Sensory organ

The sensory organs are sense organs, which are sensitive to various types of stimuli from the external and internal environment. The sensory organs are part of the sensory system that transform the perceived stimuli into nerve impulses that are transmitted to the brain where they are interpreted to obtain information from the environment and generate an appropriate response.
There are external sensory organs, which obtain information from the outside world such as the tongue, the skin, the nose, the eyes, the ear. At the same time, it is necessary to receive information on the functioning of the internal organs, for example through the nerves or the circumventricular neurohematic organs in the cerebral ventricles, in order to promote a state of metabolic equilibrium called homeostasis.
The eyes receive and transform energy in the form of light. The ears capture and perceive energy in the form of sound. The skin is sensitive to the energy that reaches the body through temperature, pressure and contact. The chemical reactions that occur on the tongue and in the nose cause electrical reactions that ultimately lead to taste and smell. Neurohematic organs perceive chemical stimuli in the form of concentrations of hormones and other molecules.

Receivers

The sensory organs have different receptors that can be classified according to the origin of the stimuli in:

• Exteroceptors: eyes and ears. They receive external stimuli such as changes in the environment.
• Visceroreceptors or interceptors: they are located inside the body and are stimulated by activities that are performed in the viscera.
• Propioreceptors: are located in muscles, tendons, joints, inner ear and neurohematic.

They receive stimuli from muscles and adjacent areas, such as joints.

Receptors are also classified according to the type of stimulus to which they are sensitive into:

• Quimiorreceptors: They are stimulated with chemicals in solution, as in the senses of taste, smell and neurohematic.
• Mechanorreceptors: They are stimulated with mechanical pressures and sound, as in the sense of touch, ear and balance.
• Photoreceptors: They are stimulated by light and radiation as in sight.
• Thermoreceptors: Respond to the increase in temperature or decrease of this (heat-cold)
• Nociceptors or pain receptors: They respond to excess heat or pressure or the presence of irritating substances, producing an unpleasant sensation known as pain.

The senses

The sensory organs allow us to perceive the senses and interact with the environment.

Sense of smell

The sense of smell is located in the inner part of the nose, precisely in the mucosa of the olfactory epithelium. It is made up of branched hair cells connected to the receptors of the fibers of the first pair of cranial nerves (olfactory), which cross the ethmoid bone and enter the olfactory bulb, and from there connect with the cerebral cortex.

The olfactory receptors are very sensitive, because if they are stimulated by mild odors they are activated. Aromatic substances give off particles, generally in a gaseous state, which are carried away by the air. Upon penetrating to the region of the olfactory epithelium, they dissolve and chemically act on the olfactory cells. The stimuli are conducted to the olfactory bulb and, through the first pair of cranial nerves, to the brain.

To appreciate delicate odors you must inhale forcefully through your nose. If the stimuli are frequent and intense, the receptors fatigue easily. Conditions in the nasal mucosa, inhalants and very intense odors affect the sense of smell.

We capture stimuli produced by the presence of chemicals in the air or in the food that enters the mouth. Parts of the nose, organ in which smell is found:

• Nose stuff.
• Nose cornets.
• Olfactory mucosa.

Sense of taste

The five basic or primary sensations are (these sensations are associated and produce more taste sensations):

• Acid.
• Sweet. Captured by " fungiform" taste buds.
• Salado.
• Amargo. Captured by "caliciform" taste buds.
• Umami.

In general, there are receptors distributed throughout the tongue, and the map of the tongue in which the perception of different flavors is located in certain areas of the tongue is a very common misconception.

Innervation of the sense of taste

• Related to cranial pair IX and cranial pair VII bis.
• In the mouth, the pharynx and the tongue are a tasteful receptor (like buttons). They're mimiorreceptors.
• Wrisberg's intermediary nerve brings the sensations to two thirds of the previous part of the tongue.
• The glosopharyngeal nerve deals with regulating the sensitivity of one third of the back of the tongue and the sensitivity of the palate.
• The X pair has a nice function in the faringe.
• The sensations of taste come in principle to the rachid bulb and then, consciously, to the cerebral cortex.

Taste resides in the tongue, it contains taste buds, which are the sensory organs of taste. On the surface of the tongue there are small projections or papillae, which contain microscopically sized buds or buttons and are open to the surface of the tongue by means of pores (these cells are chemoreceptors).

Sense of hearing and balance

It has a double function:

• Head of audition.
• Regulates the sense of balance that depends on the ear

The specialized hearing cells are the mechanoreceptors (sensitive to pressure changes), housed in the inner ear. Responsible for hearing and sense of balance.

Anatomy

There are three parts.

1. External hearing
2. Heard half
3. Internal hearing: the stirrup communicates with the inner ear through an hole called an oval window and through the round window. It consists of the following parts:
   1. The gum. She's snail-shaped and responsible for hearing.
   2. Semicircular ducts. They are responsible for balance.

The inner ear has a bony part that contains fluid called perilymph and a membranous part that contains fluid called endolymph.

Basic Mechanisms of Hearing

• The stirrup comes into contact with the oval window.
• The oval window is in contact with the perilinph that transmits the vibration of the middle ear bones through waves (pressure).
• Pressure is produced in the perilinfa of the cochlear vestibular ramp.
• The Reissner membrane is stimulated and the vibration is transmitted through the cochlear duct endolinfa.
• Through receptors with specialized cells called cylios the excitation of the organ of Corti (the main organ of hearing) occurs.
• The organ of Corti transforms the mechanical impulse (waves) into a nervous impulse that is transmitted by the nerve cochlear to the temporal cortex to have the consciousness of hearing.

Basic mechanisms of balance

Responsible for the sense of balance are the semicircular canals of the inner ear oriented in all directions.

• It's three and they're housed in the temporary bone.
• They consist of a bone part (perilinfa) and a membranous part (endolinfa).
• These semicircular ducts communicate with the utricle of the cochle.
• The movement of endolinfa stimulates specialized neurons that are located in an ampoule called acoustic crest that transmit vibrations through the vestibular nerve (part that corresponds to the balance).

Sense of sight

It consists of the ability to detect light and interpret it. Vision is typical of animals, having a system dedicated to it called the visual system. Machine vision extends vision to machines.

The first part of the visual system is responsible for forming the optical image of the visual stimulus on the retina. This is the function of the cornea and lens of the eye.

Cells in the retina make up the sensory system of the eye. The first to intervene are the photoreceptors, which capture the light that falls on them. Its two types are cones and rods. Other cells in the retina are responsible for transforming said light into electrochemical impulses and transporting them to the optic nerve. From there, they project to important regions such as the lateral geniculate nucleus and the visual cortex of the brain.

In the brain begins the process of reconstructing the distances, colors, movements and shapes of the objects that surround us.

Anatomy of the Eye

• Vitreous humor
• Iris
• Membrana conjuntiva
• Crystalline
• Cornea
• ciliar processes
• Corps ciliar
• Eyeball Caps:

1. Sclerotic. External layer in continuity with the cornea. He's the target of the eyes. It has as its mission to protect the eye and its inner layers. It contains the conjunction.
2. Coroids. Medium vascular layer. It ends in the previous part of the ciliar body. It contains nerve and capillary plexies responsible for the nutrition of the retina.
3. Retina. Internal layer where the neurons specializing in catching the luminous signals (cones and batons). It's a very fine membrane. He's in contact with the choroid and the vitreous humor. It's wintered by the optical nerve. It is irrigated through the central artery of the retina. It has two layers.

• An external layer formed by the iris.
• An internal layer formed of radioreceptor neurons that are excited by light. These neurons are cones (especialized in daytime vision) and canes (especialized in night vision).

The retina also contains:

• Optical papill. It's where the optical nerve comes from. It is not light sensitive, so it is used as an exploration area. There are no cones or canes in the optical papill.
• The central vault. It is the area where there is a higher concentration of cones. Inside is the optical macula that is the center of greater visual acuity.

Sense of Touch

The sense of touch is one that allows organisms to perceive qualities of objects and media such as pressure, temperature, roughness or softness, hardness. In the skin there are different classes of nerve receptors that are responsible for transforming the different types of external stimuli into susceptible information to be interpreted by the brain.

Skin is divided into three layers: the epidermis, which is the superficial layer, the dermis, and the hypodermis, which is the deepest layer. The epidermis is made up of epithelial tissue and in its basal or germinal layer we find the so-called melanin, which is the pigment that gives color to the skin, and the dermis by connective tissue. In this layer we find the cutaneous annexes that are the sebaceous glands, the sweat glands, the hair and the nails and the hypodermis formed by adipose connective tissue. We must bear in mind that although the sense of touch is mainly found in the skin, we also find it in the internal nerve endings of the organism, being able to perceive high temperature changes or pain. Therefore, it is the most important of the five senses, allowing us to perceive the risks to our health, both internal and external. The part that governs touch in the brain is the parietal lobe.

The function of the skin is vital for the organism: it draws the attention of the central nervous system to wounds, burns, bites and any other mechanical, thermal or chemical aggression suffered by the organism. Without this alarm system, the organisms would run the risk of not realizing that they are being attacked. These stimuli are picked up by receptors distributed throughout the dermis and epidermis, which are generally specialized in one or more types of sensations.

Chemical sense

Chemosensitivity occurs in all cells, depending on the chemoreceptors they express and possess.
By monitoring (or sensing) internal circulating molecules and responding to them, the circumventricular neurohematic organs (NHO/CVO) maintain body homeostasis.
Neurons within the NHO/CVO sensory organs respond to concentrations of certain molecules in the blood, because areas in the third and fourth ventricle lack the usual blood-brain barrier. NHO/CVO detect plasma Na+ levels and osmotic pressure. Neurons have been shown to respond to increases in angiotensin II and Na+ levels in plasma and CSF. CVOs also detect circulating hormones such as cholecystokinin, amylin, and ghrelin.
Neural signals generated by hormonal action on these sensory VOCs are transmitted to various sites in the cerebral cortex to stimulate or inhibit thirst or hunger. For thirst, the likely sites for synaptic binding would be the median preoptic nucleus and thalamic paraventricular nucleus, and the lateral hypothalamus have been identified as pathways from the subfornical organ (SFO) and lamina terminalis organo vasculosum (OVLT) to the cerebral cortex..