Hearing, Chemical senses and touch Flashcards
What is another name for smell?
Olfaction
In what way is smell similar across species?
- Olfactory sensory neurons project endings through glomeruli
- Projections through mitral cells (mammals)/ Projection neurons (insects) to
- Higher order brain systems (cortex in mammals)
How does smell work in the human system?
- Olfactory epithelium is in the top of nasal cavity
- Odours come up into the nose to the olfactory bulb regions
- We find the endings of olfactory receptor neurons in olfactory bulb regions
- Our cilia project out onto air space in which the olfactory receptor neurons have their receptors, which are activated by different odorants.
- reception of odours causes change to action potential activity in the O RN (c-olfactory receptor) neurons
- neurons will then project into glomeruli within the olfactory bulb and each glomerulus has input from similar types of neurons. So there is convergence of information in glomeruli.
What type of receptors are human olfactory receptors?
GPCRs
What does odorant binding lead to?
opening of a cyclic nucleotide-gated channel and depolarisation of olfactory receptor neurons.
Which pathway does odorant binding activate?
cAMP pathway
How does the odorant binding lead to depolarisation?
- Odorant receptor causes activation of a g-protein, GTP is turned into GDP this causes activation of adenylate cyclase that causes ATP to be broken down to cAMP and cyclic GMP opens sodium channels causing depolarisation.
- When cyclic nucleotide gated channels open they allow is calcium ions. This influx of calcium in turn activates calcium activated chloride channels. Chloride ions then leave the cell leading to increased depolarisation
What does it mean that smell has combinatorial coding?
- Odorants have diverse chemical structure, and we cannot really predict how something smells based on the structure of the molecule
- Each odorant binds to various receptors and activates many neurons, and in turn each neuron is activated by many odorants – combinatorial code
In which direction is information flow in both olfaction and vision?
From top to bottom
What additional olfactory organ do most vertebrates have and what is it’s function?
In addition to their nose, most vertebrates have an additional olfactory organ – the vomeronasal organ located in the nasal cavity, just above the roof of the mouth, and its function appears to be to respond to non-volatile chemical cues in the environment.
What type of signals does the vomeronasal organ respond to?
responds to a wide range of signals. Some will provide information about prey, but others will give the animal information about the status of members of the same species
What are intraspecies signals called?
pheromones
Why do pheromones have the potential to produce profound changes in the behaviour of an animal?
- the signalling pathway that the VNO uses, sends signals to the hypothalamus, which is a major neuroendocrine centre
- The hypothalamus influences the reproductive system and the production of adrenal steroids
What do we detect sound as?
Variations in air pressure
What are normal hearing ranges for humans?
20 Hz to 20, 000 Hz
What does it mean if a sound has lower frequency and lower intensity waves?
- Lower frequency waves = lower pitch
* lower intensity = quieter
What is the auditory system made up of?
- External ear
- Middle ear (bones: malleus, incus, stapes)
- Inner ear (cochlea)
What is the vestibular system made up of?
- Semi-circular canals (posterior, horizontal, anterior)
2. Otolith organs (utricle, saccule)
What is the cochlea and how is it involved with hearing?
- Spiral structure full of fluid
- Sound waves set up through movement of basement membrane: tensor tympani (muscle)
- Movement of Hair cells transduce sound into electrical signals. Outer hair cells provide active amplification, inner hair cells send signal to brain
What are the bones of the middle ear?
- Incus
- Malleus
- Stapes
How do the hair cells of the ear work?
- Have cilia on the hair cells which are permeable to potassium, mechanosensitive (when they are moved they are subject to stress and this opens channels) potassium channel
- Potassium enters cells and causes depolarisation
What is the tonotopy of the cochlea?
- Frequency of response of hair cells arranged in ordered manner
- High frequency sounds being perceived closer to the base of tonotopy
- Alike inputs come together
- Spiral ganglion
What is sound localisation in space?
Position of sound source is detected by comparing the time of the sound arrival to both ears (interaural time difference)
What is the vestibular system?
The balance system
What is the vestibular system made up of?
- Two organs:
otolith organs Saccule and Utricle which are involved with acceleration
Semi-circular canals detect head rotation and balance
What do we have inside the organs of the vestibular system?
hair cells which are held between the cell bodies
What do Otolith organs do?
- Otolith organs use calcium carbonate (CaCO3) crystals to detect force of gravity and acceleration
- As fluid moves in semi-circular canals the crystals move, this bends hair cells, potassium channels open
What contains mechanosensation cells?
The dermis and epidermis
What are different types of mechanosensation cells?
- Merkel cells
- Ruffini ending
- Meissner corpuscle
- Pacinian corpuscle
- Free nerve endings
When do all the mechanosensation cells respond and what do the endings allow you to dictate?
- They all respond at different times of stimulus
- The endings allow you to dictate strong, sharp, dull sustained types of pressure on your skin
What do you do to measure Piezo in Merkel cells (touch)
- Record intracellularly using a patch electrode
- Have a stimulus probe which you cause to deform membrane of cell
- See a whole cell inward current as sodium comes into cell due to mechanosensitive excitation of channels
Using physiology and genetics what can we identify with mechanosensation cells?
What sort of channels are present in what type of cells
What does the somatosensory cortex make sense of?
all the different inputs from the sensory areas
