Chapter 3 Cells of the Nervous System; Resting Membrane and Synaptic Potentials

What are the three main types of ion channels?

1. Passive 'Leak' Channels – Always open, allow ions to move down their concentration gradient.

2. Ligand-Gated Channels – Open in response to the binding of a chemical messenger (neurotransmitter).

3. Voltage-Gated Channels – Open or close in response to changes in membrane potential.

What is transcription?

The process by which DNA is copied into mRNA.

What is translation?

The process by which ribosomes use mRNA to build proteins.

What are proteins and their function?

Proteins are chains of amino acids that perform structural, enzymatic, signaling, and regulatory functions in the body.

What are enzymes?

Enzymes are proteins that catalyze (speed up) chemical reactions.

What is the plasma membrane?

A lipid bilayer that encloses the cell, controlling movement of substances in and out.

What are receptors and ligands?

Receptors are proteins on the cell surface or inside the cell that bind to ligands—signaling molecules like neurotransmitters or hormones.

What happens after a ligand binds to a receptor?

It triggers a cellular response; the ligand may be degraded, recycled, or released.

What are ions?

Charged atoms or molecules (e.g., Na⁺, K⁺, Cl⁻) that carry electrical current in cells.

What are transport proteins and ion channels?

• Transport proteins help move substances across the membrane.

• Ion channels are a type of transport protein that allows specific ions to pass through the membrane.

Approximately how many neurons are in the human nervous system?

More than 100 billion

Are most behaviors produced by single neurons or groups of neurons?

By groups of hundreds or thousands of neurons.

Do neurons maintain a fixed structure?

No, neurons can grow and shrink—they continuously change shape.

Are most CNS neurons replaced over your lifetime?

No, most CNS neurons last a lifetime and are not replaced.

Are most CNS neurons replaced over your lifetime?

No, most CNS neurons last a lifetime and are not replaced.

Does neurogenesis occur in adulthood?

Yes, but it is rare.

What are neurons specialized for?

The reception, conduction, and transmission of electrochemical signals.

What are the three basic subdivisions of a neuron?

Dendrites, Soma (cell body), and Axon.

What is the function of dendrites?

They gather information from other neurons.

What is the function of the soma (cell body)?

It contains the nucleus and integrates information.

What is the function of the axon?

It starts at the axon hillock, carries information, and ends at the axon terminals to pass signals to other cells.

What is the dendritic tree?

A collection of dendrites from a single neuron that receives input from other neurons.

How many inputs can a dendritic tree receive?

Inputs may number in the thousands.

What are dendritic spines?

Protrusions from a dendrite that increase surface area and are the typical point of contact with axons to form synapses.

Why are dendritic spines important?

They increase the neuron's surface area for synaptic input.

Are dendritic spines static or dynamic structures?

They are dynamic—spines are constantly being formed or eliminated.

What influences the formation and elimination of dendritic spines?

The type and amount of synaptic activity.

What are apical dendrites?

Dendrites that extend from the apex (top) of a pyramidal neuron's soma, usually toward the cortical surface.

What are basal dendrites?

Dendrites that extend from the base of a pyramidal neuron's soma, typically spreading horizontally.

How do apical and basal dendrites differ in location?

Apical dendrites project upward toward the brain's surface, while basal dendrites spread laterally from the base of the neuron.

Do apical and basal dendrites receive different inputs?

Yes, they often receive inputs from different sources and contribute to distinct aspects of neuronal processing.

What are filopodia dendritic spines?

Long, thin protrusions with no distinct head; immature spines often involved in initial synapse formation.

What are long thin dendritic spines?

Slender spines with a small head and long neck; thought to be highly plastic and involved in learning.

What are thin dendritic spines?

Shorter than long thin spines but still have a small head and thin neck; also associated with synaptic plasticity.

What are stubby dendritic spines?

Short and thick spines with no clear neck; considered to be more stable and possibly less plastic.

What are mushroom dendritic spines?

Spines with a large, bulbous head and narrow neck; typically stable and associated with mature, strong synapses.

What are branched dendritic spines?

Spines with multiple heads or branches; rare and may represent complex or multiple synaptic contacts.

What is the soma (cell body) of a neuron?

The central part of a neuron that contains the nucleus and integrates incoming signals from dendrites.

What is the function of the nucleus in the soma?

It contains DNA and is the site of transcription.

What does the cytoplasm in the soma contain and do?

It contains organelles like ribosomes and is the site of translation (protein synthesis).

What two types of support does the soma provide to the neuron?

Metabolic support (energy) and synthetic support (protein production).

What role does the soma play in signal integration?

It gates information from the dendrites to the axon hillock, integrating signals from various sources.

What is the axon hillock?

The region where the axon joins the cell body (soma).

What happens at the axon hillock?

It integrates all incoming signals from the dendrites.

What important electrical event is initiated at the axon hillock?

The action potential is generated here.

What is the primary function of the axon?

To conduct the action potential.

How many axons does a typical neuron have?

One axon (compared to many dendrites).

What is the role of the myelin sheath?

It provides insulation for faster signal transmission and allows for a smaller diameter axon.

Which cells form the myelin sheath in the CNS?

Oligodendrocytes.

Which cells form the myelin sheath in the PNS?

Schwann cells.

What are Nodes of Ranvier?

Gaps between myelinated segments of the axon where action potentials are regenerated.

What is the function of microtubules in the axon?

They are responsible for axonal transport—both anterograde and retrograde

What is the role of neurofilaments in the axon?

They provide structural support to the axon.

What do microfilaments do in the axon?

They may assist in the reorganization of neuronal branches.

What are collaterals in a neuron?

Branches that arise from the axon.

What is a terminal in a neuron?

A swelling at the end of axon collaterals.

What is the function of mitochondria in the axon terminal?

They provide energy for synaptic transmission.

What is stored in synaptic vesicles in the axon terminal?

Neurotransmitters.

What is a synapse?

A junction between a presynaptic axon terminal and a postsynaptic dendrite.

What are the three principal components of a synapse?

1. Action Zone

2. Presynaptic Cleft

3. Postsynaptic Density (PSD)

What is the function of the action zone in a synapse?

It is the site in the presynaptic terminal where neurotransmitters are released.

What is the presynaptic cleft?

The space between the presynaptic and postsynaptic membranes where neurotransmitters diffuse.

What is the postsynaptic density (PSD)?

A protein-rich region on the postsynaptic membrane that contains neurotransmitter receptors and signaling molecules.

What is a monopolar (unipolar) neuron?

A neuron with a single branch extending from the cell body.

What is a bipolar neuron?

A neuron with two branches extending from the cell body—one axon and one dendrite.

What is a multipolar neuron?

A neuron with many branches from the cell body—typically one axon and multiple dendrites.

What are sensory neurons?

Neurons specialized to receive information from the outside world and from within the body.

What are motor neurons?

Neurons that transmit commands from the central nervous system (CNS) directly to muscles and glands.

What are interneurons?

Neurons that act as bridges between the sensory and motor systems.

What are astrocytes?

Star-shaped glial cells that provide structural support, regulate blood flow, maintain the blood-brain barrier, and help with neurotransmitter uptake.

What are oligodendrocytes?

Glial cells in the CNS that form the myelin sheath around axons.

What are Schwann cells?

Glial cells in the PNS that form the myelin sheath around axons.

What are microglia?

Small glial cells that act as the brain’s immune system by removing waste and pathogens through phagocytosis.

What shape do astrocytes have?

Star-shaped.

What are the main functions of astrocytes?

Provide structural and nutritional support for neurons, transport substances between neurons and capillaries, and isolate the synapse.

What role do astrocytes play in the blood-brain barrier?

They help form the blood-brain barrier and transport substances between neurons and capillaries.

How do astrocytes respond to CNS trauma?

They contribute to scar tissue formation.

What is the tripartite synapse?

It is the functional interaction between the presynaptic neuron, postsynaptic neuron, and astrocytes.

What is the Blood Brain Barrier (BBB)?

A selectively permeable barrier between the brain and blood supply.

What is the primary function of the Blood Brain Barrier?

To protect the brain from pathogens and certain molecules from entering.

What cells form the Blood Brain Barrier?

Endothelial cells and astrocyte end feet.

Name areas of the brain that are not covered by the Blood Brain Barrier.

Posterior pituitary gland, pineal gland, median eminence of the hypothalamus, and the area postrema.

What type of glial cell insulates axons in the CNS?

Oligodendroglia.

How does one oligodendroglia cell myelinate axons?

It can contribute to several segments of myelin on multiple axons.

What type of glial cell insulates axons in the PNS?

Schwann cells.

How does one Schwann cell myelinate axons?

One Schwann cell myelinates one segment on one axon.

What is a special function of Schwann cells after axon injury?

They help guide the regrowth of damaged axons.

What type of immune cell are microglia in the brain?

Resident immune cells; a type of macrophage.

What is the primary function of microglia?

Cleaning up cellular damage and digesting debris (phagocytosis).

How do microglia contribute to neural circuit remodeling?

They are involved in synaptic pruning.

What role do microglia play after brain injury?

Wound healing and repair activity.

What molecules do microglia synthesize and release?

Cytokines and growth factors.

What disorders have microglia been implicated in?

Several neurodegenerative disorders.

What is the function of dendrites in a neuron?

Receive input from other neurons.

What is the function of the cell body (soma) in a neuron?

Integrates information and provides metabolic and synthetic support.

What is the function of the axon in a neuron?

Conducts action potentials to transmit information to other cells.

How does the morphology of dendritic spines impact neuron function?

Different shapes affect synaptic strength and plasticity, influencing signal reception and neural connectivity.

What are the major functions of Microglia?

Immune defense, cleaning debris, synaptic pruning, and repair after injury.

What are the major functions of Astrocytes?

Structural and nutritional support, blood-brain barrier formation, synapse isolation, and scar formation after CNS trauma.

What are the major functions of Schwann cells?

Myelinate axons in the PNS and guide regrowth of damaged axons.