1. Synapse and its types

3. The Synapse The Synapse Site at which neurons communicate Site at which neurons communicate Signals pass across synapse in one direction Signals pass across synapse in one direction Types of cells in synapse Types of cells in synapse Presynaptic neuron - conducts impulse toward the synapse Presynaptic neuron - conducts impulse toward the synapse Postsynaptic neuron - conducts impulse away from the synapse Postsynaptic neuron - conducts impulse away from the synapse Average postsynaptic neuron has up to 10,000 synapses Average postsynaptic neuron has up to 10,000 synapses Some in cerebellum have up to 100,000 synapses Some in cerebellum have up to 100,000 synapses Two major types of synapses Two major types of synapses Electrical - not common in nervous system Electrical - not common in nervous system Chemical - most common type Chemical - most common type

4. Types of Chemical Synapses Types of Chemical Synapses Axodendritic Axodendritic Between axon terminals of presynaptic neuron and dendrite of postsynaptic neuron Between axon terminals of presynaptic neuron and dendrite of postsynaptic neuron Most common type of synapse Most common type of synapse Axosomatic Axosomatic Between axon of pre- and soma (cell body) of post-synaptic neuron Between axon of pre- and soma (cell body) of post-synaptic neuron Axoaxonic Axoaxonic Between two axons Between two axons Not common Not common

5. Types of Neural Synapses Types of Neural Synapses

6. Presynaptic bulb has secretory Presynaptic bulb has secretory vesicles that contain neurotrans- vesicles that contain neurotrans- mitter chemical (NT) mitter chemical (NT) NT must pass across the NT must pass across the synaptic cleft, space that synaptic cleft, space that separates pre- and separates pre- and postsynaptic membranes postsynaptic membranes Postsynaptic membrane Postsynaptic membrane contains receptors specific contains receptors specific for each type of NT for each type of NT Binding of NT to its receptor Binding of NT to its receptor causes ion channels to open causes ion channels to open or close or close

7. Chemical Synapse Chemical Synapse

8. Lecture 2

9. Receptors Receptors Receptors are specialized cells for detecting particular changes in the environment. Receptors are specialized cells for detecting particular changes in the environment.

10. Exteroceptors include receptors affected mainly by the external environment: Meissner's corpuscles, Merkel's corpuscles, and hair cells for touch; Krause's end- bulbs for cold; Ruffini's corpuscles for warmth; and free nerve endings for pain. Exteroceptors include receptors affected mainly by the external environment: Meissner's corpuscles, Merkel's corpuscles, and hair cells for touch; Krause's end- bulbs for cold; Ruffini's corpuscles for warmth; and free nerve endings for pain.

12. Receptors are not absolutely specific for a given sensation; strong stimuli can cause various sensations, even pain, even though the inciting stimuli are not necessarily painful. Receptors are not absolutely specific for a given sensation; strong stimuli can cause various sensations, even pain, even though the inciting stimuli are not necessarily painful.

13. Proprioceptors receive impulses mainly from pacinian corpuscles, joint receptors, muscle spindles, and Golgi tendon organs Proprioceptors receive impulses mainly from pacinian corpuscles, joint receptors, muscle spindles, and Golgi tendon organs

14. Each efferent fiber from a receptor relays stimuli that originate in a receptive field and gives rise to a component of an afferent sensory system. Each individual receptor fires either completely or not at all when stimulated. The greater the intensity of a stimulus, the more end- organs that are stimulated, the higher the rate of discharge is, and the longer the duration of effect is. Each efferent fiber from a receptor relays stimuli that originate in a receptive field and gives rise to a component of an afferent sensory system. Each individual receptor fires either completely or not at all when stimulated. The greater the intensity of a stimulus, the more end- organs that are stimulated, the higher the rate of discharge is, and the longer the duration of effect is.

15. Adaptation denotes the diminution in rate of discharge of some receptors on repeated or continuous stimulation of constant intensity; the sensation of sitting in a chair or walking on even ground is suppressed. Adaptation denotes the diminution in rate of discharge of some receptors on repeated or continuous stimulation of constant intensity; the sensation of sitting in a chair or walking on even ground is suppressed.

16. today s today s

17. Adaptation of Sensory Receptors Change in sensitivity to long-lasting stimuli Change in sensitivity to long-lasting stimuli decrease in responsiveness of a receptor decrease in responsiveness of a receptor bad smells disappear bad smells disappear very hot water starts to feel only warm very hot water starts to feel only warm

18. Receptors vary in their ability to adapt Receptors vary in their ability to adapt Rapidly adapting receptors (smell, pressure, touch) Rapidly adapting receptors (smell, pressure, touch) adapt quickly; specialized for signaling stimulus changes adapt quickly; specialized for signaling stimulus changes Slowly adapting receptors (pain, body position) Slowly adapting receptors (pain, body position) continuation of nerve impulses as long as stimulus persists continuation of nerve impulses as long as stimulus persists

19. Specialized cell or cell process that monitors specific conditions Specialized cell or cell process that monitors specific conditions Arriving information is a sensation Arriving information is a sensation Awareness of a sensation is a perception Awareness of a sensation is a perception Sensory Receptors and their Classification

20. Peripheral Sensory Receptors Structures that pick up sensory stimuli Structures that pick up sensory stimuli Initiate signals in sensory axons Initiate signals in sensory axons

21. Peripheral Sensory Receptors Two main categories of sensory receptors Two main categories of sensory receptors Special nerve endings of sensory neurons Special nerve endings of sensory neurons Monitor general sensory information Monitor general sensory information Independent receptor cells – specialized epithelial cells or small neurons Independent receptor cells – specialized epithelial cells or small neurons Monitor most types of special sensory information Monitor most types of special sensory information

22. Peripheral Sensory Receptors Sensory receptors also classified according to: Sensory receptors also classified according to: Location Location Type of stimulus detected Type of stimulus detected Structure Structure

23. Classification by Location Exteroceptors – sensitive to stimuli arising from outside the body Exteroceptors – sensitive to stimuli arising from outside the body Located at or near body surfaces Located at or near body surfaces Include receptors for touch, pressure, pain, and temperature Include receptors for touch, pressure, pain, and temperature

24. Interoceptors – (visceroceptors) receive stimuli from internal viscera Interoceptors – (visceroceptors) receive stimuli from internal viscera Monitor a variety of stimuli Monitor a variety of stimuli

25. Proprioceptors – monitor degree of stretch Proprioceptors – monitor degree of stretch Located in musculoskeletal organs Located in musculoskeletal organs

26. Classification by Modality Mechanoreceptors – respond to mechanical forces Mechanoreceptors – respond to mechanical forces Thermoreceptors – respond to temperature changes Thermoreceptors – respond to temperature changes Chemoreceptors – respond to chemicals in solution Chemoreceptors – respond to chemicals in solution Photoreceptors – respond to light – located in the eye Photoreceptors – respond to light – located in the eye Nociceptors – respond to harmful stimuli that result in pain Nociceptors – respond to harmful stimuli that result in pain

27. Elecromagnetic receptors Elecromagnetic receptors Thermo and photo Thermo and photo Rods and cones Rods and cones

28. Chemoreceptors are located in Chemoreceptors are located in Carotid bodies Carotid bodies Aortic bodies Aortic bodies Special senses of taste and smell Special senses of taste and smell Respiratory area of medulla Respiratory area of medulla Chemoreceptors

29. Classification by Structure General sensory receptors General sensory receptors Widely distributed Widely distributed Nerve endings of sensory neurons monitor: Nerve endings of sensory neurons monitor: Touch, pressure, vibration, stretch Touch, pressure, vibration, stretch Pain, temperature, proprioception Pain, temperature, proprioception Divided into two groups Divided into two groups Non encapsulated Non encapsulated Free nerve endings Free nerve endings Merkels disc Merkels disc Hair follicle receptors

30. Encapsulated nerve endings Encapsulated nerve endings Meisners corposcles Pacinian corposcles Ruffinis corposcles

31. Encapsulated nerve endings Encapsulated nerve endings

32. Meissner’s Corpuscle

33. Dermal papilla of palms and soles Dermal papilla of palms and soles Ovoid in shape Ovoid in shape Stack of modified flattened schwaan cells Stack of modified flattened schwaan cells Capsule is continous with endoneurium Capsule is continous with endoneurium Rapidly adapting Rapidly adapting Two point tactile discrimination Two point tactile discrimination

34. Pacinian corpuscle Onion-like connective tissue capsule enclosing a dendrite Onion-like connective tissue capsule enclosing a dendrite Found in subcutaneous tissues,ligaments,joint capsules Found in subcutaneous tissues,ligaments,joint capsules Rapidly adapting Rapidly adapting high-frequency vibration high-frequency vibration

35. Ruffini Corpuscle Found deep in dermis of hairy skin Found deep in dermis of hairy skin Detect heavy touch, continuous touch, & pressure Detect heavy touch, continuous touch, & pressure Slowly adapting Slowly adapting

36. Non encapsulated Free nerve endings Free nerve endings Epithelial cells of skin,cornea,dermis fascia Epithelial cells of skin,cornea,dermis fascia Pain, crude touch,pressure Pain, crude touch,pressure

37. Free nerve endings found around follicles, detects movement of hair

38. Merkel’s Disc Flattened dendrites touching cells of stratum basale Flattened dendrites touching cells of stratum basale Used in discriminative touch Used in discriminative touch

39. Hairless skin fingertips Hairless skin fingertips

40. CUTANEOUS RECEPTORS End organ of Ruffini  crude touch End organ of Ruffini  crude touch Merkel discs  discriminative touch Merkel discs  discriminative touch Root hair plexus  hair movement Root hair plexus  hair movement

41. Tactile Receptors in the Skin

45. Proprioceptors Monitor stretch in locomotory organs Monitor stretch in locomotory organs Three types of proprioceptors Three types of proprioceptors

46. Two Types of Proprioceptors Muscle spindles – measure the changing length of a muscle Muscle spindles – measure the changing length of a muscle Imbedded in the perimysium between muscle fascicles Imbedded in the perimysium between muscle fascicles Golgi tendon organs – located near the muscle-tendon junction Golgi tendon organs – located near the muscle-tendon junction Monitor tension within tendons Monitor tension within tendons

47. Anatomy of the muscle spindle and Golgi tendon organ Primary sensory endings (type Ia fiber) Muscle spindle Connective tissue capsule  Efferent motor fiber to extrafusal muscle fibers Extrafusal muscle fiber Intrafusal muscle fibers Tendon  Efferent motor fiber to spindle Secondary sensory endings (type II fiber) Golgi tendon organ Capsule Sensory fiber

48. MUSCEL SPINDLE FIBERS Monitor changes in length of skeletal muscle Monitor changes in length of skeletal muscle Degree of muscle stretch Degree of muscle stretch Aid in coordination & efficiency of muscle contraction Aid in coordination & efficiency of muscle contraction

49. TENDON ORGANS (GOLGI TENDON ORGANS) Junction of tendon & muscle Junction of tendon & muscle Monitors force of muscle contraction Monitors force of muscle contraction Detect tension applied to tendon Detect tension applied to tendon Protects tendon & muscle from excessive tension Protects tendon & muscle from excessive tension