Human Sensory Organs and Effectors: Functions and Structures
The Eye
The eye receives light where the photoreceptors are located. Photoreceptors in the eye transform stimuli into electrical impulses and transmit the information to the optic nerve.
- Lens: transparent and elastic organ
- Retina: innermost layer, two types of photoreceptor cells (rods and cones)
- Choroid: second layer, the iris appears colored. In the center of the iris there is an orifice called pupil.
- Sclera: outermost layer, frontal part (transparent, forming the cornea)
- Fovea: best visibility
- Blind spot: part of the retina where the nerve ending exits. There is no sight, no photoreceptor cells.
- Optic nerve: group of nerve cells, communicate with rods and cones.
- Eyebrows: divert sweat, protect the eye.
- Eyelids: protect the ocular globe. Conjunctiva covers the frontal part of the eye.
- Eyelashes: diffuse light.
- Ocular muscles: move the ocular globe, to direct our sight to the object.
- Lacrimal glands: secrete tears, keep the eye humid to avoid dryness, contain a substance that kills bacteria.
The Function of the Ocular Globe
The function of the ocular globe is to allow light to stimulate cones and rods in the retina. Produce a nervous impulse by the optic nerve.
- Regulation of light intensity: The pupil intervenes in this mechanism of light regulation, opening and closing according to light conditions. Contracting and relaxing tiny muscles located in the iris.
- Focusing on images: By modifying the lens, it flattens to focus on objects that are far away and widens to see objects that are near
The Ear
The ear perceives two types of stimuli (sounds and changes of body posture ”balance”)
- The outer ear: formed by the pina and auditory canal, which penetrates. Elastic membrane called the eardrum.
- The middle ear: starts at the eardrum. Three small bones (the hammer, anvil, and stirrup)
- The inner ear: separating the two labyrinths there is a fluid, perilymph, another type of fluid, endolymph. Cochlea detects sounds. Vestibular system, is responsible for spatial awareness and balance. Composed of three semicircular canals and two vesicles (the utricle and saccule)
Hearing Mechanism
Vibrations in molecules found in the air produce sound waves. Waves reach the eardrum, it vibrates and transmits the vibration thought to the ossicles. The last bone, the stirrup, transfers the vibration perilymph to vibrate. As a consequence, certain cells (located inside the cochlea, forming the organ of Corti) are stimulated. A nervous impulse through the nerve to the brain.
Balance Mechanism
- Perception of static balance: Inside the utricle and saccule, there are sensory cells that have cilia covered by a gelatinous mass containing small mineral particles. Varying the position of the head, change the position of the cilia, generating a nerve impulse that reaches the cerebellum. The cerebellum receives information about balance.
- Perception of dynamic balance: it occurs in the semicircular canals. Relative movement between the endolymph and certain cells in the vestibular system. The cells are covered in a gelatinous mass and have cilia. This generates a nerve impulse that reaches the brain.
The Skin
The skin is an organ that has sensory receptors that perceive very diverse stimuli through touch.
- The shape and texture that objects have
- Pressure occurring as a result of strong tactile sensations
- Heat and cold
- Pain: pain receptors which are just free nerve endings, the other touch receptors.
In addition to sensory receptors, the skin has other structures responsible:
- Melanocytes: cells that contain dark pigments (melanin) that protect the body from solar radiation.
- Adipose tissue: fat, protects the body from cold temperatures and acts as an energy reserve.
- Sweat glands: cooling the body surface when necessary and removing certain waste substances.
- Hair: this covers the entire body surface, except the palms, protect us against the cold.
- Sebaceous glands: secrete substances that lubricate the skin and hair.
Taste
Taste detects chemical substances from foods as they dissolve in our saliva. Five basic tastes (sweet, salty, bitter, sour, and umami). Taste receptors are cells that group in taste buds, which are located inside the mouth, especially on the tongue.
Smell
Our sense of smell allows us to perceive gas molecules that reach our nose. In the interior of the nasal passages, an area called the olfactory epithelium where the olfactory receptor cells group, forming the olfactory bulb.
Effectors
The muscles are responsible for changing the position of bones.
Bones
Bones contain calcium salts that make them hard, formed of bone tissue, two types (spongy bone that has cavities, and compact bone that has no internal spaces)
- Long bones: they support and move the body, (the bones found in our limbs)
- Short bones: these are rounded (vertebrae)
- Flat bones: these are plate-shaped, the function of this bone is protective (skull bone)
Cartilages
The skeleton also has cartilage, isn’t as hard as bone because it doesn’t contain calcium salts. (Located in the ears,….) it also forms the skeleton of embryos. Long bones have, for a long period of time, cartilaginous substances that allow them to grow.
Joints
- Fixed: stop the movement of bones, (cranium bones)
- Mobile: these allow bones to move, (knee)
- Semi-mobile: these only allow limited movements of the bones, (vertebrae).
The functions of bones are as follows:
- Anchor the muscles
- Support the body
- Protect delicate organs
- Calcium reserve
- In the interior of bones, blood cells are created
Muscles
Muscles are in charge of maintaining the posture of the body and performing its movements. They work as a lever connected with bones, to which they are joined by tendons.
Types of Muscles
- Striated muscle fiber: muscles join with bones, contract voluntarily.
- Smooth muscle fiber: internal organs, contraction is involuntary.
According to their shape:
- Long or fusiform: the biceps and triceps are fusiform muscles.
- Flat: protect organs (abdomen)
- Circular or sphincters: close or open a cavity or duct (eyer and lips)
Muscle Contraction
Muscles contract by widening and shortening their fibers. Muscles that cooperate to perform one unique movement are called agonists, perform movements in opposite directions.