Chapter 2: Basic Principles of Sensory Physiology Flashcards
What are the three main components of a neuron and their function?
Cell body: contains the mechanisms to keep the cell alive
Dendrites: branches that receive electrical signals and through neurotransmitters from other cells
Axons: fibers that are filled with fluid to conduct electrical signals. These are covered in a myelin sheath (produced by schwann cells) to improve conductivity. Gaps between the myelin are called nodes of Ranvier
What is a neuron’s charge at rest? During an Action Potential?
Resting Potential: -70mV
Action Potential: +40mV
What are the basic properties of an action potential?
- They last approx. 1 millisecond
- They are propagated response, they stay the same “size” (charge) as they travel down the axon.
- They travel down the down the axon, jumping between the node’s of Ranvier
- All action potentials are the same “size” regardless of the strength of the stimuli that triggered them. The NUMBER of action potentials triggered by a stimulus reflects it’s strength.
What is the chemical basis inside and out of neurons that allow for action potentials. What chemical changes occur to trigger the action potential?
Neurons sit a in liquid solution that is rich in ions.
- the outside solution is rich with na+ (sodium)
- the inside solution is rich with k+ (potassium).
- There are also Cl- (chlorine) ions.
- Overall the charge of the solution inside the solution is -70mV. The selective permeability of the membrane maintains this resting potential. When the permeability of the membrane changes, the ions move differently, changing the cells charge.
When a stimulus occurs, sodium ion channels open and allow na+ into the cell. Because they are concentrated outside, the sodium rushes into the cell depolarizing it from -70mV to +40mV. (rising phase of an action potential)
When the cell reaches +40mV, (and triggers an action potential), the sodium ion channels close and the K+ leaves the cell to transition back to -70mV (falling phase of an action potential)
How do neurons communicate between cells?
Synaptic vesicles at the axon terminals release neurotransmitters into the synapse (the gab between the axons of one cell and the dendrite of the other). When the neurotransmitter flows across the synapse, they bind to receptor sites on the dendritic spines.
When neurotransmitters bind to receptors, they can trigger one of two responses:
- Exicitatory response (depolarizes the cell, makes it LESS negative, brings it closer to an Action Potential)
- Inhibitory response (hyperpolarizes the cell, makes it more negative and brings it further from an action potential.
What is sensory coding? What are the three different types of coding?
Sensory Coding: How neurons represent various characteristics of the environment at a neural level.
Three different proposed types of coding
1. Specificity coding: a neuron is specialized to only respond to a single stimulus (e.g. we have a cat neuron, an orange neuron, a spruce tree neuron etc.) Today this idea is largely rejected.
- Sparse Coding: a particular stimulus is represented by a pattern of firing of only a small group of neurons with the majority of other neurons remaining silent. Odor identification seems to work this way.
- Population Coding: our experiences are represented by a pattern of firing across a large number of neurons.
- Population coding is a strong theory because a larger number of stimuli are able to represented. Why? large groups of neurons can create more combinations of patterns than smaller groups of neurons.
What is the difference between modularity and distributed representation?
modularity is the idea that specific brain areas are specialized to respond to specific types of stimuli (e.g. Broca’s Area, Wernicke’s Area, Fusiform Area.
Distributed Representation: the idea that the brain represents information in patterns distributed across the cortex. Came from the realization in the late 1900’s that areas of the brain are not as modular as we thought, they actually communicate quite extensively.
What are two approaches to understanding connectivity in the brain? How are these approaches related?
Structural Connectivity: the road map of fibres which connect the areas of the brain.
Functional Connectivity: neural activity associated with a particular function.
Functional connectivity flows through the structural network. Areas that are functionally connected can be structurally connected but also can be not.
What is the refractory period?
A period of 1ms where the cell is unable to produce an Action potential, occurs right after an action potential has occurred. The refractory period “limits” the cell to a ~600-800 Action potentials per second.
What is spontaneous activity?
Spontaneous activity is when an action potential occurs without a preceding stimulus.
