گیرنده های حسی پیکری

2. گیرنده های حسی پیکری Sensory Transduction

3. Sensory Receptors Sensory receptors are structures that are specialized to respond to changes in their environment Such environmental changes are called stimuli Typically activation of a sensory receptor by an adequate stimulus results in depolarization or graded potentials that trigger nerve impulses along the afferent fibers coursing to the CNS

5. Somatic (= general) senses Touch Temperature Vibration Nociception Itch Proprioception Special senses Vision Hearing Taste Smell Equilibrium Classification of Sensory System by Structural Complexity

7. تقسیم بندی انواع گيرنده ها؛ بر اساس: 1- مكان قرارگيری (Location) 2- نوع تحريك(Type of stimulus detected) 3- ساختار(Structure) 4- تطابق پذيری (Adaptation) 7

8. 1- Classification by Location • Proprioceptors : monitor degree of stretch • Interoceptors (visceroceptors) : receive stimuli from internal viscera • Monitor a variety of stimuli • Exteroceptors: sensitive to stimuli arising from outside the body • Located at or near body surfaces • Include receptors for touch, pressure, pain, and temperature (, …)

9. Proprioceptors • Muscle spindle • Golgi tendon organ • Joint receptor

11. Structure of Proprioceptors

12. Proprioceptors provide information about the position of body parts

13. Muscle Spindles Encapsulated fibers within the muscle belly Monitor changes in muscle length Monitor the rate of change in muscle length Respond by causing muscle contraction

14. Structure of Muscle Spindle • Each spindle is 3 to 10mm long. • It is built around 3 to 12 tiny intrafusal muscle fibers that are pointed at their ends and attached to the glycocalyx of the surrounding large extrafusal skeletal muscle fibers.

15. Structure of Muscle Spindle • Each intrafusal muscle fiber is a tiny skeletal muscle fiber. • central region of each of these fibers has few or no actin and myosin filaments. • Therefore, this central portion does not contract when the ends do. Instead, it functions as a sensory receptor.

16. Motor Innervation of Muscle Spindle • The end portions that do contract are excited by smallgamma motor nerve fibers (gamma efferent fibers)that originate from small type A gamma motor neurons in the anterior horns of the spinal cord. • the largealpha efferent fibers (type A alpha nerve fibers) innervatethe extrafusal skeletal muscle.

17. Sensory Innervation of the Muscle Spindle • The receptor portion of the muscle spindle is its central portion. • In this area, the intrafusal muscle fibers do not have myosin and actin contractile elements. • sensory fibers originate in this area. • They are stimulated by stretching of this midportion of the spindle.

18. Muscle spindle, showing its relation to the large extrafusal skeletal muscle fibers. Note also both motor and sensory innervation of the muscle spindle.

19. Sensory Innervation of the Muscle Spindle muscle spindle receptor can be excited in two ways: • Lengtheningthe whole muscle stretches the midportion of the spindle and, therefore, excites the receptor. • contractionof the end portions of the spindle's intrafusal fibers stretches the midportion of the spindle and therefore excites the receptor.

20. Sensory Innervation of the Muscle Spindle Two types of sensory endings are found in this central receptor area of the muscle spindle : • primary ending • secondary ending

21. Primary Ending • In the center of the receptor area, a large sensory nerve fiber encircles the central portion of each intrafusal fiber, forming the so-called primary ending or annulospiral ending. • This nerve fiber is a type Ia fiber averaging 17 micrometersin diameter • it transmits sensory signals to the spinal cord at a velocity of 70 to 120 m/sec, as rapidly as any type of nerve fiber in the entire body.

22. Secondary Ending • Usually one but sometimes two smaller sensory nerve fibers- type II fibers with an average diameter of 8 micrometers-innervate the receptor region on one or both sides of the primary ending, This sensory ending is called the secondary ending; • sometimes it encircles the intrafusal fibers in the same way that the type Ia fiber does, but often it spreads like branches on a bush.

24. Division of the Intrafusal Fibers into Nuclear Bag and Nuclear Chain Fibers- Dynamic and Static Responses of the Muscle Spindle

25. Division of the Intrafusal Fibers two types of muscle spindle intrafusal fibers: • nuclear bag muscle fibers (one to three in each spindle), in which several muscle fiber nuclei are congregated in expanded "bags" in the central portion of the receptor area • nuclear chain fibers (three to nine), which are about half as large in diameter and half as long as the nuclear bag fibers and have nuclei aligned in a chainthroughout the receptor area.

26. Division of the Intrafusal Fibers • The primary sensory nerve ending (17-micrometer) is excitedby both the nuclear bag intrafusal fibers and the nuclear chain fibers. • Conversely, the secondary ending ( 8 micrometer) is usually excited only by nuclear chain fibers.

27. Details of nerve connections from the nuclear bag and nuclear chain muscle spindle fibers.

28. Dorsal M S + + - + Ventral +

29. Golgi Tendon Organ Helps Control Muscle Tension • is an encapsulated sensory receptor • About 10 to 15 muscle fibers are usually connected to each Golgi tendon organ • is stimulated when this small bundle of muscle fibers is "tensed" by contracting or stretching the muscle.

30. Thus, the major difference in excitation of the Golgi tendon organ versus the muscle spindle is that • the spindle detects muscle length and changes in muscle length, • whereas the tendon organ detects muscle tension as reflected by the tension in itself.

31. Golgi Tendon Organs (GTO) Encapsulated receptors Located at the musculotendinous junction Monitor tension within the tendon Respond by causing the muscle to relax

32. Golgi Tendon Organ Helps Control Muscle Tension • The tendon organ, like the primary receptor of the muscle spindle, has both a dynamic response and a static response: • dynamic response : reacting intensely when the muscle tension suddenly increases • static response : settling down within a fraction of a second to a lower level of steady-state firing that is almost directly proportional to the muscle tension. • Thus, Golgi tendon organs provide the nervous system with instantaneous information on the degree of tension in each small segment of each muscle.

33. Transmission of Impulses from the Tendon Organ into the Central Nervous System • are transmitted through large, rapidly conducting type Ib nerve fibers that average 16 micrometers in diameter. • These fibers, like those from the primary spindle endings, transmit signals both into local areas of the cord and, after synapsing in a dorsal horn of the cord, through long fiber pathways such as the spinocerebellartracts into the cerebellum and through still other tracts to the cerebral cortex

34. The local cord signal excites a single inhibitory interneuron that inhibits the anterior motor neuron (by releasing Glycine). • This local circuit directly inhibits the individual muscle without affecting adjacent muscles.

35. Inhibitory Nature of the Tendon Reflex and Its Importance • When the Golgi tendon organs of a muscle tendon are stimulated by increased tension in the connecting muscle, signals are transmitted to the spinal cord to cause reflex effects in the respective muscle. • This reflex is entirely inhibitory. • Thus, this reflex provides a negative feedback mechanism that prevents the development of too much tension on the muscle anda protective mechanism to prevent tearing of the muscle or avulsion of the tendon from its attachments to the bone.

36. Dorsal GTO + - Ventral Inhibits alpha motor neuron +

37. Classification by Location Interoceptors Detect stimuli from inside the body and include receptors that respond to pH, oxygen level in arterial blood, carbon dioxide concentration, osmolality of body fluids, distention and spasm (e.g., gut), and flow (e.g., urethra)

38. Classification by Location • Exteroceptors • Sensitive to stimuli arising from outside of the body • Typically located near the surface of the body • Include receptors for • Touch • Pressure • vibration • Pain • Temperature • Special sense receptors • …..

39. 2- Classification by Stimulus Detected

40. 2- Classification by Stimulus Detected Mechanoreceptors– respond to mechanical forces Thermoreceptors – respond to temperature changes Chemoreceptors – respond to chemicals in solution Photoreceptors – respond to light – located in the eye Nociceptors – respond to harmful stimuli that result in pain

41. 3- Classification by Structure • General sensory receptors • Widely distributed • Nerve endings of sensory neurons monitor: • Touch, pressure, vibration, stretch • Pain, temperature, proprioception • Divided into two groups • Free nerve endings • Encapsulated nerve endings

42. Skin Receptors

43. Skin Sensors

46. Krause Receptor

48. 4- Classification by Adapting