Sensation Chapter 46 Natasha McDougal and Kaleb Hood
Background and Purpose Nerve impulses occur because of a change in action potential Graded potentials in the dendrites and cell body can have either temporal or spatial summation The purpose of this chapter is to discuss how sensory receptors change sensory stimuli into nerve signals that are conveyed to the nervous system and work through the functions listed above
Types of Receptors Mechanoreceptors Detects mechanical compression or stretching of the receptor or of tissues adjacent to the receptor Thermoreceptors Detect changes in temperature with some receptors detecting cold and others warmth Nociceptors (pain receptors) Detect damage occurring in the tissues, either physical or chemical
Types of Receptors Electromagnetic Receptors Detect light on the retina of the eye Chemoreceptors Detect taste in the mouth, smell in the nose, oxygen level in the arterial blood, osmolality of the body fluids, carbon dioxide concentration, and other chemical factors of the body
Classes of Receptors (Table 46-1) Mechanoreceptors Skin Tactile Sensibilities Free Nerve Endings Expanded Tip Endings Merkel s discs Several other variants Spray Endings Ruffini s Endings Encapsulated Endings Meissner s corpuscles Krause s corpuscles Hair End-organs Deep Tissue Sensibilities Free Nerve Endings Expanded Tip Endings
Classes Of Receptors Deep Tissue Sensibilities (cont ) Ruffini s Endings Encapsulated Endings Pacinian corpuscles Plus a few other variants Muscle endings Muscle Spindles Golgi tendon receptors Hearing Sounds Receptors of Cochlea Equilibrium Vestibular Receptors Arterial Pressure Baroreceptors of carotid sinuses and aorta Thermoreceptors Cold Cold Receptors Warmth Warm Receptors
Classes Of Receptors Nociceptors Pain Free Nerve Endings Electromagnetic Receptors Vision Rods Cones Chemoreceptors Taste Smell Receptors of Taste Buds Receptors of olfactory epithelium Arterial Oxygen Receptors of Olfactory Epithelium Osmolality Neurons in or near supraoptic nuclei Blood CO 2 Receptors in or on surface of medulla and in aortic and carotid bodies Blood Glucose, amino acids, fatty acids Receptors in hypothalamus
Specialization of Sensory Receptors Differential Sensitivities Each receptor is sensitive to one type of stimulus and nonresponsive to other types Labeled Line Principle Each nerve fiber transmits only one modality of sensation Receptor components of sensory receptors are dendrites
Receptor Potential Regardless of the type of stimulus receptor potentials all have the immediate effect of changing the membrane electrical potential of the receptor. Ways to cause receptor potentials: 1. Mechanical deformation of the receptor Stretches the membrane and opens ion channels 2. Application of a chemical to the membrane Opens ion channels
Receptor Potential 3. Change of the temperature of the membrane Alters membrane permeability 4. Electromagnetic Radiation Directly or indirectly changes the receptor membrane characteristics and allows ions to flow through membrane channels All result in changes to the transmembrane potential by changes in membrane permeability Receptor action potentials are graded Allows sensitivity to weak signals Receptors do not reach a maximum firing rate until signals are very intense
Receptor Potential and Action Potentials Figure 46-2 When receptor potential rises above threshold it elicits an action potential in the nerve fiber The more that the receptor potential rises above threshold level the greater the action potential frequency
Clicker Question Receptor potentials are caused by: A.Mechanical Deformations B.Chemical Application C.Temperature Change D.Electromagnetic Radiation E. All of the Above
Signal Transduction in Nerves Spatial Summation Signal strength is increased by stimulation of more fibers Each individual nerve is a free nerve ending Together, these create a receptor field Signals are stronger at the center of the field Strong signals will spread to more fibers Temporal Summation Frequency of stimulation affects the strength of the stimulus
Signal Transduction in Nerves Figure 46-7
Signal Transduction in Nerves Figure 46-8
Clicker Question True or False: In spatial summation signal strength is decreased by the stimulation of more fibers
Receptor Adaptation Sensory receptors will adapt partially or completely to a constant stimulus Various receptors adapt at different rates, some very quickly and some barely at all Some sensory receptors are nonadapting receptors Adaptation of receptors is an individual quality
Receptor Adaptation In mechanoreceptors adaptation occurs two ways: 1. Physical changes reducing stimulation 2. Accommodation Changes to nerve fibril that inactivate sodium channels Tonic receptors detect continuous stimulus strength Phasic receptors detect changes as they are actually taking place
Receptor Adaptation Figure 46-5: Adaption of different types of receptors, showing rapid adaption of some receptors and slow adaption of others.
Pacinian Corpuscle An example of a sensory receptor Capsule layers can be compressed or altered in many ways Once compressed, ion channels are opened to sodium This creates a local circuit This leads to the standard action potential signals to the central nervous system The corpuscle is not myelinated, but soon after the central nerve leaves it becomes that way
Clicker Question True of False: Sensory receptors are not myelinated.
Figure 46-3
Figure 46-4