Nervous System Flashcards
What are some ways communication takes place in our cells? Why are most of them not as productive? (3)
What is an ideal way to communicate?
- Connections between cells through Gap Junctions (in animals) or Plasmodermeta (in Plants)
- Hormones - centrally secreted, active locally
- Secondary Messenger - Signal Transduction within the cell
The methods listed above work via diffusion, making them slow
ELECTRICITY is the best (fastest) way to communicate.
What is the most effective way to communicate within our bodies and between cells?
Communication via electrical signals through nerve cells known as NEURONS
This uses electricity which is much faster.
What are the components of a Neuron?
- Cell Body - Includes the Nucleus. Mitochondria, Golgi Bodies, Ribosomes, ER, etc.
It is connected to the dendrites and axon terminal. - Dendrites - Detect Stimulus and Recieve a signal. They covert the chemical signals into electrical signals (Increase SA)
- Axon - Conducts electrical signals and stores neurotransmitters
What are connections between neurons called?
Connection between axon-dendrites is called a SYNAPSE
The chemical signal moves between axon terminal and dendrite
What are electrical and membrane potentials?
A difference in charge between 2 points creates an ELECTRICAL POTENTIAL or a voltage.
When an electrical potential exists across a plasma membrane, the separation of charges is called a MEMBRANE POTENTIAL.
What is Resting Potential?
Describe what is happening to the charges during this state. (K+)
When a neuron is not communicating with other cells, the difference in charge across the membrane is called the Resting Potential.
In Resting potential, the membrane is selectively permeable to K+.
K+ slowly leaves the cell along its concentration gradient, leaving the inside negatively charged relative to the outside. (-65 mV)
In this state the neuron is POLARIZED
How does the Sodium-Potassium Pump work?
(AKA as the Na+/K+ - ATPase).
The sodium-potassium pump is a form of active transport (needs ATP) that brings
TWO K+ ions in and sends THREE Na+ ions out.
(High conc of K+ inside, Low conc of Na+ inside)
Attached is a photo that shows the process in intricate (big words) detail 🦧.
What are the K+ leak channels?
At rest, the membrane of the neuron is relatively impermeable to most cations, however, the neuron membrane has a high number of potassium channels that allow K+ ions to leak across the membrane.
They are known as K+ Leak Channels
What is the Equilibrium Potential for K+?
(4)
- The K+ gradient established by the Na+/K+ ATPase (high K+ inside the cell, low K+ outside) favours the net diffusion of K+ out of the cells via leak channels
- Results in a more and more negatively charged inside relative to the outside.
The buildup of a negative inside begins to attract K+ ions which are positively charged. - There is now a CONCENTRATION gradient that favours K+ OUT and an ELECTRICAL gradient that favours K+ IN
- Results in the Equilibrium Potential for K+. There is no longer a net movement of K+ 🦧
There are other channels on the membrane such as the Sodium channel. The sodium channel is usually closed and tightly controlled. What would happen in the Sodium channel was opened? (5)
- The Sodium-Potassium pump is actively pumping 3 Na+ ions out of the cell. This results in a higher concentration of Na+ outside of the cell
- If the Sodium Channel were to open, Na+ ions would follow their concentration gradient and enter the cell where there are fewer Na+ ions.
- Furthermore, since the inside of the cell is already negatively charged (-65 mV) this attracts even more of the positively charged sodium ions inside.
- Now the OUTSIDE of the cell is LESS POSITIVE and the INSIDE of the cell is LESS NEGATIVE.
The net result is that the charge inside the cell goes from -65 mV to +40 mV - The neuron is now DEPOLARIZED
How and When does Polarity change in the Neuron?
(4) (PDRH)
- At the resting potential, inside the cell, there are high K+ ions and low Na+ ions. The inside is -65 mV relative to the outside.
The neuron is POLARIZED.
- When the sodium channels open at the beginning of an impulse, Na+ ions flow into the cell. The inside is now +40 mV relative to the outside
The neuron is DEPOLARIZED.
- Once the Na+ channels close again, the Na+/K+ pump and K+ leak channels will continue working and
The neuron is REPOLARIZED
- After the action potential, there is a refractory period where the membrane potential is lower than when at rest.
The neuron is HYPERPOLARIZED
What is an Action Potential?
An action potential is a rapid, temporary change in membrane potential. It may qualify as the most important type of electrical signal in cells.
Allows neurons to communicate with other neurons, muscles or glands.
Occurs when the neuron switches from polarization to depolarization.
Graph what is happening during an action potential.
What do the different slopes represent?
- Starts at rest (-65 mV) sodium gates closed (polarized)
- Sodium Gates open (+40 mV) (depolarized)
- Sodium Gates close again (repolarization)
- Refractory Period where membrane potential is slightly lower than resting. (< -60 mV) (Hyperpolarization)
What is the “All or None” Principle in the Neuron?
There are no big or small action potentials in one nerve cell - all action potentials are the same size.
Therefore, the neuron either does not reach the threshold or a full action potential is fired
What causes the opening of the Na+ channel?
Change in membrane potential known as Threshold Potential (somewhere above -60 mV)
Why do Action Potentials only travel in one direction? Why not backwards?
Because the Hyperpolization stage leads to a refractory period that makes it harder to reach the threshold potential.
What affects the speed at which the action potential moves down the axon?
Depends on the Diameter of the Axon:
the larger the axon, the faster charges will move
invertebrates have large axons (“giant axons”)
but fewer neurons
* squid
* locust 😫
* earthworm
Neurologists prefer to work with these species when studying the nervous system!
We (Vertebrates) need far more neurons than invertebrates. Therefore our neurons need to be smaller and work faster. How do we achieve this?
Schwann cells wrap around the axon and help insulate it with Myelin Sheaths
What are Schwann Cells? What are their functions?
Schwann cells wrap around the axon and help insulate it with Myelin Sheaths.
Leads to complete isolation and does not allow anything to pass through
What are the Nodes of Ranvier?
The Nodes of Ranvier are the gaps between the myelin insulation of Schwann cells which insulate the axon of neurons.
Their function is to speed up propagation of action potentials along the axon
How do the Nodes of Ranvier, Schwann cells and Myelin Sheath work together?
I have no clue, look at the photo 👹
How long are axons?
Axons can be very long or short
The longest-known axon is in the giraffe.
The motor neuron of the giraffe originates from the spinal cord and ends up in the foot. (3m-4m)
What are Tetrodotoxins?
A neurotoxin from the pufferfish that blocks sodium channels: action potential cannot be generated. Neurons don’t work
What are the areas before and after the synapse called?
The Presynaptic Neuron (on the axon side)
and
The Postsynaptic Neuron (on the dendrite side)
What is in between the Pre and Post Synaptic Neurons?
The Synaptic Cleft (liquid filled)
What types of signals are used when an action potential goes down the synapse? (3)
The Action Potential moves down the Axon
via an ELECTRICAL signal
The Action Potential moves down the Synaptic Cleft
via a CHEMICAL signal carried in molecules called NEUROTRANSMITTERS
The Action Potential moves down the DENDRITE
via an ELECTRICAL signal
What happens when an action potential reaches the presynaptic cleft?
The (Ca 2+) Calcium Channels open in the presynaptic membrane and Ca2+ rushes into the presynaptic terminal.
IMPORTANT
The vesicles containing neurotransmitters fuse with the axon membrane and release them into the synaptic cleft
What happens to Neurotransmitters in a Synapse? (2)
As the action potential goes through the axon and calcium gates have opened, the vesicles carrying neurotransmitters fuse with the axon membrane and release the neurotransmitters into the synaptic cleft.
From there, they diffuse across the synaptic cleft and fit into receptor sites on the dendrites.
What happens once the Neurotransmitters have bonded with the receptors on the dendrites?
The receptors on the dendrites are actually ion channels called Ligand-Gated ion channels.
Once the Neurotransmitters have bonded with the receptors on the dendrites, they open up and allow ions to enter the dendrite.
This alters the membrane potential and can lead to an action potential in the next neuron.
A quick review of the steps. 🦧
Does the binding of neurons guarantee an action potential?
No there are two different things that can take place.
- The neurotransmitters can be excitatory which means increasing the chance of an action potential
- The neurotransmitters can be inhibitory which means decreasing the chance of an action potential
What are some common neurotransmitters?
- acetylcholine
- noradrenaline
- dopamine
- serotonin
- glutamate
What would happen if the postsynaptic neuron is constantly being activated?
Could Lead to paralysis.
What is EPSP and IPSP? (3)
Excitatory Post-Synaptic Potentials.
(make action potentials more likely)
(depolarization begins again)
and
Inhibitory Post-Synaptic Potentials.
(make action potentials less likely)
(hyperpolarization takes place)
Can Cancel each other out
What are the neurons that connect Sensors, Integrators and Effectors?
Interneurons
What is the difference between Interneurons and Sensory Neurons?
Sensory Neurons; Generate an action potential in response to external stimulus (TRANSDUCTION
Interneurons; Generate an action potential in response to receiving an action potential (TRANSMISSION)
What are some examples of Sensory Neurons? (7)
(don’t memorize goof👺)
- Mechanoreceptors - detect distortion or pressure
- Photoreceptors - detect light of specific wavelength
- Chemoreceptors - detect specific molecules
- Thermoreceptors - detect temperature change
- Nocireceptors - detect pain (harmful stimuli)
- Electroreceptors - detect electric fields
- Magnetoreceptors - detect magnetic fields
Draw a Diagram of an Interneuron and connecting elements.
I definitely drew this 👍🏽
Shown on top is the normal action potential propagated through the axon of a neutron, and below the signal in the same cell after treatment with a neurotoxin. Based on the graph, propose a mechanism for how the neurotoxin works.
Apparently, the action potential is not proceeding as normal, although the incoming signal depolarizes the membrane to reach the threshold value for opening the sodium channel and the rapid depolarization. This indicates that the sodium channel is not opening, Therefore, the neurotoxin most likely is a sodium channel blocker that binds to the channel, and prevents Na+ ions to pass through the channel.
If the activity of the sodium—potassium pump was completely stopped, what would happen to the neuron’s membrane potential?
slow rise in membrane potential
True or False
Ion pumps and ion channels establish and maintain a resting potential membrane
TRUE
True or False
Information coded in action potentials is transmitted from cell to cell at Gap Junction
FALSE
at the synapses (gap junctions are connections between plant cells)
True or False
Cells have a relatively negative charge on the inside of the membrane due to the loss of K+ ions
TRUE
True or False
Depolarization causes an action potential
TRUE
True or False
Voltage-gated ion channels are open at resting potential
FALSE
they are closed and open during depolarization (for Na+ ions) or at hyperpolarization (for K+ ions)
True or False
Action potentials move in both directions, but current spreads in only one direction down an axon.
FALSE
action potentials move in one direction and current goes both directions along an axon
True or False
The spinal cord can act independently of the brain in simple nerve circuits.
TRUE
these are reflexes or automatic responses
The cell membrane is selectively permeable to ions, which ion has the higher permeability (Na+ or K+)?
K+
What maintains concentration gradients of Na+ and K+?
Na and K pumps (not the channels)
In what direction are Na+ and K+ pumped across the cell membrane and at what ratio?
3 Na+ are pumped out for every 2K+ pumped into the cell
In which direction do Na+ and K+ “leak” out of their respective channels?
Na+ leaks into the cell
K+ leak out of the cell
Which ion has more channels K+ or Na+?
K+