NEET MDS Lessons
Anatomy
Muscles of the Pharynx
- This consists of three constrictor muscles and three muscles that descend from the styloid process, the cartilaginous part of the auditory tube and the soft palate.
External Muscles of the Pharynx
- The paired superior, middle, and inferior constrictor muscles form the external circular part of the muscular layer of the wall.
- These muscles overlap each other and are arranged so that the superior one is innermost and the inferior one is outermost.
- These muscles contract involuntarily in a way that results in contraction taking place sequentially from the superior to inferior end of the pharynx.
- This action propels food into the oesophagus.
- All three constrictors of the pharynx are supplied by the pharyngeal plexus of nerves, which lies on the lateral wall of the pharynx, mainly on the middle constrictor of the pharynx.
- This plexus is formed by pharyngeal branches of the glossopharyngeal (CN IX) and vagus (CN X) nerves.
The Superior Constrictor Muscle
- Origin: pterygoid hamulus, pterygomandibular raphe, posterior end of the mylohyoid line of the mandible, and side of tongue.
- Insertion: median raphe of pharynx and pharyngeal tubercle.
- Innervation: though the pharyngeal plexus of nerves.
- The pterygomandibular raphe is the fibrous line of junction between the buccinator and superior constrictor muscles.
The Middle Constrictor Muscle
- Origin: stylohyoid ligament and greater and lesser horns of hyoid bone.
- Insertion: median raphe of pharynx.
- Innervation: through the pharyngeal plexus of nerves.
The Inferior Constrictor Muscle
- Origin: oblique line of thyroid cartilage and side of cricoid cartilage.
- Insertion: median raphe of pharynx.
- Innervation: through the pharyngeal plexus of nerves.
- The fibres arising from the cricoid cartilage are believed to act as a sphincter, preventing air from entering the oesophagus.
Gaps in the Pharyngeal Musculature
- The overlapping arrangement of the three constrictor muscles leaves 4 deficiencies or gaps in the pharyngeal musculature.
- Various structures enter and leave the pharynx through these gaps.
- Superior to the superior constrictor muscle, the levator veli palatini muscle, the auditory tube, and the ascending palatine artery pass through a gap between the superior constrictor muscle and the skull.
- Superior to the superior border of the superior constrictor, the pharyngobasilar fascia blends with the buccopharyngeal fascia to form, with the mucous membrane, the thin wall of the pharyngeal recess.
- Between the superior and middle constrictor muscles, the gateway to the mouth, though which pass the stylopharyngeus muscle, the glossopharyngeal nerve (CN IX), and the stylohyoid ligament.
- Between the middle and inferior constrictor muscles, the internal laryngeal nerve and the superior laryngeal artery and vein pass to the larynx.
- Inferior to the inferior constrictor muscles, the recurrent laryngeal nerve and inferior laryngeal artery pass superiorly into the larynx.
The Paranasal Sinuses
- These sinuses are air-filled extensions of the respiratory part of the nasal cavity.
- They are in the following bones, frontal, ethmoid, sphenoid and the maxilla.
The Frontal Sinuses
- These are located between the outer and inner tables of the frontal bone, posterior to the superciliary arches.
The Ethmoidal Sinuses
- These comprise of several small cavities, called ethmoidal air cells, within the ethmoidal labyrinth (G. labyrinthos, a maze) of the lateral mass of the ethmoid bone.
The Sphenoidal Sinuses
- These occupy a variable amount in the body of the sphenoid bone and may extend into the wings.
The Maxillary Sinuses
- These are the largest pair of paranasal sinuses.
- They are pyramidal-shaped cavities that may occupy the entire bodies of the maxillae.
-> 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.
The Tongue
- The tongue (L. lingua; G. glossa) is a highly mobile muscular organ that can vary greatly in shape.
- It consists of three parts, a root, body, and tip.
- The tongue is concerned with mastication, taste, deglutition (swallowing), articulation (speech), and oral cleansing.
- Its main functions are squeezing food into the pharynx when swallowing, and forming words during speech.
- Provides a rigid support system
- Protects delicate structures (e. g., the protection provided by the bones of the vertebral column to the spinal cord)
- Bones supply calcium to the blood; are involved In the formation of blood cells (hemopoiesis)
- Bones serve as the basis of attachment of muscles; form levers in the joint areas, aIlowing movement
The Submandibular Glands
- Each of these U-shaped salivary glands is about the size of a thumb and lies along the body of the mandible.
- It is partly superior and partly inferior to the posterior 1/2 of the base of the mandible.
- It is partly superficial and partly deep to the mylohyoid muscle.
- The submandibular duct arises from the portion of the gland that lies between the mylohyoid and hyoglossus muscle.
- The duct passes deep and then superficial to the lingual nerve.
- It opens by one to three orifices on a small sublingual papilla beside the lingual frenulum.
- The submandibular gland is supplied by parasympathetic, secretomotor fibres from the submandibular ganglion (preganglionic fibres from the chorda tympani via the lingual nerve).
The Muscles of Facial Expression
- These lie in the subcutaneous tissue and are attached to the skin of the face.
- They enable us to move our skin and change our facial expression. They produce their effects by pulling on the skin but do not move the facial skeleton.
- These muscles surround the facial orifices and act as sphincters and dilators.
- All facial muscles receive their innervation from the branches of the facial nerve (CN VII)-temporal, zygomatic, buccal, marginal mandibular, cervical.