Continued: Structure & Function of Cells of the Nervous system Flashcards
Cell body (soma)
contains nucleus, ribosomes, mitochondria
metabolic work of neuron occurs here
dendrites
branching fibers
surface lined with synaptic receptors that bring info into neuron
some also include dendritic spines that increase dendritic surface area
Axon
single, thin fiber
transmits nerve impulses toward other neurons, organs, muscles
some covered with myelin sheath
(have presynaptic terminals on their ends)
action potential
like a brief pulse- it is a brief electrical OR chemical event that starts at the end of the axon next to the cell body and travels toward the terminal buttons
presynaptic terminals
bud at end point of an axon where the release of chemicals to communicate with other neurons occurs
located at synapse
synapse
junction between terminal button of an axon and membrane of another neuron
Santiago Ramon y Cajal was 1st to demonstrate individual neurons remained separate (Golgi staining)
Neurons- what’s inside
Membrane
Cytoplasm-viscous semiliquid substance inside cell
Cytoskeleton-forms perimeter
Nucleus- contains nucleolus and chromosomes
Nucleolus
in nucleus; produces ribosomes
Ribosome
site of production of proteins translated from mRNA
Chromosome
strand of DNA; carries genetic info
when active, portions of chromosomes/genes produce messenger RNA
Messenger Ribonucleic Acid (mRNA)
receives a copy of genetic info from gene
leaves nuclear membrane and attaches to a ribosome
causes production of a protein
Why are proteins important in cell functions?
provide structure to cell
act as enzymes (molecule that controls chemical reaction)
can combine 2 substances or break a substance into 2
act as a catalyst- cause chemical reaction w/o being a part of final product
mitochondrion
responsible for extracting energy from nutrients
produces ATP-molecule important for cell energy metabolism
endoplasmic reticulum
storage reservoir
found in cytoplasm
channel for transporting chemicals through cytoplasm
rough: contains ribosomes; involved with production of proteins secreted by cell
smooth: site of lipid synthesis; provides channels for segregation of molecules involved in various cellular processes
golgi apparatus
(like UPS) form of smooth endoplasmic reticulum some complex molecules are made and wrapped here wrapping or packaging agent produces lysosomes
lysosome
small sacs containing enzymes that break down waste products
microtubule
part of cytoskeleton involved in transporting substances from place to place w/in cell
glia
“nerve glue”
supports cells of the CNS
functions include: nutrients, support, insulation, housekeeping
3 most important: astrocytes, oligodendrocytes, microglia
blood brain barrier (BBB)
not an actual structure; not the same throughout entire brain
describes tight junction between walls in blood capillaries
selectively permeable
Where is the blood brain barrier weak?
Area postrema
region of medulla; poisons can be detected there; can initiate vomiting
How do you cross the blood-brain barrier?
small uncharged molecules (e.g. oxygen, CO2, H20)
molecules that dissolve in fats (vit. A and D, drugs that affect the brain)
For everything else? active transport required
protein-mediated process expending energy to pump chemicals across
direct agonist
binds with and activates a receptor
acts like a neurotransmitter
direct antagonist
receptor blocker
binds with receptor but does not activate it
prevents neurotransmitter from binding
In the brain, most synaptic communication is by…
- Glutamate- excitatory effects
- GABA- inhibitory effects
(Glycine is inhibitory/in spinal cord and lower brain stem)
These 3 have information-transmitting effects
All other neurotransmitters have modulating effects-they activate or inhibit neuronal circuits. What are they?
Acetylcholine- cerebral cortex- learning
Norepinephrine-increases vigilance, enhances readiness
Serotonin- supresses species-typical behavior; reduces impulsivity
Dopamine- activates voluntary movement in some areas, reinforces ongoing behavior in other areas
What drugs affect Ach?
Affect rel,ase of Ach: botulinum toxin, black widow spider venom (leads to muscle spasms)
Affect Ach receptors: atropine, curare
Monoamines
Catecholamines: Dopamine, norepinephrine, epinephrine (synthesized from tyrosine)
Indolamine: serotonin (synthesized from tryptophan)
Ethylamine: histamine (derived from histidine)
What 2 neurotransmitters are affected by addictive substances?
Dopamine and Norepinephrine synapses (example- rats kept pressing lever 2,000x/hour to stimulate DA release)
What disease is Dopamine implicated in?
Parkinsons
Serotonin synthesis?
Serotonin can’t pass BBB
CNS creates it with tryptophan
enters through diet-serotonergic cells collect it- enzyme transforms it into 5HTP-5HTP enzyme transforms it to serotonin
What are the major amino acids?
Glutamate-principle excitatory neurotransmitter in CNS (NMDA receptor important for learning/memory)
GABA- inhibitory (epilepsy may be caused by abnormal GABA system; benzos bind to 2nd site on GABA receptor)
Glycine- inhibitory; in spinal cord and lower brain stem; tetanus bacteria releases chemical that prevents release of glycine- removing this inhibitory effect causes muscles to contract continuously. Strychnine-causes convulsions/death
Which cranial nerves are responsible for sensory? Which are motor only? Which are mixed?
Sensory only: Olfactory, Optic
Motor only: Oculomotor
Both: Trochlear, Abducens, Vestibulocochlear, Hypoglossal, Accessory, Trigeminal, Facial, Glossopharyngeal, Vagus
Describe vagus nerve
10th cranial nerve- the largest
has parasympathetic efferent (outgoing) fibers to organs of thorax and abdomen
