Kap 2. Struktur og funksjon av nervesystemet Flashcards
Hvor mange nerve celler er det i menneskers hjerne?
omtrent 86 billioner nevroner
Sentral nerve systemet (CNS) består av
hjernen og ryggmargen
Annet ord for “receiving cell”
the postsynaptic cell
Det perifere nervesystemet består av
nerver og det meste av de sensoriske organene (se bilde s. 38)
Det har et somatisk system som responderer til stimuli fra miljøet, og et automatisk system som deles i to. Sympatisk (activation) og parasympatisk (homostasis)
Myelin Sheath
Fatty substance that provides insulation for the electrical message
Annet ord for “sending cell”
the presynaptic cell
Area Postrema
part of the brain that controls vomiting
The interior of the neuron (Framework)
cytoskeleton
Cytoskeleton består av 3 proteiner. Hva heter de?
Microtubules (thinkest) - 13 proteins filaments arranged around a hollow core. Form the “tracks” for axoplasmic transport
Cytoplasm - Semiliquid/jellylike - fills the space surrounded by the membrane - Organelle
Nucleus
se s. 40 figur 2.5
Chromosomes
consist of long strands of deoxyribonucleid acid (DNA) and is the recipe for protein
23 par
- structures made up by a double helix, holding the organism’s DNA sequence.
DNA
Deoxyribonucleic acid
Genes
responsible for initiating the process of protein synthesis in the cell
segments of DNA encoding for particular proteins
It can be splitted up into nucleotides
mRNA
Messenger ribonucleic acid
- Kopierer informasjon fra genet
which are complementary strands of nucleotides
required for protein synthesis.
The blood – brain barrier
A barrier exists betweem the blood and the fluid that surrounds the cells of the brain
The blood - brain barrier is Selectivly permeable. What does that mean?
some membrane can pass, some cannot
Myelin Sheath
Fatty substance that provides insulation for the electrical message (axon)
(White matter)
Astrocytes (CNS)
- star cell
- fysical support to nevrons and clean up debris of the brain
- sorounding somatic and dendritic membranes
Phagocytosic
the prosess of a astrocyte contact a piece of debris from a dead neuron, they engulf and digest it
Oligodendrocytes (CNS)
- provide support to axons
- produce the myelin sheath and isluates the axons from eachother
- one can produce up to 50 segments of myelin
- “Node of Ranvier”
Microglia (CNS)
- smallest of glia cells
- act as phagocytes + protecting brain from invading microorganisms (helping immune system)
Schwann Cells (PNS)
- preform same process as oligodendrocytes , but provide myelin for only one axon and the whole cell sorrounds the axon
+ facilitate recovery from injury to neurons
What is the membrane potensial?
Most neurons are ca. 70 units, or - 70 mV , more negatively charged inside the axon xomåared to outside. Any difference in charge (postive or negative) agross the membrane is called the membrane potensial.
Its affected by to opposing forces: diffusion and electrostatic pressure
Potensial = stored up energy
Resting potensial
The neuron are resting, the membrane potensial remains at -70 mV
Hyperpolarization
is when the inside of an axon becomes more negative (from resting potensial) relative to the outside
- less likely to send a message
Depolarization
When the inside of the axon becomes more positive (from resting potensial) relative to the outside
- more likely to send a message
The action potensial
a burt of rapud depolarixation followed by
……
??repolarization??
Another world for a “set point” (AP)
” threshold of excitation”
Diffusion
prosessen der molekyler fordeler seg jevnt gjennom mediet de er oppløst i
Cations
+
Electrostatic pressure
The force exerted by the repulsion ( + and - tiltrekkes)
Anions
-
Intracellular fluid
fluid inside cells
Extracellular fluid
fluid surrounding cells
Sodium (Na + ) - potassium (K + ) transporters
molecules that exchange Na+ for K +, pumping three sodium ions for every two potassium ions they pump in
Voltage - dependent ion channel
channels that only open by changes in the membrane potential.
The sodium channels open first, cause potassium require a greater level of depolarization before they begin to open
Saltatory conduction
Transmission of this message, appearing to jump from node to node.
- speed and economical
decremental condution
the decrease in the size of the electrical message
ligand
a chemical that attaches to a binding site
dendritic spines
small protrusions that stud the dendrites of several types of large neurons on the brain
synpatic vesicle
small, rounded structures made of membrane and filled with molecules. They are neurotransmitters that are released at the synapse
Exocytosis
a process where the cell secrets molecules of neurotransmitter.
The membrane-wrapped product migrates to the inside of the outer membrane of the cell, fuses with the membrane, and bursts, spilling its content into the fluid surrounding the cell. neurons communicate with one another by secreting chemicals by this means.
fusion pore
a hole through both membranes that enables them to fuse together. The prosess of fusion take ca. 0.1 msec
3 distinct pools of synaptic vesicles
- Release-ready vesicles - docked against the inside of the presynaptic membrane, ready to release their contents when an action potensial arrives.
- kiss and run
Less than 1 % found in the terminal
2. Recycling pool - 10-15 %
- merge and recycle
3. Reserve pool - 85-90 %
- Bulk Endocytosis
Endocytosis means ..
the process of entering a cell
Neurotransmitter-dependent/ligand-gated ion channels
chanels that permit the passage of specific ions into or out of the cell
Ionotropic receptor
An ionotropic receptor is a type of receptor on the cell membrane that, when bound by a neurotransmitter, opens a channel to allow specific ions (such as Na⁺, K⁺, or Cl⁻) to pass through. This ion movement changes the electrical potential of the cell, leading to rapid and direct signaling. Ionotropic receptors are key for quick synaptic responses in the nervous system. Examples include NMDA, AMPA, and GABA receptors, each responsive to specific neurotransmitters and affecting neuron excitability.
Metabotropic receptors
A metabotropic receptor is a type of cell membrane receptor that, instead of directly opening ion channels, activates a signaling cascade inside the cell through G-proteins and second messengers.
When a neurotransmitter binds to a metabotropic receptor, it triggers intracellular processes that may eventually affect ion channels or other cellular functions.
- slower, but more complex
EPSP
Exitatory postsynaptic potential (depolarization)
IPSP
Inhibitory postsynaptic potential (hyperpolarize)
Neural integration
the interaction of the effects of excitatory and inhibitory synapses on a particular neuron
Enzymatic deactivation
is accomplished by an enzyme that destroys molecules of the neurotransmitter.
F.eks postsynaptic potentials are terminated in this way for acetylcholine (ACh) and for neurotransmitters that concist of peptide molecyles.
Reuptake
the postsynaptic potential produces by most neurotransmitters are terminated by reuptake. This process is an extremly rapid removal of neurotransmitters from the synaptic cleft ny the terminal button
Autoreceptors
” self” or “same”
they are part of a negative feedback mechanism that allows presynaptic cells to monitor the amount of neurotransmitters they release into the synapse and adjust the amounts to fine-tune their chemical message.
Presynaptic inhibition
Effect if the activity of the axoaxonic synapse decreases the release of the neurotransmitter.
Presynaptic facilitation
Effect, if the activity of the axoaxonic synapse increases the release of the neurotransmitter
What is a neuron?
Cells specialized for the conduction and transmission of electrical signals in the nervous system
Axons
Neuronal process that carries the action potential from the nerve cell body to a target
Axon hillock
Point of the cell that is the site of an action potential`s initiation
Dendrite
Neuronal process arising from the nerve cell body that receives synaptic input
Nucleotides
Nucleotides are molecules of genetic code,
in the picture it are the small colored bars that connect the two strings (forelesning)
Neural circuits are …
the foundation of sensation, perception, movement of behavior.
Arrangement of circuits varies a lot according to function.
But circuitries have always two directions:
- Afferent and Efferent neurons
Afferent neurons
which are nerve cells that carry information from the periphery towards the brain or spinal cord (or deeper centrally into CNS)
Efferent neurons
which are the nerve cells that carry information away from
the brain of spinal cord
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