introduction to neuroscience 1

The nervous system as many levels of organisations

• whole brain

  • population/cicit (e.g like a network)

• Sub neuron

  • neuron (can be interconnected)

Central nervous sytem

-brain & spinal cord

Peripheral nervous system (all the nerves that stand out)

Neurons: electrically excitable cells - fundamental building blocks in the nervous system.

Central nervous sytem (lots of interactive units)

4 criteria for classifying neurons

• morphology

• physiology

• mocular/gene expression

• connectivity

Dendrites → receive synaptic input from the axon terminals

the cell body/soma → responsible for protein synthesis and the imitation of electrical impulses

axon→ send output signals other neurones.

Biological systems don’t send signals as efficiently as wires

Nerons (myelin have nodes of ranvier → the signal is regenerated) its getting boosted so it can travel further distances )

Synapses: releases nurons transmitters(causes electrical signals to be created )

86B neurons in the human brain

Gilian cells : supporting the neruo signalling (don’t generally signal electrical signals (glue thatr keeps everything together

3 types of support cells

• astrocytes (formation of blood brain barrier

• oligodendrocytes

• Schwann cells

TERMINOLOGY

superior (above). anterior(in front of)

inferior (below). posterior(behind)

sagittal (through the body midline)

coronal (frontal)

horizontal (axial)

cerebral cortex → is extensively folded, forming ridges called gyri

GRAY MATTER → cell bodies

WHITE MATTER → Myelinated axons

F-P-O-T

Frontal:

parietal

occipital

temporal

TURTORIAL

brain basics ( 2 min nuro science )→ YouTube video

frontal lobe—> important for exitcuting functions and motot control e.g speech production

parital lobe→ samotosenosry (touch) processing and attention

temporal lobe → important for memory, hearing, speech comprehension (understanding what someone is saying & facial recognition

occiptial → important for vison

Gyrus: folded of cortex on the surface

Sulcus: dives gyri from one another

Central sulcus : divides the fontal lobe and the partital lobe

supiror→ referring to the gyris (of the brain)

dorsal = sensory

ventral → telling your muscles to move (motor)

Pre central Gyrus: controls voluntary movement on the opposite side of the body

Post central gyrus: responsible for proprioception( samatosensory cortex

L2: electrical signals of nerve cells

There is more K+ within a cell rather than outside (K+)in >(k+) out

What governs the equilibrium state

—> diffusion and electromagnetic “forces”

Diffusion: drives concentration gradients using the widest channels available

→ only let throughs either grey or black stuff (black=wide,grey=narrow)

Elctromegnetism :little elements that carry charge (can be either postive or negative

→ some postive charges can make it out of the outside but will make it back within the inside

Flux:concentration of things passing through

The stronger the force is the more it gonna overwhnelm it

Initially (V=0) V in &out= -58MV

Active signaling → when the neuron increases

Active transporters → actively move selected ins against concentration gradient (happens within the cel =uses energy)

Ion channels→ allows ions to diffuse down concentration gradient

When solutes don’t have any physical barriers they are evenly distributed through diffusion

→ equilibrium is reached when the concentration of each ion is evenly distributed

Neurons are surrounded by a plasma membrane = this is impermeable to ions

• The hydrophobic interior of the bilayer prevents the movement of ions across the membrane (can only pass through specialized channels

The action poteinal is divided into 6 phases

-resting potential ( threshold)

-rising phase( depolarization)

-overshoot phase ( Peak)

-falling phase ( repolrisation)

-undershoot phase ( Hyperpolarization)

-recovery phase

Membrane potential: refers to the difference in electrical charge in the outside and inside of a neuronThe voltage clamp method

→ the increased activation of the sodium conductance with depolarization causes the regenerative rise of the action poteinal at voltages more postive than threshold

(This technique controls or clamps the voltage across the membrane_

• If VM is not equal to VC the compartoar generates a different signal

• TTX(toxin found in puffer fish)→ block sodium channels

-The voltage clamp allows us to examine current across the membrane at a fixed membrane potential

(Current flow can tell us about membrane permeability

Voltage clamp allows us to examine across the membrane at a fixed membrane potential

Early transient inward → NA+

Late delayed outwards → K+

Conductance → A function of membrane potentials and time

→ when a neuron is at rest the sodium ions and chloride ions are more prevalent

Sodium potassium pump:a protein that uses energy constantly to pump 3 sodium ions

The action potential: Occurs when the cell’s membrane potential reaches threshold

Impulse conduction in axons

Active potential conduction reunites both azctive and passive current flow (the amplitude of the action potential is constant along the length of the axon)

Propagation is called saltatory→ meaning that the action potential appears to jump from node to node

Towards 0=depolarization

Myleination increases the speed that action potential propagate

Diameter increases speed as well but meliantion is better

WEEK 4

Ion Channels and Transporters

Patch clamp method →suctioned on to a patch,the technique can be used to compare the response characteristics of different channels

• the conductivity to sodium has increased and has allowed sodium to pump into the cell

• With multiple sodium ions it gradually reaches a peak and geradully reaches decay

The sodium gate opens then quickly gets decactivated, this is distinguished from deactivation

Voltage clamp→ Just put electrons inside and outside Single channel currents: depolarization triggers brief Na+ currents

Inactivation: channels open in first 1-2ms,then inactivate

Stochastic behavior: individual channel behavior varies

Microscopic + macroscopic:single-channel and whole-cell currents show similar time courses (macroscopic looks like the average of many microscopic)

Voltage dependence: higher depolarization increases Na+ channel opening probability

( If the channels opended they have high conductance if the channels are closed they have low conductance)

Na+ = sodium

K+ = Potassium

Resting (hypolarized) - both Na+ and K+ channels closed

Activation(depolarization) - Na+ channels open first followed by K+

Inactivation - Na+ channels inactivate with prolonged deprolaization,many K+ channels remain open

STRUCTURE OF A SIMPLE BACTERIA K+ CHANNEL

Subunit structure→ two membrane spanning domains and a pore loop

Channel architecture → four subunits form the channel ; top view shows k+ ion in pore

Permeation pathway → large awe out cavity leads to a narrow selectivity filter

Ion selectivity → negative charges guide K+ ions through the filter after dehydration

Structure of a mannalian voltage-gated K+ channel

Subunit structure → four subunits,each with a transmembrane and T1 domain ; B subunits attached

Channel architecture → separate voltage-sensing and K+ conducting pore domains

Voltage -dependent Gating → depolarization moves voltage sensors up,pulling linker to open pore ; hyper polarization moves sensor down,closing pore

Voltage Sensor movement → Paddle-like sensor shifts outwards with deprolarization,inward with hyperolarizatoion

TYPES OF VOLTAGE-GATED ION CHANNELS

Na+,Ca2+,K+,CI- Channels: selectively permeable to specific ions

Sturucture: multiple transmembrane domains form pores

Selectively filter : Determiens which ions pass through

Voltage sensing & gating : Controls channel opening/closing based on membrane potential

Channel similaties: Na+,Ca2+ and K+ channels share structural features

K,2,1: LIttle inactivation,involved in action potential repolarization

K,4,1: Inactivate during depolarization

HERG: Inactivates rapidly, current flows at depolarization end

Inward Rectifiers: Preferentially conduct k+ at hyperpolized potentials

2-P: respond to chemical signals not voltage

Calcium activated: open in response to intracellular Ca 2+

LIGAND-GATED ION CHANNELS

Nurerotransmitter-gated : activated by extra cellular glutamate

Proton-gated : activated by intracellular Ca2+

Cyclic Nucleotide-Gated: activated by cAMP or cGMP(these are intrcellular)

Thermosenentive = sensitive to heat

Mechnosenesitve = sensitive to pressure

Ion movements due to the Na+ pump

1. Normal pump in action

2. Breaking the pump by removingg K

3. Fixing the pump by replacing K

4. Break the pump by blocking ATP

5. Fix the pump by recovering ATP

Examples of ion exchangers

Energy source : Use electrochemical gradients of co-transported ions

Antiporters: swap ions across the memrbrane (A,B)

Co-transporters: Move multiple ions on the same direction

Tutorial (resting membrane potential)

What is the voltage /ectrical potenial differenace

→ the amount of energy needed to move a charge form one point to another in an electric Al field

What gives rise to the resting membrane poetical

-< different concentrations of ions and outside the neurons

How are the intracellular and extracellular ions distributed across the membrane?

Potassium is high inside the cell and low outside the cell

Sodium is low inside the cell and high outside the cell

What happens to the resting membrane potential if the concentration of K+ outside the neuron is raised

→ Whenr the external concentration K+ is raised high enough to equal the interaml concentration of K+ the K+ ewualibrium potential becomes omV and the resting membrane potential is also omV

Describe the electrical properties of a nerve cell= they are relatively poor conductors of electricity