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Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
Psych b sensory system
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Psych b sensory system

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  • 1. Sensory Functions • General Sensations Mechanical – touch, pressure, vibration, stretch Chemical • Special Sensations Vision Hearing Taste Smell
  • 2. Sensory area in the brain FF A NT RE E Touch stimulus Receptor Sensory modality Ascending Sensory pathway Central Connections Sensory nerve
  • 3. • stimulation of a receptor usually produces only one sensation modality specific • But some receptors are stimulated by more than one sensory modality eg. free nerve endings
  • 4. Classification of receptors • Mechanoreceptors • Thermoreceptors • Nociceptors pain • Chemoreceptors taste, smell, visceral • Electromagnetic receptors visual Guyton p.496
  • 5. Mechanoreceptors • Mainly cutaneous Touch Pressure Vibration • Crude or Fine mechanosensations • Others: auditory, vestibular, stretch
  • 6. Mechanoreceptors • Pacinian corpuscle • Meissner’s corpuscle • Krause’s corpuscle • Ruffini’s end organ • Merkel’s disc • Hair end organ • Free nerve endings Guyton p.496
  • 7. Mechanoreceptors • Pacinian corpuscle deep, pressure sensitive, fast adapting • Ruffini’s end organ deep, tension sensitive, slow adapting • Merkel’s disc superficial, sensitive to deformation of skin, slowly adapting Guyton p.496
  • 8. Mechanoreceptors • Meissner’s corpuscle superficial, sensitive to sideways movements • Krause’s endings • Hair end organ • Free nerve endings Guyton p.496
  • 9. Pacinian Corpuscle Nerve fibre Capsule
  • 10. What happens inside a receptor? • TRANSDUCTION Stimulus energy is converted to action potentials  Inside the nervous system signals are always action potentials  Language of the nervous system contains only 1 word: action potentials • At the brain opposite happens in order to feel the sensation PERCEPTION
  • 11. Transduction Stimulus Receptor potential (Generator potential) Action potential
  • 12. Receptor potentials • are graded • do not follow all-or-none law • amplitude depends on the strength • of the stimulus when reaches the threshold: triggers the action potentials
  • 13. Action Potentials Threshold Resting Membrane Potential
  • 14. Resting
  • 15. Receptor potentials • mechanical transformation on the capsule
  • 16. Physical Stimulus
  • 17. Receptor potentials • Opens up Na+ channels • Na+ influx
  • 18. Physical Stimulus
  • 19. Receptor potentials • Membrane inside the capsule: • depolarisation thus receptor potential is generated
  • 20. Physical Stimulus local current
  • 21. Physical Stimulus Action Potentials are generated
  • 22. • Stimulus strength is coded as the • • frequency of AP Higher the stimulus more frequent are the APs Amplitude of AP is constant
  • 23. Action potentials Receptor potentials Stimulus
  • 24. Adaptation • “getting used to” • after a period of time sensory receptors adapt partially or completely • different types fast adapting receptors slowly adapting receptors
  • 25. Adaptation • after a period of time sensory • receptors adapt partially or completely different types fast adapting receptors slowly adapting receptors
  • 26. Impulses per second Pain Muscle spindle Pacinian corpuscle Time
  • 27. Mechanism of adaptation • In the Pacinian corpuscle mechanical deformation is transmitted throughout the capsule and pressure redistributes Na+ channels inactivates after some time
  • 28. Stimulus Impulse Redistribution of pressure inside the capsule Stimulus No Impulse
  • 29. • Rapidly adapting receptors phasic or rate or movement receptors  detect changes in stimulus strength  eg. Pacinian corpuscle, hair end-organ • Slowly adapting receptors tonic receptors  detect continuous stimulus strength  eg. muscle spindles, Golgi tendon organ, baroreceptors, Ruffini endings and Merkel’s discs, pain receptors
  • 30. Sensory area in the brain Ascending Sensory pathway Central Connections Sensory nerve Touch stimulus Receptor Sensory modality
  • 31. Two ascending pathways • Dorsal column - medial lemniscus pathway fast pathway • Spinothalamic pathway slow pathway These two pathways come together at the level of thalamus
  • 32. Posterior (dorsal) Dorsal root ganglion Dorsal root Dorsal columns Dorsal horn Spinothalamic tracts Anterior (ventral)
  • 33. Spinothalamic pathway Dorsal column pathway Lateral Spinothalamic tract Anterior Spinothalamic tract
  • 34. Dorsal column pathway • • • • • • touch: fine degree highly localised touch sensations vibratory sensations sensations signalling movement position sense pressure: fine degree Spinothalamic pathway • • • • • • Pain Thermal sensations Crude touch & pressure crude localising sensations tickle & itch sexual sensations
  • 35. n se x te or internal capsule c ry so thalamocortical tracts 3rd order neuron thalamus Medial lemniscus Dorsal column nuclei 2nd order neuron (cuneate & gracile nucleus) Dorsal column 1st order neuron
  • 36. Dorsal column medial lemniscus pathway sensory cortex thalamocortical tracts thalamus M ed ul la Medial lemniscus 3rd order neuron cross over Dorsal column nuclei 2nd order neuron (cuneate & gracile nucleus) Dorsal column Dorsal root Dorsal root ganglion 1st order neuron
  • 37. dorsal column - medial lemniscus pathway • after entering the spinal cord lateral branch: participates in spinal cord reflexes medial branch: turns upwards • forms the dorsal columns • spatial orientation: medial: lower parts of the body lateral: upper part of the body
  • 38. dorsal column - medial lemniscus pathway • synapse in the dorsal column nuclei nucleus cuneatus & nucleus gracilus • 2nd order neuron cross over to the • • opposite side and ascends upwards as medial lemniscus as this travels along the brain stem fibres from head and neck are joined (trigeminal) ends in the thalamus (ventrobasal complex)  ventral posterolateral nuclei
  • 39. dorsal column - medial lemniscus pathway • spatial orientation in the thalamus medial: upper part of the body lateral: lower part of the body
  • 40. n se x te or internal capsule c ry so thalamocortical tracts 3rd order neuron thalamus Spinothalamic tracts 2nd order neuron 1st order neuron
  • 41. Spinothalamic pathway sensory cortex thalamocortical tracts 3rd order neuron thalamus anterior lateral 2nd order neuron Spinothalamic tracts cross over Dorsal horn Dorsal root Dorsal root ganglion 1st order neuron
  • 42. spinothalamic pathway • after entering the spinal cord synapse in the dorsal horn • cross over to the opposite side • divide in to two tracts lateral spinothalamic tract:  pain and temperature anterior spinothalamic tract  crude touch
  • 43. spinothalamic pathway • spatial orientation medial: upper part of the body lateral: lower part of the body
  • 44. Note the spatial orientation of
  • 45. Spinothalamic pathway Dorsal column pathway Lateral Spinothalamic tract Anterior Spinothalamic tract
  • 46. thalamocortical tracts • from the thalamus 3rd order neuron • • ascends up through the internal capsule up to the sensory cortex thalamocortical radiation tracts diverge
  • 47. Sensory cortical areas • parietal cortex • a distinct spatial orientation exists
  • 48. Sensory cortex • different areas of the body are represented in different cortical areas in the sensory cortex • sensory homunculus somatotopic representation not proportionate distorted map upside down map
  • 49. Sensory homunculus
  • 50. Brodmann areas
  • 51. Sensory cortical areas • primary somatosensory cortex (SI) postcentral gyrus (Brodmann areas 3a, 3b, 1, 2) • secondary somatosensory cortex (SII) parietal cortex behind postcentral gyrus (Brodmann areas 5, 7)
  • 52. somatosensory cortex Functions • Localisation of somatic sensations • to judge critical degree of pressure • identify objects by their weight, shape, form - stereognosis • to judge texture of materials • localisation of pain & temperature
  • 53. Abnormalities • Sensory loss • Anaesthesia absence of sensation • Paraesthesia abnormal sensation • Hemianaesthesia Loss of sensation of one half of the body • Astereognosis
  • 54. Localisation of the abnormality • Peripheral nerve part of a limb is affected • Roots dermatomal pattern of sensory loss • spinal cord a sensory level • internal capsule one half of the body

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