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Chapter 2: Neurons and Glia (Cell biology (Nucleus (gene expression: "…
Chapter 2: Neurons and Glia
Brain is composed of gray matter and white matter
gray matter: neurons and glia
white matter: myelinated axons of neurons (also neurons and glia)
Subdivisions of nervous system
CNS: brain and spinal cord
PNS: nerves
Efferent, motor: motor neurons move AWAY from CNS
Afferent, sensory: neurons move TOWARD the CNS
Brain has 4 major lobes
gyri: bumps
sulci: grooves
Nervous system is made up of glia and neurons
glia (glue): insulate, support, nourish neurons
Astrocytes: regulates contents of extracellular space neurotransmitters
K+ spatial buffering: when extracellular K+ increases, K+ enters astrocytes through channels, causing astrocyte membrane to depolarize. Entry of K+ INCREASES internal K+ concentration which dissipates over a large area
blood-brain barrier
myelinating glia
oligodendrocytes (CNS) one cell can myelinate SEVERAL axons
Schwann cells (PNS) one cell myelinates a SINGLE axon
Node of Ranvier: region where axonal membrane is exposed
neurons
sense environmental changes (external, internal)
process information
communicates changes to other neurons
command body's responses to sensations
Histology: study of tissue structure
Nissl Stain: stains nucleic acids, mainly RNA on rough ER (ribosomes)
Nissl Stain stains ALL cell somas
Golgi stain: silver chromate solution
stains SMALL PERCENTAGE of neurons in their ENTIRETY
shows 2 parts of neurons
cell body = soma
neurites: axons and dendrites
Reticular theory: neurites of different cells are fused into a "nerve net"
Neuron Doctrine
neurons communicate with each other by CONTACT, NOT CONTINUITY
Neuron composition (information flows in one direction: dendrites --> soma --> axon)
Neurites
axons (neuron SENDS an outgoing signal)
long, thinner, smooth
fewer branches
diameter more uniform
Segments of Axon
Axon hillock (beginning)
Axon proper (middle
Axon terminal (end)
presence of synaptic vesicles (site where axon comes in contact with other neurons and cells)
synapse
point of contact
presynaptic/postsynaptic membrane
synaptic cleft
info passed from presynaptic cell to postsynaptic cell
Axon collaterals (branches)
dendrites (neuron RECEIVES a signal)
highly branched "tree"
tapered as it goes further away from soma
short, stubby, spiny
covered with neurotransmitter receptors
cell body (soma)
Cytosol: watery fluid INSIDE the cell
organelles: membrane-enclosed structures within SOMA
cytoplasm: contents within CELL MEMBRANE
Cell biology
Nucleus
genes: segments of DNA that code for specific proteins
gene expression: "reading" of DNA resulting in protein synthesis
DNA --> transcription --> mRNA --> translation --> protein
chromosomes: contain DNA
Rough ER (Nissl substance)
membrane with ribosomes (site of protein synthesis)
free ribosomes: produce proteins that are released into the cytosol and used within the cell
bound ribosomes on rough ER produce proteins that inserted into the plasma membrane
Smooth ER
folds proteins giving them 3D structures, regulates internal Ca++ concentration
Golgi apparatus
packages molecules, sends them to appropriate destination in the cell
Mitochondria
site of cellular respiration, yields ATP
Neuronal membrane
membrane is a LIPID BILAYER
hydrophilic, polar heads on the outside
hydrophobic, non-polar tails on the inside
Cytoskeleton
internal scaffolding of neuron, gives neuron its shape
3 bones
microtubules: dynamic, form long scaffolds down neurites
neurofilaments: most abundant, very stable
microfilaments: dynamic, near plasma membrane
Axoplasmic transport
anterograde (uses KINESIN)
proteins are synthesized in soma --> shipped down to the axon terminal
Retrograde (uses DYNEIN)
signals to soma about metabolic needs of axon terminal
terminal --> transport
Classifying Neurons
based on number of neurites
2+ neurites: bipolar, multipolar
single neurite (unipolar)
Somatic morphology
star-shaped (stellate)
pyramidal
spiny or aspinous (without spines)
based on connections with CNS
based on neurotransmitter type
Other non-neuronal cells
microglia: remove dead neurons/glia
ependymal cells: line brain's ventricular system