Chapter 2 Flashcards
Neurons
Structures through which/where ELECTRICAL SIGNALS occur; a SPECIALIZED CELL transmitting nerve impulses
Components of a neuron
CELL BODY: Contains mechanisms to keep the cell alive
DENDRITES: Branch out from the CELL BODY to RECEIVE electrical signals from other neurons
AXON/NERVE FIBER: Component filled with a fluid that CONDUCTS ELECTRICAL SIGNALS (some neurons have long axons, others short axons, and yet others no axons at all)
Sensory Receptors
Neurons specialized to respond to environmental stimuli (receptors for touch, sound, smell, taste, etc.)
Resting Potential
Voltage value of a neuron when the AXON is at REST, in which the difference in the INSIDE OF THE AXON is 70mV MORE NEGATIVE THAN THE OUTSIDE (or -70mV)
Action Potential
Signal identified by the predictable rise and fall of the charge INSIDE THE AXON OF A NEURON (relative to the outside) and that lasts about 1 millisecond → neurons “FIRING”=NEURONS HAVING ACTION POTENTIALS
When the neuron’s receptor is stimulated, the signal is transmitted DOWN THE AXON, causing the CHARGE INSIDE THE FIBER to MOMENTARILY RISE TO +40mV COMPARED TO THE OUTSIDE, and then reverses BACK to -70mV as it returns to rest
What are the basic properties of Action Potentials? (Just list)
- Passed on by PROPAGATED RESPONSE
- Constant size and intensity regardless
of the size of the stimulus - Are followed by a REFRACTORY PERIOD
- Can happen spontaneously
(SPONTANEOUS ACTIVITY)
Propagated Response
Once the action potential (response to stimulation) is triggered, it travels all the way down the axon WITHOUT DECREASING IN SIZE, and triggering propagated reactions, like dominoes that topple over each other
Propagated response it what enables neurons to transmit signals over long distances
Refractory Period
The interval between the time ONE nerve impulse occurs and when the NEXT ONE can be generated
Refractory period of most neurons is 1 millisecond
Upper limit of a neuron’s firing rate is about 500-800 impulses per second
Spontaneous Activity
Action potentials that occur in the ABSENCE OF STIMULI from the environment
Spontaneous activity establishes a baseline level of firing for the neuron, so the presence of actual stimulation usually causes an INCREASE IN ACTIVITY ABOVE THE SPONTANEOUS BASELINE LEVEL
Transmission of Action Potentials Across Synapse (Steps)
When the action potential reaches the presynaptic terminal, it is converted from an electrical signal into a chemical signal.
1. The action potential causes Ca2+ to enter the presynaptic terminal.
2. Ca2+ causes vesicles loaded with neurotransmitters to fuse with the presynaptic membrane.
3. Neurotransmitters in the vesicles are released into the synaptic cleft. There,
4. Neurotransmitters diffuse in the synapse and eventually bind to receptors that swim in the membrane of the postsynaptic cell
5. Binding with a neurotransmitter can cause a specific action of the receptor. Some receptors can form channels that allow electrically charged molecules (ions) to enter the postsynaptic terminal. Now the chemical signal has been converted back into an electrical signal.
6. Consequent influx of electrically charged molecules can cause a depolarisation of the postsynaptic neuron, which can then lead to the neuron firing another action potential. Some neurotransmitters can have the opposite outcome, they are inhibitory, not excitatory.
Synapse
The small space/area BETWEEN NEURONS (neurons never touch)
Neurotransmitters
Small molecules stored in SYNAPTIC VESICLES in the TERMINAL BUTTONS of a neuron (presynaptic terminal) responsible for transmitting neural signals
Synaptic Vesicles
Small spheres or containers in the terminal button which FUSE with the membrane to release neurotransmitters into the synapse
Receptor Sites
Small areas/proteins that are SENSITIVE to SPECIFIC NEUROTRANSMITTERS, and that when BOUND TO ITS MATCHING NEUROTRANSMITTER, TRIGGER A VOLTAGE CHANGE IN THE RECEIVING NEURON
Excitatory Neurotransmitter
A neurotransmitter that INCREASES the chance of an action potential occurring because it DEPOLARIZES the neuron, making it MORE LIKELY to fire
Inhibitory Neurotransmitter
Neurotransmitter that decreases the chance of an action potential occurring because it HYPERPOLARIZES the neuron, making it LESS LIKELY to fire
How do researchers record signals in neurons?
Electrical signals are recorded from the axons of neurons, using small electrodes to pick up the signals
Sensory Coding
Information processing that occurs in the CNS, where sensory code refers to HOW neurons represent various characteristics of the environment (sight, taste, etc.)
What is the term used to refer to the “problem of neural representation” and why is it a problem?
The “Problem of Sensory Coding”
Considered a problem because it is a highly complex process which took scientists a long time to understand
Specificity Coding
The notion of a “SPECIALIZED NEURON” that responds only to one concept or stimulus (like a “salt neuron” only firing when you eat something salty)
Idea dates back to the 1960’s with HEROME LETTVIN
Grandmother Cell
HIGHLY SPECIFIC NEURON hypothesized by Lettvin, which would respond ONLY TO YOUR GRANDMOTHER, from any angle, representation (photos, drawings) etc.
Part of Lettvin’s Specificity Coding hypothesis
What is an alternative to Specificity Coding? (In terms of how to understand perceptual experience)
The idea that a number of neurons are involved in representing perceptual experience, as opposed to a hyperspecific neuron
Sparse Coding
Process that occurs when stimulus is represented by a pattern of firing of ONLY A SMALL GROUP OF NEURONS, with the MAJORITY OF NEURONS remaining “silent”
There is evidence that the “code” for representing objects in the visual, auditory and olfactory system may involve PATTERN ACTIVITY across a relatively small number of neurons, as sparse coding suggest
Population Coding
Proposes that our experiences are represented by a pattern of firing across a LARGE NUMBER OF NEURONS
An advantage of population coding is that a LARGE NUMBER OF STIMULI can be represented because large groups of neurons can create a huge number of DIFFERENT PATTERNS
