The Nervous System Part 3 Flashcards
What is a 1000 times thinner than paper and more numerous in you than grains of sand on a beach?
The Synapse. The meeting point between two neurons. The neurons strength and purpose lies in their connections. Synapse comes from the greek for clasp or join.
How many neurons does a human brain have?
The human brain has over 100 billion neurons
How many synapses does your brain have?
Each neuron has 1,000 to 10,000 synapses so your brain has between 100 and 1000 trillion synapses
In simple terms explain a synapse’s role in an action potentials journey
An action potential travels down an axon and hits a synapse that converts it into a different type of signal and flings it over to another neuron
What do synapses allow us to do?
Synapses are able to change and adapt in response to neuron firing patterns which allows us to learn and remember
What are the two main ways nerve cells communicate?
Electrical - Much more abundant in embryonic nervous tissue where they help guide neural development (The group texts) and Chemical - Used more often than electrical, messages are more controlled and personal
How do nerve cells send electrical messages?
Electrical synapses send an ion directly from the cytoplasm of one nerve cell to another through small junctures called gap junctions. This action potential in one neuron creates an action potential in the other cells across the synapse. This message is super fast as it is never converted
Where are electrical messages important?
Electrical synapses and messages are important in autonomic functions where it is important for muscles to be triggered in synchrony ie muscle cells of the heart
What do nerve cells use to send chemical messages throughout the nervous system?
These messages use neurotransmitters or chemical signals which defuse across a synaptic gap in order to deliver their message
What is the main advantage of chemical messages over electrical?
The main advantage chemical synapses have over electrical is they can effectively convert the message in steps from electrical to chemical back to electrical which allows for different ways to control that impulse
What can the long term translation of messages in chemical synapses be the result of?
Potentiation, or the strengthening of a synapse through classic conditioning Habituation or when a synapse decreases its response to a common stimulus Sensitisation, when a reaction to one stimulus causes other synapses to be more sensitive to reactions
What is the cell sending the action potential referred to as?
The presynaptic neuron
What does a neuron transmit an action potential through?
The presynaptic terminal (usually an axon terminal). There terminals are filled with tiny synaptic vesicles (sacks) each filled with 1000s of molecules of a given neurotransmitter
What is a cell that receives an action potential referred to as?
The postsynaptic neuron. It accepts the neurotransmitters in its receptor region (usually on the dendrite)
Do neurons touch?
Negatory. Neurons do not touch there is a small gap between synapses and receptro regions, this is called the synaptic cleft and it is less than 5 millionths of a cm apart
When an action potential races along an axon activating the sodium and potassium channel in a wave, what occurs when it reaches the presynaptic terminal?
When an action potential reaches a presynaptic terminal it activates the voltage-gated calcium channels (Ca2) opening them and releasing calcium ions into the neuron’s cytoplasm
What does the flow of positevly charged calcium ions into a neruons cytoplasm cause in a presynaptic terminal?
This flow of positively charged ions causes all the tiny synaptic vesicles to fuse with cell membrane and purge their chemical messengers
What do neurotransmitters released from a presynaptic terminal act as?
These neurotransmitters act like couriers defusing across the synaptic cleft and binding to receptor sites on the post synaptic neuron
Once a presynaptic neuron has successfully converted an electrical impulse to a chemical message and diffused it across the synaptic cleft utilising neurotransmitters what needs to happen in order for the message to continue traveling throughout the nervous system?
It needs to be converted back to electrical. This conversion back occurs once a neurotransmitter binds to a receptor because thats what causes the ion channels to open
What do neurotransmitters tell neurons?
The neurotransmitter tells the neuron what to do. Depending on which particular neurotransmitter binds to which receptro the neuron might either get excited or inhibited
What are Excitatory Neurotransmitters?
Excitatory Post-Synaptic Potentials (EPSPs):
Graded potentials that push the neuron closer to threshold and make an action potential more likely to fire
They depolarise the post synaptic neuron by making it’s inside more positive bringing it closer to threshold
What are Inhibitory Neurotransmitters?
Inhibitory Post-Synaptic Potentials(IPSPs)
Graded potentials that push the neuron further from the threshold which makes an action potential harder to achieve
They hyperpolarise the postsynaptic neuron making it’s inside more negative
What does the likelihood of a postsynaptic neuron developing an action potential depend on?
Any region of a single neuron might have 100s of synapses each with different excitatory or inhibitory neurotransmitters. The likelihood of the postsynaptic neuron developing an action potential depends on the sum of all the excitations and inhibitions in that area
How many naturally occurring neurotransmitters do we have?
We have over 100 naturally occurring neurotransmitters
What happens to neurotransmitters once they are binded to a receptor?
Neurotransmitters only stay bonded to receptros for a few milliseconds then either degrade or get recycled. Some kinds of neurotransmitters get reabsorbed by the presynaptic neuron in a process called reuptake. Others are broken down by enzymes in the synaptic cleft or sent away by diffusion
How do psychoactive drugs work?
Psychoactive drugs excite or inhibit the production of neurotransmitters or mimic neurotransmitters
Which 3 neurotransmitters does cocaine target?
Serotonin, Dopamine and Norepinephrine
What are the basic properties of serotonin?
Serotonin
Mainly inhibitory - plays role in regulating mood, apetite, circadian rhythm and sleep
Some antidepressants help stabalise mood by stabalising serotonin levels
What are the basic properties of dopamine?
Dopamine
Released when you hug a loved one, have great sex or eat a kick ass donut
Influences emotion and attention mostly makes you feel awesome
What are the basic properties of norepinephrine?
Norepinephrine
Amps you up by triggering your fight or flight response
Increases heart rate and primes muscles to engage
Under supply depresses normal mood
How does cocaine work?
Cocaine blocks the reuptake of neurotransmitters by blocking channels of presynaptic neurons. This allows these powerful chemicals to float around and accumulate
What happens to your neurons after using cocaine?
Because you have a limited supply of serotonin, dopamine and norepinephrine, and they take time to replenish, the depletion of chemicals eventually leaves you feeling terrible in a number of ways. Feeling sick, anxious, aggressive, upset, tired and weak etc.
Prolonged use may cause the brain to adapt as all your receptors remember how great those chemicals feel. Over time you start to lose receptors
