Sensory system

THE SENSORY SYSTEM
?Sensory receptors
?Neural pathway
?Parts of the brain
Receptors
?Transducers (energy ? action potentials)
?Differential sensitivity of receptors
i.Rods and cons
ii.Osmoreceptors
?The Labeled Line Principle (Modality of sensation)
oType of sensation
oSpecific nerve fibers
oExcitation of specific receptors
oSpecific point in the CNS.
Modality of Sensation
?Q. : How that different nerve fiber transmits different modalities of sensation??
? Answer: Each nerve tract terminates at a specific point in the CNS.
?i.e., stimulating pain fiber ? person perceives pain regardless of what type of stimulus excites the fiber.
Neural Pathway in the Sensory System
?A sensory pathway is made up of a group of neuron chains.
?Each chain consists of three or more neurons connected end to end by synapse.
?1st: enters spinal cord from periphery
?2nd: crosses over (decussates), ascends in spinal cord to thalamus
?3rd: projects to somatosensory cortex
Sensory Units
?Afferent neuron divides into many fine branches, each terminating at a receptor.
?Single neuron with all its receptors endings ? sensory unit.
?Single receptor (few cases).
The Receptive Field
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