BIPN 142mt1

BIPN 142mt1 - BIPN 142 Midterm 1 Mechanoreceptors 1...

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BIPN 142- Midterm 1 Mechanoreceptors 1. Mechanoreceptor afferents include merkel, meisner, rufini and pacinian afferents 2. Merkel has smallest receptor fields so smallest 2 point discrimination which means it can discriminate between two stimuli the best. Also is slowly adapting 3. Meisner afferents have larger receptor fields and are rapidly adapting 4. Rufini have larger receptor fields and are slowly adapting 5. Pacinian have largest receptor fields and are rapidly adapting 6. Smallest to largest receptor fields = Merkel, meisner, rufini, pacinian 7. Mechanoreceptors- Afferent fibers encapsulated by specialized receptor cells (where as pain afferents don’t have capsules and are free ending nerves) 8. Merkel- surface of skin, then meisner, then pacinian and finally Ruffini is in deepest layer of skin Mechano Generator Potentials 1. Open in response to deformation that causes stretch and stretching provides stimulus to increase membrane permeability to cations to cause GP which if sufficient enough will cause AP 2. Deformation of capsule leads to stretching Different Somatic Sensory Afferents 1. Proprioception- muscle spindles that have the largest axons of all afferents ad thus fastest conduction velocity 2. Touch- Merkel, meissner, Ruffini and pacinian receptors with 2 nd largest axon/velocity 3. Pain/temperature- Free nerve endings with some myelination (A-delta fibers) 4. Pain/Temp/Itch- free endings with no myelination (C fibers) and slowest conduction vel/smallest axon diameter Distinguishing Features of SSAs (Spatial) 1. Axon diameter which determines AP velocity
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2. Receptor Field size which is area of skin surface which stimulation results in a significant change in APs 3. The smaller the Receptor field means the more densely innervated a region is with afferents where RF size and innervation limit spatial accuracy with which tactile stimuli can be sensed. 4. Two Point discrimination- smallest for small RFs and highly dense areas of afferents and is defined as the minimum distance to perceive 2 stimuli simultaneously applied as distinct smallest in fingers/lips/cheek/nose Temporal Features of SSAs 1. Slowly adapting mechanoreceptors continue in responding to a stimulus ( merkel/Ruffini) Ex: Apply stimulus: |||| | | | | | | | 2. Rapidly adapting mr’s respond only at the onset and offset of a stimulation Ex: Apply Stim: ||| || 3. This difference in response allows mechanoreceptors to provide info about static via slow and dynamic via rapid, qualities of stimulus. 4. Rapidly adapting convey info about movement and slowly adapting convey info about spatial attributes of stimulus 5. Pacinian afferents are rapidly adapting but become slowly adapting when corpuscle is removed Mechanoreceptors Have Specialized Responses 1. Somatic sensory afferents constitute parallel pathways that differ in conduction velocity, receptor field size, dynamics and effective stimulus features 2. Specialized to receive tactile info 3. Structures associated with touch sensory terminals define the properties
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BIPN 142mt1 - BIPN 142 Midterm 1 Mechanoreceptors 1...

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