47.pptx

Types of Sensory Receptors • Mechanoreceptors - detect deformation • Thermoreceptors - detect change in temperature • Nociceptors - detect damage (pain receptors) Noci - is derived • Electromagnetic - detect light from the Latin term for “hurt” • Chemoreceptors - taste, smell, CO2, O2 etc. Types...

Types of Sensory Receptors • Mechanoreceptors - detect deformation • Thermoreceptors - detect change in temperature • Nociceptors - detect damage (pain receptors) Noci - is derived • Electromagnetic - detect light from the Latin term for “hurt” • Chemoreceptors - taste, smell, CO2, O2 etc. Types of Sensory Receptors Figure 47-1 Locations of skin sensory receptors in the fingertip Glabrous skin (non-hairy skin) Epidermis Dermis Subcutaneous layer Purves. Neuroscience. 5th ed, 2012. Figure 9.5 Sensation • Each of the principal types of sensation: touch, pain, sight, sound, is called a modality of sensation. • How the sensation is perceived is determined by the characteristics of the receptor and the central connections of the axon connected to the receptor. • Specificity of nerve fibers for transmitting only one modality of sensation is called Labeled-line principle refers to a the concept each receptor responds to a labeled linethat principle. limited range of stimuli and has a direct line to the brain. What factors generate receptor potentials? • Mechanical deformation - stretches the membrane and opens ion channels. • Application of chemicals - also opens ion channels. • Change in temperature - alters membrane permeability. • Electromagnetic radiation - changes membraneNote permeability tostimuli ions. lead to that all these changes in membrane permeability to ions; this can cause either hyperpolarization or hypopolarization (i.e., depolarization). Generation of receptor potential by mechanism distortion Mechanical distortion increases Na+ conductance causing a receptor potential. The receptor potential is an electrotonic potential. ? Why is there no AP except in the axon? Figure 47-3 Pacinian corpuscle Relationship between receptor potentials and action potentials - APs occur when receptor potential (green line) rises above threshold Figure 47-2 - Increased stimulus intensity causes increased receptor potential, which increases AP frequency. Stimulus strength and receptor potential in Pacinian corpuscle Only larges changes in stimulus strength can be discerned when stimulus strength is high Small changes in stimulus strength can be discerned when stimulus strength is low This relationship allows receptors to have a wide range of response Figure 47-4 Adaptation of Receptors Figure 47-5 Adaptation of Receptors (cont.) Rate of adaptation varies with type of receptor. Adapted from Kandel, Schwartz And Jessell 4th addition 2000 Rapidl y adapti ng Slowly adapti ng Rapidl y adapti ng Slowly adapti ng Mechanism of Adaptation - varies with the type of receptor. • Mechanoreceptors – fluid redistribution in Pacinian corpuscle decreases distorting force. • Photoreceptors – the amount of light sensitive chemicals is changed. Slowly Adapting (Tonic) Receptors • Continue to transmit impulses to brain for long periods of time while stimulus is present. S • Keep brain apprised of the status of the body with respect to its surroundings. • Will adapt to extinction if stimulus is present but this may take hours or days. • These receptors include muscle spindle, Golgi tendon apparatus, Ruffini endings, Merkel discs, Macula, pain, temperature, chemo- and baroreceptors. Rapidly Adapting (Phasic) Receptors • Respond only when change is taking place. S • Rate and strength of response is related to rate and intensity of stimulus. • Important for predicting future position or condition of body. • Very important for balance and movement. • Types of rapidly adapting receptors: Pacinian corpuscle, Meissner’s corpuscle, semicircular canals. Slowly and rapidly adapting mechanoreceptors provide different information Stimulus Slowly adapting 0 1 2 Time (s) 3 Rapidly adapting 0 Slowly adapting receptors (aka, tonic receptors) continue to respond to a stimulus. 4 Rapidly adapting receptors (aka, phasic receptors) – respond only at the onset (and often the offset) of stimulation. 1 2 Time (s) 3 4 Sensory Nerve Classification Transmission of receptor information to brain by different types of neurons Figure 47-6 Somatic sensory afferents that link receptors to CNS Purves. Neuroscience. 5th ed, 2012. Table 9.1 Importance of Signal Intensity • Signal intensity is critical for interpretation of signal by brain (e.g., pain). • Gradations in signal intensity can be achieved by: 1) Spatial summation - increasing the number of fibers stimulated. An example of spatial summati on 2) Temporal summation - increasing the rate of firing in a given number of fibers. Figure 47-7 Excitation and Facilitation Figure 47-9 Neuron ‘1’ excites neuron ‘a’, and facilitates neurons ‘b’ and ‘c’ Figure 47-10 Neuronal Pools • Groups of neurons with special characteristics of organization. • Comprise many different types of neuronal circuits. – converging – diverging – reverberating – inhibitory Divergence in neuronal pathways Figure 47-11 Amplifying type of divergence. Signal is transmitted in two directions. Example: single pyramidal cell in motor cortex can stimulate several hundred Example: information from dorsal columns of spinal cord takes two directions (1) cerebellum, (2) Convergence of multiple input fibers Figure 47-12 - Multiple terminals from single incoming fiber terminate on same neuron. - Provides spatial summation - Allows summation of information from multiple sources. - Correlates, summates, and sorts information. Inhibitory circuit excite no AP Figure 47-13 Important for controlling all antagonistic pairs of muscles… called the reciprocal inhibition circuit. Important in preventing over-activity in brain Reverberatory or Oscillatory Circuits Output signals from reverberatory circuit after single input stimulus Hall, Guyton. Figure 47-15 Figure 47-14 • A single input stimulus (1 msec) causes a prolonged output (msec to minutes). • Caused by Positive feedback within neuronal circuit (the input to the circuit is re-excited). • What Note: causes the circuit can cessation be facilitated sudden of or inhibited as shown. reverberation? Reverberatory circuits (cont.) This is positive feedback - What stops it? fatigue of synaptic junctions What is the mechanism of fatigue? A. Transmitter depletion B. Receptor inactivation C. Abnormal ion concn in axon D. All of the above Control of synaptic sensitivity Underactivity leads to upregulation of membrane receptors Overactivity leads to downregulation of membrane receptors. ot all reverberatory circuits fatigue Shows continuous output from reverberating circuit that can be enhanced or suppressed ANS uses this type of information transmission to control vascular tone, gut tone, heart rate, etc. Figure 47-16