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The image shows an apocrine gland. There is shedding of the apical portion of the cell during the secretion.

Types of glands:

Apocrine

Apical partof cellsheds offdur ing discharge

Eg:Apocrine sweat glands in axilla and groin, mammary gl ands, the external auditory ca nal (ceruminous glands) and eyelids (glands of Moll)

Holocrine

Whole-cell disintegratesdurin g discharge

Eg:Glands of Zeis and Meibo mian glandMontgomery tube rcle: Nipple and areolaTyson' s gland: External fold of the p repuceFordyce' spot: Vermilli on border of lips and mucosa

Eccrine(Merocrine)

Thecell is intactandsecretions are thrown out by exocytosis

Eg:Sweat glands on palms an d solesFound everywhere exc ept clitoris, glans penis, labia minora, external auditory ca nal and lips

Notice that for the sweat glands, the duct mostly goes to the skin surface v/s Sebaceous gland which mostly opens to the hair follicle.

The structures marked X and Y are the endothelium and Bowman's membrane, respectively.

The human cornea has five layers. From the anterior to posterior, the layers of the human cornea are as follows:

• Corneal epithelium - It is the outermost layer made up of non-keratinized stratified squamous epithelium. It is continuous with the conjunctival epithelium.
• Bowman's layer - The anterior-limiting lamina lies behind the corneal epithelium. It contains a dense mass of collagen (mainly type I collagen fibrils) set in a matrix similar to that of the

substantia propria.

• Corneal stroma (also substantia propria) - It is a thick, transparent middle layer, consisting of regularly arranged collagen fibers along with sparsely distributed interconnected keratocytes.
• Descemet's membrane - It is a thin acellular layer that serves as the modified basement membrane of the corneal endothelium, from which the cells are derived. This layer is composed mainly of collagen type IV fibrils.
• Corneal endothelium - The endothelium covers the posterior surface of the cornea and consists of a single layer of squamous cells.

The sixth layer called Dua’s layer or pre-Descemet’s layer has been recently discovered, located between the stroma and the Descemet’s membrane.

The above histological image is that of the cochlea which can be identified by the presence of characteristic organ of Corti.

The cochlea consists of a bony canal that makes 2.75 spiral turns around an axis of bone known as the modiolus. A shelf of bone from the modiolus forms a ridge known as the spiral lamina.

The basilar membrane supporting the organ of Corti extends from the spiral lamina to the outer wall of the cochlea. The vestibular membrane runs from the spiral lamina to the outer wall above the basilar membrane. These two membranes divide the bony labyrinth into three cavities:

• Scala vestibule - located between the roof of the labyrinth and the vestibular membrane, is lined by mesenchymal cells and contains perilymph.
• Scala media - located between the vestibular membrane and basilar membrane, contains endolymph.
• Scala tympani - located between the basilar membrane and the floor of the labyrinth, is lined by mesenchymal cells and contains perilymph.

The olfactory nerve is a pure sensory nerve. It carries no motor fibers.

Mnemonic: Some Say Money Matters But My Brother Says Big Brains Matter More. S - Purely sensory

M - Purely motor

B - Both sensory and motor

The placement of the words in the mnemonic corresponds to the cranial nerve number i.e; "Some" corresponds to the 1st cranial nerve (olfactory), "Say" corresponds to the 2nd cranial nerve (optic), and so on.

Pure sensory

Olfactory (1)

Optic (2)

Vestibulocochlear (˜)

Pure motor

Oculomotor (3)

Trochlear (4)

Abducent (6)

Spinal Accessory (11)

Hypoglossal (12)

Mixed-sensory and mo tor

Trigeminal (5)

Facial (7)

Glossopharyngeal (9)

Vagus (1™)

The VII nerve (facial) does not contain neurons from the somatic efferent column.

The general somatic efferent (GSE) is the most ventral column in the basal plate. It is represented by the oculomotor (III), trochlear (IV), abducens (VI), and hypoglossal (XII) nuclei.

The facial (VII) nerve contains neurons from:

• Special visceral efferent (SVE) column - supplies facial muscles derived from the second pharyngeal arch.
• General visceral efferent (GVE) column - from the superior salivatory nucleus, is parasympathetic to the lacrimal gland, submandibular and sublingual salivary glands.

The special visceral efferent column does not include the dorsal nucleus of the vagus.

The special visceral efferent column contains neurons innervating muscles developed from the pharyngeal arches:

• Motor nucleus of V nerve - muscles of mastication
• Motor nucleus of VII nerve - muscles of facial expression
• Nucleus ambiguus (IX, X, XI) - stylopharyngeus, pharyngeal, external laryngeal, oesophageal striated muscles, muscles of the soft palate, sternocleidomastoid, and trapezius.

The dorsal nucleus of vagus contains neurons from the general visceral efferent column and it sends parasympathetic fibers to the glands and smooth muscles in the pharynx, larynx, thoracic and abdominal viscera.

Nucleus ambiguus does not belong to the general visceral efferent (GVE) column.

The general visceral efferent columns contain nuclei of parasympathetic cranial nerves:

• III - Edinger-Westphal nucleus
• VII - Superior salivatory nucleus
• IX - Inferior salivatory nucleus
• X - Dorsal motor nucleus of vagus.

Nucleus ambiguus belongs to the special visceral efferent (SVE) column.

The special visceral efferent column contains neurons innervating muscles developed from the pharyngeal arches:

• Motor nucleus of V nerve- muscles of mastication
• Motor nucleus of VII nerve- muscles of facial expression
• Nucleus ambiguus (IX, X, XI)- stylopharyngeus, pharyngeal, external laryngeal, oesophageal striated muscles, muscles of the soft palate, sternocleidomastoid, and trapezius.

Oculomotor nerve nuclei are present in both general somatic efferent (GSE) and general visceral efferent (GVE) columns in the brainstem.

The fibers from the nucleus ambiguus emerge through the postero-lateral sulcus of the brainstem.

Nucleus ambiguus is made of cranial nerves IX, X, and XI.

The following table describes the components of the vagal nerve and the associated nuclei.

Component

Parasympath etic

Motor

Viscero-senso ry

Chemosensor y

Somatosensor y

Associated Nucleus Dorsal vagal nucleus

Nucleus ambiguus Nucleus tractus solitarius

Nucleus tractus solitarius Spinal nucleus of trigeminal

Innervated Structures

Autonomic ganglia of thorax and abdomen

Pharynx, larynx, palate

Pharynx, larynx, esophagus, t horacic and abdominal viscer a

Taste buds on epiglottis Outer ear canal, pinna, dura

The lateral rectus muscle is likely to be paralyzed as it is innervated by the VI cranial nerve, which emerges from the pontomedullary junction (PMJ).

Cranial nerves VI, VII, and VIII arise at the PMJ.

Extraocular muscles are innervated by the III, IV, and VI cranial nerves. The superior oblique is innervated by CN IV, the lateral rectus by CN VI, and all the other muscles by CN III.

The trochlear nerve is the only nerve that exits the brainstem on the dorsal surface and thus can be injured in this patient.

All other cranial nerves exit the brainstem from the ventral surface.

The structure marked is the olive. The hypoglossal nerve emerges anterior to the olive, from the groove between the pyramid and the olive—anterolateral sulcus.

The olivary bodies are rounded, oval prominences on the surface of the medulla oblongata in the brain. Nerve fibers in the olivopontocerebellar pathway connect the olives to the pons and cerebellum.

The trigeminal nerve is the thickest cranial nerve. The trochlear nerve is the most slender cranial nerve.

The trochlear nerve does not carry parasympathetic fibers.

The cranial nerves carrying parasympathetic fibers are listed below:

Cranial nerve Oculomotor(III) Facial(VII)

Glossopharyngeal(I X)

Vagus(X)

Associated Ganglion Ciliary ganglion

Pterygopalatine and subman dibular ganglion

Otic ganglion Visceral ganglions

The image shows oculomotor nerve palsy. The nerve to inferior oblique carries parasympathetic fibers to the ciliary ganglion, not the nerve to inferior rectus.

Course of the oculomotor nerve:

• The nerve lies on the anterior surface of the midbrain in between the posterior cerebral artery and the superior cerebellar artery in the interpeduncular fossa.
• It then passes to the middle cranial fossa along the lateral dural wall of the cavernous sinus and divides into superior and inferior in its anterior part.
• It enters the superior orbital fissure through the common tendinous ring.

The abducens nerve forms the content of Dorello's canal and hence is susceptible to injury in this case.

Dorello's canal is located at the petrous apex of the temporal bone and is formed by the petrosphenoidal/petroclinoid/Gruber's ligament.

Leptomeninges refer to the arachnoid mater and pia mater. Terminologies for meninges:

• Outer Pachymeninx - Dura mater
• Inner Leptomeninges - Arachnoid + Pia mater (L-AP)

Radiological importance: Pachymeningeal and leptomeningeal enhancement may be diffuse or focal and can aid in the diagnosis of some conditions.

Conditions that may show meningeal enhancement:

• Meningitis
• Encephalitis
• Tumors
• Metastasis
• Inflammatory vasculitides
• Post-ictal
• Post-traumatic and post-operative scarring

The MRI of medulloblastoma below shows leptomeningeal enhancement (arrows).

Both the endosteal and meningeal layers contain fibroblasts, but only the endosteal layer contains osteoblasts.

The dura mater is made of the following 2 layers:

The dural venous sinuses are present between the meningeal and the endosteal layer of the dura mater.

Endosteal layer

Periosteum of the skull bones

Contains fibroblasts and oste oblasts

Not continuous with the spin al dura mater

Meningeal layer Dura mater proper

Contains only fibroblasts (no osteoblasts)

Continuous with the spinal d ura mater

It forms 4 septa that divide t he cranial cavity into spaces r estricting the displacement of the brain

The four septa that divide the cranial cavity into freely communicating spaces are:

• Falx cerebri
• Tentorium cerebelli
• Falx cerebelli
• Diaphragma sellae

The superior sagittal sinus is present in the falx cerebri. Falx cerebri is a sickle-shaped dura mater fold that seperates the two cerebral hemispheres. The superior sagittal sinus runs along its upper fixed margin, the inferior sagittal sinus runs along its lower free margin, and the straight sinus runs along its attachment to the tentorium cerebelli.

Option A: Tentorium cerebelli separates the cerebellum from the occipital lobes of the cerebrum.

Options B and D: Falx cerebelli separates the cerebellar hemispheres and contains the occipital sinus.

The image below shows the falx cerebri and tentorium cerebelli.

The image below shows the dural folds.

The marked structure is the cranial dura mater and this structure is not innervated by facial nerve branches.

The innervation of the cranial dura mater is derived mainly from:

• The three divisions of the trigeminal nerve
• C2 and C3 spinal nerves
• Cervical sympathetic trunk.

The dura of the anterior cranial fossa is supplied by all three branches of the trigeminal nerve. The nerves involved are:

• Ophthalmic division - anterior and posterior ethmoidal nerves
• Maxillary division - nervus meningeus medius
• Mandibular division - nervus spinosus

Evagination of the lower layer of the tentorium cerebelli at the petrous apex is called Meckel's cave.

It is a dural recess in the middle cranial fossa that houses the èasserian ganglion and proximal rootlets of the trigeminal nerve.

The sinus marked in the image is the sigmoid sinus. It drains from the transverse sinus.

It passes through an S-shaped groove in the mastoid process of the temporal bone, courses over the êugular process of the occipital bone, and emerges posterior to the êugular foramen.

The sigmoid sinus receives tributaries:

• Mastoid emissary veins
• Condylar emissary veins
• Venous plexus of the hypoglossal canal
• Inferior cerebellar veins
• ‘nnamed tributaries from the pons and medulla

It joins the inferior petrosal sinus to form the internal jugular vein.

Sigmoid/lateral sinus thrombosis occurs as a complication of ear or mastoid infection.

The abducens nerve is likely to be affected first.

The abducent nerve runs within the cavernous sinus in close proximity to the internal carotid artery. Therefore, an aneurysm of the ICA may impinge on the nerve and may lead to sixth nerve palsy.

The oculomotor nerve, trochlear nerve, and the ophthalmic division of the trigeminal nerve lie in the lateral wall of the cavernous sinus. They are involved in the pathologies of the sinus much later.

The maxillary division of the trigeminal nerve does not run through the cavernous sinus or its lateral wall. It passes beneath the dura of the middle cranial fossa underneath the cavernous sinus.

The history and examination findings suggest cavernous sinus thrombosis.

The deep middle cerebral vein is not a tributary of the cavernous sinus. It joins the anterior cerebral and striate veins to form the basal vein.

The tributaries of cavernous sinus are:

• From orbit - superior and inferior ophthalmic veins
• From cranium - sphenoparietal sinus, superficial middle cerebral vein, inferior cerebral vein.
• The cavernous sinus drains into:
• Transverse sinus via superior petrosal sinus
• Internal jugular vein via inferior petrosal sinus
• Pterygoid plexus of veins via emissary veins
• Superior ophthalmic vein

The contents of the cavernous venous sinus include:

• Cavernous segment of the internal carotid artery
• Perivascular sympathetic plexus
• Abducens nerve (running through the Dorello’s canal)
• Oculomotor nerve, trochlear nerve, and the ophthalmic division of the trigeminal nerve as part of the lateral wall.