Ch. 39 Neurons

What are the four components of neural signaling?

Reception, Transmission, Integration, Response

What is the role of afferent neurons?

They transmit stimuli from sensory receptors to interneurons.

What do interneurons do?

They integrate information to formulate an appropriate response.

What is the function of efferent neurons?

They carry signals indicating a response away from interneurons to effectors.

What are effectors in the context of neural signaling?

Muscles and glands that carry out the response.

What are glial cells?

Non-neuronal cells that provide nutrition and support to neurons.

What is the function of astrocytes?

They provide physical support and maintain ion concentrations in the interstitial fluid.

What do oligodendrocytes and Schwann cells do?

They wrap around axons to form insulating myelin sheaths.

What is a ganglion?

A group of neurons lying outside the central nervous system (CNS).

What is a nucleus in the context of the nervous system?

A concentration of nerve cells within the central nervous system (CNS).

What is membrane potential?

A separation of positive and negative charges across the plasma membrane that produces an electrical potential (voltage).

What is resting potential?

The membrane potential of a neuron when it is not being stimulated, typically around -70 mV.

How is resting potential created?

Through the sodium-potassium pump and ion leak channels.

What does the sodium-potassium pump do?

It brings two K+ ions into the cell for every three Na+ ions it pumps out.

What is depolarization in the context of action potential?

An abrupt change in membrane potential where positive charges flow inward, making the cytoplasmic side less negative.

What is threshold potential?

The membrane potential that must be reached for an action potential to occur, typically 10-20 mV more positive than resting potential.

What is the typical range of resting potential in neurons?

Between -40 to -90 millivolts (mV), averaging about -70 mV.

What happens during an action potential?

An abrupt change in membrane potential occurs, leading to the transmission of an electrical impulse.

What is the role of ion leak channels?

They allow specific ions to move freely across the membrane, contributing to membrane potential.

What is the difference between the peripheral nervous system (PNS) and the central nervous system (CNS)?

PNS consists of afferent and efferent neurons, while CNS consists of interneurons forming the brain and spinal cord.

What is the significance of nodes of Ranvier?

They are gaps between Schwann cells that speed up signal transmission along myelinated axons.

What is the electro-chemical potential?

The combined effect of electrical potential and concentration gradient on ion movement across the membrane.

What is the typical structure of a neural circuit?

It contains an afferent neuron, one or more interneurons, and an efferent neuron.

What is the primary function of the sodium-potassium pump?

To maintain the concentration gradient of sodium and potassium ions across the neuron's membrane.

What are voltage-gated channels?

Channels that open and close in response to changes in membrane potential, specifically Na+ and K+ channels in neurons.

What triggers the opening of voltage-gated Na+ and K+ channels?

A stimulation that causes changes in the membrane potential.

What happens to the membrane potential when the action potential fires?

The membrane potential suddenly increases, becoming positive due to an influx of positive ions.

What is the peak membrane potential during an action potential?

About +30 mV or more.

What occurs after the peak of an action potential?

The membrane potential falls below the resting value to about -80 mV (hyperpolarization) before returning to resting potential.

What is the refractory period?

A phase after an action potential where the neuron cannot be restimulated, consisting of two phases.

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

An action potential is produced only if a stimulus is strong enough to reach the threshold; once triggered, it occurs fully regardless of stimulus strength.

How does an action potential propagate along an axon?

It travels as a wave of depolarization, initiated at the dendrite and moving away from the stimulation point.

What role does the refractory period play in action potential propagation?

It prevents the action potential from reversing direction along the axon, ensuring one-way movement.

How is the frequency of action potentials related to stimulus intensity?

The greater the stimulus, the higher the frequency of action potentials, up to 100 per second.

What effect does myelin have on action potential conduction?

Myelin increases the rate of conduction, allowing action potentials to 'hop' along myelin-coated axons.

What are nodes of Ranvier?

Uncoated sections of the axon that expose the membrane to extracellular fluids, allowing for rapid conduction of action potentials.

What occurs at chemical synapses?

Neurotransmitter molecules are released by the presynaptic membrane and diffuse across the synaptic cleft to alter ion conduction in the postsynaptic membrane.

What distinguishes electrical synapses from chemical synapses?

Electrical synapses allow direct ion flow between cells through gap junctions, while chemical synapses involve neurotransmitter release across a synaptic cleft.

What is the function of neurotransmitters in chemical synapses?

They bind to receptors in the postsynaptic cell membrane, potentially generating a new electrical impulse.

What is a synapse?

The junction where a neuron communicates with another neuron or an effector.

What happens when an electrical impulse arrives at an axon terminal in a chemical synapse?

A neurotransmitter is released into the synaptic cleft.

What is the role of ligand-gated ion channels in postsynaptic cells?

They are activated by neurotransmitters and alter ion conduction in the postsynaptic membrane.

What is hyperpolarization?

A drop in membrane potential below the resting value, typically around -80 mV.

What is the significance of the threshold potential?

It is the level of depolarization that must be reached to trigger an action potential.

What are neurotransmitters stored in?

Synaptic vesicles in the cytoplasm of an axon terminal.

How are neurotransmitters released from the axon terminal?

By exocytosis upon the arrival of an action potential.

What role do voltage-gated Ca2+ channels play in neurotransmitter release?

They allow Ca2+ to flow into the cytoplasm, triggering exocytosis of synaptic vesicles.

What happens to Ca2+ channels when action potentials stop arriving?

Voltage-gated Ca2+ channels close, and Ca2+ is pumped out of the axon cytoplasm.

What is the effect of a drop in cytoplasmic Ca2+ concentration?

It stops vesicles from fusing with the presynaptic membrane, halting neurotransmitter release.

What determines whether a postsynaptic neuron triggers an action potential?

The combined effects of stimulatory and inhibitory neurotransmitters at all chemical synapses.

What is an excitatory postsynaptic potential (EPSP)?

A change in membrane potential that pushes the neuron closer to threshold, caused by Na+ influx.

What is an inhibitory postsynaptic potential (IPSP)?

A change in membrane potential that pushes the neuron farther from threshold, caused by Cl- influx or K+ efflux.

What is temporal summation?

The summation of EPSPs produced by successive firing of a single presynaptic neuron over a short period.

What is spatial summation?

The summation of EPSPs produced by simultaneous firing of multiple presynaptic neurons.

What occurs during summation resulting in cancellation?

EPSPs and IPSPs can cancel each other out, resulting in no change in membrane potential.

What is the significance of synaptic connections in the nervous system?

They control internal activities and regulate behavior through the combined activities of neurons.

How many synapses can a single interneuron in the human brain form?

Up to 100,000 synapses.

What happens to synapses as animals mature?

They can change through modification, addition, or removal of synaptic connections.

What is the role of neurotransmitters in the postsynaptic membrane?

They open or close ligand-gated ion channels that conduct Na+, K+, or Cl-.

What is the effect of altered ion flow in the postsynaptic membrane?

It may stimulate or inhibit the generation of action potentials in the postsynaptic cell.

What is the relationship between neurotransmitter type and receptor type?

The same neurotransmitter may stimulate or inhibit action potentials depending on the receptor it binds to.

What is the primary factor in the integration of signals by neurons?

The patterns, number, types, and activity of synapses.

What is the function of the presynaptic neuron?

It releases neurotransmitters into the synaptic cleft.

What is the role of the postsynaptic neuron?

It receives neurotransmitter signals and may generate an action potential.

What triggers the opening of ligand-gated ion channels in the postsynaptic membrane?

The binding of neurotransmitters to their receptors.

What is the effect of an EPSP on the postsynaptic neuron?

It causes depolarization, moving the membrane potential closer to the threshold for action potential generation.

What is the effect of an IPSP on the postsynaptic neuron?

It causes hyperpolarization, moving the membrane potential further from the threshold for action potential generation.

How do neurotransmitters influence the postsynaptic membrane?

They can either stimulate or inhibit the generation of action potentials based on their type and receptor interaction.

What is the role of calcium ions (Ca2+) in neurotransmitter release?

Ca2+ influx triggers the fusion of synaptic vesicles with the presynaptic membrane for neurotransmitter release.

What happens to neurotransmitter release when Ca2+ concentration decreases?

Neurotransmitter release stops as vesicles can no longer fuse with the presynaptic membrane.