Chapter 3 - Biology And Behaviour Flashcards
(29 cards)
What is Materialism? What is dualism? Which one is more strongly supported in this day and age?
Materialism: Behaviour and cognition are fully explained by the workings of the brain and the best of the nervous system, the mind controls the body and vice versa — they have a strong connection. The mind is the part of the physical world, and all mental phenomena are explained through physical processes — drugs act on biological processes to relieve physiological disorders. Consciousness comes from complex interactions in ten brain, and the mind IS NOT A SEPARATE SUBSTANCE BUT AN EMERGENT PROPERTY OF THE BRAIN’S PHYSICAL STRUCTURE.
Dualism: The mind and body are distinct entities. The less extreme version of this is that the mind is not completely reducible to the material body or brain, and is partly independent of the body. The mind functions in a way that cannot be fully explained through physical processes. This is slowly being phased out because neuroscience is coming up with more explanations for certain processes.
Materialism is much more supported due to the neuroscience research that is being done.
What was the two possible pathways from stimulus to perceptions based on these two theories? How have we transitioned from one to another? What things has neuroscience begun to explain? what is still left as a correlation and what belief does this support?
Stimulus —> perception (dualism)
Stimulus —> physiology —> perception (materialism)
At first we started with stimulus and perception having a correlation, but as more neuroscience was discovered physiological responses became an intermediate response. Neuroscience has explained a causation effect between the stimulus and the physiological response, and this has been contributing to materialism.
However, neuroscience has not yet explained the causation of physiology and perception, and this is leading to the dualism idea because we cannot find a causation relationship for this.
What advancements in neuroscience have begun to support materialism?
FMRI and EEG’s have allowed scientists to observe brain activity in real time, revealing correlations between specific mental states and neural patterns. But we can’t get causal relationships because we can’t manipulate people’s brains.
Brain diseases have provided further insight into the physical basis of mental functions.
What are the basic functional units of the nervous system and what are their support cells called? How much do the support cells outnumber neurons? How much brain volume do they take up and what do they do?
Neurons are the basic structural and functional units of the nervous system. Glial cells are the support cells for these neurons and they outnumber neurons 10 to 1, and make up 50% of the brain volume. They support, nourish neurons, and remove their wastes.
What are the 4 different types of neurons? What does each neuron usually do?
1: Unipolar neurons: These neurons have the cell body at one end, dendrites in the middle and the terminal bulbs at the end. These are found in some spinal and cranial nerves in vertebrates, but are mostly found in the CNS of invertebrates.
- Pseudo-unipolar: They appear bipolar but are still unipolar (still have one axon). So they have dendrites on one side and terminal bulbs on the other side, and the cell body is a branch off the middle. These are used for sensory neurons and are in spinal nerves and also connected to sensory receptors in extremities.
- Bipolar: These neuron has two distinct axons/processes. Dendrite on one end with no myelinated sheath, and the axon and terminal bulbs on the other end. The cell body separates these. These are found in the rod and cone cells of the retina olfactory system, and are mostly interneuron cells.
- Multipolar: This is where the cell body has dendrites coming off of it, and then the axon extends from the other end. This is for motor nerves, and the majority of neurons in the CNS and PNS.
What is the direction of a neuronal impulse coming from the stimulus? What types of neurons does it go through?
What is an afferent and efferent neuron? In a simple circuit, which is which?
Are interneurons myelinated?
First it goes to the dendrites of the sensory neurons does, which is a pseudo-unipolar cell. Then it attaches to the cell body of a multipolar or bipolar interneuron. This then connects to a multipolar neuron cells which is a motor neuron, and in the synapses it releases ACh which causes a motor response.
Afferent neuron = the neuron going into something
Efferent neuron = neuron coming out
Interneurons are not usually myelinated because they integrate the information they don’t want quick transfer of signals.
In a simple circuit, the afferent neuron is the sensory / receptor neuron, and the efferent neuron is the motor neuron or effector.
How does a signal pass through a neuron? Name the structures in the order they are passed through.
First it goes into the dendrites which receive a signal from neurotransmitters. Then it does to the axon where it bounces from node to fancier to node of ranvier zooming through the myelinated sheath. Then it reaches the terminal buttons which causes voltage gated Ca2+ channels to open, which releases synaptic vesicles which release neurotransmitters into the synapse. This passes the signal onto the next neuron.
What is the myelin sheath made of and what does it do? What does a degeneration of it lead to?
The myelin sheath is made up of thin Schwann cells that wrap around the axon and support and insulate that axon to speed up signal transmission. It does this by allowing sodium channels to only open at the gaps rather then all the way down the axon, and so the change in potential can travel down the axon in that way. This is mostly found in peripheral neurons, as the CNS integrates information and therefore does not need to speed up transmission.
A degeneration of the myelin sheath will lead to MS, loss of muscle control, weakness and paralysis, vision difficulties, etc. This is just because the signals do not transmit as quickly or efficiently as they should which results in these difficulties.
How does an axon end? How does the signal get transferred to the next neuron if they don’t touch?
The axon ends in branches of terminal buttons, which contain synaptic vesicles that hold neurotransmitters,m which are chemical messengers. When a signal reaches a terminal bulb, it opens voltage gated calcium channels, and calcium binds with the synaptic vesicles and causes them to merge with the pre synaptic neurons membrane and release via exocytosis. These neurotransmitters then move through the membrane and merge with receptors on the post synaptic neuron to activate the opening of sodium channels and lead to that signal being passed on to the next neuron.
What is the voltage of the inside of a neuron in resting state? What causes this potential and why is it kept at this charge?
At resting state, a neuron is at -70mV inside the cell, because this potential has to be maintained in order to create an action potential naturally when the potential is disrupted. This potential is created by the sodium potassium pump which brings out 3 Na+ and brings in 2K+, making a larger positive charge ratio on the outside. There are also some negatively charged ions (chlorine) and proteins which cause the inside to be negative.
When signals are created in the dendrites via neurotransmitters, how and when does that signal propagate down the neuron? What is summation and where does this occur in the multi-polar neuron? What is threshold and what does surpassing it do? Does the amount by which you initially pass threshold determine the strength of the response?
when signals are created in the dendrites via neurotransmitters, it can either open up sodium channels which increases the voltage inside the neuron, depolarizing it. Or it can open up channels that let in negative charge and hence hyper polarizes the neuron.
Depolarization makes it easier to stimulate the neuron because less charge has to be changed to reach threshold.
When it’s hyper polarized it requires more stimulation than normal and this would be an inhibitory signal.
Summation occurs at the axon hillock in multipolar neurons, and is the addition of all inhibitory and excitatory signals. Whatever the net result is will determine if an action potential is produced or not. If the voltage increases by 15mV (bringing it to -55mV total), then an action potential will occur because this will cause voltage gated sodium channels to open and the signal to propagate down the neuron.
If you initially increase the charge to -40mV, it WILL NOT create a larger response then -55mV would. For both, as soon as that threshold is reached all sodium channels in the area will open, and this will create an equal strength signal.
The only way you can increase the strength of a signal is to increase the frequency of stimulation. As soon as the refractory period is over you have to stimulate again, and this will produce a stronger response.
This is all due to the ALL OR NONE RESPONSE that the neurons follow.
Describe each step of an action potential, including the difference between the absolute and relative refractory periods. How long is the absolute refractory period? Also describe how it occurs as it moves down the neuron.
- Neurotransmitters stimulate the opening or inhibiting of sodium channels, and based on the summation of all signals coming from all dendrites, if the overall neuron reaches -55mV, then an action potential will occur.
- If it reaches this charge, then voltage gates sodium channels will open, allowing sodium in a depolarizing the neuron (bringing it back to neutral). At this point sodium-potassium pumps already start working to try to restore that gradient but this takes energy and is much slower then the natural flow of Na+ in. This will then flow to the right as the charge tries to diffuse, opening more voltage gated sodium channels and allowing more sodium in. Then it will reach the myelin sheath and will speed through those sections until it can slow down at a node of Ranvier again. This will keep occurring until it reaches the end of the axon. And due to the depolarization and absolute refractory period that occurs, the signal will only propagate in one direction down the axon, since there is already sodium in the opposite direction. The sodium channels will close when they reach their own potential of +35mV.
- Once sodium streams in, voltage gated potassium channels will open and potassium will leave the cell, trying to bring the neuron back to neutral and then -70 again, through REPOLARIZATION. This is where the pump really starts being active, moving sodium back out and potassium back in.
The period is the absolute refractory period, because ions are on the wrong sides and the inside is positive so no new signal can occur. The sodium channels are essentially deactivated. This is why sodium doesn’t move backwards once it streams in: potassium has left and so its an excess of sodium to the left of the signal. - Potassium channels begin to close as it approaches -70mV, but are very slow and leaky so they will not close completely. This leads to hyper polarization where the cell foes to -90mV, as too much potassium has left. At this point, the pumps are working in overdrive and some sodium has come back in, and it is after hyperpolarization that the relative refractory period occurs because there are a few ions in the right place, its just that the cell requires more stimulus for a response to occur. And so this leads to some signals if strong enough to occur.
*THESE ACTION POTENTIALS ONLY OCCUR IN THE NODES OF RANVIER!
- Eventually once both channels close the pumps can catch up and bring sodium out and potassium back in, creating resting potential. This requires energy.
The absolute refractory period lasts about 1 to 2 ms and is due to repolarization (potassium is leading the cell and sodium is already in so no action potential can occur).
Relative refractory is during and after hyperpolarization, while the pumps work to restore resting potential.
What is the all or none law, and how does the thickness of the axon effect signal strength? How can we increase intensity of a signal?
The all or none law is that as long as a membrane reaches -55mV, it doesn’t matter by how much it surpasses that voltage, it will produce the same strength action potential. Voltage gated sodium channels will open as soon as it reaches this net potential, and therefore anything larger will not change the strength of the signal.
The thicker the axon, the more sodium that can travel down it at once, allowing for quicker transmission and diffusion and hence a quicker signal.
For a stronger signal, the neuron needs to fire at a higher frequency, meaning action potentials must occur one after the other continuously.
What happens when the signal reaches a terminal button? (6 steps)
- Action potential will reach the button.
- Voltage gated Ca2+ channels open.
- Ca2+ enters the neuron
- Ca2+ binds to certain receptors on the synaptic vesicles, causing them to move to the membrane.
- Vesicles will dock to a protein on the membrane and then release their contents via exocytosis.
- The neurotransmitter will diffuse across the synaptic cleft and bind to receptors on the post synaptic neuron.
What are the 4 options for what can happen to a neurotransmitter when it reaches the synaptic cleft, and how can three of them cause termination of the chemicals?
- Reuptake: The neurotransmitters can be reuptaken by the presynaptic neuron into the terminal buttons.
- Enzyme deactivation: an enzyme destroys the neurotransmitter in the synapse.
- Auto reception: it binds with a receptor on the presynaptic neuron to monitor how much is present. The more that bind, the less synaptic vesicles the neuron will release.
These first three terminate the signal.
- The neurotransmitter can reach a receptor on the post synaptic neuron and initiate a response in that neuron.
What do excitatory transmitters do? What do inhibitory transmitters do?
Excitatory: Cause depolarization, making the membrane more positive so it is easier to stimulate and Na+ will open more willingly. Higher temporary resting potential.
Inhibitory: Cause hyper polarization so the neurons have a lower resting potential and more stimulus is required to reach threshold, and this decreases the likelihood of an action potential. This is where the the relative refractory period occurs.
What happens when a neurotransmitter and a receptor molecule combine? What is this called and what is its acronym?
When they combine, the reactions in the cell membrane will cause a post synaptic potential, which is a voltage change at the receptor site due to the opening of some channels.
These postsynaptic potentials (PSP’s) are graded, not all-or-none responses. It is the summation of many signals from the presynaptic neuron, and the net result will determine this voltage change and hence potential. the size and direction of a PSP (which is essentially what the summation at the axon hillock is) will increase or decrease the probability of a neural impulse in the receiving cell.
If the net summation of this post synaptic potentials is positive then it will be excitatory, and if it is negative then it will be inhibitory. This will determine how easy/hard it is for a change in potential to occur.
Excitatory: Positive voltage shift, so increases likelihood of a postsynaptic neuron firing action potentials.
Inhibitory: Negative voltage shift, decreases likelihood of the postsynaptic neuron firing action potentials.
What does dopamine do and what does an excess or limit of it do? What about serotonin?
Dopamine: Influences movement, learning, attention and emotion, and an excess leads to schizophrenia whereas a lack leads to Parkinson’s and limited mobility.
Serotonin: Effects mood, hunger, sleep and an undersupply leads o depression. Antidepressant drugs raise serotonin levels.
What are agonists, and what are three ways they work? What are antagonists and what are three ways they work?
What are some agonists and antagonist examples?
What do amphetamine, chlorpromazine and cocaine do?
Agonists: Enhance the actions of neurotransmitters. They do this by:
1) Introducing a substance that helps produce the neurotransmitter so more vesicles are made and released, can also increase the number of neurotransmitters placed in each vesicle.
2) They can block receptors on presynaptic cells to prevent the reuptake of the neurotransmitter so it stays in the synapse longer.
3) It can mimics the action of a neurotransmittter on a postsynaptic cell, increasing the number of ligand gated channels that will open because it acts as the key to open those channels.
Antagonist: These inhibit the actions of a neurotransmitter.
1) They can introduce a substance that reduces the amount of neurotransmitter made in the synapse and reduces the amount present in each synaptic vesicle.
2) Introduces a substance that destroys the neurotransmitter, reducing time in the synapse.
3) Block post-synaptic receptors, preventing neurotransmitters from accessing them.
Agonists: Try to reduce Parkinson’s (L-DOPA), addictive drugs are agonists because similar effects to endorphins. Also antidepressant drugs try to raise serotonin levels or the effects that they have.
Amphetamine and cocaine black the reuptake of dopamine, allowing it to stay in the synapse longer. Amphetamine promotes the release of dopamine, increasing exocytosis rates.
Antagonists: Used to treat schizophrenia and reduce the impact of dopamine. Specifically chlorpromazine occupies the dopamine site on the D2 receptor, preventing receptor activation.
What is the section of the brain that connects both hemispheres? How are the the eyes and brain connected and which side fo the brain controls which side of body? How does this affect split brain patients?
What is a hemisphere and visual field?
The corpus callosum is the fibre connecting both hemispheres of the brain, so that the halves can communicate. When they can’t communicate, people are still pretty normal, there are just certain things that each half can do individually and without that connection it leads to people missing certain functions.
The left eye has the left visual field go to its right side, and the right visual field go to its left side. Then all the cords from the right visual field goes to the left hemisphere and the other wires cross and go to the right hemisphere.
The right eye has the left visual field go to its right side and right visual field go to left side. Then all cords from the left visual field go to the right hemisphere, and the right visual field cross over and go to the left hemisphere.
The hemisphere is the part of the brain that analyzes the information coming in, and the visual field is the side of the person that the info is coming from.
What part of the brain specializes in communication, and what part of the brain specializes in spatial relationships? How does this affect responses when they are not connected?
The right hemisphere specializes in spatial relationships, and the left hemisphere specilzaes in language. When they are not connected, the left hemisphere is able to take in information and communicate based on it. However, the right hemisphere can take in information but can’t send it to the left hemisphere, and hence people can’t communicate what they are seeing on the left hemisphere.
The right brain is essentially mute, so even if someone sees something in their left visual field they can’t articulate it. However they could point to something matching what they saw, they just wouldn’t be able to explain why.
If a patient has a picture flashed to both visual fields, which one will they say they can see?
They will say that they saw the one in their right visual field, because this is taken in by the left hemisphere which can communicate what it saw. They subconsciously will know what they saw but they can’t communicate it because their left brain doesn’t know what happen.
If a split brain patient is given blocks and a drawing for how to arrange them, then which hand will be able to do it?
The right hemisphere is the one that has good spatial arrangement and so the left hand will be able to easily arrange the blocks to match the picture. But the left hemisphere cannot do this and so it will not be able to replicate the picture.
If a snow scene is flashed to the right hemisphere via the left visual field, and a chicken leg is flashed to the left hemisphere via the right visual field, what will the person point to for each (if there are a bunch of picture below?) And how will they explain each thing they point to?
The right hemisphere will see the snow scene and point to a shovel subconsciously. However, it has no language capabilities and the left brain has no access to this information so it can’t explain why it does this. Instead it might say it’s used to clean the chicken coop, even though subconsciously they know why they chose it.
The left hemisphere will point to a chicken head and explain because it saw a chicken leg.
