Special Senses PDF - Z18SCI

Special Senses Z18SCI – Foundations of Anatomy & Physiology Special How many senses do humans have? Senses How many senses can you name? Which of your senses would you least like to lose? What are Special Senses? There are 5 special s...

Special Senses Z18SCI – Foundations of Anatomy & Physiology Special How many senses do humans have? Senses How many senses can you name? Which of your senses would you least like to lose? What are Special Senses? There are 5 special senses – Vision, Hearing, Taste (Gustation), Smell (Olfaction) & Balance (Equilibrioception) Our other senses are known as general senses What makes the special senses different from the general senses? Special Senses vs. General Senses The special senses all have specialised sensory organs devoted to them: Eyes Ears Nose Tongue Vestibular apparatus Vision The eyes are composed of: An optical component, which focuses the visual image on the receptor cells A neural component, which transforms the visual image into a pattern of graded & action potentials 6 Anatomy of the Human Eye Fig. 7-22 7 Vision The lens bends the light & focuses it on the retina at the back of the eye, which is full of nerve cells. These cells are shaped like rods & cones & are named accordingly. Each eye contains ~ 120 million rod cells & six million cone cells; Rods are more sensitive to light & help us to see in dim light, while Cones function in bright light, allowing us to see colour & fine detail. The information translated from the light by rod & cone cells is sent as electrical impulses to the brain via the optic nerve (CN II) Photoreceptor cells Fig. 7-27 9 Hearing: Sound Fig. 7-36 10 Anatomy of the Human Ear Fig. 7-37 11 Hearing The sense of hearing is based on the physics of sound & the physiology of the external, middle, & inner ear, the nerves to the brain, & the brain regions involved in processing acoustic information. Sound energy is transmitted through gaseous, liquid, or solid medium by setting up a vibration of the medium’s molecules, air being the most common medium. When there are no molecules, as in a vacuum, there can be no sound. 12  Hearing Sound is funnelled from the outside, along the external auditory canal (ear canal). Then, sound waves reach the tympanic membrane, (eardrum) - a thin sheet of connective tissue that vibrates when sound waves strike it. These vibrations travel to the middle ear, causing three tiny bones (the malleus, incus & stapes) — to vibrate. The stapes then pushes the oval window in & out, sending vibrations to the organ of Corti, which is the organ for hearing. Tiny hair cells in the organ of Corti translate the vibrations into electrical impulses which travel to the brain via sensory nerves. Balance (Equilibrioception) We retain our sense of balance because the Eustachian tube in the middle ear equalizes the air pressure in this part of the ear with atmospheric pressure. The vestibular apparatus (vestibular complex) in the inner ear is also important for balance because it contains receptors that regulate a sense of equilibrium. The inner ear is connected to the vestibulocochlear nerve (CN VII), which carries information about Hearing & balance to the brain. Chemical Senses Chemicals binding to specific chemoreceptors are responsible for the detection of taste & smell. 15  Types of Taste Receptors Different chemicals can generate the sensation of taste by differentially activating a few basic types of taste receptors: Sweet Sour Salty Bitter Umami (pronounced “oo-MAH- mee”). Umami is associated with the taste of glutamate & similar amino acids - sometimes described as conveying the sense of savouryness or flavourfulness. 16 Signalling of Taste Receptors Each group of tastes has a distinct signal transduction mechanism. Salt taste = Na+ Sour taste = H+ Sweet taste = glucose Bitter flavour is associated with many poisonous substances, especially plant alkaloids Umami receptor cells are activated by glutamate. 17 Olfactory Receptors The olfactory receptor neurons lie in the olfactory epithelium, in the upper part of the nasal cavity. Olfactory receptor neurons live for ~ 2 months - are constantly being replaced via stem cells in the olfactory epithelium. The cilia contain the receptor proteins that provide the binding sites for odour molecules. The axons of the neurons form the olfactory nerve (CN I). 18 Olfactory receptors Fig. 7-48 19