C2.2 Neural signalling

What is the role of the endocrine system?

The endocrine system consists of glands that release hormones for internal communication.

What is the role of the nervous system?

The nervous system consists of neurons that transmit nerve impulses for internal communication.

How many neurons are in the human nervous system?

There are about 85 billion neurons in the human nervous system.

What are neurons?

Neurons are nerve cells that help with internal communication by transmitting nerve impulses.

What is a nerve impulse?

A nerve impulse is an electrical signal transmitted by neurons.

What is the structure of a neuron?

What are dendrites?

Dendrites are short, branched nerve fibers that transmit impulses between neurons in one part of the brain or spinal cord.

What are axons?

Axons are elongated nerve fibers that transmit impulses from the tips of the fingers or toes to the spinal cord.

What is the membrane potential?

The membrane potential is the voltage across a membrane, usually between 10 and 100 millivolts.

What is the resting potential of a neuron?

The resting potential of a neuron is typically around −70mV.

What contributes to the resting potential?

Three factors: sodium-potassium pumps, leakage of ions, and negatively charged proteins inside the cell.

What do sodium-potassium pumps do?

They transfer sodium ions (Na+) out of the neuron and potassium ions (K+) into the neuron, creating a charge imbalance.

What is the role of ion leakage in the resting potential?

The leakage of K+ ions increases the charge imbalance, contributing to the resting potential.

How do negatively charged proteins contribute to the resting potential?

They contribute to the charge imbalance by being inside the neuron and creating a more negative internal environment.

What is depolarization?

Depolarization is a change in membrane potential from negative to positive.

What is repolarization?

Repolarization is a change in membrane potential from positive to negative.

What causes depolarization?

The opening of sodium channels allows Na+ ions to diffuse into the neuron, reversing the charge across the membrane.

What causes repolarization?

The closing of sodium channels and the opening of potassium channels, allowing K+ ions to diffuse out.

What is an action potential?

An action potential is a rapid, all-or-nothing change in membrane potential.

What is the threshold potential?

The threshold potential is the membrane potential at which sodium channels open, triggering depolarization.

What happens during depolarization?

Sodium ions (Na+) diffuse into the neuron, raising the membrane potential from −70mV to +30mV.

What happens during repolarization?

Potassium ions (K+) diffuse out of the neuron, returning the membrane potential to −70mV.

What is the refractory period?

The refractory period is the time after an action potential during which another action potential cannot be initiated.

What is the role of local currents in the propagation of action potentials?

Local currents cause sodium ions to diffuse to neighboring parts of the axon, triggering depolarization in adjacent areas.

What is saltatory conduction?

Saltatory conduction is the process where nerve impulses jump from one node of Ranvier to the next, speeding up transmission.

What is myelination?

Myelination is the coating of nerve fibers with Schwann cells, which speeds up nerve impulse transmission.

What are nodes of Ranvier?

Nodes of Ranvier are gaps between Schwann cells where action potentials are triggered.

How does myelination speed up nerve impulse transmission?

Myelinated fibers allow nerve impulses to jump from node to node, speeding up transmission.

What is the diameter of most nerve fibers?

The diameter of most nerve fibers is about 1µm.

How does the diameter of nerve fibers affect the speed of nerve impulses?

Larger diameter nerve fibers reduce resistance and allow faster impulse transmission.

What is the speed of nerve impulse transmission in humans?

Nerve impulses in humans typically travel at about 1 meter per second.

How do giant axons in squid affect their nerve impulse speed?

Giant axons in squid can conduct impulses at 25 meters per second due to their larger diameter.

What is the function of synapses?

Synapses are junctions between cells in the nervous system that transmit signals between neurons or neurons and effectors.

What are the three main types of synapses?

Synapses between sensory receptor cells and neurons, between neurons, and between neurons and muscle fibers or gland cells.

What is the direction of signal transmission across a synapse?

Signals pass in one direction from the presynaptic neuron to the postsynaptic neuron.

What are neurotransmitters?

Neurotransmitters are chemicals that carry signals across the synaptic gap.

What happens when a nerve impulse reaches the presynaptic membrane?

Calcium ions (Ca2+) enter the neuron, triggering the release of neurotransmitters.

How are neurotransmitters released into the synaptic gap?

Neurotransmitters are released by exocytosis from vesicles in the presynaptic neuron.

What happens after neurotransmitters diffuse across the synaptic gap?

Neurotransmitters bind to receptors on the postsynaptic membrane, causing ion channels to open.

What is an excitatory postsynaptic potential?

An excitatory postsynaptic potential is a change in membrane potential that makes it more likely for an action potential to occur.

How is acetylcholine involved in synaptic transmission?

Acetylcholine is a neurotransmitter that opens ion channels, causing excitatory postsynaptic potentials.

What enzyme breaks down acetylcholine in the synaptic gap?

Acetylcholinesterase breaks down acetylcholine into choline and acetate.

What is the role of GABA in synaptic transmission?

GABA is an inhibitory neurotransmitter that causes hyperpolarization, making it harder for the postsynaptic neuron to fire.

What is cocaine’s effect on synaptic transmission?

Cocaine blocks dopamine reuptake transporters, leading to a build-up of dopamine in the synaptic gap and continuous excitation of the postsynaptic neuron.

What is neonicotinoid’s effect on synaptic transmission in insects?

Neonicotinoids block acetylcholine receptors, preventing synaptic transmission and causing paralysis in insects.

How does the sodium-potassium pump work?

It uses energy from ATP to transport sodium ions (Na+) out of the neuron and potassium ions (K+) into the neuron.

What happens when sodium channels open during depolarization?

Sodium ions diffuse into the neuron, causing the membrane potential to become more positive.

What happens when potassium channels open during repolarization?

Potassium ions diffuse out of the neuron, restoring the membrane potential to a negative value.

What is voltage-gating?

Voltage-gating is the process where changes in membrane potential trigger the opening of sodium and potassium channels.

What is the all-or-nothing principle of action potentials?

An action potential either occurs fully or not at all, depending on whether the threshold potential is reached.

What is the importance of calcium ions in synaptic transmission?

Calcium ions trigger the release of neurotransmitters from vesicles in the presynaptic neuron.

How does the sodium-potassium pump restore the resting potential after an action potential?

The pump actively transports sodium out and potassium in to re-establish the resting potential.

What is the difference between inhibitory and excitatory neurotransmitters?

Inhibitory neurotransmitters make it harder for the postsynaptic neuron to fire, while excitatory neurotransmitters make it easier.

What is summation in synaptic transmission?

Summation occurs when multiple excitatory postsynaptic potentials combine to trigger an action potential.

What is the role of the postsynaptic neuron in synaptic transmission?

The postsynaptic neuron carries the signal away from the synapse, usually in the form of a nerve impulse.

What happens to acetylcholine after it binds to its receptor?

Acetylcholine causes sodium ions to diffuse into the postsynaptic neuron, creating an excitatory postsynaptic potential.

What is hyperpolarization?

Hyperpolarization is when the membrane potential becomes more negative, making it harder for an action potential to occur.

What is consciousness?

Consciousness is the state of being aware of and able to think about multiple things simultaneously.

What is the physiological basis of consciousness?

Consciousness emerges from the interaction of individual neurons in the brain.

What is sleep?

Sleep is a state of reduced or partial consciousness.

What are general anaesthetics?

General anaesthetics are drugs used during surgery to induce unconsciousness, though their mechanism is not fully understood.

What is an emergent property?

An emergent property is a property of a system that arises from the interactions between its components, rather than being a property of any single component.

What is an example of an emergent property in biology?

The catalytic activity of enzymes is an example of an emergent property.

How does a nerve impulse travel along an axon?

A nerve impulse travels along the axon by the diffusion of sodium ions, creating local currents that propagate depolarization and repolarization.

What is the function of Schwann cells?

Schwann cells wrap around nerve fibers, forming the myelin sheath and speeding up nerve impulse transmission.

What is the function of acetylcholine in neuromuscular junctions?

Acetylcholine binds to receptors on muscle fibers, causing sodium ions to enter the muscle cells and initiate contraction.

What happens when acetylcholine is broken down by acetylcholinesterase?

The breakdown of acetylcholine prevents continuous stimulation of the postsynaptic neuron.

What is the resting potential of a neuron?

The resting potential is the membrane potential of a neuron when it is not transmitting an impulse, typically around −70mV.

What causes the rapid change in membrane potential during an action potential?

The rapid change is caused by the opening of sodium channels during depolarization and potassium channels during repolarization.

What is the role of neurotransmitter receptors?

Neurotransmitter receptors bind to neurotransmitters and trigger ion channels to open, influencing the postsynaptic neuron.

What is the role of local currents in nerve impulse propagation?

Local currents help to spread depolarization and repolarization along the axon.

What is the speed of nerve impulses in larger nerve fibers?

Larger nerve fibers conduct impulses more quickly, up to 25 meters per second in squid giant axons.

How do local currents affect neighboring parts of the axon?

Local currents cause depolarization in neighboring parts of the axon, triggering the opening of sodium channels and propagating the action potential.

What is the effect of hyperpolarization on the postsynaptic neuron?

Hyperpolarization makes it more difficult for the postsynaptic neuron to reach the threshold potential and fire an action potential.

What is the role of chloride ions in synaptic transmission?

Chloride ions contribute to hyperpolarization in inhibitory synapses, making it harder for the postsynaptic neuron to fire.

What is the role of acetylcholine in muscle contraction?

Acetylcholine binds to muscle receptors, causing sodium ions to enter muscle cells, triggering contraction.

What happens during the depolarization phase of an action potential?

During depolarization, sodium ions rush into the neuron, causing the membrane potential to become positive.

How does myelination affect nerve impulse speed?

Myelination speeds up impulse transmission by allowing the action potential to jump from one node of Ranvier to the next.

What is the function of axon terminals?

Axon terminals release neurotransmitters into the synapse to transmit signals to other neurons or effectors.

What is the role of calcium ions in neurotransmitter release?

Calcium ions trigger the fusion of neurotransmitter vesicles with the presynaptic membrane, releasing the neurotransmitter into the synaptic gap.

What is a synaptic vesicle?

A synaptic vesicle is a small structure in the presynaptic neuron that stores neurotransmitters.

How does a neurotransmitter affect the postsynaptic neuron?

A neurotransmitter binds to receptors on the postsynaptic neuron, causing ion channels to open and changing the postsynaptic potential.

What is the effect of acetylcholine on the heart?

Acetylcholine can slow down the heart rate by inhibiting the depolarization of the heart muscle.

What is the role of neurotransmitter reuptake?

Neurotransmitter reuptake involves the reabsorption of neurotransmitters by the presynaptic neuron, terminating the signal.

What is the role of dopamine in the brain?

Dopamine is involved in reward, motivation, and motor control.