Copyright ©Mark Nelson, 2002. All rights reserved.
Chapter 10: The Coding and Control of Sensory Information
What you need to know

(exam questions will be a drawn from this subset of material)

How is information about stimulus strength usually encoded by sensory afferents?   (p. 234-235)
    stimulus strength is usually reflected in the firing frequency (spikes per second) of the afferent fiber

How does the coding of stimulus strength differ for tonic and phasic sensory afferents? (p. 234-235)
    the firing frequency of tonic afferents reflects absolute stimulus strength,
    whereas the firing frequency of phasic afferents reflects changes in stimulus strength

How are other qualities of the stimulus (e.g. position, wavelength, frequency, etc.) encoded by sensory afferents?  (p. 235-237)
    1) changes in the temporal pattern of spike activity on a single fiber
        (Morse code example - transmitting a sequence of letters on a single line)
    2) labeled line coding - a dedicated line for each quality  (for example, 26 lines, each representing a single letter of the alphabet)
    3) across fiber coding - the quality is encoded as a pattern across multiple lines
        (ASCII code used by your computer; 7 lines:  A = 1000001; B = 1000010; C = 1000011; D = 100100; etc.)

What are some neurobiological examples of a labeled line code?  (p. 236-237)
     -chemoreceptors that are highly specific to one particular chemical substance (e.g. insect pheromones)
     -dedicated sensory receptors for different stimulus modalities in the somatosensory system (touch,  pain, cold, etc.)

What are some neurobiological examples of an across-fiber (population) code?  (p. 238-240)
    - broadly tuned chemosensory receptors that respond to many different odorants
       (e.g., apple pie is represented as an across-fiber code in the mammalian olfactory system)
    - sense organs that use range fractionation with broad, overlapping receptive fields
       (e.g. statocyst organ coding of tilt angle in crayfish; proprioceptor encoding of arm position)

What does it mean for a sense organ to be under efferent control?  (p. 243)
     the sense organ receives efferent synapses from the CNS that typically modulate the responsiveness of the sense organ

What functional benefits are derived from efferent control of sense organs ?  (p. 243)
    1) reflex tuning
    2) reafference suppression
    3) protection from damage
    4) suppression of unimportant stimuli (sensory gating)

What are muscle spindle organs?  (p. 244-245)
    stretch receptors (mechanosensory) associated with vertebrate skeletal muscle

What are extrafusal and intrafusal muscle fibers; which ones are muscle spindle organs associated with?  (p. 244-245)
    -extrafusal muscle fibers make up the bulk of skeletal muscle and provide the contractile force
    -intrafusal muscle fibers are thin, thread-like fibers running in parallel with the extrafusal muscle
    -muscle spindle organs are associated with the intrafusal fibers

What is the functional role of muscle spindle organs?  (p. 245-248)
    they play a key role in reflex tuning by providing the CNS with information about
    the length of a muscle compared to its "intended" length

What is sensory reafference?  (p. 249-250)
     the sensory input that an animal receives as a consequence of its own movements
    for example, neuromast organs in the llateral line system of fish are stimulated by the fish's own swimming movements

    or the visual stimulation that occurs when an animal moves its eyes across a static visual scene

How does efferent control influence sensory reafference?  (p. 249-250)
     by decreasing sense organ sensitivity at the appropriate time, efferent control can  reduce sensory responses responses to reafferent signals

What is an example of efferent control in protecting a sense organ from physical damage?  (p. 250)
     efferent signals help protect the ear from excessively loud noises (more details in Chapter 12)

What is an example of efferent control in selective suppression of sensory input?  (p. 250-251)
     when a cat attends to a salient visual stimulus (like a mouse),  responses to other stimulus modalities can be suppressed