Sensory Mechanisms and Neuron Synapses Flashcards
What are sensations
- are triggered by sensory stimuli
- travel to brain as action potentials (APs) via sensory pathways
- awareness of sensory stimuli
What are three problems with sensory mechanisms that the body must overcome
Conversion of stimulus energy into a neuronal signal
Encoding information about stimulus
Interpretation of information
What are the three parts of information processing
- Information processing
- sensory input
- external and internal information from sensory receptors
- Integration
- interpretation of input
- association of input with responses
- Motor output
- signals from integration centre(s) to effector cells
- sensory input
What do you call neurons that travel to / from the CNS
- Afferent neurons: from periphery to the central nervous system (CNS)
- efferent neurons: from CNS to the periphery
What is the solution to the problem of converting stimulus energy into a neuronal signal
Problem: conversion of stimulus energy into a neuronal signal
Solution: Transduction
Stimulus → sensory receptors → change in receptor membrane permeability → receptor potential (graded change in membrane potential)
Amplification (e.g. by activation of a cascade) and sensory adaptation (continued stimulation → lowers responsiveness)
Transmission:
If receptor = sensory neuron: it conducts APs to CNS
if receptor ≠ sensory neuron: sensory neuron generates APs
how does chemoreception work
Sugar molecule activates sweet receptor → G protein → Phospholipase C → PIP2 → IP3 (second messenger) → IP3-dated calcium channel → sodium channel → sodium is taken in
Perceptions of taste and smell are usually interrelated
what are the two ways a receptor can exist
A receptor can be an afferent neuron, or it can regulate an afferent neuron through neurotransmitter release in the receptor cell to the afferent neuron
What are the four solutions to the problem of Encoding information about stimulus
Problem: Encoding information about stimulus
Solution: Type of stimulus
Type of activated receptor
Solution: Intensity
Number of activated receptors
Frequency of action potentials
Solution: Location
location of activated receptors
timing of receptor activation (for sound and smell)
Solution: duration
Patter of action potentials
what are the receptor types
- chemoreceptors
- mechanoreceptors
- thermoreceptors
- nociceptors
- electromagnetic receptors
what are the solutions to the problem of interpretation of information
Problem: Interpretation of information
Solution: Process and integrate sensory information, starting in the sensory pathways and culminating in the brain
Solution: Hierarchical and parallel processing of information
Solution: different parts of the brain process different perceptions
Solution: incorporation of information from different modalities in higher association centres
what is perception
- ability to discriminate various aspects of the stimulus
- meaningful interpretation of sensory data
what did Luigi Galvani say/do
Luigi Galvani (~1750): The role of electricity in nerves was first observed in dissected frog muscle, led him to propose the theory of animal electricity.
What did Alessandro Volta think
Alessandro Volta: electrical current is generated by contact between different metals.
what did Alessandro Volta do
Dissimilar metals create electricity, which merely stimulates the frog muscle.
That animal tissue creates electricity is non-sense! (According to Alessandro Volta) (wrong)
led to creation of batteries.
what did the 1794 experiment reveal
The 1794 experiment: when the surface of sections of the nerve touches the muscle the leg contracts.
what did the 1797 experiment reveal
The 1797 experiment: when the surface of a section of the right sciatic nerve touches the intact surface of the left sciatic nerve, both legs contract
what did Galvani say
According to Galvani … in the animal, there is a particular machine capable of generating such disequilibrium, and it will be convenient to refer to this form of electricity as to animal electricity
what did Carlo Matteucci do
Only 40 years after Galvani did Carlo Matteucci, a physicist at Pisa ~ convincingly demonstrated the existence of animal electricity using a ‘galvanometer’
what is membrane potential
Every cell has voltage (difference in electrical charge) across its plasma membrane called a membrane potential
what is resting potential
The resting potential is the membrane potential of a neuron not sending signals
what is an action potential
Changes in membrane potential is used for transmitting information across large distances
This brief, all or none signal is called the action potential
what is the state at resting potential
- K+ selective ion channels are the main (but not only) channels that are open at rest
- Neurons maintain a certain concentration gradient across their membranes which is different for each ion. E.g. KCl is higher inside and lower outside
- K+ diffuses out, down its concentration gradient
- Negative charges (Cl-) builds up along the inner membrane creating an opposing electrical force
- At equilibrium, both electrical and chemical forces are balanced (Equilibrium potential)
How does Na+/K+ ATPase maintain the Na+/k+ gradients
- Pumps 3 Na+ out, 2 K+ in per 1 ATP
- Energy use: ~20-30% of body’s resting energy
- Brain demand: ~60% of neuronal ATP
- Discovery: Jens Skou (1957, Nobel Prize 1997) in crab nerves
- Maintains resting potential. Essential for nerves, muscles, heart
- Drug target: Digoxin (heart medication) blocks it and Oubain (a plant that makes arrow poison in Somalia) targets it
What is the Nernst Equation what what does it tell us
Ex(mV)=RT/zF *ln([x]out/[x]in)=61.5log([x]out/[x]in)/z
At T = 37ºC you can reduce RT/F to 61.5 mV when converting ln to log form; still need to account for z (valence)
Given: [K+]in = 120 mM, [K+]out = 4.5 mM
Ek=61.5log(4.5/120)=61.5log(0.0375)=-88mV
Typical resting membrane potential for neurons ~ -80mV to -65 mV
