NEET MDS Lessons
Anatomy
The Lateral Wall of the Orbit
- This wall is thick, particularly its posterior part, which separates the orbit from the middle cranial fossa.
- The lateral wall is formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid bone.
- Anteriorly, the lateral wall lies between the orbit and the temporal fossa.
- The lateral wall is partially separated from the roof by the superior orbital fissure.
The Auditory Ossicles
The Malleus
- Its superior part, the head, lies in the epitympanic recess.
- The head articulates with the incus.
- The neck, lies against the flaccid part of the tympanic membrane.
- The chorda tympani nerve crosses the medial surface of the neck of the malleus.
- The handle of the malleus (L. hammer) is embedded in the tympanic membrane and moves with it.
- The tendon of the tensor tympani muscle inserts into the handle.
The Incus
- Its large body lies in the epitympanic recess where it articulates with the head of the malleus.
- The long process of the incus (L. an anvil) articulates with the stapes.
- The short process is connected by a ligament to the posterior wall of the tympanic cavity.
The Stapes
- The base (footplate) of the stapes (L. a stirrup), the smallest ossicle, fits into the fenestra vestibuli or oval window on the medial wall of the tympanic cavity.
Functions of the Auditory Ossicles
- The auditory ossicles increase the force but decrease the amplitude of the vibrations transmitted from the tympanic membrane.
MUSCLE
Types:
Skeletal (voluntary)
Cardiac (involuntary)
Smooth (involuntary)
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First pouch |
Auditory tube, which comes in contact with epithelial line of first pharyngeal cleft, where future external acoustic meatus will form. Distal portion will form tympanic cavity (lining will become eardrum) Proximal portion will become auditory tube |
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Second pouch |
Forms buds that penetrate surrounding mesenchyme, which together form the palatine tonsils |
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Third pouch |
Forms thymus and inferior parathyroid glands |
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Fourth pouch |
Forms superior parathyroid glands |
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Fifth pouch |
Forms utlimobranchial body |
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.
Muscles of the larynx
Extrinsic muscles
suprahyoid: raise larynx, depress mandible for swallowing
infrahyoid: lower larynx for swallowing
both stabilize hyoid for tongue movements
The Medial Pterygoid Muscle
- This is a thick, quadrilateral muscle that also has two heads or origin.
- It embraces the inferior head of the lateral pterygoid muscle.
- It is located deep to the ramus of the mandible.
- Origin: deep head—medial surface of lateral pterygoid plate and pyramidal process of palatine bone, superficial head—tuberosity of maxilla.
- Insertion: medial surface of ramus of mandible, inferior to mandibular foramen.
- Innervation: mandibular nerve via medial pterygoid nerve.
- It helps to elevate the mandible and closes the jaws.
- Acting together, they help to protrude the mandible.
- Acting alone, it protrudes the side of the jaw.
- Acting alternately, they produce a grinding motion.