The Nervous System: Structure + Intracellular Signal Transmission Flashcards
Why do complex organisms need a nervous system?
-cells inside body are not in direct contact with outside world
-cells live in different environments + are specialised so they need to be co ordinated to function
How do communication systems help cells function in a co ordinated way?
-keep cell activity constant and adjusts activity when needed
-signals from one group or group of cells change properties of receiving cell
What are the functions of a neuron?
-generation + transmission of elec impulses that reach specific targets
-modify activity and allows selective control of specific target structures
-elec activity modulated by integrated input from other cells (structured communication)
What is the form + size of a neuron?
-vague pyramid shape that has long extensions coming from soma
-cant store energy (glucose + 02 needs to be supplied)
Life span of a neuron?
- develop from neural stem cells
-when neurogenesis complete dead neurons not replaced
What does neurogenesis mean?
generation of neurons
Around what time is neurogenesis complete?
around 5 months after conception
What are glia cells?
provide a protected environment for neurons to survive
How do glia cells develop?
from neural stem cells
Name 3 glia cells
Astrocytes
Microglia
Oligodendroglia
What do astrocytes look like and do?
they are star shaped
-transport nutrients from blood vessels to neurons
-waste products taken away from neurons and hold neurons in place
What do microglia look like and do?
they are small and are the mobile for defensive function
- produce chemicals that aid repair of damaged neurons and digest dead neurons (phagocytosis)
What do oligodendroglia look like and do?
they are large flat branches wrapping around axons
-they contain myelin sheath
Where is the axon hillock?
where the axon meets the soma
How do we get a signal in the neuron?
in the axon there is internal space filled with chemical fluid surrounded by a thin membrane (this has holes that have gates where signal transmission occurs)
- if gate in dendrite opens and its - inside the cell, + ions will move in
-go down axon hillock and adjacent part will burst open and suck in + charge and get rid of other part in membrane
- this will release chemicals at axon terminals
How does the signal transmission work?
electro-chemical gradients
What percentage of dead neurons are there in brain development?
20-80%
Why do neurons have internal space filled with fluid?
neurons are not empty and do not exist in a vaccum (they are a thick chemical soup of electrically charged particles)
How does our body get to resting state?
What is resting potential?
The difference in ion concentrations between the inside and outside of a cell at rest
Resting potential is essential for the generation of action potentials in neurons.
What role do ion gradients play in resting potential?
They create a difference in concentration of ions across the cell membrane
Ion gradients are crucial for the electrical activity of neurons.
What happens if the membrane is non-permeable?
Electrical activity remains static
A non-permeable membrane prevents any ion movement, maintaining the resting state.
What allows ions to enter and leave the neuron?
Protein channels in the membrane
These channels are specific to certain ions, regulating their movement.
What is an example of an ion that has a concentration gradient affecting resting potential?
K+ (potassium)
The concentration of K+ is higher inside the cell compared to outside.
What forces act on K+ ions in the resting potential?
- Concentration gradient pulls K+ out
- Electrical gradient pulls K+ in
These opposing forces are crucial for maintaining the resting potential.
What would happen if the channels in the membrane acted as holes?
The membrane would depolarize, leading to no electrical activity
This would disrupt the neuron’s ability to transmit signals.
What is the function of the sodium/potassium pump?
It works against the concentration gradients to maintain resting potential
The pump actively transports Na+ out and K+ into the cell, requiring energy.
Why do neurons need energy to maintain resting potential?
Active channels work against equilibrium
Maintaining resting potential is an active process that consumes ATP.
What is the basis of electrical activity in signal transmission?
Movement of electrically charged particles (ions)
This includes the movement of both positive and negative ions across the membrane.
What are ion specific channels?
Gates that can open due to chance or response to stimulation
These channels regulate the flow of specific ions across the cell membrane.
What happens when positive ions enter a cell?
The membrane depolarises
This change in membrane potential is crucial for initiating action potentials.
What happens when negative ions enter a cell?
The membrane hyperpolarises
Hyperpolarisation makes the inside of the cell more negative compared to the outside.
What is electrotonic transmission?
Passive and graded transmission of electrical signals along the membrane
It involves electrochemical gradients that sweep ions along, but signals can decay before reaching the axon hillock.
What is the key characteristic of action potentials?
Active and not graded transmission of electrical signals
Action potentials maintain the same strength of signal regardless of distance.
How do voltage-gated membrane channels work?
They open/close in response to electrical changes at the membrane
This mechanism is crucial for the initiation and propagation of action potentials.
What is the sequence of events during membrane depolarisation?
- Membrane depolarises
- Some NA+ channels open
- NA+ ions enter cell
- Membrane depolarises, depending on threshold
- All nearby NA+ channels open
- Membrane is depolarised (more positive inside than outside)
This sequence describes the rapid changes in membrane potential that occur during the action potential.
Fill in the blank: The movement of ions across the membrane can lead to _______.
membrane depolarisation or hyperpolarisation
True or False: Electrotonic transmission is graded and can decay before reaching the axon hillock.
True
What happens to the membrane potential at the axon hillock if it remains below threshold?
Resting potential returns
The axon hillock is the part of the neuron where action potentials are initiated.
What occurs when the membrane depolarizes at the axon hillock?
NA+ channels open, resulting in action potential
This is the initial step in generating an action potential.
What must happen for an action potential to occur?
Enough + ions must arrive to reach threshold
The threshold is the critical level of depolarization needed to trigger an action potential.
What happens to the cell when NA+ enters during depolarization?
The inside of the cell becomes positive
This influx of sodium ions is crucial for the depolarization phase of the action potential.
What occurs after complete depolarization in the action potential process?
Closing of NA+ channels and opening of K+ channels
This transition helps restore the resting membrane potential.
When do K+ channels close during the action potential process?
When resting potential is restored
This typically occurs after the cell has hyperpolarized.
Where does the action potential originate?
At the axon hillock
This is the site where the decision to fire an action potential is made.
How does the action potential travel down the axon?
Each burst of depolarization acts as a trigger for adjacent sections
This sequential opening of sodium channels propagates the action potential.
Why does the action potential not travel backwards?
During hyperpolarization, the membrane is difficult to depolarize
The refractory period ensures unidirectional propagation of the action potential.
What are the properties of an action potential?
- No decay
- Either generated or not
- Minimal time between subsequent action potentials
- Speed of 1-10m/s
These properties ensure reliable and efficient signal transmission in neurons.
What is saltatory conduction?
The jumping of action potentials from node to node in myelinated axons
This process greatly increases the speed of conduction in sensory and motor neurons.
What does myelination do to axons?
Insulates the axon, preventing ion inflow and outflow
Myelination is essential for efficient nerve signal transmission.
What are nodes of Ranvier?
Gaps in myelination where action potentials are generated
These nodes facilitate the rapid propagation of action potentials along myelinated axons.
How does the nervous system code information qualitatively?
By location
Qualitative coding refers to how different types of information are represented based on where they originate in the nervous system.
How does the nervous system code information quantitatively?
By the strength of a stimulus
Quantitative coding involves measuring the intensity of a stimulus and how it affects neuronal responses.
What effect does a strong input have on a neuron’s firing rate?
Increases the likelihood of sending out action potentials (APs)
A stronger stimulus can lead to a higher frequency of action potentials in response.
Can microglia swim through the brain?
Yes
