding the brain are:

  • Dura Mater (pachymenix)
  • Arachnoid and pia mater (leptomeninges)
• Dura mater of the brain has two layers:

  • Endosteal layer: periosteum covering the inner surface of the skull bones
  • Meningeal layer: dense strong fibrous membrane covering the brain and continuous through the foramen magnum with the dura mater of the spinal cord
• The Arachnoid is the middle layer, a thin and fragile layer surrounding the brain, with the subarachnoid space between it and the pia mater
• The Pia Mater is the innermost layer, a mesh-like vascular membrane deriving blood supply from the internal carotid and vertebral arteries
• Dural Arterial Supply:

  • Middle meningeal artery is commonly damaged in head injuries
• • Medium for exchange of nutrients and waste products between blood and adjacent nerve tissue
• Cerebrospinal Fluid (CSF):

  • Clear, colorless liquid composed primarily of water
  • Protects the brain and spinal cord from chemical and physical injuries
  • Carries small amounts of oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia
  • Functions:
  • Mechanical protection
  • Homeostatic function
  • Circulation
  • Acts as a shock-absorbing medium that protects brain tissues and helps the brain float in the cranial cavity
  • pH affects pulmonary ventilation and cerebral blood flow, important for maintaining homeostatic controls in brain tissue
• Formation, circulation, and absorption of cerebrospinal fluid (CSF):

  • Total volume of CSF in an adult is 80 to 150 mL
  • Majority of CSF production comes from the choroid plexus
• Venous Blood Sinuses:

  • Venous sinuses of the cranial cavity are blood-filled spaces between layers of the dura mater
  • Superior Sagittal Sinus:
  • Lies on the upper fixed border of the falx cerebelli
  • Continuous with right and left transverse sinuses
  • Receives the superior cerebral vein
  • Inferior Sagittal Sinus:
  • Lies in the free lower margin of the falx cerebelli
  • Receives veins from the medial surface of the cerebral hemisphere
  • Straight Sinus:
  • Lies at the junction of the falx cerebelli with the tentorium cerebelli
• • S-shaped, leaving a deep impression in the inferior surface of the temporal bone
  • All venous sinuses ultimately drain into sigmoid sinuses
• • Formed by the union of the inferior sagittal sinus with the great cerebral vein
  • Ends by turning to form the transverse sinus
  • Transverse Sinus:
  • Paired structures beginning at the internal occipital protuberance
  • Right transverse sinus usually continuous with superior sagittal sinus, left continuous with straight sinus
  • Occipital Sinus:
  • Small sinus near the foramen magnum
  • Communicates with vertebral veins and drains into the confluence of sinuses
  • Sigmoid Sinuses:
  • Direct continuation of transverse sinuses
• Scalp:

  • Consists of five layers
  • Skin is thin, hair-bearing, and contains numerous sebaceous glands
  • Connective tissue beneath the skin is fibrofatty
  • Aponeurosis (epicranial) is a thin, tendinous sheet uniting occipital and frontal bellies of occipitofrontalis muscle
  • Loose areolar tissue connects epicranial aponeurosis to periosteum of the skull
  • Pericranium is the periosteum covering the outer surface of the skull bones
• Muscle of the Scalp:

  • Occipitofrontalis muscle contracts to move the first three layers of the scalp forward or backward
  • Frontal bellies of occipitofrontalis can raise eyebrows in expressions of surprise
• Sensory Nerve Supply of the Scalp:

  • Supratrochlear Nerve:
  • Branch of ophthalmic division of trigeminal nerve
  • Supplies the scalp, reaching nearly as far as the vertex of the skull
  • Supraorbital Nerve:
  • Branch of ophthalmic division of trigeminal nerve
  • Supplies the scalp as far backward as the vertex
  • Zygomaticotemporal Nerve:
  • Branch of maxillary division of trigeminal nerve
  • Supplies the scalp over the temple
  • Auriculotemporal Nerve:
  • Branch of mandibular division of trigeminal nerve
  • Supplies skin over temporal region
  • Lesser Occipital Nerve:
• • Branch of cervical plexus (C2)
  • Supplies scalp over lateral part of occipital region and skin over medial surface of auricle
  • Greater Occipital Nerve:
  • Branch of posterior ramus of 2nd cervical nerve
  • Supplies skin as far forward as the vertex of the skull
• • Occipital artery:
  • Branch of external carotid artery
  • Ascends from apex of posterior triangle, in company with greater occipital nerve
  • Supplies skin over back of scalp, reaching as high as vertex of skull
• Arterial Supply of the Scalp:

  • Supratrochlear and Supraorbital arteries:
  • Branches of ophthalmic artery
  • Ascend over forehead in company with supratrochlear and supraorbital nerves
  • Superficial temporal artery:
  • Smaller terminal branch of external carotid artery
  • Ascends in front of auricle in company with auriculotemporal nerve
  • Divides into anterior and posterior branches, supplying skin over frontal and temporal regions
  • Posterior auricular artery:
  • Branch of external carotid artery
  • Ascends behind auricle to supply scalp above and behind auricle
• Venous Drainage of the Scalp:

  • Supratrochlear and Supraorbital veins
  • Superficial temporal vein
  • Posterior auricular vein
  • Occipital vein
• Lymph Drainage of the Scalp:

  • Lymph from forehead and anterior part of face drains into submandibular lymph nodes
  • Lateral part of face, including lateral parts of eyelids, drains into parotid lymph nodes
  • Central part of lower lip and skin of chin drain into submental lymph nodes
• Muscles of the Face (Muscles of Facial Expression):

  • Embedded in superficial fascia
  • Arise from bones of skull and are inserted into skin
  • Function as sphincters or dilators of facial structures
  • Modify expression of the face
• Muscles of the Eyelids:

  • Orbicularis Oris surrounds/closes mouth
• Sensory Nerves of the Face:

  • Facial and superficial temporal arteries provide rich blood supply to the face
• Venous Drainage of the Face:

  • Facial vein formed at medial angle of eye by union of supraorbital and supratrochlear veins
  • Connected to cavernous sinus via superior ophthalmic vein
• Lymph Drainage of the Face:

  • Forehead and anterior face drain into submandibular lymph nodes
  • Lateral face, including eyelids, drain into parotid lymph nodes
  • Central lower lip and chin skin drain into submental lymph nodes