Wk 4 - Neurons Flashcards
What are neuron’s and what are there basic functions
- The basic functional cell units of the nervous system (CNS and PNS).
- Take info from one neuron (reception) then passes this to another neuron (transmission).
- Very simple cells, but connections are what makes it complex.
- There is estimated to be 100 Billion neurons in the brain.
What are glial cells and their functions? Name one type of glial cell and what it does.
- Glial cells nourish, protect and support neuron’s. They are critical for brain development.
- One type = Oligodendrocyte. Covers the axons of neurons with myelin.
Name the four basic parts of a neuron and what do they do (visualise in the mind)
- Dendrites: Take information and send to the Soma.
- Soma (Cell body): Controls metabolic maintenance of the cell. Collates (def: assembles in proper order) information from the other cells.
- Axons: Carries messages to other cells.
- Terminal Buttons. (or axon button): Secretes neurotransmitters at the end of axon. Affects the activity of other cells (passes it along).
What is the connection between neurons called?
- Neurons don’t touch. The gap between them is called a synapse or synaptic cleft.
What are the names of neurons that connect?
- The neuron before the synapse connecting by the terminal buttons is called the presynaptic neuron and the neuron connecting after the synapse connecting by the dendrites is called the postsynaptic neuron.
What is the cell membrane or “skin” of the neuron called and what are its characteristics
The lipid bilayer.
- It is comprised of two layers of fatty molecules.
- Nothing can cross lipid bilayer so it has channels created by proteins that open and close.
- At rest these channels are closed to prevent the interchange between the intracellular and extracellular materials.
Describe the process which allows neurons to send electrical currents and thus information
- This process is called action potential
-The action potential process happens when the channels in the lipid bilayer open and allow..
What is resting membrane potential (RMP)? What is there more of outside than inside
- It is the difference in chemical composition inside and outside the cell at rest.
- Result of relative concentrations of Potassium ions (K+), Chloride ions (Cl-) negatively charged protein ions and sodium ions (Na+)
- It is approximately equal to -70mV (between -50mV to -80mV)
What is action potential (A.P)?
- Reversal in charge of a resting neuron.
- Triggered by exchange of the ions across the neuron membrane.
- Action potential is created when the neuron membrane is sufficiently depolarised (the RMP moves toward 0mV)
- When the depolarisation reaches the threshold of about -55mV, the neuron fires an action potential.
- Does not happen if it doesn’t to reach this critical threshold level.
- The action potential will fire if this threshold is reached. The size of the action potential is always the same for all neutrons.
- Can’t be a little bot pregnant. Either you are or you aren’t.
What are the three stages of the action potential?
- Depolarisation
- Repolarisation
- Hyperpolarisation
What happens during the action potential?
- The sodium channels open. The sodium ions enter the neuron, reversing the membrane potential. (depolarisation).
- Potassium channels open. Potassium ions leave, restoring membrane potential. (repolarisation).
- Ion transporters pump the sodium and potassium ions back to their original locations.
What determines the speed of propagation of the action potential
The diameter of the axon and the presence or absence of a myelin sheath.
- Neurons with a greater diameter fire faster.
What is the myelin sheath why is it there?
- It is an electric insulator.
- An electric current can only flow in the breaks between the myelin i.e. the Nodes of Ranvier
- Sodium channels are concentrated in the Nodes of Ranvier (action potential can only be generated in these gaps.
- These breaks in the axon creates a jumping effect between each Node of Ranvier which massively increases the speed of the action potential.
- non-Myelinated axons are much slower as the action potential is generated repeatedly across the whole of length of the axon.
Describe the process of synaptic transmission
Stage 1: Before action potential arrives, neurotransmitters are stored in vesicles inside the terminal button.
Stage 2: The action potential triggers release of neurotransmitters into the synaptic cleft.
Stage 3: neurotransmitters spread out across the synaptic cleft. Some attach to receptor molecules in the post synaptic membrane and activate them.
- This either inhibits or enables the postsynaptic neuron to generate an action potential.
What are neurotransmitters and their different types
- Neurotransmitter = chemical substances which carry signals across the synaptic cleft that then bind to receptors on the postsynaptic neuron.
- If a neurotransmitter binds with a receptor and depolarises the membrane, it is excitatory. increasing the likelihood that the postsynaptic neuron will fire an action potential.
- If the neurotransmitter’s binding hyperpolarises the membrane, it is inhibitory and makes the receiving neuron less likely to fire an action potential.
What receives neurotransmitters and what are they.
- Receptors = specialised protein molecules.
- The binding of neurotransmitters to receptors causes ion channels to open.
- This changes the membrane potential affecting the probability that the neuron will fire an action potential.
