Psych 261 Lecture 9 Oct 7 2025 - Completed

The Cholinergic Systems

• Neurons in the basal forebrain will release acetylcholine (neurotransmitter) and send it to the cortex and the limbic system

• Neurons in the pons and midbrain will release acetylcholine and send it to the amygdala, thalamus, brainstem and cerebellum

The dopaminergic systems

The dopaminergic system includes the pathways ..

• The mesocortical system has dopaminergic neurons and it will send dopamine from the ventral tegmental area (VTA) to the cerebral cortex

• The mesolimbic system has dopaminergic neurons that will send dopamine from the ventral tegmental area to limbic structures and the basal ganglia

• The nigrostriatal system has dopaminergic neurons and it will send dopamine from the substantia nigra to the basal ganglia

• Dopaminergic neurons = neurons that releases dopamine 

The noradrenergic system

• Includes neurons that releases norepinephrine from the locus coeruleus to various parts of the brain

The serotonergic system

• Includes neurons that releases serotonin from the raphe nuclei of the brainstem to most parts of the brain

Visible light transmission microscopy: Removal

Animal is euthanized (put to death) and the brain is removed from skull

Visible light transmission microscopy: Fixation

Structures of the tissue are stabilized with a chemical to prevent breakdown of organelles

Visible light transmission microscopy: Dehydration

Water is removed from the tissue using a solvent

Visible light transmission microscopy: Embedding

Tissue is hardened by a medium

Visible light transmission microscopy: Microtomy

A microtome (a tool) is used to slice the brain into thin sections 

Visible light transmission microscopy: Staining

A chemical that attaches to specific structures is used to make them opaque to light —> structures become darker so that its easier to be seen under the microscope

Stains for visible light microscopy: Nissl stain

Highlights cell bodies using dyes like methylene blue or cresyl violet 

• Makes cell bodies more visible under the microscope

Stains for visible light microscopy: Myelin stain

Highlights axon bundles using dyes like luxol fast blue or osmium tetroxide

• Axons are covered in myelin

Stains for visible light microscopy: Golgi stain

Highlights all parts of the neuron using a silver-based compound

Fluorescence microscopy

Fluorophore is inserted into a tissue to highlight a particular structure

Two photon microscopy

1. A laser is used to release two photos simultaneously

2. Photons converge simultaneously on a single point in the tissue, therefore exciting the fluorophore

3. The photons that are emitted from the fluorophore are detected by a sensor

• The fluorophore produces (gives off) photons, and the microscope detects them to create the picture.

Transmission Electron Microscopy (TEM)

A electron beam passes through the tissue and the tissue can be stained with heavy metals 

Scanning electron microscopy (SEM)

An electron beam scans the surface of a tissue block and backscattered electrons are recorded

• Backscattered electrons are electrons that bounces back to the sensor so that it can be recorded

Computer axial tomography

• Produces x-rays that pass through the head

• Some x-rays are absorbed depending on the tissue’s density

Magnetic resonance imaging (MRI)

• Uses a strong magnetic field created by electromagnets made of coils that conduct electricity

• Smaller coils perpendicular to the main coil send and receive radio frequencies that influence the alignment of hydrogen atoms and produces signals used to form images of the body inside

• Focuses on hydrogen atoms

Diffusion tensor imaging (DTI)

An advanced MRI technique that visualizes the brains white matter by measuring the diffusion of water molecules to create a map that shows the neural pathways and how they are connected

• Measures how water molecules move in the brain

Diffusion tensor imaging (DTI): Unconstrained medium and constrained medium

Water molecules can move in two ways:

1. Unconstrained medium

• Isotropic movement: water molecules move in all directions

2. Constrained medium

• Anisotropic movement: water molecules only move in one direction, which is moving perpendicular to the axon 

Lesion-related techniques: Ablation

The removal or destruction of part of a biological tissue or structure by a surgical procedure or a toxic substance

Lesion-related techniques: Lesion

Any disruption or damage (e.g surgery, disease, injury) to the normal structure or function of an organ

Lesion-related techniques: temporary lesion

A nonpermanent disruption of the normal functioning of a specific brain area by an injection of drugs into that brain area or by electromagnetic stimulation of the area

Lesion-related techniques: aspiration

Removing a segment of the skull, pealing back the meninges and taking out a portion of the brain

Lesion-related techniques: Excitotoxic

Delivering a neurotoxin to cause neuronal overstimulation which kills the neuron

Lesion-related techniques: Heat (Thermal)

Destroying brain tissue by overheating it

Lesion-related techniques: Chemical

Injecting a chemical into a brain area that reduces activity of neurons

Lesion-related techniques: Cryogenic

Cooling a brain region to reduce activity in that region and slow down function

Stereotaxic surgery

• Target specific brain areas using a 3D coordinate system

• It holds the head still and guides electrodes or cannulas based on the brain’s map

• Bregma is a skull landmark where the coronal and sagittal sutures meet.

  • Used for measuring brain coordinates in stereotaxic surgery.