Neural Transmission Flashcards
Describe the structure of multipolar neuron.
*Cell body (soma) - nucleus and metabolic apparatus.
* A semi-permeable cell membrane encases the neuron.
On the axon this is known as the axon membrane.
* Dendrites receive information.
* Axon hillock
* Axon: conduction of electrical activity.
* Axon Terminals: vesicles filled with neurotransmitter (NT).
* Myelinated (glial cells)& unmyelinated axons
* The axons make up nerves in the PNS and tracts in CNS.
What is an ion?
Is an atom or group of atoms with a positive or negative charge.
- inside cellular membranes (intracellular fluid) or outside the cells (extracellular fluid).
- Charged ions
- Uneven concentration of ions when a neuron is at rest (polarised)
- The ions in the intracellular and extracellular fluid of a neuron are:
– potassium (K+) sodium (Na+)
– chloride (Cl-) large protein molecules (A-).
What is the resting potential?
Is the difference in potential (voltage) between the inside and the outside of the neuron.
* inside of the neuron is negatively charged relative to the outside of the neuron.
* The normal resting membrane potential inside cells is around -70mV.
* the resting potential or membrane potential.
* a neuron is polarized.
* axon membrane is selectively permeable.
* potassium (K+), sodium (Na+), chloride (Cl-), large protein molecules (A-)
- permeability to potassium (K+) chloride ions (Cl-)
- sodium (Na+) ions.
- distribution of ions normally.
1. ions tend to move from areas of high concentration to areas of low concentration, this is known as moving down their concentration gradient.
2. electrostatic pressure - like charges repel each other & are attracted to opposite charges.
What creates the unequal distribution of ions?
- The axon membrane is not freely permeable to all ions.
- Hodgkin and Keynes (1955) - a sodium-potassium pump. Located on the axon membrane.
– Sodium potassium transporter
What happens when a neuron is stimulated?
- The neuron may become less negatively charged or more negatively charged.
- More negatively charged caused by chloride entry and known as hyperpolarisation
- Less negatively charged known as depolaristion
- If it is sufficiently strong it may reduce the voltage difference across the membrane past the excitation threshold.
- If level of threshold (-55millivolts) is reached an action potential will occur.
- A brief reversal of the interior charge from -ve to +ve.
- A change in the membrane potential
- An all or none event.
- Depolarised
- Non decremental.
What causes the change in charge from negative to positive?
- Excitatory stimulation: Na+ gates open and Na+ diffuses into the cell.
- Voltage dependent ion channels
- level of threshold
- potassium ion channels open and potassium leaves the cell.
- lasts about a millisecond and quickly subsides.
- Refractory period
Why are myelination and saltatory conduction crucial mechanisms for rapid and efficient communication within the nervous system?
Myelin is a fatty substance produced by oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS).
Myelin insulates axons, providing electrical insulation.
This insulation increases the speed of action potential propagation along axons.
The increase in speed is due to the action potential “leaping” between the nodes of Ranvier rather than traveling continuously along the entire length of the axon.
This process is known as saltatory conduction.
Saltatory conduction significantly speeds up the transmission of nerve impulses.
Give a summary of events making up action potential.
- NA+ channels open
- K+ channels open
- NA+ channels close
- K+ continues to flow
out - Refractory period
- K+ channels close
- Membrane potential returns to -70mV
What happens to a neuron in response to a signal?
The soma end of the axon becomes deplorised.
The deplorization spreads down the azon. Meanwhile, the first part of the membrane replorizes. Because NA+ channels are inactivated and additional K+ channels have opened the membrane cannot open again.
The action portential continues to travel down the axon.
What are the communication between neurons?
Presynaptic membrane
Postsynaptic membrane
Synaptic cleft
What is a presynaptic membrane?
Membrane of terminal button that lies adjacent to postsynaptic membrane and through which neurotransmitter is released.
What is a postsynaptic membrane?
Cell membrane opposite the terminal button in synapse; membrane of cell that receives message.
What is a synaptic cleft?
Space between presynaptic membrane and postsynaptic membrane.
What is synaptic transmission?
*Synaptic transmission is the process by which neurons communicate with each other in the nervous system.
*It begins when an action potential, an electrical impulse, travels along the axon of a presynaptic neuron and reaches the terminal buttons at its end. Within these terminal buttons are synaptic vesicles, which contain neurotransmitter molecules.
*As the action potential arrives, it triggers the fusion of these vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft, the small gap between the presynaptic and postsynaptic neurons. These neurotransmitters then diffuse across the synaptic cleft and bind to specific receptor sites on the dendrites or cell body of the postsynaptic neuron in a lock-and-key fashion.
What is exocytosis?
Same process as synaptic transmission except calcium is involved.
