NEET MDS Lessons
Anatomy
Muscles Around the Mouth
- The sphincter of the mouth is orbicularis oris and the dilator muscles radiate outward from the lips like the spokes of a wheel.
Orbicularis Oris Muscle
- This muscle encircles the mouth and is the sphincter of the oral aperture
- This muscle (1) closes the lips, (2) protrudes them and (3) compresses them against the teeth.
- It plays an important role in articulation and mastication. Together with the buccinator muscle, it helps to hold the food between the teeth during mastication.
Zygomaticus Major Muscle
- It extends from the zygomatic bone to the angle of the mouth.
- It draws the corner of the moth superolaterally during smiling and laughing.
Zygomaticus Minor Muscle
- This is a narrow slip of muscle, and passes obliquely from the zygomatic bone to the orbicularis oris.
- It helps raise the upper lip when showing contempt or to deepen the nasolabial sulcus when showing sadness.
The Buccinator Muscle
- This is a thin, flat, rectangular muscle.
- It is attached laterally to the alveolar processes of the maxilla and mandible, opposite the molar teeth and the pterygomandibular raphe.
- Medially, its fibres mingle with those of orbicularis oris.Innervation: the buccal branch of facial.
- It aids mastication and swallowing by pushing the cheeks against the molar teeth during chewing.
Muscles Moving the Auditory Ossicles
The Tensor Tympani Muscle
- This muscle is about 2 cm long.
- Origin: superior surface of the cartilaginous part of the auditory tube, the greater wing of the sphenoid bone, and the petrous part of the temporal bone.
- Insertion: handle of the malleus.
- Innervation: mandibular nerve (CN V3) through the nerve to medial pterygoid.
- The tensor tympani muscle pulls the handle of the malleus medially, tensing the tympanic membrane, and reducing the amplitude of its oscillations.
- This tends to prevent damage to the internal ear when one is exposed to load sounds.
The Stapedius Muscle
- This tiny muscle is in the pyramidal eminence or the pyramid.
- Origin: pyramidal eminence on the posterior wall of the tympanic cavity. Its tendon enters the tympanic cavity by traversing a pinpoint foramen in the apex of the pyramid.
- Insertion: neck of the stapes.
- Innervation: nerve to the stapedius muscle, which arises from the facial nerve (CN VII).
- The stapedius muscle pulls the stapes posteriorly and tilts its base in the fenestra vestibuli or oval window, thereby tightening the anular ligament and reducing the oscillatory range.
- It also prevents excessive movement of the stapes.
Blood Supply to the Head and Neck
- Most arteries in the anterior cervical triangle arise from the common carotid artery or one of the branches of the external carotid artery.
- Most veins in the anterior cervical triangle are tributaries of the large internal jugular vein.
The Common Carotid Arteries
- The right common carotid artery begins at the bifurcation of the brachiocephalic trunk, posterior to the right sternoclavicular joint.
- The left common carotid artery begins arises from the arch of the aorta and ascends into the neck, posterior to the left sternoclavicular joint.
- Each common carotid artery ascends into the neck within the carotid sheath to the level of the superior border of the thyroid cartilage.
- Here it terminates by dividing into the internal and external carotid arteries.
The Internal Carotid Artery
- This is the direct continuation of the common carotid artery and it has no branches in the neck.
- It supplies structures inside the skull.
- The internal carotid arteries are two of the four main arteries that supply blood to the brain.
- Each artery arises from the common carotid at the level of the superior border of the thyroid cartilage.
- It then passes superiorly, almost in a vertical plane, to enter the carotid canal in the petrous part of the temporal bone.
- A plexus of sympathetic fibres accompany it.
- During its course through the neck, the internal carotid artery lies on the longus capitis muscle and the sympathetic trunk.
- The vagus nerve (CN X) lies posterolateral to it.
- The internal carotid artery enters the middle cranial fossa beside the dorsum sellae of the sphenoid bone.
- Within the cranial cavity, the internal carotid artery and its branches supply the hypophysis cerebri (pituitary gland), the orbit, and most of the supratentorial part of the brain.
The External Carotid Arteries
- This vessel begins at the bifurcation of the common carotid, at the level of the superior border of the thyroid cartilage.
- It supplies structures external to the skull.
- The external carotid artery runs posterosuperiorly to the region between the neck of the mandible and the lobule of the auricle.
- It terminates by dividing into two branches, the maxillary and superficial temporal arteries.
- The stems of most of the six branches of the external carotid artery are in the carotid triangle.
The Superior Thyroid Artery
- This is the most inferior of the 3 anterior branches of the external carotid.
- It arises close to the origin of the vessel, just inferior to the greater horn of the hyoid.
- The superior thyroid artery runs anteroinferiorly, deep to the infrahyoid muscles and gives off the superior laryngeal artery. This artery pierces the thyrohyoid membrane in company with the internal laryngeal nerve and supplies the larynx.
The Lingual Artery
- This arises from the external carotid artery as it lies on the middle constrictor muscle of the pharynx.
- It arches superoanteriorly, about 5 mm superior to the tip of the greater horn of the hyoid bone, and then passes deep to the hypoglossal nerve, the stylohyoid muscle, and the posterior belly of digastric muscle.
- It disappears deep to the hyoglossus muscle.
- At the anterior border of this muscle, it turns superiorly and ends by becoming the deep lingual artery.
The Facial Artery
- This arises from the carotid artery either, in common with the lingual artery, or immediately superior to it.
- In the neck the facial artery gives off its important tonsillar branch and branches to the palate and submandibular gland.
- The facial artery then passes superiorly under the cover of the digastric and stylohyoid muscles and the angle of the mandible.
- It loops anteriorly and enters a deep groove in the submandibular gland.
- The facial artery hooks around the inferior border of the mandible and enters the face. Here the pulsation of this artery can be felt (anterior to the masseter muscle).
The Ascending Pharyngeal Artery
- This is the 1st or 2nd branch of the external carotid artery.
- This small vessel ascends on the pharynx, deep to the internal carotid artery.
- It sends branches to the pharynx, prevertebral muscles, middle ear and meninges.
The Occipital Artery
- This arises from the posterior surface of the external carotid near the level of the facial artery.
- It passes posteriorly along the inferior border of the posterior belly of digastric.
- It ends in the posterior part of the scalp.
- During its course, it is superficial to the internal carotid artery and three cranial nerves (CN IX, CN X and CN XI).
The Posterior Auricular Artery
- This is a small posterior branch of the external carotid artery.
- It arises from it at the superior border of the posterior belly of the digastric muscle.
- It ascends posteriorly to the external acoustic meatus and supplies adjacent muscles, the parotid gland, the facial nerve, structures in the temporal bone, the auricle, and the scalp.
The Internal Jugular Vein
- This is usually the largest vein in the neck.
- The internal jugular vein drains blood from the brain and superficial parts of the face and neck.
- Its course corresponds to a line drawn from a point immediately inferior to the external acoustic meatus to the medial end of the clavicle.
- This large vein commences at the jugular foramen in the posterior cranial fossa, as the direct continuation of the sigmoid sinus.
- The dilation at its origin is called the superior bulb of the internal jugular vein.
- From here it runs inferiorly through the neck in the carotid sheath.
- The internal jugular vein leaves the anterior triangle of the neck by passing deep to the SCM muscle.
- Posterior to the sternal end of the clavicle, it unites with the subclavian vein to form the brachiocephalic vein.
- Near its termination is the inferior bulb of the jugular vein contains a bicuspid valve similar to that of the subclavian vein.
- The deep cervical lymph nodes lie along the course of the internal jugular vein, mostly lateral and posterior.
Tributaries of the Internal Jugular Vein
- This large vein is joined at its origin by the: inferior petrosal sinus, the facial, lingual, pharyngeal, superior and middle thyroid veins, and often the occipital vein.
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Motor Innervation | All muscles by hypoglossal nerve (CN XII) except palatoglossus muscle (by the pharyngeal plexus) | ||
General Sensory Innervation |
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Special Sensory Innervation |
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- 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)
- The palate has a rich blood supply from branches of the maxillary artery.
Connective Tissue
Functions of Connective tissue:
→ joins together other tissues
→ supporting framework for the body (bone)
→ fat stores energy
→ blood transports substances
Connective tissue is usually characterized by large amounts of extracellular materials that separate cells from each other, whereas epithelial tissue is mostly cells with very little extracellular material. The extracellular substance of connective tissue consists of protein fibers which are embedded in ground substance containing tissue fluid.
Fibers in connective tissue can be divided into three types:
→ Collagen fibers are the most abundant protein fibers in the body.
→ Elastic fibers are made of elastin and have the ability to recoil to original shape.
→ Reticular fibers are very fine collagen fibers that join connective tissues to other tissues.
Connective tissue cells are named according to their functions:
→ Blast cells produce the matrix of connective tissues
→ Cyte cells maintains the matrix of connective tissues
→ Clast cells breaks down the matrix for remodeling (found in bone)