~Chapter 2 - Lectures Flashcards
What are Dendrites?
Dendrites are the receiving part of the neuron. Incoming signals arrive here. Dendrites gather inputs
What does the cell body do?
The Cell Body (Soma) provides life support for the cell/neuron
What does the Axon do?
Axons transmit signals from one location to another.
What do the Terminal Boutons do?
The Terminal Boutons pass signals from one neuron to the next in the chain of info processing.
What signals do Neurons process and transmit?
The Bioelectric Signal
What is the Resting Potential of a neuron/cell?
The Resting Potential of a neuron/cell is about -70mV
What does it mean when a cell is at its Resting Potential?
When the cell/neuron is not stimulated or involved in passage of an impulse. This is when the neuron is just sitting there not doing anything
How do Neurons derive their electrical properties?
By separating ions
When a cell is in a resting state, where is most Na+?
Outside
When a cell is in a resting state, where is most K+?
Inside
How is separation of ions maintained?
By ATP-driven ion pumps or exchange mechanisms (e.g. Na+/K+ ATPase).
What does it mean if the cell is Polarized?
It means the cell is at rest, there is a separation of ion types, like the North and South poles.
What does Hyperpolarization mean?
Hyperpolarization is a change in a cell’s membrane potential that makes it more negative, it becomes even more polarized. (Example: -70mV → -90mV)
What does Depolarization mean?
Depolarization is a change in a cell’s membrane potential that makes it less negative, it becomes less polarized. (Example: -70mV → -20mV)
What are action potentials?
Action potentials are the way neurons/cells communicate with each other.
-AKA – spikes, nerve impulses
How do action potentials propagate?
Action potentials propagate when the axon becomes selectively permeable to ions
What are the steps of an action potential?
Sodium flows in → produces depolarization to about +40mV → Potassium flows out → re polarization/hyperpolarize → Returning back to its regular levels
What Causes Selective Permeability?
Ion channels
What are ion channels?
Little tunnels in the membrane that let only 1 type of ion pass through
How do neurons “talk” to each other?
Neurons talk to each other through synaptic transmission
Where does the sending neuron release chemical neurotransmitter from?
The sending neuron releases chemical neurotransmitter from its terminal boutons/synaptic boutons.
What is the synapse?
The synapse is the tiny gap between the two neurons,
What do neurotransmitters bind to after passing through the synapse?
Neurotransmitters will bind to receptors on the receiving neuron’s dendrites and cell body.
What are the two types of Neurotransmitters?
Excitatory and Inhibitory
What are two types of Excitatory Neurotransmitters?
Acetylcholine & Glutamate
What does an Excitatory Neurotransmitter do?
Causes a cell to become less negatively charged when these bind to their receptors, it produces Depolarization.
What do Excitatory Post-Synaptic Potentials (EPSP) do?
EPSPs increase the likelihood that the neuron will fire an action potential
What increases the likelihood that the neuron will fire an action potential?
Excitatory Post-Synaptic Potentials (EPSP)
What is a type of Inhibitory Neurotransmitter?
GABA
What does an Inhibitory Neurotransmitter do?
Causes a Cell to become more negatively charged (Hyperpolarization)
What do Inhibitory Post-Synaptic Potentials (IPSP) do?
IPSPs decrease the likelihood that the neuron will fire an action potential
What decreases the likelihood that the neuron will fire an action potential?
Inhibitory Post-Synaptic Potentials (IPSP)
What happens if the summated inputs are greater than the threshold of the cell at the axon hillock?
An action potential is produced.
How does a neuron handle all the inputs from its many dendrite and receptor sites?
All of the inputs that are coming into a neuron are summed together.
What Post-Synaptic Potential tries to make the cell spike?
EPSP’s pool together to try to make the cell spike
What Post-Synaptic Potential tries to stop the cell from spiking?
IPSP’s pool together to stop the cell from spiking
How do neurons make calculations on incoming signals?
Summation of signals
Can EPSP’s and IPSP’s be combined?
Yes. Neurons can sum different signals and weight them over their inputs and over time, and combine EPSPs and IPSPs. So they’re performing calculations before they send an output down to another area of the brain.
What does an Action Potential being Non-Attenuating mean?
The Action potential remains the same size as it propagates from the cell body to the terminal boutons.
- This is why you can have very long axons.
- Example: You can have motor neurons leaving your spinal cord, going all the way down your leg, allowing you to wiggle your toes.
What is All-or-None Rate Coding?
The Action potential remains the same size no matter how intense the input. Instead of creating bigger action potentials, the neuron creates more action potentials for stronger stimuli.
What is the Refractory Period?
The period where the neuron cannot fire one action potential after it has just fired an action potential. The minimum time period after one action potential fires before the next one can fire
How long is a refractory period?
A refractory period is typically about 1 millisecond
What is a typical neuron firing rate?
100 spikes/second
What is the upper limit on a neurons firing rate?
500-800 spikes/second
What is Spontaneous Activity?
Many neurons fire action potentials at a low rate even when there is no input. This occurs in most neurons
What is Spontaneous Firing?
The period before and after a stimulus is presented, the neuron is still firing action potentials, this is called spontaneous firing.
- Spontaneous firing allows the neuron to signal both increases and decreases in activity.
- Generally, this is the way that neurons, especially in the cortex, will act.
What is light?
Light can be described as both a particle (known as a photon) and a wave
What is the distance of a Wavelength of a light?
The Wavelength of a light is the distance of one complete cycle of the wave.
Can humans see all wavelengths of light?
No. Humans can only see a certain wavelength of light that we call Visible Light
What are the wavelengths of Visible Light?
Visible light has wavelengths from about 400nm (blue-ish light) to 700nm (red-ish light). Wavelengths longer and shorter than this are invisible to us.
How is wavelength related to the ability to view colour?
Wavelength of light is related to its perceived color.
What is the Electromagnetic Spectrum?
The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies
What kinds of things have shorter wavelengths than Visible Light?
Gamma Rays, X-Rays, and Ultra-Violet Rays
What kinds of things have longer wavelengths than Visible Light?
Infrared Rays, Radar, Broadcast Bands, and AC Circuits
How does white react to light/photons?
White absorbs little light, reflects all wavelengths of light equally, and reflects much of the light.
How does black react to light/photons?
Absorbs much light, about equally across wavelength. Reflects little to none of the light.
How does green react to light/photons?
Reflects green light (reflects medium wavelength more than short or long wavelengths)
How do coloured objects react to light/photons?
Coloured objects selectively reflect different wavelengths more than others
Why is the eye compared to a camera?
The eye works like a camera, using a lens to focus light onto a photo-sensitive surface at the back of a sealed structure
What are the optics at the front of the eye?
The Cornea and Lens
What focuses objects in the environment onto the retina?
The optics of the eye
What is Accomodation?
When the eye changes its optical properties. The lens becomes fatter, which then bends the light more, which allows the retinal image to come into focus right at the retina. It brings the focal point from behind the eye to right on the retina.
What optic of the eye provides the most focusing power?
The Cornea (80%)
What provides 80% of the eye’s focusing power?
The Cornea
Can the Cornea change shape?
No
What does the Lens do?
The Lens Provides ~20% of the focusing power. The Lens can change shape which then changes the focusing power.
What does it mean when the Lens is thin?
Less light bending/less refraction (for focusing on far objects)
What does it mean when the Lens is fat
More light-bending (for focusing on near objects).
What is the shape of the Lens controlled by?
The Ciliary muscles, a ring-shaped sphincter muscle
What happens when the Ciliary muscle is relaxed?
When the Ciliary muscle is relaxed, it creates a circle that has a large circumference. This creates a lot of tension on the zonule fibres, and it pulls the lens into a flattened thin shape.
Contracted Ciliary muscles = ?
Fat Lens
What happens during Accommodation?
During accommodation, the ciliary muscle contracts, and the sphincter muscle becomes a circle of a smaller circumference, which makes the zonule fibers slack, which then allows the lens to bunch up into a thick round shape.
What is Presbyopia?
The Ciliary muscles can only contract so far, and the Near-point moves farther away, as the Lens gets harder with age