Sense Organs BIO 252
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This 4 page Class Notes was uploaded by Pauline A. Champlin on Wednesday January 20, 2016. The Class Notes belongs to BIO 252 at Clarion University of Pennsylvania taught by Dr. Bonita Bailey in Winter 2016. Since its upload, it has received 84 views. For similar materials see Human Anatomy and Physiology 2 in Biology at Clarion University of Pennsylvania.
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Date Created: 01/20/16
1/19/2016&1/21/2016 CH.16 SENSE ORGANS 1. SENSATION Subjective awareness of the stimulus. A. 4 kinds of information transmitted from sensory receptors i. MODALITY : Refers to the type of stimulus or the sensation it produces. (ex. hearing, vision taste) *How can the brain differentiate between different signals? If the signal comes from a taste bud, it must be a taste. If the signal comes from the ear, it must be a sound. This theory is the LABELED LINE CODE. ii. LOCATION :Encoded by which nerve fibers issue signals to the brain. RECEPTIVE FIELD: The area where sensory neurons detect stimuli. A sensory nerve can cover up to 7 cm in diameter. No matter where the skin is touched it will stimulate the same neuron. *For example: Open one hand. Take two fingers from the opposite hand and touch one spot on your open hand. It should feel like you’re touching one spot with your two fingers when you are touching two. This means the same neuron is being stimulated. Now take your two fingers and touch different spots on your hand. Now you can feel each both fingers in different spots because different neurons are being stimulated. SENSORY PROJECTION: Ability of the brain to identify the site of stimulation. The pathway of sensory signals to their destinations in the CNS are called PROJECTION PATHWAYS. iii. Intensity :Refers to whether a sound is loud or soft, a light is bright or dim, pain is mild or excruciating Etc. Encoded in 3 ways: a. Stimulus intensity rises/ firing frequencies of sensory nerve fibers rise. b. Intense stimuli recruit greater numbers of nerve fibers to fire. c. Weak stimuli activate only the most sensitive group of fibers with higher thresholds. iv. Duration :How long stimulus lasts. Encoded by changes in firing frequency with the passage of time. -Sensory Adaption: The longer the stimulus, the less the neurons will fir and the less stimulus you feel. -Phasic Receptors: Quick to adapt and sharply reduce or stop signaling even if stimulus continues. (ex. smell and cutaneous pressure) Tonic Receptors: Slow to adapt and generate signals slowly. (ex: proprioceptors) 2. CLASSIFICATION OF RECEPTORS A. STIMULUS MODALITY 1. THERMORECEPTORS: Respond to heat & cold 2. PHOTORECEPTORS: The eyes respond to light33 3. NOCIEPTORS: Pain receptors; respond to tissue injury or situations that threaten to damage tissue 4. CHEMORECEPTORS: Respond to chemicals, including odors, tastes, and body fluid composition. 2 5. MECHANORECPTORS: Respond to physical deformation of a cell or tissue caused by vibration, touch, pressure, stretch, tension. B. ORIGIN OF STIMULUS 1. EXTEROCEPTERS: Sense of stimuli external to the body. (Ex. Vision, hearing, taste, smell and cutaneous sensations such as touch , heat, cold, pain.) 2. INTEROCEPTORS: Detect stimuli in the internal organs. Produces feelings of stretch, pressure, visceral pain and nausea. 3. PROPRIOCEPTERS: Sense of position and movement of the body or its parts. (Ex. Muscles, tendons, joint capsule) C. DISTRIBUTION OF RECEPTORS IN THE BODY GENERAL SENSES (SOMATOSENSORY, SOMESTHETIC) 1. Touch 2. Pressure 3. Stretch 4. Heat 5. Cold 6. Pain 7. *Blood Pressure 8. *Composition (* = do not perceive consciously) SPECIAL SENSES (LIMITED TO THE HEAD, INNERVATED BY CRANIAL NERVES) 1. Vision 2. Hearing 3. Equilibrium 3 4. Taste 5. Smell 4
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