PSYC 110: Nervous System; Cell Structure/Function; Neurodevelopment

PSYC110: The Brain & Behavior (SP 2025). Covers Lectures 1, 2, and 3.

Neurodevelopment

Development of the central nervous system; how axons find their end targets.

Neural Tube

A early hollow, elongated form/structure that the CNS begins embryonic life as.

Starts as a single cell (fertilized egg).

Pluripotent Cells

Early-stage cells that can become any cell type in the body.

Referred to as embryonic stem cells.

Stem Cells

Cells that can divide or develop into adult cells.

Neurulation

The creation of the neural tube and neural crest; happens ~24 days after conception.

Differentiation

The process of structures becoming more complex and functionally specialized.

Neuronal Proliferation

The creation of neurons.

3 Primary Vesicles (4 Weeks) of the Neural Tube

Prosencephalon, Mesencephalon, Rhombencephalon

5 Secondary Brain Vesicles (5 Weeks) of the Neural Tube

Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon.

Symmetrical Cell Division

Progenitor cells in the ventricular zone split to produce 2 new progenitor cells.

Creates the ventricular (VZ) & subventricular zones (SVZ).

Asymmetrical Cell Division

After 7 weeks, cells divide into 1 progenitor + 1 brain cell.

First brain cells produced are radial glia.

Radial Migration

1. Radial glia extends fibers from the ventricular zone (VZ) to the pia mater.

2. Glia fibers grow longer as new layers are added to the cortex

3. Neurons migrate along the radial glia to their place.

Tangential Migration

New cells push out previously formed cells from the proliferation zone.

Proliferation Zone

Where neurons were generated, in the ventricular or subventricular zones.

Spatiotemporal Gradient

Structures that are layered/constructed from the inside out.

Usually present for inner structures: thalamus, hypothalamus, cortex, etc.

Synaptogenesis

Neurons at their final location begin to form connections with other neurons by growing axons & dendrites and creating synapses.

Apoptosis

Death of neurons.

[e.g.]: Radial glial cells go through apoptosis and are transformed into astrocytes after the layers are created.

Synaptic Pruning

Death of synapses by apoptosis.

Continues after birth into the late-20s.

Myelination

Forming of the myelin sheath on axons.

Postnatal Brain Development

The human brain continues to grow after birth for ~25 years, growing up to 5x its size:

• Growth of synaptic connections between neurons.

• Myelination of axons.

Neurogenesis

Production of new neurons in the adult brain, which still contains some stem cells.

Neuroplasticity

The ability of the nervous system to change its activity to intrinsic or extrinsic stimuli by reorganizing its structure, functions, and connections.

Learning strengthens brain connections, which decay when neglected.

Biopsychology in Ancient Cultures

Ancient Chinese, Egyptian, and Indian cultures believed that the heart was the seat of thoughts and emotions; behavior was dependent on our body’s inner physiology.

Reticular Theory

Camillo Golgi’s hypothesis: Neurites of different neurons are fused together to form a continuous reticulum.

Early 1950s microscopes showed that neurites are not continuous with other neurons.

Neuron Doctrine

Santiago Ramon y Cajal’s hypothesis: Neurons are separate cells that communicate by contact.

Shared a Nobel Prize (Physiology or Medicine) with Golgi in 1908.

Visualizing Cells: Golgi Stain

Makes only a few neurons stand out so they can be seen separately.

Developed by Golgi and applied by Cajal to prove that brain cells are separate.

Immunofluorescent Staining

Uses protein-specific antibodies chemically labeled with fluorescent dyes.

Allows visualization of those proteins using light microscopy.

Brainbow

Genetic-cell labeling method that allows visualization of individual neurons in a brain slice using hundreds of hues of fluorescent proteins.

Dr. Suzanne Herculano-Houzel

Used a “brain soup” method to count the number of human brain cells:

1. Liquefied the brain & took a sample.

2. Stained the neurons’ nuclei.

3. Counted them under a microscope.

Number of Neurons in a Human Brain

~86 billion neurons that receive an avg. of ~5000 synaptic contacts each.

DNA Transportation Out the Nucleus

DNA cannot leave the nucleus on it’s own. It must go through:

Transcription: DNA ⇒ mRNA

Translation: mRNA ⇒ Proteins

Transportation: Proteins ⇒ Out

Nucleus

Located in the neuron’s cell body (soma) and contains genetic material.

Semipermeable Membrane

Outer surface of the neuron; allows smaller molecules without electric charges to pass through it. Stops larger or highly charged molecules.

Soma

Cell body of the cell; makes up the gray matter of the brain.

Dendrites

Antennae that protrude from a neuron’s soma to receive synapses.

Covered in dendritic spikes that change over time with specialized receptors.

Classifies neurons.

Axon Hillock

A part of the soma that integrates all messages in the neuron & initiates action potentials.

Axon

A wirelike structure that protrudes from the soma to axon terminals.

Insulated by a myelin sheath.

Myelin Sheath

A fatty membrane that insulates the axon and helps speed neural impulses.

Nodes of Ranvier

Gaps in the myelin sheath.

Axon Terminals

Branches at the end of an axon (on the opposite side of the dendrites & soma) that forms junctions with other cells.

Contains the terminal buttons & synaptic vesicles.

Terminal Buttons

The region in the axon terminal where signals traveling down the axons end at.

Synaptic Vesicles

Parts of the terminal buttons (in the axon terminal) that house neurotransmitters.

Glial Cells

Provide physical & metabolic support to neurons.

Notable Neuroglia: Oligodendrocytes (CNS), Schwann Cells (PNS), Microglia, Astrocytes

Astrocytes

Clears neurotransmitters from the synaptic cleft.

Secretes proteins that help neurons from connections.

Most numerous glial cell in the brain.

Astrocytic Process

The process of astrocytes wrapping around synapses to isolate them &regulate neurotransmitter levels.

Microglia (Phagocytes)

Clean up cellular debris, pathogens, foreign material, etc. produced by damage

Oligodendrocytes

Central nervous system (CNS) cells that produce the myelin sheath.

Forms multiple (>30) sheaths around different axons.

Schwann Cells

Peripheral nervous system (PNS) cells that form the myelin sheath, regenerate nerves, and provide nutrients to axons.

Forms a single sheath around one axon.

Central Nervous System (CNS)

Part of the nervous system composed of the brain + spinal cord.

Peripheral Nervous System (PNS)

Part of the nervous system composed of the autonomic + somatic nervous system.

Gray Matter

The part of the brain that contains the cell bodies (somas) in the CNS.

White Matter

The part of the brain that contains myelinated axons running to and from neurons.

Somatic Nervous System

Part of the PNS; relays sensory & motor information to/from the CNS.

Connects the CNS to the organs, limbs, and skin.

Autonomic Nervous System

Part of the PNS; controls our internal organs & glands.

Can be divided into the sympathetic + parasympathetic nervous systems.

Sympathetic Nervous System

“Fight or Flight”: Physiological changes that direct blood flow and oxygen to skeletal muscles.

Enables the organism to move quickly if threatened.

Parasympathetic Nervous System

“Rest & Digest”: Physiological changes that signify resting and gathering energy.

Meninges

3 protective layers around the brain:

1. Dura Mater “Tough Mother”

2. Arachnoid Mater

3. Pia Mater “Tender Mother”

Dura Mater “Tough Mother”

Tough, outermost, flexible layer of meninge.

Arachnoid Mater

Middle meninge layer, resembles spiderwebs.

Subarachnoid Space

Hollow-ish space between the arachnoid and pia mater meninges that is filled with cerebrospinal fluid (CSF).

Pia Mater “Tender Mother”

Delicate, innermost layer of meninge.

Cerebrospinal Fluid (CSF)

A filtrate of blood plasma that provides nourishment, removes waste, and protects the brain.

Fills the ventricular system and subarachnoid space.

Ventricular System

Consists of ventricles: interconnected cavities in the brain.

Cerebral Aqueduct

The ventricle that connects the 3rd ⇔ 4th ventricles.

Interventricular Foramen

The ventricle that connects the lateral ⇔ third ventricles

Choroid Plexus

A network of blood vessels in each ventricle of the brain; derived from the pia mater

Secretes cerebrospinal fluid.

Provides a barrier between the blood and the brain.

Spinal Cord

Part of the CNS; acts as a relay system connecting the brain to the world.

Starts at the brain stem and ends just below the ribs.

Surrounded by spinal meninges.

Dorsal Horn

“In the door…”: Sensory/Afferent information IN → from the sensory pathways (gray matter) of the PNS

Ventral Horn

“Out the vent…”: Motor/Efferent information OUT ← from the sensory pathways (gray matter) of the PNS

Neuron Circuit

Groups of neurons connected by synapses that process specific types of information.

Gyri

The bumps on the cerebrum’s (brain’s) surface.

Sulci

The grooves in the cerebrum’s (brain’s) surface.

Fissures

Especially deep sulci (grooves) in the brain’s surface.

[e.g.]: Medial longitudinal, lateral, central

Medial Longitudinal Fissure

The fissure that splits the brain from front to back into its two hemispheres.

Lateral (Sylvian) Fissure

The fissure in between the frontal/parietal and temporal lobes

Central Fissure

The fissure in between the frontal and parietal lobes.

Resting Membrane Potential

The tendency of the cell’s inside to be more negative (-65mV) compared to the outside when at rest.

Membrane Potential

The difference in charge between the intracellular and extracellular space of a neuron.

Potential

The separation of electrical charge across the membrane; has the potential to be excitable.

Sodium (NA+)

A positively-charged ion that is more concentrated outside the cell in extracellular fluid.

Tendency to move inside the cell.

Potassium (K+)

A positively-charged ion that is more concentrated inside the cell near the membrane in intracellular fluid.

Tendency to move outside the cell.

Chloride (CL-)

A negatively-charged ion that is evenly distributed on both sides of the membrane.

All-or-None Phenomenon

An incoming signal from another neuron will either be sufficient or insufficient to reach the threshold of excitation.

No in-between; no stopping it when it has started.

The action potential is propagated at its full strength at every gap of the axon.

Stronger stimulus = more frequent signal.

Action Potential

1. Ions are lined up on either side of the membrane

   • NA+ outside; K+ inside

2. A neuron receives a signal/stimulus from the dendrites and abruptly changes its state

3. Depolarization

4. Threshold of excitement is triggered for an action potential

5. The peak of the NA+ ion surge is reached

6. Repolarization

7. Hyperpolarization

8. Resumes resting potential

Depolarization

Sodium (NA+) channels open and NA+ ions flow into the cell.

Threshold of Excitement

When enough NA+ is inside the cell (making it more positively-charged), a threshold (-50 to -55 mV) is triggered for an action potential.

An action potential only happens when the threshold is reached by the signal/stimulus.

Repolarization

Potassium (K+) channels open and K+ ions flow out the cell.

Hyperpolarization

The state after repolarization; the cell overcorrects the positive charge and becomes too negative.

Saltatory Conduction

The process by which NA+ ions skip from one Node of Ranvier to the next.

1. NA+ ions enter the axon via depolarization

2. NA+ ions repel each other down the axon (positive charges push against one another)

3. The next area in the axon becomes overly positive (polarized)

   • New NA+ channels open

   • More NA+ surges into the axon

4. The previous area hyperpolarizes (becomes overly negative)

   • NA+ channels cannot open there

   • An action potential only goes in one direction

5. No new sodium channels where myelin covers the axon ⇒ NA+ “skips” ahead, speeding up the process

2 Types of Neuronal Communication

Neurons send both chemical & electrical signals:

• Chemical: Neurotransmitters transmit intercommunication.

• Electrical: Transfer of ions

Chemical Communication

1. Neurotransmitter (NT) synthesis

2. NTs are loaded into synaptic vesicles at the terminal buttons (end of axons)

   • Waiting for an action potential to reach the presynaptic terminal to be released

3. The action potential reaches the presynaptic cleft

4. NTs release

5. Vesicles (loaded with NTs) fuse with the presynaptic terminal

6. NTs bind to postsynaptic receptors

7. Biochemical/electrical changes in postsynaptic cells occur

8. Excess NTs are cleared:

   • Reuptake

   • Get broken down

   • Drift away naturally/get taken away by astrocytes

Neurotransmitter Reuptake

Neurotransmitters are reabsorbed back into the axon terminal they were released from.

Electrical Communication

Electrical signals are passed through the connexon between two neurons.

Faster at conducting nerve impulses, but can only produce simple behavior.

Connexon

A protein structure that physically bridges two neurons at their gap junctions and allows for electrical communication.

Allows both electrical signals and small molecules to pass between neurons in both directions.

Excitatory Synapse

When the synapse releases positively-charged ions; triggers depolarization and a reactionary potential in the next synapse.

Inhibitory Synapse

When the synapse releases negatively-charged ions; triggers hyperpolarization and stops the neuron action chain.