Psychology 304: Brain and Behaviour Lecture 10

The Cells of the Nervous System 1. What is the structure of the neuron? 2. What are glial cells?

By the end of today’s class, you should be able to: 1. describe the external structural features of the neuron. 2. describe the internal structural features of the neuron. 3. distinguish between unipolar, bipolar, and multipolar neurons. 4. identify the types and functions of glial cells.

What is the structure of the neuron? The external structure of the neuron is characterized by eight features:

Cell body: The metabolic center of the neuron. Also called the soma. Cell membrane: A semipermeable membrane that encloses the neuron. Axon: A long, narrow extension that projects from the cell body. Axon hillock: The cone-shaped region at the junction between the axon and cell body.

Myelin sheath: Fatty insulation surrounding the axon. Nodes of Ranvier: Gaps between sections of myelin. Dendrite: A short extension emanating from the cell body that receives contacts from other neurons. Terminal buttons (axon terminals): Button-like endings on axon branches that contain chemicals for communication between cells (i.e., neurotransmitters).

External Features of a Typical Neuron Dendrite Terminal button Cell body Nodes of Ranvier Axon Cell membrane Myelin sheath Axon hillock External Features of a Typical Neuron

Image of a Neuron Produced by Light Microscopy

The internal structure of the neuron is characterized by The internal structure of the neuron is characterized by nine features:

Nucleus: The spherical DNA-containing structure of the cell body. Cytoplasm: The clear internal fluid of a cell. Mitochondria: Sites of energy production and release. Endoplasmic reticulum: A system of folded membranes; Rough portions are involved in protein synthesis. Smooth portions are involved in fat synthesis.

Ribosomes: Located on rough endoplasmic reticulum Ribosomes: Located on rough endoplasmic reticulum. Cellular structures on which proteins are synthesized. Golgi complex: A system of membranes that packages molecules in vesicles. Microtubules: Tubules that allow for the rapid transport of material throughout neurons.

Endoplasmic reticulum Golgi complex Endoplasmic reticulum Ribosomes Internal Features of the Cell Body

Photomicrograph of a Neuron Cell Body

Synaptic vesicles: Spherical membrane packages that store neurotransmitter molecules ready for release from the terminal button. Neurotransmitters: Molecules that are released from the terminal buttons of active neurons and influence the activity of other cells.

Internal Features of the Terminal Button Microtubule Terminal button Mitochondrion Synaptic vesicles Neurotransmitters Internal Features of the Terminal Button

Images of Synaptic Vesicles Produced by Electron Micrography Synaptic contact Mitochondria Synaptic vesicles Images of Synaptic Vesicles Produced by Electron Micrography

There are three primary classes of neurons: 1. Unipolar (monopolar) neurons: Have one projection extending from the cell body. 2. Bipolar neurons: Have two projections extending from the cell body. 3. Mutlipolar neurons: Have more than two projections extending from the cell body (e.g., one axon and many dendrites). The most common type of neuron found in the CNS.

Bipolar neuron 1. 2. Multipolar neuron 3. Unipolar neuron Dendrites Axon Bipolar neuron 1. 2. Multipolar neuron 3. Unipolar neuron Classes of Neurons

Neurons vary substantially in size and complexity. In contrast to small neurons, large neurons detect and transmit more information and cover greater distances.

Variability in the Size and Complexity of Neurons

What are glial cells? Found throughout the nervous system; more common than neurons. Surround and support neurons, control the supply of nutrients to neurons, assisting in the exchange of chemicals between neurons, destroy and remove neurons damaged by disease or injury. Four types of glial cells have been identified:

1. Oligodendrocytes: Produce the myelin sheaths that 1. Oligodendrocytes: Produce the myelin sheaths that surround the axons of neurons of the CNS. Extensions from a single oligodendrocyte wrap around the axons of multiple neurons.

Myelination of Axons in the CNS by Oligodendrocytes

2. Schwann cells: Produce the myelin sheaths that 2. Schwann cells: Produce the myelin sheaths that surround the axons of neurons of the PNS. Multiple Schwann cells wrap around the axon of a single neuron. .

Myelination of Axons in the CNS by Oligodendrocytes vs Myelination of Axons in the CNS by Oligodendrocytes vs. Myelination of Axons in the PNS by Schwann Cells

3. Microglia: The smallest glial cells. Trigger 3. Microglia: The smallest glial cells. Trigger inflammatory responses to brain damage and remove injured or dead neurons. 4. Astrocytes: The largest glial cells. Hold neurons in place, provide nutrients (e.g., lactate) to neurons, limit the “dispersion” of neurotransmitters released by terminal buttons, and remove injured or dead neurons.

Microglia

Microglia

Structure of Astrocytes

Microglia Astrocytes

The Cells of the Nervous System 1. What is the structure of the neuron? 2. What are glial cells?