Special Senses - Lecture notes WEEK 9 PDF

Preview

Summary

Special Senses it allows the human body to interpret what is happening around them and respond accordingly. These are the color of the environment, the sound of laughters at party, the scent of eucalyptus and pine, the taste of freshly baked bread all would be meaningless without the senses. Traditi...

Description

Special Senses

- Enclosed and protected by the cushion of fat and the walls of the bony orbit.

- it allows the human body to interpret what is happening around them and respond accordingly.

External and Accessory Structures - These are the color of the environment, the sound of laughters at party, the scent of eucalyptus and pine, the taste of freshly baked bread all would be meaningless without the senses.

●

● -

-

-

Traditionally we have 5 senses: the sense of sight,hearing, smell, and sense of touch touch is the senses that we need to consider why? Because touch has small sensory receptors and does not have specialized organ involved within our human body. Kalat and sense of touch within our skin and even in our visceral organ has a mechanism.

●

●

●

Have only 4 special senses: sense of sight, hearing, smell, and taste. Why they are called special senses? Because they have specialized organ devoted to its own senses.

●

Special Senses -Includes the senses of smell, taste, sight, hearing and equilibrium (pertaining to the sense of hearing; maintains with the ear). - pertaining to a large complex of sensory receptor organs or localized clusters of receptors

● ●

● - Touch is a mixture of general senses (temperature, pressure and pain receptors of the skin and the proprioceptors of muscles and joints).

The eyes are protected by the eyelids, which meet at the medial and lateral canthus(the corner of the eye where the upper and lower eyelids meet.) Palpebral fissure- the only space between the medial and lateral canthus Eyelashes- hair structures that grow at the edge of the eyelids and protect the eye from debris such as dust and some small particles that can come through in our eyes. Tarsal glands - associated with the eyelid edges produce an oily secretion that lubricates the eye. The lacrimal apparatus- consist of lacrimal gland ( our tears; it contains antibodies and lysozymes (destroys bacteria)) and a number of ducts that drain the lacrimal secretions into the nasal cavity. Lacrimal glands continually release a dilute salt solution (tears) onto the anterior surface of the eyeball. ➔ Mechanism: The tears flush across the eyeball into the lacrimal canaliculi medially then into the lacrimal sac, and finally into the nasolacrimal duct which empties into the nasal cavity. Lacrimal duct is connected to nasal cavity mucosa and vise versa The tears cleanses and protects the eye surface as it moistens and lubricates it. Six extrinsic/external eye muscles are attached to the outer surface of each eye that produces gross eye movements and make it possible for the eyes to follow a moving object.

Internal Structures: The Eyeball The Eye and Vision ● - The adult eye is a sphere that measures about one inch in

●

The eye itself, commonly called the eyeball, is a hollow sphere. Its wall is composed of tunics (3

diameter, of which only the anterior one-sixth of the surface can normally be seen.

layers for tunics) or layers and the interior is filled with fluids called humors (fluids inside the eye that

●

helps to maintain the shape of the eyeball). The lens (main focusing apparatus of the eye) divides the eyes into two chambers: the anterior chamber and the posterior chamber

●

Layers (tunics) Forming the wall of the Eyeball: FIBROUS LAYER- the outermost later ●

● ●

Sclera- is a thick white connective tissue. It is seen anteriorly as the “white of the eye”. Cornea- the crystal clear structure of the eye anterior to the pupil and iris. The central anterior portion of the sclera is modified so that it is crystal clear. This transparent “window” is the cornea through which light enters the eye.

Layers Forming the wall of the Eyeball: VASCULAR LAYER -The middle coat of the eyeball. ● The choroid, which is the most posterior region of the vascular tunic, is a blood-rich nutritive tunic that contains a dark pigment. This pigment prevents light from scattering inside the eye. ● The anterior part of the choroid is modified to form two smooth muscles structures: the ciliary body(attached to the lens by a supporting ligament called the Ciliary zonule) and the iris (regulates the amount of light entering to the eye). ● The pigmented iris has a rounded opening called the pupil through which light passes. ● Cranial nerve III (oculomotor) involvement which controls the muscles of the iris. Layers Forming the wall of the Eyeball: SENSORY LAYER- innermost sensory tunic of the eye is the delicate two-layered Retina: ● Pigmented layer – outer layer of retina; composed of pigmented cells. - Mechanism of pigmented cells: absorbs light and prevents light from scattering inside the eye just like the

●

●

receptor cells and stores vitamin A needed for vision. Neural layer –inner layer of retina; contains millions of receptor cells, the rods and cones, which are called photoreceptors = The result is vision. - Mechanism of photoreceptor in our vision: the electrical signal pass from the photoreceptors via a two-neuron chain—bipolar cells and then ganglion cells—before leaving the retina via the optic nerve and being transmitted to, and interpreted by, the optic cortex. The result is vision. The photoreceptor cells are distributed over the entire retina, except where the optic nerve leaves the eyeball. This site is called the optic disc (there is no photoreceptors that may result in blind spot). When light from an object is focused on the optic disc, it disappears from view.

Layers Forming the wall of the Eyeball: SENSORY LAYER: Rods- both rods and cones are not evenly distributed in the retina. ●

●

The rods are most dense at the periphery or edge of the retina and decrease in number as the center of the retina is approached. The rods allows us to see in gray tones in dim light and provide for our peripheral vision.

Layers Forming the wall of the Eyeball: SENSORY LAYER: Cones ●

● ● ●

Cones are most dense in the center of the retina and decrease in number toward the retinal edge. Cones allow us to see the world in color under bright light conditions. Considered as the point of sharpest vision. Anything that we wish to view critically it is focused to the fovea centralis.

choroid vascular layer. Also acts as phagocytes to remove dead/ damage

Layers Forming the wall of the Eyeball: SENSORY LAYER: Varieties of Cones

●

●

There are three varieties of cones: One responds most vigorously to blue light, another to green light. The third responds to a range including both green and red wavelengths of light. Impulses received at the same time from more than one type of cone by the visual cortex are interpreted as intermediate colors.

Lens ● Light entering the eye is focused on the retina by the lens, a flexible biconvex crystal-like structure. ● The lens divides the eye into two segments/chambers: Anterior and Posterior chambers

●

●

●

2 chambers under the lens: The anterior (aqueous) segment, anterior to the lens- it contains a clear watery fluid called aqueous humor (secreted by the choroid). It is similar to blood plasma, and provides nutrient for the lens and cornea. It is reabsorbed into the venous blood through the scleral venous sinus (canal of Schlemm). The posterior (vitreous) segment, posterior to the lens, is filled with gel-like substance called vitreous humor or vitreous body. Prevents the eyeball from collapsing inward by reinforcing it internally. Both fluid, the aqueous humor and vitreous humor maintains intraocular pressure.

Pathway of Light through the Eye and Light Refraction ● Relative convexity of the lens during focusing from a distant and close vision ● Light rays from a distant object are nearly parallel as they reach the eye and can be focused without requiring changes in lens convexity.

●

Diverging light rays from close objects require that the lens bulge more to focus the image sharply on the retina.

●

Light is refracted or bent as it passes substances that has different densities. Light rays are bent in the eye as they encounter the cornea, aqueous humor, lens and vitreous humor. The refractive, or bending power of the cornea and humors is constant. But those of the lens can be changed by changing its shape, that is, by making it more or less convex, so that light can be properly focused on the retina.

.

●

●

● The ciliary body contracts allowing the lens to become more convex. ● The ability of the eye to focus specifically for close objects is called accommodation. The Ear: Hearing and Balance ● To stimulate the receptors of the ear, fluids must be stirred. Sound vibrations move fluid to stimulate hearing receptors, whereas gross movement of the head disturb fluids surrounding the balance organs. ● Receptors that respond to such physical forces are called mechanoreceptors. Anatomy of the Ear ● The ear is divided into three areas: the outer or external ear, the middle ear, and the inner or internal ear.

● The outer and middle ear are involved in hearing only. The

inner ear functions in both equilibrium and hearing. Outer/External Ear ● Pinna or auricle is the shell-shaped structure surrounding the auditory canal opening. ● The external acoustic meatus (auditory canal) is a short, narrow chamber carved into the temporal bone. ● Ceruminous glands can be found in its skin lined walls, which secrete a waxy yellow substance called cerumen or earwax. ● Sound waves entering the external auditory canal eventually hit the tympanic membrane, or eardrum and cause it to vibrate. ● Eardrum or tympanic membrane separates the external from the middle ear. Middle Ear ● The middle ear or tympanic cavity is an air-filled cavity within the temporal bone. ● It is flanked laterally by the eardrum and medially by a bony wall with two openings: the oval window and the round window. ● The pharyngotympanic (auditory) tube runs obliquely downward to link the middle ear with the throat. ● Mechanism of pharyngotympanic (auditory) tube: flattened and closed, but swallowing or yawning can open it briefly to equalize the pressure in the middle ear cavity with the external, or atmospheric, pressure. ● This is an important function because the eardrum will not vibrate freely unless pressure on both of its surface is the same. ● The tympanic cavity is spanned by the three smallest bones in the

3 smallest bones in the body: ➔ hammer (malleus), ➔ anvil (incus), ➔ and stirrup (stapes). ● When the eardrum moves, the hammer moves with it and transfers the vibrations to the anvil. The anvil in turn, passes it on the stirrup which presses on the oval window of the inner ear. Inner/Internal Ear ● The inner ear is a maze of bony chambers called the osseous labyrinth or bony labyrinth. ● subdivided into three: the cochlea, vestibule and the semicircular canals. ● The bony labyrinth is filled with a plasma like fluid called perilymph. Mechanisms of Equilibrium ● The equilibrium receptors of the inner ear, sometimes called the vestibular apparatus ● Mechanism of vestibular apparatus: the sense that cannot be seen, be heard and even felt what it does is to respond

divided into two branches: ● One responsible for monitoring static equilibrium, ● and the other involved with dynamic equilibrium. Static Equilibrium ● Within the vestibule are receptors called maculae that is essential for the sense of static equilibrium. ● The maculae report on the position of the head through the structure of vestibule with respect...