Microanatomy and Neurotransmission

Question 1

Soma

Answer 1

Core region of the nervous system.

Processes information.

Cell body.

Question 2

Dendrites

Answer 2

Branching extensions of the nervous system that receive information.

of dendrites = amount of incoming information.

Question 3

Dendritic Spines

Answer 3

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

Question 4

Axons

Answer 4

Carries information to other neurons.

White matter.

The axon is a nerve when outside the CNS.

The axon is a tract within the CNS.

Question 5

Myelin Sheath

Answer 5

Insulates axons.

Signal travels further, faster, stronger.

This is what makes the neurons white.

Question 6

Axon Hillock

Answer 6

Point at which the axon leaves the soma.

Question 7

Axon Collateral(s)

Answer 7

Point at which axon branches out.

Allows message to be sent in multiple directions simultaneously.

Question 8

Terminal Button

Answer 8

Stops extremely close to dendritic spine of another neuron.

DOES NOT TOUCH OTHER NEURONS.

Question 9

Synapse

Answer 9

Junction between one neuron and the other.

Space between terminal button and dendritic spine.

Question 10

What are the two major cell types?

Answer 10

Neurons & Glia Cells.

Question 11

Neurons

Answer 11

Carry out brain’s major functions.

Many different types.

Can be very specialized.

Question 12

Glia Cells

Answer 12

Aid and modulate activity of neurons.

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

Provide insulation, nutrients, and support to all neurons.

Question 13

What are the different types of neurons?

Answer 13

Sensory neurons, Interneurons, Motor Neurons

Question 14

Sensory Neurons

Answer 14

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.

Question 15

Interneurons

Answer 15

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)

Question 16

Motor Neurons

Answer 16

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

Question 17

What are the subtypes of Glia Cells?

Answer 17

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

Question 18

Ependymal (Subtypes of Glial Cells)

Answer 18

Located on walls of ventricles, produce CSF.

Small ovoid.

Question 19

Astrocyte (Subtypes of Glial Cells)

Answer 19

Provides structural support, regulates blood brain barrier.

Star shaped, symmetrical.

Question 20

Microglia (Subtypes of Glial Cells)

Answer 20

Insulates axons in the CNS.

Asymmetrical.

Question 21

Schwann Cell (Subtypes of Glial Cells)

Answer 21

Insulates axons in the PNS.

Asymmetrical; wraps around peripheral nerves to form myelin.

Question 22

Explain the role of Glial Cells in neuronal repair?

Answer 22

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.

Question 23

Neurotransmission occurs in what two different ways?

Answer 23

Electrical and Chemical.

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

Question 24

Describe electrical communication.

Answer 24

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.

Question 25

Hyperpolarization

Answer 25

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

Question 26

Depolarization

Answer 26

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

Question 27

Action Potential

Answer 27

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.

Question 28

Voltage-Gated Ion Channels (Action Potentials)

Answer 28

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.

Question 29

Chemical Communication

Answer 29

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.

Question 30

Neurotransmitter

Answer 30

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.

Question 31

Synthesis (Chemical Transmission)

Answer 31

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

Question 32

Release (Chemical Transmission)

Answer 32

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

Question 33

Receptor Action (Chemical Transmission)

Answer 33

Activate target receptors on post-synaptic membrane.

Depending on the receptor, the post-synaptic cell can be excited or inhibited.

Question 34

Inactivation (Chemical Transmission)

Answer 34

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.

Question 35

Monoamines (Class of NT)

Answer 35

Dopamine, Norepinephrine, Epinephrine, Serotonin, and Histamine.

Question 36

Amino Acid (Class of NT)

Answer 36

Glutamate, GABA, Glycine, and D-Serine.

Question 37

Peptide (Class of NT)

Answer 37

Somatostatin, Substance P, Opioid Peptides.

Question 38

Transmitter Gases (Class of NT)

Answer 38

Nitric Oxide, Carbon Monoxide.