Comprehensive Head and Neck Anatomy Notes

Head and Neck Anatomy

Cranial Bones

  • Formed from eight large bones.
  • Paired Bones:
    • Temporal bones.
    • Parietal bones.
  • Unpaired Bones:
    • Frontal bone.
    • Occipital bone.
    • Sphenoid bone.
    • Ethmoid bone.

Facial Bones

  • Unpaired Bones:
    • Mandible.
    • Vomer.
  • Paired Bones:
    • Maxillae.
    • Zygomatic bones.
    • Nasal bones.
    • Lacrimal bones.
    • Palatine bones.
    • Inferior nasal conchae.

Protection of the Brain

  • The brain is protected from injury by:
    • Skull.
    • Meninges.
    • Cerebrospinal fluid.
    • Blood-brain barrier.

Cerebral Meninges

  • Both the brain and spinal cord are covered by meninges.
  • Layers:
    • Dura mater.
    • Arachnoid mater.
    • Pia mater.

Cerebrospinal Fluid (CSF)

  • Brain and spinal cord are suspended in CSF found in the subarachnoid space.
  • Functions:
    • Cover and protect the CNS.
    • Enclose and protect the vessels that supply the CNS.
    • Contain the cerebrospinal fluid between the pia and arachnoid maters.

Dura Mater

  • Strongest of the meninges.
  • Composed of two layers:
    • Periosteal layer.
    • Meningeal layer.
  • The two layers are fused except to enclose the dural sinuses.
  • Largest sinus: the superior sagittal sinus.
  • The dura mater extends inward to subdivide the cranial cavity

Arachnoid Mater

  • Located beneath the dura mater.
  • Arachnoid villi project through the dura mater, allowing CSF to pass into the dural blood sinuses.

Pia Mater

  • Delicate connective tissue.
  • Clings tightly to the surface of the brain.
  • Follows all convolutions of the cortex.

Meningitis

  • Diagnosis by collecting CSF via Lumbar Puncture.

Cerebrospinal Fluid (CSF)

  • Flows in the subarachnoid space.
  • Formed in choroid plexuses in the brain ventricles.
  • Choroid plexus:
    • Located in the ventricles.
    • Composed of ependymal cells surrounding capillaries.
  • Arises from blood.
  • 500 ml produced per day.
  • Only 100–160 ml present at any one time.

Ventricles of the Brain

  • Expansions of the brain’s central cavity.
  • Filled with cerebrospinal fluid.
  • Lined with ependymal cells.
  • Continuous with each other.
  • Continuous with the central canal of the spinal cord.

Choroid Plexus

  • Modified ependymal cells interacting with capillary endothelium.
  • Allows for CSF to be filtered from the blood.
  • Located in the ventricles.
  • CSF is recycled back into the blood through the dural sinuses via the sagittal sinus.

Hydrocephalus

  • Accumulation of excess CSF within the ventricular system.
  • Either from the overproduction of CSF or decreased reabsorption.

Blood-Brain Barrier

  • Astrocyte foot-processes surround vasculature.
  • Prevents most blood-borne toxins from entering the brain.
  • Impermeable capillaries.
  • Not an absolute barrier.
  • Nutrients such as oxygen pass through.
  • Allows passage of alcohol, nicotine, and anesthetics.

Basic Parts and Organization of the Brain

  • Organization:
    • Centrally located gray matter.
    • Externally located white matter.
    • Additional layer of gray matter external to white matter (cortex).
  • Cortex:
    • Outer layer of gray matter.
    • Formed from neuronal cell bodies.
    • Located in cerebrum and cerebellum.

Classification of Brain Regions

  • Brain stem
    • Midbrain, pons, and medulla
  • Cerebellum
  • Diencephalon
  • Cerebral hemispheres (also known as cerebrum)

The Brain Stem

  • Includes the midbrain, pons, and medulla oblongata.
  • General Functions:
    • Passageway for all fiber tracts running between the cerebrum and spinal cord.
    • Heavily involved with the innervation of the face and head.
    • Origin of 10 of the 12 pairs of cranial nerves.
    • Produces automatic behaviors necessary for survival.
    • Integrates auditory and visual reflexes.

Medulla Oblongata

  • Most caudal level of the brain stem; continuous with the spinal cord.
  • Decussation of the pyramids: crossing over of motor tracts.
  • Cranial Nerves Attaching to the Medulla Oblongata:
    • VIII—vestibulocochlear nerve
    • IX—glossopharyngeal nerve
    • X—vagus nerve
    • XII—hypoglossal nerve

Medulla's Core

  • Much of the reticular formation.
  • Network of nerve pathways that influence autonomic functions.
  • Visceral Centers:
    • Cardiac center.
    • Vasomotor center.
    • Respiratory center.
    • Centers for hiccupping, sneezing, swallowing, and coughing.

The Pons

  • A “bridge” between the midbrain and medulla oblongata.
  • Cranial Nerves Nuclei within in the Pons:
    • V—trigeminal nerve
    • VI—abducens nerve
    • VII—facial nerve
  • Contains motor tracts coming from the cerebral cortex.

The Midbrain

  • Lies between the diencephalon and the pons.
  • Cerebral aqueduct: periaqueductal gray matter surrounds it.
  • Involved in fight-or-flight reaction and mediating response to visceral pain.
  • Corpora Quadrigemina:
    • Largest nuclei, divided into the superior and inferior colliculi.
    • Superior colliculi: act in visual reflexes.
    • Inferior colliculi: act in reflexive response to sound.
  • Embedded in the white matter are two pigmented nuclei:
    • Substantia nigra: neuronal cell bodies containing melanin; affected in Parkinson's disease.
    • Red nucleus: involved with limb control.

The Cerebellum

  • Located dorsal to the pons and medulla.
  • Functions in smoothing and coordinating body movements, and maintaining equilibrium.
  • Consists of two cerebellar hemispheres.
  • Surface folded into ridges called folia.
  • **Hemispheres Subdivided: