L5 - Sensory Neurons

Question 1

What is transduction, and how does it relate to sensory cells?

Answer 1

Transduction: conversion of one form of energy into another

Sensory cells transduce physical or chemical energy stimuli into electrical signals. The receptor protein directly or indirectly opens or closes ion channels, affecting the resting potential of the cell.
This change in resting potential then either causes the sensory cell to fire an AP or, through NT release, leads an associated neuron one or even 2 synapses away to fire APs.

Question 2

How is transduction similar to post synaptic potential?

Answer 2

Each result in the flow of ions through channels in the cell membrane

Question 3

What is Stimulus transduction?

Answer 3

1) membrane receptor proteins respond to a stimulus by altering ion flow across a cell membrane
2) this causes a receptor potential
3) In some, this regulates spike production; in others it directly regulates synaptic transmission from the neuron
4) Stimulus intensity is initially encoded as amplitude of receptor potential

Question 4

What is a metabotropic receptor?

Answer 4

A metabotropic receptor is a type of membrane receptor of eukaryotic cells that acts through a secondary messenger.

It is indirectly linked with an ion channel or channels on the plasma membrane through signal transduction:

• of G proteins
• e.g.: tyrosine kinases, guanylyl cyclase

Question 5

What are the 2 types of receptor neurotransmitter receptor?

Answer 5

Based on their structural and functional characteristics, the neurotransmitter receptor can be classified into two broad categories: metabotropic and ionotropic receptors.

Question 6

What is an ionotropic receptor

Answer 6

Ionotropic receptors form an ion channel pore.

They usually have 2 different domains:

• trans membrane domain - includes an ion pore
• extracellular domain - ligand bonding location

Question 7

Describe how the Crayfish stretch receptor works?

Answer 7

1) Detects downward tail bending in special think muscle strands (an accessory structure)
2) Stimulus stretch opens ion channels in dendrites (transduction)
3) Ion flow causes receptor potential which spreads to axon hillock

Question 8

How do most sensory neurons deal with maintained stimulation? (e.g.: a tickle)

Answer 8

The response wanes if the stimulus is maintained = adaption - is anti tickle.

Allows animals to ignore background or unchanging conditions, while remaining aware for new information or changes.

Question 9

What is a proprioceptor?

Answer 9

A proprioceptor is a sense organ that monitors the position or a change in position of an animal’s body parts

Question 10

How many muscle receptor organs are there per segment in a crayfish abdomen?

Answer 10

4 per segment

Question 11

How does pressure equilibrate between the middle ear and the outside?

Answer 11

The middle ear is also connected to the estuation tube, which is also filled with air, and therefore pressure equilibrates between the middle ear and the outside atmosphere.

Question 12

What 3 bones make up the inner ear?

Answer 12

Ossicles:

Malleus
Incus
Stapes

Question 13

What are the 2 windows in the middle ear called and what membrane do they sit on?

Answer 13

Oval window, round window

They sit on the

Question 14

What is the function of the Ossicles?

Answer 14

They transmit vibrations to the oval window.

They act as a lever, translating large movements of the tympanic membrane to smaller movements for the oval window.

Question 15

How is sound transmitted from the middle ear to the inner ear?

Answer 15

The vibrations created by the stapes on the oval window creates pressure waves in the fluid-filled cochlear canals.

Question 16

Describe the inner ear structure

Answer 16

The inner ear is a long tapered coiled chamber called the cochlea.

It is comprised of 3 parallel canals separated by 2 membranes:

• Reissners membrane
• Basilar membrane

Sitting on the basilar membrane is the organ of Corti, which transduces pressure waves into APs.

Question 17

How does the organ of Corti work?

Answer 17

It contains hair cells with stereocillia that are in contact with the tectorial membrane. These hair cells are in contact with synapses and therefore neurones that form the auditory nerve.

When the basilar membrane –> the tectorial membrane flexes –> the stereocillia flex –> they alter the membrane potential of the hair cell and the rate at which they release NT, therefore they rate of APs travelling down the auditory nerve.

Question 18

How do different pitches of sound vibrate the basilar membrane in different places.

Answer 18

Slow vibrations:
if the movement of the oval window is slow, the pressure waves in the cochlear travel all the way along the canal, vibrate and transmit through the BM at the end and then come back down the second canal to displace the round window.

Fast vibrations:
the pressure waves only travel partly along on the canal, and then short cut over the BM and back to the round window, creating vibrations which are faster.

This occurs because the BM varies in stiffness along its length, therefore different frequency’s affect it at different places

Question 19

How do different pitches of sound vibrate the basilar membrane in different places.

Answer 19

Slow vibrations:
if the movement of the oval window is slow, the pressure waves in the cochlear travel all the way along the canal, vibrate and transmit through the BM at the end and then come back down the second canal to displace the round window.

Fast vibrations:
the pressure waves only travel partly along on the canal, and then short cut over the BM and back to the round window, creating vibrations which are faster.

This occurs because the BM varies in stiffness along its length, therefore different frequency’s affect it at different places. TONALTOPIC

Question 20

How many:

a) hair cells are in the inner ear in humans?
b) synapse with sensory neurones are there in humans?
c) motile outer hair cells in humans?

Answer 20

a) Transduction by inner hair cells: 3,500 in humans.
b) Synapse with sensory neurons (long axons, & send spikes to brain). 40,000 in humans.
c) In addition to inner hair cells, mammals have motile outer hair cells: 12,500 in humans