Borders of the Fourth ventricle, Rhomboid Fossa

• The 4th ventricle is the ventricular component of the pons and medulla.
• Location: between the cerebellum and the pons and medulla.
• Connections:
• Superiorly - connects to the cerebral aqueduct in the midbrain.
• Inferiorly - connects to the central canal in the spinal cord.
• Laterally - has 2 openings, 1 on each side, - Foramen of Luschka. Also called the lateral aperture. Connect the 4th ventricle to the part of the subarachnoid space called the cistern of the great cerebral vein(Superior cistern, Quadrigeminal cistern)
• Lateral recess - The area in the ventricle adjacent to the foramen of Luschka.
• Posteriorly - 1 opening - Foramen of Magendie. Also called the median aperture. Connect the 4th ventricle to the part of the subarachnoid space called cisterna magna(also called Cisterna cerebellomedullaris).
• As all ventricular spaces, the 4th ventricle has an ependymal cell layer.
• Ependymal cells are a specialized type of epithelial cells that line the ventricular system of the brain and play a key role in the production of cerebrospinal fluid.

Borders of the 4th ventricle:

• Lateral: Superior and Inferior cerebellar peduncles.
• Roof (posterior):
• superior half - superior medullary vellum.
• inferior half - inferior medullary vellum, and choroid plexus connect it at the inferior part.
• include the foramina of Magendie and Luschka.
• Floor(anterior): rhomboid fossa.

Rhomboid Fossa:

• The floor of the 4th ventricle. Anterior in anatomical position.
• It has a diamond shape. Formed by tegmentum (back) of pons (superior half) and medulla (inferior half). Both parts are separated by the Striae Medullares of the rhomboid fossa.
• Structures at the superior part (pons):
• Median sulcus
• Medial eminence - bulges on the sides of median sulcus.
• Facial colliculus - inferior to medial eminence. It contains the abducent nucleus and internal genu of the facial nerve - fibers of motor nucleus of facial nerve that turn around the abducent nucleus.
• Sulcus Limitans - separates the ala plate from the basal plate.
• Locus Ceruleus - It contains the largest collection of norepinephrinergic neurons in the CNS. Lateral to the Sulcus Limitans.
• Striae Medullares of the rhomboid fossa - also called Striae Acustic. Horizontal lines that divide the rhomboid fossa into the superior pontine portion and the inferior medullary portion.
• Vestibular region - partly in the pons. Overlay the vestibular nuclei.
• Superior fovea - lateral to facial colliculus.

• Structure of inferior part (Open medulla):
• Striae Medullares of the rhomboid fossa - Horizontal lines, also called Striae Acustic.
• Inferior Fovea - small depression in the limiting sulcus below the Striae Medullares. Lateral to the hypoglossal and vagal trigones.
• Calamus scriptorius - consists of the hypoglossal trigone and vagal trigone (more lateral and inferior). Each covers its nucleus.
• Sulcus Limitans - both in medulla and pons.
• Area Postrema (Vomitting center) - it is a circumventricular organ. It has loose blood-brain barrier that enables it to identify substances in the blood.
• Obex - inferior angle.

The roof of the 4th Ventricle:

• The roof is made by few structures.
• Openings: 
• in the middle of the roof - Foramen of Magendie.
• at the lateral part of the roof - Foramen of Luschka.
• Borders:
• Superior part:
• Superior Cerebellar peduncle.
• Superior medullary vellum between the peduncles.
• Inferior part: Inferior medullary vellum. 
• From its inferior part - the choroid plexus of the 4th ventricle is suspended. 
• Part of it extends out of the ventricle through the foramen of Luschka. 
• This extension through the foramen of Luschka is called the "Bochdalek's flower basket" It is barely seen.
• Fastigium: Top of the roof, At the angle between the superior and inferior parts. Protrudes into the cerebellum.
  
• Lateral: Inferior cerebellar peduncles.

Classification of the cranial nerves:

1. General/Special. Special are the things that relate to taste and smell.
2. Voluntary and conscious (Somatic) vs. Involuntary and unconscious (Visceral).
3. Motor (Efferent) or Sensory (Afferent).

• General Somatic efferent (GSE): Voluntary functions of eyes and tongue: CN. 3,4,6,12.
• Special Somatic efferent (SSE): Motor function of food and air intake: CN. 5,7,9,10,11.
• Special Visceral efferent(SVE): Motor function of food intake: CN. 9,10.
• General Visceral efferent (GVE): Parasympathetic motor function of eyes (CN.3) glands (CN. 9,10) and internal organs as cardiac muscle, lung, and GI. (CN.10). Pass through ganglia.
• General Somatic afferent (GSA): sensation and proprioception from the head. CN. 5,9,10.
• Special Visceral afferent (SVA): sensation from taste buds: CN. 7,9,10.
• General Visceral afferent (GVA): input from the internal organ (unconscious): CN. 9,10.

Sensory nuclei-

• Solitary nucleus:
• Location: Medulla, All fibers first enter the solitary tract, and then end in the solitary nucleus.
• Function: Receives all visceral afferent information from all cranial nerves.
• Superior part - Receives taste information (Special VA) - gustatory nucleus.
• Inferior part - Receives visceral sensation - sometimes called the cardiorespiratory nucleus.
• Gustatory nucleus: Located on the superior part of the solitary nucleus.
• Function: Receives taste sensation from CN. 7,9,10

• Trigeminal sensory nuclei:
• The trigeminal nerve originates from three sensory nuclei (mesencephalic, principal sensory, spinal) and one motor nucleus (the motor nucleus of the trigeminal nerve) extending from the midbrain to the medulla.
• Only the spinal nucleus is associated with few cranial nerves.
• Spinal trigeminal nucleus: somatic sensory receiving center of the brainstem - thermal information, crud touch, and pain (nociception). Receive sensation from the face, head, and neck, through cranial nerves 5,7,9,10. Fibers enter through spinal trigeminal tract.

Motor nuclei-

• Nucleus Ambiguus: (SVE) column of motor neurons situated dorsal to the inferior olivary nucleus. Delivered by CN. 9,10,11.
• Supply; striated muscles of the soft palate, pharynx, and larynx (except tensor veli palatine, by CN5), together with striated muscle fibers in the upper part of the esophagus.
• Salivatory nuclei:
• Location: consists of groups of neurons located lateral and medial to the facial motor nucleus.
• Function: (GVE) they give parasympathetic fibers to CN.7 and 9, to produce saliva.
• It is divided into superior and inferior salivatory nuclei:
• Superior salivatory nucleus: It gives parasympathetic fibers to the facial nerve. Its axons exit the brainstem as the intermediate nerve and then join the facial nerve.
• The lacrimal nucleus can be considered as part of the superior salivatory nucleus, that supplies the lacrimal gland.
• its fibers supply: 
1. The lacrimal gland, and nasal and palate mucous glands through the pterygopalatine ganglion. Through the greater petrosal nerve and pterygopalatine ganglion.
2. Sublingual and submandibular glands. Through the chorda tympani and the submandibular ganglion.
• Inferior salivatory nucleus: Innervates the parotid gland, through CN.9 > tympanic nerve > lesser petrosal nerve > otic ganglion > auriculotemporal > parotid gland.

Arrangement of sensory nuclei:

• In the lateral aspect of the brainstem, from medial to lateral:
• Solitary nucleus, vestibular nuclei, trigeminal nuclei, cochlear nuclei.
• Arrangement of the Vestibular and cochlear nuclei:
• Location: medial and inferior vestibular nuclei in the medulla, anterior and posterior cochlear nuclei in the pontomedullary junction, superior and lateral vestibular nuclei in the pons.
• Function: receive information about hearing, balance, and equilibrium from the middle ear through CN8.

Arrangement of motor nuclei:

• 3 columns, from medial to lateral-
• Motor nuclei of CN. 3,4,6,12 are next to the midline, and all innervate skeletal muscles (SE).
• Motor nuclei of the PNS (GVE): dorsal motor vagal nucleus, inferior and superior salivatory nuclei, Edinger-Westphal nucleus (CN3). all terminate in peripheral ganglia.
• Nucleus Ambiguus, facial motor nucleus, trigeminal motor nucleus. (SVE) form a discontinuous column.

Motor nuclei in red, Sensory nuclei in blue.

• Motor nuclei are located more medially, and sensory nuclei are located more laterally since the motor nuclei originate from the basal plate, and sensory nuclei originate from the alar plate.
• There are 2 somatomotor nuclei columns -
• Dorsomedial column: cranial nerves 3,4,6,12 General Somatic Efferent
• Ventrolateral column: cranial nerves 5,7,9,10,11 Special Visceral Efferent
• The other nuclei are visceromotor: 3,7,9,10 General Visceral Efferent, between the 2 others.

• Developmentally, sensory nuclei develop from the alar plate, more lateral and posterior, the motor nuclei are formed by the basal plate, more medial and anterior. Both are separated by sulcus limitans.