Lectures: Week 2, Cells of the Nervous System

Central Nervous System (CNS)

The part of the nervous system consisting of the brain and spinal cord.

Peripheral Nervous System (PNS)

All nerves that relay information between the central nervous system and the body.

Neuroglia

Supporting cells in the nervous system that constitute about half the volume of the CNS.

VGG

An example of an artificial neural network that mimics biological neural network structure and is useful for vision-based applications and brain research.

Soma (Cell Body)

The part of a neuron containing the nucleus and most internal structures; the nucleus holds DNA which directs protein synthesis critical to cell functioning.

Mitochondria

Organelles that convert nutrients into ATP for the cell's functions.

Microtubules

Structures responsible for axoplasmic transport, moving substances along the axon from the cell body to terminal buttons.

Dendrites

Thin, branching fibers (from the Greek for 'tree') that receive information from other cells; typically shorter than axons and may have dendritic spines.

Axon

A single, thicker, longer fiber that carries information away from the cell body via the action potential; begins at the axon hillock.

Myelin sheath

An insulating lipid material found on many neurons that prevents signal spreading to neighboring neurons and speeds transmission.

Nodes of Ranvier

Small gaps of unmyelinated axon between myelin segments, found only in the CNS, that help speed neurotransmission.

Terminal buttons

Knobby structures at the axon's end where synapses form and neurotransmitters are released via synaptic vesicles.

Synapse

A junction where information is transmitted from one neuron to another, which can form on either the cell body or dendrites.

Multipolar neurons

The most common type of neuron in the brain, characterized by many branching dendrites; includes motor neurons whose cell bodies are in the CNS but whose axons project into the PNS.

Bipolar neurons

Neurons having two axon-like processes (one toward dendrites, one toward terminal buttons), typically associated with visual and auditory sensory systems.

Unipolar neurons

Neurons characterized by a single axonal stalk that branches into both dendrites and terminal buttons, typically associated with somatosensory systems and found deep in the skin.

Astrocytes

CNS supporting cells that provide nutrients to neurons, regulate extracellular chemical composition, isolate synapses to limit neurotransmitter dispersion, perform phagocytosis of damaged cells, and critically form the blood-brain barrier.

Microglia

The smallest glial cells, making up $5-10\%$ of brain cells, which serve as the primary active immune defense of the CNS by acting as phagocytes.

Oligodendrocytes

CNS supporting cells that form the myelin sheath by wrapping paddle-shaped processes around axon segments, leaving gaps called nodes of Ranvier.

Schwann cells

PNS supporting cells that form myelin in the PNS by wrapping their entire cell body around peripheral neurons, with one cell forming one myelin segment and leaving no nodes of Ranvier.

Blood-Brain Barrier

A functional barrier formed by astrocytes around brain blood vessels with very few gaps, maintaining electrolyte balance and protecting the brain from toxins.

Paul Ehrlich

The researcher who demonstrated the existence of the blood-brain barrier by showing that blue dye injected into the bloodstream stained other organs but not the brain.

Methylene blue

A substance notable for randomly crossing the blood-brain barrier, increasing oxygen in the bloodstream, and having medical uses such as treating cyanide poisoning.

Area postrema

A region of the medulla where the blood-brain barrier is weak, allowing small amounts of ingested toxins to signal the brain to induce vomiting.

L-dopa (levodopa)

A dopamine precursor discovered in the 1950s that crosses the blood-brain barrier and is converted to dopamine in the brain, used as the standard treatment for Parkinson's disease.

Myelin Sheath

Insulates the axon and speeds signal transmission, up to $120\,m/s$.

Central Nervous System (CNS)

System consisting of the brain and spinal cord, in which primary neurons are multipolar neurons.

Peripheral Nervous System (PNS)

All nerves that relay information between the central nervous system and the rest of the body.

Sensory Neurons

Neurons that send sensory information to the brain.

Motor Neurons

Neurons that send signals from the central nervous system to muscles.

Interneurons

Neurons that relay signals between sensory neurons and motor neurons.

Withdrawal Reflex

A circuit where a sensory neuron detects a stimulus and sends an excitatory signal to the spinal cord so a motor neuron contracts the muscle, which can be inhibited by the brain via an interneuron.

Alan Hodgkin and Andrew Huxley

Scientists who experimentally confirmed the discovery of the action potential in 1952 using the giant axon of a squid.

Squid Giant Axon

Axon used in 1952 experiments that measured up to $1\,mm$ in diameter, making it approximately 100 times larger than human axons.

Resting Membrane Potential

The charge of a neuron at rest, measuring $-70\,mV$ inside relative to the outside.

Depolarization

The movement of a neuron's membrane potential toward zero caused by applying a positive charge.

Action Potential

An all-or-none electrical event occurring when the threshold of excitation is reached, briefly making the potential inside the neuron positive.

Hyperpolarization

A brief phase following an action potential where the neuron's potential becomes more negative than $-70\,mV$ before resetting.

Diffusion

The movement of molecules from high to low concentration, which pushes potassium ($\text{K}^+$) out of the cell and sodium ($\text{Na}^+$) and chloride ($\text{Cl}^-$) into the cell.

Electrostatic Pressure

The force created by charge attraction and repulsion, which attracts potassium ($\text{K}^+$) and sodium ($\text{Na}^+$) inside the negative cell interior and repels chloride ($\text{Cl}^-$) to the outside.

Ion Channels

Specialized protein molecules that allow specific ions to enter or leave the cell in an organized manner.

Sodium-Potassium Pump

A protein pump requiring ATP from mitochondria that actively transports $3\,\text{Na}^+$ out of the neuron for every $2\,\text{K}^+$ brought in.

Nodes of Ranvier

Gaps along myelinated axons where extracellular fluid contacts the axon, allowing sodium ($\text{Na}^+$) to rush in and regenerate the action potential.

Saltatory Conduction

The process where an action potential effectively jumps from node to node along a myelinated axon to maintain signal strength and increase transmission speed.

Axodendritic synapse

A synapse where a terminal button connects to the dendrites of a postsynaptic cell, which may form on a smooth dendrite or dendritic spines.

Axosomatic synapse

A synapse where a terminal button connects to the cell body (soma) of a postsynaptic cell.

Axoaxonic synapse

A synapse where a terminal button connects to the axon of a postsynaptic cell; it does not directly cause action potentials but modulates neurotransmitter release at the primary synapse.

Presynaptic membrane

The membrane of the terminal button where neurotransmitters are released into the synaptic cleft.

Synaptic cleft

The gap between the terminal button and the postsynaptic cell.

Postsynaptic membrane

The membrane that receives the chemical message, containing receptor sites and ion channels in a region called the postsynaptic density.

Postsynaptic density

A region within the postsynaptic membrane that contains receptor sites and ion channels.

Microtubules

Structures that transport synaptic vesicles carrying neurotransmitters from the soma down the axon to the terminal button.

Agonists

Drugs that mimic neurotransmitters and activate the receptor site.

Antagonists

Drugs that bind to the receptor site but block it without activating it.

Ionotropic receptors (ligand-gated ion channels)

Receptors where neurotransmitter binding directly opens the ion channel, resulting in a faster onset and shorter duration.

Metabotropic receptors (G protein-coupled)

Receptors where neurotransmitter binding activates a G protein, triggering a secondary messenger cascade that opens an ion channel elsewhere in the membrane, producing a slower onset and longer duration.

Excitatory Postsynaptic Potential (EPSP)

A change in membrane potential where the membrane depolarizes (becomes less negative), bringing the cell closer to its firing threshold.

Inhibitory Postsynaptic Potential (IPSP)

A change in membrane potential where the membrane hyperpolarizes (becomes more negative), making firing less likely.

Neural Integration

The process by which EPSPs and IPSPs sum together across thousands of simultaneous synapses to determine whether a neuron fires.

Reuptake

A neurotransmitter termination process where a transporter protein on the terminal button removes the neurotransmitter from the cleft to be recycled or broken down.

SSRIs (Selective Serotonin Reuptake Inhibitors)

Drugs (e.g., Prozac, Zoloft) that block serotonin reuptake, increasing serotonin levels and duration in the synapse.

Enzymatic deactivation

A neurotransmitter termination process where a specific enzyme destroys the neurotransmitter.

Acetylcholinesterase

An enzyme that deactivates acetylcholine, a neurotransmitter involved in attention, motivation, arousal, and muscular contraction.

Autoreceptors

Receptors on the presynaptic membrane that detect the neuron's own neurotransmitters and slow production and release as a feedback mechanism when enough accumulate.

Hormones

Chemicals secreted by endocrine glands or cells in various organs that affect cells responsible for broader bodily functions.

Leptin

A hormone that decreases hunger by inhibiting neurons that signal low blood sugar.

GLP-1 medications

Medications (e.g., Ozempic) that mimic the function of leptin to reduce hunger, used for diabetes and weight loss.

Axodendritic synapse

A synapse where a terminal button connects to the dendrites of a postsynaptic cell, which may form on a smooth dendrite or dendritic spines.

Axosomatic synapse

A synapse where a terminal button connects to the cell body (soma) of a postsynaptic cell.

Axoaxonic synapse

A synapse where a terminal button connects to the axon of a postsynaptic cell; it does not directly cause action potentials but modulates neurotransmitter release at the primary synapse.

Presynaptic membrane

The membrane of the terminal button where neurotransmitters are released into the synaptic cleft.

Synaptic cleft

The gap between the terminal button and the postsynaptic cell.

Postsynaptic membrane

The membrane that receives the chemical message, containing receptor sites and ion channels in a region called the postsynaptic density.

Postsynaptic density

A region within the postsynaptic membrane that contains receptor sites and ion channels.

Microtubules

Structures that transport synaptic vesicles carrying neurotransmitters from the soma down the axon to the terminal button.

Agonists

Drugs that mimic neurotransmitters and activate the receptor site.

Antagonists

Drugs that bind to the receptor site but block it without activating it.

Ionotropic receptors (ligand-gated ion channels)

Receptors where neurotransmitter binding directly opens the ion channel, resulting in a faster onset and shorter duration.

Metabotropic receptors (G protein-coupled)

Receptors where neurotransmitter binding activates a G protein, triggering a secondary messenger cascade that opens an ion channel elsewhere in the membrane, producing a slower onset and longer duration.

Excitatory Postsynaptic Potential (EPSP)

A change in membrane potential where the membrane depolarizes (becomes less negative), bringing the cell closer to its firing threshold.

Inhibitory Postsynaptic Potential (IPSP)

A change in membrane potential where the membrane hyperpolarizes (becomes more negative), making firing less likely.

Neural Integration

The process by which EPSPs and IPSPs sum together across thousands of simultaneous synapses to determine whether a neuron fires.

Reuptake

A neurotransmitter termination process where a transporter protein on the terminal button removes the neurotransmitter from the cleft to be recycled or broken down.

SSRIs (Selective Serotonin Reuptake Inhibitors)

Drugs (e.g., Prozac, Zoloft) that block serotonin reuptake, increasing serotonin levels and duration in the synapse.

Enzymatic deactivation

A neurotransmitter termination process where a specific enzyme destroys the neurotransmitter.

Acetylcholinesterase

An enzyme that deactivates acetylcholine, a neurotransmitter involved in attention, motivation, arousal, and muscular contraction.

Autoreceptors

Receptors on the presynaptic membrane that detect the neuron's own neurotransmitters and slow production and release as a feedback mechanism when enough accumulate.

Hormones

Chemicals secreted by endocrine glands or cells in various organs that affect cells responsible for broader bodily functions.

Leptin

A hormone that decreases hunger by inhibiting neurons that signal low blood sugar.

GLP-1 medications

Medications (e.g., Ozempic) that mimic the function of leptin to reduce hunger, used for diabetes and weight loss.

Central Nervous System (CNS)

The part of the nervous system consisting of the brain and spinal cord.

Peripheral Nervous System (PNS)

All nerves that relay information between the central nervous system and the body.

Neuroglia

Supporting cells in the nervous system that constitute about half the volume of the CNS.

VGG

An example of an artificial neural network that mimics biological neural network structure and is useful for vision-based applications and brain research.

Soma (Cell Body)

The part of a neuron containing the nucleus and most internal structures; the nucleus holds DNA which directs protein synthesis critical to cell functioning.

Mitochondria

Organelles that convert nutrients into ATP for the cell's functions.

Microtubules

Structures responsible for axoplasmic transport, moving substances along the axon from the cell body to terminal buttons.

Dendrites

Thin, branching fibers (from the Greek for 'tree') that receive information from other cells; typically shorter than axons and may have dendritic spines.

Axon

A single, thicker, longer fiber that carries information away from the cell body via the action potential; begins at the axon hillock.

Myelin sheath

An insulating lipid material found on many neurons that prevents signal spreading to neighboring neurons and speeds transmission.