BCSC 240 Neurobiology Exam 1 - Cellular Anatomy

Functional Unit of the Nervous System

The functional unit of the nervous system is the neuron

Neuron

Neurons are cells specialized for the reception, conduction, and transmission of electro-chemical signals. They have many sizes and shapes: ~100 billion neurons and ~100 trillion connections

What are the major external features of a neuron?

A neuron has a soma (cell body) and neurites (dendrites and an axon)

How does the flow of information work in a neuron?

Dendrites receive inputs from other neurons. The soma integrates (processes) information. The axon transmits the output of processing to other neurons

What internal features are similar in other cells?

Neurons have a soma which contains a nucleus (DNA) and organelles that are enclosed by a membrane that protects the cell

How do neurons differ from other cells?

Neurons stop dividing (reproducing) after birth. They also have dendrites and axons, which are specialized structures designed to receive and transmit information

Cytosol

The watery fluid inside the cell. It is a salty, potassium-rich solution that is separated from the outside by the plasma membrane

Cytoplasm

Everything inside the membrane, excluding the nucleus. All the organelles and the cytosol

Is all DNA in every cell the same?

Yes! All the DNA in every cell is the same. What distinguishes a neuron from a liver cell are the specific parts of the DNA that are used to assemble the cell. These segments are called genes

Ribosomes

Ribosomes are dense globular structures found in the cytoplasm that serve as the site of biological protein synthesis (translation). They consist of two major components which join to translate: small subunits and large subunits

Small subunits of RNA

Reads the mRNA transcript. Reads mRNA with 3 nucleotides equaling one codon

Large subunits of RNA

Joins the amino acids to form a polypeptide chain

Where are ribosomes found?

Ribosomes are found floating freely in the cytosol or bound to stacks of membrane called rough ER

How do ribosomes facilitate decoding of mRNA and making a protein chain?

The ribosome does this by inducing the binding of complementary tRNA anticodon sequences to mRNA codons. 20 different amino acids are possible. The tRNAs carry specific amino acids that are chained together into a polypeptide as the mRNA passes through and is “read” by the ribosome

Protein synthesis starts on free ribosomes. What are SRPs and what do they do?

SRPs stand for signal recognition particles and they may direct the ribosome to the rough ER for completion. They have to detect the ER signal sequence

Proteins synthesized on free ribosomes are destined for?

Internal structures, cytosol, nucleus, mitochondrion

Proteins synthesized on the rough ER are destined for?

plasma membrane (giving neurons their special information-processing abilities) or enclosed in vesicles to be released from neurons as neurotransmitters

What is the role of the Golgi Apparatus?

The Golgi apparatus is a stack of membrane-enclosed disks in the soma. It serves as the site for extensive “post-translational” chemical processing of proteins released from the rough ER. It also serves an important function by directing transmembrane and secretory proteins to their destination (soma, dendrites, or axon)

What are the two major degradation pathways?

Lysosomal proteolysis and the ubiquitin-proteasome system

Lysosomal proteolysis

Degradation process that allows any biomolecule including large, long-lived proteins to be degraded

Ubiquitin-Proteasome System

Degradation process that degrades only proteins that are small and short-lived

What is the role of Mitochondria?

Abundant organelles in the soma that produces ATP (energy source of the cell). The breakdown of ATP to ADP provides the energy to fuel most of the necessary reactions of the neuron

What is the role of the neuronal membrane?

It serves as a barrier to enclose the cytoplasm and to exclude certain substances that float in the fluid that bathes the neuron

What are DNA microarrays?

DNA microarrays can be used to determine which genes by their abundance of mRNAs are expressed uniquely n neurons, or which genes are more-or-less abundant in normal vs diseased brains

Describe the process of microarrays?

Gather cells, isolate their mRNA, use reverse transcriptase to make cDNAs labeled with fluorescent dyes, combine cDNAs and hybridize to DNA microarray

What genetic engineering methods can be used to edit the genes in an organism?

delete (knockout), insert (knock-in), mutate (single nucleotides)

Genetic engineering methods have two important properties?

Target specificity (strand break), temporal control (inducible-drugs)

Current methods of genetic engineering?

Gene-editing technique that cuts DNA to ID which part of the gene

Cre-Lox

Zinc Finger proteins (ZNFs),

transcription activator-like effector nucleases (TALENs): Knockout, Deletion, “NHEJ”

CRISPR/Cas: Knock-In, Insertion, Homologous Recombination

What are neurites?

Neurites are protoplasmic protrusions that extrude from the cell body of a neuron. There are two types: dendrites and axons

How many types of neurites are there and what are they?

Dendrites and axons

List the differences between dendrites and axons?

Dendrites:

• Receive all input and are specialized to receive external signals

• They start thick and become more narrow

• They branch everywhere

• Shorter than axons

• Have no myelin sheaths

Axons:

• Transmits all the information

• Axons are essentially a uniform radius

• Axons do not branch too much (90 degree angles)

• Axons have myelin sheaths

What is the cytoskeleton?

• The cytoskeleton is the scaffolding that give a neuron its shape

• Consists of microtubules, microfilaments, and neuron-filaments

  • microtubules are the most important and they are the longest that longitudinally run down neurites

• These elements are dynamically regulated (assembled and disassembled) thus neuron shape changes continually

Microtubules

• microtubules are the most important and they are the longest that longitudinally run down neurites

Microfilaments

Are like the train tracks that help with alignment

What are the functions of the cytoskeleton?

• It is the scaffolding that gives a neuron its shape

• it also provides mechanical support, aids in transport of substances, allows cells to migrate, and plays a role in segregating chromosomes during cell division

What is the axon and what does it do?

The axon is the structure for the transmission of information, in the form of electrical activity, over long distances

Axon Hillock

The beginning region of the axon, which tapers away from the soma to form the initial segment of the axon

What distinguishes the axon from the soma?

• There are very few ribsomomes in the axon so there is no protein synthesis

• Protein composition of the axonal membrane is different from the soma

  • Focus is to transmit information

Why are axons variable in diameter?

The thicker the axon, the faster the transfer of information

• More myelin calls for quicker communication

What are axon collaterals and what are their purpose?

Axon collaterals are branches that stem from the original line of the axon. This allows neurons to communicate with many parts of the nervous system. They may also return to contact the cell itself which is called recurrent)

What is the axon terminal and what is its purpose?

The axon ends at the axon terminal or terminal button. It is the site where the axon comes in close proximity to other neurons (usually their dendrites or cell body) and passes information on to them. The point of near-contact is called the synapse

How does the cytoplasm of the axon terminal differ from that of the axon proper?

• Microtubules do not extend into the terminal

• The terminal contains numerous small bubbles of membrane called synaptic vesicles which aid in relaying information from neuron to neuron

• the terminal contains many mitochondria indicating high energy needs

How does information flow from axon terminal (of original cell) to dendrite or soma of the next cell?

Information (in the form of neurotransmitters) flows in a direction from the presynaptic axon terminal to the postsynaptic dendrite. It basically goes to the axon terminal of one neuron to the dendrite or soma of the next neuron

Since axons do not produce proteins of their own (due to their lack of ribosomes), how do they get proteins then?

Proteins must first be synthesized in the soma and then shipped down the axon. Axoplasmic transport can be slow or fast

What are the two methods of axoplasmic transport?

Diffusion: Slow

• Protein just moves slowly along the axon proper

Microtubules: Fast

• Material is enclosed in vesicles, which are then walked along the microtubules at the expense of ATP

• The “legs” differ depending on the direction of movement:

  • anterograde

  • retrograde

Anterograde

Microtubule movement in the direction towards the terminal. The leg that moves this is the kinesin

Retrograde

Microtubule movement in the direction towards the soma. The leg that moves this is the dynein

What is the difference between anterograde and retrograde?

Anterograde moves in the direction of the terminal and uses kinesin. Retrograde moves in the direction of the soma and uses dyenein

What is tract tracing used for?

Tract tracing is used to trace the paths of axons

What are the overall functions of dendrites?

Dendrites essentially function as the antennae of the neuron and receive tremendous order of input and integrates information together. They are covered with thousands of synapses and have a variety of large shapes and sizes to enhance functionality. They also have special proteins called receptors that detect chemicals released at the synapse

What are dendritic spines and what are their purpose?

Some neurons are covered with specialized structures called dendritic spines.

• They are thought to isolate various chemical reactions that are triggered by some types of synaptic activity

• Majority of the cytoplasm of dendrites resembles that of axons. However, free ribosomes have been observed at the base of dendritic spines suggesting protein synthesis occurring here for memory storage

What classifies neurons?

• Number of neurites: 1 (unipolar), 2 (bipolar), and 3 or more (multipolar)

• Dendritic tree shape and/or presence of spines: spiny vs aspinous

  • Pyramidal and Stellate Shape

• Connections: sensory, motor, interneurons

• Axon Length: Golgi type I (projection neurons, long), Golgi type II (local circuit, short)

What are the differences between a stellate cell and a pyramidal cell?

Pyramidal cells appear to have the shape of a pyramid (pine tree)

• All pyramidal cells have spines and therefore can learn and memorize

Stellate cells appear to have dendrites from all directions (sprouting)

• Half of the stellate cells have spines and the other half do not (aspinous)

  • This means only half can learn and memorize

What type of cells are Golgi type I?

Only pyramidal cells are Golgi type I

What type of cells are Golgi type II?

Only stellate cells are Golgi type II

All sensory neurons are?

All sensory neurons are unipolar

All motor neurons and interneurons are?

All motor neurons and interneurons are multipolar

What are non-Neuronal cells called?

These are called glial cells

What are glial cells?

Glial cells are known as helper cells. They outnumber neurons up to 5:1. They provide structural/metabolic support to neurons

What are the main types of glial cells?

• Oligodendrocytes

• Schwann Cells

• Microglia

• Astrocytes

• Satellite Cells

What cells are in the central nervous system?

Oligodendrocytes, Microglia, and Astrocytes

What cells are in the peripheral nervous system?

Schwann Cells and Satellite Cells

What are the main functions of oligodendrocytes?

Oligodendrocytes are extensions rich in myelin. They create myelin sheaths around axons in the central nervous system. These have processes that provide myelin to several parts of nearby neurons

What are the main functions of Microglia?

These are involved in response to injury or disease in the central nervous system. They act as white blood cells. Microglia exist in a ramified state at rest. When activated, these cells retract their processes the move towards the injured or diseased tissue and engulfs it

What are the main functions of astrocytes?

Astrocytes are the largest glia, they are star-shaped, and they control for the microenvironment in the central nervous system. Astrocytes have processes that contact many nearby neurons and blood vessels. They also form a barrier to unwanted substances entering the brain and spinal cord. They also control blood flow to neurons. Neurons cannot come into contact with blood.

What are the main functions of Schwann Cells?

Schwann cells are similar to function of oligodendrocytes, but are in the peripheral nervous system. They myelinate only one part of the neuron. They also can guide axonal regeneration.

What are the main functions of Satellite Cells?

These cells are flattened shape and control the microenvironment in the peripheral nervous system. They contact only one neuron

What is the main difference between Oligodendrocytes and Schwann Cells?

Oligodendrocytes are located in the CNS and they myeline many nearby neurons, while Schwann Cells myelinates only one part of one neuron

How are Astrocytes and Satellite Cells similar?

Besides controlling their respective microenvironments, they also:

• maintain the proper chemical state outside of neurons

• send nutrients to neurons

• They participate in tripartite synapses by responding to neurotransmitters and secreting gliotransmitters

How are Astrocytes and Satellite Cells different?

Astrocytes are located in the CNS while Satellite cells are located in the PNS.

• Astrocytes contact many nearby neurons

• Satellite cells only contain contact neuron

• Astrocytes also form barriers to unwanted substances for the brain and spinal cord. They also control blood flow to neurons