Chapter 6- Neurons And Synapses Flashcards
What are the two systems in the body that are used for internal communication ?
Endocrine system
Nervous system
What does the endocrine system consist of?
Glands that release hormones
What does the nervous system consist of?
Nerve cells called neurons
Explain the parts of a neuron
1) have a cell body with cytoplasm and a nucleus
2) dendrites
3) axons
4) skeletal muscle
What are the functions of dendrites?
Short branches nerve fibres, used to transmit impulses between neurone in one part of the brain or spinal cord
What are axons? /functions
Are elongated nerve fibres, they transmit impulses from tips of toes or the fingers to the spinal cord
What does the myelination of nerve fibres allow for?
Saltatory conduction
What is saltatory conduction?
There is gap between the myelin deposited by adjacent Schwann cells and these are called the node of ranvier- in myelinated nerve fibres the nerve impulse can jump from one node of ranvier to the next
Why do neurons pump sodium and potassium ions across there membranes?
To generate a resting potential
What is a resting potential
A neuron that is not transmitting a signal has a potential difference or voltage across its membrane that is called a resting potential
What is the resting potential due to?
An imbalance of positive and negative charges across the membrane
explain the process of a resting potential
1) sodium potassium pumps transfer (Na+) and potassium (K+) ions across the membrane - sodium pumped in, potassium pumped out- number of ions pumped are unequal 3:2
2) membrane is 50 times more permeable to potassium so it leaks back in quicker then sodium and the result is a concentration gradient steeper than the potassium gradient
What does an action potential consist of?
Depolarisation and repolarisation of the neuron
What is an action potential?
An action potential is a rapid change in membrane potential, consisting of two phases-
1) depolarisation- a change from negative to positive
2) repolarisation- opposite
What is depolarisation due to in an action potential due to?
Is due to the opening of sodium channels in the membrane allowing sodium ions to diffuse into the neuron down the concentration gradient- reverses the charge imbalance
What is repolarisation due to in an action potential due to?
Happens rapidly after repolarisation and is due to the closing of sodium channels and opening of potassium channels - this allows potassium to diffuse out of the neuron- which makes inside of cell negative again and make sit go back to resting potential
What is a nerve impulse?
Is an action potential that starts at one end of a neuron and is then propagated along the axon to the other end of a neuron
How does the propagation of thre action potential begin?
Because the ion movements that depolarise one part of the neuron triggers depolarisation in the neighbouring part of the neuron
Why do nerve impulses only happen in one direction in humans?
Because an impulse can only be initiated at one terminal of a neuron and can only be passed on to another neuron or deifferent cell types at the other terminal
What is the propagation of an action potential due to?
Movement of sodium ions - leads to reduced sodium conc outside axon and increased inside- the depolarised part of the axon therefore has different sodium ion concentrations to the neighbouring part of the axon that has not yet depolarised - result is sodium ions diffuse between these regions both inside and out
What do local currents do?
Reduce the concentration gradient in the part of the neuron that has not yet been depolarised - makes resting potentials rise - Sodium gates are voltage- gated and open when a membrane potential of -50mV has been reached (resting is -70mV) - opening of sodium gates causes depolarisation
What are synapses?
Junctions between neurons and between neurons and receptors or effector cells
What is a neurotransmitter?
Chemicals that are used to send signals across synapses
What happens when pre-synaptic neurons are depolarised X?
They release a neurotransmitter into the synapse
Explain the 9 step synaptic transmission
1) nerve impulse is propagated along pre-synaptic neuron until it reaches end of the neuron
2) depolarisation of pre-synaptic membrane causes calcium ions to diffuse through channels into neuron
3) influx of calcium causes vesicles containing neurotransmitter to move to the pre-synaptic membrane and fuse with it
4) neurotransmitter is released by exocytosis
5) neurotransmitter diffuses along synapse and binds to receptors on post synoatic membrane
6) binding of neurotransmitter causes adjacent sodium ions channels to open
7) sodium ions diffuse down conc gradient
8) action potential is triggered in post synoatic membrane
9) neurotransmitter is rapidly broken Down
8
What is acetylcholine ?
Is used as the neurotransmitter in many synapses
When is a nerve impulse only initiated?
If the threshold potential is reached
Why is an actio potential only initiated if the threshold potential is reached?
Because only at this potential do voltage gated sodium Open, causing depolarisation
What do neutrons do?
Transmit electrical impulses
