Sensory Systems (Book 2, Ch. 9 and Book 3, Ch. 5)

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Sensory coding (Book 3, Ch 5.2)

How the brain is able to receive such accurate information about external stimuli.

Stimulus quality: type of receptor and afferent nerve pathway activated. Specific projection pathways (tracts) in CNS to different areas of brain (cortex).

Stimulus intensity: frequency of AP firing; number of neurons activated

Stimulus timing: Duration and temporal pattern of AP firing

Stimulus location:
touch - receptive fields
 

individual receptive fields (Fig.7) Dermatomes
 
 
 
 
 
 

organised within dermatomes (Fig.6);

 
 
 
 
 
 

topographical representation of inputs to cortex.
topographical representation


Sensory pathways

Receptors - Biological transducers. Convert particular form of stimulus energy into electrical signal (receptor potentials) and then generate action potentials

Afferent neurons - functional differences (by size) in axon types. (Book 3, Ch 5)
 

somatosensory pathways

CNS pathways (Book 2, §9.5 and Book 3, Ch 5)

The peripheral neurons terminate in specific areas of the spinal cord, e.g. the dorsal horn.
Dorsal horn neurons project to the thalamus, crossing the midline on the way.

Dorsal Columns - fine touch,

proprioception

Spinothalamic tracts- coarse touch,

thermosensation,

nociception

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