Lecture 3 Flashcards
ventricles
go all the way through the CNS - contain cerebrospinal fluid (CSF) - CSF bathes and cushions brain - CSF produced from cells that line ventricles - prevents damage - pedicured all the time - replaced 3-4 times a day gets into extracellular volume around cells and contains lots of sodium
blood supply
- brain needs lots of energy
- has specialised bloody supply
- stroke-blocked cerebral blood vessels starve the area fed by that vessel
- 20% of our energy is used to fuel the brain
incredible dense blood supply
exploring the brain
as a whole, the nervous system takes inputs (senses) and performs computations and generates outputs (behaviours)
different parts of N.S perform different functions but are interconnected
parts of neurone
dendrites: receive input from neurone
cell body/soma: integrates information
neurone makes decision at axon hiluc
to do something, need axon potential along axon
axon terminal releases neurotransmitters to form output
myelin sheath increases speed of action potential
- neurones have soma, axons and dendrites
- neurones transmit info electrically and chemically
astrocytes
- support functions
- touch blood vessels
- consume neurotransmitters
- modify neuronal function
oligodendrocytes
- make myelin
- wrap myelin around axons
- helps action potentials go fast
microglia
- immune cell
- survey brain for any infections
- blood brain barrier
electricity
- electrical currents are flows of charged particles (electrons)
- like charges repel, opposite charges attract
- currents only flow through materials that conduct electricity
- voltage is a measure of how much potential there is for charge to move - how much stored electrical energy
Ohm’s Law
current = potential x conductance
current -> charge per second or amps
potential -> volts
current = potential / resistance
conduction in nerves
Hermann von Helmholtz 1849
- measured speed of nerve conduction by stimulating frog sciatic nerve and measuring time to constrict muscle
- nerve conduction is slower than in a wire
current flows down nerves as a wave of charge movement
wave of current down axon= action potential
how do cells signal electrically?
- movement of ions
- electrically charged particles
- e.g. NaCl (Na+ and Cl-)
- different sized particles
some ion flux (flow) happens at rest - this sets the neurone up to be ready to send an electrical signal
- some ion flux happens during signalling
resting potential
cells aren’t surrounded by a lipid membrane
- water soluble things can’t pass through
- hydrophilic heads and hydrophobic tails
concentration gradients
outside the membrane:
Na+ / Cl- / bit of Ca2+
inside the membrane:
proteins (negative) / k+
HOLES IN MEMBRANE = ION CHANNELS
k+ channel only lets k+ through
- more k+ ions on inside of cell than outside so this creates a conc gradient
electrical gradient: now inside negative relative to more positive outside
this stops more k+ leaving the cell
electrochemical gradient
inside of cell now more negative
- K+ start to get attracted outside
results in equilibrium as there is no net ion movement
equilibrium potential:
potential across membrane at which there is no net flow of an ion
- equilibrium potential (E) dictated by concentration difference and ion charge
the resting membrane potential of neurones is near to the equilibrium potential for K+
this is because at rest the membrane is more permeable to potassium than any other ions so more k+ channels open
equilibrium potentials
E k+ = -80mV
E Na+ = +62mV
A- ions and K+ ions have higher concentration inside the axon relative to outside
whereas Cl- ions and Na+ ions are more concentrated outside axon
