18 The Nervous System: General and Special Senses PowerPoint® Lecture Presentations prepared by Steven Bassett Southeast Community College Lincoln, Nebraska © 2012 Pearson Education, Inc. Introduction • Sensory information arrives at the CNS • Information is “picked up” by sensory receptors • Sensory receptors are the interface between the nervous system and the internal and external environment • General senses • Refers to temperature, pain, touch, pressure, vibration, and proprioception • Special senses • Refers to smell, taste, balance, hearing, and vision © 2012 Pearson Education, Inc. Receptors • Receptors and Receptive Fields • Free nerve endings are the simplest receptors • These respond to a variety of stimuli • Receptors of the retina (for example) are very specific and only respond to light • Receptive fields • Large receptive fields have receptors spread far apart, which makes it difficult to localize a stimulus • Small receptive fields have receptors close together, which makes it easy to localize a stimulus. © 2012 Pearson Education, Inc. Figure 18.1 Receptors and Receptive Fields Receptive Receptive field 1 field 2 Receptive fields © 2012 Pearson Education, Inc. Receptors • Interpretation of Sensory Information • Information is relayed from the receptor to a specific neuron in the CNS • The connection between a receptor and a neuron is called a labeled line • Each labeled line transmits its own specific sensation © 2012 Pearson Education, Inc. Interpretation of Sensory Information • Classification of Receptors • Tonic receptors • Always active • Photoreceptors of the eye constantly monitor body position • Phasic receptors • Normally inactive but become active when necessary (for short periods of time) • Touch and pressure receptors of the skin (for example) © 2012 Pearson Education, Inc. Receptors • Central Processing and Adaptation • Adaptation • Reduction in sensitivity due to a constant stimulus • Peripheral adaptation • Receptors respond strongly at first and then decline • Central adaptation • Adaptation within the CNS • Consciously aware of a stimulus, which quickly disappears © 2012 Pearson Education, Inc. The General Senses • Classification of the General Senses • One classification scheme: • Exteroceptors: provide information about the external environment • Proprioceptors: provide information about the position of the body • Interoceptors: provide information about the inside of the body © 2012 Pearson Education, Inc. The General Senses • Classification of the General Senses • Another classification scheme: • Nociceptors: respond to the sensation of pain • Thermoreceptors: respond to changes in temperature • Mechanoreceptors: activated by physical distortion of cell membranes • Chemoreceptors: monitor the chemical composition of body fluids © 2012 Pearson Education, Inc. The General Senses • Nociceptors • Known as pain receptors • Associated with free nerve endings and large receptor fields. This makes it difficult to “pinpoint” the location of the origin of the pain • Three types • Receptors sensitive to extreme temperatures • Receptors sensitive to mechanical damage • Receptors sensitive to chemicals © 2012 Pearson Education, Inc. The General Senses • Nociceptors • Fast pain: • Sensations reach the CNS fast • Associated with pricking pain or cuts • Slow pain: • Sensations reach the CNS slowly • Associated with burns or aching pains • Referred pain: • Sensations reach the spinal cord via the dorsal roots • Some visceral organ pain sensations may reach the spinal cord via the same dorsal root © 2012 Pearson Education, Inc. Figure 18.2 Referred Pain Heart Liver and gallbladder Stomach Small intestine Ureters Appendix Colon © 2012 Pearson Education, Inc. The General Senses • Thermoreceptors • Found in the dermis, skeletal muscles, liver, and hypothalamus • Cold receptors are more numerous than hot receptors • Exist as free nerve endings • These are phasic receptors • Information is transmitted along the same pathway as pain information © 2012 Pearson Education, Inc. The General Senses • Mechanoreceptors • Receptors that are sensitive to stretch, compression, twisting, or distortion of the plasmalemmae • There are three types • Tactile receptors • Baroreceptors • Proprioceptors © 2012 Pearson Education, Inc. The General Senses • Mechanoreceptors • Tactile receptors • Provide sensations of touch, pressure, and vibrations • Unencapsulated tactile receptors: free nerve endings, tactile disc, and root hair plexus • Encapsulated tactile receptors: tactile corpuscle, Ruffini corpuscle, and lamellated corpuscle © 2012 Pearson Education, Inc. The General Senses • Mechanoreceptors • Unencapsulated tactile receptors • Free nerve endings are common in the dermis • Tactile discs are in the stratum basale layer • Root hair plexus monitors distortions and movements of the body surface © 2012 Pearson Education, Inc. Figure 18.3a Tactile Receptors in the Skin Hair Merkel cells and Tactile Free nerve tactile discs corpuscle ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Free nerve endings Sensory nerves © 2012 Pearson Education, Inc. Figure 18.3b Tactile Receptors in the Skin Hair Merkel cells and Tactile Free nerve tactile discs corpuscle ending Merkel cells Ruffini corpuscle Tactile disc Lamellated corpuscle Root hair plexus Merkel cells and tactile discs Sensory nerves © 2012 Pearson Education, Inc. Figure 18.3c Tactile Receptors in the Skin Hair Merkel cells and Tactile Free nerve tactile discs corpuscle ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Free nerve endings of root hair plexus Sensory nerves © 2012 Pearson Education, Inc. The General Senses • Mechanoreceptors • Encapsulated tactile receptors • Tactile corpuscle: common on eyelids, lips, fingertips, nipples, and genitalia • Ruffini corpuscle: in the dermis, sensitive to pressure and distortion • Lamellated corpuscle: consists of concentric cellular layers / sensitive to vibrations © 2012 Pearson Education, Inc. Figure 18.3d Tactile Receptors in the Skin Hair Merkel cells and Tactile Free nerve Tactile tactile discs corpuscle ending corpuscle Epidermis Ruffini corpuscle Lamellated corpuscle Root hair plexus Dermis Tactile corpuscle LM 550 Sensory nerves Capsule Accessory cells Dendrites Sensory nerve fiber Tactile corpuscle; the capsule boundary in the micrograph is indicated by a dashed line. © 2012 Pearson Education, Inc. Figure 18.3e Tactile Receptors in the Skin Hair Merkel cells and Tactile Free nerve tactile discs corpuscle ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Collagen Sensory Capsule fibers nerve fiber Dendrites Sensory nerves Ruffini corpuscle © 2012 Pearson Education, Inc. Figure 18.3f Tactile Receptors in the Skin Hair Merkel cells and Tactile Free nerve tactile discs corpuscle ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Dermis Dendritic process Accessory cells (specialized fibrocytes) Concentric layers (lamellae) of collagen fibers Sensory separated by fluid nerves Lamellated corpuscle LM 125 Concentric layers (lamellae) of collagen fibers separated by fluid Dendritic process Lamellated corpuscle © 2012 Pearson Education, Inc. The General Senses • Mechanoreceptors • Baroreceptors • Stretch receptors that monitor changes in the stretch of organs • Found in the stomach, small intestine, urinary bladder, carotid artery, lungs, and large intestine © 2012 Pearson Education, Inc. Figure 18.4 Baroreceptors and the Regulation of Autonomic Functions Baroreceptors of Carotid Sinus and Aortic Sinus Provide information on blood pressure to cardiovascular and respiratory control centers Baroreceptors of Lung Baroreceptors of Digestive Provide information on lung Tract stretching to respiratory Provide information on volume of rhythmicity centers for tract segments, trigger reflex control of respiratory rate movement of materials along tract Baroreceptors of Colon Baroreceptors of Bladder Provide information on volume Wall of fecal material in colon, Provide information on volume of trigger defecation reflex urinary bladder, trigger urinary reflex © 2012 Pearson Education, Inc. The General Senses • Mechanoreceptors • Proprioceptors • Monitor the position of joints, tension in the tendons and ligaments, and the length of muscle fibers upon contraction • Muscle spindles are receptors in the muscles • Golgi tendon organs are the receptors in the tendons © 2012 Pearson Education, Inc. The General Senses • Chemoreceptors • Detect small changes in the concentration of chemicals • Respond to water-soluble or lipid-soluble compounds • Found in respiratory centers of the medulla oblongata, carotid arteries, and aortic arch © 2012 Pearson Education, Inc. Figure 18.5 Chemoreceptors Chemoreceptive neurons Blood vessel Chemoreceptors in and Trigger reflexive near Respiratory Centers adjustments in of Medulla Oblongata depth and rate of Sensitive to changes in pH respiration and PCO2 in cerebrospinal fluid Chemoreceptors of Carotid Bodies Via cranial nerve IX Sensitive to changes in pH, PCO2, and PO2 in blood Via cranial Trigger reflexive Chemoreceptors nerve X adjustments in of Aortic Bodies respiratory and cardiovascular Sensitive to changes in activity pH, PCO2, and PO2 in blood Carotid body LM 1500 © 2012 Pearson Education, Inc. The Special Senses • The special senses include: • Olfaction (smell) • Gustation (taste) • Equilibrium • Hearing • Vision © 2012 Pearson Education, Inc. Olfaction (Smell) • Olfaction • The olfactory epithelium consists of: • Olfactory receptors • Supporting cells