Anatomy Summary PDF

10L Embryology: 1. Origin and Formation Time of Origin: 3rd week of development. Cell Type: Ectoderm. Process: Neurulation: The ectoderm thickens above the notochord to form the neural plate. Lateral edges elevate to create neural folds,...

10L Embryology: 1. Origin and Formation Time of Origin: 3rd week of development. Cell Type: Ectoderm. Process: Neurulation: The ectoderm thickens above the notochord to form the neural plate. Lateral edges elevate to create neural folds, with the central part forming the neural groove. Neural folds fuse in the midline, forming the neural tube. Fusion starts in the cervical region and extends both cranially and caudally. Cranial neuropore closes on day 25, while caudal neuropore closes around day 28. Upper neural tube develops into the brain; lower part forms the spinal cord. 2. Primary and Secondary Brain Vesicles Primary Brain Vesicles: 1. Prosencephalon (forebrain). 2. Mesencephalon (midbrain). 3. Rhombencephalon (hindbrain). Secondary Vesicles (5th week): Forebrain divides into: 1. Telencephalon (cerebral hemispheres). 2. Diencephalon (optic vesicles, thalamus, hypothalamus). Hindbrain divides into: 1. Metencephalon (pons and cerebellum). 2. Myelencephalon (medulla oblongata). 3. Spinal Cord Development Derived from the caudal neural tube. Differentiates into three zones: 1. Inner Ventricular Zone: Neuroepithelial cells give rise to neurons and macroglial cells. 2. Intermediate Mantle Layer: Forms gray matter of the spinal cord. 3. Outer Marginal Zone: Contains nerve fibers and becomes white matter. Neuroepithelial Cells: Differentiate into neuroblasts (neurons) and glioblasts (astrocytes, oligodendrocytes). 4. Neural Crest Cells Migrate from neural folds and give rise to: 1. Autonomic ganglia. 2. Sensory ganglia (spinal and cranial nerves). 3. Melanocytes. 4. Cells of the adrenal medulla. 5. Key Positional Changes Spinal Cord Length: During development, the spinal cord extends the full length of the embryo. At birth: Ends at L3. In adults: Ends at L1, with the cauda equina extending downward. 6. Brain Regions and Structures Hindbrain (Rhombencephalon): Myelencephalon: Forms the medulla; motor and sensory nuclei differentiate. Metencephalon: Develops into the cerebellum and pons. Midbrain (Mesencephalon): Contains motor nuclei for oculomotor and trochlear nerves. Superior and inferior colliculi arise from alar plates. Forebrain (Prosencephalon): Diencephalon: Forms thalamus, hypothalamus, and third ventricle. Telencephalon: Grows into cerebral hemispheres with frontal, parietal, temporal, and occipital lobes. 7. Clinical Anomalies Neural Tube Defects (NTDs): Caused by improper closure of neural folds. Examples: Spina Bifida Occulta: Mild defect, marked by a patch of hair. Spina Bifida Cystica: Severe defect with meninges or neural tissue protruding. Anencephaly: Failure of cranial neuropore closure, leading to brain malformation. Hydrocephalus: Accumulation of CSF due to blockage, enlarging the head.  11L Face and Scalp 1. Anatomy of the Scalp - Definition: The scalp consists of: - Skin (normally hair-bearing) - Subcutaneous tissue - Covers the calvaria. - Extension: - Posteriorly from the superior nuchal lines of the occipital bone. - Anteriorly from the supraorbital margin of the frontal bone. - Laterally to the superior temporal lines. 2. Structure of the Scalp - The scalp consists of five layers: 1. Skin 2. Connective tissue 3. Aponeurosis 4. Loose areolar tissue 5. Pericranium 3. Connective Tissue - Arteries are branches of the external and internal carotid arteries, with free anastomosis occurring between them. - Contains numerous arteries and superficial veins of the scalp. 4. Aponeurosis - Known as the epicranial aponeurosis. - A thin, tendinous sheet that unites the occipital and frontal bellies of the occipitofrontalis muscle. 5. Subaponeurotic Space - A potential space beneath the epicranial aponeurosis, occupied by loose areolar tissue. 6. Loose Areolar Tissue - Loosely connects the epicranial aponeurosis to the periosteum of the skull. 7. Muscles of the Scalp - Occipitofrontalis (Epicranius): Composed of four bellies, two occipital and two frontal, connected by an aponeurosis. - Nerve Supply: Supplied by branches of the facial nerve. 8. Sensory Nerve Supply of the Scalp - Main trunks of sensory nerves lie in the superficial fascia. 9. Arterial Supply of the Scalp - Rich blood supply nourishes hair follicles; small cuts can bleed profusely. 10. Venous Drainage of the Scalp - Scalp veins freely anastomose and connect to the diploic veins of the skull and intracranial venous sinuses via valveless emissary veins. 11. Skin of the Face - Thick, highly vascular, rich in sweat and sebaceous glands. - Receives the insertion of facial muscles. 12. Muscles of Facial Expression - Arranged around the eyes, nose, and mouth; have bony origins and insert into the skin of the face. - Supplied by branches of the facial nerve. 13. Main Muscles of the Face - Orbicularis oculi: Sphincter muscle of the eyelids. - Orbicularis oris: Sphincter muscle of the mouth. - Buccinator: Muscle of the cheek. 14. Arterial Supply of the Face - Supplied by the facial artery, superficial temporal artery, and other branches that provide nourishment. 15. Venous Drainage of the Face - Facial vein formed at the medial angle of the eye connects to the cavernous sinus, allowing for potential infection spread. 16. Lymph Drainage of the Face - Lymph from the forehead and anterior face drains into submandibular lymph nodes; lateral parts drain into parotid lymph nodes. 17. Nerve Supply of the Face - Supplied by the facial nerve and branches of the trigeminal nerve, providing both sensory and motor functions.  L12 Infratemporal Fossa 1. Definition of Infratemporal Fossa - The infratemporal fossa is a region located below and medial to the zygomatic arch, behind the maxilla, and deep to the ramus of the mandible. 2. Boundaries of the Infratemporal Fossa - Superficial (Lateral): Ramus of the mandible. - Deep (Medial): Lateral pterygoid plate. - Superior: Infratemporal surface of the greater wing of the sphenoid bone. - Anterior: Back of the maxilla. 3. Communications of the Infratemporal Fossa - With Temporal Fossa: Through a gap deep to the zygomatic arch. - With Cranial Cavity: Through foramen ovale, foramen spinosum, and foramen lacerum. - With Orbit: Through the inferior orbital fissure. - With Pterygopalatine Fossa: Through the pterygomaxillary fissure. 4. Contents of the Infratemporal Fossa - Lateral and medial pterygoid muscles, and the insertion of the temporalis muscle. - Mandibular nerve and its branches. - Otic ganglion. - Chorda tympani. - A part of the maxillary artery and two of its branches. - Pterygoid plexus of veins. - Temporomandibular joint.  L13 Maxillary Nerve 1. Origin of the Maxillary Nerve - The maxillary nerve arises from the trigeminal ganglion located in the middle cranial fossa. 2. Type of Fibers - The maxillary nerve is purely sensory (general somatic afferent). 3. Course of the Maxillary Nerve - In the Cranial Cavity: It passes along the lateral wall of the cavernous sinus and through the foramen rotundum to enter the pterygopalatine fossa. - In the Pterygopalatine Fossa: It crosses through the pterygomaxillary fissure into the infratemporal fossa. - In the Infratemporal Fossa: It passes through the inferior orbital fissure to enter the orbit, where it becomes the infraorbital nerve. - In the Orbit: The infraorbital nerve runs on the floor of the orbit and passes through the infraorbital groove, canal, and foramen to reach the face. 4. Branches of the Maxillary Nerve - In the Cranial Cavity: - Meningeal Nerve: Supplies the dura mater of the anterior and middle cranial fossae. - In the Pterygopalatine Fossa: - Ganglionic Branches: Connect to the pterygopalatine ganglion; contain secretomotor fibers to the lacrimal gland and sensory fibers to the orbital periosteum, nasal mucosa, palate, and pharynx. - Zygomatic Nerve: Divides into zygomaticofacial and zygomaticotemporal branches, supplying skin over the zygomatic bone and anterior temporal fossa. - Posterior Superior Alveolar Nerve: Supplies upper molar teeth and maxillary sinus. - In the Infraorbital Canal (Infraorbital Nerve): - Middle Superior Alveolar Nerve: Supplies maxillary premolars and the mesiobuccal root of the first molar. - Anterior Superior Alveolar Nerve: Supplies canine and incisor teeth; has a nasal branch that ends in the nasal septum. - Branches Given on the Face: - Palpebral Branches: Supply the skin over the lower eyelid. - Nasal Branches: Supply the skin of the nose and nasal septum. - Superior Labial Branches: Supply the skin over the anterior cheek and upper lip, including the mucous membrane and labial glands.  14L Maxillary Artery 1. Origin of the Maxillary Artery - The maxillary artery is the larger of the two terminal branches of the external carotid artery, located behind the neck of the mandible within the parotid gland. 2. Course of the Maxillary Artery - The artery is divided into three parts: - First Part: Runs deep to the neck of the mandible, below the auriculotemporal nerve, and emerges from the lower border of the lateral pterygoid muscle. - Second Part: Ascends superficially (or sometimes deeply) to the lower head of the lateral pterygoid muscle. - Third Part: Passes between the two heads of the lateral pterygoid and through the pterygomaxillary fissure to reach the pterygopalatine fossa, where it terminates. 3. Branches of the Maxillary Artery - From the First Part: 1. Middle Meningeal Artery: Supplies the dura mater and enters the cranial cavity through foramen spinosum. 2. Accessory Meningeal Artery: Supplies the dura mater and trigeminal ganglion; passes through foramen ovale. 3. Inferior Alveolar Artery: Supplies the mandible and lower teeth; divides into incisive and mental branches. 4. Anterior Tympanic Artery: Supplies the tympanic membrane via the petrotympanic fissure. 5. Deep Auricular Artery: Supplies the external auditory meatus and tympanic membrane.  - From the Second Part: 1. Muscular Branches: Supply the muscles of mastication. 3. Buccal Artery: Follows the course of the buccal nerve. - From the Third Part: 1. Posterior Superior Alveolar Artery: Supplies upper molars, premolars, and the maxillary sinus. 2. Infraorbital Artery: Supplies the remaining upper teeth, skin of the lower eyelid, ala of the nose, and upper lip. 3. Greater Palatine Artery: Supplies the hard palate and gums, ascending through the incisive canal. 4. Sphenopalatine Artery: Supplies the nasal cavity and nasal septum. 5. Artery of Pterygoid Canal: Supplies the auditory tube, tympanic cavity, and pharynx. 6. Pharyngeal Artery: Supplies the nasopharynx and sphenoidal air sinuses. 4. Pterygoid Plexus of Veins - Located in the substance of the lateral pterygoid muscle. - Tributaries correspond to branches of the maxillary artery. - Forms the maxillary vein, which unites with the superficial temporal vein to create the retromandibular vein. - Communicates with the cavernous sinus and facial vein through emissary veins. 5. Muscles of Mastication - Main Muscles: 1. Temporalis: Elevates and retracts the mandible. 2. Masseter: Elevates and protrudes the mandible. 3. Lateral Pterygoid: Protrudes and depresses the mandible; allows side- to-side movement. 4. Medial Pterygoid: Elevates and protrudes the mandible.  15L Muscles of Mastication & Temporomandibular Joint (TMJ) 1. Muscles of Mastication - Main Muscles: 1. Temporalis 2. Masseter 3. Lateral Pterygoid 4. Medial Pterygoid - Characteristics: - Originate from the temporal or infratemporal fossa. - Insert into the ramus of the mandible. - Supplied by branches of the mandibular nerve. - Function in the movements of the temporomandibular joint. 2.Detailed Actions and Anatomy of Muscles: - Temporalis: - Origin: Floor of the temporal fossa. - Insertion: Coronoid process and anterior border of the ramus. - Action: Elevates and retracts the mandible. - Masseter: - Origin: Zygomatic arch. - Insertion: Lateral surface of the ramus. - Action: Elevates and protrudes the mandible; allows side-to-side movement.  - Lateral Pterygoid: - Origin: Infratemporal surface of the greater wing of the sphenoid and lateral surface of the lateral pterygoid plate. - Insertion: Pterygoid fovea; capsule and articular disc of TMJ. - Action: Protrudes and depresses the mandible; allows side-to-side movement. - Medial Pterygoid: - Origin: Tuberosity of maxilla and medial surface of the lateral pterygoid plate. - Insertion: Medial surface of the ramus and angle of the mandible. - Action: Elevates and protrudes the mandible; allows side-to-side movement. 3. Temporomandibular Joint (TMJ) - Type: Synovial, condylar joint. - Components: 1. Mandibular fossa and articular tubercle of the temporal bone. 2. Head of the mandible. 4. Capsule and articular disc of fibrocartilage. - Movements: - Depression: Involves rotation around a horizontal axis; primarily by lateral pterygoid and gravity. - Elevation: Involves reversing depression movements; primarily by temporalis, masseter, and medial pterygoid. - Protrusion and Retrusion: Involves lateral and medial pterygoid muscles. - Side-to-Side Movement: Facilitated by both pterygoid muscles acting alternately. 4. Ligaments of the TMJ: - Lateral Temporomandibular Ligament: Provides lateral stability and prevents posterior dislocation. - Sphenomandibular Ligament: Connects the sphenoid bone to the mandible. - Stylomandibular Ligament: Separates the parotid and submandibular glands. - Pterygomandibular Ligament: Extends from the pterygoid hamulus to the mandible. 5. Clinical Notes: - Dislocation of the TMJ is common, often anteriorly, especially in older individuals due to laxity of ligaments. - TMJ arthritis can lead to inflammation and functional issues, including joint clicking and altered dental occlusion.  16L Anatomy of the Eye 1. Orbit Anatomy - The orbit is a pear-shaped structure with a four-sided pyramid shape, apex posterior and base anterior. - Orbital Margins: - Superior: Frontal bone - Lateral: Zygomatic bone - Inferior: Zygomatic and maxillary bones - Medial: Maxilla, lacrimal, and frontal bones 2. Orbital Walls - Roof: Formed by the frontal bone and lesser wing of the sphenoid; contains the optic canal. - Floor: Composed of maxilla, palatine, and zygomatic bones. - Medial Wall: Formed by maxilla, lacrimal, ethmoidal, and sphenoid bones. - Lateral Wall: Composed of the zygomatic bone and greater wing of the sphenoid. 3. Key Structures - Superior Orbital Fissure: Allows communication of cranial nerves, arteries, and veins with the eye. - Optic Canal: Transmits the optic nerve to the brain. - Optic Nerve (Cranial Nerve II): Transmits visual information from the retina. 4. Extraocular Muscles - Levator Palpebrae Superioris: - Origin: Lesser wing of the sphenoid above the optic canal. - Insertion: Superior tarsal plate and skin of the upper eyelid. - Nerve Supply: Oculomotor nerve (superior division). - Action: Elevates the upper eyelid. - Recti Muscles: Superior, inferior, medial, and lateral rectus muscles originate from the common tendinous ring. - Nerve Supply: Oculomotor nerve for three recti; abducens for lateral rectus. - Oblique Muscles: Superior and inferior oblique muscles assist in eye movement. - Nerve Supply: Trochlear nerve for superior oblique; oculomotor for inferior oblique. 5. Nervous Supply - Sensory Nerves: Optic nerve and branches from the ophthalmic division of the trigeminal nerve. - Motor Nerves: Oculomotor, trochlear, and abducens nerves. - Ciliary Ganglion: Contains postganglionic fibers for the constrictor pupillae and ciliary muscle. 6. Vascular Supply - Arterial Supply: Primarily from the ophthalmic artery (branch of the internal carotid artery). - Key branches include central artery of the retina and ciliary arteries. - Venous Drainage: Via superior and inferior ophthalmic veins, which drain into the cavernous sinus. 7. Clinical Notes - Lesions of the oculomotor nerve can lead to symptoms such as diplopia, ptosis, and pupil dilation. - There are no lymph vessels or lymph nodes in the orbital cavity.  17L Ear anatomy 1. Parts of the Ear The ear is divided into: External Ear: Includes the auricle, external auditory canal, and tympanic membrane (eardrum). Middle Ear: Contains the auditory ossicles (malleus, incus, stapes) and connects the external ear to the inner ear. Inner Ear: Houses the organs responsible for hearing and balance, such as the cochlea and vestibular system. 2. External Ear Auricle (Pinna): Composed of elastic cartilage covered by skin (except for the lobule, which has no cartilage). Key parts: helix, antihelix, concha, tragus, antitragus, and lobule. Nerve supply: Motor: Facial nerve (CN VII). Sensory: Auriculotemporal, lesser occipital, great auricular, and auricular branch of the vagus nerve. External Auditory Canal: Curved tube conducting sound to the tympanic membrane. Outer third: Cartilaginous; inner two-thirds: Bony. Lined with skin, hairs, and ceruminous glands producing protective wax. Tympanic Membrane (Eardrum): Separates the external ear from the middle ear. Parts include the "Pars tensa" (fibrous tissue) and "Pars flaccida." 3. Middle Ear Tympanic Cavity: Irregular air-filled space within the petrous part of the temporal bone. Contains: Auditory Ossicles: Malleus (Hammer): Connected to the tympanic membrane. Incus (Anvil): Links the malleus and stapes. Stapes (Stirrup): Footplate closes the oval window of the inner ear. Muscles: Tensor tympani: Dampens vibrations of the tympanic membrane. Stapedius: Controls excessive movement of the stapes. Nerves: Tympanic plexus, chorda tympani, and facial nerve. 4. Inner Ear Cochlea: Responsible for hearing; contains the organ of Corti with hair cells transmitting sound signals via the cochlear nerve. Vestibular System: Maintains balance; includes the utricle, saccule, and semicircular canals. Signals are transmitted through the vestibular nerve. Vestibulocochlear Nerve (CN VIII): Combines the cochlear and vestibular nerves, transmitting hearing and balance information to the brainstem.  18L Anatomy of the Mandibular Nerve 1. Mandibular Nerve Overview - Course: - The mandibular nerve emerges through the foramen ovale into the infratemporal fossa. - It consists of two roots that unite below the foramen ovale, dividing into a small anterior division and a large posterior division. 2. Relations - Superficial: Lateral pterygoid muscle. - Deep: Otic ganglion. - Posterior: Middle meningeal artery. 3. Branches from the Trunk of the Mandibular Nerve - Motor Branch: - Nerve to medial pterygoid, which supplies the medial pterygoid muscle and branches to the tensor veli palatini and tensor tympani muscles. - Sensory Branch: - Meningeal branch (nervus spinosus) that supplies the meninges of the middle cranial fossa. 4. Branches from the Anterior Division - Motor Branches: 1. Masseteric Nerve: Supplies the masseter muscle. 2. Deep Temporal Nerves: Supply the temporalis muscle. 3. Nerve to Lateral Pterygoid: Supplies the lateral pterygoid muscle. - Sensory Branch: - Buccal Nerve: Supplies the skin and mucous membrane over the buccinator. 5. Branches from the Posterior Division - Sensory Branches: 1. Auriculotemporal Nerve: Supplies the skin of the auricle, temple, TMJ, and parotid gland; carries parasympathetic fibers to the parotid gland. 2. Lingual Nerve: Supplies general sensations from the anterior two-thirds of the tongue; it joins the chorda tympani. 3. Inferior Alveolar Nerve: Supplies the lower teeth and emerges as the mental nerve to supply the skin of the lower lip and chin. - Motor Branch: - Mylohyoid Nerve: Supplies the mylohyoid muscle and the anterior belly of the digastric muscle. 6. Motor Branches of the Trigeminal Nerve - Control the movements of the following muscles: - Muscles of Mastication: Masseter, temporalis, medial pterygoid, lateral pterygoid. - Other Muscles: Tensor veli palatini, mylohyoid, anterior belly of digastric, tensor tympani.  19L Anatomy of the Posterior Triangle of the Neck 1. Overview of the Posterior Triangle - The side of the neck has a quadrilateral outline: - Upper Limit: Lower border of the mandible and an imaginary line from the angle of the mandible to the mastoid process. - Lower Limit: Upper border of the clavicle. - Medial Limit: Midline of the neck. - Posterior Limit: Anterior border of the trapezius muscle. 2. Division of the Neck - The sternocleidomastoid muscle divides the side of the neck into two triangles: - Posterior Triangle - Anterior Triangle 3. Boundaries of the Posterior Triangle - Anterior Boundary: Sternocleidomastoid muscle. - Posterior Boundary: Trapezius muscle. - Base: Intermediate third of the clavicle. - Apex: Superior nuchal line. 4. Roof of the Posterior Triangle - Composed of: - Skin - Superficial fascia - Investing layer of deep cervical fascia - The roof is pierced by: - Veins: External jugular vein and its tributaries. - Nerves: - Lesser occipital nerve - Great auricular nerve - Transverse cutaneous nerves of the neck - Supraclavicular nerves - Lymph Vessels 5. Floor of the Posterior Triangle - Composed of the following muscles: - Splenius capitis - Levator scapulae - Scalenus medius - Semispinalis capitis - Scalenus anterior 6. Nerve Supply - Cutaneous Branches of the Cervical Plexus: - Great auricular nerve - Lesser occipital nerve - Transverse cervical nerve - Supraclavicular nerves - Spinal Accessory Nerve: Supplies the sternocleidomastoid and trapezius muscles. - Brachial Plexus: Includes roots and trunks. 7. Vascular Supply - Subclavian Artery and Vein: Third part of the subclavian artery and vein. - Additional Vessels: - Suprascapular vessels - Transverse cervical vessels - Dorsal scapular artery 8. Muscle Actions - The sternocleidomastoid muscle: - Flexes and rotates the head. - Elevates the sternum, aiding in forceful inhalation. - Conditions: - Torticollis can result from muscle contraction or spasms.  20L Anatomy of the Anterior Triangle of the Neck 1. Overview of the Anterior Triangle - The neck is divided into anterior and posterior triangles by the sternocleidomastoid muscle: - Anterior Triangle: Located in front of the sternocleidomastoid muscle. - Posterior Triangle: Located behind the sternocleidomastoid muscle. 2. Boundaries of the Anterior Triangle - Anterior Boundary: Median plane of the neck. - Posterior Boundary: Anterior border of the sternocleidomastoid muscle. - Superior Boundary: Base of the mandible. 3. Subdivisions of the Anterior Triangle - The anterior triangle is divided into four smaller triangles: 1. Submental Triangle 2. Submandibular Triangle 3. Carotid Triangle 4. Muscular Triangle 4. Submental Triangle - Boundaries: - Apex: Symphysis menti. - Base: Hyoid bone. - Sides: Anterior bellies of the digastric muscle. - Floor: Mylohyoid muscle. - Contents: - Submental lymph nodes. - Submental artery (from the facial artery). - Submental veins (form the anterior jugular vein). - Nerve to mylohyoid. 5. Submandibular Triangle - Boundaries: - Superior: Base of the mandible. - Anterior: Anterior belly of the digastric muscle. - Posterior: Posterior belly of the digastric and stylohyoid muscles. - Floor: Mylohyoid and hyoglossus muscles. - Contents: - Submandibular salivary gland. - Submandibular lymph nodes. - Parts of the facial artery and vein. - Hypoglossal nerve and mylohyoid nerve. 6. Carotid Triangle - Boundaries: - Sternocleidomastoid muscle. - Posterior belly of the digastric muscle. - Superior belly of the omohyoid muscle. - Contents: - Common carotid, internal carotid, and external carotid arteries and their branches. - Internal jugular vein. - Cranial nerves (X, XI, XII) and cervical sympathetic chain. - Cervical lymph nodes. 7. Muscular Triangle - Boundaries: - Sternocleidomastoid muscle. - Superior belly of the omohyoid muscle. - Midline from hyoid bone to jugular notch. - Contents: - Larynx. - Thyroid gland. - Lymph nodes. 8. Suprahyoid and Infrahyoid Muscles - Suprahyoid Muscles: Elevate the hyoid bone. - Digastric muscle: Two bellies; nerve supply from facial nerve (posterior) and mylohyoid nerve (anterior). - Stylohyoid: Retracts and raises the hyoid; supplied by the facial nerve. - Geniohyoid: Elevates the hyoid, supplied by the hypoglossal nerve. - Mylohyoid: Forms the floor of the mouth; supplied by the mylohyoid nerve. - Infrahyoid Muscles: Depress the larynx. - Sternohyoid: Supplied by ansa cervicalis. - Omohyoid: Supplied by ansa cervicalis. - Thyrohyoid: Supplied by hypoglossal nerve and C1 fibers. - Sternothyroid: Supplied by ansa cervicalis.  21L Suprahyoid and Infrahyoid Muscles 1. Overview of Neck Muscles - The neck muscles can move the cervical spine and head based on their positioning: - Muscles that cross posteriorly extend the neck. - Muscles that cross anteriorly flex the neck. - Lateral crossing muscles allow lateral flexion. - Wrapping muscles facilitate rotation. 2. Anterior and Posterior Triangle of the Neck - The sternocleidomastoid muscle divides the neck into anterior and posterior triangles: - Anterior Triangle: Lies in front of the sternocleidomastoid muscle. - Posterior Triangle: Lies behind the sternocleidomastoid muscle. -Hyoid Bone - A unique bone that does not articulate with other bones. - Serves as a movable base for the tongue. 3. Muscles of the Anterior Neck - Divided into: - Infrahyoid Muscles -Suprahyoid Muscles 4. Infrahyoid Muscles - Strap-like muscles that extend from the hyoid bone to the manubrium sterni. - Function: Depress the hyoid bone during swallowing and are important for chewing and speech. - Muscle Arrangement: - Superficial Layer: - Sternohyoid: Depresses the hyoid; innervated by ansa cervicalis. - Omohyoid: Depresses and stabilizes the hyoid; innervated by ansa cervicalis. - Deep Layer: - Sternothyroid: Depresses the hyoid and elevates the thyroid cartilage; innervated by CN XII. - Thyrohyoid: Depresses the hyoid and elevates the larynx; innervated by C1 fibers via CN XII. 5. Suprahyoid Muscles - Function: Elevate the hyoid bone and assist in swallowing. - Muscle Components: - Digastric Muscle: Consists of anterior and posterior bellies; anterior belly innervated by CN V, posterior belly by CN VII. - Mylohyoid Muscle: Forms the floor of the mouth; innervated by CN XII. - Geniohyoid Muscle: Elevates the hyoid; innervated by CN XII. - Stylohyoid Muscle: Elevates the hyoid; innervated by CN VII. - Hyoglossus Muscle: Draws the tongue downwards; innervated by CN XII. 6. Triangles of the Anterior Neck - Digastric Triangle: Bounded by the lower border of the mandible and the anterior and posterior bellies of the digastric muscle. - Carotid Triangle: Bounded by the sternocleidomastoid muscle, posterior belly of the digastric muscle, and superior belly of the omohyoid muscle. - Muscular Triangle: Bounded by the midline of the neck, superior belly of the omohyoid, and sternocleidomastoid muscle. - Submental Triangle: Bounded by the symphysis menti, anterior bellies of the digastric muscle, and the hyoid bone. ‫ادعوا لي‬