14 October 2011Chapter 7: Sensory PhysiologyChapter 9: Muscle Physiology

Lab next week: Part 1: Visual System B (lecture/demo)Part 2: Sensory physiology experiment: Cutaneous receptor distributionPart 3: Auditory System (lecture/demo)

Read Ch 7 sections on Vision, Hearing, and Equilibrium before lab.

Monday Quiz on Cranial Nerves: Name, number & function

Change in course topics: Next is Muscle Physiology Ch. 9

Will return to Digestive System later.

1QQ # 17 for 8:30 class1. Which of the following are correct statements:

a) The intensity of a stimulus is proportional to the size of the graded potential in the receptive membrane.b) The modality of a stimulus is encoded by which type or types of sensory receptors are activated.c) The intensity of a stimulus is encoded by the frequency of action potentials.d) Some ascending spinal neurons receive synaptic inputs from more than one part of the body.e) Each taste receptor cell has at least two different categories of tastant receptor proteins.

2. What is the meaning of labeled line in the context of sensory physiology?

1QQ # 17 for 9:30 class1. Which of the following are correct statements:

a) The intensity of a stimulus is proportional to the size of the generator potential.b) The modality of a stimulus is encoded by which type or types of sensory receptors are activated.c) The intensity of a stimulus is encoded by the frequency of graded potentials.d) Some ascending spinal neurons receive synaptic inputs from skin and internal organs.e) Each hair receptor cell has mechanically-gated and voltage-gated ion channels.

2. What is the meaning of the term “adequate stimulus” and what is the adequate stimulus for a taste receptor cell?

Receptive field = the area of the body that, when stimulated, leads to activity in a neuron.

= 1st order sensory neuron

Could be encapsulated

S 17

Dorsal column-medial lemniscal tract1st order axons ascend in ipsilateral dorsal columns to synapses onto 2nd order in dorsal column nuclei of brainstem, 2nd order axon decussates in brainstem, travel to thalamus to synpases onto 3rd order neuron, which sends it axons to SSC.

Right side

Right sideRight side

Right side

Proprioception

Receptive field = the area of the bodythat, when stimulated, leads to activity in a neuron.

1st, 2nd, and 3rd order sensory neurons each have receptive fields.

S 18

Activation of mechanically gated channels

Receptors and transduction

Could be encapsulated

S 20

Sensations to touchMechanoreceptors contain receptor proteins that respond to

stretching, distortion, or pressure on the peripheral plasma membrane

S 21

Fig. 07.05

Activation of mechanically gated channels and convergence of graded receptor potentials from different parts of the dendritic arbor of the receptor. Thus a receptor cell with a more extensive arbor will likely be more ____________. Why?

S 22

Summary to now:

Modality encoded by _______.Intensity encoded by _______.

What’s left?Location encoded by _______.Duration encoded by _______.

S 23

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 (in lab!)

Stimulus LocalizationS 24

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.)

Stimulus Localization& Intensity

S 25

Lateral inhibition exaggerates the difference in stimulus intensity detected by adjacent neurons, aids with LOCALIZATION.

Stimulus Localization & Intensity

PresynpaticInhibition

Mildinhibition

Massiveinhibition

S 26

Lateral inhibition improves stimulus localization.

Stimulus Localization& Intensity

S 27

Which is easier to localize and why: a light touch or a moderate touch?

Adaptation = decrease in frequency of APs with sustained stimulus

S 28

Coding for stimulus duration.

Figure 7.11

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

YouTube

S 29

“Flutter” receptors are rapidly adapting.