Physiology of the sensory system

1. Physiology of the sensory system

4. Types of sensation • types of sensations • General sensation • Somatic • visceral • Special senses • Smell, taste, vision etc exteroceptor Proprioceptor : muscle length and tension, joint position and their motion

5. Somatosensory Pathways

6. PCML Pathway

7. PCML Pathway

8. PCML Pathway

9. PCML Pathway

12. Relationship Between Receptive Fields and Cortical Representation Text Fig. 17-3 Text Fig. 17-12 Inverse relationship in the cortex. Smaller the receptive fields larger the cortical area Larger the receptive fields smaller the cortical area Smaller the receptive fields, greater the density of receptors.This relationship allows for greater discrimination in sensory inputs.

13. ALS Pathway

14. Conduction speed • Number of synapses • Myelination • Nerve axon size

16. Sensations modalities Fast Slow Temperature Crud touch (itch & rub) Pain • Prorioception • Fine touch & pressure • Vibration Posterior Column-Medial lemniscus Pathway (PCML) Antero-lateral system (ALS) Other name: Spinothalamic pathway

18. Sensations receptors Hair root plexus Merkel discs

19. Types of Sensory Receptors • Mechanoreceptors • detect deformation • Thermoreceptors • detect change in temperature • Nociceptors • detect damage (pain receptors) • Electromagnetic • detect light • Chemoreceptors • taste, smell

20. Classification of Somatic Sensations • mechanoreceptive - stimulated by mechanical displacement. • tactile • touch • pressure • vibration • tickle and itch • position or proprioceptive • static position • rate of change

21. Classification of Somatic Sensations • thermoreceptive. • detect heat and cold. • nociceptive. • detect pain and are activated by any factor that damages tissue.

22. Receptor Excitation Figure 46-03

23. Receptor Potential • the membrane potential of the receptor. • excitation of the receptor results from a change in this potential. • when the receptor potential rises above the threshold, action potentials appear and the receptor is active. • the greater the intensity of the stimulus, the greater the receptor potential, and the greater the rate of action potential generation.

24. Relationship between receptor potential and action potentials Figure 46-2

25. Adaptation of Receptors • when a continuous stimulus is applied, receptors respond rapidly at first, but response declines until all receptors stop firing.

26. Adaptation of Receptors • when a continuous stimulus is applied, receptors respond rapidly at first, but response declines until all receptors stop firing. Figure 46-5

27. Slowly Adapting (Tonic) Receptors • continue to transmit impulses to the brain for long periods of time while the stimulus is present. • keep brain apprised of the status of the body with respect to its surroundings.

28. Rapidly Adapting (Phasic) Receptors • respond only when change is taking place. • rate and strength of the response is related to the rate and intensity of the stimulus. • .

29. Sensations receptors

30. Sensations receptors muscle length and rate of change muscle tension and force joint position and their motion PCML pathway • Prorioception • Fine touch • Vibration

32. Sensations receptors ALS pathway Temperature Crud touch (itch & rub) Pain

33. Tactile Receptors • Expand free nerve endings. • detect touch and pressure. • found everywhere in the skin and other tissues.

34. Pain Receptors and Their Stimulation • all pain receptors are free nerve endings. • can be stimulated by: • mechanical (stretch). • thermal. • chemical. • bradykinin, serotonin, histamine, potassium ions, acids, acetylcholine and proteolytic enzymes. • prostaglandins and substance P enhance the sensitivity of pain endings but do not directly excite them.

35. Sensations receptors ALS pathway Temperature Cold receptors Heat receptors

36. Sensations receptors ALS pathway Temperature Crud touch (itch & rub) Pain Free nerve endings rub Free nerve endings