fundamentals of neuroscience unit 1

bell and magendie discovered

dorsal and ventral roots carry information in opposite directions

franz J gall

phrenology: bumps on the surface of skull reflect brain surface and related personality traits

Paul Broca discovered

broca aphasia/expressive aphasia

broca / expressive aphasia

acquired damage to the frontal regions of brain such as broca area/frontal lobe of dominant hemisphere

• discrete region of human cerebrum for speech

Charles Darwin and evolution of the nervous system

• nervous systems of diff species may share common mechanisms

• common ancestors

damage to the broca area means

struggle with speech

in the 19th century the neuron was discovered and this allowed us to study

• cell theory

• cells

• nerve cells

levels of analysis in modern neuroscience

molecular, cellular, systems, behavioral, cognitive

Alzheimers disease

a progressive degenerative disease of the brain characterized by dementia and always fatal

autism

impairments in communication and social interactions and restricted and repetitive behaviors

cerebral palsy

a motor disorder caused by damage to the cerebrum before during or soon after birth

neuropathologist vs neurosurgeon

neuropathologist trained to recognize the tissues that result from disease

neuroethologist

studies the neural basis of species-specific animal behaviors in natural settings

Glia cells

insulate, support and nourish neurons

neurons do what

• process information

• sense environmental changes

• communicate changes to other neurons

• command body response

Santiago ramón y Cajal and Camilo Golgi

• sanitgo = neuron doctrine

• golgi = reticular doctrine

obstacles to study cellular neuroscience

• small cell size .01 and .05 mm

• soft tissue

• colorless

histology workflow

the gain in the brain is mainly in the stain

• fixation

• embedding

• sectioning

• staining

• microscope

nissl staining / cresyl violet

• franz Nissl

• class of basic dyes stain the nuclei of all cells

• clump of material surrounding the neuronal nuclei: nissl bodies

• facilitates the study of cytoarchitecture in the cns

golgi staining/ silver stain

• invented by Italian histologist Camillo golgi

• silver chromate solution

• thicker section

• small fraction of neurons became darkly colored

• reveals the entire neuronal cell

• great for studying morphology

golgi stain revealed two parts of neurons

• cell body, soma or perikaryon

• neurites: axons, dendrites

axons

• usually one axon

• Uniform in diameter

• any branches extend at right angle

• longer distance

• carry outputs

dendrites

• usually multiple

• short

• antennae of neuron to receive signals

1 - soma

2- dendrites

3- axon

cajals neuron doctrine

• use of golgi stain

• neural circuitry in fine details

• neurons communicate by contact not continuity

• brain adheres to cell theory

golgis reticulum doctrine

• use of golgi stain

• neurites of different cells are fused together to form a continuous reticulum or network

• brain is an exception of the cell theory

neurites of different neurons are not continuous with one another and this was found by

• the electron microscope in the 1950s owing to the increased resolving power

the soma/cell body/ perikaryon

spherical central part

cytosol

watery fluid inside the cell

organelles: membrane enclosed structures in the neuron include

• nucleus

• rough endoplasmic reticulum

• smooth endoplasmic reticulum

• golgi apparatus

• mitochondria

the cytoplasm

contents within a cell membrane excluding the nucleus

the nucleus of a neuron

• contained with a perforated double nuclear membrane aka nuclear envelope

• 5-10 um

• inside chromosome

• dna is highly packed 2 meter linear length

the reading of the DNA is known as

gene expression

nissl staining

golgi staining

different cell types have the same dna but

different gene expression

in neurons translation into protein happens where

in the cytoplasm

ribosomes in neurons

• convert the information in genes by synthesizing proteins

• mrna transcripts bind to the ribosomes and the ribosomes translate the information in the mRNA to assemble a protein molecule

rough ER

• abounds in neurons

• nissl bodies are staining of rough ER

• there are free floating ribosomes

free ribosome proteins are destined to reside within _____ of the neuron

cytosol

rough ER proteins inserted into the membrane of a cell or an organelle and then they are

synthesized on the rough ER

why is there a high number of rough ER in neurons

brain function heavily counts on membrane protein

smooth endoplasmic reticulum

• stacks of membranous organelles without ribosomes

• some is continuous with rough ER to process proteins

• others may regulate the internal concentrations of substances such as calcium in muscle cells

Golgi apparatus

• described by golgi

• membrane enclosed disks farthest from the nucleus

• sites for post translation chemical processing

• sorting proteins for delivery to different cell regions

mitochondria in neurons

• very abundant in the soma

• about 1um long

• inner membrane folds: cristae

• inner space: matrix

• site of cellular respiration

• generates atp, which is cells energy source

the cytoskeleton of the neuron

• shape is not static

• internal scaffolding of neuronal membrane

the three structures of the cytoskeleton of a neuron

• microtubules

• neurofilaments

• microfilaments

microtubules in the cytoskeleton

• 20 nm in diameter run longitudinally down neurites

• a thick walled hollow pipe that is composed of strands

• each strand consists of tubulin

• polymerization and depolymerization can regulate neuronal shape

MAP (microtubule associated protein) is implicated in

alzheimers

neurofilaments

• consists of multiple subunits that are wound into rope like structure

• each strand consists of long protein molecules making neurofilaments mechanically strong

microfilaments in neurons

• 5 nm in diameter

• numerous in the neurites

• two strings of polymers of actin

• constantly assemble and disassemble

• run longitudinally down the neurite and closely associated with the membrane

the axon: only found in neurons

axon hillock: beginning

proper: middle

terminal: end

axon collateral: branch

differences between axon and soma

ER does not extend into axon, needs protein from soma

protein composition is unique

axon terminal:

bouton

where the axon contacts with other neurons

the synapse

when a neuron makes a synaptic contact with another cell it is called

innervation

axon terminal is called

presynaptic

1= microtubule

2= neurofilament

3=microfilament

a= axon collaterals

b=axon hillock

postsynaptic is where

dendrite

differences between the cytoplasm of axon terminal and axon

• no microtubules in terminal

• presence of synaptic vesicles in the terminal

• abundance of membrane proteins in the terminal

• large number of mitochondria inthe axon terminal

the synaptic transmission

electrical → chemical → electrical

disfunction of synaptic transmission leads to

mental disorders and is the target of toxin or drug development

1 = neurotransmitters

2 = presynaptic terminal

3 = synaptic cleft

4= postsynaptic terminal

5= receptors

axoplasmic transport

• no ribosome proteins ship down the axon

• anterograde (soma to terminal)

• wallerian degeneration 1-10mm per day

• transport is fast with radioactive amino acid injection, 1000 mm per day

• walk down microtubules thru kinesin and atp

retrograde transport

• the enzyme horseradish peroxidase is selectively taken up by axon terminals and then transported retrogradely to the soma

• some viruses exploit retrograde transport to infect neurons

• regulated by dynein protein

dendrites

• antennae of neurons

• dendritic tree: all dendrites from a single neuron

• synapse - receptors

• dendritic spines

dendritic spines

• post synaptic

• isolate various chemical reactions

• dynamic and sensitive to synaptic activity

• unusual changes in disorders

classifications of neurons based on number of neurites

• single neuritis = unipolar

• two or more neurites = bipolar or multipolar

1= unipolar

2= bipolar

3= multipolar

classifying neurons based on dendritic and somatic morphology

• stellate cells (star shaped)

• pyramidal cells

• spiny or aspiny

• classification can overlap

neurons connected within the pns

• primary sensory neurons, motor neurons, interneurons

golgi type 1 (classifying neurons based on axonal length)

projection neuron; from one part of brain to another

golgi type II neuron

local circuit neuron, short axon, only in vicinity

functions of glia

support neuronal functions, nutrition, insulation

astrocytes

• most numerous glia in the brain

• fill spaces between neurons

• influence neurite growth

• regulate chemical contents of extracellular space

• express neurotransmitter receptors

myelinating glia types

Oligodendrocyte (CNS)

Schwann cells (PNS)

function: insulating axons

Oligodendrocytes and nodes of Ranvier

Nodes= region where axonal membrane is exposed

Oligodendrocytes= myelinated sheath protecting axon

microglia as phagocytes

can migrate out from blood and take away debris

ependymal cells

line up the ventricles

the reflex from stepping on a thumb tack

• signals travel up sensory nerve fibers

• spinal cord some send axons to brain where pain is felt and others synapse on motor neurons which send signals to muscles to retract

• the motor commands trigger muscle contraction and withdrawal

challenges in neurons conducting information through electric impulse

• cytosol is far less conductive

• axon is bathed in salty ECF: leaking

• axon alone is not well insulated

action potential refers to

• potential refers to separation of electrical charges across the membrane

action potential and distance

they are signals of fixed size and duration, they do not diminish over distance

the frequency of action potentials of individual neurons gives us

information that is encoded

there is excitable membrane for action potential in

both neurons and muscle cells

resting potential is described as

when the neuron is not generating impulses

in neurons the inside surface of the membrane is _______ charged

negatively

the electrical charge across the membrane is called the

resting membrane potential

action potential

brief reversal of resting potential and for an instant (example 1/1000 of a second)

factors of resting potential

• salty fluids on either side of the membrane, cytosol, ECF

• the membrane

• the proteins that span the membrane,: ion channels, pumps

water as it relates to ICF and ECF

polar solvent, uneven distribution of electrical charge

allows for solvent of other charged or polar molecules

ions in the intracellular and extracellular fluid

NA+, K+, CA2+, Cl-

the membrane of a neuron

phospholipid bilayer

proteins that span the phospholipid bilayer include

enzymes, cytoskeletal elements, receptors

• control resting and action potentials

ion channel proteins components

• polar r groups hydrophilic exposed to water on either sides of the membrane

  • nonpolar R groups: hydrophobic inside the membrane

  • ion channel selectivity

  • ion channel gates

enzymes use energy from atp breakdown and these pumps include

• neuronal signaling

• sodium/potassium pump

• calcium pump

ion channel driving forces

diffusion and electricity

movement of ions with diffusion

• dissolved ions distribute evenly

• diffusion is a net movement of ions from regions of high con to low con