NEET MDS Lessons
Anatomy
Muscles of the Tongue
- The tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
- In each half of the tongue there are four extrinsic and four intrinsic muscles.
- The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
- The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.
Extrinsic Muscles of the Tongue
The Genioglossus Muscle
- This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
- It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
- It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
- Its most inferior fibres insert into the body of the hyoid bone.
- The genioglossus muscle depresses the tongue and its posterior part protrudes it.
The Hyoglossus Muscle
- This is a thin, quadrilateral muscle.
- It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
- It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.
The Styloglossus Muscle
- This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
- It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
- The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.
The Palatopharyngeus Muscle
- Superior attachment: hard palate and palatine aponeurosis.
- Inferior attachment: lateral wall of pharynx.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
- It passes posteroinferiorly in this arch.
- This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing.
Intrinsic Muscles of the Tongue
The Superior Longitudinal Muscle of the Tongue
- The muscle forms a thin layer deep to the mucous membrane on the dorsum of the tongue, running from its tip to its root.
- It arises from the submucosal fibrous layer and the lingual septum and inserts mainly into the mucous membrane.
- This muscle curls the tip and sides of the tongue superiorly, making the dorsum of the tongue concave.
The Inferior Longitudinal Muscle of the Tongue
- This muscle consists of a narrow band close to the inferior surface of the tongue.
- It extends from the tip to the root of the tongue.
- Some of its fibres attach to the hyoid bone.
- This muscle curls the tip of the tongue inferiorly, making the dorsum of the tongue convex.
The Transverse Muscle of the Tongue
- This muscle lies deep to the superior longitudinal muscle.
- It arises from the fibrous lingual septum and runs lateral to its right and left margins.
- Its fibres are inserted into the submucosal fibrous tissue.
- The transverse muscle narrows and increases the height of the tongue.
The Vertical Muscle of the Tongue
- This muscle runs inferolaterally from the dorsum of the tongue.
- It flattens and broadens the tongue.
- Acting with the transverse muscle, it increases the length of the tongue.
The External Nose
- Noses vary considerably in size and shape, mainly as a result of the differences in the nasal cartilages and the depth of the glabella.
- The inferior surface of the nose is pierced by two apertures, called the anterior nares (L. nostrils).
- These are separated from each other by the nasal septum (septum nasi).
- Each naris is bounded laterally by an ala (L. wing), i.e., the side of the nose.
- The posterior nares apertures or choanae open into the nasopharynx.
Digastric Muscle
- Origin:
- Anterior Belly: Digastric fossa of the mandible.
- Posterior Belly: Mastoid notch of the temporal bone.
- Insertion: Intermediate tendon attached to the body of the hyoid bone.
- Nerve Supply:
- Anterior Belly: Nerve to mylohyoid (branch of the trigeminal nerve, CN V3).
- Posterior Belly: Facial nerve (CN VII).
- Arterial Supply:
- Anterior Belly: Branch of the submental artery.
- Posterior Belly: Muscular branch of the posterior auricular artery and occipital artery.
- Action: Raises the hyoid bone and base of the tongue, steadies the hyoid bone, and opens the mouth by lowering the mandible.
The Medial Wall of the Orbit
- This wall is paper-thin and is formed by the orbital lamina or lamina papyracea of the ethmoid bone, along with contributions from the frontal, lacrimal, and sphenoid bones (L. papyraceus, "made of papyrus" or parchment paper).
- There is a vertical lacrimal groove in the medial wall, which is formed anteriorly by the maxilla and posteriorly by the lacrimal bone.
- It forms a fossa for the lacrimal sac and the adjacent part of the nasolacrimal duct.
- Along the suture between the ethmoid and frontal bones are two small foramina; the anterior and posterior ethmoidal foramina.
- These transmit nerves and vessels of the same name.
- Long bones (e.g.. femur and humerus)
- Short bones (e.g.. wrist and ankle bones)
- Flat bones (e.g.. ribs)
- Irregular bones (e.g.. vertebrae)
-> This bone forms much of the base and posterior aspect of the skull.
-> It has a large opening called the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
-> It is also where the spinal cord becomes continuous with the medulla (oblongata) of the brain stem.
-> The occipital bone is saucer-shaped and can be divided into four parts: a squamous part (squama), a basilar part (basioccipital part), and two lateral parts (condylar parts).
-> These four parts develop separately around the foramen magnum and unite at about the age of 6 years to form one bone.
-> On the inferior surfaces of the lateral parts of the occipital bone are occipital condyles, where the skull articulates with C1 vertebra (the atlas) at the atlanto-occipital joints.
-> The internal aspect of the squamous part of the occipital bone is divided into four fossae: the superior two for the occipital poles of the cerebral hemispheres, and the inferior two, called cerebellar fossae, for the cerebellar hemispheres.
Extrinsic Muscles of the Tongue (p. 746)
The Genioglossus Muscle
- This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
- It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
- It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
- Its most inferior fibres insert into the body of the hyoid bone.
- The genioglossus muscle depresses the tongue and its posterior part protrudes it.
The Hyoglossus Muscle
- This is a thin, quadrilateral muscle.
- It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
- It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.
The Styloglossus Muscle
- This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
- It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
- The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.
The Palatoglossus Muscle
- Superior attachment: palatine aponeurosis.
- Inferior attachment: side of tongue.
- Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.
- This muscle, covered by mucous membrane, forms the palatoglossal arch.
- The palatoglossus elevates the posterior part of the tongue and draws the soft palate inferiorly onto the tongue.