13.2 Nervous System Flashcards
Neurobiological reserach on nervous system made on…
Giant squid (axon up to 1mm in diameter)
The function of the nervous system is to?
Produce behaviour
3 tasks performed by nervous system?
- Detection and analysis of sensory signals
- Decision making
- Generation of coordinated motor output
Nervous system in…
A) Sea anemone?
B) Earthworm + squid?
C) Human?
A) Nerve net
B) Ganglia + nerves
C) CNS + PNS
Nervous systems consist of nerve cells and….
Glia (electrical isolation or nerve cells + blood-brain barrier + uptake of transmitter)
Role of neurons?
Generate and transmit electrical signals
Role of glial cells?
Provide nutrients, oxygen, maintain extracellular environment, make the bloodbrain barrier, fight infections, insulate neurons
Which is more present - neurons or glial cells?
Glial cells (5-10x)
How do neurons work?
Electrochemically
What prevents the free movement of ions?
Lipid biulayer
What control the ion flux across the membrane?
Ion channels and ion transporter proteins
Typical ion concentration - intracellular?
A lot of K+, a medium amount of Na+, a bit of Cl-, a lot of A-
Typical ion concentration - extracellular?
Little K+, lots of Na+, lots of Cl-, no A-
What is the membrane potential?
The electrical potential difference across membrane
What is the resting potential?
-65 mV
The interaction of …. determines membrane potential
Two forces
- Diffusion: favours net movement of ions down their concentration gradient (intra–>extracellular)
- Electromagnetic force: favours net movement of ions according to potential difference (extra–>intracellular)
What is equilibrium potential?
When the diffusion force and the electromagnetic force are balanced for a given ion
What ion shows sizable leak current at rest?
K+
Resting membrane potential is dominated by ….. equilibrium potential
K+
What happens when channels open?
Ions follow their electrochemical gradient, which moves the membrane potential towards the equilibrium potential of that ion
How are ion channels gated?
- Voltage-gated
- Mechanically-gated
- Chemically-gated
Use of energy by ion channels?
None
At resting potential - what happens to voltage-gated Na+ channels?
They are closed
When membrane is depolarized, what happens to voltage-gated Na+ channels?
They open
What happens during the depolarization phase?
Na+ flows into the cell
What happens during the repolarization phase?
K+ flows out of the cell
What happens when threshold level of depolarization reached at - 50mv?
Depolarization becomes regenerative: action potential
What happens after repolarization?
Membrane is briefly hyperpolarized, but then returns to resting potential with only K+ leak channels open
The ion flux during a single spike …….. the concentration gradients.
Barely changes. (Neurons can fire many spikes before concentration gradients are lost)
How are cocnentration gradients of ions maintained in the long run?
By active (energetically expensive) processes - Na+/K+ pump moves 3 Na+ out for every 2 K+ it moves in - requires ATP
Action potentials are …… events
- All-or-none events - they do not decay with distance along the axon (they get “regenerated” along the axon)
What are graded potential?
- Strength and temporal pattern of input determines membrane potential
- Decays with distance along nerve fiber
- Only works over short distances
.
.
