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

7. تقسیم بندی انواع گيرنده ها؛ بر اساس:
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
neuro4e-fig jpg

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 13 13

14. Structure of Muscle Spindle
Each spindle is 3 to 10 mm 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 small gamma motor nerve fibers (gamma efferent fibers) that originate from small type A gamma motor neurons in the anterior horns of the spinal cord.
the large alpha efferent fibers (type A alpha nerve fibers) innervate the 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:
Lengthening the whole muscle stretches the midportion of the spindle and, therefore, excites the receptor.
contraction of 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 micrometers in 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 chain throughout the receptor area.

26. Division of the Intrafusal Fibers
The primary sensory nerve ending (17-micrometer) is excited by 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
Ventral + M S - + + +

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 31 31

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 spinocerebellar tracts 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 and a protective mechanism to prevent tearing of the muscle or avulsion of the tendon from its attachments to the bone.

36. Dorsal
Ventral +
GTO -
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) 37

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 43

46. Krause Receptor

48. 4- Classification by Adapting

52. Receptor (Generator) Potential

54. Tonic & Phasic Receptors
Transduction: translation of a stimulus into an action potential.
Transferred to an afferent fiber which then travels to the CNS.
Tonic Receptors-always sending signals.
Phasic Receptors: only when the conditions they monitor change.
Fast-adapting receptors are phasic and slow-adapting are tonic.

55. Receptor Adaptation Slowly adapting (SA) Rapidly adapting (RA)
Different rates of adaptation
¯ response to continued stimulation
Slowly adapting (SA)
steady pattern of firing
Rapidly adapting (RA)
fire only at onset of stimulus

58. Adaptation – static & dynamic responses58

61. Receptive field sizes vary by type: Meissner’s corpuscles - small
Pacinian corpuscles - large 61

62. Receptive Field Size Small Large Meissner’s Corpuscle Pacinian
Rapid
Slow
Adaptation
Merkel’s
Disks
Ruffini
Ending