Nervous System Part 2 Flashcards
How do neurons communicate?
Neurons communicate with identical pings (impulse) When a neuron is stimulated enough it fires an electrical impulse that zips down its axon to its neighbouring neurons. Neurons have only got one signal they can send and it only transmits at one uniform strength and speed. What varies is the frequency of pulses
How does your brain decode neural impulses?
Your brain decodes the impulses reading them like binary code organising them by location, sensation, magnitude and importance so you know the difference between turn up the thermostat and OH MY GOSH IM ON FIRE!
What is the buzz or impulse of a neuron called?
The action potential
What is the charge of your body as a whole?
The body as a whole is electrically neutral with equal amounts of positive and negative charges.
Certain areas of the body are more positively charged or negatively charged than others
What keeps the charges of the body seperate to create potential energy form their attraction?
Because opposites attract we need barriers, or membranes, to keep charges seperate until we are ready to use the energy their attraction creates
Keep em seperated to build potential
What allows charges from neurons to flow towards one another?
Neurons are like batteries with positive and negative charges but don’t do anything until an “event” which allows charges to flow towards one another
The event allows the charges to flow towards one another
In what terms can you think of neurons in?
You can think of neurons in same terms an electrician might use
- Voltage - is the measure of potential energy generated by seperated charges. In the body it is measured in millivolts (m/v)
- In a cell the difference in charge is called membrane potential
- Current - The flow of electricity from one point to another current = Voltage
Resistance
- Resistance - whatever is getting in the way of the current
Something with a high resistance is an insulator like plastic
Something with a low resistance is a conductor like metal
What do currents indicate?
Currents indicate the flow of positively or negatively charged ions across the resistance of your cells membranes
What do membranes provide?
Membranes provide the potential to convert electricity into something useful
What is a resting neuron like?
A resting neuron is like a battery just sitting there. It is more negative on the inside relative to the more positively charged space around it
What is resting membrane potential?
The difference between inside and outside charge is called resting membrane potential. Resting membrane potential sits around -70m/v
What is floating outside a resting neuron?
Outside the resting neuron there is a bunch of sodium ions floating around which are positively charged
What is inside a resting neuron?
Inside a resting neuron there are potassium ions that are positive aswell but they are mingled with bigger, negatively charged proteins
What is the overall charge of a resting neuron?
Since there are more sodium ions outside then there are potassium ions inside the neuron has an overall negative charge
What is it called when a neuron has a negative membrane potential?
When a neuron has a negative membrane potential it is said to be polarised
What is the sodium-potassium pump and what is its purpose?
Sodium-potassium pumps are proteins that stradle the membrane of the neuron and there are tonnes of them along the axon. The sodium-potassium pump transfers sodium ions and potassium ions through the cell membrane. For every 2 potassium ions it pumps into the cell it pumps out 3 sodium ions
What else is the cell membrane also riddled with?
The neuron membrane is also riddled with Ion Channels. Large proteins that provide safe passage along the membrane when their gates are open. The gates open and close for different reasons depending on their structure and purpose
What are most Ion Channels?
Most Ion Channels are Voltage-Gated Channels which open and close in response to changes in membrane potential
Which gates open only when a neurotransmitter latches onto its receptor?
Ligand-Gated Channels only open when a neurotransmitter latches onto its receptor
Which gates open due to the physical stretching of the membrane?
Mechanically-Gated Channels open in response to the physical stretching of the membrane
What happens when ion channels open?
When the ion channels open ions run in attempting to balance the gradient in charges. This movement of ions is the key to all electrical events in neurons - it is the force behind everything we think, do and feel.
What is graded potential?
Small changes in movements of ions can cause a slight local change in charge in the membrane called graded potential
What do you need to send messages from neuron to neuron?
To send messages you need a big enough transfer in ions to activate voltage-gated channels, this is called action potential
What initiates the process of increasing the charge of a neuron?
Some environmental stimulus occurs (ie spider brushes against skin) triggering those sodium channels to open up allowing positively charged sodium ions to flow in increasing the charge inside the membrane
What is the threshold a neuron charge must pass for true action potential to kick in?
The stimulus and resulting change in charge have to be strong enough to cross a threshold for the true action potential to kick in - this threshold is about -55m/v
What happens when the charge of a neuron reaches the all or none phenomenon threshold?
At the threshold the voltage gates open letting in all the positively charged sodium ions drastically changing the charge of the neuron up to about +40m/v “Action Potential in Action”
This is called Peak Depolarisation
What does the action potential kick off?
An action potential kicks off a biological chain reaction which sends that electrical signal down the axon. Each neuron has lots of voltage gates which are triggered by neighbouring neurons becoming positive
What is Repolarisation?
Repolarisation is the process of a neuron losing its positive charge. The sodium voltage-gates close and the potassium channels open allowing potassium ions to flow out of the neuron
What is hyperpolarisation?
Hyperpolarisation is the stage when a neuron is losing charge an it ends up at a lower charge than its resting state. Usually about -75mv
At this stage all gates close and the sodium-potassium pumps kick back in to return the charge to resting state - 70mv
What affects an action potentials speed the most?
The factor that affects the speed of an action potential the most is whether or not there is a myelin sheath on the axon.
In the PNS those myelin sheaths are formed by Schwann cells wrapping themselves around the axon. These cells don’t actually touch so all along the axon you’ll see little gaps in between the myelin sheath called the Nodes of Ranvier
The leaping from node to node is Saltatory Conduction
