For foreign first-year students for autumn term Module Methodical elaboration for practice class on human anatomy for foreign first-year students for autumn term

The Refracting Media

Aqueous humor.

Vitreous body.

Crystalline lens.

The hyaloid membrane envelopes the vitreous body. The portion in front of the ora serrata is thickened by the accession of radial fibers and is termed the zonula ciliaris (zonule of Zinn). Here it presents a series of radially arranged furrows, in which the ciliary processes are accommodated and to which they adhere, as is shown by the fact that when they are removed some of their pigment remains attached to the zonula. The zonula ciliaris splits into two layers, one of which is thin and lines the hyaloid fossa; the other is named the suspensory ligament of the lens: it is thicker, and passes over the ciliary body to be attached to the capsule of the lens a short distance in front of its equator. Scattered and delicate fibers are also attached to the region of the equator itself. This ligament retains the lens in position, and is relaxed by the contraction of the meridional fibers of the Ciliaris muscle, so that the lens is allowed to become more convex. Behind the suspensory ligament there is a sacculated canal, the spatia zonularis (canal of Petit), which encircles the equator of the lens; it can be easily inflated through a fine blowpipe inserted under the suspensory ligament.

No bloodvessels penetrate the vitreous body, so that its nutrition must be carried on by vessels of the retina and ciliary processes, situated upon its exterior.

The Crystalline Lens (lens crystallina).—The crystalline lens, enclosed in its capsule, is situated immediately behind the iris, in front of the vitreous body, and encircled by the ciliary processes, which slightly overlap its margin.

The capsule of the lens (capsula lentis) is a transparent, structureless membrane which closely surrounds the lens, and is thicker in front than behind. It is brittle but highly elastic, and when ruptured the edges roll up with the outer surface innermost. It rests, behind, in the hyaloid fossa in the forepart of the vitreous body; in front, it is in contact with the free border of the iris, but recedes from it at the circumference, thus forming the posterior chamber of the eye; it is retained in its position chiefly by the suspensory ligament of the lens, already described.

The ciliary veins are seen on the outer surface of the choroid, and are named, from their arrangement, the venæ vorticosæ; they converge to four or five equidistant trunks which pierce the sclera midway between the sclero-corneal junction and the porus opticus. Another set of veins accompanies the anterior ciliary arteries. All of these veins open into the ophthalmic veins.

The ciliary nerves are derived from the nasociliary nerve and from the ciliary ganglion.
7. Methodic of class work:

a) interrogation of the students on the home task;

b) study of samples (topic according to the plan);

c) fill in the protocol of current lesson;

d) checking and signing the protocols by teacher.
8. Forms and methods of the self-checking.

Questions:

10. Sources of the information: Human anatomy

11. The program of self-preparation of students:

1. To learn the appropriate sections under the textbook

2. To consider preparations and to study them according to the plan of practical class.

3. To fill in the report of practical class.

4. To be able to show on a preparation of the Organ of Sight.

Methodical elaboration for practice class on human anatomy

for foreign first-year students
1. The topic: The Organ of Hearing, The External Ear, The Middle Ear or Tympanic Cavity, The Auditory Ossicles, The Internal Ear or Labyrinth, The Organs of Taste.

2. The place: classroom of the department of human anatomy.

3. The aim: to know the structure of the Organ of Hearing, The External Ear, The Middle Ear or Tympanic Cavity, The Auditory Ossicles, The Internal Ear or Labyrinth, The Organs of Taste.

4. The professional orientation of students: The knowledge of this topic are necessary for doctors of all specialities, it represents special interest for therapists.

5. The basic of knowledge:

6. The plan of the practice class:

A. Checking of the home task: interrogation or the test control – 30 min

B. Summary lecture on the topic by teacher – 20 min

а) The Organ of Hearing;

b) The External Ear;

c) The Middle Ear or Tympanic Cavity;

4. 
   The Auditory Ossicles;
   
5. 
   The Internal Ear or Labyrinth;
   
6. 
   The Organs of Taste;
   

Working plan:

The ear, or organ of hearing, is divisible into three parts: the external ear, the middle ear or tympanic cavity, and the internal ear or labyrinth.

The middle ear and auditory tube are developed from the first pharyngeal pouch. The entodermal lining of the dorsal end of this pouch is in contact with the ectoderm of the corresponding pharyngeal groove; by the extension of the mesoderm between these two layers the tympanic membrane is formed. During the sixth or seventh month the tympanic antrum appears as an upward and backward expansion of the tympanic cavity. With regard to the exact mode of development of the ossicles of the middle ear there is some difference of opinion. The view generally held is that the malleus is developed from the proximal end of the mandibular (Meckel’s) cartilage, the incus in the proximal end of the mandibular arch, and that the stapes is formed from the proximal end of the hyoid arch. The malleus, with the exception of its anterior process is ossified from a single center which appears near the neck of the bone; the anterior process is ossified separately in membrane and joins the main part of the bone about the sixth month of fetal life. The incus is ossified from one center which appears in the upper part of its long crus and ultimately extends into its lenticular process. The stapes first appears as a ring (annulus stapedius) encircling a small vessel, the stapedial artery, which subsequently undergoes atrophy; it is ossified from a single center which appears in its base.

The external acoustic meatus is developed from the first branchial groove. The lower part of this groove extends inward as a funnel-shaped tube (primary meatus) from which the cartilaginous portion and a small part of the roof of the osseous portion of the meatus are developed. From the lower part of the funnel-shaped tube an epithelial lamina extends downward and inward along the inferior wall of the primitive tympanic cavity; by the splitting of this lamina the inner part of the meatus (secondary meatus) is produced, while the inner portion of the lamina forms the cutaneous stratum of the tympanic membrane. The auricula or pinna is developed by the gradual differentiation of tubercles which appear around the margin of the first branchial groove. The rudiment of the acoustic nerve appears about the end of the third week as a group of ganglion cells closely applied to the cephalic edge of the auditory vesicle. Whether these cells are derived from the ectoderm adjoining the auditory vesicle, or have migrated from the wall of the neural tube, is as yet uncertain. The ganglion gradually splits into two parts, the vestibular ganglion and the spiral ganglion. The peripheral branches of the vestibular ganglion pass in two divisions, the pars superior giving rami to the superior ampulla of the superior semicircular duct, to the lateral ampulla and to the utricle; and the pars inferior giving rami to the saccule and the posterior ampulla. The proximal fibers of the vestibular ganglion form the vestibular nerve; the proximal fibers of the spiral ganglion form the cochlear nerve.
The External Ear

The external ear consists of the expanded portion named the auricula or pinna, and the external acoustic meatus. The former projects from the side of the head and serves to collect the vibrations of the air by which sound is produced; the latter leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity.

The Auricula or Pinna is of an ovoid form, with its larger end directed upward. Its lateral surface is irregularly concave, directed slightly forward, and presents numerous eminences and depressions to which names have been assigned. The prominent rim of the auricula is called the helix; where the helix turns downward behind, a small tubercle, the auricular tubercle of Darwin, is frequently seen; this tubercle is very evident about the sixth month of fetal life when the whole auricula has a close resemblance to that of some of the adult monkeys. Another curved prominence, parallel with and in front of the helix, is called the antihelix; this divides above into two crura, between which is a triangular depression, the fossa triangularis. The narrow-curved depression between the helix and the antihelix is called the scapha; the antihelix describes a curve around a deep, capacious cavity, the concha, which is partially divided into two parts by the crus or commencement of the helix; the upper part is termed the cymba conchæ, the lower part the cavum conchæ. In front of the concha, and projecting backward over the meatus, is a small pointed eminence, the tragus, so called from its being generally covered on its under surface with a tuft of hair, resembling a goat’s beard. Opposite the tragus, and separated from it by the intertragic notch, is a small tubercle, the antitragus. Below this is the lobule, composed of tough areolar and adipose tissues, and wanting the firmness and elasticity of the rest of the auricula.

The cranial surface of the auricula presents elevations which correspond to the depressions on its lateral surface and after which they are named, e. g., eminentia conchæ, eminentia triangularis, etc.

The skin is thin, closely adherent to the cartilage, and covered with fine hairs furnished with sebaceous glands, which are most numerous in the concha and scaphoid fossa. On the tragus and antitragus the hairs are strong and numerous. The skin of the auricula is continuous with that lining the external acoustic meatus.

The cartilage of the auricula (cartilago auriculæ; cartilage of the pinna) consists of a single piece; it gives form to this part of the ear, and upon its surface are found the eminences and depressions above described. It is absent from the lobule; it is deficient, also, between the tragus and beginning of the helix, the gap being filled up by dense fibrous tissue. At the front part of the auricula, where the helix bends upward, is a small projection of cartilage, called the spina helicis, while in the lower part of the helix the cartilage is prolonged downward as a tail-like process, the cauda helicis; this is separated from the antihelix by a fissure, the fissura antitragohelicina. The cranial aspect of the cartilage exhibits a transverse furrow, the sulcus antihelicis transversus, which corresponds with the inferior crus of the antihelix and separates the eminentia conchæ from the eminentia triangularis. The eminentia conchæ is crossed by a vertical ridge (ponticulus), which gives attachment to the Auricularis posterior muscle. In the cartilage of the auricula are two fissures, one behind the crus helicis and another in the tragus.

The ligaments of the auricula (ligamenti auricularia [Valsalva]; ligaments of the pinna) consist of two sets: (1) extrinsic, connecting it to the side of the head; (2) intrinsic, connecting various parts of its cartilage together.

The extrinsic ligaments are two in number, anterior and posterior. The anterior ligament extends from the tragus and spina helicis to the root of the zygomatic process of the temporal bone. The posterior ligament passes from the posterior surface of the concha to the outer surface of the mastoid process.

The chief intrinsic ligaments are: (a) a strong fibrous band, stretching from the tragus to the commencement of the helix, completing the meatus in front, and partly encircling the boundary of the concha; and (b) a band between the antihelix and the cauda helicis. Other less important bands are found on the cranial surface of the pinna.

The muscles of the auricula consist of two sets: (1) the extrinsic, which connect it with the skull and scalp and move the auricula as a whole; and (2) the intrinsic, which extend from one part of the auricle to another.

The extrinsic muscles are the Auriculares anterior, superior, and posterior.

The Auricularis anterior (Attrahens aurem), the smallest of the three, is thin, fan-shaped, and its fibers are pale and indistinct. It arises from the lateral edge of the galea aponeurotica, and its fibers converge to be inserted into a projection on the front of the helix.

The Auricularis superior (Attolens aurem), the largest of the three, is thin and fan-shaped. Its fibers arise from the galea aponeurotica, and converge to be inserted by a thin, flattened tendon into the upper part of the cranial surface of the auricula.

The Auricularis posterior (Retrahens aurem) consists of two or three fleshy fasciculi, which arise from the mastoid portion of the temporal bone by short aponeurotic fibers. They are inserted into the lower part of the cranial surface of the concha.

Actions.—In man, these muscles possess very little action: the Auricularis anterior draws the auricula forward and upward; the Auricularis superior slightly raises it; and the Auricularis posterior draws it backward.

The intrinsic muscles are the:

Helicis major.

Antitragicus.

Helicis minor.

Transversus auriculæ.

Tragicus.

Obliquus auriculæ.

The Helicis major is a narrow vertical band situated upon the anterior margin of the helix.

It arises below, from the spina helicis, and is inserted into the anterior border of the helix, just where it is about to curve backward.

The Helicis minor is an oblique fasciculus, covering the crus helicis.

The Tragicus is a short, flattened vertical band on the lateral surface of the tragus.

The Antitragicus arises from the outer part of the antitragus, and is inserted into the cauda helicis and antihelix.

The Transversus auriculæ is placed on the cranial surface of the pinna. It consists of scattered fibers, partly tendinous and partly muscular, extending from the eminentia conchæ to the prominence corresponding with the scapha.

The Obliquus auriculæ, also on the cranial surface, consists of a few fibers extending from the upper and back part of the concha to the convexity immediately above it.

Nerves.—The Auriculares anterior and superior and the intrinsic muscles on the lateral surface are supplied by the temporal branch of the facial nerve, the Auricularis posterior and the intrinsic muscles on the cranial surface by the posterior auricular branch of the same nerve.

The arteries of the auricula are the posterior auricular from the external carotid, the anterior auricular from the superficial temporal, and a branch from the occipital artery.

The veins accompany the corresponding arteries.

The sensory nerves are: the great auricular, from the cervical plexus; the auricular branch of the vagus; the auriculotemporal branch of the mandibular nerve; and the lesser occipital from the cervical plexus.

The External Acoustic Meatus (meatus acusticus externus; external auditory canal or meatus) extends from the bottom of the concha to the tympanic membrane. It is about 4 cm. in length if measured from the tragus; from the bottom of the concha its length is about 2.5 cm. It forms an S-shaped curve, and is directed at first inward, forward, and slightly upward (pars externa); it then passes inward and backward (pars media), and lastly is carried inward, forward, and slightly downward (pars interna). It is an oval cylindrical canal, the greatest diameter being directed downward and backward at the external orifice, but nearly horizontally at the inner end. It presents two constrictions, one near the inner end of the cartilaginous portion, and another, the isthmus, in the osseous portion, about 2 cm. from the bottom of the concha. The tympanic membrane, which closes the inner end of the meatus, is obliquely directed; in consequence of this the floor and anterior wall of the meatus are longer than the roof and posterior wall.

The external acoustic meatus is formed partly by cartilage and membrane, and partly by bone, and is lined by skin.

The cartilaginous portion (meatus acusticus externus cartilagineus) is about 8 mm. in length; it is continuous with the cartilage of the auricula, and firmly attached to the circumference of the auditory process of the temporal bone. The cartilage is deficient at the upper and back part of the meatus, its place being supplied by fibrous membrane; two or three deep fissures are present in the anterior part of the cartilage.

The osseous portion (meatus acusticus externus osseus) is about 16 mm. in length, and is narrower than the cartilaginous portion. It is directed inward and a little forward, forming in its course a slight curve the convexity of which is upward and backward. Its inner end is smaller than the outer, and sloped, the anterior wall projecting beyond the posterior for about 4 mm.; it is marked, except at its upper part, by a narrow groove, the tympanic sulcus, in which the circumference of the tympanic membrane is attached. Its outer end is dilated and rough in the greater part of its circumference, for the attachment of the cartilage of the auricula. The front and lower parts of the osseous portion are formed by a curved plate of bone, the tympanic part of the temporal, which, in the fetus, exists as a separate ring (annulus tympanicus,) incomplete at its upper part.

The skin lining the meatus is very thin; adheres closely to the cartilaginous and osseous portions of the tube, and covers the outer surface of the tympanic membrane. After maceration, the thin pouch of epidermis, when withdrawn, preserves the form of the meatus. In the thick subcutaneous tissue of the cartilaginous part of the meatus are numerous ceruminous glands, which secrete the ear-wax; their structure resembles that of the sudoriferous glands.