Copyright ©Mark Nelson, 2002. All rights reserved.
Chapter 14: Somatic and Other Senses
What you need to know
(exam questions will be a drawn from this subset of material)

Describe the peripheral and CNS pathway that carries  tactile information from your fingertip to your cortex?  (p. 334-335)
    receptor ending in skin => dorsal root ganglion (contains receptor cell body) => spinal cord =>
    medulla (dorsal column nuclei) => thalamus via the medial lemniscus => primary somatosensory cortex
    This route is called the lemniscal pathway.
 
Describe the peripheral and CNS pathway that carries pain information from your fingertip to your cortex?  (p. 334-335)
   receptor ending in skin => dorsal root ganglion (contains receptor cell body) => spinal cord =>
   => thalamus => primary somatosensory cortex
    This route is called the spinothalamic pathway.
 
Which of the two pathways generally has faster conducting axons?  (p. 335)
   The lemniscal pathway (tactile) generally has faster conduction velocities.
    The spinothalamic pathway (pain and temperature) tends to have slower conduction velocities.
 
Describe the receptor endings of temperature and pain receptors?  (p.336-337)
   Pain and temperature receptors terminate as free nerve endings in the skin (no specialized receptor organ structure)
 
Describe the receptor ending of a Pacinian corpuscle? What does it respond to ?  (p. 339-341)
   The nerve terminal of a Pacinian corpuscle is surrounded by a spherical capsule with multiple layers (like an onion)
    Pacinian corpuscles respond best to vibrational stimuli.
 
What happens when you remove the capsule from the end of a Pacinian corpuscle?  (p. 341, Fig. 14-4)
   the normally phasic generator potential becomes more tonic
 
In addition to the skin, where else are Pacinian corpuscles  found ?  (p. 340)
   The are also found in tendons, where they serve as proprioceptors.
 
What are some other types of proprioceptors associated with tendons and muscles?  (p. 340)
   In addition to Pacinian corpuscles, there are golgi tendon organ, muscle spindle organs, and Ruffini's end organs.
 
What are two ways in which pain information can be modulated in the spinal cord?  (p. 342-343)
   1) by stimulation of nearby pressure receptors in the skin (thats why squeezing or rubbing a wound helps alleviate pain)
   2) descending  control  from higher brain centers via endorphins
 
What are some of the key organizational features of primary somatosensory cortex?  (p. 346-347, also Figs. 9-16, 9-17)
   topographic organization;
    distorted reprentation of different body parts (in proportion to receptor density) - Fig. 9-16 (p. 228)
    columnar organization of pain, temperature, tactile submodalities - Fig. 9-17 (p. 230)
 
What are the major chambers of the vertebrate inner ear? What type of stimuli does each region process?  (p. 348-351)
    cochlea - sound
    semicircular canals (three) - rotational acceleration of the head in 3 angular directions
    utricle - orientation with respect to gravity (head tilt), linear accel. in horizontal plane
    saccule - linear acceleration in vertical plane
 
What is a macula?  (p. 349)
   a patch of hair cells and supporting cells where sensory transduction takes place in each of the chambers listed above
 
What are otoliths?  (p. 349-350)
   small particles of calcium carbonate in the saccule or utricle of the inner ear.
    enhances the physical stimulus arising from acceleration and gravity
 
What is the cupula?  (p. 350-351)
   a gelatinous mound covering the hair cells in the semicircular canals
    relative motion of the fluid in the canal (endolymph) deflects the cupula, which activates the hair cells at the base
 
What is the difference between a passive and an active electric sense ?  (p. 354-355)
   animals with a passive electric sense can detect externally-generated electric fields (sharks, catfish, platypus)
    animals with an active electric sense can detect changes in a self-generated electric field (weakly electric fish)
 
What two broad categories of functions are assocatied with an active electric sense?  (p. 355)
   electrolocation - detecting objects in the environment (analgous to echoloction in bats)
    electrocommunication - sending signals to other fish (analgous to vocal communication)
 
What kind of sense organs are associated with the passive electric sense? with the active electric sense?  (p. 355, Fig. 14-16)
   passive - ampullary organs;
    active - tuberous organs
 
What are the first two stages of electrosensory processing in the CNS?  How are they organized (p. 356-357)
   primary afferents => medulla (ELL) => midbrain (torus semicircularis)
    the electrosensory regions in the medulla and midbrain contain topographic maps of the body surface
 
What organisms have been shown to have a magnetic sense?  (p. 357-358)
   certain bacteria, birds (e.g. homing pigeons), honey bees, sharks; perhaps humans