Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

The Study of Viscera (splanchnologia)
Anatomical Characteristics of Analyzers
General esthesiology. Structure of the olfactory and gustatory organs. The organ of vision. Structure, centers, and pathways of the visual analyzer. Organs of hearing and the vestibular apparatus. Structure, centers, and pathways of the auditory and vestibular analyzers. Structure of the skin

Lecture Plan:

1. Concept of analyzers. General structural plan of analyzers.

2. Cutaneous analyzer (Organ of Touch, Temperature, and pain).

3. Proprioceptive analyzer.

4. Visual analyzer.

5. Auditory and Vestibular analyzers.

6. Gustatory analyzer.

7. Olfactory analyzer.

Neural impulses arising from stimuli are perceived by us as various sensations. Sensation is the reflection in human consciousness of objects and phenomena of the external world resulting from their impact on Sense Organs. The Emergence of sensations requires structures that perceive stimuli (information), nerves through which the stimulus is transmitted, and the Cerebral Cortex, where the stimulus is transformed into a fact of consciousness. I. P. Pavlov called this entire apparatus an analyzer: «An analyzer is a complex neural mechanism beginning with the external receptive apparatus and ending in the Brain». Each analyzer consists of three parts:

1) peripheral part – the receptor (or sense organ, or effector);

2) conductor – The pathway of nerve excitation;

3) central part – the cortical end of the analyzer.

The peripheral section of the analyzer is represented by sense organs with embedded receptors, through which a person perceives the surrounding world, receives information, and forms sensations. There are two groups of sensations:

- sensations reflecting The properties of objects and phenomena of the external material world – touch and pressure, temperature, pain, auditory, visual, gustatory, olfactory sensations, and the sensation of gravity;

- sensations reflecting the movements of individual body parts and the state of Internal Organs – kinesthetic, equilibrium, and visceral sensations.

Accordingly, all sense organs are divided into two groups:

1) organs of external sense, which receive nerve impulses from the external environment – exteroceptors – The Organ of touch, temperature, pain (Skin), Organ of Vision, Organ of Hearing, Organ of Equilibrium, taste, and smell;

2) organs of internal sense:

a) those receiving nerve impulses from the proprioceptive field (Muscle-joint sensation associated with movements within the gravitational field) – proprioceptors;

b) those receiving nerve impulses from the interoceptive field (viscera and Blood Vessels) – interoceptors.

In addition to dividing sense organs into two groups, all analyzers, from the perspective of I. P. Pavlov’s DOCTRINE OF THE two signaling systems, can be classified as follows:

1) analyzers of the first signaling system:

a) analyzers of the external world – exteroceptors (organ of touch,

temperature, pain, organs of hearing, vision, taste, smell, and gravity);

b) analyzers of the internal environment of the body:

- proprioceptors (muscle and joint sense);

- interoceptors, which convey stimuli from autonomic organs and blood vessels.

2) analyzers of the second signaling system:

a) analyzers of spoken language;

b) analyzers of written language.

The analyzers of the First and Second signaling systems differ significantly: analyzers of the first signaling system comprise all three components (peripheral part, conductor, central part), whereas analyzers of the second signaling system lack receptors and conductors, consisting solely of the central part — the cortical end of the analyzer. Analyzers of the second signaling system process their signals on The basis of the first signaling system's analyzers, without which they cannot function.

The cutaneous analyzer ensures the perception, transmission, and conscious Processing of exteroceptive information. The receptor apparatus of these Sensory systems is located in the skin. The skin protects the body from external influences, participates in thermoregulation and metabolic processes, performs a respiratory function, and serves as an energy storage site. The skin is divided into a superficial layer, the epidermis, and a deep layer, the dermis. The epidermis consists of stratified squamous epithelium, the Superficial layer of which gradually keratinizes and desquamates. The dermis is composed of Connective Tissue, elastic fibers, and muscle Cells.

The peripheral part of the cutaneous analyzer is represented by specialized nerve endings located in various layers of the skin, mucous membranes, tendons, ligaments, and other anatomical structures. Tactile receptors perceive stimuli that form the sensation of touch and pressure. These receptors include tactile corpuscles (Meissner's corpuscles), lamellar corpuscles (Pacinian corpuscles), and tactile menisci (Merkel discs). They are distributed in the epidermis, blood vessels, and deep layers of the skin on the palmar surface of the hand (especially fingertips), Lips, tendons, Peritoneum, and intestinal mesentery.

Temperature sensitivity is the sensation of warmth and cold. Thermal stimuli are perceived by Ruffini endings, while cold stimuli are perceived by Krause end bulbs, which are located in the connective tissue stroma of the mucous membrane beneath the epidermis.

Pain receptors are specialized free nerve endings found not only in the skin but also in Muscles, bones, and internal organs. When reaching a certain intensity, pain stimuli trigger the sensation of pain. Information from pain receptors travels via the spinothalamic pathway — through the Spinal Cord and thalamus to the cortex of the postcentral gyrus.

Stimuli from cutaneous sensitivity receptors are transmitted to the cortical end of the cutaneous analyzer, which is located in the postcentral gyrus.

The proprioceptive analyzer ensures the perception, transmission, and conscious awareness of proprioceptive information regarding muscle and joint sense, as well as the response to any external stimulus. Muscle and joint sense arises from Changes in the degree of tension in the Joint Capsule, tendons, and Muscle contraction. Thanks to muscle and joint sense, an awareness of the body's position and THE POSITION OF its parts in space, as well as changes in this position, is formed. The receptor part of the proprioceptive analyzer is represented by proprioceptors. From the proprioceptors of tendons, muscles, bones, and joints, information travels via proprioceptive pathways to the precentral gyrus of the cerebral cortex or to the Cerebellum.

The visual analyzer. The peripheral part of the visual analyzer is the eye, the conductive part is the Optic nerve, and the central part is the visual cortex of the occipital lobe of the cerebral hemispheres (calcarine sulcus).

The eye consists of the Eyeball and surrounding accessory structures. The eyeball is located in the Orbit. It features an anterior pole (the most protruding point of the cornea) and a posterior pole (located laterally to the exit point of the optic nerve). The axis connecting these two poles is called the external axis. The internal axis of the eye is the axis drawn from the posterior surface of the cornea to the retina. If the internal axis is longer, light rays after refraction converge at a focal point in front of the retina (myopia); if it is shorter, they converge behind the retina (hyperopia). The visual axis is the axis drawn from the anterior pole to the fovea centralis of the retina. The wall of the eyeball is formed by three tunics: external, middle, and internal.

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The external tunic is fibrous and performs a protective function; it is divided into a large posterior part, the sclera, and a smaller anterior part, the transparent, avascular cornea. The anterior surface of the cornea is convex, while the posterior surface is concave.

The middle vascular tunic (uvea) has three sections: the iris, the ciliary body, and the choroid proper. The iris is rich in blood vessels, with a circular opening in the center called the pupil. The Base of the iris is formed by the sphincter pupillae muscle and the dilator pupillae muscle, which alter the pupil size and act as a Diaphragm for light rays entering the eye. The iris contains pigment, The amount of which determines eye color. The ciliary body is located behind the iris; a significant part of it is the ciliary muscle, which participates in visual accommodation. The choroid proper consists of three layers of blood vessels that provide Nutrition to the eye.

The internal tunic of the eyeball is the retina — the peripheral part of the visual analyzer, which performs a photosensitive function and consists of 10 layers. The primary components are photoreceptor Neurons, bipolar neurons, and ganglion cells.

Photoreceptor neurons include rods and cones. Rods are receptors for dim-light (scotopic/evening) vision, highly photosensitive, scattered throughout the retina, and provide information on object outlines and movement. Cones are receptors for daylight (photopic) vision, color-sensitive, located in the macula lutea, and provide information on object color and sharp form. Bipolar (conduction) neurons transmit information; the axons of ganglion cells form the optic nerve. The posterior region of the retina, known as the fundus, features the macula lutea and the optic disc. The macula lutea is the area of cone Cell concentration and maximum visual acuity. The optic disc is the site where the optic nerve exits the eyeball; this

area is insensitive to light and does not produce visual sensation. The core of the eyeball comprises the transparent refractive media of the eye:

- the lens — transparent, avascular, enclosed in a capsule;

- the vitreous body — located behind the posterior capsule of the lens;

- the anterior chamber of the eye — situated between the cornea and the iris, filled with aqueous humor;

- the posterior chamber of the eye — located between the iris, the lens, and the suspensory ligament (ciliary zonule), filled with aqueous humor.

The core of the eyeball Functions as the optical apparatus. Accessory structures include the eyebrows, eyelashes, eyelids, conjunctiva (lining the inner surface of the eyelids and the outer surface of the eyeball), and extraocular muscles.

The peripheral part of the auditory and vestibular analyzer is the sensory organ—the Vestibulocochlear Organ, located within the Inner ear. The ear is divided into the outer ear, Middle ear, and inner ear.

The outer ear consists of the auricle (pinna) and the external acoustic meatus. The auricle is formed by Cartilage covered with skin and serves to capture sound waves. The external acoustic meatus is a continuation of the auricle, lined with skin containing glands that produce earwax (cerumen).

The middle ear consists of the tympanic cavity and the auditory (Eustachian) tube; it is filled with air and separated from the outer ear by the tympanic membrane. The outer surface of the tympanic membrane is covered with skin, and the inner surface is lined with mucous membrane. The tympanic cavity communicates with the mastoid antrum of the Temporal bone and is situated within the petrous part of the temporal bone. The tympanic cavity contains three small bones (ossicles): the malleus, incus, and stapes. The malleus is fused with the tympanic membrane and articulates with the incus, which in turn articulates with the stapes. The chain of auditory ossicles performs two functions: the osseous conduction of sound and the mechanical transmission of sound vibrations to the oval window of the vestibule. The Movements of the ossicles are regulated by two muscles: the tensor tympani and the stapedius muscle. The auditory tube lies within the musculotubal canal, connecting the tympanic cavity to the Pharynx.

The inner ear—the vestibulocochlear organ, or labyrinth—is located within the petrous part of the temporal bone between the tympanic cavity and the internal acoustic meatus. It is divided into the outer (osseous) and inner (membranous) labyrinths. The osseous labyrinth includes:

- the vestibule: its medial wall features the internal opening of the vestibular aqueduct; the vestibule forms the central part of the labyrinth, which communicates via openings with the semicircular canals and the cochlear canal;

- the semicircular canals, which open into the posterior wall of the vestibule via five openings; there are three such canals—the anterior (superior, sagittal), posterior (frontal), and lateral (horizontal). Each semicircular canal has two limbs: a simple limb and an ampullary limb, which features a dilation called the ampulla; the simple limbs of the anterior and posterior canals merge into a common crus (limb);

- the cochlea, which opens via an aperture on the anterior wall of the vestibule; the cochlea is a spiral canal making 2.5 turns around the cochlear axis. The axis of the cochlea is a bony pillar around which the osseous spiral lamina winds. At the base of the cochlea lies the internal opening of the cochlear canaliculus. The membranous labyrinth lies inside the osseous labyrinth and includes:

o the utricle: its internal surface features an elevation known as the macula, which serves as an equilibrium receptor for linear movements; these elevations bear otoliths (microscopic crystalline structures made of calcium carbonate) that stimulate the maculae during movement;

o the semicircular ducts with their ampullae, which contain the equilibrium receptors for rotational movements—the cristae ampullares; located on the internal surface of the semicircular canals, these specialized sensory cells are stimulated by the movement of endolymph as the body moves through space, thereby maintaining balance;

o the cochlear duct, which occupies the middle portion of the spiral canal of the cochlea, dividing it into the lower scala tympani and upper scala vestibuli; sensory cells arranged like cilia (the organ of Corti) are located on the basilar membrane of the tympanic wall.

The peripheral part of the gustatory analyzer is represented by taste receptors located in the taste papillae of the Tongue, which contain ellipse-shaped taste buds with a pore (pit) at the apex; fluid containing dissolved substances that stimulate taste receptors flows into this pit. The conductive pathway of the gustatory analyzer: information from receptors located on the anterior 2/3 of the tongue travels via the trigeminal and facial nerves, while information from receptors on the posterior 1/3 travels via the Glossopharyngeal nerve to the Medulla Oblongata, then via the thalamus to the parahippocampal gyrus in the temporal lobe of the cerebral cortex (the central part of the analyzer).

The peripheral part of the olfactory analyzer consists of olfactory receptor cells located in the mucous membrane of the superior nasal meatus and the nasal septum. The conductive pathway of the olfactory analyzer originates from the olfactory cells in the nasal mucosa, passes through the cribriform plate of the Ethmoid bone as 15–20 delicate filaments into the olfactory bulb, and from there via the olfactory tract and subcortical olfactory centers reaches the parahippocampal gyrus in the temporal lobe of the cerebral cortex (the central part of the analyzer).