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

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206 Terms

1
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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.

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What is transcription?

The process by which DNA is copied into mRNA.

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What is translation?

The process by which ribosomes use mRNA to build proteins.

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What are proteins and their function?

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

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What are enzymes?

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

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What is the plasma membrane?

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

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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.

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What happens after a ligand binds to a receptor?

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

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What are ions?

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

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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.

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Approximately how many neurons are in the human nervous system?

More than 100 billion

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

By groups of hundreds or thousands of neurons.

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Do neurons maintain a fixed structure?

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

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Are most CNS neurons replaced over your lifetime?

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

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Are most CNS neurons replaced over your lifetime?

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

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Does neurogenesis occur in adulthood?

Yes, but it is rare.

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What are neurons specialized for?

The reception, conduction, and transmission of electrochemical signals.

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What are the three basic subdivisions of a neuron?

Dendrites, Soma (cell body), and Axon.

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What is the function of dendrites?

They gather information from other neurons.

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

It contains the nucleus and integrates information.

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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.

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What is the dendritic tree?

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

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How many inputs can a dendritic tree receive?

Inputs may number in the thousands.

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What are dendritic spines?

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

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Why are dendritic spines important?

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

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Are dendritic spines static or dynamic structures?

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

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What influences the formation and elimination of dendritic spines?

The type and amount of synaptic activity.

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What are apical dendrites?

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

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What are basal dendrites?

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

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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.

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Do apical and basal dendrites receive different inputs?

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

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What are filopodia dendritic spines?

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

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What are long thin dendritic spines?

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

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What are thin dendritic spines?

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

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What are stubby dendritic spines?

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

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What are mushroom dendritic spines?

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

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What are branched dendritic spines?

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

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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.

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What is the function of the nucleus in the soma?

It contains DNA and is the site of transcription.

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What does the cytoplasm in the soma contain and do?

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

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

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

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What role does the soma play in signal integration?

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

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What is the axon hillock?

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

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What happens at the axon hillock?

It integrates all incoming signals from the dendrites.

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What important electrical event is initiated at the axon hillock?

The action potential is generated here.

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What is the primary function of the axon?

To conduct the action potential.

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How many axons does a typical neuron have?

One axon (compared to many dendrites).

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What is the role of the myelin sheath?

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

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Which cells form the myelin sheath in the CNS?

Oligodendrocytes.

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Which cells form the myelin sheath in the PNS?

Schwann cells.

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What are Nodes of Ranvier?

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

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What is the function of microtubules in the axon?

They are responsible for axonal transport—both anterograde and retrograde

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What is the role of neurofilaments in the axon?

They provide structural support to the axon.

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What do microfilaments do in the axon?

They may assist in the reorganization of neuronal branches.

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What are collaterals in a neuron?

Branches that arise from the axon.

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What is a terminal in a neuron?

A swelling at the end of axon collaterals.

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What is the function of mitochondria in the axon terminal?

They provide energy for synaptic transmission.

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What is stored in synaptic vesicles in the axon terminal?

Neurotransmitters.

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What is a synapse?

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

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What are the three principal components of a synapse?

  1. Action Zone

  2. Presynaptic Cleft

  3. Postsynaptic Density (PSD)

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

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

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What is the presynaptic cleft?

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

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What is the postsynaptic density (PSD)?

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

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What is a monopolar (unipolar) neuron?

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

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What is a bipolar neuron?

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

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What is a multipolar neuron?

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

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What are sensory neurons?

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

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What are motor neurons?

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

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What are interneurons?

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

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What are astrocytes?

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

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What are oligodendrocytes?

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

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What are Schwann cells?

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

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What are microglia?

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

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What shape do astrocytes have?

Star-shaped.

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What are the main functions of astrocytes?

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

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

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

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How do astrocytes respond to CNS trauma?

They contribute to scar tissue formation.

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What is the tripartite synapse?

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

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What is the Blood Brain Barrier (BBB)?

A selectively permeable barrier between the brain and blood supply.

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What is the primary function of the Blood Brain Barrier?

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

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What cells form the Blood Brain Barrier?

Endothelial cells and astrocyte end feet.

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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.

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What type of glial cell insulates axons in the CNS?

Oligodendroglia.

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How does one oligodendroglia cell myelinate axons?

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

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What type of glial cell insulates axons in the PNS?

Schwann cells.

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How does one Schwann cell myelinate axons?

One Schwann cell myelinates one segment on one axon.

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

They help guide the regrowth of damaged axons.

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What type of immune cell are microglia in the brain?

Resident immune cells; a type of macrophage.

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What is the primary function of microglia?

Cleaning up cellular damage and digesting debris (phagocytosis).

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How do microglia contribute to neural circuit remodeling?

They are involved in synaptic pruning.

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What role do microglia play after brain injury?

Wound healing and repair activity.

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What molecules do microglia synthesize and release?

Cytokines and growth factors.

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What disorders have microglia been implicated in?

Several neurodegenerative disorders.

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What is the function of dendrites in a neuron?

Receive input from other neurons.

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

Integrates information and provides metabolic and synthetic support.

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What is the function of the axon in a neuron?

Conducts action potentials to transmit information to other cells.

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How does the morphology of dendritic spines impact neuron function?

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

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What are the major functions of Microglia?

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

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What are the major functions of Astrocytes?

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

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What are the major functions of Schwann cells?

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