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101374458 ch 2 neuro notes

101374458 ch 2 neuro notes

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CH 2 – Neurons and Glia

Introduction

• Glia outnumber neurons by tenfold (about 100 billion neurons)

• Neurons sense changes in the enviro and communicate these changes to other neurons and

command the body’s responses to these sensations

• Glia or glial cells mostly insulate, support, and nourish neighboring neurons

The Neuron Doctrine

• Most cells are .01-.05 mm in diameter

• to study, do histology – the microscopic study of the structure of tissues – by “fixing” tissues

by immersing them in formaldehyde and cutting them in thin slices using microtome

• Can stain nuclei of all cells and also the clumps of material surrounding the nuclei of neurons

– these clumps are called Nissl bodies and the stain is Nissl stain

o Distinguishes neurons and glia from each otherenables study of the arrangement

(cytoarchitecture) of neurons in diff. parts of the brain

o In fact is staining the Rough ER

The Golgi Stain

• Golgi Stain - Soaking brain tissue in silver chromate solution results in small percentage of

neurons becoming darkly colored in their entirety

o Shows central region that contains the nucleus and numerous thin tubes radiating

away from central region

• Swollen region around cell nucleus = cell body, soma, perikaryon

• Thin tubes radiating from soma = neurites, two types being dendrites and axons

• Axons extend long distances and there is usually only 1 from cell body – act like “wires” that

carry the output of the neurons

• Dendrites rarely extend more than 2mm – act as antennae of neuron to receive incoming

signals, or input

Cajal’s Contribution

• First to argue that neurons are not continuous w/ 1 another and must communicate by contact,

not continuity – this idea that neurons adhered to the cell theory = neuron doctrine

The Prototypical Neuron

• The inside of the neuron is separated from the outside by the limiting skin (neuronal

membrane) which lies like a circus tent on an intricate internal scaffolding, giving each part

of the cell its 3D appearance

The Soma

• ~20 um in diameter

• Watery fluid inside = cytosol, salty, K

rich soln

• Nucleus

o 5-10 um across, contained w/i dbl membrane (nuclear envelope) perforated by pores

0.1 um across

o Inside are chromosomes containing DNA, and thus the genes expressed by neuron

▪ By process of RNA splicing, introns are removed and remaining exons are

fused together and read during transcription

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• Rough ER

o Enclosed stacks of membrane dotted w/ ribosomes that measure 25 nm in diameter

▪ There are also free ribosomes, and some may appear to be attached to several

others by a thread = polyribosomes (thread is single strand mRNA and the

associated ribosomes are working on it to make multiple copies of the same

protein)

• If protein molecules is destined to reside w/i cytosol of neuron, then

the protein’s mRNA transcript gravitates toward free ribosomes, but if

it is destined to be inserted into membrane of cell or organelle, it’s

synthesized on RER

o Many more RER in neurons in part b/c of special membrane proteins unique to them

• Smooth ER & Golgi Apparatus

o SER performs diff. functions in diff. locations → if attached to RER, folds

membrane-bound proteins to give unique 3D shape, if not, regulates internal

substances like calcium

o Golgi is site of extensive “post-translational” chemical processing of proteins

• Mitochondrion

o ~1 um length

o w/i outer memberan, multiple folds are inner membrane = cristae, w/i which is the

matrix

o site of cellular respiration, pulling in pyruvic acid (derived from sugars and digested

proteins and fats) and oxygen → the acid enters the Krebs cycle, providing energy in

another series of rxns w/i the cristae called the e- transport chain, resulting in

addition of phosphate to ADP ➔ ATP

▪ each “exhalation” of mitochondrion releases 17 ATP molecules per molecule

acid

The Neuronal Membrane

• ~5nm thick and studded w/ proteins

• In neurons, proteins composition of the membrane varies depending on whether it is in the

soma, dendrites or axon

The Cytoskeleton

• Gives neurons their characteristic shape (scaffolding)

• The “bones” of the cytoskeleton are the microtubules, microfilaments, and neurofilaments

• Microtubules

o ~20nm diameters, are big and run longitudinally down neuritis

o Appears as straight, thick-walled, hollow pipe, the wall of which is composed of

smaller strands braided like rope around the hollow core, that consist of the protein

tubulin. Process of joining small proteins to form long strand of tubulin is called

polymerization and the strand is known as a polymer

o MAPs – microtubule-associated proteins that anchor them to one another and to other

parts of the neuron

▪ Pathological changes in an axonal MAP, tau, are implicated in dementia that

accompanies Alzheimer’s disease

• Microfilaments

o 5 nm diameter, about same thickness as cell membrane

o Found throughout neurons, particularly in neuritis

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CH 2 – Neurons and Glia Introduction • Glia outnumber neurons by tenfold (about 100 billion neurons) • Neurons sense changes in the enviro and communicate these changes to other neurons and command the body’s responses to these sensations • Glia or glial cells mostly insulate, support, and nourish neighboring neurons The Neuron Doctrine • Most cells are .01-.05 mm in diameter • to study, do histology – the microscopic study of the structure of tissues – by “fixing” tissues by immersing them in formaldehyde and cutting them in thin slices using microtome • Can stain nuclei of all cells and also the clumps of material surrounding the nuclei of neurons – these clumps are called Nissl bodies and the stain is Nissl stain o Distinguishes neurons and glia from each otherenables study of the arrangement (cytoarchitecture) of neurons in diff. parts of the brain o In fact is staining the Rough ER The Golgi Stain • Golgi Stain - Soaking brain tissue in silver chromate solution results in small percentage of neurons becoming darkly colored in their entirety o Shows central region that contains the nucleus and numerous thin tubes radiating away from central region • Swollen region around cell nucleus = cell body, soma, perikaryon • Thin tubes radiating from soma = neurites, two types being dendrites and axons • Axons extend long distances and there is usually only 1 from cell body – act like “wires” that carry the output of the neurons • Dendrites ...
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