SENSORY RECEPTION Chapter 18 Senses s convert stimulus energy to action potentials s 1. Are specialized cells, or 2. Specialized endings that detect stimuli All stimuli are forms of energy s in eyes detect light energy s in taste buds detect chemicals such as sugar or salt 1 2 Receptors Sense changes in internal and external environment Interoceptors - detect stimuli inside body Includes s for blood pressure, blood volume, and ph of the blood. Directly involved in homeostasis, regulated by negative feedback Exteroceptors - detect stimuli outside body Includes s for taste, smell, vision, hearing, and equilibrium. They function to inform the CNS about environmental conditions 3 Types of Receptors Chemos: chemical stimuli, smell, blood ph Photos: changes in light Vision (light) Mechanos: mechanical stimuli Hearing, gravity, motion, body position Thermos: temperature Cold, heat 4 Detection occurs when environmental changes, such as pressure to the fingertips or light to the eye, stimulate sensory s Sensation occurs when impulses arrive at the cerebral cortex of the brain Perception occurs when the brain interprets the meaning of stimuli 5 inputs become sensations and perceptions in the brain Perception Figure 29.1 Black Splotches Or a person riding on a horse Is the brain s integration of sensations s provide information to brain and brain processes it 6 1
mv 10/21/2011 How Sensation Occurs Transduction Energy from a chemical or physical stimulus is converted into an electrical signal ( impulse) The stronger the stimulus, the more frequent the action potentials The sensation that results depends on the part of the brain receiving the impulses 7 transduction converts stimulus energy into potentials Which trigger action potentials that are transmitted to the brain Tongue 1. Sugar molecule enters taste bud 2. It binds a specific protein on taste and initiates a signal transduction pathway 3. That causes some ion channels on the to close and others to open; thus generating potential bud pore Action potential Neurotransmitter neuron 4. In response neurotransmitter is released at synapse with sensory neuron and an action potential is No sugar Sugar present generated 5 Action potentials 8 1 Sugar molecule cells neuron Sugar molecule (stimulus) cell Signal transduction pathway Ion channels Receptor potential 2 Ion 3 Membrane of sensory cell 4 Action potential frequency Reflects stimulus strength Action potential generated by distinct stimuli activate distinct interneurons bud Sugar Sugar interneuron Brain neurons Salt interneuron Salt bud Adaptation Repeated stimulus May lead to adaptation, a decrease in sensitivity of sensory s Adaptation of sensory s to a constant stimulus is called sensory adaptation This prevents our nervous system from being overloaded with useless information No sugar Increasing sweetness No salt Increasing saltiness How action potentials transmit different taste sensations? 9 10 Specialized sensory s detect five categories of stimuli Pain s Thermos Mechanos Chemos Photos 11 Pain Receptors Distributed throughout the body externally and internally Detect dangerous stimuli Pain s may respond to excess heat (thermo) pressure (mechano) chemicals released from damaged or inflamed tissues (Chemo; Histamines and acids trigger pain) Thermos Distributed widely on skin Detect heat or cold 12 2
Mechanos Present on skin, internal ears Respond to mechanical energy such as touch, pressure, and sound All these forces produce their effects by bending or stretching the plasma of a cell A variety of mechanos collectively called hair cells detect sound waves in ears Photos Present in eyes Respond to light energy Specialized cells contain different pigments Some responsible for night vision (black and white) Others responsible for color vision (distinct colors) Hairs of cell Neurotransmitter at synapse neuron Action potentials More neurotransmitter Less neurotransmitter Chemos Present in taste buds and nasal cavity Respond to chemicals in foods and odors Specialized cells have proteins to bind specific chemicals Combination of chemicals stimulate specific sets of cells Leads to sensation of specific taste and smell Action potentials 1 Receptor cell at rest 2 Fluid moving in one direction 3 Fluid moving in other direction 13 14 Free endings (pain, heat, cold) Cutaneous Receptors in the Human Skin epidermis Meissner corpuscles (touch) Senses of and Smell and odor s detect chemicals present in solution or air and smell Depend on chemos that bind specific molecules Merkel disks (touch) Pacinian corpuscles (pressure) Krause end bulbs (touch) Ruffini endings (pressure) root hair plexus (touch) dermis 15 16 Sense of buds contain chemos and are located in the tongue (primarily), hard palate, pharynx, epiglottis Different s for salty, sour, bitter, and sweet tastes Umami for amino acid glutamate tonsils epiglottis Buds in Humans sensory fiber supporting cell taste pore Sense of Smell 80-90% of what we perceive as taste is actually smell Olfactory Cells Chemos (modified neurons) located high in nasal cavity Olfactory cells have a tuft of olfactory cilia with s for odor molecules a. Tongue connective tissue d. One taste bud taste cell microvilli 17 18 3
Olfactory Cell Location and Anatomy Sense of Smell frontal lobe of cerebral hemisphere olfactory bulb Olfactory epithelium nasal cavity odor molecules a. sensory fibers olfactory epithelium olfactory bulb neuron olfactory tract Sense of Smell How the Brain Receives Odor Information Each olfactory cell has only one out of about 1,000 different types of proteins Nerve fibers lead to olfactory bulb, an extension of the brain A single odor is composed of many different molecules which activates a characteristic combination of proteins Odor s signature is interpreted by brain supporting olfactory cell cell b. olfactory cilia of olfactory cell odor molecules 19 20 In the human eye The cornea and flexible lens focus light on photo cells in the retina To focus, a lens changes position or shape Focusing Involves changing the shape of the lens Ciliary muscle contracted Choroid Ligaments slacken Sclera Ciliary body Ligament Choroid Light from a near object (diverging rays) Lens Cornea Iris Pupil Fovea (center of visual field) Optic Near vision (accommodation) Ciliary muscle relaxed Ligaments pull on lens Aqueous humor Lens Vitreous humor Artery and vein Blind spot 21 Light from a distant object (parallel rays) Distance vision 22 Corrective lenses Bend the light rays to compensate Shape of A nearsighted eye (eyeball too long) normal eyeball Diverging corrective Focal lens Lens Focal Our photos are rods and cones Rods Allow us to see shades of gray in dim light Cones Allow us to see color in bright light Cell body Rod A farsighted eye (eyeball too short) Shape of normal eyeball Focal Converging corrective lens Focal Cone 23 Synaptic knobs Membranous disks containing visual pigments 24 4
Pressure 10/21/2011 Rods and cones absorb light And send action potentials to the brain Optic fibers Neurons Photos Cone Rod Sense of Hearing and Balance The Ear Has Two Functions Hearing and Balance (equilibrium) s for both of these are located in the inner ear Each consists of hair cells with stereocilia (long microvilli) that are sensitive to mechanical stimulation Mechanos Optic 25 26 The ear converts air pressure waves to action potentials that are perceived as sound The human ear Channels sound waves through the outer ear to the eardrum The sound waves are then transmitted by bones in the middle ear To the fluid in the coiled cochlea of the inner ear Anvil Stirrup Skull bones Semicircular s (function in balance) Auditory, to brain Outer Ear Inner ear Hammer Pinna Auditory Eardrum Middle ear Cochlea Eustachian tube 27 Eardrum Oval window (behind stirrup) Eustachian tube 28 Pressure waves in the fluid of the cochlea Middle Bend hair cells in the organ of Corti against a, triggering signals to the brain Bone Hair cells Tectorial Vibrations from the sound waves Are amplified as they are transferred through the ear Outer Ear Middle Ear Inner Ear Upper Auditory Pinna Auditory Eardrum Hammer, anvil, stirrup Oval window Cochlear s Upper and middle Lower Lower neurons Cross section through cochlea Organ of Corti (Hearing Organ) Basilar To auditory One vibration Amplitude Amplification in middle ear Organ of Corti stimulated Time 29 30 5
SENSE OF BALANCE Volume and Pitch Louder sounds Generate more action potentials Pitches Stimulate different regions of the organ of Corti The inner ear houses our organs of balance The organs of balance Are three Semicircular Canals and Utricle and Saccule located in the inner ear These organs Sense body position and movement 31 32 Sense of Balance (Equilibrium) Mechanos for Equilibrium Rotational Balance (SEMICIRCULAR CANALS) Three semicircular s arranged so that one is in each plane of motion Each semicircular has an enlarged base called an ampulla Each ampulla contains hair cells with stereocilia embedded in a cupula As fluid within a flows and bends a cupula, the stereocilia are bent and this changes the pattern of impulses carried in the vestibular to brain Brain uses this information to make postural corrections semicircular s ampullae cupula stereocilia hair cell supporting cell Vestitular flow of liquid Receptor in ampulla vestibular cochlea liquid 33 34 Sense of Balance (Equilibrium) Mechanos for Equilibrium Gravitational Balance (UTRICLE AND SACCULE) Depends on utricle and saccule Utricle is sensitive to horizontal movements of the head Saccule is sensitive to vertical movements of the head Both contain hair cells with stereocilia embedded in an otolithic Calcium carbonate granules (otoliths) rest on otolithic When head or body moves in horizontal or vertical plane the otoliths are displaced and the otolithic sags, bending stereocilia otoliths otolithic hair cell supporting cell vestibular liquid utricle saccule kinocilium flow of otolithic 35 stereocilia 36 6