Extraocular Muscles PDF

BLOCK 4 Explain the attachments, actions and nerve supply of extraocular muscles and levator palpebrae superioris Extraocular Muscles: 1. Medial Rectus Muscle: Attachments: Originates from the common tendinous ring (annulus of Zinn) and inserts into the medial aspect of the eyeball. Action: Primaril...

BLOCK 4 Explain the attachments, actions and nerve supply of extraocular muscles and levator palpebrae superioris Extraocular Muscles: 1. Medial Rectus Muscle: Attachments: Originates from the common tendinous ring (annulus of Zinn) and inserts into the medial aspect of the eyeball. Action: Primarily responsible for adduction, i.e., moving the eye inward toward the nose. 2. Lateral Rectus Muscle: Attachments: Originates from the common tendinous ring and inserts into the lateral aspect of the eyeball. Action: Primarily responsible for abduction, i.e., moving the eye outward away from the nose. 3. Superior Rectus Muscle: Attachments: Originates from the common tendinous ring and inserts into the superior aspect of the eyeball. Action: Primarily responsible for elevation and adduction, i.e., moving the eye upward and inward. 4. Inferior Rectus Muscle: Attachments: Originates from the common tendinous ring and inserts into the inferior aspect of the eyeball. Action: Primarily responsible for depression and adduction, i.e., moving the eye downward and inward. 5. Superior Oblique Muscle: Attachments: Originates from the body of the sphenoid bone, passes through a fibrocartilaginous sling called the trochlea, and inserts into the superior aspect of the eyeball. Action: Primarily responsible for depression and abduction, i.e., moving the eye downward and outward. 6. Inferior Oblique Muscle: Attachments: Originates from the maxillary bone near the medial orbital rim and inserts into the inferior aspect of the eyeball. Action: Primarily responsible for elevation and abduction, i.e., moving the eye upward and outward. Nerve Supply of Extraocular Muscles: All extraocular muscles, except for the superior oblique (innervated by the trochlear nerve, CN IV), are innervated by the oculomotor nerve (CN III). The oculomotor nerve also supplies the levator palpebrae superioris. Levator Palpebrae Superioris Muscle: 1. Attachments: Originates from the lesser wing of the sphenoid bone above the optic canal. Inserts into the upper eyelid. 2. Action: Elevates the upper eyelid, allowing for opening of the eye (palpebral fissure). 3. Nerve Supply: Innervated by the oculomotor nerve (CN III), specifically its superior division. Explain the applied anatomy of contents of the orbit. 1. Eyeball (Globe): The eyeball is the primary structure within the orbit and is responsible for vision. It is composed of several layers, including the outer fibrous layer (sclera and cornea), middle vascular layer (choroid, ciliary body, and iris), and inner neural layer (retina). The optic nerve (CN II) enters the orbit through the optic canal and connects the eyeball to the brain, transmitting visual information to the brain for processing. 2. Extraocular Muscles: The orbit contains six extraocular muscles responsible for moving the eyeball in different directions. These muscles include the medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique muscles. They are innervated by the oculomotor nerve (CN III), trochlear nerve (CN IV), and abducens nerve (CN VI), which control eye movements. 3. Optic Nerve (CN II): The optic nerve transmits visual information from the retina to the brain. It enters the orbit through the optic canal, along with the ophthalmic artery. The optic nerve is surrounded by sheaths of dura mater, arachnoid mater, and pia mater, forming the optic nerve meninges. 4. Blood Vessels: The orbit contains several blood vessels that supply oxygen and nutrients to the eye and surrounding tissues. The ophthalmic artery, a branch of the internal carotid artery, provides arterial supply to the orbit, while the ophthalmic vein drains venous blood from the orbit. 5. Lacrimal Gland and Ducts: The lacrimal gland is located in the superolateral aspect of the orbit and produces tears that lubricate the surface of the eyeball. Tears drain from the eye through lacrimal puncta, located medially on the upper and lower eyelids, into the lacrimal canaliculi, lacrimal sac, and nasolacrimal duct, which empties into the nasal cavity. 6. Nerves and Sensory Structures: Sensory nerves, including branches of the ophthalmic nerve (CN V1), provide sensory innervation to the orbit, eyelids, and cornea. Structures such as the ciliary ganglion and sympathetic and parasympathetic nerve fibers also play roles in regulating pupillary size, accommodation, and tear production. Explain the applied anatomy of pons 1. Location and External Features: The pons is located between the midbrain (superiorly) and the medulla oblongata (inferiorly). It appears as a bulge on the ventral aspect of the brainstem, forming part of the anterior aspect of the brainstem. 2. Internal Structures: The pons consists of various nuclei, tracts, and fiber bundles that serve different functions. It contains ascending and descending fiber tracts that relay sensory and motor information between the spinal cord, cerebellum, and higher brain centers. Important structures within the pons include the pontine nuclei, corticospinal tracts, pontocerebellar fibers, and pontine respiratory centers. 3. Cranial Nerve Nuclei: The pons houses several cranial nerve nuclei, including the trigeminal (CN V), abducens (CN VI), facial (CN VII), and vestibulocochlear (CN VIII) nuclei. These nuclei are responsible for controlling various motor and sensory functions of the face, eyes, and ears. 4. Role in Motor Control: The pons is involved in coordinating voluntary motor movements, particularly those related to facial expression, eye movement, and mastication. It serves as a relay center for signals traveling between the cerebral cortex, basal ganglia, cerebellum, and spinal cord, contributing to motor planning and execution. 5. Role in Respiratory Control: The pons contains respiratory centers that help regulate breathing patterns and respiratory rhythm. These centers work in coordination with the medullary respiratory centers to adjust breathing rate and depth in response to changing oxygen and carbon dioxide levels in the blood. 6. Vascular Supply: Blood supply to the pons is primarily provided by branches of the basilar artery, including the pontine branches. Interruption of blood flow to the pons, such as in the case of a pontine stroke or ischemia, can lead to significant neurological deficits and lifethreatening complications. Explain and illustrate the internal features of the transverse section of the pons at the level of (a) Lower part (level of facial colliculus) (b) Upper part Transverse Section of the Pons - Lower Part (Level of Facial Colliculus): 1. Cranial Nerve Nuclei: Facial Nucleus: Located laterally, it is responsible for controlling the muscles of facial expression. Abducens Nucleus: Located medially, it innervates the lateral rectus muscle of the eye. 2. Corticospinal Tracts: Descending motor fibers originating from the primary motor cortex (precentral gyrus) pass through the pons. At this level, the corticospinal tracts are descending towards the medulla oblongata, where they decussate (cross over) to control voluntary movements on the opposite side of the body. 3. Pontine Tegmentum: Consists of ascending sensory pathways and descending motor pathways. Contains the pontine reticular formation, involved in regulating arousal and consciousness. 4. Pontine Nuclei: Located dorsally and laterally within the pontine tegmentum. Relay sensory information from the cerebrum to the cerebellum via the middle cerebellar peduncles. 5. Formatio Reticularis: A network of neurons scattered throughout the brainstem, including the pons. Plays a role in regulating sleep-wake cycles, autonomic functions, and motor control. 6. Superior Cerebellar Peduncles: Fiber bundles connecting the cerebellum to the midbrain and thalamus. Carry efferent signals from the deep cerebellar nuclei to the thalamus and cerebral cortex. Transverse Section of the Pons - Upper Part: 1. Cranial Nerve Nuclei: Trigeminal Nucleus: Located laterally, it receives sensory input from the face and controls muscles involved in chewing. Vestibulocochlear Nuclei: Located dorsolaterally, they receive auditory and vestibular input. 2. Corticospinal Tracts: At this level, the corticospinal tracts are descending towards the medulla oblongata, where they eventually synapse with lower motor neurons. 3. Superior Cerebellar Peduncles: Traverse through the upper part of the pons, connecting the cerebellum to the midbrain and thalamus. 4. Reticular Formation: Extends throughout the brainstem, including the pons. Plays a role in regulating arousal, attention, and autonomic functions. 5. Ascending Sensory Pathways: Includes the medial lemniscus, carrying tactile and proprioceptive information, and the spinothalamic tract, carrying pain and temperature sensations. 6. Descending Motor Pathways: Comprise the corticospinal tracts, conveying voluntary motor commands from the cerebral cortex to the spinal cord. Explain the applied anatomy of pons 1. Cranial Nerve Nuclei: The pons contains nuclei of several cranial nerves, including the trigeminal (V), abducens (VI), facial (VII), and vestibulocochlear (VIII) nerves. Understanding the anatomy of these nuclei is crucial for diagnosing and managing conditions affecting facial sensation, eye movement, facial expression, and hearing. 2. Respiratory Centers: The pons contains respiratory centers that regulate breathing patterns and respiratory rhythm. Dysfunction of these centers can lead to respiratory disorders such as central sleep apnea or respiratory failure. 3. Corticospinal Tracts: Descending motor fibers from the cerebral cortex pass through the pons as part of the corticospinal tracts. Lesions or damage to these tracts within the pons can result in motor deficits such as weakness or paralysis on the contralateral side of the body. 4. Ascending Sensory Pathways: Sensory pathways carrying tactile, proprioceptive, and pain sensations ascend through the pons. Disruption of these pathways can lead to sensory deficits or abnormal sensations. 5. Reticular Formation: The pons is part of the reticular formation, a network of neurons involved in regulating arousal, consciousness, and attention. Dysfunction of the reticular formation can result in altered levels of consciousness or coma. 6. Vascular Supply: The pons receives blood supply from branches of the basilar artery, including the pontine branches. Ischemia or infarction of these vessels can lead to pontine strokes, causing neurological deficits such as weakness, sensory loss, or cranial nerve dysfunction. 7. Sleep-Wake Regulation: The pons is involved in regulating sleep-wake cycles, along with other brainstem structures. Dysfunction of the pons can disrupt sleep patterns and lead to sleep disorders such as insomnia or hypersomnia. Explain the boundaries of choroid fissure of lateral ventricle and interventricular foramen Choroid Fissure of Lateral Ventricle: The choroid fissure is a cleft-like opening located in the roof of the lateral ventricles, extending from the interventricular foramen anteriorly to the posterior end of the lateral ventricle. It is where the choroid plexus attaches to the ventricular wall. The boundaries of the choroid fissure include: 1. Anterior Boundary: The interventricular foramen (foramen of Monro) marks the anterior boundary of the choroid fissure. This foramen connects the lateral ventricles to the third ventricle in the midline. 2. Posterior Boundary: The posterior end of the lateral ventricle forms the posterior boundary of the choroid fissure. This region extends backward and downward toward the occipital horn of the lateral ventricle. 3. Medial Boundary: The medial boundary of the choroid fissure is formed by the septum pellucidum, a thin membrane that separates the two lateral ventricles in the midline. 4. Lateral Boundary: The lateral boundary is formed by the fornix, a C-shaped bundle of white matter fibers that arches over the thalamus. The choroid plexus, a specialized structure that produces cerebrospinal fluid, is attached along the inner surface of the choroid fissure. Interventricular Foramen (Foramen of Monro): The interventricular foramen is a narrow channel that connects the lateral ventricles to the third ventricle in the midline. It allows for the flow of cerebrospinal fluid between these ventricles. The boundaries of the interventricular foramen include: 1. Anterior Boundary: The anterior boundary of the interventricular foramen is formed by the column of the fornix, which is a paired structure of white matter. 2. Posterior Boundary: The posterior boundary is formed by the anterior surface of the thalamus, a paired gray matter structure located deep within the brain. 3. Superior Boundary: The roof of the interventricular foramen is formed by the tela choroidea, a thin membrane that covers the foramen and is continuous with the choroid plexus of the lateral ventricles. 4. Inferior Boundary: The floor of the interventricular foramen is formed by the hypothalamic sulcus, which separates the thalamus from the hypothalamus, a region important for controlling various physiological functions. Explain the applied anatomy of the lateral ventricle 1. Location and Structure: The lateral ventricles are located within the cerebral hemispheres, separated by the septum pellucidum in the midline. Each lateral ventricle has four main components: the anterior horn, body, atrium, and posterior (occipital) horn. The inferior horn extends into the temporal lobe. The lateral ventricles communicate with the third ventricle via the interventricular foramen (foramen of Monro). 2. Functions: The lateral ventricles contain cerebrospinal fluid (CSF), which provides buoyancy and protection for the brain, removes waste products, and helps regulate intracranial pressure. CSF circulation within the ventricles facilitates the exchange of nutrients and waste products between the brain and bloodstream. 3. Boundaries and Landmarks: Anterior Horn: Extends anteriorly from the interventricular foramen and lies within the frontal lobe. It is bounded laterally by the head of the caudate nucleus. Body: Forms the central portion of the lateral ventricle, situated within the parietal lobe. It is bounded laterally by the body of the caudate nucleus and the thalamus. Atrium: Enlarged portion of the lateral ventricle where the body meets the posterior (occipital) horn. It is adjacent to the atrium of the temporal horn. Posterior (Occipital) Horn: Extends posteriorly and medially into the occipital lobe. It is bounded medially by the splenium of the corpus callosum. 4. Clinical Considerations: Hydrocephalus: Enlargement of the lateral ventricles due to an imbalance between CSF production and absorption or obstruction of CSF flow. Ventriculomegaly: Enlargement of the lateral ventricles without increased intracranial pressure, often seen in neurodevelopmental disorders or neurodegenerative diseases. Intraventricular Hemorrhage: Bleeding into the lateral ventricles, often seen in premature infants with fragile blood vessels. Tumors: Tumors originating within the ventricles or adjacent structures can obstruct CSF flow and cause ventricular enlargement. 5. Imaging Modalities: Magnetic resonance imaging (MRI) and computed tomography (CT) scans are commonly used to visualize the lateral ventricles and assess their size, shape, and internal structures. These imaging modalities help in diagnosing ventricular abnormalities, identifying lesions, and planning surgical interventions such as ventriculostomy or ventriculoperitoneal shunting. Describe formation, circulation and absorption of CSF Formation of CSF: 1. Choroid Plexus: The majority of CSF is produced by the choroid plexus, specialized structures located within the ventricles of the brain. 2. Ultrafiltration: Blood plasma is filtered through the choroid plexus epithelial cells, where water, ions, and small molecules diffuse into the ventricles. 3. Secretion: Choroid plexus cells actively secrete additional substances, such as electrolytes and proteins, into the CSF. 4. Composition: CSF has a composition similar to plasma but with lower protein and glucose levels and higher concentrations of sodium and chloride ions. Circulation of CSF: 1. Lateral Ventricles: CSF is produced primarily in the lateral ventricles by the choroid plexus. 2. Third Ventricle: CSF flows from the lateral ventricles into the third ventricle via the interventricular foramina (foramina of Monro). 3. Cerebral Aqueduct: CSF passes from the third ventricle through the cerebral aqueduct (aqueduct of Sylvius) into the fourth ventricle. 4. Fourth Ventricle: CSF in the fourth ventricle can exit the ventricular system through three openings: the median aperture (foramen of Magendie) and two lateral apertures (foramina of Luschka). 5. Subarachnoid Space: CSF flows into the subarachnoid space surrounding the brain and spinal cord, where it provides mechanical support and buoyancy, and helps remove waste products. Absorption of CSF: 1. Arachnoid Granulations (Villi): CSF is absorbed back into the bloodstream primarily through arachnoid granulations, also known as arachnoid villi. 2. Location: Arachnoid granulations protrude into the dural venous sinuses, such as the superior sagittal sinus or transverse sinuses. 3. Pressure Gradient: CSF flows from the subarachnoid space through the arachnoid granulations into the venous sinuses, driven by a pressure gradient between the CSF and venous systems. 4. Bulk Flow: CSF absorption occurs via bulk flow, where fluid and solutes are transported across the arachnoid membrane into the bloodstream. 5. Lymphatic Drainage: Some CSF is also absorbed by lymphatic vessels within the brain and spinal cord, contributing to the overall clearance of waste products and metabolic byproducts. Explain the location, boundaries, communications of 4th ventricle and name its recesses Location: The fourth ventricle is situated within the posterior cranial fossa of the skull, between the brainstem and the cerebellum. It extends from the cerebral aqueduct (aqueduct of Sylvius) superiorly to the obex, a small depression in the medulla oblongata, inferiorly. Boundaries: 1. Anterior: The anterior boundary of the fourth ventricle is formed by the posterior surface of the pons and the superior medulla. 2. Posterior: The posterior boundary is formed by the cerebellum, specifically the superior vermis and the inferior surface of the cerebellar hemispheres. 3. Lateral: The lateral boundaries are formed by the superior cerebellar peduncles, which connect the cerebellum to the brainstem. 4. Roof: The roof of the fourth ventricle is formed by the dorsal surface of the cerebellum, specifically by the superior medullary velum and the inferior medullary velum. Communications: The fourth ventricle communicates with the third ventricle via the cerebral aqueduct (aqueduct of Sylvius), which connects the third and fourth ventricles, allowing for the flow of cerebrospinal fluid (CSF) between them. CSF can exit the fourth ventricle through three openings: 1. Median Aperture (Foramen of Magendie): Located at the inferior end of the fourth ventricle, allowing CSF to enter the subarachnoid space of the brainstem. 2. Lateral Apertures (Foramina of Luschka): Two openings located laterally on each side of the fourth ventricle, allowing CSF to exit into the subarachnoid space around the cerebellum. Recesses: The fourth ventricle contains several recesses or extensions that project from its main cavity: 1. Superior Medullary Velum Recess: Located between the superior medullary velum and the superior cerebellar peduncles. 2. Inferior Medullary Velum Recess: Located between the inferior medullary velum and the posterior surface of the medulla. 3. Lateral Recesses: Extend laterally from the main cavity of the fourth ventricle toward the foramina of Luschka.