Lab 3 - nerve action potentials

Question 1

Define: mechanoreceptor

Answer 1

Specialized sensory nerve cells that respond to touch, pressure, sound, movement, stretch

Question 2

Internal and external mechanical signals:

Answer 2

Internal - muscle position, contraction, movement; positioning in space.
External - vibrations/touches created by wind, sound, water, or those that are transmitted through the substrate.

Question 3

Proprioreceptors:

Answer 3

Receptors that provide info about position in space.

Question 4

What happens when a mechanoreceptor is stimulated?

Answer 4

An AP (triggered in the mechanoreceptor neuron) travels to higher ganglion for processing.

Question 5

Types of cockroach mechanoreceptors:

Answer 5

1. Setae - short hairs
2. Hair plates - clusters of hair; bend when adjoining surfaces of the cuticle touch during movement
3. Campaniform sensilla - dome-like structures; distorted with the movement of the spines that protrude from the surface of the sensilla, or with the movements of the leg
4. Chordotonal organs - structures under the cuticle; change in length when joints are extended or flexed.

Question 6

Motor response in cockroaches:

Answer 6

Neuronal axons of tibia receptors travel through a sensory nerve in the femur. Stretch receptors synapse with interneurons in CNS. AP rate increases.

Question 7

Define: sensory receptor adaptation

Answer 7

A decline in receptor firing rate with prolonged stimulus. Speed of adaptation differs across receptors.

Question 8

Example of stress receptor found in human skin:

Answer 8

Pacinian corpuscles. Display very fast sensory receptor adaptation.

Question 9

Sources of electrical noise:

Answer 9

Pickup - caused by electrical radiation that produces currents in the electrodes and wires leading to the amplifiers in the recording system.
Ground loop - ground cable serving as an antenna for the noise in the room.

Question 10

Ways to reduce electrical noise:

Answer 10

Faraday cage - a grounded, screened enclosure around the preparation and the electrodes. It separates the source of the radiation from the electrodes. Does not affect ground loops.
Use simple cables with alligator clips to avoid ground loops.

Question 11

Cockroach leg anatomy:

Answer 11

Hinds legs are metathoracic and move the cockroach forward.

Coxa - top
Trochanter - knee
Femur - thigh
Tibia - shin
Tarsus - ankle and foot

Question 12

Which way is flexion and which was is extension?

Answer 12

Flexion is towards the trochanter.

Question 13

Experiment 1: flexion/extension of leggy

Answer 13

Move and hold. Take sweep with the highest firing rate.

Question 14

Chordotonal organ response:

Answer 14

Length changes with tibia flexion/extension

Question 15

AP of one neuron…

Answer 15

Amplitude is the same always. Intracellular recording is accurate; extracellular recording varies depending on neuron diameter and the distance of the electrode from the neuron. Large diameter = large amplitude.

Question 16

Patterns of sensory receptor adaptation:

Answer 16

Phasic - immediate drop in firing rate. Typically associated with changes in stimulus intensity.
Tonic - slow decline in firing rate. Typically associated with prolonged stimulus.
Phasictonic - phasic, then tonic.

Question 17

Experiment 2: constant stimulation of leggy

Answer 17

Record at different angles. Take largest response (highest firing rate).

Question 18

How stretch receptors work:

Answer 18

Mechanical deformation of ion chambers opens channels more and allows more ion movement and AP generation.

Question 19

Calculating firing rate:

Answer 19

AP/s. One sweep is 500 ms.