Sensory Systems and Somatosensation

1
Sensory Systems and Somatosensation
Josh Martin jpmartin_at_email.arizona.edu
Material from Nicholls pp.333-340,
355-363 Additional material in Kandel chs. 20,
21, and 23
2
A sensory stimulus presents different kinds of
information

• Modality
• What kind?
• Intensity
• How much?
• Duration
• How long?
• Location
• Where?

3
Different modalities are encoded by different
receptor types
Somatosensation
Proprioception
Olfaction
Gustation
Audition
Vision
4
Several receptor types respond to
somatosensory/touch stimuli
5
Receptor cells transduce stimuli into neural
activity
Stimulus
Receptor Cell
Response
6
The intensity of a stimulus is transmitted by the
frequency of the neural response
Maximum response (Saturation)
Firing Rate
Sigmoidal response function/curve
Threshold
Stimulus Intensity
7
The response curve of a neuron is related to the
probability of detection
Firing Rate
Probability of Detection
Stimulus Intensity
Stimulus Intensity
8
Receptor cells adapt to persistent stimuli
Rapid
Slow
9
Different receptors adapt at different rates
Slow
Slow
Rapid
Very Rapid
10
Different receptors adapt at different rates
Rapid
Slow
Slow
Very Rapid
11
The Pacinian Corpuscle is a rapidly adapting
receptor cell
Capsule
Rebound
off
on
12
The capsule of the Pacinian corpuscle is
responsible for its rapid adaptation
Rebound
13
The Pacinian Corpuscle responds to vibrations on
the skin
14
The receptive field of a receptor cell is
determined by its morphology
15
The receptive field of a receptor cell is
determined by its morphology
16
Lateral inhibition refines the receptive field of
higher-order cells
17
Lateral inhibition improves precision in
higher-order cells
18
Lateral inhibition improves discrimination
19
Lateral inhibition produces a center-on,
surround-off receptive field
20
Touch information travels through the spinal
chord and thalamus to the sensory cortex
21
Somatosensory Cortex
Central Sulcus
22
Neurons in the somatosensory cortex have larger,
overlapping receptive fields
23
Neurons in the somatosensory cortex have
center-on, surround-off receptive fields
24
Receptive fields in the somatosensory cortex
comprise a somatotopic map of the body
25
The homunculus reflects the density of receptor
cells
26
Naked Mole Rat
27
Naked Mole Rat
28
Star-nosed Mole
29
Star-nosed Mole
30
In Class exercise

• Modality
• Intensity
• Duration
• Location

31
Modality

• Labeled line
• Receptor type

32
Intensity

• Sigmoidal response curve

Firing Rate
Stimulus Intensity
33
Duration

• Adaptation
• Vibrations

34
Location

• Receptive Field
• Lateral Inhibition
• Homunculus