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Neurons:
a type of nervous system cell
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Are neurons capable of conducting an impulse?
yes
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Neurons conduct impulses in the form of what?
action potentials
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What other cells can produce action potentials?
skeletal muscles
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How many neurons are in the body?
100 billion
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Neurons are heterogenous:
take many different forms, but basically function the same
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What is a soma?
cell body of a neuron
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Describe the cell body of a neuron:
- fairly large (4-135 microns in diameter)
- shape varies (heterogenous)
- contents are similar to that of other cells in the body
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What are the characteristics of the cell body/neuronal cell of a neuron?
- nucleus
- non-nuclear structures (cellular organelles)
- mitochondria (power house)
- lysosomes
- rough endoplasmic reticulum
- smooth endoplasmic reticulum
- golgi apparatus (golgi body)
- cytoskeleton
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nucleus:
middle of cell body
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If the nucleus is not in the middle of the cell body, the cell is considered:
pathological
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Is the nucleus large or small?
large
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What is the shape of the nucleus?
spherical
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The nucleus has a nuclear membrane (envelope) with a distinct:
double layer
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What allow for passage of large macromolecules back and forth w/ cytoplasm through the nuclear membrane of a neuron?
nuclear pores
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What is the nuclear membrane continuous w/?
endoplasmic reticulum
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What is contained in the nucleus?
46 chromosomes and DNA
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Where does DNA undergo transcription for mRNA?
in the nuclues
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Where does translation occur?
rough ER in cytosol
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Where does protein synthesis occur?
rough ER in cytosol
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Nucleolus:
large inclusion w/in the nucleus where ribosomal RNA is synthesized and produced
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What is rRNA involved w/ and where?
involved w/ protein synthesis at ribosome
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Non-nuclear structures (cellular organelles):
can malfunction in neurons
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What is the power house of a neuron?
mitochondria
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Where are mitochondria found?
in the cytoplasm scattered throughout cell body
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What are mitochondria involved with?
engergy production (ADP -> ATP)
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What can neurons use for energy?
only glucose or glucose products (will not utilize fats or amino acids to make energy)
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What chemical does the mitochondria require?
oxygen
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Can neurons store glycogen?
- no, but skeletal muscle can
- once energy supply is gone, there is no more energy (unconsciousness)
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What is utilized during cellular respiration?
oxygen
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Lysosomes:
double membrane-bound vesicles that contain hydrolytic enzymes (50 or more)
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What is the function of lysosomes?
digest things w/in cell [substances that orignate in and out of cell]
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What are two ways that lysosomes can do to cause cell death?
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Necrosis:
lysosomes rupture and digest contents of cell (self-digesting)
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apoptosis:
- pre-programmed cell breakdown (natural prosses in which cells are programmed to die off)
- genetically determined cellular self-destruction process
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What is another name for Rough Endoplasmic reticulum?
nissl substance
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What is the rough endoplasmic reticulum?
- a bunch of ribosomes
- flattened, double-layered membrane structures lined w/ ribosomes giving it rough appearance
- very active part of cytoplasm
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Where is the rough endoplasmic reticulum located?
cell body and dendrites (close to nucleus)
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What occurs in the rough ER?
Translation and synthesis
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What general proteins are involved with translation and synthesis of the rough ER?
enzymes: hundreds needed for cells to work
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What structural components are involved with translation and synthesis in the rough ER?
- actin
- tubulin
- neurofilaments
- microfilaments
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What other proteins are involved in translation and synthesis in the rough ER?
- plasma membrane proteins
- neuro-transmitters and neuro-modulators
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The rough ER is the site of:
protein synthesis
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The smooth ER is a continuation of:
rough ER
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Does the smooth ER contain ribosomes?
no, therefore, it is smooth
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What is the function of the smooth ER?
to channel proteins produced in the Rough ER to the golgi apparatus
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What is another name for golgi apparatus?
golgi body
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What is the golgi apparatus?
double-membrane, flattened channels (sometimes a sac-like appearance)
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What is the function of the golgi apparatus?
- receive products (protein molecules) from smooth ER
- modify, sort, and package protein molecules into specific membrane-enclosed vesicles
- then migrate to where they are needed
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The packaged protein molecules from the golgi apparatus can go to:
- cell membrane regions for growth (contains growth protein)
- lysosome (contains hydrolytic enzyme)
- forms neuro tubular to be transported elsewhere
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What normally causes diseased w/ golgi apparatus?
genetics
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Review:
Nucleus (DNA) -> cytosol (cytoplasm) -> rough ER -> smooth ER -> golgi apparatus ->
cell membrane regions, lysosomes, neurotubules, numerous types of vesicles, etc.
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What is the function of the cytoskeleton?
- gives integrity to cells
- forms shape and gives support to neuron
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Is the cytoskeleton an organelle?
no
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Where is the cytoskeleton found?
cytosol
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What 3 fibular organelles (protein molecules) make up the cytoskeleton?
- microfilaments
- microtubules
- neurofilaments
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What makes up microfilaments?
primarily actin (protein molecules) --smalles in diameter
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Where is actin found?
- axoplasm of the neuron in the axon
- close to cell membrane
- lots in growth cone
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How many microfilaments does each neuron have?
they are in constant flux (some days you have more, some less) due to inconsistencies in the size of the cell bodies
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When there is less actin, does this change the form of the cell?
less actin causes cell shape to be smaller, but the basic form is still there
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Growth cone production:
as dendrites grow throughout development, so neuron can get from point a->b
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What is another name for microtubules?
neurotubles
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What are microtubules?
- fibular organelle that makes the cytoskeleton
- long tubular structures that form tracts to transport metabolites, vesicles, and ions
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Tubulin:
- found in microtubules
- molecule proteins, largest of the 3 fibrillar proteins (25nm in diameter)
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Where are microtubules located?
cytoplasm, axon, and dendrites
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What are microtubules very important to?
axonal transport mechanism
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What is another name for neurofilaments?
neurofibrils
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What is the most abundant of fibrillar proteins?
neurofilaments
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Where are neurofilaments found?
- cytoplasm
- in axons-neurofilament protein
- oriented along the axis of the axon (run parallel)
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What is the function of neurofilaments?
add strength (resiliency) and diameter (caliber) to axon
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What is the diameter of a neurofilament?
10nm
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When neurofilaments are defected, they cause what disease?
Alzheimer's
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Microscopically, neurofilaments are seen as clumps in cells of which parts of the brain?
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What is the Axonal Transport System?
transportation of substances from cell body to cellular processes and conversely utilizing microtubules
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What are the two directions that the axonal transport system can take?
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What is another name for anterograde?
orthograde
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Anterograde:
transport away from cell body to the cellular processes (efferent)
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Retrograde:
transport from cellular process towards cell body (afferent)
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What are the two rates that the axonal transport system work at?
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Fast axonal transport system:
- 200-400mm per day
- both anterograde and retrograde (16in/day)
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Slow axonal transport system:
- 1-5 mm per day
- only in anterograde
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What movement direction and speed combonations are found in the axonal transport system?
- fast anterograde
- fast retrograde
- slow anterograde
- NO slow retrograde...
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What molecules travel the axonal transport system during fast anterograde?
- plasma membrane components
- smooth ER
- synaptic vesicles containing neurotransmitter
- mitochondria
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What molecules travel the axonal transport system during fast retrograde?
- mitochondria
- degenerated structures
- vesicles and molecules: nerve growth factor and other trophic molecules
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What molecules travel the axonal transport system during slow anterograde?
- soluble enzymes
- proteins for regeneration
- proteins to renew cytoskeleton and plasma membranes (actin)
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What are force-generating motor proteins?
- drives axonal transport system
- how material is transported along neurotubules
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What are the two categories of force-generating motor proteins?
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kinesin:
protein molecule for anterograde movement
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dynein:
protein molecule for retrograde moement
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What is the energy source for the force-generating motor proteins?
ATP
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How do the force generating motor proteins work?
- bind substance to be transported to neurotubule
- neurotubule acts as a guide through the axon
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What are the 3 options for movement of the force-generating proteins in the axonal transport system?
- 1. can pass another vesicle moving in the same direction on the same neurotubule
- 2. two vesicles can move bi-directional (opposite directions) on the same neurotubule
- 3. vesicles can shift b/w adjacent neurotubules
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