Sensory system

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:

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.?

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.

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.

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.

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)

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)

• 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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