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Unformatted text preview: SENSES
Sensory organs are "windows of the brain" Stimulation of sensory receptors sends nerve impulses to CNS cortex = cerebral cortex interprets meaning of sensations = nerve impulses arrive at cerebral Senses are associated with Senses serve Types of Sensory Receptors
= respond to chemical substances (e.g. taste, smell, blood composition, pain) = respond to light energy (e.g. vision) = stimulated by mechanical forces, pressure waves (e.g. hearing, touch, balance) = stimulated by changes in temperature (in skin & hypothalamus) = detect tissue damage (e.g. pain) = detect changes in fluid volume 1 Perception Requires the Brain
Pain stimulus activates pain receptors in skin Sensory neuron carries the message to the CNS via spinal nerve A second neuron carries the message to the other side and then up the cord to a relay center called the thalamus A third neuron carries the message to the area of the brain where the message is decoded as pain Pain in the left finger is "perceived" by the right side of the brain How does the brain "know" where the impulse came from?
Answer: It has a map! 2 Chemical Senses: Pain Millions of nociceptors distributed throughout skin and internal tissues, except brain Damaged cells release chemicals that activate pain receptors; brain responds by releasing natural opiates skin, skeletal muscles, joints & tendons internal organs, muscle spasms/fatigue sensation of pain from internal organs may be wrongly projected to different areas of skin sense presence of missing body part, response of sensory nerves severed during amputation Chemical Senses: Taste Composed of number of taste cells ending in microvilli Microvilli have receptor proteins for certain molecules of taste receptors, concentrated in different regions 3 Chemical Senses: Smell (modified neurons) located in epithelium Each cell has receptor proteins for specific odor molecules Odor recognized by combination of stimulated neurons Smell linked to Eyes
Vision utilizes eyes and brain (~1/3 of cerebral cortex involved in processing visual info) to brain = outer, white layer - transparent = middle, pigmented layer color of eye, regulates size of pupil hole allows light to enter eyeball refracts and focuses light rays = inner layer, contains photoreceptors sensory nerves carry impulses 4 Focusing Requires
Light rays pass through pupil, focused on retina light rays bent (refracted) by cornea and lens image on retina is To focus distant objects, the lens must To focus near objects, the lens must 5 Vision stimulated by light hitting retina sensitive to light & plentiful; provide night vision, peripheral vision & motion perception activated by bright light; provide color vision and fine detail, central vision processing begins in retina before nerve impulses are sent to brain impulses synapse thru rods & cones in back so light must penetrate to back before stimulating impulse Retina Anatomy 6 Medical Problems (elongated eyeball) - lack particular type of cone distant objects out of focus close objects out of focus (short eyeball) fuzzy image (uneven cornea or lens) blocked drainage ducts, fluid pressure destroys nerves opaque lens, can't transmit light cones destroyed Farsighted and Nearsighted Eyes 7 This disease increases the fluid pressure inside the eye, leading to loss of side vision and eventually total blindness. The increased pressure destroys the optic nerve. With early detection, it can be kept under control with pressure reducing eye drops and surgery. Chances of developing it increase with age. There are over five million people blind from glaucoma worldwide There are over 1 million Cataract operations performed annually in the USA. Cataract surgery is an outpatient procedure with a very high success rate. Due to the lack of modern medical technology in the developing world, it is also the world's leading cause of blindness. Over 16 million people are blind from cataracts. 8 Ears
Ears' sensory functions= (external flap) lined with hairs & sweat glands (eardrum) 3 small bones filled with fluid semicircular canals & vestibule cochlea-- The Human Ear 9 Mechanism of Hearing sound waves enter auditory canal, vibrate tympanic membrane ossicles vibrates oval window, pressure passes bends hair cells, sends nerve impulses thru pitch of sound depends on volume depends on Mechanism of Hearing 10 Deafness
What causes hearing loss? Some possibilities are: Hearing Loss
Loud noises can damage hair cells and associated nerves
Hours to damage Loudness Range 1/ Jet takeoff (200ft) 4
1/ 4 Rock concert Subway; Loud headphones 2 8 Motorcycle; Lawnmower Urban Street Normal Talking Quiet Background 0 20 40 60 80 100 120 Loudness (decibels) 11 Cochlear Implants A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf or severely hard-of-hearing. The implant consists of an external portion that sits behind the ear and a second portion that is surgically placed under the skin. An implant has the following parts: , which picks up sound from the environment. A , which selects and arranges sounds picked up by the microphone. A , which receive signals from the speech processor and convert them into electric impulses. An , which is a group of electrodes that collects the impulses from the stimulator and sends them to different regions of the auditory nerve. An implant does not restore normal hearing. Instead, it can give a deaf person a useful representation of sounds in the environment and help him or her to understand speech. 12 ...
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This note was uploaded on 04/17/2008 for the course BIO 1004.212.0 taught by Professor Douglasmerrill during the Winter '07 term at RIT.
- Winter '07