Ch. 2 Cells of the Nervous System

2 major nerve cell types

neurons and glia

neuron function

transmit information (electrical/chemical) over long distances

glia function

provide physical support to neurons, maintain CNS, environment, transmit information, and provide immune function

how many neurons and glia does the human brain contain?

85 billion of each

distribution of neurons and glia in cerebral cortex

16 billion neurons/60 billion glia

distribution of neurons and glia in cerebellum

70 billion neurons/16 billion glia

what made studying neurons challenging?

their small size

what inventions made studying neurons easier?

microscope, method of “fixing” (preserving) the brain with formaldehyde, sectioning the brain (cutting into thin slices), and staining the brain

Nissil stain

stains Nissil bodies; general look of neuron; less detailed; tells if cell is alive or dead

Golgi stain

more detailed; stains entire neuron but not all neurons

T or F: you can study an unstained brain

false; it is impossible to study a brain that hasn’t been stained

which stain was developed first?

golgi stain

T or F: Both Nissil and golgi stains are used for visualizing neuronal structures

true

what does the cell theory state?

1. all organisms are composed of one or more cells
2. the cell is the basic unit of structure
3. cells arise from pre-existing cells

who developed cell theory?

schwann and schlieden

what did Golgi specialize in?

tissue staining

what did Cajal specialize in?

drawings of the nervous system

golgi and cajal were _______

rivals

how did Golgi think the nervous system was structured?

Golgi thought the nervous system was a continuous network of interconnected cells (reticular theory)

how did Cajal think the nervous system was structured?

Cajal thought the brain was composed of individual cells which communicated by **contact**

who was mostly correct about how the nervous system was structured? how?

Cajal was mostly right. The brain is composed of individual cells, but these cells communicate **without contact** via the synapse

who was wrong about how the nervous system was structured?

Golgi

Neuron doctrine

concept that the nervous system is made up of discrete individual cells

who coined the term neuron?

Waldeyer-Hartz

cell body

most prominent part of the neuron

what does the cell body of a neuron contain?

1. nucleus (surrounded by nuclear membrane
2. Specialized structures called organelles

Other names for the cell body

soma, perikaryon

organelles to know

1. cell membrane
2. cytoplasm
3. mitochondrion
4. nucleus
5. ribosome
6. endoplasmic reticulum
7. golgi apparatus

cell membrane function

protects the cell

cytoplasm function

cell buffer

mitochondrion function

**generates energy (ATP)**, involved in signaling, cellular differntiation, cell death, maintain control of cell cycle/cellular growth

nucleus function

contains genetic material

rough endoplasmic reticulum function

makes proteins

smooth endoplasmic reticulum function

makes lipids, folds proteins, regulates calcium

golgi apparatus function

modifies, packages, and transports lipids and proteins

which organelles are not present throughout the entire neuron?

nucleus and rough endoplasmic reticulum

how much total body ATP does the brain consume?

20%

T or F: mitochondria are found throughout the entire neuron

true -mitochondria distribution

where are mitochondria concentrated?

in pre and post synaptic neuron

T or F: each neuron contains the same genetic code, but uses the genetic code differently to make different proteins

true

nucleotide

molecule consisting of a nitrogen-containing base, a phosphate group, and a sugar that forms the basic structural unit of a nucleic acid

genes

segment of DNA that codes for the manufacture of a specific protein

DNA

molecule that carries genetic instructions for the development and functioning of all organisms and some viruses

chromosomes

long strands of DNA

transcription steps

1. RNA polymerase, with the help of transcription factors, binds to a specific sequence within a gene (the promoter) and splits the two strands of DNA apart
2. One strand is the template strand that RNA polymerase moves down to synthesize mRNA
3. Once RNA polymerase reaches the end of the gene termination occurs. This is when the enzyme detaches from the gene and the DNA is returned to its original state.
4. mRNA leaves the nucleus of the cell and moves into the cytoplasm where it will find a free ribosome.

exons

coding regions on pre-mRNA

introns

noncoding regions on pre-mRNA; cut out of the RNA strand during splicing after transcription has occurred

T or F: introns are included in mRNA

false

T or F: 1 section of a gene can make a variety of different proteins by splicing exons together differently

true - splicing

disruption of transcription: DNA methylation

occurs by the addition of a methyl (CH3) group to the DNA promoter

disruption of transcription: histone modification

a modification of how tightly histones are wrapped

disruption of transcription: non-coding RNA

introns can attach to exons resulting in a breakdown of the exon OR introns can recruit proteins that modify histones

T or F: Environmental events can alter the process of transcription while leaving DNA intact

true - environment and DNA

different types of ribosomes

1. attached
2. detached
3. poly

steps of translation

1. mRNA codon (3 nucleotides) will pair with a specific transfer RNA (tRNA) anticodon
2. Each tRNA anticodon is linked to an amino acid
3. As the process continues down the mRNA, ribosomes link the amino acids together forming a polypeptide chain
4. Once completed the polypeptide chain folds into a protein and exits the ribosome (or the polypeptide chain can exit the ribosome and then fold into a protein)

T or F: Proteins can be made of one or more polypeptides

true

protein folding after translation

1. this process involves four stages (primary, secondary, tertiary and quaternary structure) that gives rise to various 3D protein structures
2. amino acid sequence accounts for diff conformations

T or F: Some neurological impairments arise as a result of protein production problems or protein misfolding

true - neurological impairments

T or F: smooth ER is not found throughout all parts of the neuron

false - smooth ER

neurons contain _____ amounts of endoplasmic reticulum

large

where is rough ER found in neurons?

mostly cell body and dendrites (little to no amount in axons)

cytoskeleton function

gives a neuron its characteristic shape

what 3 structures make up the cytoskeleton (in order of size largest to smallest)

1. microtubules
2. neurofilaments
3. microfilaments

protein that makes up microtubules

tubulin

microtubule associated proteins (MAPs)

proteins that interact with tubulin and microtubules to regulate their function and transport cargo; anchor neurons to one another and other parts of the neuron

microtubules are involved in ______-range axoplasmic transport

long

T or F: microtubules are not static and can change (lengthen/shorten) as the neuron changes

true - microtubules

MAP protein Tau

when Tau becomes misfolded this leads to Alzheimers disease. Misfolded Tau causes breakdown of microtubules and eventually axon/neuron death

neurofilament protein

intermediate filament

neurofilament function

important for structure, shape, space filling (fill axons which increases connections/communication between neurons. increased filling also increases axon diameter and this leads to faster signaling)

neurofilaments move _________ along microtubules

bidirectionally

another name for neurofilaments

intermediate filaments

T or F: neurotubules have tracks for transport

false; neurotubules do not have tracks

another name for microfilaments

actin filaments

microfilament protein

actin

T or F: microfilaments are not static and can change (lengthen/shorten) as the neuron changes

true -microfilaments

microfilaments are involved in ______-range axoplasmic transport

short

____ is one of the most abundant proteins in cells of all types and plays a role in changing ____ shape (usually muscle contraction)

Actin; cell

T or F: microtubules extend all the way to the axon terminal

false

dendrites

projections that receive chemical signals (neurotransmitters) from other nerve cells

axon

slender projection that conducts the action potential

how many axons are there per neuron? how long is an axon?

1; long

how many dendrites are there per neuron? how long is a dendrite?

many; short

2 types of neurites

1. dendrites
2. axons

axon hillock

portion of the axon adjacent to the cell body that generates the action potential

axon collaterals

axons that split into numerous branches (how signal travels to other neurons)

axon varicosities

swellings that release NT along length of an axon

axon terminal

small enlargement at the end of an axon that stores and releases neurotransmitter

T or F: axons and dendrites are continuous (connected)

false

Wallerian degeneration

an active process of degeneration that results when a nerve fiber is cut which causes death to an axon distal to the injury

what kind of axons did Wallerian damage

frog axons

retrograde degeneration

injury occurs close to the cell body; neuron dies because damage moves backwards from site on injury to the soma

anterograde regeneration

injury occurs close to the axon terminal; neuron can regenerate because damage moves forwards from site of injury away from the soma

which MAP is responsible for anterograde transport?

MAP Kinesin

which MAP is responsible for retrograde transport?

MAP Dynein

anterograde transport

**newly synthesized proteins** are packaged in the soma and transported toward the axon terminal

retrograde transport

**vesicles, organelles, and signaling molecules** are carried from the axon terminal to the cell body for recycling

what uses slow axoplasmic transport?

cytosolic and cytoskeletal proteins

who discovered slow axoplasmic transport?

Weiss and Hiscoe; used a ligature to block transport in a rat’s sciatic nerve

T or F: slow axoplasmic transport gets its name because the speed/rate of transport is slower than fast axoplasmic transport

F: slow axoplasmic transport runs at the same speed/rate as fast axonal transport but it makes more stops