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Anatomy - NEETMDS- courses
NEET MDS Lessons
Anatomy

The Ear

  • The ear contains the vestibulocochlear organ and consists of three main parts: external, middle, and internal.
  • It has two functions, balance and hearing.
  • The tympanic membrane (eardrum) separates the external ear from the middle ear.
  • The auditory tube joins the middle ear or tympanic cavity to the nasopharynx.

-> 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.

 

Eye 

At week 4, two depressions are evident on each of the forebrain hemispheres.  As the anterior neural fold closes, the optic pits elongate to form the optic vesicles.  The optic vesicles remain connected to the forebrain by optic stalks. 
The invagination of the optic vesicles forms a bilayered optic cup.  The bilayered cup becomes the dual layered retina (neural and pigmented layer)
Surface ectoderm forms the lens placode, which invaginates with the optic cup.
The optic stalk is deficient ventrally to contain choroids fissure to allow blood vessels into the eye (hyaloid artery).  The artery feeds the growing lens, but will its distal portion will eventually degenerate such that the adult lens receives no hyaloid vasculature.
At the 7th week, the choroids fissure closes and walls fuse as the retinal nerve get bigger.
The anterior rim of the optic vesicles forms the retina and iris.  The iris is an outgrowth of the distal edge of the retina.
Optic vesicles induces/maintains the development of the lens vesicle, which forms the definitive lens.  Following separation of the lens vesicle from the surface ectoderm, the cornea develops in the anterior 1/5th of the eye.
The lens and retina are surrounded by mesenchyme which forms a tough connective tissue, the sclera, that is continuous with the dura mater around the optic nerve.  
Iridopupillary membrane forms to separate the anterior and posterior chambers of the eye.  The membrane breaks down to allow for the pupil
Mesenchyme surrounding the forming eye forms musculature (ciliary muscles and pupillary muscles – from somitomeres 1 and 2; innervated by CN III), supportive connective tissue elements and vasculature.


Eyelids

Formed by an outgrowth of ectoderm that is fused at its midline in the 2nd trimester, but later reopen.

Nerve Supply of the Muscles of the Orbit (pp. 715-6)

  • Three cranial nerves supply the muscles of the eyeball; the oculomotor (CN III), trochlear (CN IV) and abducent (CN IV) nerves.
  • All three enter the orbit via the superior orbital fissure.
  • The trochlear nerve supplies the superior oblique muscle.
  • The abducent nerve supplies the lateral rectus muscle.
  • The oculomotor nerve supplies everything else.
  • A mnemonic that is used is this formula for this strange sulfate: SO4(LR6)3

  • This is the second cranial nerve (CN II) and is the nerve of sight.

Muscle

 

Emotion

 

Epicranius

 

Surprise

 

Orbicularisoculi

 

Squinting

 

Orbicularisoris

Pouting

Nasalis

 

Smelling

 

Zygomaticus

 

Smiling

 

Buccinator

 

Chewing

 

Mentalis

 

Doubt

 

Triangularis

 

Sadness

 

Platysma

 

Sadness

 

Masseter

 

Chewing

 

Temporalis

 

Sternness

 

Pterygoid

 

Conternation

 

Genioglossus and Styloglossus

 

Swallowing, Speaking, Chewing

 

 

The Pharynx

  • The pharynx is the continuation of the digestive system from the oral cavity.
  • It is a funnel-shaped fibromuscular tube that is the common route for both food and air.
  • The pharynx is located posterior to the nasal and oral cavities, and the larynx.
  • For the convenience of description, the pharynx is divided into three parts: (1) the nasopharynx, posterior to the nose and superior to the soft palate; (2) the oropharynx, posterior to the mouth; and (3) the laryngopharynx, posterior to the larynx.
  • The pharynx is about 15 cm long.
  • It extends from the base of the skull to the inferior border of the cricoid cartilage anteriorly, and to the inferior border of C6 vertebra posteriorly.
  • It is widest (about 5 cm) opposite the hyoid bone and narrowest (about 1.5) at its inferior end, where it is continuous with the oesophagus.
  • The posterior wall of the pharynx lies against the prevertebral fascia, with the potential retropharyngeal space between them.

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