Exam 2 Flashcards
Describe the origins of a neuron.
Arisen from multifunctional cells gradually becoming more specialized
Organisms with the ability to detect, other able to monitor and respond, came together with a wiring system connecting these parts
Wiring is the neuron
What is the purpose of the nervous system?
To communicate and control with the network of neurons
Uses sensory neurons (afferent), central nervous system (brain and spinal cord) and efferent neurons
Interneurons
All of the pieces and structure within the central nervous system (brain and spinal cord), makes up 99% of all neurons
What are the parts of a neuron? Describe
Dendrites- receiving end
Cell body (soma)- contains nucleus and other organelles
Axon- sends signals away from cell
Axon terminals- where neurotransmitters are released and stored
Axon hillock- trigger zone, forms action potential
What are the support cells in the nervous system called?
Glial cells or Neuroglia
What glial cells form the myelin sheath and how?
Schwann cells in peripheral and Oligodendrocytes in the central nervous system
Wrap themselves around the axon
Myelin sheath
wrapped around axon to protect and insulate, not all neurons have them but the ones that do propagate action potentials more rapidly
What glial cells form barriers between compartments? Describe how it works
Astrocytes and ependymal in central
Create a blood/brain barrier- surround a blood vessel in the brain to protect a toxin from getting to the nervous cells
What glial cells are in charge of clean up? what are they made of and what do they look for?
Microglia
modified immune (white blood) cells
Dead cells, metabolic waste
What is the membrane potential at rest of a neuron?
-70 mV
What are the two mechanisms of membrane potential and describe?
Sodium Potassium Pump- biggest factor, establishes a concentration gradient generating negative potential.
Leak channels- always open, allows Na+ to move back in and K+ to move back out, there is more K+ leaving than Na+ coming back in because there is more potassium channels
Depolarization
When movement reduced charge separation/imbalance, approaching neutrality (zero) from the resting potential
Repolarize
Movement back toward resting potential, getting more negative
Hyperpolarization
development of more negative charge inside the cell, going past resting
Overshoot
inside of the neuron becomes positive when Depolarizing
Synapse
space between the two neurons where the electrical activity one neuron influences the activity of the other.
Describe Graded potentials
When a chemical signal binds to the post-synaptic cell a response is initiated
Produced by the opening of Ligand gated channels producing an electrical charge by the flux of sodium ions. As graded potentials travel they lose strength.
What does the effect of the graded potential depend on? What charge must it have?
The strength of the graded potential when it reaches the trigger zone
It must be -55 mV at the threshold to trigger an action potential or a sub-threshold response will be triggered
What are the two types of graded potentials and describe them
EPSP- excitatory, bring closer to threshold increasing the chance of an action potential, caused by the opening of ligand gated channels, depolarization
IPSP- hyperpolarization, suppresses the cell making it harder to get an action potential, caused by opening of K+ ligand channels casuing K+ to leave the cell
Define summation, why its needed, list the two types and describe
Addition of multiple graded potentials, and additive effect
Rarely can one excitatory graded potential reach threshold
Temporal- graded potentials from the same neuron, occurring over a short time and added together
Spatial- multiple neurons separated by space producing graded potentials at the same time and adding together
What are the steps of an action potential
- Graded potential above threshold reaches trigger zone
- Voltage gates Na+ channels open and Na+ enters the axon, depolarizing the membrane, triggering release of more Na+ channels as it spreading into the negative parts of the cell.
- Voltage gated K+ channels open slowly, allowing K+ out as Na+ gates close, repolarizing the membrane
- K+ gates stay open hyperpolarizing the membrane
- K+ gates close but K+ can still exit through leak channels
- Cell returns to resting potential
What is the refractory period, What is its purpose?
Reduces the excitability of a neuron, reducing the tendency for an action potential and assures one way propagation of action potentials
Absolute refractory
Zero chance for an action potential, inactivation gates are closed, unresponsive to stimulus, the channels are already open
Relative refractory
reduced excitably but can get second action potential, would need a stronger graded potential to counteract the hyperpolarization
Saltatory Conduction
Action potentials jump from one node to the next as they propagate along a myelinated axon
Nodes of Ranvier
Gaps between the myelinated portion of the axon where bare axon is showing
This is the only place where action potentials occur in myelinated neurons
What is conduction velocity and what effects it?
Speed of conduction
Myelination- precent is faster than absent
Diameter of axon- increasing the diameter increases the velocity by reducing resistance of ion flow
What are the two types of synaptic transmission?
Electrical-uses gap junctions, very fast
Chemical- synaptic cleft, most common, slightly slower
Electrical synapse
Permits the flow of electrical signals form the pre to post synaptic neuron across gap junctions.
Gap Junctions and what forms them?
Integral membrane proteins that physically connects the cytoplasm of two cells, ions are able to flow directly through.
Connexons- proteins
Chemical synapse and steps
action potential reaches terminal triggering release of neurotransmitter form pre-synaptic neuron
1. Action potential depolarizes the axon terminal where neurotransmitters are stored in vesicles
2. Depolarization opens voltage gated Ca ion channel and Ca ions enters the cell (will always be calcium at the axon terminal)
3. Calcium entry triggers exocytosis of synaptic vesical contents by vesicles moving to membrane and anchoring at docking proteins (Synaptotagmin) and wrapped up b SNARE proteins.
4. Neurotransmitter diffuses across synaptic cleft and binds to receptors on postsynaptic cell
5. Neurotransmitter binding (ligand gated channel) initiates a response in post synaptic cell
Classes of Neurotransmitters with examples
1.Acetylcholine- most common, muscle contraction, receptors: Muscarinic- GPCR, Nicotinic- ligand gated ion channels
2.Biogenic Amines- Catecholamines derived from tyrosine (dopamine-reward pathway, norepinephrine-alertness, epinephrine-hormone), Serotonin derived from tryptophan mimicking dopamine
3.Amino Acids- glutamate (EPSP), GABA (IPSP), Glycine (IPSP)
4.Neuropeptides- proteins (85) endogenous opioids (beta-endorphins, dynorphins(stimulation), Substance P (pain transmission))
5. Miscellaneous- purines(ATP), gases(NO, carbon monoxide), lipids(prostaglandins), Cannabinoids (anandmide- high affinity for THC)
Nicotine
Acetylcholine receptor agonist, stimulant leading to the production of: Norepinephrine (alternes), Dopamine (reward pathway), Beta endorphins (lower anxiety), crosses the blood brain barrier within 10-20 seconds, metabolizing in the liver
MAO
Monoamine oxidase
Breaks down Catecholamines
MAO inhibitors- prevents the breakdown
ex: Hydrazine, Nardil, Niamid - treat depression/anxiety
SSRI
Slow the reuptake of serotonin, allowing it to remain in synapse for longer
Prozac, Paxil, Celaxa - treat anxiety and depression
Much more specific
Benzos
Xanax, Valium, Ambien - reduce anxiety, induce sleep, Anti-seizure
Bind to GABA receptor to induce chloride flux (does not mimic GABA), changes the activity for the receptor, creates hyperpolarization inhibiting effects
Sympathetic vs parasympathetic
Both regulate involuntary bodily activates
Has two neurons- preganglionic (acetylcholine), postganglionic
Para- governs bodily activities during restful conditions, rest and digest, post: acetylcholine-short, released from cranial nerves or sacral region
Sym- fight or flight, prepares the body for stressful or emergency situations, pre: norepinephrine/adrenaline -long, thoracic and lumbar.
Synaptic plasticity
Change in strength over time and formation of new synapses, strengthen increases graded potential increasing amount of action potential
Long-term potentiation
Occurs in the hippocampus, long lasting enhancement of synaptic transmissions following stimulation, changes take place on post-synaptic neuron, stronger graded potential
AMPA
Glutamate receptor, Result in EPSP, glutamate binds to ligand gates channel, triggering response
NMDA
Glutamate receptor, At rest blocked by Mg ions, post-synaptic cell mush be depolarized to (0 mV) to function, when open allow Ca ion to enter, Ca ion channel
Long-term potentiation mechanism
- depolarization of post-synaptic cell (AMPA)
- Removes Mg ions form NMDA receptor
- Ca ion flux into neuron
- Phosphorylation and insertion of additional AMPA receptors
- Increased amplitude of synaptic response (more likely to cause an action potential)
What is the role of Calcium in LTP
induces gene expression and protein synthesis, results in the structural modification of the synapse
Growth or decay of dendric spines
Doogie Mouse
Genetically engineered mice that over express NMDA, more LTP because more Ca ions enter the receptors.