Lecture 1: Cell Biology of the Nervous System

Question 1

What is unique about a neurons?

Answer 1

It is able to generate and self-propagate electrical signals

Question 2

Where does the electrical signal of a neuron begin?

Answer 2

In the cell body (somata)

Question 3

What is a Golgi Stain?

Answer 3

A silver stain. It stains a limited number of cells at random in their entirety. The mechanism by which this happens is still largely unknown.

Question 4

What is the cell body (soma) of a neuron?

Answer 4

Consists of a nucleus surrounded by cytoplasm (perikarya). Contains genetic material, protein production and processing, as well as metabolic maintenance.

Question 5

What is in the nucleus of a neuron?

Answer 5

Contains genetic material and proteins for processing of genetic material. Clumping or condensations in nucleus called chromatin and large dense spherical masses called nucleoli are seen in nucleus.

Question 6

What stains/dyes can be used to stain the cytoplasm? There are 3. What is a name for this kind of stain?

Answer 6

Toludine Blue, Cresyl Violet, Methylene Blue - Stain a very basophilic component in the perikarya – which is called nissl substance – the stain is called a nissl stain.

Question 7

What can Nissl stains be used for?

Answer 7

Differentiation of neurons. It was also found to be disrupted by stresses (excess stimulation, cutting axon).

Question 8

What is the Endoplasmic Reticulum? What about Rough ER?

Answer 8

ER are layers of flattened cisternae. When they are studded with ribosomes (producing proteins) it is called rough or granular endoplasmic reticulum. Proteins are secreted into the cisternae. Without ribosomes it is called smooth or agranular endoplasmic reticulum, involved in the transport of proteins.

Question 9

What is the GOLGI apparatus?

Answer 9

Cisternae involved in post-translational modifications of protein and packaging for transport.

Question 10

What is an axon?

Answer 10

Process of soma specialized for transmitting electrical impulses over a distance without losing energy (self propagating) and passing (or transmitting) signal to a second neuron or cell.

Question 11

What is the axon terminal?

Answer 11

The portion of the axon specialized for transmitting nerve impulses to another cell via a specialized connection. The axon terminal is not myelinated.

Question 12

What is the connection to the target (of the signal) called?

Answer 12

The synapse

Question 13

What usually surrounds axons? What is its purpose?

Answer 13

Myelin – a membranous wrapping around the axon, forming an insulating sheath that increases the speed of conduction.

Question 14

What are “Nodes of Ranvier”?

Answer 14

Breaks along the myelination of the axon. Action potentials passively flow from node to node, where voltage gated channels serve to renew the action potential.

Question 15

What is Actin? How big is it?

Answer 15

Microfilament. It acts as support, helps with compartmentalization and protein trafficking. This is the smallest filament at 5nm in diameter.

Question 16

What is a neurofilament and how big is it?

Answer 16

These are from a family of “intermediate filaments”. They are found in all parts of the neuron but are most concentrated in the axon and the axon terminal. Thus neurofilament stains have been used to localize axons and their terminals. It is 10 nm in diameter.

Question 17

What are microtubules and how big are they?

Answer 17

Wider, long tubular elements involved in protein transport/trafficking within cells, found in almost all cell types. Special function in axonal transport. 20-26 nm in diameter.

Question 18

What is axoplasmic flow? What is its timescale? Does it use any filaments or proteins?

Answer 18

Bulk flow of cytoplasm from cell body through processes. It is slow, 1-10 mm/day. This does not require any filaments; it is simply diffusion from the cell body.

Question 19

What is axoplasmic transport?

Answer 19

Only in axons. Faster, uses microtubules (and can be stopped by colchicine which disrupts microtubules). Flow is both ways from cell body to axon terminal and from axon terminal to cell body.

Question 20

What is retrograde transport? What is its timescale? What proteins and filaments does it use?

Answer 20

A type of axoplasmic transport. From terminal to cell body. 50-250 mm/day. Uses dynein and microtubules. Uptake in terminals (e.g. growth factors) and transport to soma in one function. NOTE: Slower than anterograde transport.

Question 21

What is anterograde transport? What is its timescale? What proteins and filaments does it use?

Answer 21

A type of axoplasmic transport. From cell body to axon terminal. 100-400 mm/day. Uses kinesin and microtubules. Proteins such as neurotransmitters are sent to terminal. NOTE: Faster than retrograde transport.

Question 22

What are the plus and minus ends of the microtubules? Which way and with what proteins does a vesicle travel along the microtubules?

Answer 22

In neurons, as the microtubules grow from the cell body through the processes, the plus end is more peripheral. Dynein moves vesicles or other cargo towards the minus end (towards soma) and Kinesins move vesicles or other cargo towards the plus end (the axon terminal)

Question 23

What is contained in the axon terminal and what happens during depolarization? Define synaptic cleft.

Answer 23

Contains mitochondria, packages of chemical neurotransmitters called “vesicles”, synapses and vesicles related proteins and a presynaptic specialization that forms a pre-synaptic density. The terminal when depolarized allows entrance of calcium and subsequent release of the contents of vesicles into the space between the axon terminal and its target. This space is called the synaptic cleft.

Question 24

Define an electrical synapse.

Answer 24

An electrical signals passes directly between neurons using gap junctions. Uncommon in mammals.

Question 25

Define a chemical synapse.

Answer 25

Has a “chemical” intermediary between neurons, that allows for processing. Different chemicals can be released with different post-synaptic actions. The action is the function of the receptor not the transmitter/modulator itself. The same transmitter can have very different post-synaptic actions depending on the receptor. Chemical synapses are most often unidirectional.

Question 26

Why would we want to have a chemical synapse rather than an electrical synapse?

Answer 26

Allows for the integration between inhibitory and excitatory synapses; different neurotransmitters affect the cell and each synapse is neurotransmitter specific.

Question 27

What is an ionotropic channel?

Answer 27

A ligand gated ion channel. The ligand binds to a receptor subunit and influences the opening of the channel.

Question 28

What is a metabotropic channel?

Answer 28

A receptor that is linked to a second messenger (often G-proteins). Binding of the ligand to the receptor starts a pathway that can lead to excitation or inhibition.

Question 29

What is a dendrite?

Answer 29

Process of the soma specialized for receiving inputs, processing inputs and generating electrical impulses. Multiple dendrites can create a much larger area for receiving input than just the soma. Dendrites can branch to form primary, then secondary, then tertiary, etc branches.

Question 30

What are dendritic spines?

Answer 30

Thorn-like protrusions or evaginations from the dendrite form spines. Spines on the dendrite that create additional area and allow for processing to be able to occur (plasticity and signal integrations).

Question 31

What are ion channels and what do they do?

Answer 31

Ion channels (including K, Na, Cl, and Ca) are proteins in the membrane that allow ions to pass through. They influence post -synaptic response. Some are voltage gated, influenced by the depolarization or hyperpolarization, others are downstream to the actions of second messengers and other intracellular pathways.

Question 32

Name three types of synapses.

Answer 32

Axo-somatic, axo-dendritic (somtimes on spines), axo-axonal.

Question 33

What is an excitatory synapse?

Answer 33

Often has large round vesicles (excitatory amino acid - glutamate). Makes an asymmetric synapse (more post-synaptic density than pre).

Question 34

What is an inhibitory synapse?

Answer 34

Often has flattened (glycine) or oval (GABA) vesicles. Makes a symmetric synapse (equal pre and postsynaptic densities). Note: Flattened glycine vesicles are a consequence of the methods used to look at them. By using flash freezing, we see that these vesicles are not flattened.

Question 35

What are some differences between excitatory and inhibitory synapses?

Answer 35

Shape of vesicles, prominence of presynaptic densities, total area of the active zone, width of the synaptic cleft, and presence of a dense basement membrane. Excitatory synapses end on dendritic shafts, but frequently contact dendritic spines. Inhibitory synapses often end on the cell body.

Question 36

How does position vs number of inputs dictate signaling in the neuron?

Answer 36

The closer to the axon hillock or point of summation, the greater the influence of the synapse – regardless of number. Equidistance implies quantity matters.

Question 37

What is a unipolar neuron?

Answer 37

A cell body and one process (an axon). Only found in invertebrates.

Question 38

What is a pseudo-unipolar neuron?

Answer 38

A cell body and two processes, joined to give the appearance of one process. Found in certain sensory systems (e.g. spinal cord)

Question 39

What is a bipolar neuron?

Answer 39

A cell body and two processes, an axon and a dendrite or a central and peripheral process. Found in certain sensory systems (e.g. retina and auditory nerve).

Question 40

Draw a unipolar neuron.

Answer 40

Question 41

Draw a bipolar neuron.

Answer 41

Question 42

Draw a pseudo-unipolar neuron.

Answer 42

Question 43

What is a multipolar neuron?

Answer 43

Multipolar neurons have a soma and axon with many dendrites. These are the most common type of neuron in the central nervous system.

Question 44

Draw a multipolar neuron.

Answer 44

Many answers are correct. Here is one example.

Question 45

How can neurons be differentiated based on size and function?

Answer 45

Size: Golgi Type 1 = Large, Golgi Type 2 = Small

Function: Projection neuron (axons go far away) vs interneuron (local connections).

Question 46

What are four ways neurons can be differentiated?

Answer 46

Size, shape, function, excitatory vs inhibitory.

Question 47

What are Glial cells? What are they called in the PNS? CNS?

Answer 47

Cells that provide support and help maintane homeostasis.

CNS = Oligodendrocytes

PNS = Schwann Cells

Question 48

What are oligodendrocytes?

Answer 48

Glial cells found in the CNS. They form myelin to warp around axons in the CNS. Each oligodendrocyte forms many internodal segments.

Question 49

What are Schwann Cells?

Answer 49

Glial cells in the PNS. They form myelin to wrap around axon in the PNS. Each Schwann cell forms one internodal segment. The external surface is covered by a basal lamin, and then three connective tissue sheates (endoneurium (inner most), perinerium, and epineurium (outermost).

Question 50

What are satellite cells?

Answer 50

Glia that surround peripheral ganglion (neuronal soma) in the PNS.

Question 51

What is a group of neuron cell bodies in the CNS called?

Answer 51

Nucleus.

Question 52

What is a group of neuron cell bodies in the PNS called?

Answer 52

Ganglions.

Question 53

What are microglia?

Answer 53

Glia cells that respond to injury or foreign substance and are part of an immune response including phagocytosis - acting as macrophages when activated. They can secrete cytokines and prostoglandins - can actually cause damage to neurons as well as respond to damage. Sometimes referred to as “Surveying microglia”. They have processes that can interface with synaptic spines and participate in synaptic plasticity. They can also release trophic factors.

Question 54

What are astrocytes (macroglia)?

Answer 54

Glia cells. They have glial fibrillary acidic protein (GFAP) as intermediate filament. They function as part of the bood brain barrier (endfeet) and can also multiply upon trauma to form barries to damaged areas.

They provide a framework for neuronal migration and neuronal process migration during development.

Can secrete growth factors and cytokines - that can support and maintan neurons

Can release neurotransmitters.

Can influences neuronal excitability and synaptic transmission and plasticity.

Their signaling can regulate neural network function.

Question 55

What do astroglial cells do?

Answer 55

Play a critical role in the uptake of many transmitters. Important to stop effect of transmitter as well as to provent excitotoxicity.

Question 56

What are fibrous astrocytes?

Answer 56

Astrocytes in the white matter.

Question 57

What are protoplasmic astrocytes?

Answer 57

Astrocytes in gray matter. They have more intermediate filaments (GFAP) so look different - the number increases even more under stress/pathological conditions and can be visible using abs to the intermediate filament.

Involved in regulation of brain metabolism, uptake of nutrients, elimination of waste and toxins.