Topic 6.5: Neurons and Synapses Flashcards
Define neuron
Neurons are specialised cells that function to transmit electrical impulses within the nervous system
What is a dendrite?
Dendrites – Short-branched fibres that convert chemical information from other neurons or receptor cells into electrical signals
What is an axon?
Axon – An elongated fibre that transmits electrical signals to terminal regions for communication with other neurons or effectors
What is a soma?
Soma – A cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival
Define resting potential
A resting potential is the difference in charge across the membrane when a neuron is not firing
In a typical resting potential, the inside of the neuron is more negative relative to the outside (approximately –70 mV)
What is the sodium-potassium pump?
The sodium-potassium pump is a transmembrane protein that actively exchanges sodium and potassium ions (antiport)
How is a resting potential generated?
Sodium-potassium pump expels 3 Na+ ions for every 2 K+ ions admitted (additionally, some K+ ions will then leak back out of the cell)
This creates an electrochemical gradient whereby the cell interior is relatively negative compared to the extracellular environment (as there are more positively charged ions outside of the cell and more negatively charged ions inside the cell)
What is an action potential?
Action potentials are the rapid changes in charge across the membrane that occur when a neuron is firing
What are the 3 main stages of the action potentials?
Action potentials occur in three main stages: depolarization, repolarization and a refractory period
What is depolarization?
Depolarisation refers to a sudden change in membrane potential – usually from a (relatively) negative to positive internal charge
What is the first step of depolarization?
In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon
After In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon, what is the next step of depolarization?
As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium
As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium, what is the last step of depolarization?
The influx of sodium causes the membrane potential to become more positive (depolarisation)
What is repolarization?
Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge)
What is the first step of repolarization?
Following an influx of sodium, potassium channels open within the membrane of the axon
After Following an influx of sodium, potassium channels open within the membrane of the axon, what is the next step of repolarization?
As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium
After As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium, what is the last step of repolarization?
The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarisation)
What is the refractory period?
The refractory period refers to the period of time following a nerve impulse before the neuron is able to fire again
Describe the refractory period
In a normal resting state, sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential) Following depolarisation (sodium influx) and repolarisation (potassium efflux), this ionic distribution is largely reversed Before a neuron can fire again, the resting potential must be restored via the antiport action of the sodium-potassium pump
Define nerve impulses
Nerve impulses are action potentials that move along the length of an axon as a wave of depolarisation
What is the propagation of nerve impulses caused by?
Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential
Define synapses
Synapses are junctions between neurons and between neurons and receptor or effector cells
What is the first step of chemical transfer across synapses?
When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels
After When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels, what is the next step of chemical transfer across synapses?
Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane
After Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane, what is the next step of chemical transfer across synapses?
The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft
After The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft, what is the next step of chemical transfer across synapses?
Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels
After Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels, what is the next step of chemical transfer across synapses?
The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal
After The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal, what is the last step of chemical transfer across synapses?
The neurotransmitters released into the synapse are either recycled (by reuptake pumps) or degraded (by enzymatic activity)
Define neurotransmitter
Neurotransmitters are chemical messengers released from neurons and function to transmit signals across the synaptic cleft
What does the central nervous system consist of?
brain and spinal cord
What does the peripheral nervous system consist of?
peripheral nerves (cranial and spinal)
What is the function of the central nervous system?
integrative control center
What is the function of the peripheral nervous system?
communication between CNS and body
What is the function of the sensory neurons?
conducts signals from receptors to CNS
What is the function of the motor neurons?
conducts signals from CNS to effectors
What is the function of the autonomic nervous system?
controls involuntary responses
What is the function of the somatic nervous system?
controls voluntary movement
What is the function of the sympathetic division?
mobilizes body system; flight or fight responses
What is the function of the parasympathetic division?
conserves energy; rest and digest responses
Define stimulus
A stimulus is a change in the environment (either external or internal) that is detected by a receptor
Define effectors
Effectors are organs (either muscles or glands) that produce a response to a stimulus
Define response
A response is a change in the organism resulting from the detection of a stimulus
What is the first step of stimulus-response model?
A stimulus is detected by a receptor
After A stimulus is detected by a receptor, what is the next step of the stimulus-response model?
Receptors transform environmental stimuli into electrical nerve impulses
After Receptors transform environmental stimuli into electrical nerve impulses, what is the next step of the stimulus-response model?
These impulses are then transmitted via neurons to the central nervous system where decision-making occurs
After These impulses are then transmitted via neurons to the central nervous system where decision-making occurs, what is the next step of the stimulus-response model?
When a response is selected (consciously or unconsciously), the signal is transmitted via neurons to effectors
After When a response is selected (consciously or unconsciously), the signal is transmitted via neurons to effectors, what is the last step of the stimulus-response model?
effectors produce a response to stimulus
Define reflex
A reflex is a rapid and involuntary response to a stimulus, resulting from a simple signalling pathway called a reflex arc
What is the function of excitatory neurotransmitters?
Excitatory neurotransmitters trigger depolarisation, increasing the likelihood of a response
What is the function of inhibitory neurotransmitters?
Inhibitory neurotransmitters trigger hyperpolarisation, decreasing the likelihood of a response
