1. Peripheral Nervous System & Reflex Activity Part A Prepared by Janice Meeking & W. Rose. Figures from Marieb & Hoehn 8 th, 9 th ed. Portions copyright Pearson Education

2. Figure 13.1 Central nervous system (CNS)Peripheral nervous system (PNS) Motor (efferent) divisionSensory (afferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Peripheral Nervous System (PNS) All neural structures outside the brain Sensory receptors Peripheral nerves and associated ganglia Motor endings

3. Sensory Receptors Specialized structures which respond to changes in their environment (stimuli) Some receptors are simply ends of sensory nerve fibers. Other receptors are cells adjacent to sensory nerrve fibers. Other receptors are sensory nerve fiber endings plus specialized supporting cells and/or extracellular material Receptor activation results in graded potentials that may trigger action potentials Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain

4. Classifying receptors Receptors have been classified according to: – The type of stimulus they detect (best) – Receptor location in the body – Structural complexity of the receptor

5. Classification by Stimulus Type Mechanoreceptors—respond to touch, pressure, vibration, stretch, and itch Thermoreceptors—sensitive to changes in temperature Photoreceptors—respond to light energy (e.g., retina) Chemoreceptors—respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)

6. Classification by Location Exteroceptors Respond to stimuli arising outside the body: receptors in the skin for touch, pressure, pain, and temperature; also most special sense organs (eyes, ears, etc) Interoceptors (visceroceptors) Respond to stimuli arising in internal viscera and blood vessels: chemical environment, tissue stretch, temperature Proprioceptors Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles; inform the brain of one’s movements

7. Classification by Structural Complexity Complex receptors: Special sense organs Vision, hearing, equilibrium, smell, taste (ch. 15) Simple receptors: General sensation Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense Unencapsulated (free) dendritic endings Encapsulated dendritic endings

8. Table 13.1 Unencapsulated (free) dendritic endings

9. Table 13.1 Encapsulated dendritic endings

10. From Sensation to Perception Survival depends upon sensation and perception Sensation: awareness of changes in the internal and external environment Perception: conscious interpretation of those stimuli

11. Figure 13.2 1 2 3 Receptor level (sensory reception and transmission to CNS) Circuit level (processing in ascending pathways) Spinal cord Cerebellum Reticular formation Pons Muscle spindle Joint kinesthetic receptor Free nerve endings (pain, cold, warmth) Medulla Perceptual level (processing in cortical sensory centers) Motor cortex Somatosensory cortex Thalamus

12. Processing at the Receptor Level Different receptors respond to different stimuli Light, pressure, temperature, chemicals, etc. Receptive field Physical region over which each receptor can detect stimuli Transduction occurs Stimulus energy is converted into a graded potential called a receptor potential

13. Receptor processing in general sense receptors (receptors in which there are not separate receptor cells) Stimulus Receptor Potential (graded potential) at distal end of afferent neuron Action Potential(s) (if threshold is reached)  

14. Receptor processing in special sense receptors stimulus  receptor potential in receptor cell  release of neurotransmitter  generator potential in first-order sensory neuron  action potentials (if threshold is reached)

15. Adaptation of Sensory Receptors Change in response in the presence of a constant stimulus Receptor membranes become less responsive Receptor potentials decline in frequency or stop Phasic (fast-adapting) receptors signal beginning or end of stimulus Examples: receptors for pressure, touch, smell Tonic receptors adapt slowly or not at all Examples: nociceptors; most proprioceptors

16. Processing at the Circuit Level 3-neuron pathway conducts sensory impulses upward to appropriate brain regions First-order neurons (cell body in DRG or other peripheral ganglion): conduct impulses from receptor to second-order neurons in the CNS Second-order neurons (in CNS): transmit impulses to thalamus or cerebellum Third-order (thalamic) neurons: conduct impulses from the thalamus to the somatosensory cortex (perceptual level)

17. Processing at the Perceptual Level Identification of the sensation depends on the specific location of the target neurons in the sensory cortex Aspects of sensory perception Stimulus detection: requires multiple impulses Magnitude estimation: intensity coded by frequency of APs & number of neurons active “Spatial” discrimination: identify the site or pattern of stimulus (e.g. two-point discrimination test)

18. Further Processing at the Perceptual Level Feature abstraction—identification of more complex aspects and several stimulus properties Quality discrimination: identification of submodalities of a sensation (e.g., sweet or sour tastes) Pattern recognition: identification of familiar or significant patterns in stimuli (face, melody, etc.)

19. Figure 13.2 1 2 3 Receptor level (sensory reception and transmission to CNS) Circuit level (processing in ascending pathways) Spinal cord Cerebellum Reticular formation Pons Muscle spindle Joint kinesthetic receptor Free nerve endings (pain, cold, warmth) Medulla Perceptual level (processing in cortical sensory centers) Motor cortex Somatosensory cortex Thalamus

20. Nerve Structure Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue Connective tissue coverings, from inside to outside: – Endoneurium, perineurium, epineurium

21. Figure 13.3b Blood vessels Fascicle Epineurium Perineurium Endoneurium Axon Myelin sheath (b)

22. Classification of Nerves Most nerves are mixed: afferent and efferent fibers and somatic and autonomic (visceral) fibers Pure sensory (afferent) or motor (efferent) nerves are rare Cranial and spinal nerves (12 pair cranial, Roman numerals; 31 pair spinal, named for the nearby vertebra, e.g. C5 or L4)

23. Ganglion (plural: ganglia) A group of neuron cell bodies outside the CNS (analogous to nuclei inside the CNS) associated with nerves Examples dorsal root ganglia (sensory, somatic; ch. 12) autonomic ganglia, such as sympathetic trunk ganglia (motor, visceral; ch.14)