Published on February 9, 2014
Chapter 12 The Senses
Introduction • General senses • Receptors are widely distributed throughout the body • Skin, various organs and joints • Touch, pain, temperature, pressure, ect. • Special senses • Specialized receptors confined to structures in the head • Vision, Taste, Smell, Hearing 2
Receptors, Sensation, and Perception • Sensory receptors • Specialized cells or multicellular structures that collect information from the environment • Stimulate neurons to send impulses along sensory fibers to the brain • Sensation • A feeling that occurs when brain becomes aware of sensory impulse • Perception • A person’s view of the stimulus; the way the brain interprets the information 3
Receptor Types • Chemoreceptors • Respond to changes in chemical concentrations (smell, taste, pH) • Pain receptors (nociceptors) • Respond to tissue damage • Thermoreceptors • Respond to changes in temperature • Mechanoreceptors • Respond to mechanical forces • Stretch receptors, proprioceptors, baroreceptors • Photoreceptors • Respond to light 5
Sensations and Perception • Projection • Process in which the brain projects the sensation back to the apparent source • It allows a person to pinpoint the region of stimulation
Sensory Adaptation • Ability to ignore unimportant stimuli • Involves a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the cerebral cortex (central adaptation) • Sensory impulses become less frequent and may cease • Stronger stimulus is required to trigger impulses
12.3: General Senses • Senses associated with skin, muscles, joints and viscera • Three (3) groups: • Exteroceptive senses (exteroceptors) • Senses associated with body surface such as touch, pressure, temperature, and pain • Visceroceptive senses (interoceptors) • Senses associated with changes in the viscera such as blood pressure stretching blood vessels and ingestion of a meal • Proprioceptive senses • Senses associated with changes in muscles and tendons such as at joints 8
Touch and Pressure Senses Free nerve endings • Common in epithelial tissues • Simplest receptors • Sense itching Tactile (Meissner’s) corpuscles • Abundant in hairless portions of skin and lips • Detect fine touch; distinguish between two points on the skin Lamellated (Pacinian) corpuscles • Common in deeper subcutaneous tissues, tendons and ligaments • Detect heavy pressure and vibrations 9
Touch and Pressure Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Free nerve endings Section of skin Epithelial cells Epidermis (a) Sensory nerve fiber Epithelial cells Dermis Tactile (Meissner’s) corpuscle (touch receptor) (b) Sensory nerve fiber Lamellated (Pacinian) corpuscle (pressure receptor) Connective tissue cells Sensory nerve fiber (c) b, c: © Ed Reschke 10
Temperature Senses • Warm receptors • Sensitive to temperatures above 25oC (77o F) • Unresponsive to temperature above 45oC (113oF) • Cold receptors • Sensitive to temperatures between 10oC (50oF) and 20oC (68oF) • Pain receptors • Respond to temperatures below 10oC • Respond to temperatures above 45oC 11
Sense of Pain • Free nerve endings • Widely distributed • Nervous tissue of brain lacks pain receptors • Stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature • Adapt very little, if at all 12
Visceral Pain • Pain receptors are the only receptors in viscera whose stimulation produces sensations • Pain receptors respond differently to stimulation • Pain receptors are not well localized • Pain receptors may feel as if coming from some other part of the body • Known as referred pain… 13
Referred Pain • May occur due to sensory impulses from two regions following a common nerve pathway to brain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Liver and gallbladder Lung and diaphragm Liver and gallbladder Heart Stomach Pancreas Small intestine Appendix Ovary (female) Colon Kidney Ureter Urinary bladder 14
Pain Nerve Pathways • Acute pain fibers • Chronic pain fibers • A-delta fibers • C fibers • Thin, myelinated • Thin, unmyelinated • Conduct impulses rapidly • Conduct impulses more • Associated with sharp pain slowly • Well localized • Associated with dull, aching pain • Difficult to pinpoint 15
Regulation of Pain Impulses • Thalamus • Allows person to be aware of pain • Cerebral cortex • Judges intensity of pain • Locates source of pain • Produces emotional and motor responses to pain • Pain inhibiting substances: • Enkephalins • Serotonin • Endorphins 16
Proprioception • Mechanoreceptors • Send information to spinal cord and CNS about body position and length, and tension of muscles • Main kinds of proprioceptors: • Pacinian corpuscles – in joints • Muscle spindles – in skeletal muscles* • Golgi tendon organs – in tendons* *considered to be stretch receptors 17
Stretch Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sensory nerve fiber Sensory nerve endings Golgi tendon organ Sensory nerve fiber Tendon Intrafusal fiber Skeletal muscle fiber Muscle spindle Skeletal muscle fiber Connective tissue sheath (a) (b) 1818
Visceral Senses • Receptors in internal organs • Convey information that includes the sense of fullness after eating a meal as well as the discomfort of intestinal gas and the pain that signals a heart attack 19
Summary of Receptors of the General Senses End of Section 1, chapter 12
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