Microanatomy and Neurotransmission Flashcards by Ramona Charbel

Soma

Core region of the nervous system.

Processes information.

Cell body.

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Dendrites

Branching extensions of the nervous system that receive information.

of dendrites = amount of incoming information.

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Dendritic Spines

Protrusions from a dendrite that serves as a point of “contact” with other axons.

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Axons

Carries information to other neurons.

White matter.

The axon is a nerve when outside the CNS.

The axon is a tract within the CNS.

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Myelin Sheath

Insulates axons.

Signal travels further, faster, stronger.

This is what makes the neurons white.

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Axon Hillock

Point at which the axon leaves the soma.

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Axon Collateral(s)

Point at which axon branches out.

Allows message to be sent in multiple directions simultaneously.

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Terminal Button

Stops extremely close to dendritic spine of another neuron.

DOES NOT TOUCH OTHER NEURONS.

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Synapse

Junction between one neuron and the other.

Space between terminal button and dendritic spine.

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What are the two major cell types?

Neurons & Glia Cells.

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Neurons

Carry out brain’s major functions.

Many different types.

Can be very specialized.

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Glia Cells

Aid and modulate activity of neurons.

Maintenance, nourishment, metabolism, synthesis, and clean-up.

Provide insulation, nutrients, and support to all neurons.

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What are the different types of neurons?

Sensory neurons, Interneurons, Motor Neurons

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Sensory Neurons

Brings information to the brain (afferent).

Simplest type of neuron.

One single dendrite on one side, cell body, and single axon on the other side.

Transmits sensory information.

Subtypes:
Bipolar and Somatosensory neurons.

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Interneurons

Associate sensory and motor neurons.

Branch extensively to collect more information.

Subtypes: 
Stellate Cell (very small, many dendrites)

Pyramidal Cell (long axon with two sets of dendrites)

Prukinje Cell (output cell; extremely branched dendrites)

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Motor Neurons

Carry information (motor instructions) from brain into spinal cord and muscles (efferent).

Extensive dendritic networks to collect information from multiple sources.

Large cell bodies to process information.

All outgoing information must pass through motor neurons to reach target muscles.

Upper Motor Neuron vs. Lower Motor Neuron

What are the subtypes of Glia Cells?

Ependymal Cell, Astrocyte, Microglia, Oligodendroglia, Schwann Cell.

Ependymal (Subtypes of Glial Cells)

Located on walls of ventricles, produce CSF.

Small ovoid.

Astrocyte (Subtypes of Glial Cells)

Provides structural support, regulates blood brain barrier.

Star shaped, symmetrical.

Microglia (Subtypes of Glial Cells)

Insulates axons in the CNS.

Asymmetrical.

Schwann Cell (Subtypes of Glial Cells)

Insulates axons in the PNS.

Asymmetrical; wraps around peripheral nerves to form myelin.

Explain the role of Glial Cells in neuronal repair?

Microglia and Schwann cells play a role in repairing damaged neurones in the PNS:

The Microglia will remove debris.

Schwann cells form path for new axons to follow and insulate new axons.

Unfortunately, repair is much less common in CNS damage.

Neurotransmission occurs in what two different ways?

Electrical and Chemical.

In order for a neuron to communicate with another neuron, it must use both electrical and chemical signals.

Describe electrical communication.

Each neuron has a resting membrane potential (-70mV).

This occurs because the inside of the cell is negatively charged, relative to the outside cell.

Large negatively charged proteins (A-) inside.

Sodium ions (Na+) outside.

Potassium ions (K+) inside.

Chloride ions (Cl-) outside.

We rely on sodium-potassium pumps to keep this balance. Exchanges 3 Na+ (outbound) for 2 K+ (inbound) (-1 charge inside the cell, relative to outside the cell). Use up -2/3 of a cell’s energy expenditure.

Without any intervention, a cell will remain at -70mC indefinitely.

A stimulation is required to elicit a change in membrane potential (hyper- and de-polarization).

Channels and pores on the cell membrane surface allow ions in and out of the cell.

Different stimulations will open different pores/channels and allow ions to enter/exit the cell.

Hyperpolarization

Membrane potential is exaggerated, so difference between inside and outside are greater.

Depolarization

Membrane potential is diminished, so difference between inside and outside are lessened.

Action Potential

Brief (~1ms), but very large, reversal in polarity of an axon's membrane. The inside of the cell becomes positive relative to outside. Change is abruptly reversed, thanks to the Na+/K+ pumps, and the resting membrane potential is restored. Reversal of membrane polarity is due to an influx of Na+ and efflux of K+. Threshold potential is -50mV. Stimulation of cell is required to depolarize a membrane to -50mV, and depolarization continues until the inside of the cell reaches +30mV. Voltage-gated Ion Channels.

Voltage-Gated Ion Channels (Action Potentials)

Gated channels that opens/closes in relation to membrane potential. Na+ channels are sensitive to small changes in the membrane potential, so any ion fluctuations will cause them to open. Voltage gated K+ channels are attuned to -50mV. Once this threshold is met, they all open. The entire axon of a neuron is filled with voltage gated ion channels, and therefore an action potential propagates the entire length of an axon; from cell body -> terminal.

Chemical Communication

This communication between two neurons occurs via trading of neurotransmitters. Neurotransmitters are released into the synaptic clef - small space that separates two neurons. 1) An electrical signal arrives and triggers the release of neurotransmitters into the synaptic cleft. 2) Neurotransmitters bind to receptors on the post-synaptic neuron that triggers an action potential. 3) The neurotransmitter is recycled back into the pre-synaptic cell by reuptake transporters. Chemical transmission occurs in 4 steps: Synthesis, Release, Receptor Action, and Inactivation.

Neurotransmitter

Chemical released by a neuron onto a target site. Causes excitatory or inhibitory effect. Some debate over what constitutes neurotransmitter. There are different types, each of which conveys a different message. Exact number of neurotransmitters in unknown, but over 200 unique ones have been identified. Classes: Monoamines, Amino Acid, Peptide, and Transmitter Gases.

Synthesis (Chemical Transmission)

Synthesized from DNA/RNA and stored in vesicles located in the axon terminal.

Release (Chemical Transmission)

Transported to pre-synaptic membrane, released in response to action potential.

Receptor Action (Chemical Transmission)

Activate target receptors on post-synaptic membrane. Depending on the receptor, the post-synaptic cell can be excited or inhibited.

Inactivation (Chemical Transmission)

Must be inactivated or will continuously stimulate (or inhibit) post-synaptic neuron. Modes of inactivation are glial cell uptake, enzymatic degradation, diffusion and/or reuptake.

Monoamines (Class of NT)

Dopamine, Norepinephrine, Epinephrine, Serotonin, and Histamine.

Amino Acid (Class of NT)

Glutamate, GABA, Glycine, and D-Serine.

Peptide (Class of NT)

Somatostatin, Substance P, Opioid Peptides.

Transmitter Gases (Class of NT)

Nitric Oxide, Carbon Monoxide.