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02. Chemical Aspects of Physiology
03. Cell Physiology
07. Respiratory Physiology
09. Nervous System
10. Sense Organs
11. Muscle Physiology
14. Reproductive Physiology
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10. Sense Organs
Sensory organs are essential for smooth function of our bodies. Every time we hear, smell, see, touch, or taste anything we are using our sense organs. Most of us don't even realize how important our sense organs are until something goes wrong with them. It usually will take blurry vision, plugged ears or nose, or maybe experiencing numbness, before we pay slight attention to our senses. This chapter educates us on the importance of the sensory organs and how they function. I will further discuss the vestibular apparatus and its connection with the sense of equilibrium, taste cells, and the types of sensory receptors in our bodies.
1.) Vestibular Apparatus and Equilibrium
The inner ear contains the vestibular apparatus which is the bodies sense organ for motion and gravity detecting. The vestibular apparatus is made up of the utricle and saccule, collectively known as the otolith organs, and the semicircular canals. At the bottom of the semicircular canal is the ampulla which contains sensory hair cells. Our state of physical balance, also known as equilibrium is influenced by the vestibular apparatus. Head movement causes fluid within the structures of the vestibular apparatus to bend extensions of the sensory hairs, located on the bottom of the ampulla. These structures that bend the extensions are located within the membranous labyrinth, which is filled with fluid called endolymph. We experience two types of equilibrium, static and dynamic. Static equilibrium is concerened with the orientation of the body equal with the ground. Static equilibrium is sensed by the utricle and saccule, which allow the body to sense linear acceleration. Linear acceleration is when velocity changes as we are traveling horizontally or vertically. Dynamic equilibrium is concerned with posture and rotational movement. The semicircular canal senses rotational or angular acceleration such as when we turn our head are spinning or tumbling. Movements of the body are detected by the tiny hair cells in the ear. Otolithic membrane is a gelatinous substance in the ear that the hairs of the utricle and saccule are embedded in. When a person is upright the hairs in the utricle and veritcal and the hairs in the saccule are horizontal. Linear acceleration then bends the sterocilia that is supported by the hair cells and sensory endings are stimulated to tell the body what is happening. The semicircular canals also have hair cells embeded in gelatinous cupula, which stick into the endolymph of the membranous labyrinth. Movement of the endolymph then bends the hair cells which stimulates the vestibulocochlear nerve and sends signals to the brain about what movement in happening.
2.) Taste Cells
Taste cells are located on the taste buds and help us determine the flavor of our foods. There are over 10,000 taste cells in our mouths, they cover the tongue,palate, epiglottis and pharynx. Taste cells serve as receptors for taste and make synaptic contact with sensory nerve fibers. Small hairs lie in a pore on a taste cell. When we put something in our mouths, the taste cells bind to it and we are able to sense five categories of flavor- salty, sour, sweet, bitter and umami (savory). Salty taste is caused by the presence of Na+ ions, which activate specific receptors in the taste cell, signaling that the taste is salty. Sour taste does the same but with H+ ions. Sweet, bitter and umami bind with protein receptors that interact with G-proteins to trigger specific receptors and tell us what we are tasting. The facial nerve and glossopharyngeal nerves control the taste buds. The facial nerve is in charge of the anterior two-thirds of the tongue and have dendtritic endings around the taste buds that can help sense touch and temperature. When we taste food the sensations are passed from the medulla oblongata, to the thalamus and then to the cortex. This work fast, imagine having to wait a second to taste your food!
3.) Types of Sensory Receptors
Sensory receptors allow our bodies to respond to environmental stimuli. They help us smell, taste, touch, see, and hear. Sensory receptors work hard all day long without our awareness. Chemoreceptors are sensory receptors that sense chemical stimuli in the environment or the blood. Chemoreceptors respond to our taste buds, olfactory epithelium, and aortic and carotid bodies. Photoreceptors sense stimuli in the rods and cones of the retina of the eye. Thermoreceptors sense stimuli that deal with cold and heat and mechanoreceptors respond to touch and pressure receptors in the skin, hair, and inner ear. Nociceptors are a type of sensory receptor that sense pain. They take longer to activate and require a more intense cause. Proprioceptors consist of muscle spindles, golgi tendon organs, and joint receptors. Proprioceptors help our bodies tell what position they are in and allow detailed skeletal movements. Cutaneous receptors are located on the skin and help us sense touch and pressure, heat and cold, and pain. Special Senses are receptors that sense sight, hearing, taste, smell and equilibrium. All of these sensory receptors can be broke down into two different durations- tonic and phasic. Tonic receptors will fire as long as it is being stimulated, such as if you placed your hand on a hot stove. Phasic receptors will fire fast and then decrease and allow us to adapt to a stimuli. An example of this would be when you put on a fuzzy sweatshirt in the morning and by noon you don't even realize it's fuzzy anymore.
1.) Outer ear funnels in sound waves to the tympanic membrane --> Vibrating tympanic membrane move middle ear ossicles--> Middle ear ossicles move the oval window--> Vibrating oval window send wave of perilymph to scala vestivuli --> Wave moves into the scala media--> Wave moves the basilar membrane--> Basilar membrane moves tiny hairs--> Hairs stimulate nerve impulses
2.) Light enters the cornea of the eye, passes through the pupil and then through the lens which is suspended between the aqueous humour and the iterous humour, the fluid that fills the indside of the eye, at which point it is projected to the retina int he back of the eye. Light must pass through the axons and cell bodies of other neurons before reaching the photoreceptors. Light rays are refracted by the cornea and lens; because of this the image on the retina is upside down and right to left. The right half of the visual field is projected to the right half of the retina in each eye. The optic nerve, composed of the axons of the retina's ganglion cells, then transmits these impulses from the eye to the first visual relay in the brain. The neural pathway leads from the retina to the lateral geniculate body and then to the visual cortex. Since the crossing of the optic fibers the visual cortex of each cerebral hemisphere receives input from the opposite visual field.
Application to Nursing
Senses play and enormous role in our bodies and the bodies of our patients. As a nurse we will be using our senses every second of the day to do our jobs. When first assessing a patient, we will use our eyes to check the appearance of the patient and asses their injury or illness. We will use our hearing to listen to their heart beats and lung sounds, complaints of pain, or breathing. Our sense of smell will tell us if a wound is infected, our hands will be able to touch their skin when doing assessments, take pulse readings and most importantly comfort. Knowing how the sense organs work will allow us to understand the science behind those patients who have suffered vision and hearing loss. Some patients, especially those who are elderly will have problems with their taste receptors. As a nurse we might encounter those who can not taste flavor at all, or those who perceive tastes differently. Many different diseases and symptoms are related to the sense organs and knowing how they work will benefit us greatly.
Human Physiology textbook 11th Ed. Stuart Ira Fox
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