Dorsal column medial leminiscus

physiology

1. Somatic sensations and mechanical receptors

2. Classify somatic sensations Classify mechanical receptors

3. Classification of Sensations The somatic senses are the nervous mechanisms that collect sensory information from all over the body. Special senses , which mean specifically vision, hearing, smell, taste, and equilibrium.

4. CLASSIFICATION OF SOMATIC SENSES The mechanoreceptive somatic senses, which include both tactile and position sensations. The thermoreceptive senses, which detect heat and cold The pain sense, which is activated by any factor that damages the tissues.

5. M echanoreceptive somatic senses The tactile senses include touch, pressure, vibration, and tickle the position senses include static position and rate of movement

6. Detection and Transmission of Tactile Sensations T ouch, pressure, and vibration are all detected by the same types of receptors called t actile receptors. There are at least six entirely different types of tactile receptors

7. Free nerve endings F ree nerve endings, which are found everywhere in the skin and in many other tissues, can detect touch and pressure

8. Meissner’s corpuscle Elongated encapsulated nerve ending of a large (type A B) myelinated nerve fiber. Inside the capsulation are many branching terminal nerve filaments. These corpuscles are present in the non hairy parts of the skin . Meissner’s corpuscles adapt in a fraction of a second after they are stimulated, Detect low frequency vibration.

9. Merkel’s discs The hairy parts and non hairy part of the skin also contain moderate numbers of expanded tip receptors they transmit an initially strong but partially adapting signal and then a continuing weaker signal adapts only slowly. Therefore, they are responsible for giving steady-state signals

10. Iggo dome receptor Merkel’s discs are often grouped together in a receptor organ called the Iggo dome receptor, which projects upward against the underside of the epithelium of the skin

11. Hair end-organ This receptor adapts readily and, like Meissner’s corpuscles, detects mainly (a)movement of objects on the surface of the body or (b)initial contact with the body.

12. Ruffini’s end-organs multibranched , encapsulated endings, These endings adapt very slowly They are also found in joint capsules and help to signal the degree of joint rotation Found in skin and deeper tissues

13. Pacinian corpuscles Lie both immediately beneath the skin and deep in the fascial tissues of the body. They are stimulated only by rapid local compression of the tissues because they adapt in a few hundredths of a second. Important for detecting tissue vibration or other rapid changes in the mechanical state of the tissues.

14. Transmission of Tactile Signals in Peripheral Nerve Fibers Transmit their signals in type A-beta nerve fibers that have transmission velocities ranging from 30 to 70 m/sec. free nerve ending tactile receptors transmit signals mainly by way of the small type A-delta myelinated fibers that conduct at velocities of only 5 to 30 m/sec. Some tactile free nerve endings transmit by way of type C unmyelinated fibers (up to 2 m/sec ;) these send signals into the spinal cord and lower brain stem, mainly the sensation of tickle.

15. Detection of Vibration Pacinian corpuscles can detect signal vibrations from 30 to 800 cycles per second and they also transmit their signals over type A-beta nerve fibers. Meissner’s corpuscles detect vibrations from 2 to 80 cycles per seconds

16. TICKLE AND ITCH rapidly adapting mechanoreceptive free nerve endings elicit only the tickle and itch sensations. These sensations are transmitted by very small type C, unmyelinated fibers similar to those that transmit the aching, slow type of pain.

17. Receptors afferents dorsal root ganglia gray column ascending tracts thalamus sensory cortex

18. Dorsal Column–Medial Lemniscal System 1. Touch sensations requiring a high degree of localization of the stimulus 2. Touch sensations requiring transmission of fine gradations of intensity 3. Phasic sensations, such as vibratory sensations 4. Sensations that signal movement against the skin 5. Position sensations from the joints 6. Pressure sensations having to do with fine degrees of judgment of pressure intensity Anterolateral System 1. Pain 2. Thermal sensations, including both warmth and cold sensations 3. Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body 4. Tickle and itch sensations 5. Sexual sensations

19. OBJECTIVES: Understand Structure of spinal cord and thalamus Understand the structure of sensory cortex and clinical application when sensory cortex is not working

20. Functional anatomy of spinal cord

21. Comparison of Structural Details in Different Regions of the Spinal Cord

22. OBJECTIVES Understand the structure of sensory cortex and clinical application when sensory cortex is not working Understand the pathway of two main Ascending pathways

23. Molecular layer External granular layer External pyramidal layer Internal granular layer Internal pyramidal layer Polymorphic layer

24. Functions of Somatosensory Area I Localize and discriminate discretely the different sensations in the different parts of the body judge critical degrees of pressure against the body judge the texture, weights, shapes or forms of objects by touch. This is called stereognosis . Judge the shape by drawing. graphaesthesia Bilateral excision of somatosensory area Pt is unable to Localize and discriminate discretely the different sensations in the different parts of the body judge critical degrees of pressure against the body judge the texture, weights, shapes or forms of objects. This is called astereognosis . Judge the shape by drawing. Agraphaesthesia

25. Effect of Removing the Somatosensory Association Area—(5,7) Amorphosynthesis The person loses ability to recognize complex objects and complex forms felt on the opposite side of the body. He or she loses most of the sense of form of his or her own body parts on the opposite side and forgets that it is there . When feeling objects, the person tends to recognize only one side of the object and forgets that the other side even exists.

26. Ascending tracts Dorsal column medial- leminiscal system Anterolateral tract 3. Anterior and posterior spinocerebellar 4. Cuneocerebellar 5. Olivocerebellar 6. Spinotectal 7. Spinoreticular 8. Visceral afferents

27. Dorsal Column–Medial Lemniscal System Touch sensations requiring a high degree of localization and discrimination of the stimulus Phasic sensations, such as vibratory sensations Sensations that signal movement against the skin Position sensations from the joints Pressure sensations having to do with fine degrees of judgment of pressure intensity Anterolateral System Pain Thermal sensations, including both warmth and cold sensations Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body Tickle and itch sensations Sexual sensations

28. Transmission in the Dorsal Column–Medial Lemniscal System Anatomy of the Dorsal Column–Medial Lemniscal System nerve fibers entering the dorsal columns pass uninterrupted up to the dorsal medulla, where they synapse in the dorsal column nuclei (the cuneate and gracile nuclei).

29. SPINOTHALAMIC TRACT

30. Lesions of Dorsal Column Tract Sensory ataxia Loss of vibration Loss of tactile discrimination Loss of tactile localization

31. Dorsal Column–Medial Lemniscal System Touch sensations requiring a high degree of localization of the stimulus Touch sensations requiring transmission of fine gradations of intensity Phasic sensations, such as vibratory sensations Sensations that signal movement against the skin Position sensations from the joints Pressure sensations having to do with fine degrees of judgment of pressure intensity Anterolateral System Pain Thermal sensations, including both warmth and cold sensations Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body Tickle and itch sensations Sexual sensations

32. Organization in dorsal column and anterolateral pathways Dorsal column system Composed of large,myelinated nerve fibers that transmit signals to the brain at velocities of 30 to 110 m/sec, high degree of spatial orientation of the nerve fibers with respect to their origin Fine gradation of intensity Termination VPL & SC Anterolateral Pathway The velocities of transmission are only one third to one half those in the dorsal column–medial lemniscal system , ranging between 8 and 40 m/sec; The degree of spatial localization of signals is poor; The gradations of intensities are also far less accurate Termination in RN, ILN, VPL, SC

33. Anterior and posterior spinocerebellar Cuneocerebellar Olivocerebellar Spinotectal Spinoreticular Visceral afferents

34. Judgment of Stimulus Intensity Spatial & temporal summation Lateral inhibition increases contrast

35. Judgment of Stimulus Intensity by sensory cortex Weber-Fechner Principle Interpreted signal strength = Log (stimulus) + constant Power Law Interpreted signal strength = K ( stimulus-k)y

36. Position sense Static Rate of movement called kinesthesia Receptors M uscle spindles Golgi tendon organs Ruffni’s endings P acinian

37. Texture meissner & merkel Localization meissner & merkel Discrimination meissner Vibration meissner & pacinian Prolonged touch merkel’s Prolonged deep touch & pressure ruffni’s

38. Dermatome Segment of skin supplied by the spinal nerve