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Learn about the structure of skeletal muscle, sensory receptors, stimuli types, and conversion processes involved in sensory transduction. Understand the different types of receptors and their adaptations. Video included.
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Sensory Physiology Adelia Handoko, dr., M.Si Physiologiy Department University of Jember 2019
References: Boron WF, Boulpaep E, 2012. Medical physiology. 2nd ed. A cellular and molecular approach. Updated ed. Elsevier Saunders, Philadelphia. Ganong WF, 2005. Review of medical physiology. 22nd ed. McGraw Hill, New York. Guyton AC, Hall JE, 2011. Textbook of medical physiology. 12th ed. WB Saunders Co, Elsevier Inc. Sherwood L, 2010. Human Physiology from Cells to Systems. 7th ed. Brooks/Cole, Cengage Learning. Silverthorn DU, 2010. Human Physiology– An Integrated Approach 5th ed. Pearson Education Inc. San Francisco, CA 94111.
Learning Objection • Structure of Skeletal Muscle • Levels of organization in muscle • Thick- and thin-filament composition • Molecular Basis of Skeletal Muscle Contraction • Sliding filament mechanism • Excitation–contraction coupling • Motor Unit • Neuromuscular Junction • Slow & fast twitch muscle fibers • Neurosensory • Arc reflex • Pain
RECEPTOR PHYSIOLOGY • A stimulusis a change detectable by the body. • Stimuli exist in various energy forms, or modalities, such as heat, light, sound, pressure, and chemical changes. • These stimuli are those associated with the specialsenses of vision, hearing, taste, smell, and equilibrium, and the somatic senses of touch, temperature, pain, itch, and proprioception. • Proprioception, which is defined as the awareness of body movement and position in space, is mediated by muscle and joint sensory receptors called proprioceptors and may be either unconscious or conscious
Afferent neurons have sensory receptors (receptors) at their peripheral endings that respond to stimuli (external and internal) • Because the only way afferent neurons can transmit information to the CNS about stimuli is via action potential propagation, receptors mustconvert these other forms of energy into electrical signals. • The conversion of stimulus energy into a receptor potential is known as sensory transduction.
If the stimulus is above threshold, action potentials pass along a sensory neuron to the central nervous system, where incoming signals are integrated. • Some stimuli pass upward to the cerebral cortex, where they reach conscious perception, but others are acted on subconsciously, without our awareness
“Receptors have differential sensitivities to various stimuli“ • Each type of receptor is specialized to respond to one type of stimulus, its adequate stimulus. • Receptors in the eye are sensitive to light, receptors in the ear to sound waves, and heat receptors in the skin to heat energy
Types of receptors according to their adequate stimulus : • Photoreceptors • are responsive to visible wavelengths of light. • Mechanoreceptors • are sensitive to mechanical energy. • Examples include skeletal muscle receptors sensitive to stretch, the receptors in the ear containing fne hairs that are bent as a result of sound waves, and blood pressure–monitoring baroreceptors. • Termoreceptors • are sensitive to heat and cold.
Osmoreceptors • detect changes in the concentration of sol utes in the extracellular fluid (ECF) and the resultant changes inosmotic activity • Chemoreceptors • are sensitive to specifc chemicals. • Chemoreceptors include the receptors for taste and smell, as well as those located deeper within the body that detect O2 and CO2 concentrations in the blood or the chemical content of the digestive tract. • Nociceptors, or pain receptors, • are sensitive to tissue damage such as cutting or burning.
A receptor may be either • (1) a specialized ending of the afferent neuron or • (2) a separate receptor cell closely associated with the peripheral ending of the neuron. • Stimulation of a receptor alters its membrane permeability, usually by causing nonspecifc cation channels to open.
SOMATIC SENSE • There are four somatosensory modalities: touch, proprioception, temperature, and nociception, which includes pain and itch
Touch Receptors Respondto Many Different Stimuli • Touch receptors are among the most common receptors in the body. • These receptors respond to many forms of physical contact, such as stretch, steady pressure, fluttering or stroking movement, vibration, and texture.
Touch receptors come in many forms • Some are free nerve endings, such as those that wrap around the base of hairs. Others are more complex. • Most touch receptors are difficult to study because of their small size. • However, Pacinian corpuscles, which respond to vibration, are some of the largest receptors in the body, and much of what we know about so matosensory receptors comes from studies on these structures. • Pacinian corpuscles are composed of nerve endings encapsulated in layers of connective tissue
The concentric layers of connective tissue in the corpuscles create large receptive fields. • Pacinian corpuscles respond best to high-frequency vibrations, whose energy is transferred through the connective tissue capsule to the nerve ending, where the energy opens mechanically gated ion channels • Pacinian corpuscles are rapidly adapting phasic receptors, and this property allows them to respond to a change in touch but then ignore it
Definition of pain • "Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage". (The International Association for the Study of Pain)
