P215Sensory Systems(Chapter 15, pp 518 - 522) Spring 2000
I. INTRODUCTION
A. Basic Components of Sensory Systems
1. sensory receptors
2. sensory afferent neurons and ascending pathways
3. CNS sensory centers (thalamus and sensory areas of cerebral cortex)
B. Basic Functions
1. detect stimulus; (site of transduction***)
2. convey information to CNS and carry it to the brain
3. process and analyze information
***(converts stimulus energy into a change in membrane potential)

Click for Chart Summarizing Basic Components and Basic Functions

C. Sensory Coding
1. what is it?
2. how strong is it?
3. where is it?

II. SOMATOSENSORY SYSTEM
A. Somatosensory Modalities
1. cutaneous sensation
2. proprioception
3. nocioception
B. Somatosensory Receptors
1. several types
2. site of sensory transduction
C. Somatosensory Pathways
1. multi-neuron projection (from touch on hand, for example)
stimulus ---------> sensory receptors
sensory receptors ----------> sensory afferent neurons
sensory afferent neurons ----------> spinal cord interneurons
spinal cord interneurons ----------> thalamic neurons
thalamic neurons ----------> neurons of somatosensory cortex

(Click to See Projection from Sensory Receptor to Sensory Cortex)
2. somatosensory cortex
a. in cortex of parietal lobe
b. map of body surface
1) large hand, face regions
2) "crosses over" to opposite side of brain
D. Pain
1. characteristics and usefulness
2. transmission along pain pathways
3. treatment
4. referred pain and phantom limb pain

(Click to Take a Short Look at Special Kinds of Pain)

Sensory System Objectives


1. Explain in general terms, what sensory systems do.
Describe how sensory information enters the sensory centersof the CNS.
What type of neurons are involved?
In what form of signals do these neurons carry their sensory information?

2. Explain what is meant by SENSORY TRANSDUCTION.
What do sensory receptors do?
Can there be any sort of sensory function without sensory receptors?
Can specialized dendrites of sensory afferent neurons act as sensory receptors?
Are all sensory receptors part of a sensory afferent neuron?
Why are the changes in membrane potentials regarded as types of graded potentials?
What might the size of these sensory say about the stimulus that lead to their appearance in sensory receptors?
How do these these sensory receptor potentials lead to the firing of action potentials in sensory afferent neurons?

3. Describe SENSORY CODING.
How does the nervous system signal the intensity of sensory stimulation?
Why can we perceive different kinds of sensory stimulation?
Why don't different kinds of sensory input always mix
together as soon as they enter the nervous system?
Are there neurons in the CNS that receive input from more than one sensory system?
What is a "receptive field"?
What happens to a neuron when its receptive field is stimulated?
What does this have to do with identifying the location of a sensory stimulus?

4. Identify the different modalities of the somatosensory system.
How does information about touch reach the somatosensory cortex?
At a minimum, how many neurons and how many synapses are involved?
Where does temperature information from the left hand go?
What parts of the body are "mapped" across the largest regions of somatosensory cortex?
What does this say about our sense of touch in these parts of the body?
Where does a person loose sense of touch if the left cerebral hemisphere is damaged?
Where does a person loose sense of touch if the right parietal lobe is damaged?

5. Become familiar with pain (but hopefully not too familiar).
Why is pain useful? What are the different characteristics of pain?
What are the pain receptors? What are the axons that carry information about pain?
What do referred pain and phantom limb pain say about sensory processing in the human CNS?
What does sensory processing in the cerebral cortex do for us that sensory
processing in the spinal cord, for instance, cannot do?