Physiology 3120 Lecture 3: Neuro1
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr. Pruszynski
Lecture 3
Transduction of Environmental Information
Getting the outside world into the brain
- How does info about the outside world get into the nervous system?
- You see a cup and you perceive it to be there
- But you don’t have a direct access to what is in the outside world you
only have access to what is sent through our nervous system
What does the brain see?
- The inside of the nervous system is dark
- There is nothing in there that directly represents the cup, the only thing we have are the AP
- There are photons that hit your retina (back of eye), then the only thing
left is the pattern of AP, patterns of electrical activity in our brain
- Then your nervous system needs figure out how these spikes relate to
the outside world
- How the photons turn into the spikes? (input) (encoding)
- How do the spikes get recoded into the cup? (output) (decoding)
Basic Concepts
- you need to turn the diff energies in the outside world into AP
- you can do this in various modalities
o photons – light energy
o mechanical energy – something touches skin, waves that hit ear etc
o chemical energy – chemical processes within tissue that might release to give you senses
of pain, itch etc
- all the way out in periphery, there is a sensory receptor
- Sensory receptor: a specialized ending in a nerve cell that is sensitive (aka tuned) to one form of
environmental energy
- Adequate stimulus: form of energy that receptor is most sensitive to
o rods in eye are sensitive to pressure in eye so punch to eye can be perceived as flash of
light.
o Auditory system you have hair cells in cochlea
▪ Sound wave (energies) hit the hairs and the motion of the hairs is turned into
spikes
o In somatosensory system you have diff receptors in skin, muscles or free nerve endings
(unspecialized – used in general sensations of pain
- Transduction: how the energy is turned into spikes
- sensory receptors are a specialized kind of ending at the interface bw inside and outside world
of nervous system and is able to transduce kinds of environmental energy
- we usually talk about one kinds of energy bc we are talking within the domain of that receptors
adequate stimulus
find more resources at oneclass.com
find more resources at oneclass.com
- adequate stimulus:
o form of energy that the receptor is most sensitive to
o bc these receptors are usually sensitive to various things
▪ ex: rods in eye also have mechanically sensitive ion channels so that if you push
the eye (punched in eye) you will perceive light
▪ it doesn’t give you a sensation of pressure bc the CNS has learned that from
these kinds of receptors comes visual inputs
- transduction is conserved within all the modalities
Transduction Mechanisms
- Mechanical (skin, muscles, tendons, etc.)
o Dominates your sense of touch, proprioception, general inputs from somatosensory
system, auditory system, vestibular system (sense of position in space)
o Physical forces stretch open ion channels
o Works in domain of auditory system (hair cells moving), vestibular system
- Temperature
o Hot and cold act on specific receptors to open ion channels in PNS (skin)
- Chemical (nociceptors)
o Tissue damage locally releases chemicals that bind to receptors and open chemically
gated ion channels
o This is how you get sensations of pain, itch etc.
- Light
o Photon absorption by rods and cones closes ion channel
- Mechanical, temperatures, chemical OPEN ion channels but light CLOSES ion channels
Generator/receptor Potentials
- Cause depolarization due to increased permeability to Na+/K+ (like EPSP)
- Local and non-propagated, graded in proportion to the stimulus
- Can sum and will cause action potential if neuron reaches threshold.
- This is a Pacinian receptor
- At the periphery of the nervous system (interface with outside world) there is no other neuron
there
- Its not like the normal situation where you have an excitatory or inhibitory synapse from one
neuron causing the neuron next to it to hyperpolarize or depolarize – there is nothing there, just
the interface bw the inside and outside world
- There you usually get this specialized ending
- This is similar to EPSP
o Pressure is applied to skin
o This deforms the specialized receptor
o Inside the specialized receptor is a neuron
o This neuron has mechanically sensitive ion channels in middle of receptor
o This means that pressure on skin rips open ion channels, allowing Na+ to flow it (it
literally pulls the channels open)
o This is called generator/receptor potentials (not actually EPSP)
o The more pressure/deformation that happens, the more ion channels are pulled open
and the more the ending is depolarized
o SO, the more environmental energy given to the neuron, the more it is depolarized
- Somewhere near the first node of Ranvier, you have VG Na+ channels that are stimulated to
create AP (they turn graded potentials into AP)
- If you have enough pressure, you cause the neuron to reach its threshold and at the spot you
have VG Na+ channels you will cause an AP
- Now, you have info in nervous system that is related to the amount of pressure impinged on that
particular receptor
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
You see a cup and you perceive it to be there. But you don"t have a direct access to what is in the outside world you only have access to what is sent through our nervous system. The inside of the nervous system is dark. There is nothing in there that directly represents the cup, the only thing we have are the ap. There are photons that hit your retina (back of eye), then the only thing left is the pattern of ap, patterns of electrical activity in our brain. Then your nervous system needs figure out how these spikes relate to the outside world. How the photons turn into the spikes? (input) (encoding) How do the spikes get recoded into the cup? (output) (decoding) Sensory receptor: a specialized ending in a nerve cell that is sensitive (aka tuned) to one form of environmental energy of pain, itch etc.
