Cranial Cavity PDF

Cranial Cavity DPM Program Learning Objectives: 1.Describe the structural relationships of the head within the context of sectional anatomy. 3.0 2. Describe the osteological features of the skull. 3.0 3. Identify the sutures of the skull. 3.0 4. Define fontanel. Locate and give the times of closure...

Cranial Cavity DPM Program Learning Objectives: 1.Describe the structural relationships of the head within the context of sectional anatomy. 3.0 2. Describe the osteological features of the skull. 3.0 3. Identify the sutures of the skull. 3.0 4. Define fontanel. Locate and give the times of closure of the anterior and posterior fontanels. 3.0 5. Identify the position, palpable and imaging landmarks of the bones of the skull and calvaria. 3.0 6. Describe the boundaries, walls, floors, and contents of the cranial fossae. 3.0 7. Describe the cranial foramina and fissures, listing the structures that each transmits. 3.0 8. Identify the major grooves for the intracranial venous sinuses. 3.0 9. Describe the relationships of three meningeal coverings of the brain. 3.0 10. Describe the dural reflections and dural venous sinuses. 3.0 11. Differentiate the appearance of extradural and subdural hematomas on transverse CT scans. 3.0 12. Describe how fractures of the cribriform plate can result in meningitis and anosmia. 3.0 13. Explain the clinical significance of emissary veins. 3.0 14. Describe each cranial nerve in terms of: 4.0 a. name and Roman numeral b. where emerges from CNS c. associated foramina d. functional components e. ganglia f. course and distribution Cross section through the thalamus Introduction to the Skull The skull is made up of 22 bones and is attached to the torso by the neck. 21 of these bones are firmly bound together by sutures and are considered immovable. One, the mandible, is movable and articulates with the remainder of the skull. The skull is comprised of the: 1) The Cranial Skeleton (neurocranium) houses: -the brain, meninges, and vasculature of the brain Made up of the: -cranial base upon which the brain sits -calvaria the protective roof of the skull 2) Facial Skeleton (viscerocranium ) -the facial skeleton formed by a total of fourteen bones 3 Introduction to the Brain The brain is a component of the central nervous system along with the spinal cord. It is an incredibly complex vital organ and is responsible for controlling and monitoring the systems of the body. It is located inside the skull and is protected by the neurocranium, the meninges and the cerebrospinal fluid Cerebral hemispheres The brain is made up of three major regions: 1. cerebrum 2. cerebellum 3. brainstem Parietal lobe Frontal lobe Occipital lobe The ventricles of the brain produce and circulate cerebrospinal fluid. This fluid nourishes and protects the brain. The grooves and ridges found in the brain are know as gyri and sulci. Temporal lobe There are two main types of tissue known as gray and white matter. Cerebellum Pons Medulla oblongata 4 Cranial Skeleton PARIETAL (2) FRONTAL (1) SPHENOID (1) ETHMOID (1) TEMPORAL (2) OCCIPITAL (1) 5 Bony Features of the Skull Ethmoid Bone: -Crista Galli -Cribiform plate Occipital bone Sella turcica Foramen magnum External Occipital protuberance Groove for sigmoid sinus Mastoid process Styloid process NOTE: In between the mastoid process and styloid process is the stylomastoid foramen which transmits the facial n. (CN VII) Groove for transverse sinus Internal occipital protuberance 6 Bones of the Cranial Fossae The cranial fossae are a series of step-like depressions within the internal surface of the cranial cavity which allows for the cerebrum, cerebellum, and brainstem to rest against the skull. Anterior cranial fossa -Cribriform plate of the ethmoid bone -Frontal lobes Anterior cranial fossa Sphenoidal ridge Middle cranial fossa -Optic Canal, Superior orbital fissure, Foramen Rotundum, Foramen Ovale, Foramen spinosum -Temporal lobes -Pituitary gland Posterior cranial fossa -Internal auditory meatus, Jugular foramen, Hypoglossal canal, Foramen magnum -Cerebellum -Pons -Medulla Middle cranial fossa Petrous ridge Posterior cranial fossa 7 **Divisions of CN V exit owing to Standing Room Only Foramina of the Cranial Base (Superior View) Hypoglossal canal: • [XII Hypoglossal nerve 8 Sutures of the Skull Most of the joints of the skull are fixed fibrous joints, called sutures. Sutures are where the edges of the bones firmly fit together and are united by connective tissue, called periosteum. CORONAL SUTURE The suture where the parietal bones articulate with the frontal bone. LAMBOIDAL SUTURE The suture where the parietal bones articulate with the occipital bone. SAGITTAL SUTURE The suture where the parietal bones articulate with each other. SQUAMOSAL SUTURE -Laterally located it is the suture where the parietal bones articulate with the temporal bones. PTERION -Lateral aspect of the skull where the parietal, frontal, greater wing of the sphenoid, and the squamous portion of the temporal bone articulate -Important clinically because the pterion represents one of the thinnest areas of the skull, therefore, it is prone to fractures. The anterior branch of the MIDDLE MENINGEAL ARTERY lies in a groove on the internal aspect of the pterion. BREGMA -The junction between the sagittal and coronal sutures. -Membranous at birth to accommodate the rapidly enlarging postnatal brain, forming the ANTERIOR FONTANELLE (i.e., ―soft spot; typically closes by the end of the 2nd year). LAMBDA -The junction between the sagittal and lambdoidal sutures. -Membranous at birth to accommodate the rapidly enlarging postnatal brain, forming the POSTERIOR FONTANELLE (i.e., the other ―soft spot; typically closes by the 2nd – 9th month). Bregma Coronal suture Sagittal suture Lambda Lambdoid suture Coronal suture Sagittal suture Squamosal suture Lambdoid suture Pterion -The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity. Anterior fontanelle Posterior fontanelle In the fetus and newborn, large membranous and ossified gaps (fontanelles) between the bones of the skull, particularly between the large flat bones that cover the top of the cranial cavity. (allow the skull to deform for easier passage through the birth canal) 10 Cranial Meninges DURA MATER (derived from mesoderm) -toughest layer -has infoldings known as meningeal infoldings -forms small cavities known as sinuses (responsible for draining venous blood out of the brain -Adherent to periosteum of the endocranium throughout most of its course and is, therefore, considered to be a two-layered structures with an inner meningeal layer and outer periosteal layer - Innervation: Sensitive to pain (one cause of headaches) - anterior and middle cranial fossae by branches of V1, V2, V3 - posterior cranial fossa by V1, C2, C3, (CN X) - Blood supply: - middle meningeal artery – anterior division crosses the pterion - small branches of occipital, ophthalmic and vertebral arteries ARACHNOID MATER (derived from neural crest) -soft, translucent, avascular membrane -has a web-like appearance -this layer is tightly attached to the inner layer of the dura mater due to the presence of the CSF in the subarachnoid space -excess CSF drains to the venous system via arachnoid granulations PIA MATER (derived from neural crest) -thin, delicate membranous layer -highly vascularized -tightly adhered to the surface of the brain (gyria and sulci) Meningeal Spaces Subarachnoid space: - located between the arachnoid and pia mater where CSF flows Epidural space: -potential space between dura mater and skull/vertebral column containing fat and blood vessels. -site of blood collection associated with middle meningeal artery injury 11 Pia mater Arachnoid mater Skull Intracranial venous structure (superior sagittal sinus) Dura mater Inner meningeal layer of dura mater Outer periosteal layer of dura mater Subarachnoid space Dural partition (falx cerebri) 12 Cranial Meninges (Superior View) Anterior Periosteal layer of dura Meningeal layer of dura Arachnoid granulations – prolongations of arachnoid that protrude through the meningeal layer of the dura mater into the dural venous sinuses. They provide for absorption of excess CSF into the venous system. Arachnoid Superior sagittal sinus Anterior Posterior Branches of middle meningeal artery and vein Arachnoid granulations Opened Closed Posterior At the foramen magnum (and all other cranial foramina) the periosteal layer of dura becomes continuous with the periosteum on the external surface of the cranium NOTE on EMISSARY VEINS -Veins which connect the dural venous sinuses within the cranium with veins external to it. They are valveless and, as a consequence, may conduct blood either inward or outward depending upon the pressures existing in the sinuses and in the external veins. These veins pass through small foramina in the skull (e.g., parietal foramina) at right angles to the layers of the scalp. Examples of major emissary veins include the superior ophthalmic vein and parietal emissary veins. The clinical significance of emissary veins is that they provide another route by which infection can spread internally to the dural sinuses from the outside (e.g., from the scalp). 13 Dural Infoldings The dural infoldings are partitions or reflections of the inner meningeal dura mater. They are located between the large gaps in the brain known as fissures. Superior sagittal sinus Straight sinus Crista galli of the ethmoid bone Pituitary gland FALX CEREBRI -separates the left and right cerebral hemispheres. -anteriorly attaches to the frontal crest of the frontal bone and the crista galli of the ethmoid bone. -posteriorly attaches to the internal occipital protuberance TENTORIUM CEREBELLI -a horizontal sheet of meningeal dura mater separating the left and right occipital lobes of the cerebral hemispheres from the cerebellum -posteriorly attaches to the transverse ridge of the occipital bone FALX CEREBELLI -separates the left and right cerebellar hemisphere -superiorly continuous with the inferior portion of the tentorium cerebelli -posteriorly is attached to the internal occipital protuberance 14 15 Dural Venous Sinuses The dural venous sinuses are endothelial lined spaces formed between the meningeal and periosteal layers of the dura. These sinuses are important for draining blood from brain the back into the internal jugular vein. -these dural venous sinuses drain blood from cerebral veins and receive CSF from arachnoid granulations Venous drainage of the brain: -cerebral vascular venous drainage occurs via small venous channels which form cerebral veins that empty into the internal jugular vein -small vessels within the brain form the cerebral veins, which ascend vertically and pierce the periosteal and meningeal layer of the dura to drain into the nearest dural venous sinus -the venous drainage of the brain has a superficial division and a deep division: -the superficial and deep divisions of the venous drainage meet up at the posterior aspect of the brain at the confluence of the sinuses. The confluence collects blood from the brain and sends it back down and out through the skull by the bilateral transverse sinuses. -the blood will flow from the transverse sinuses into the S-shaped sigmoid sinuses before -blood then flows into the internal jugular vein via the jugular foramen Falx cerebri Falx cerebri Cavernous Sinues Superior sagittal sinus Tentorium cerebelli Tentorium cerebelli Inferior sagittal sinus Straight sinus Sigmoid sinus Confluence of sinus Straight sinus Transverse sinus Transverse sinus Sigmoid sinus Confluence of Sinuses Superior view Lateral view 17 Arterial Supply to the Brain The metabolic demand of the brain requires approximately 20% of the total oxygen consumed by the body. In order for the brain to meet the metabolic demand. Two pairs of major arteries----the internal carotid arteries and the vertebral arteries---provide the main supply of oxygenated blood to the brain. Circle of Willis -a loop of arteries at the base of the brain allowing for collateral circulations of the brain. 19 Blood Supply to the Head Vertebral a. External Carotid Artery Branches -Supply the structures of the face Internal Carotid Artery -Arises as a branch of the common carotid artery -Supplies the brain (frontal, temporal, and parietal lobe of the cerebrum along the midline Vertebral Artery -Arises from the subclavian artery bilaterally -Ascends up through the transverse foramina to the base of the skull traveling through the foramen magnum -Supplies the cerebellum, brainstem and occipital lobe of the cerebrum 21 Middle Meningeal Artery Middle Meningeal Artery MIDDLE MENINGEAL ARTERY -Gives arterial supply to the meninges -A branch of the maxillary artery -Enters the skull via the foramen spinosum -Provides blood supply to calvarium -Located superficial to the dura mater. -Tearing of the middle meningeal artery will result in epidural (extradural) hemorrhaging (i.e., epidural hematoma) which if undetected may be life threatening. 22 Cranial Nerves A group of 12 pairs of nerve fibers arise from the brain and connect to their respective nuclei within the brainstem. The cranial nerves carry nerve fibers which may be defined as purely motor, sensory or both. Cranial nerves refers or relates to the skull and these nerves are all going to pass through specific openings called foramina (pl. foramen) through the skull. The name of each of the cranial nerves tells us what the nerve does, the target structures it reaches, or sometimes the description of its path. 23 FUNCTIONAL COMPONENTS OF CRANIAL NERVES (MODALITIES/ FIBER TYPES) SENSORY GSA-General Somatic Afferent -sensory from somatic structures like skin and mucous membranes (pain, touch, pressure, temperature) GVA-General Visceral Afferent -sensation (ischemia, distension, cramping..) -somatic / visceral structures (carotid body & sinus, pharynx, some mucosa of pharynx, larynx & trachea...) SA -SPECIAL AFFERENT (includes SVA & SSA) -sensations of taste, hearing, equilibrium, smell, vision MOTOR GSE-General Somatic Efferent -motor to skeletal muscle (includes SVE a.k.a. BE = branchial motor) GVEp-General Visceral Efferent (only Parasympathetics are found in cranial nerves) -motor to cardiac muscle, smooth muscle & gland -presynaptic parasympathetic axons destined for structures in the head & neck will synapse in parasympathetic ganglia (otic, ciliary, pterygopalatine, submandibular) These parasympathetic ganglia are suspended from branches of CNV (Trigeminal nerve) and the postsynaptics will travel with postsynaptic sympathetics on the branches of trigeminal to reach their target organ. NOTE: -none of the cranial nerves are associated with preganglionic sympathetic neurons, but they may have postganglionic sympathetic fibers hitchhiking with them 24 One of the major differences between the organization of cranial nerves vs. spinal nerves is that there are several cranial nerves that contain only motor or only sensory fibers. Motor ONLY cranial nerves: -Oculomotor nerve (CNIII) (GVEp, GSE) -Trochlear nerve (CNIV) (GSE) -Abducens (CNVI) (GSE) -Spinal Accessory (CNXI) (GSE) -Hypoglossal (CNXII) (GSE) Special Sensory ONLY cranial nerves (SA): -Olfactory (CNI) -Optic (CNII) -Vestibulocochlear (CN VIII) The remaining cranial nerves are all ‘Mixed nerves’ -Each contains GSA and is associated with its own sensory ganglion. -Each contains SA for taste -Each contains motor innervation (GSE) to striated muscles developed from the pharyngeal arches*. -They may also contain other fiber types (GVA, GVEp). These cranial nerves are: -Trigeminal (CNV) -Facial (CNVII) -Glossopharyngeal (CNIX) -Va g u s ( C N X ) NOTE: This type of motor innervation is often called branchial motor, or, Special Visceral Efferent (SVE), however, it is functionally the same 25 as GSE we will continue to use GSE. CN I-Olfactory Nerve Functional Component SA (special afferent) Function Sensory (smell) Foramen Cribriform plate of ethmoid bone 26 Clinical Note of Olfactory Nerve The sense of smell is variable and decreases with age (degeneration of the olfactory nerve fibers increases with age). Lesions of the olfactory nerves results in the loss of the sense of smell (i.e., ANOSMIA). 1) May result from fractures of the cribriform plate which tear the olfactory fibers. Fractures of the cribriform plate may also result in the tearing of the meninges and leaking of CSF through the nose (i.e., CSF RHINORRHEA). 2) The central processes forming the olfactory nerve may also be sheared off as a result of a traumatic blow to the head (e.g., punches delivered to the head during fisticuff exhibitions [this explains why many boxers are anosmic] or the intimate contact between head and windshield during a front end collision). TESTING a. The sense of smell may be easily tested by having the patient close their eyes and sniff a strong odor (e.g., peppermint, oil of clove, coffee) through one nostril, then through the other. CN II-Optic Nerve Functional Component SA (sensory afferent) Function Sensory (vision) Foramen Optic canal 28 CN III-Oculomotor Nerve Functional Component GSE, GVE Function GSE: levator palpebrae superioris, superior rectus, inferior rectus, and inferior oblique muscles GVE: sphincter pupillae for pupillary constriction; ciliary muscles for accommodation of the lens for near vision Foramen Superior orbital fissure 29 CN IV-Trochlear Nerve Functional Component GSE Function GSE: Superior oblique muscle Foramen Superior orbital fissure 30 CN V-Trigeminal Nerve Functional Component: GSA, GSE Function -Mixed (sensory and motor) function Ophthalmic: sensations from the forehead, eyelids, and nose Maxillary: sensations from lower eyelid, upper lip, and cheek Mandibular: controls mastication Associated Ganglia: Trigeminal ganglia (GSA) Major Branches: V1 - Ophthalmic division (GSA) Nasociliary short ciliary Frontal Supraorbital Lacrimal V2 - Maxillary division (GSA) Infraorbital Nasopalatine Greater/lesser palatine V3 - Mandibular division (GSA, GSE) Auriculotemporal Lingual Inferior alveolar Mental Foramen Ophthalmic (V1): Superior orbital fissure Maxillary (V2): Foramen rotundum Mandibular (V3): Foramen ovale 31 CN V-Trigeminal Nerve Continued 32 GVE Innervation to Cranial Structures Postsynaptic parasympathetics will meet with postsynaptic sympathetics at these parasympathetic ganglia. These postsynaptic GVE fibers will travel with (‘hitchhike’ on) the branches of Trigeminal (CNV) to reach their target organs. The parasympathetic fibers begin in the central nervous system. The nerves supplying the head and neck are situated within four nuclei, located within the brainstem. Each nucleus is associated with a cranial nerve (the oculomotor, facial, glossopharyngeal and vagus nerves) – these nerves carry the parasympathetic fibers out of the brain. After leaving the brain, the parasympathetic fibers from each nuclei synapse in a peripheral ganglion (a collection of neuron cell bodies outside the CNS). These ganglia are typically located near to the target viscera. From the ganglia, post-ganglionic parasympathetic fibers continue to the organs in the head and neck, providing parasympathetic innervation. There are four parasympathetic ganglia located within the head – the ciliary, otic, pterygopalatine and submandibular. They receive fibers from the oculomotor, facial and glossopharyngeal nerves (the vagus nerve only innervates structures in the thorax and abdomen). Note: Most ganglia are associated with some sensory and sympathetic nerves – these do not synapse in the ganglia, they merely travel through it. 33 Trigeminal and its Relationship to Parasympathetic Ganglia Presynaptic parasympathetic axons destined for structures in the head & neck will synapse in parasympathetic ganglia (otic, ciliary, pterygopalatine, submandibular). Oculomotor nerve (III) These parasympathetic ganglia are ‘suspended’ from branches of CNV (Trigeminal nerve). Trigeminal nerve (V) Facial nerve (VII) Vagus nerve (X) Glossopharyngeal nerve (IX) 34 CN VI-Abducens Nerve Functional Component GSE Function GSE: lateral rectus muscle Foramen Superior orbital fissure 35 CN VII-Facial Nerve Functional Component GSE, GVEp, GSA, SA Function-Mixed (sensory and motor) GSE - muscles of facial expression (+ some) GVEp - sublingual and submandibular salivary glands, lacrimal gland, glands of nose & palate GSA - part of external auditory meatus SA - taste from anterior 2/3 of tongue and palate Associated ganglia: Geniculate (GSA, SA) Pterygopalatine (GVEp) Submandibular (GVEp) Major branches: Greater petrosal (GVEp) Chorda Tympani (GVEp, SA) GSE - Temporal, zygomatic, buccal, mandibular, cervical Foramen Internal acoustic meatus Stylomastoid foramen 36 CN VII-Facial Nerve Continued 37 CN VIII-Vestibulocochlear Nerve Functional Component: SA Function: Vestibular division: balance Cochlear division: hearing Foramen: Nerve leaves cranial cavity through internal acoustic meatus 38 CN IX-Glossopharyngeal Nerve Functional component: GSE, GVEp, GSA, GVA, SA Function GSE - stylopharyngeus m. GVE - parotid gland GSA - part of external ear, post tongue GVA - pharynx, carotid body & sinus (chemoreceptor & baroreceptor) SA - taste from posterior 1/3 of tongue Associated Ganglia: Otic ganglion (GVE) Foramen: Jugular foramen 39 CN X-Vagus Nerve Functional components GSE, GVEp, GSA, GVA, SA Function & GSE - most muscles of palate, pharynx and larynx GVE - smooth m. of trachea & glands of pharynx (in head neck) GSA - parts of External acoustic meatus and cranial dura GVA - pharynx, larynx (in head & neck) SA - taste from epiglottis & part of tongue Foramina Jugular foramen Major branches Superior laryngeal Internal laryngeal External laryngeal Recurrent laryngeal Pharyngeal 40 CN XI-Spinal Accessory Nerve Functional Component: GSE Function GSE: Sternocleidomastoid and trapezius muscle Foramen Jugular foramen 41 CN XII-Hypoglossal Nerve Functional component GSE Function GSE: Most extrinsic and all intrinsic muscles of the tongue Foramen Hypoglossal canal 42