MIDTERM 1 (L01-08) Flashcards
1
Q
What is the mind? What is consciousness? Where is it located?
A
- Let’s define consciousness as the state or quality of awareness - awareness of our thoughts, perceptions, memories, and feelings
- The state of awareness creates a subjective experience
- If a being is capable of having subjective experiences, then there is something that it is like to be that being
- What is it like to be a rock, or house plant, or ant?
- What is it like to be a calculator, computer, or AI robot?
2
Q
What was the frontal lobotomy used for at first, in the 1940s?
A
- The frontal lobotomy was used to treat psychosis, depression, anxiety, etc.
- The Nobel Prize was awarded for this procedure in 1949
- By the 1950s, over 20,000 lobotomies had been performed in the US alone
3
Q
What is split-brain operation?
A
An outdated surgical approach for treating seizure disorder (epilepsy) that involves cutting the corpus callosum
This surgery is generally effective, but it has unacceptable side effects
4
Q
What is the corpus callosum?
A
the bundle of nerve fibres that interconnect the left and right sides of the cerebral cortex
it enables the two hemispheres to share information so that each side knows what the other side is perceiving and doing
it is the largest commisural pathway in the brain consisting of over 200 million nerve fibers-axons
5
Q
What is the anterior commissure?
A
The anterior commissure is a small band of approximately 50,000 axons that connects the cerebral hemispheres
6
Q
What are our cerebral hemispheres used for?
A
- Our cerebral hemispheres are critical for our ability to CONSCIOUSLY process sensory information (sights, sounds, touch, etc.)
- Our cerebral hemispheres are also critical for our ability to CONSCIOUSLY (purposefully) move our body in space (e.g., hand and leg movements)
- Each cerebral hemisphere is responsible for one half of the body, but the nerve fibre mostly crisscross
- The left brain is largely responsible for the right side of the body
- The right brain is largely responsible for the left side of the body
7
Q
How do the left/right distinction in cerebral hemispheres apply to visual processing?
A
When you look at something (fixation point), everything you see to the left of that spot is processed by the right brain, and everything you see to the right of that spot is processed by the left brain
8
Q
What happens when the corpus callosum is cut?
A
the two cerebral hemispheres cannot directly talk to each other
but they can still send information downwards (to the brainstem and spinal cord) to control muscles
9
Q
What do the brainstem and spinal cord help our bodies do?
A
These lower brain areas help coordinate body movements by integrating the information they receive from the two cerebral hemispheres
it is impressive how well they can do this job (coordinate bilateral movements) when the two cerebral hemispheres lose the ability to talk to each other
10
Q
What did Roger Sperry find during his experiments done on corpus callosum?
A
He became confident the corpus callosum was important for something
His lab cut the corpus callosum of cats and monkeys, where they could be confident the surgeries were clean and complete
They found that it caused cognitive peculiarities
11
Q
What are the intersting dilemmas found in split-brain patients?
A
- In general, when these new split-brain patients were recovering from their surgery, they reported that they felt fine, no different than before
- Often the frequency and/or severity of their seizures were reduced
- The surgeries were a success
- BUT some of these patients later said that their left hand sometimes seemed to have a mind of its own
- Their left hand sometimes actively worked against what the person was consciously trying to accomplish
- It seemed that their left hand was being controlled by processes outside their conscious awareness
- The right hand, controlled by the left brain, never acted out of the ordinary
- Its actions were always consistent with the person’s conscious intentions
12
Q
What happens when a split-brain patient closes their eyes and touch a familiar but unidentified object with their left hand?
A
When a split-brain patient closes their eyes and touches a familiar but unidentified object with their left hand, they cannot identify the object out loud
13
Q
What happens when a split-brain patient sees an image only in their left peripheral vision?
A
When a split-brain patient sees an image only in their left peripheral vision, which is processed on the right side of the brain, they cannot verbalize what they see
Split-brain patients cannot say out loud something that only the right brain sees
14
Q
TRUE or FALSE: Split-brain patients appear to be unconscious of - cannot verbalize - any stimuli directed exclusively to their right brain
A
TRUE
15
Q
How do split-brain patients compensate for their deficits in perception?
A
- Often one hemisphere seemed to take the lead in controlling behaviour in a situation dependent manner, and well-practiced bimanual skills could be coordinated by subcortical structures
16
Q
Where is language located in the brain?
A
our comprehension of language and our ability to talk and write is generally located in the left cerebral hemisphere
17
Q
What did Sperry discover in the mute right cerebral cortex of some split-brain patients?
A
That they could understand simple phrases
- It seemed to retain a bit of a “dictionary” and could understand simple numbers, letters, and short statements
He also found that split-brain patients could use their left hand (controlled by their mute right brain) to indicate answers to simple questions
18
Q
What is Gazzaniga’s Interpreter Theory?
A
Gazzaniga’s Interpreter Theory says that behaviour is fully controlled by unconscious processes, and that the function of our left-brain consciousness is to create narratives in an attempt to make sense of the world
Our consciousness doesn’t directly influence behaviour
- It weaves disparate points of information into a story that has meaning
The underlying premise is that free will is an illusion, and consciousness is just storytelling
- Since storytelling relies on language, consciousness must only be located in the left cerebral hemisphere of the human brain
19
Q
What is the Mind-Body Dualism?
A
- Cartesian doubt or hyperbolic skepticism
- “I think, therefore I am”
- But what is thinking? What are thoughts and ideas? You can’t touch them nor hold them. You can’t find them by cutting open the head; they are immaterial
- For Descartes, the act of thinking proved that an immaterial world exists
- Mind-Body Dualism
- While the body may be a mechanical device and the world deterministic, the mind (or soul) is something else, something immaterial that exists outside the body
20
Q
What is the Cartesian impasse? (in relation to the mind-body dualism)
A
If the movement of all atoms can be well explained by the physical laws of nature, how can our immaterial souls control our material bodies?
21
Q
How does evolution “solve” the Cartesian impasse?
A
- Neural networks have the function of controlling movement, but in service of this function they seem to have gained the ability to control their own dynamics through storytelling and theorizing
- Ideas exist as patterns of brain activity
- Once generated, they act to constrain and direct future brain activity (by harnessing the laws of physics)
- It is by theorizing about cause and effect that we generate the idea that things happen for a reason, that things have meaning
- Self-awareness may stem form the realization that our thought do influence the future
- It is perhaps by envisioning a potential future that neural networks gain influence over or to some extent construct the future
22
Q
What is thinking?
A
-Thinking is not calculating
- Rather, it is an act of creation that involves theorizing, not only about what we are and how the world is, but how these things ought to be, how they might otherwise be
23
Q
What atoms make up >99.99% of the universe’s atoms?
A
hydrogen and helium
24
Q
What is ordinary matter made of?
A
all ordinary matter in the universe is made from elements on the periodic table
25
What is a chemical element?
An atom
26
What are salts?
Molecules held together by ionic bonds (e.g., NaCl)
27
Where do ionic bonds usually break apart/dissolve in?
water
28
What are the main elements of cells (of life on Earth)?
CHNOPS
- stands for Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur, which are the most important chemical elements whose covalent combinations make up most biological molecules on Earth
- 59% hydrogen
- 24% oxygen
- 11% carbon
- 4% nitrogen
- 2% others (phosphorus, sulfur, ...)
29
What are the five different types of molecules we find in cells?
water
sugar
fat (lipid)
nucleic acids
amino acid
30
What is the molecular composition of cells?
- water (70% of total cell mass)
- 15% sugar (carbohydrates)
- 10% fat (lipid molecules form CELL MEMBRANES and VESICLES)
- 15% nucleic acids RNA & DNA - when strung together, we say there is a strand of RNA or a strand of DNA)
- 50% amino acids (long strings of amino acids called PROTEINS)
- 10% other organic molecules (comprised of the CHNOPS atoms) and salts (e.g., NaCl)
31
What does RNA refer to?
Refers to a type of nucleic acid, specifically a ribonucleic acid
32
What is the role of strands of RNA?
- Strands of RNA can naturally fold up into complex 3-dimensional shapes
- some strands of RNA can catalyze chemical reactions
- Researchers have identified ribozymes that can put together new strands of RNA or new strands of DNA
- There are also ribozymes that can make new proteins by stringing together amino acids
33
What do we call a strand of RNA that can catalyze a chemical reaction?
A ribozyme
34
What do we call a protein that can catalyze a chemical reaction?
An enzyme
35
What is tRNA and what is its role?
- tRNAs are small strands of RNA that can hold an amino acid
- these amino acids can easily be strung together to make new proteins
- tRNA molecules play an important part in protein synthesis
36
What is a ribosome?
A ribosome consists of strands of RNA and strands of amino acids (i.e., proteins)
37
What is the role of a ribosome?
it creates new proteins by linking together the amino acids held by tRNA molecules
38
How does the creation of new proteins work?
- one part of the ribosome (the small subunit) grabs onto a long strand of RNA
- then the large subunit of the ribosome identifies free floating tRNA molecules that complement the long RNA strand held by the small subunit
- ribosomes slide across long strands of RNA, taking one step every time they find a tRNA molecule that complements the section of the long RNA strand held by the small subunit
- When a ribosome finds one of these tRNA molecules, it removes its amino acid and attaches it to the amino acid of the next complementary tRNA molecule
- Step by step, the ribosome links together the amino acids held by tRNA molecules
39
How do ribosomes synthesize new proteins?
By TRANSLATING long strands of RNA
40
What is the main catalyst of life's chemical reactions?
protein enzymes
41
Why is DNA so important?
RNA breaks apart easily
DNA is much better for long term information storage
DNA became the information storage molecule for all of life
42
What are phospholipids?
Phospholipids are strands of fat (lipid) with a phosphate cap
43
Describe the phospholipid bilayer
- Lipids prefer the company of other lipids, while phosphate caps prefer to interact with water
- Phospholipids often form bilayer sheets if left undisturbed
- When shaken, phospholipids form micelles (soap bubbles)
- Under the right conditions, micelles can pop and reform as liposomes
- The cell membrane is basically a liposome
- consists of phospholipids embedded with proteis
- Diffusion through the membrane is limited
- The interior is full of salt water
44
What is a prokaryotic cell?
The prokaryotic cell is basically a CELL MEMBRANE filled with CYTOPLASM (a solution of water, salt, and sugar)
45
In prokaryotic cells, what is floating in the cytoplasm?
1. Very long, loose strands of DNA (strings of nucleic acids) as well as shorter loose strands of RNA (also strings of nucleic acids)
2. RIBOSOMES (which are made of strands of RNA and strands of amino acids)
- the function of ribosome is to string together the AMINO ACIDS held by tRNA in the order dictated by the genetic code
- Thus, ribosomes make PROTEINS
46
What are proteins?
Proteins are what do things in cells
- The enzymes that catalyze the chemical reactions of life are proteins
- The receptors that sense the world around us are proteins
- The scaffolding and roads of a cell are made of proteins
- Proteins also mediate transport and storage and serve as messengers
47
What is a eukaryotic cell?
a eukaryotic cell is like a prokaryotic cell, but it has
1. MITOCHONDRIA, which extract energy from nutrients
- Mitochondria create ATP molecules by digesting sugar molecules
2. a NUCLEUS which safely imprisons the cell's long strands of DNA
- Compacted strands of DNA within a nucleus are called CHROMOSOMES
- Chromosomes are never allowed to leave the nucleus
48
What is all the DNA of a cell (or multicellular organism) called?
its genome
49
What does the genome of a cell or multicellular organism provide?
The information necessary to synthesize all the cell's proteins
50
What are the sections of the genome that get transcribed into RNA and translated into proteins called?
Genes
51
What is a gene?
it is a section of DNA that codes for a specific protein
52
What happens when a gene is read?
that segment of DNA is transcribed into RNA
53
TRUE or FALSE: RNA is not allowed to leave the nucleus
FALSE
RNA is allowed to leave to nucleus, and after it leaves, RIBOSOMES TRANSLATE RNA TO CREATE PROTEINS
54
When different versions of a protein are made from a single gene, what do we call these proteins?
protein isoforms
55
What is the soma?
The cell body (or SOMA) of a cell is where the NUCLEUS is located
56
How are neurons typically defined?
Neurons are typically defined by where their soma is located
- example: a hippocampal neuron
57
What are mitochondria?
Mitochondria are semi-autonomous double membrane-bound organelles
They are known as the "powerhouse" of the cell because they generate ATP, the cell's main source of chemical energy
58
What do microtubules do?
Microtubules allow for rapid transport of material throughout the neuron
59
What person advanced the field of neuroscience the most?
Charles Darwin
60
What can you do to understand how human neurons work?
You can study a squid
61
What was the 1963 Nobel Prize awarded for?
describing how neurons transmit electrical signals (i.e., action potentials)
62
What was the 2000 Nobel Prize awarded for?
describing the neuronal basis of learning and memory
This work was done in a sea slug
63
TRUE or FALSE: In the mammalian kingdom, brain size does not vary that much between species, but brain structure is highly different
FALSE
In the mammalian kingdom, brain size varies massively between species, but brain structure is highly similar
64
What mammal is evolutionary closer to humans?
Rodents
65
Why did rodents become the dominant species used in neuroscience research?
Because of the genetic and behavioural similarities between humans and rodents, as well as their small size
66
To what species is our genomes very similar?
The great apes (i.e., chimpanzees, gorillas, and orangutans)
Humans and chimpanzees share 98.8% of their DNA
67
How much does the average human brain weigh at birth?
350 grams
68
How much does the average human brain weigh by late adolescence?
close to 1400 grams
69
TRUE or FALSE: neurons stop growing and cease to establish new connections with other neurons
FALSE
While the production of new neurons almost ceases at birth, neurons continue to grow and establish new connections with other neurons throughout life
Other types of brain cells, which protect and support neurons, continue to replicate
70
What is neoteny?
"Extended youth"
prolongation of maturation
71
What is the Fermi Paradox?
Within our local area of space (the Milky Way galaxy) there is estimated to be 40 billion earth-like planets that could support life
The Milky Way galaxy is over 13 billion years old, so there must be earth-like planets nearby that are way older than Earth
If interstellar travel is possible, even the "slow" kind that is nearly within our reach, it would likely only take 5 to 50 million years for us to colonize the entire Milky Way galaxy
And there are more than 2 trillion galaxies in the observable universe
So... where is everybody? Are we really alone in the Universe?
72
Who won the Nobel Prize in 1906 for their work on the structure of the nervous system?
Camillo Golgi & Santiago Ramon y Cajal
Their work was made possible by the discovery of the Golgi stain - a mixture of silver nitrate and potassium chromate that causes 2% of brain cells to darken in colour as silver chromate crystallizes inside of them, in every nook and cranny
73
Extending off the soma are a bunch of protrusions. What are they?
All but one of these protrusions are DENDRITES
The other one is called an AXON
74
What are dendrites?
Dendrites are branched, treelike extensions from the soma
They are responsible for sensing the external environment (for collecting information relevant to the cell)
75
What is an axon?
Every neuron only has one axon, but axons can branch many times
These branches are called axon collaterals
The axon is responsible for rapidly transmitting messages
76
What is at the end of every axon (and axon collateral)?
an AXON TERMINAL (or TERMINAL BUTTON)
- When an axon terminal receives a message from the soma, it releases signalling molecules (neurotransmitters) into the extracellular space
- These signalling molecules are detected by downstream neurons
77
What is the space between the axon terminal of one cell and the dendrite of the next cell called?
a synapse
78
How do voltmeters measure the voltage of a membrane potential?
voltmeters let a negligible amount of electricity to flow from one wire to another
The amount of resistance needed to let just a little electricity flow indicates the charge difference (the voltage) across the two wires (measured in mV)
79
What is the resting membrane potential of a neuron and what does it entail?
-40 to -90 mV
This means that the electrostatic pressure across the membrane promotes movement of positively charged ions into the cell and negatively charged ions out of the cell
80
What is an electrostatic pressure?
attractive force between molecules that are oppositely charged (i.e., positive and negative) or repulsive force between molecules that are similarly charged (e.g., positive and positive)
81
What are ion channels?
Specialized protein molecules that sit in the cell membrane
They have a pore (hole) in them through which specific ions can enter or leave the cells
82
What is a leak channel?
An ion channel protein that is in the membrane and has a pore that is always open (e.g., potassium leak channel)
83
What are the positively charged ions found in/out of cells?
Monovalent cations:
- sodium (Na+): more abundant outside of cells
- potassium (K+): more abundant inside of cells
Divalent cations:
- Calcium (Ca2+): more abundant outside of cells
- Magnesium (Mg2+): more abundant outside of cells
84
What are the negatively charged ions related to cells?
monovalent anions:
- chloride (Cl-): more abundant outside of cells
85
TRUE or FALSE: The lipid bilayer is impermeable to ions
TRUE
86
What are the two proteins responsible for setting up and maintaining the resting membrane potential in neurons?
1. Sodium-Potassium transporter: requires ATP, concentrates sodium and potassium outside and inside the cell, respectively
- The number of these pumps and their activity is never a limiting factor for neurons
- These pumps make it so there is basically 30x more K+ inside the cell than out and 15x more Na+ outside the cell than in
- These concentrations never ever change, no matter what, unless the cell dies
2. Leak potassium channels: always open, the number of these channels largely determines the resting membrane potential
- The cell membrane of neurons contains K+ leak channels, which are selectively permeable to K+
- if K+ was the only ion that could cross the membrane, the electrical potential of the membrane would settle at -90 mV, because this is when the force of diffusion encouraging K+ to leave is equal and opposite to the electrostatic pressure driving K+ in
- The resting membrane potential of most neurons is less negative than -90 mV because other ions can move across the membrane through other types of leak channels
- The more K+ leak channels a neuron has, the more permeable it will be to K+ relative to other ions and the closer its membrane potential will be to -90 mV
87
What is the function of the Sodium-Potassium pump?
Pump Na+ atoms out of the cell and K+ atoms in
88
How does the sodium-potassium pump do its job?
- The sodium-potassium pump binds three sodium ions and a molecule of ATP
- The splitting of ATP (ATP --> ADP) provides energy to change the shape of the channel. The sodium ions are driven through the channel
- The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind
- Release of the phosphate (which came from the ATP) allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane
89
What is the proportion of K+ ions and Na+ ions in the cell that the sodium-potassium pump creates?
- It causes K+ ions to be 30x more concentrated inside the cell than out
- It causes Na+ ions to be 15x more concentrated outside the cell than in
90
TRUE or FALSE: the concentration gradients in the cell regularly change
FALSE
These concentration gradients never change, ever, unless the cell dies
91
Describe what the force of diffusion is
If there is a concentration gradient and no forces or barriers to prevent free movement of molecules, then molecules will move, on average, from regions of high concentration to regions of low concentration
92
How do K+ ions leave the cell?
Neuronal membranes are filled with K+ leak channels
Given the ability to travel freely, K+ ions leave the cell on account of the force of diffusion
93
What does having more K+ leak channels mean for a cell membrane potential?
The more K+ leak channels a neuron has, the more permeable it will be to K+ and the closer its membrane potential will be to the true electrochemical equilibrium of K+
94
Why do neurons put receptor proteins on their dendrites?
To sense the external world
There are sensors for detecting:
- The presence of certain molecules (e.g., neurotransmitters)
- Physical pressure (movement, touch)
- Electrical pressure (voltage)
- Temperature
- pH (acidity, basicity)
- Electromagnetic radiation (light)
95
Many of the receptors on the ________ of neurons are ________ channels
dendrites, ion
96
What does the activation of ion channels do?
the activation of these receptors opens a pore (hole or gate) that lets ions pass through
the flow of ions across a neuron's membrane can depolarize or hyperpolarize the neuron's membrane potential
97
What does it mean for a membrane potential to be depolarized?
When the membrane potential of a cell becomes less negative than it normally is at rest
For example, when positive sodium ions enter a cell through a receptor protien ion channel, they might depolarize a neuron from -70 to -60 mV
98
What happens when positive Na+ ions enter the neuron through an ion channel?
When positive Na+ ions enter a neuron through an ion channel, causing membrane depolarization, it causes K+ ions to immediately leave the cell through leak channels, which restores the resting membrane potential
99
What are the 5 proteins involved in action potential?
1) Sodium-Potassium transporter
2) Leak potassium channels
3) Voltage-gated sodium channel (to initiate and propagate the action potential)
4) Voltage-gated potassium channel (to restore the resting membrane potential)
5) Voltage-gated calcium channel (located in the axon terminal; triggers release of neurotransmitter)
100
Where in the neuron can we find voltage-gated sodium channels?
These ion channels are found all over the axon, along its entire length
101
How do voltage-gated sodium channel function?
The gate opens whenever the membrane potential becomes less negative than -40 mV
- The initial cause of this depolarized state is usually the activation of receptor protein ion channels that let in sodium
Inactivation lasts until the membrane potential gets back down to -70 mV (about 1/2 a millisecond)
These channels are only permeable to Na+
102
What happens when one voltage-gated sodium channel opens?
The opening of one Na+ channel allows the Na+ ions to rush in, propelled by both diffusion and electrostatic forces
This influx of Na+ depolarizes the membrane further, which in turn causes additional voltage-gated Na+ channels to open
Soon there is an avalanche effect as all voltage-gated Na+ channels open causing the membrane potential to shoot up to +40 mV
103
What is an action potential?
The ACTION POTENTIAL is a brief electrical impulse that provides the basis for conduction of information along the axon
- It is a rapid change in the membrane potential caused by the opening and closing of voltage-gated ion channels
104
What is meant by "threshold of excitation"?
the value of the membrane potential that must be reached to produce an action potential (between -55 and -65 mV)
105
TRUE or FALSE: the first ions that enter the cell do so through voltage-gated ion channels?
FALSE
The initial depolarization that starts an action potential is usually driven by the activation of a receptor that lets Na+ ions enter
- These first ions enter through an ion channel, but not a voltage-gated ion channel, because those are closed when a cell is at rest
106
What is the voltage of the membrane potential at the peak of an action potential?
+40 mV (all voltage-gated Na= channels are now inactivated)
107
Why do cells use another voltage-gated ion channel to restore membrane potential instead of just relying on potassium leak channels?
Potassium leak channels are always open
- They will restore the resting membrane potential soon, but that could take many milliseconds, which it too long to support rapid action potential firing
To speed up restoration of the membrane potential, the cell uses another voltage-gated ion channel
108
When do voltage-gated potassium channels open?
when the membrane potential is more positive than 0 (no difference in charge between inside and outside of cell)
- the opening of the voltage-gated K+ channels helps bring the membrane potential back down to -70 mV
voltage-gated potassium channels open in the middle of an action potential, when the membrane potential is around 0
109
When do all voltage-gated ion channels close and reset?
When the membrane potential gets back down to rest
However, by the time all the voltage-gated K+ channels close, the membrane will have fallen below what it normally is at rest
110
What is the post action potential hyperpolarization period called?
refractory period, and it can last 1 ms
it is very hard to trigger another action potential during this time
111
Why does the falling phase of the action potential occur as rapidly as the rising phase?
it is due to the closing of the Na+ channels and opening of the voltage-gated K+ channels
112
In what direction does an action potential travel?
It is sent from the soma down the axon to the terminal button
Conduction occurs in a UNIDIRECTIONAL manner
113
How does recording from an axon work?
1. the ground wire ELECTRODE is placed in the extracellular fluid
2. The GLASS MICROELECTRODE is inserted into the axon
3. the OSCILLOSCOPE is a sensitive voltmeter that measures the electrical charge across the membrane (i.e., the neuron's membrane potential in mV)
114
Does action potential diminish in size as it travels down the axon?
No. The size of the action potential remains CONSTANT
115
How can the speed of conduction of an action potential be calculated?
can be calculated from the delay between the stimulus and the action potential
116
When do voltage-gated calcium channel open?
when the axon terminal becomes depolarized (i.e., in response to an action potential)
Calcium is 1000x more concentrated outside the cell than in
117
What does the entry of calcium through voltage-gated calcium channels activate?
Activates vesicles release machinery
It triggers the release of signalling molecules (neurotransmitters) into the synapse
118
What is the primary means of communication between neurons?
Synaptic transmission
- transmission of messages from one neuron to another via the release of signalling molecules into the synapse
- these signaling molecules activate the receptor proteins on downstream neurons
119
What is the movement of the information along the axon referred to as?
conduction of the action potential
120
What does the All-or-None law state?
states that the action potential occurs or does not occur, and once triggered, will propagate down the axon without growing or diminishing in size, to the end of the axon
121
What does the rate law state?
States that the strength of the stimulus is represented by the rate of the firing axon
122
How is it that an ion channel can be permeable to K+ but not Na+?
The human genome contains 40 distinct genes for the voltage-gated potassium channel
There is no perfect voltage-gated potassium channel
- There are 40
- Each cell can choose to express one or any combination of them to optimize cell function
123
In genetics, what is a promoter?
It is a region of DNA that initiates transcription of a particular gene
They indicate what kind of cells should read the gene and when
Promoters are typically located just before the gene
124
What are neuroglia (or glial cells)?
Supporting cells of the CNS
Glia found all around neurons and even physically encapsulate some parts of them
- They help traffic nutrients and maintain molecular (ionic) stability in the extracellular space
- They support many functions of the nervous system
- It is estimated that glia cells outnumber neurons in the brain somewhere between 2:1 and 5:1
125
What are astrocytes?
Astrocytes are glia cells that provide physical support and clean up debris in the brain through PHAGOCYTOSIS
- They control the chemical composition of the surrounding environment and help nourish neurons
126
What are microglia?
microglia are the smallest of the glial cells
- They provide an immune system for the brain and protect the brain from invading microorganisms
127
What are oligodendrocytes?
Oligodendrocytes produce the MYELINE SHEATH, which encapsulates axons
- The sheath is not continuous; it is a series of segments
- The exposed axon is called the NODE OF RANVIER
128
During development of the CNS, what forms processes shaped something like canoe paddles?
oligodendrocytes
Each of these paddle-shaped processes then wraps itself many times around a segment of an axon and, while doing so, produces layers of myelin that make up part of the axon's myelin sheath
129
What is saltatory conduction?
IN MYELINATED AXONS
Action potentials traveling down the axon "jump" from node to node
Saltatory conduction is a faster way to travel down an axon than travelling in an axon without myelin
The strength of the action potential's signal is regenerated at nodes of Ranvier with additional voltage-gated Na+ channels
130
What is synaptic communication and how does it work?
This communication across the synapse is achieved by the release of a molecule from an axon terminal
This molecule is called a neurotransmitter and it can have a simple excitatory or inhibitory effect or a complex modulatory effect on the receiving neuron
131
What are synaptic vesicles?
They contain molecules of neurotransmitter
They attach to the presynaptic membrane and release neurotransmitter into the synaptic cleft
132
What is the synaptic cleft?
It is the space between the pre- and postsynaptic membranes
It is filled with an extracellular fluid
133
What does electron microscopy allow us to do?
Allows us to see small anatomical structures (e..g, synaptic vesicles and details of cell organelles) using a special electron microscope
134
What are signalling molecules that bind to protein receptors called?
Ligands
135
What are the two categories of neurotransmitter receptors?
- ionotropic receptors, which are ion channels
- the direct effect of ionotropic receptor activation is always an immediate change in the permeability of the membrane to specific ions
- metabotropic receptors, which are g protein coupled receptors that can open ion channels through an intracellular signalling cascade
- they are not ion channels
- the effects of metabotropic receptor signallingh can be quite large, but they are often delayed (because they rely on signalling cascades and diffusion)
136
Where can receptors be found?
on the cell membrane (surface receptors) or inside the cell (intracellular receptors)
137
What can neurotransmitter receptors that are on the cell membrane be?
- Postsynaptic receptors - located on postsynaptic membrane
- Presynaptic receptors - located on presynaptic membrane
- Extrasynaptic receptors - located near to but outside the synapse
138
What is a postsynaptic receptor?
Receptor protein in postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter
139
What is a ligand-gated ion channel?
A receptor that is an ion channel
Also known as an IONOTROPIC RECEPTOR
The ion channel opens when the ligand (e.g., the neurotransmitter) binds to it
140
What are the two mechanisms that keep the neurotransmitter signalling in the synapse brief?
- Enzymatic deactivation: destruction of a neurotransmitter by enzyme after its release
- Example: destruction of acetylcholine by acetylcholinesterase
- Reuptake: reentry of a neurotransmitter just liberated by a terminal button back through its membrane, thus terminating postsynaptic potential
141
How is a postsynaptic potential defined?
Alterations in the membrane potential of a postsynaptic neuron, produced by neurotransmitter release into the synapse and receptor activation
Postsynaptic potentials can either be:
- Excitatory (influx of positive sodium ions depolarize the cell)
- Inhibitory (influx of negative chloride ions hyperpolarize the cell)
142
What are excitatory postsynaptic potentials (EPSPs)?
- Excitatory depolarization of postsynaptic membrane caused by neurotransmitter binding to a postsynaptic receptor protein
- EPSPs are mediated by receptor proteins that open ion channels permeable to sodium (making the membrane more permeable to sodium will depolarize the cell)
143
To trigger an action potential, what must occur? (Hint: EPSPs)
Many EPSPs must occur at nearly the same time
For the membrane to depolarize to the threshold of activation (starting an action potential), sodium ions must come in at a faster rate than potassium ions leave
This depolarization must reach the beginning of the axon (the axon hillock) where tons of voltage-gated sodium channels are congregated
This is the pool of ion channels that typically start an action potential
144
What are inhibitory postsynaptic potentials (IPSPs)?
- Inhibitory hyperpolarization of postsynaptic membrane caused by neurotransmitter binding to a postsynaptic receptor protein
- IPSPs are mediated by receptor proteins that open ion channels permeable to chloride (making the membrane more permeable to chloride will hyperpolarize the cell)
145
What is the interaction of the excitatory and inhibitory synapses on a particular neuron called?
Neural integration
146
What happens when EPSPs and IPSPs occur at the same time?
The influx of negatively charged chloride ions diminish the impact of the positively charged sodium ions
IPSPs decrease the likelihood that the cell will fire
147
What determines the direction of the postsynaptic potential (EPSP vs. IPSP)?
not the neurotransmitter, but rather the receptor
example: some serotonin receptors cause EPSDPs, and other serotonin receptors cause IPSPs
- it is the postsynaptic cell that expresses the receptor that determines whether the detection of serotonin will be excitatory or inhibitory
148
What happens when the dendrites of a sensory neuron are stimulated by a noxious stimulus?
It sends messages down the axon to terminal buttons located in the spinal cord
The sensory neuron will activate an interneuron, which in turn will activate a motor neuron and cause a withdrawal reflex
149
What is an example of a contest between two competing drives? (Hint: holding onto a hot pan)
a cortical neuron could send an action potentials down the spinal cord to excite an inhibitory interneuron, which is a neuron that generally causes IPSCs (inhibitory postsynaptic currents) in downstream neurons
this interneuron would induce IPSCs in the motor neuron and block (counteract) the withdrawal reflex
this circuit provides an example of a contest between two competing drives: one to drop the hot pan and another to keep holding it
150
What is the difference between neural excitation and behavioural excitation?
An inhibitory neuron is a neuron that reliably causes IPSCs in downstream neurons (i.e., it reduces the spiking activity of downstream neurons)
Keep in mind that the net result of inhibitory neuron activity may not be to inhibit an animal's behaviour
Sometimes, inhibitory neuron activity can cause a movement
- this is often the case when the inhibitory neuron makes synaptic connections on other inhibitory neurons
- INHIBITION OF INHIBITORY NEURONS CAN MAKE A BEHAVIOUR MORE LIKELY TO OCCUR
For every neuron trying to change behaviour in one way, there are usually other neurons trying to do the opposite
- Both types of neurons will often be regulated by inhibitory neurons
- And those inhibitory neurons may be controlled by other inhibitory neurons
- We often see long chains of inhibitory neurons in a row, which can make it really hard to determine which ones are trying to cause or prevent a behaviour
NEURAL EXCITATION IS NOT THE SAME THING AS BEHAVIOURAL EXCITATION
NEURAL INHIBITION IS NOT THE SAME THING AS BEHAVIOURAL INHIBITION
151
What are GPCRs?
g protein-coupled receptors
all g protein-coupled receptors are metabotropic receptors
152
What are metabotropic receptors and g proteins?
Metabotropic receptors that turn toward metabolism to mediate their effects
- Metabolism just refers to chemical reactions that occur inside the cells
- Metabotropic receptors trigger intracellular signals to catalyze chemical reactions
- The end result can be almost anything
- Most metabotropic receptors mediate their effects by activating g proteins
The name "g protein" symbolizes that these proteins use GTP molecules, instead of ATP molecules, for the energy they need to perform chemical reactions
G proteins are like molecular switches
- when a protein is bound to GTP, it is "ON" or activated, because in this state it can trigger chemical reactions
- This state is temporary, however, because G proteins have a natural tendency to convert GTP to GDP
- When this happens, the g protein is "OFF" or inactivated
G proteins have a hard time letting go of GDP
- The only way they can do so is by finding an activated metabotropic receptor
- They use the intracellular side of an activated metabotropic receptors to pry off their GDP molecule
- When this happens, they bind another GTP molecule and the process starts over again
153
How does activation cycle of g proteins start?
when a metabotropic receptor binds to its ligand
Ligand binding to a metabotropic receptor induces a conformational change that facilitates the exchange of GDP for GTP on the α subunit of the g protein complex
The g proteins then dissociate and diffuse away to activate downstream enzymes
Once the GTP molecule is metabolized (GTP --> GDP), the original g protein-couple receptor complex is restored
154
What are g protein-gated ion channels?
Some ion channels are gated by g proteins
- G proteins are a family of intracellular proteins that are involed in intracellular signalling cascades
- they all use the GTP molecule for energy
155
Describe the generalized illustration of a metabotropic GPCR receptor causing ion channel opening
1) Neurotransmitter binds to a metabotropic receptor
2) Activated g proteins transmit the message intracellularly
3) Some ion channels are gated (directly or indirectly) by activated g proteins
156
In what way do g-protein signalling cascades affect multiple downstream processes?
- opening g protein-gated ion channels
- changes in gene transcription
- secretion of substances from the cell
- really anything the cell wants
157
Where can synapses form?
Synapses can form between axon terminals and...
1) dendrites (dendritic shafts)
2) dendritic spines
3) the soma (cell body)
4) other axon terminals (axoaxonic synapses)
The point of the 1), 2), and 3) positions is to cause an action potential
158
What do axoaxonic synapses do?
Regulate the amount of neurotransmitter that the second neuron (the postsynaptic terminal neuron) will release when it has an action potential
159
In axoaxonic synapses, what is the net effect of presynaptic inhibition?
Axoaxonic synapse can hyperpolarize the axon of the downstream neuron (the postsynaptic terminal button), so that its voltage-gated calcium channels will not open at all or for very long when an action potential arrives
The net effect is to reduce neurotransmitter release from the postsynaptic terminal button when it has an action potential
160
In axoaxonic synapses, what is the net effect of presynaptic facilitation?
Axoaxonic synapse can depolarize the axon terminal of the downstream neuron (postsynaptic terminal button), so that its voltage-gated calcium channels are more likely to open when an action potential arrives
The net effect is to increase neurotransmitter release from the postsynaptic terminal button when it has a action potential
161
What is an autoreceptor?
a receptor located on presynaptic membrane that gets activated when the cell releases its own neurotransmitter
Autoreceptors are gated by the neurotransmitter that the cell releases
- Autoreceptors are generally metabotropic and inhibitory
- They are the main source of presynaptic inhibition
162
What is the neuraxis?
imaginary line that runs along the length of the CNS
163
What does a mid-sagittal cut mean?
a mid-sagittal cut means the exact middle (between the eyes)
164
What does it mean for a structure to be contralateral?
Structures on the opposite side of the body (e.g., the motor cortex controls movements of the contralateral hand)
165
What does it mean for a structure to be ipsilateral?
Structures on the same side of body (e.g., taste information is processed ipsilaterally, which means that taste receptors on the left side of your tongue are processed by your left cerebral hemisphere. Taste and smell are the only sensory systems that do not have contralateral organization)
166
What does brain nuclei mean?
in the brain, the word nuclei means a collection of neurons that are clustered together that all work together to serve some function
- e.g., there are many different brain nuclei in the hindbrain
- one controls breathing, another controls vomiting, etc.
167
What is the central nervous system comprised of? (what parts of the body)
Everything in the brain AND spinal cord
168
What is the peripheral nervous system comprised of? (what body parts)
Any part of the nervous system outside of the brain and spinal cord
169
In the central nervous system, what creates myelin?
oligodendrocytes
170
In the peripheral nervous system, what creates myelin?
Schwann cells
171
What is the blood-brain barrier?
a semipermeable barrier between the blood and the brain
172
Outside the brain and spinal cord, where does all the extracellular fluid come from?
blood
173
What allows the liquid part of blood to continually leak out?
Blood vessels in the body have small holes in them, which allows the liquid part of blood (blood plasma) to continually leak out
174
When blood leaks out of blood vessels, what does it become?
Lymph - the extracellular fluid of the body
175
What does lymph do for cells?
Lymph flows around cells providing nutrients and collecting waste
176
What are lymph nodes/lymph organs?
Lymph is collected into lymph vessels and brought to lymph nodes/lymph organs
These structures detect and destroy any invading organisms or foreign particles, and then they return the lymph back to the blood to start the process again
177
TRUE or FALSE: The CNS participates in the lymphatic system
False
The blood capillaries that pass through the brain and spinal cord do not have gaps in them
This property is known as the BLOOD BRAIN BARRIER
Rather than letting blood leak out, the brain simply makes its own extracellular solution by actively picking out exactly what it needs from the blood
- The solution it makes is called CEREBROSPINAL FLUID (CSF)
178
What are the 3 types of meninges?
The 3 types of meninges are tough, protective connective tissues that surround the brain
1. The DURA MATER is the outer layer
- It is thick, tough, unstretchable tissue
2. The ARACHNOID MEMBRANE is the middle layer
- It is soft and spongy and has a web-like appearance
2. The third layer that sits closest to the brain is PIA MATER
- This layer and the space above it has blood vessels in it
179
What is the subarachnoid space?
The SUBARACHNOID SPACE (between the arachnoid membrane and pia mater) is filled with cerebrospinal fluid (CSF) and blood vessels
180
What is cerebrospinal fluid made by?
Choroid plexus, a tissue that is found in each of the brain ventricles (i.e., the 4 interconnected hollow spaces within the brain)
181
What are the 4 brain ventricles?
- the two LATERAL VENTRICLES are large
- They sit underneath the cerebrum
the THIRD VENTRICLE lies between the two thalamic nuclei
- the FOURTH VENTRICLE sits between the pons and cerebellum
182
What connect the third and fourth brain ventricle?
the cerebral aqueduct
183
How often CSF made and replaced?
CSF is made continuously, and it is half replaced every three hours (its half-life)
184
Where does CSF circulate?
It flows from the brain ventricles around (and into) the brain and spinal cord before it is absorbed into the blood supply
185
What is a interneuron?
A neuron entirely located in the CNS is technically called an interneuron, but in common usage...
- the word INTERNEURON is only used for CSN neurons whose axon stays local (it only makes synapses on nearby neurons)
186
When is the term "projection neuron" used?
When the axon of a cell goes outside the area where its soma is located
187
What else is included in the PNS?
AXONS OF MOTOR NEURONS
- efferent fibers: fibers that bring information AWAY FROM the CNS, the output
- Motor neurons control muscle contraction and gland secretion
- The soma of motor neurons is located within the spinal cord (the CNS)
SENSORY NEURONS, whose axons are:
- afferent fibers: fibers that bring information towards the CNS, the inputs
- Sensory neurons detect changes in the external and internal environment
- They send this information to the CNS
188
How do the brain and spinal cord communicate with the rest of the body?
via nerves
189
In the peripheral nervous system, what are the two different types of nerves?
cranial nerves
spinal nerves
these nerves are part of peripheral nervous system, which sends sensory information to the CSN and effector information away from the CNS (targeting muscles and glands throughout the body)
190
How many pairs of spinal nerves are there?
31 pairs of spinal nerves attach to the spinal cord, about 1 pair for each vertebrae
191
How many pairs of cranial nerves are there?
12 pairs of cranial nerves attach to the ventral surface of brain
192
What do all but one cranial nerve do for us?
All cranial nerves (except the 10th) serve sensory and motor functions of head and neck region
193
What is the 10th cranial nerve called and what does it do?
vagus nerve ("wandering" nerve)
its branches wander throughout thoracic and abdominal cavities
it regulates functions of the heart, lungs, upper digestive track, and other organs in that area
194
What is the principal function of the spinal cord?
To collect sensory information to be passed on to the brain and distribute motor fibres to effector organs throughout the body (glands and muscles)
The spinal cord also has a certain degree of autonomy from the brain; various reflexive control circuits are located there
195
Where do the efferent motor fibres exit the spinal cord?
the ventral root
196
Where do the afferent motor fibres arrive from in the spinal cord?
the dorsal root
197
What are the two components of the peripheral nervous system?
SOMATIC
- Senses and interacts with the EXTERNAL environment
- Afferent nerves
- Carry sensory signals from eyes, ears, skin, etc. TO central nervous system
- Efferent nerves
- Carry motor signals FROM central nervous system to skeletal muscles
AUTONOMIC
- Regulates body's INTERNAL environment
- Afferent nerves
- Carry sensory signals from internal organs TO central nervous system
- Efferent nerves
- Carry motor signals FROM central nervous system to internal organs
198
What are the 2 components of the autonomic nervous system efferent branch?
SYMPATHETIC DIVISION
- Part of efferent autonomic nervous system that primes the body for action, particularly in life threatening situations (e.g., it mediates the FLIGHT-FIGHT-FREEZE RESPONSE when animals are threatened)
- It is always active to some extent, as it regulates heart rate, blood flow, and the activity of almost every organ in the body
- But when acutely stimulated, it shunts blood away from the organs that are not necessary for immediate survival and increases blood flow to the organs involved in intense physical activity
PARASYMPATHETIC DIVISION
- Part of the efferent autonomic nervous system that support activities that occur when the body is in a relaxed state and all is well
- It generally is involved with increasing the body's energy stores (i.e., digestion)
- Its functions also include sexual arousal, defecation, urination, and salivation
- For simplicity, people often say the parasympathetic system is involved in "FEED AND BREED" and "REST AND DIGEST" activities
199
What are the three major divisions of the brain?
Forebrain
Midbrain
Hindbrain
200
