Lecture 1 - How does the brain work? Excitability of membrane: resting & action potential Flashcards
How complex is the human brain connectome?
100 billion neurons; 10^15 synapses
What are the 3 different functions of neurons?
Sense changes in environment (sensory)
Communicate changes to other neurons (interneurons)
Command body’s responses to sensations (motor)
What is the function of glia?
Insulate, support and nourish neurons
What are neurites?
Axons and dendrites
Soma/cell body/perikaryon:
~__ ___ diameter
__-rich cytosol
contains organelles
~20 μm diameter
K+-rich cytosol
contains organelles
Vesicles enclose materials for transport from soma to terminals
- on ______/______ along microtubule “_____”
- ___-dependent process
___________: from soma to terminal, use ______
___________: from terminal to soma, use ______
Vesicles enclose materials for transport from soma to terminals
- on kinesin/dynein along microtubule “tracks”
- ATP-dependent process
Anterograde: from soma to terminal, use kinesin
Retrograde: from terminal to soma, use dynein
Axon Terminal
* also called terminal ______
* site axon contacts another neuron
* point of contact called ______
* terminal _____ - axon form many branches
* ___________: when neuron makes synaptic contact
Axon Terminal
* also called terminal bouton (“button”)
* site axon contacts another neuron
* point of contact called synapse
* terminal arbor - axon form many branches
* innervation: when neuron makes synaptic contact
Axon Terminal
*terminal cytoplasm different:
- ___________ do not extend into terminal
- numerous _______ _______ (50 nm across)
- dense _______ covering at membrane facing synapse
- numerous ____________
Axon Terminal
*terminal cytoplasm different:
- microtubules do not extend into terminal
- numerous synaptic vesicles (50 nm across)
- dense protein covering at membrane facing synapse
- numerous mitochondria
Dendritic spine
* receive some ________ ______
* hang from dendrite
* consist of _____ and ______ ____
Dendritic spine
* receive some synaptic inputs
* hang from dendrite
* consist of stalk and spine head
What forms the chemical signal in the synapse?
Neurotransmitters (stored in synaptic vesicles)
What is the site for nerve gas and psychoactive drugs?
The synapse
What is the transformation of information from pre-synaptic to post-synaptic neuron?
electrical to chemical to electrical
Concepts of Brain Function
The Brain as a LUMP of wet clay?
L: Localisation or distribution of function
U: Use It or Lose It
M: Magnification
P: Plasticity
Long-term potentiation
What is Hebb’s postulate on plasticity?
Neurons that fire together, wire together
What are the mechanisms underlying the formation of LTP?
Glutamatergic excitory synapse
Addition of postsynaptic AMPA receptors
Enlargement or maturation of spines after LTP
What is the posterior hippocampus known for?
Episodic memory, spatial information
What is the Vm (membrane potential) in a neuron and in a skeletal muscle?
In neuron
Vm = -65mV
In skeletal muscle
Vm = -80 mV
What are the characteristics of an action potential?
- also called spike, nerve pulse or discharge
- generated by a cell is similar in size and duration
- does not diminish down axon
- code: frequency and pattern
- lasts 2 msec
What are sensory receptors?
Specialised structures - contain ion channels that are involved in generating electrical signals to be decoded as specific sensations
The nervous system has to ______, _________ and _______ information
The nervous system has to collect, distribute and integrate information
Axon
* not like a telephone copper wire
* MORE like a ______ _______ _____
Passive electrical currents
* do not conduct very ___
* ____ out
Action Potentials
* do not diminish over _______
* fixed in ____
Excitable membrane
* capable of generating &
conducting APs
Axon
* not like a telephone copper wire
* MORE like a leaky garden hose
Passive electrical currents
* do not conduct very far
* leak out
Action Potentials
* do not diminish over distance
* fixed in size
Excitable membrane
* capable of generating &
conducting APs
What are the 3 main players affecting resting membrane potential?
Salts
Membrane
Channels and pumps
Ion Channels
* _____membrane
* require - subunits to form _______ pore
* important property specified by ________ of pore & pore ______
Ion Channels
* transmembrane
* require 4-6 subunits to form aqueous pore
* important property (ion selectivity, gating) specified by diameter of pore & pore lining
sodium-potassium pump
Na+/K+ ATPase
*breaks down ___ in the presence of ___
•expends ___% of total ATP used by brain
sodium-potassium pump
Na+/K+ ATPase
*breaks down ATP in the presence of Na+
•expends 70% of total ATP used by brain
What are ion transporters responsible for?
Generating concentration difference of ions
What are ion channels responsible for?
Generating electrical signals
What does amount of current flow depend on?
Electrical potential (V, volts)
Electrical conductance, g (S, siemen) = 1/R
What does equilibrium potential, Eion, depend on?
The ratio of concentration of ions in the outside vs inside of the cell (Nernst equation)
How is the resting potential determined?
Goldman-Hodgkin-Katz equation
Resting potential is determined predominantly by K+ permeability, but is also influenced by Na+ and Cl- permeabilities
What is the voltage clamp method used for?
Recording currents at specific voltages
Generation of multiple APs
* depolarise just to __________ - rate is ~ 1 hertz (1 per sec)
* higher ______________
- frequency _________, say to ___ Hz or _____ Hz (max)
- once an AP is initiated, impossible to initiate another for about _ ___ (_________ refractory period)
- ________ refractory period: after refractory period difficult to initiate another action potential
Generation of multiple APs
* depolarise just to threshold - rate is ~ 1 hertz (1 per sec)
* higher depolarisation
- frequency increases, say to 50 Hz or 1000 Hz (max)
- once an AP is initiated, impossible to initiate another for about 1 msec (absolute refractory period)
- relative refractory period: after refractory period difficult to initiate another action potential
