Chapter 10 Special Senses I. Receptors and Sensations A. Receptors commonly used for sensory 5 General Groups: 1. Changes in chemical concentration (chemoreceptors) 2. Tissue Damage 3. Changes in temperature (thermoreceptors) 4. Changes in pressure or movement in fluids (mechanoreceptors) 5. Light Energy (photoreceptors) B. Sensations a feeling that occurs when sensory impulses are interpreted by the brain. Sensory Adaptation can occur. This occurs when you become acoustom to a smell in a room. C. Somatic Senses senses associated with the skin Touch and Pressure Senses: 1. Sensory nerve fibers common in epithelial tissue (touch and pressure) 2. Meissner s corpuscles oval masses in connective tissue (many in hairless areas = lips, fingertips, palms, soles, nipples, genitals) Sensitive to motion of objects that barely touch the skin or light touch 3. Pacinian corpuscles common in deeper skin - tendons/muscles/ligaments - sensitive to heavy pressure D. Temperature Senses Heat receptors above 77 F and below 113 F - trigger pain and burning sensation Cold receptors above 50 F and 68 F - most sensitive area - If colder, the freezing sensation occurs
*Both temp. ranges can vary if stimulation is continuous. II. Sense of Pain - Have a protective function in tissues being damaged. - The pain sensation is usually unpleasant and causes a stimulus. A. Nerve Fibers 2 main types: 1. acute pain fibers are fast conducting 2. chronic pain fibers are slower conducting B. Steps to regulation of pain 1. awareness of pain occurs when impulses reach the thalamus 2. the cerebral cortex judges the intensity of pain and locates its source 3. impulses descending from the brain cause neurons to release painrelieving neuropeptides. III. Sense of Taste A. Taste Receptors - modified epithelial cells grouped together, taste buds, which are receptor - each bud has a circular opening called the taste pore with little hairs called taste hairs sensitive part of receptor - the nerve fibers are intermixed into taste cells where an impulse is triggered to the brain - taste must be dissolved in saliva from salivary glands before it can be detected. B. 4 Primary Taste Sensations 1. sweet 2. sour 3. salty 4. bitter - Some say there are two more: alkaline and metallic - Some of the taste will be mixed together - some will also trigger pain receptors to cause burning (hot peppers) - Impulses travel from taste receptors to nerve fibers and to the thalamus. It is
then relayed to the gustatory cortex in the parietal lobe of the cerebrum for recognition. IV. Sense of Smell A. Olfactory Receptors - similar to taste receptors and work together - chemoreceptors - are neurons with cilia B. Olfactory Organs - yellowish-brown masses that cover the nasal cavity - Nerve impulses travel from the olfactory receptors and olfactory tracts to interpreting centers in the temporal and frontal lobes of the cerebrum C. Olfactory Stimulation - adapt rapidly - occur when various gases combine with cilia on the receptors - some of the taste will V. Sense of Hearing Ear has 3 parts: 1. external 2. middle 3. inner The ear also has the function of equilibrium. A. External Ear 1. outer funnel-like structure called auricle (pinna) 2. S-shaped tube called external auditory meatus (external auditory canal) Sounds produced by vibrations and then transmitted through matter in the form of sound waves. B. Middle Ear 1. includes air-filled space in temporal bone called the tympanic cavity 2. tympanic membrane is the ear drum
3. 3 small bones called auditory ossicles Tympanic membrane is a semitransparent membrane covered by a thin layer of skin on its outer surface and inner surface - Sound waves that enter the auditory meatus cause pressure changes on the eardrum which moves back and forth and reproduces the vibrations of the sound wave source. 3 Auditory Ossicles - malleus, incus, stapes - covered by ligaments and covered by mucous membranes - form a bridge connecting the eardrum to the inner ear and functions to transmit vibrations beneath these parts Oval Window - leads to the inner ear - vibration of the stapes at the oval window causes motion of a fluid within the inner ear. - this causes stimulation of the hearing receptors Auditory Tube - Connects middle ear to throat - It helps maintain equal air pressure on both sides of the eardrum and is needed for normal hearing Inner Ear - 2 sections 1. Osseous labyrinth bony canal in temporal bone 2. Membranous labyrinth tube in osseous labyrinth - contains its own fluid (endolymph) - in between each labyrinth is fluid called perilymph Semicircular canals provides a sense of equilibrium Cochlea function in hearing (looks like a snail) The organ of Corti contains hearing receptors, which are stimulated by
vibrations in the fluids of the inner ear. Different frequencies of vibrations stimulate different sets of receptors. How we hear sound: 1. Sound waves enter external auditory meatus 2. Change in pressures cause eardrum to vibrate 3. Auditory ossicles (3 bones) amplify and transmit vibration to oval window. 4. Vibrations pass through inner ear to stimulate receptor cells 5. Cells release neurotransmitters to nearby sensory neurons 6. This triggers the auditory cortex of temporal lobe to interpret sensory impulses. Sense of Equilibrium Involves two senses. 1. Static Equilibrium - sense the position of the head - stability of the head and body when they are motionless - When your head is upright, the hair cells in the bony area beneath the cochlea and the semicircular canals are upwards in a gellatin like material. - Usually occurs when the head is bent forward, backward, or to the side. - This sends the message to the brain as to the position of the head. 2. Dynamic equilibrium - balancing head and body when they are moved or rotated suddenly. - the hair cells of the semicircular canals are stimulated by rapid turns of the head and body. - the hairs will bend in the opposite direction that the head is moving. - this tells the brain what position the head is in. VI. Sense of Sight - includes eyelids, lacrimal structures, and muscles as well as the eye. - these structures are inside the orbital cavity - fat, blood vessles, nerves, connective tissue, and bone are also inside the orbital
cavity. Eyelid: made of 4 layers 1. skin 2. muscle 3. connective tissue 4. conjunctiva (membrane on top of eye) Lacrimal Gland: secretes tears through ducts and keeps eyes moist and reduces chance of infections in eye Extrinsic muscles: 6 muscles that move the eye Eye: hollow, spherical structure about 2.5 cm in diameter - 3 distinct layers: fibrous tunic, vascular tunic, nervous tunic - a fluid is in the eye to provide support and maintain shape Outer Eye: 1. Cornea bulges forward in front of eye. Function: helps focus entering light Structure: thin layer with no blood vessels and few cells 2. Sclera white portion of eye Function: provides protection and attachment point of muscles Structure: collagenous and elastic fibers 3. Optic Nerve send and receive impulses 4. Blood Vessels provide nutrient supply to cells of eye Middle Eye: 1. Choroid coat goes around eye Function: contains melanin which absorbs excess light and helps keep the inside of eye dark. 2. Ciliary Body thick part that s connectedto lens 3. Lens transparent and behind iris and pupil Function: aids in viewing objects far and close
Distant objects muscles relax and tension on ligaments increase and lens becomes thinner and less convex Closer objects muscles contract and tension on ligaments relax and lens thickens and is more convex 4. Iris colored portion Function: divides eye into 2 sections 5. Pupil in center of iris Function: adjusts to let light amounts into eye Inner Eye: 1. Retina in back of eye Function: contains visual receptor cells (photoreceptors) 2. Fovea Centralis yellowish spot in center of retina Function: helps produce sharper images 3. Optical Disk nerve fibers from retina become part of optic nerve *blind spot of eye because no receptor cells 4. Vitreous humor jelly-like liquid in eye Function: supports eye and maintains shape Visual Receptors 2 types: 1. rods long thin projections - responsible for colorless vision in relatively dim light 2. cones short, blunt projections/responsible for color vision Visual pigments: - light-sensitive pigment in the rods decomposes in the presence of light and triggers a complex series of reactions that initiate nerve impulses - color-vision is related to the presence of 3 sets of cones containing different light-sensitive pigments Visual nerve Pathway - Axons leave eyes to form optic nerves
- Thus nerves then cross over each other before getting to the brain at the optic chiasma - most of the fibers enter the thalamus and synapse with others that continue to visual cortex in the occipital lobes.