NEET MDS Lessons
Anatomy
- 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)
- 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 Oral Cavity
- The oral cavity (mouth) consists of two parts: the vestibule and the mouth proper.
- The vestibule is the slit-like spaced between the cheeks and the lips and the teeth and gingivae.
- It is the entrance of the digestive tract and is also used for breathing.
- The vestibule communicates with the exterior through the orifice of the mouth.
- The oral cavity is bounded:
- Externally: by the cheeks and lips.
- Roof of oral cavity: formed by the palate.
- Posteriorly: the oral cavity communicates with the oropharynx.
Initially, four clefts exist; however, only one gives rise to a definite structure in adults.
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1st pharyngeal cleft |
Penetrates underlying mesenchyme and forms EAM. The bottom of EAM forms lateral aspect of tympanic cavity. |
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2nd pharyngeal cleft |
Undergoes active proliferation and overlaps remaining clefts. It merges with ectoderm of lower neck such that the remaining clefts lose contact with outside. Temporarily, the clefts form an ectodermally lined cavity, the cervical sinus, but this disappears during development. |
Muscles acting on the Temporomandibular Joint
- Movements of the temporomandibular joint are chiefly from the action of the muscles of mastication.
- The temporalis, masseter, and medial pterygoid muscles produce biting movements.
- The lateral pterygoid muscles protrude the mandible with the help from the medial pterygoid muscles and retruded largely by the posterior fibres of the temporalis muscle.
- Gravity is sufficient to depress the mandible, but if there is resistance, the lateral pterygoid, suprahyoid and infrahyoid, mylohyoid and anterior digastric muscles are activated.
| Actions | Muscles | |||
| Depression (Open mouth) |
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| Elevation (Close mouth) |
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| Protrusion (Protrude chin) |
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| Retrusion (Retrude chin) |
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| Side-to-side movements (grinding and chewing) |
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Internal Ear
- Osseous labyrinth: a complex system of cavities in the substance of the petrous bone.
- Membranous labyrinth: filled with endolymph, bathed in perilymph.
The Lateral Pterygoid Muscle
- This is a short, thick muscle that has two heads or origin.
- It is a conical muscle with its apex pointing posteriorly.
- Origin: superior head—infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone, inferior head—lateral surface of lateral pterygoid plate.
- Insertion: neck of mandible, articular disc, and capsule of temporomandibular joint.
- Innervation: mandibular nerve via lateral pterygoid nerve from anterior trunk, which enters it deep surface.
- Acting together, these muscles protrude the mandible and depress the chin.
- Acting alone and alternately, they produce side-to-side movements of the mandible.