Somatic Senses PDF

12/1/22 • Somatic Senses Somatic Senses • Touch • Pressure • Temperature • Pain Assoc. Prof. Dr. Cenk Serhan Özverel • Special Senses • Smell • Taste • Hearing • Equilibrium • vision [email protected] Somatic Senses Classification of Somatic Senses • 3 physiologic types; • *Nerv...

12/1/22 • Somatic Senses Somatic Senses • Touch • Pressure • Temperature • Pain Assoc. Prof. Dr. Cenk Serhan Özverel • Special Senses • Smell • Taste • Hearing • Equilibrium • vision [email protected] Somatic Senses Classification of Somatic Senses • 3 physiologic types; • *Nervous mechanisms that collect sensory information from all over the body. • These senses are in contradistinction to the special senses, which mean specifically vision, hearing, smell, taste, and equilibrium. • (1) the mechanoreceptive somatic senses, which include both tactile and position sensations that are stimulated by mechanical displacement of some tissue of the body; • (2) the thermoreceptive senses, which detect heat and cold; • (3) the pain sense, which is activated by factors that damage the tissues. 1 12/1/22 Other Classifications of Somatic Sensations. • Exteroreceptive sensations à FROM OUTSİDE OF THE BODY • Proprioceptive sensations à relating to the physical state of the body, including position sensations, tendon and muscle sensations, pressure sensations from the bottom of the fee • Visceral sensations à From viscera of body • Deep sensations à Deep tissues Tactile Receptors. • At least 6 types • Some of them are free nerve endings à pressure and touch • Meisner’s corpuscle à Great sensitivity touch receptor. An elongated encapsulated nerve ending of a large (type A ) myelinated sensory nerve fiber. • nonhairy parts of the skin • Fingertips • Lips Detection and Transmission of Tactile Sensations • Interrelations Among the Tactile Sensations of Touch, Pressure, and Vibration. • All detected by the same types of receptors. • 3 principal differences among them: • (1) Touch sensation generally results from stimulation of tactile receptors in the skin or in tissues immediately beneath the skin; • (2) Pressure sensation generally results from deformation of deeper tissues; and • (3) Vibration sensation results from rapidly repetitive sensory signals, but some of the same types of receptors as those for touch and pressure are used. • Meissner’s corpuscles with expanded tip tactile receptors, à Merkel’s discs • hairy parts of the skin • hair end-organ à slight movement of any hair on the body stimulates a nerve fiber entwining its base • Detects mainly • (a) movement of objects on the surface of the body • (b) initial contact with the body. 2 12/1/22 • Different type of somatic sensory nerve endings • Ruffini’s endings, à multibranched, encapsulated endings • signaling continuous states of deformation of the tissues, such as heavy prolonged touch and pressure signals. • Pacinian corpuscles à immediately beneath the skin and deep in the fascial tissues of the body Transmission of Tactile Signals in Peripheral Nerve Fibers. • Almost all specialized sensory receptors (Meissner’s corpuscles, Iggo dome receptors, hair receptors, pacinian corpuscles, and Ruffini’s endings )à via A-beta nerve fibers. • Velocity à 30 to 70 m/sec. • Free nerve ending à via Delta-A myleinated fibers. • Velocity à 5-30 m/sec Detection of Vibration • All tactile receptors can detect. • Pacinian corpuscles à can detect up to 30 to 800 cycles per second à transmit their signals over type A-beta nerve fibers, à1000 impulses per second • Some tactile nerve endings transmit à via Type C unmyelinated fibers. • Velocity à 2 m/sec 3 12/1/22 Sensory Pathways for Transmitting Somatic Signals into the Central Nervous System • Almost all sensory information from the somatic segments of the body enters the spinal cord through the dorsal roots of the spinal nerves. • However, from the entry point into the cord and then to the brain, the sensory signals are carried through one of two alternative sensory pathways: • (1) the dorsal column–medial lemniscal system • (2) the anterolateral system. Differences • Dorsal column–medial lemniscal system à large, myelinated nerve fibers that transmit signals to the brain at velocities of 30 to 110 m/sec, • whereas the anterolateral system à smaller myelinated fibers that transmit signals at velocities ranging from a few meters per second up to 40 m/sec. • These two systems come back together in the level of thalamus. • The dorsal column–medial lemniscal system à carries signals upward to the medulla of the brain mainly in the dorsal columns of the cord àThen, after the signals synapse and cross to the opposite side in the medulla, they continue upward through the brain stem to the thalamus by way of the medial lemniscus. • Conversely, signals in the anterolateral system, immediately after entering the spinal cord from the dorsal spinal nerve roots, synapse in the dorsal horns of the spinal gray matter, then cross to the opposite side of the cord and ascend through the anterior and lateral white columns of the cord. They terminate at all l evels of the lower brain stem and in the thalamus. • Types of sensations transmitted by two systems: • Dorsal Column—Medial Lemniscal System • 1. Touch sensations requiring a high degree of localization of the stimulus • 2. Touch sensations requiring transmission of fine gradations of intensity • 3. Phasic sensations, such as vibratory sensations • 4. Sensations that signal movement against the skin • 5. Position sensations from the joints • 6. Pressure sensations related to fine degrees of judgment of pressure intensity 4 12/1/22 • Types of sensations transmitted by two systems: • Anterolateral System 1. Pain 2. Thermal sensations, including both warmth and cold sensations 3. Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body 4. Tickle and itch sensations 5. Sexual sensations • Projection of the dorsal column–medial lemniscal system through the thalamus to the somatosensory cortex. Transmission in the Dorsal Column–Medial Lemniscal System • Anatomy of the Dorsal Column–Medial Lemniscal System • The dorsal column–medial lemniscal pathway for transmitting critical types of tactile signals. Somatosensory Cortex • 50 distinct areas called Brodmann’s areas based on histological structural differences. 5 12/1/22 • Two somatosensory cortical areas Layers of the Somatosensory Cortex and Their Function • 6 layers of neurons • 1. The incoming sensory signal excites neuronal layer IV first; then the signal spreads toward the surface of the cortex and also toward deeper layers. • Representation of the different areas of the body in somatosensory area I of the cortex • 3. The neurons in layers II and III send axons to related portions of the cerebral cortex on the opposite side of the brain through the corpus callosum. • 4. The neurons in layers V and VI send axons to the deeper parts of the nervous system. • Và basal ganglia, brain stem, and spinal cord • VIà thalamus • 2. Layers I and II receive diffuse, nonspecific input signals from lower brain centers that facilitate specific regions of the cortex 6 12/1/22 Overall Characteristics of Signal Transmission and Analysis in the Dorsal Column–Medial Lemniscal System • Basic Neuronal Circuit in the Dorsal Column– Medial Lemniscal System. Transmission of Less Critical Sensory Signals in the Anterolateral Pathway • Include pain, heat, cold, crude tactile, tickle, itch, and sexual sensations. • Do not require highly discrete localization • Do not require discrimination of fine gradations of intensity. Characteristics of Transmission in the Anterolateral Pathway. • Anterior and lateral divisions of the anterolateral sensory pathway. • (1) the velocities of transmission are only one-third to one-half those in the dorsal column–medial lemniscal system, ranging between 8 and 40 m/sec; • (2) The degree of spatial localization of signals is poor; • (3) The gradations of intensities are also far less accurate, most of the sensations being recognized in 10 to 20 gradations of strength, rather than as many as 100 gradations for the dorsal column system; • (4) The ability to transmit rapidly changing or rapidly repetitive signals is poor. 7 12/1/22 Pain • Protective mechanism • Slow pain àlow burning pain, aching pain, throbbing pain, nauseous pain, and chronic pain. • 2 major types • Fast pain 0.1 sec • Slow pain 1 sec • Fast pain à sharp pain, pricking pain, acute pain, and electric pain • à Ex: needle is stuck into the skin, when the skin is cut with a knife, or when the skin is acutely burned. Pain Receptors and Their Stimulation Dual Pathways for Transmission of Pain Signals into the Central Nervous System • Free Nerve Endings • Three Types of Stimuli Excite Pain Receptors— Mechanical, Thermal, and Chemical. • a fast- sharp pain pathway • a slow-chronic pain pathway. 8 12/1/22 • Peripheral Pain Fibers—“Fast” and “Slow” Fibers. • Fast sharp painà Elicited by either mechanical or thermal pain stimuli; • Transmitted in the peripheral nerves to the spinal cord by small type A-delta fibers at velocities between 6 and 30m/sec • Conversely, the slow-chronic type of pain is elicited mostly by chemical types of pain stimuli but sometimes by persisting mechanical or thermal stimuli. This slow-chronic pain is transmitted to the spinal cord by type C fibers at velocities bet ween 0.5 and 2 m/sec. Pain Suppression (“Analgesia”) System in the Brain and Spinal Cord • The degree to which a person reacts to pain varies tremendously • capability of the brain itself to suppress input of pain signals to the nervous system by activating a pain control system, called an analgesia system. 9 12/1/22 Referred Pain Headache • Often a person feels pain in a part of the body that is fairly remote from the tissue causing the pain. This is called referred pain. • Headaches are a type of pain referred to the surface of the head from deep head structures. • Some headaches result from pain stimuli arising inside the cranium, but others result from pain arising outside the cranium, such as from the nasal sinuses. • Areas of headache resultıng from different causes Types of Intracranial Headache • Headache of Meningitis. • One of the most severe headaches • Causes inflammation of all the meninges, including the sensitive areas of the dura and the sensitive areas around the venous sinuses. Such intense damage can cause extreme headache pain referred over the entire head. 10 12/1/22 • Headache Caused by Low Cerebrospinal Fluid Pressure. • Migraine Headache. • Removing as little as 20 milliliters of fluid from the spinal canal, particularly if the person remains in an upright position, often causes intense intracranial headache. • May result from abnormal vascular phenomena, although the exact mechanism is unknown. • Alcoholic Headache.. • toxic to tissues, • dehydration Extracranial Types of Headache • Headache Resulting from Muscle Spasm. • Emotional tension often causes many of the muscles of the head, especially those muscles attached to the scalp and the neck muscles attached to the occiput, to become spastic, and it is postulated that this is one of the common causes of headache. • Headache Caused by Eye Disorders • Difficulty in focusing one’s eyes clearly may cause excessive contraction of the eye ciliary muscles in an attempt to gain clear vision. Even though these muscles are extremely small, it is believed that tonic contraction of them can cause retro-orbital headache. 11 12/1/22 Thermal Sensations • The human being can perceive different gradations of cold and heat, from freezing cold to cold to cool to indifferent to warm to hot to burning hot. • Thermal gradations are discriminated by at least three types of sensory receptors: • Cold receptors, • warmth receptors, • pain receptors. The end 12