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SOMATOSENSORY SYSTEM

SOMATOSENSORY SYSTEM. Prof. S. Aswin, MD, PhD. OBJECTIVES. Define a sensation and list the prerequisites necessary for its transmission Describe the characteristics of sensations

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SOMATOSENSORY SYSTEM

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  1. SOMATOSENSORY SYSTEM Prof. S. Aswin, MD, PhD

  2. OBJECTIVES • Define a sensation and list the prerequisites necessary for its transmission • Describe the characteristics of sensations • List the location and function of the receptors for tactile sensations (touch, pressure, vibration), thermoreceptive sensations (heat and cold), and pain. • Distinguish somatic, visceral, referred, and phantom pain, and describe the various methods to relieve pain • Identify the proprioceptive receptors and indicate their functions

  3. 6. Describe the composition of the somatosensory cortex 7. Discuss the origin, neuronal components, and destination of the dorsal column-medial lemniscus and spinothalamic (anterolateral) pathways 8. Explain the neural pathways for pain and temperature; light touch and pressure; and discrimination touch, proprioception and vibration

  4. ESSENTIAL FUNCTIONS OF THE NERVOUS SYSTEM • Receiving sensory information • Transmitting motor impulses that result in movement or secretion • Integration: an activity that deals with memory, sleep and emotions SENSATION: a state of awareness of external or internal conditions of the body PERCEPTION: conscious registration of a sensory stimulus

  5. For sensation to occur, four prerequisites must be satisfied: • STIMULUS (change in the environment) capable of intiating a response by the nervous system must be present. • RECEPTOR (sense organ) must pick up the stimulus and transduced (convert) it to a nerve impuls. • (Receptor: specilized nervous tissue that is extremely sensitive to internal and external conditions) • The impulse must be conducted along a NEURAL PATHWAY from the receptor or sense organ to the brain. • A REGION OF THE BRAIN (cortical region: sensory area) must translate the impulse into a sensation.

  6. Sensory homunculus Stimulus Stimulus R R

  7. T H E S E N S E S OUR IMPRESSIONS OF THE WORLD ARE LIMITED AND DEFINED BY OUR SENSES IN FACT, ALL KNOWLEDGE AND AWARENESS DEPEND ON THE RECEPTION AND DECODING OF STIMULI FROM THE OUTSIDE WORLD AND FROM WITHIN OUR BODIES S E N S O R Y R E C E P T ION WE ARE ABLE TO COPE 4. CNS 2. RECEPTOR WITH CHANGES 1. STIMULUS INTERNAL CHANGES OF THE ENVIRONMENT EXTERNAL (Aff.) 2. RECEPTOR (3) (response)

  8. BASIC CHARACTERISTICS OF SENSORY RECEPTORS • SENSITIVE TO CERTAIN MINIMUM (THRESHOLD) LEVELS OF STIMULUS INTENSITY • THE STRUCTURE IS DESIGNED TO RECEIVE A SPECIFIC KIND OF STIMULUS (RECEPTOR) • THEIR PRIMARY RECEPTOR CELLS INTERACT WITH AFFERENT NEURONS THAT CONVEY IMPULSES TO THE CNS ALONG SPINAL OR CRANIAL NERVES • AFTER RECEPTOR CELLS STIMULATE AFFERENT NEURONS: • NERVE IMPULSES ARE CONVEYED ALONG NEURAL • PATHWAYS THROUGH THE BRAIN STEM AND DIENCEPHALON CEREBRAL CORTEX OF THE BRAIN (PERCEIVE THE SENSATION)

  9. INPUT PROCESSING OUTPUT Central Nervous system (CNS) (info.) (info.) RESPONSE ENVIRONMENT eff. aff. INTERNAL EXTERNAL (1) 3 classes of neurons 2. Interneuron (2) (3) 1. Afferent neuron 3. Efferent neuron

  10. FUNCTIONAL DIVISION OF CNS Effrent syst. NEURON (CNS) efferent afferent EFFECTOR* RECEPTOR Afferent syst. * Neuron * Muscles (skeletal/ smooth/cardiac) * Glandular cells Aff. Eff. MOTORIC SYSTEM SENSORY SYSTEM Somatosensory Visceromotoric Somatomotoric Visceromotoric Somatic tissues Somatic tissues Viscera/vasa Viscera/vasa

  11. SENSORY SYSTEM System that transmits and analyzes information from external and internal environments CNS PERIPHERAL (Receptors) (info) SOMATOSENSORY (GSA) Somatic structures: skin/skeletal muscles/ bones/joints (From the body & head) VISCEROSENSORY (GVA) From the visceral organs (GSA: General Somatic Afferent; GVA: General Visceral Afferent)

  12. TYPES OF NEURON B. Bipolar A. Multipolar C. Unipolar

  13. Nerve segments • (functional) • Receptive segment • Initial segment • Conductive segm. • Transmissive segment A + B: Motor neurons; C: Somatosensory neuron

  14. CUTANEOUS SENSATIONS RECEPTORS IN THE SKIN 3 1 2 1. Tactile (Merkel’s) disc 2. Free nerve ending (pain, temp.) 3. Corpuscle of touch (Meissner’s corpuscle) 4. End organ of Ruffini (mechanoreceptor) (touch) 5. Laminated (Pacini) corpuscle (pressure,vibration) 6. Root hair plexus (peritrichial receptor) hair movement 4 6 5

  15. CUTANEOUS SENSATIONS Papillary layer Epidermis Free nerve ending Meisner’s corpuscle Dermis Tactile (Merkel) corpuscle Bulbous corpuscle of Krause Reticular layer Hypodermis (Subdermis) Root hair plexus (peritrichial plexus/ perifollicular receptor) Adiposetissue (fat) Ruffini’s corpuscle RECEPTORS IN THE SKIN Pacinian corpuscle

  16. Tactile receptors: • - root hair plexus/ perifollicular receptor) • movement of the skin hairs • - free (naked) nerve ending pain • - tactile (Merkel’s) disc touch • - corpuscle of touch (Meissner’s corpuscle) • touch (in the dermal papillae of the skin: • fingertips, palms of the hands, and soles of the feet; also abundant in: the eyelids, tip of the tongue, lips, nipples, clitoris, tip of penis) • - type II cutaneous mechanoreceptor • (end organ of Ruffini) heavy and continuous touch CUTANEOUS SENSATIONS • Tactile sensations • (touch, pressure, • vibration) • 2. Thermoreceptive • sensations • (cold, warm) • 3. Pain

  17. 2. Pressure Stimulation of tactile receptor (in deeper tissues, longer lasting, felt over a larger area than touch) Receptor: free nerve endings, type II cutaneous receptors, Pacinian corpuscle (Pacinian corpuscles located in: the subcutaneous tissues under the skin, deep subcutaneous tissues under mucous membrane, in serous membrane, around joints and tendons, in the perimycium of muscles, in the mammary glands, in the external genitalia of both sexes, and in certain viscera) 3. Vibration rapidly repetitive sensory signals from tactile receptors Receptor: corpuscle of touch and laminated (Pacinian) corpuscles (detect higher-frequency vibration)

  18. 4. Thermoreceptive sensations heat and cold Receptor: free-nerve ending (?) 5. Pain sensations tissue-damaging stimuli Receptor: free-nerve ending (nociceptor) (branching ends of dendrites of certain sensory neuron) Nociceptor responds to any type of stimulus (if it reaches certain threshold stimulate the sensation of pain)

  19. PAIN SOMATIC PAIN VISCERAL PAIN Superficial somatic pain Deep somatic pain NOCICEPTORS (in the viscera) NOCICEPTORS (in the skeletal muscle, joint, tendon, fascia) NOCICEPTORS (in the skin) NOSISEPTOR: FREE NERVE ENDING

  20. NOCICEPTOR • FREE-NERVE ENDING (branching ends of dendrites of certain sensory neuron) • RESPONDS TO ANY TYPE OF STIMULUS (if it reaches certain threshold stimulate the sensation of pain)

  21. REFERRED PAIN • The ability of the cerebral cortex to locate the origin of pain which is related to the past experience • In most instances of somatic pain and in some instances of visceral pain: the cortex accurately projects the pain back to the stimulated area (our finger is burned we feel pain in our finger) • REFERRED PAIN In most instances of visceral pain: the sensation is not projected back to the point of stimulation (In general: the area of to which the pain is referred and the visceral organ involved receive their innervation from the same segment of the spinal cord)

  22. Example Afferent fibers from the heart as well as from the skin over the heart and along the medial aspect of the left upper extremity enter spinal cord segments T1-T4.Thus the pain of a heart attack is typically felt in the skin over the heart and along the left arm VISCERAL PAIN IS REFERRED TO THE SPECIFIC SKIN AREA REFERRED PAIN

  23. REFERRED PAIN

  24. PHANTOM PAIN A kind of pain frequently experienced by patients who have had a limb amputation: They still experience pain and other sensations in the extremity as if the limb were still there. The remaining proximal portions of the sensory nerves that previously received impulses from the limb are being stimulated by the trauma of the amputation Stimuli from these nerves are interpreted by the brain as coming from the nonexistent (phantom) limb

  25. PAIN SENSATIONS MAY BE CONTROLLED BY: • Interrupting the pain impulse between the receptors and the interpretation centers of the brain • chemical (pain-reducing drugs), • surgical (sympathectomy; cordotomy: spinal cord section; zhizotomy: cutting the radix of the spinal nerve; prefrontal lobotomy: cutting the prefrontal lobe; or by other means)

  26. ACUPUNCTURE • (Lat. acus: needle; pungere: sting) • Another method of inhibiting pain impulses • or anesthetize • (such as in: • tonsillectomy; dental extraction; • removing a lung etc.) • In US: mostly for childbirth, tic douloreux, • arthritis, and other nonsurgical conditions

  27. ACUPUNCTURE* - Probably works by taking advantage of the body’s natural inhibitory influences that can normally blockpain pathways, for example: • -Dorsal root ganglion releases substance P produces EPSP’s*** • Small enkephalin**-containing neurons impinge on synaptic end bulb of the sensory path fiber • blocks the release of substance P from the terminals of the sensory pain fibers inhibits pain transmission to the brain • (Fig. 8-6 b) • * Enhances the release of this inhibitory substance (enkephalin) circulates into the blood to the pain fibers • ** Endogenous opiate *** EPSP: excitatory postsynaptic potential

  28. PROPRIOCEPTIVE SENSATIONS (PROPRIOCEPTION) • An awareness of the activities of muscles, tendons, and joints and of equilibrium is provided by the proprioceptive, or kinesthetic sense • (It informs us of: - the degree to which the muscles are contracted • the amount of tension created in the tendons • the change of position of a joint • the orientation of the head relative to the ground and in response to movements (equilibrium)

  29. Enables us to recognize the location and rate of movement of one body part in relation to others • Allows us to estimate weight and determine the muscular work necessary to perform a task • We can judge the position and movements of our eyes when we walk, type or dress in the dark

  30. PROPRIOCEPTORS • Proprioceptors: receptors located in skeletal muscles, tendons in and around synovial joints, and in the ear • Muscle spindles* : delicate proprioceptive receptors interspersed among skeletal muscle fibers and oriented parallel to the fibers. * consist of 3 – 10 specialized muscle fibers: intrafusal fibers (partially enclosed in a connective tissue capsule that is filled with lymph) • (in the central region of of each intrafusal fiber (represents the sensory receptor area for a spindle: central receptors): few or no actin and myosin – contractile proteins – (a) nuclear bag fibers, (b) nuclear chain fibers) • The spindles are surrounded by skeletal muscle fibers of the muscle called extrafusal fibers

  31. The central receptor area (cannot contract lacks of myofilaments) contains two types of nerve fibers: (a) Type Iafiber, innervates the exact center of the intrafusal fibers. • The branches of type Ia fiber: primary (anulospiral) endings wrap around the center of the intrafusal fibers • (when the central part of the spindle is stretched the primary endings are stimulated and send impulses to the spinal cord) • (b) Type II fibers (their branches: secondary (flower spray) endings which are also stimulated when the central part of the spindle is stretched impulses to the spinal cord

  32. The ends of the intrafusal fibers contain actin and myosin myofilaments (contractile portions of the fibers) • (The ends of the fibers contract stimulated by gamma efferent neurons – small motor neurons located in the anterior grayhorn of the spinal cord) • EXTRAFUSAL FIBERS: • Innervated by large motor neurons: alpha efferent neurons • (located in the anterior gray horn of the spinal cord, near gamma efferent neurons) • THE MUSCLE SPINDLES: • - Stimulated in response to both sudden and maintained stretch on the central areas of the intrafusal fibers • - monitor changes in the length of muscle contraction

  33. PROPRIOCEPTORS (1) (3) Flower spray (2) (4) Articular capsule

  34. a. Muscle spindle b. Golgi tendon organ

  35. THE MUSCLE SPINDLES: • Are stimulated in response to both sudden and maintained stretch on the central areas of the intrafusal fibers • Monitor changes in the length of a skeletal muscle by responding to the rate and degree of change in length This info. is relayed to the CNS: to assist in the coordination and efficiency of muscle contraction • 2. TENDON ORGANS (Golgi tendon organs) • Proprioceptive receptors found at the junction of a tendon with a muscle • Help protect tendons and their associate muscles from damage resulting from exessive tension

  36. 3. JOINT KINESTHETIC RECEPTORS • Location: within and around the • articular capsules of synovial joints • Encapsulated receptors (similar to type II cutaneous mechanoreceptors / end organ of Ruffini) • Respond to acceleration and deceleration

  37. SENSORY PATHWAYS SOMATOSENSORY CORTEX (primary somesthetic/general sensory area) SENSORY HOMUNCULUS Represents the body parts on the somatosensory area, located on the postcentral gyrus (area 3,1,2 Brodmann) of the frontal lobe

  38. Somatosensory cortex/area (postcentral gyrus) Sensory homunculus

  39. (3, 1, 2) Primary somatosensory area/cortex Gambar 2 Brodmann’s areas (52 areas)

  40. Gambar 6 atas

  41. BODY • HEAD • CEREBRAL CORTEX CEREBRAL CORTEX • (appreciation of the somatic) • perceive/recognize a sensation • DCMLS* ALS** • INFO • RECEPTORSRECEPTORS • RECEPTORSSTIMULI STIMULI • Discriminative touch Nondescr. touch • STIMULI Position of the body Temperature • Nociception/Pain • *DCMLS: Dorsal Column-Medial Lemniscus System • **ALS : Anterolateral System • RECEPTOR: Transduces/converts one type of energy to other type of energy • (Receptor = Transducer) • Mechanical/Physical/Chemical stimulus R Electrical signals SOMATOSENSORY PATHWAYS SOMATO- SENSORY CORTEX DCML SYSTEM: perception and appreciation of mechanical stimuli (- Fine form/txture discrimiation, stereogosis (form recognition of 3-dimensional shape)/motion direction. – Conscious awareness of body position (proprioceptions) in space

  42. DCMLS • Central cortex postcentral gyrus (somatosensory/somatoaesthesia area/cortex) • VPL: ventral posterolateral nuc. of thalamus 1 VPL (2) Medial lemniscus Medial lemniscus Gracile nuc. Cuneate nuc - Proprioception, position - Touch, pressure, vibration

  43. ALS (from the body) Cerebral cortex postcentral gyrus Nonspecific thalamic nuclei (centromedian) VPL (ventral posterolateral) nuc. of thalamus Spinothalamic/ spinoreticular system Pain, temperature Pain

  44. ALS (from the head) Cerebral cortex postcentral gyrus Ventral posteromedial nuc. of thalamus • Spinal descending trigeminal nuc. • Spinal descending trigeminal tract Ventral trigeminal lemniscus Semilunar trigeminal ganglion (Gasser) • Trigeminal N (N V): • Ophthalmic n. • Maxillary n. • Mandibular n. • Facial n. (N VII) • Glossopharyngeal n. (N IX) • Vagus n. (N X) 2 1

  45. DCML SYSTEMPerception and appreciation of mechanical stimuli • (-fine form/texture discrimination/stereognosis (form recognition of 3 • dimentional shape)/motion direction • - conscious awareness of body position (proprioception) in space • BODY • HEAD • CEREBRAL CORTEX CEREBRAL CORTEX • (appreciation of the somatic) • perceive/recognize a sensation • DCML S*ALS** • INFO • RECEPTORSRECEPTORS • RECEPTORS STIMULI STIMULI • Discriminative touch Nondescr. touch • STIMULI Position of the body Temperature • Nociception/Pain • *DCMLS: Dorsal Column-Medial Lemniscus System • **ALS : Anterolateral System • RECEPTOR:Transduces/converts one type of energy to other type of energy • (Receptor = Transducer) • Mechanical/Physical/Chemical stimulus R Electrical signals THE SOMATOSENSORY SYSTEM

  46. CLASSIFICATION OF SENSORY RECEPTORS location/stimulus EXTEROCEPTORS (received from the outside: the skin) (touch- pressure, pain, temperature) A. LOCATIONTELECEPTORS (received from a distance)/ special exteroceptors (eyes, ears, nose) INTEROCEPTORS (received from inside) (VISCEROCEPTORS: receives from viscera) (changes in blood pressure, CO2, O2, H ion concentration in the blood) PROPRIOCEPTORS (received from one’s own self: position and movement) (deep body structures: joints, tendons, muscles, vestibular apparatus in the ear) Sensing: - the position of parts of the body in relation to each other - the position of the body in space

  47. CLASSIFICATION OF SENSORY RECEPTORS (cont…) B. TYPES OF STIMULUS TYPES OF SENSATION • THERMAL (cold and warm) • PAIN • LIGHT TOUCH & TOUCH PRESSURE • POSITION SENSE (elicited by the movement of joints and muscles)

  48. TYPES OF RECEPTOR ACCORDING TO ITS STIMULUS RECEPTOR STIMULUS THERMORECEPTOR THERMAL (cold/warm) NOCICEPTOR NOCICEPTIVE (harmful stimuli that produce pain) CHEMORECEPTOR CHEMICAL SUBSTANCE (smell, taste) PHOTORECEPTOR LIGHT MECHANORECEPTOR MECHANICAL (physical stimuli: touch-pressure, muscle tension, joint position changes, air vibration (in the cochlear system of the ear), head movement) BARORECEPTOR CHANGES IN BLOOD PRESSURE

  49. Morphologic types of receptors Different kinds of stimuli (Meissner’s corpuscle Tap, flutter Pacinian corpuscle Vibration) (in the skin dermis, basal epidermis) (Merkel cell Light pressure Hair follicle receptor Motion & direction of the hair) Fig. 16-1 ENCAPSULATED Cutaneous tactile receptors NONENCAPSULATED

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