The Senses Overview of the Senses Vision Hearing Taste Smell Touch Visceral Senses receptors receives information about the environment (environmental stimuli) receptors generate nerve impulses and send information to the CNS a coordinated response can be directed to maintain homeostasis. Types of receptors: 1. Photoreceptors (light stimuli) Vision – rods and cones found in the retina of the eye 2. Chemoreceptors (chemical stimuli) Taste – taste-buds found in the tongue Smell – olfactory cells found in the olfactory cavity Internal senses – osmoreceptors that regulate blood pressure, CO2 balance, etc. 3. Mechanoreceptors (mechanical enegy stimuli, touch, movement, etc) Touch / pressure / pain – receptors in the skin Hearing – hair cells in the inner ear detect sound waves Balance – hair cells in the ear detect motion Body position – proprioceptors and stretch receptors in the muscles 4. Thermoreceptors (temperature) Temperature – receptors in the skin detect changes in radiant energy Sensation – receiving and processing by the brain of neural impulses from the sensory receptors Perception- interpretation of sensory information by the cerebral cortex. Sensory adaptation/fatigue -neuron becomes accustomed to a stimulus and stops firing. -the adaptation indicates that the environment is not dangerous. Ex. Bed sheets at night, itches that go away The Eye- a photoreceptor (I spy with my little eye) regulate and focus light translate the wavelengths of light into nerve impulses. detects visible light spectrum The External Eye Eyelid –protects the eye. (5) Eyelash – keeps dust and small particles from getting into the eye. Conjunctiva – a thin protective layer on the cornea. (4) Lacrimal Glands located above and at the outer edges of the eye socket. produce salty germicidal fluid that washes dust out of the eyes and keeps them lubricated. This fluid evaporates or drains into the nasal chamber so it must be replaced. Nasal Cavity – drains fluid from the lacrimal glands into the nose. This is why a sharp smell or pinch on the nose makes your eyes water. Internal Structures of the Eye The Eye External Layer: Sclera (1) – tough elastic connective tissue that encases and protects the eyeball (this is the white posterior portion) Cornea (1a)– transparent anterior portion of the sclera, allows light in while keeping other things out, helps focus light on the retina Intermediate Layer: Choroid (2) – darkly pigmented tissue through which blood vessels nourish the back of the eye, pigment absorbs light and prevents reflections Ciliary Body (2a) – thickened portion of the choroid attached to the suspensory ligaments smooth muscle contracts / relaxes to change the shape of the lens, also secretes aqueous humour. Suspensory Ligaments (7a) – attach to the lens and the ciliary muscles Iris (2c) pigmented anterior portion of the choroid composed of circular and radial muscles that control the amount of light that enters the eye Pupil (9) – the opening of the iris that allows light into the eye Internal Layer: Retina (3) two types of photoreceptor cells, rods and cones two layers of cells (bipolar cells and ganglionic cells) that organize visual information before impulses are sent to the brain Fovea Centralis (3a) – slight depression in the back of the eye, area of highly concentrated cones, this is where light is focused for clear, precise color vision Rods – night vision, abundant in the eye, mainly in the peripheral portion of the retina, sensitive to slight movements in dim light Rhodopsin (destingusih light and dark) Pigment in the rods (low light levels) Is broken down (bleached) in high light and must be replaced Rhodospsin is rebuilt at night Vitamin A is used to make retinal Retinal + opsin = rhodopsin No vitamin A can lead to night blindness Cones (determine colors and shades)– color vision, located at the fovea centralis, sensitive to color and bright light 3 color pigment cones: red (long light waves), blue (medium light waves), green (short light waves) When a person lacks one or more of types of cones its called color blindness Other: Lens (7) – flexible, transparent body responsible for focusing light into the retina Optic Nerve (8) – carries visual information to the occipital lobe of the brain for processing Aqueous Humour (10) – thin fluid between the cornea and the lens that refracts light, also absorbs nutrients for the eye tissue Vitreous Humour (12) – jelly-like fluid in the posterior cavity of the eye, gives structure to the eye and prevents the retina from caving in Focusing and Accommodation Extrinsic eye muscles – control movements of the eyeball within the socket (side to side or up and down). There are three pairs of muscles. Ciliary muscles – found within the ciliary body, control the shape of the lens (contracted muscles make the lens round, relaxed muscles flatten the lens) Accommodation – is the flattening or rounding of the lens in order to focus objects on the retina. a focused image is inverted (upside down) The brain ‘rights’ the image To do this neurons join at the optic chiasma and then split to the right and left visual cortex this allows for stereoscopic vision and depth perception. Visual Disorders Myopia (nearsightedness) – See things near but no far away. elongated eyeball, light focuses in front of the retina Need a concave lens to correct Hyperopia (farsightedness) – See thing far away, but not close up shortened eyeball, light focuses behind the retina. Most common type of eye problem Need a convex lens to correct Corrective Lenses Astigmatism – irregular shape to the eyeball or lens causing distortions, the light rays do not converge at one point, instead they scatter Cataracts – proteins in the lens change (usually with age) because of a lack of enzymes, causing the lens to become opaque instead of transparent, mostly caused by UV light (Think of Terminator Moms!) Glaucoma – pressure built up in they eye due to the inability to absorb aqueous humour, results in degeneration of the cells in the back of the eye and eventually blindness (common in untreated diabetics) trabeculectomy The Ear-mechanoreceptor (“…all the better to hear you with my dear…”) sensitive to vibrations Deal with hearing, balance, and equilibrium The Outer Ear (1) Pinna (1a) – folds of the visible ear. Helps to funnel sound waves into the ear. Auditory Canal (1b) – carries sound waves to the middle ear (eardrum). lined with hairs, sweat and glands that produce earwax to prevent foreign bodies from getting into the ear. The Middle Ear (2) Tympanic membrane (1c) – eardrum -a flexible membrane that vibrates when hit with sound waves Ossicles – the three bones in the ear, amplify sound vibrations using leverage Malleus (2a) (hammer) Incus (anvil) (2b) Stapes (stirrup) (2c) Eustachian tube (2d)– extends from the middle ear to the naso-pharynx allows for the equalization of pressure in the ear when you swallow Inner Ear (3) Oval Window (3a) – attached to the stirrup as the stirrup moves the oval window moves creating vibrations in the fluid of the cochlea Round Window (3b) – at the far end of the cochlea puffs outwards to relieve pressure from the oval window creating waves in the cochlear fluid Cochlea (3c) – coiled, fluid filled tube that converts mechanical vibrations into nerve impulses Organ of Corti – Hearing Apparatus projects from the basilar membrane lining the bottom of the cochlear canal Ex) basil membrane has stiff and narrow hairs near the oval membrane (beginning of the cochlea): activated by high frequency wave = high pitch The basil membrane has more elestic hairs near the end wide part of the cochlea, low frequency waves activate these= low pitch Loudness and pitch– related to the amplitude of the sound waves coming into the ear, increases movement of the basilar membrane Basilar membrane lines the bottom of the cochlear canal about 25,000 small nerve fibers ending in hair cells are arranged in order of length along the organ of corti each cell vibrates with a different wavelength of sound giving the sensation of pitch Tectorial membrane sits on top of the hair cells in the basilar membrane moves up and down with the sound vibrations causes brushing and bending of the hairs in the basilar membrane which initiates a nerve impulse Auditory nerve (3d,e) – carries the nerve impulses generated by the auditory cells in the ear to the temporal lobe of the brain Hearing 1) Sound waves move through the auditory canal 2) ear drum vibrates 3) ossicles go into motion 4) oval window vibrates 5) fluid in the cochlea moves 6) fluids moves against organ of corti 7) nerve impulse 8) auditory nerve receive nerve impulse 9) message sent to temporal lobe Balance Static equilibrium: movement in one plane Ex) head movement Dynamic Equilibrium: movement in many planes Ex. Being on a roller coaster ride Static Equilibrium is maintained by: Saccule and Utricle fluid filled sacs with hair cells covered in small carbonate crystals called otoliths as the head is tilted, or the body inverted, the crystals shift and move across the hairs, the hairs bend and send signals to the cerebellum Structures for Balance Vestibular apparatus (3f) –provide information about balance Dynamic Equilibrium is maintained by: Semicircular canals (3g) 3 fluid filled tubes in the X,Y, and Z planes projecting from the cochlea gelatinous fluid moves when the head moves from side to side or back and forth to give information about dynamic equilibrium Ampulla found in the semicircular canals hair cells embedded in a gelatinous material bend with the flow of fluid in the canals, creating a sense of dynamic balance Hearing Problems Conduction Deafness: congenital defect or infection ossicles fuse restricts the ability to magnify sound waves. (hearing aids help) Nerve Deafness: exposure to loud noises and age breakage or destruction of hairs. neurons don’t fire. (hearing aids are ineffective) Tinnitus: ringing in the ears caused by damaged hair cells in the cochlea or by random “static” within the brain The Tongue - chemoreceptors. Taste buds on walls of the papillae (folds) of the tongue, palate, pharynx and the epiglottis. Taste buds can regenerate There are 4 basic taste sensations: Sour – produced by H+ ions in acids Salty – produced by cations (+ ions) from ionized salts such as NaCl Sweet – produced by compounds containing hydroxyl (OH) groups such as alcohols, amino acids, sugars, ketones and lead salts Bitter – produced by alkaloids such as quinine, strychnine and caffeine Old thinking: Taste is often a combination of all four types of receptors giving the perception of different flavors. Taste is enhanced by the sense of smell. Taste may also be genetic. http://www.bbc.co.uk/science/humanbody/body/factfiles/t aste/taste_ani_f5.swf The Nose (The nose knows. Phew!) 3000 times more receptors for smell than for taste. (VERY SENSITIVE, LOTS OF IMPULSES) receptors are located on tissue called the olfactory epithelium. The neurons have modified cilia on the ends of their dendrites that trap and receive airborne (gas or vapor) molecules. http://www.bbc.co.uk/science/humanbody/b ody/factfiles/smell/smell_ani_f5.swf Molecules with different shapes stimulate the olfactory receptors to create the sensation of different smells. These receptors then send impulses to the cerebral cortex Camphor – spherical molecules with diameter of 0.7 nm Musk – disk shaped molecules with a diameter of 1.0 nm Floral – flexible, disk shaped molecules with long side groups Etheral – thin, rod-shaped molecules Peppermint – wedge shaped molecules Olfactory fatigue: when exposed to a smell, over a long period of time, one may no longer sense the smell The Skin largest organ. receptors for touch, pressure, pain and temperature. Proprioceptors – provide information about the position of body parts, joints, tendons, muscles Stretch receptors – found in muscles and around the lungs Visceral Senses Receptors in internal organs mediated by the autonomic nervous system to promote internal homeostasis. maintain blood pH, blood pressure, oxygen levels, blood glucose levels, water re-absorption. give sensations of thirst, hunger and nausea.