sensory system
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Sensory System
Dr Saadiyah Rao
Depart Of Physiology
DIMC
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A General Sense…
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Classification Receptors:
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Sensory system
Extroceptors: Which response to stimuli arising outside the body.
Which response to stimuli arising inside the body.
Introceptors:
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Are specialized epithelial cells or neurons that transduce environmental signals into neural signals.
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Sensory Receptors:
specialized epithelial cells: E.g.?
neurons: E.g.?
environmental signals: E.g.?
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Receptive Field:Area of coverage of a sensory receptor or
sensory neuron.
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Sensory neurons:(Afferent) Carry messages toward the CNS from sensory receptors all over body.
Dermatome:Each spinal nerve innervates a segmental
field of skin.
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Sensory receptors in skin:
Receptor Sensory Modality
Meissner’s corpuscles Touch (rapidly adapting) Vibration
Pancinian corpuscles Touch (rapidly adapting)ProprioceptionPressureVibration
Merkel’s disks Touch (slowly adapting)Texture
Ruffini endings Touch (slowly adapting)Pressure
Krause’s corpuscles TouchTemperature?
Nerve endings ColdWarmthTouchPressure
Nociceptors Pain 6
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Difference between Touch , Pressure & Vibration?
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Fast pain (felt within 0.1 sec)
is also called as:
Sharp
Acute
Pricking etc
Slow pain (felt after 1 sec)
is also called as:
Aching
Chronic
Thrombing etc
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Sensory Pathway:
First order neurons: Are the primary afferent neurons that receive the transduced signal & send information to CNS.
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Second order neurons: They are located in spinal cord or brain stem.
• Receive information from primary afferent neurons in relay nucleus & transmit to thalamus.
• May cross the midline.
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Third order neurons: Are located in the relay nuclei of the thalamus.
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Forth order neurons: Are located in the appropriate sensory area of the cerebral cortex. The information received results in conscious perception of the stimulus.
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Spinal cord
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Posterior Column Sensory Pathway
• Fine Touch• Vibratory• Pressure• Proprioception• Stereognosis• Two point discrimination
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Primary afferent neurons(1st)
Posterior column
Nucleus gracilis & Nucleus cuneatus
Medulla (ipsilateral)
Cross in medulla (2nd)
Medial lemniscus
Thalamus
(cotralateral)
Sensory cortex (4th)
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Anterolateral (Spinothalmic) Sensory Pathway
• Pain(lat)• Temperature(lat)• Crude touch(ant)• Pressure(ant)
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Primary afferent neurons(1st)
Posterior horn (ipsilateral)
(2nd) cross midline
Anterolateral qud of Spinal cord
(3rd)
Thalamus
(cotralateral)
Sensory cortex (4th)
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• Is minimum distance at which 2 points of touch can be perceived as separate
• Measure of tactile acuity or distance between receptive fields
Two-point touch Discrimination
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