8 October 2008

Chapter 7 Sensory Physiology

Friday: 1)Return Take-Home Quiz on van Gammeren et al. paper.2) Take in-class quiz on Cranial Nerves and Somatic & Autonomic Motor Systems

Aspects of a stimulus that must be encoded using only action potentials

What? (modality & labeled line)Where? (location enhanced by lateral inhibition) How long (duration, onset/offset.. Adaptation)?How strong (intensity)?

Board diagram listing stimulus modal and classifications as special senses, somatic senses, and

internal (subconscious) senses.

Figure 7.01

1st order sensory neuron

1st order sensory neuron

Example: a rod or cone of the retina

Figure 7.16

Adequate Stimulus

& Labeled Line

Each type of receptor responds best to a specific stimulus called its adequate stimulus.

Figure 7.02

Figure 7.03

Figure 7.11

Examples: waistband of underwear, top of socks, earrings, mechanoreceptors in carotid arteries for blood pressure

Figure 7.04

Review definition of receptive field;

1st, 2nd, and 3rd order

sensory neurons each have receptive fields.= 1st order sensory neuron

Figure 7.05

Within a cell’s receptive field, stimulus intensity is encoded by frequency of action potentials.

Figure 7.06

The size of receptive fields varies dramatically in

different regions of skin (i.e. lips, palm, fingertip, calf).

For touch discrimination, small receptive fields allow greater accuracy in “two point discrimination” test (upcoming lab!)

Figure 7.07

This 1st order sensory neuron will have a higher

frequency of action potentials if the stimulus is in the center if its receptive

field. However, this neuron also uses action potential frequency to

encode stimulus intensity. Therefore, this neuron

would not be very good at encoding the precise location at which a

stimulus was delivered.

Figure 7.08

Receptive fields of different neurons often overlap such that any patch of skin may have several receptors of the same type (modality) and receptors of different types (different modalities I.e. touch, pain temperature, etc.)

Overlapping receptive fields of touch receptors (Meissners, Merkels) allow for more precise localization of a stimulus via the mechanism of lateral inhibition (next slide.)

Figure 7.09

Lateral inhibition exaggerates the difference in stimulus intensity detected by adjacent neurons.

Figure 7.10

Lateral inhibition improve stimulus

localization.

Figure 7.12

Descending pathways from brain (from periaqueductal gray matter) can suppress sensory input (recall example of suppression of pain.)

Figure 7.13

1st order somato-sensory neurons have cell bodies in DRG or cranial nerve

ganglia and synapse

onto second order

neurons within the

CNS.

Figure 7.14

=Post-central gyrus

Damage to specific areas (stroke) is correlated with specific sensory deficits.

Figure 7.15

Figure 7.16

Figure 7.17

Figure 7.18

Figure 7.19

Figure 7.20