receptors and neurotransmitters Flashcards
What is a telodendron?
the termination of the neuron where the impulse leaves the neuron
Name the parts of a neuron (4)
dendrites, soma (body), axon, axon (synaptic) terminal (telodendron)
What is the axon hillock?
the funne-like part where the soma narrows into the axon, there is a high concentration of voltage gated sodium channels there, it is where the action potential is generated
Name two types of receptors present in neurons
1) ligand gated ion channels (ionotropic, fast),
2) g protein coupled receptors (metabotropic, slow but can have long lasting implications)
Which ions have an ion channal present in the neurons?
Na+
K+
Cl-
Ca++
Two types of ion channels
1) leaky (permanently open) - maintain the intra- and extracellular ion concentration
2) gated (gates that open or close in response to a stimulus) - generation and propagation of the action potential
Name the main intra- and extracellular ions
Name two types of postsynaptic potentials (PSP)
excitatory PSP (EPSP) and inhibitory PSP (IPSP)
What is the resting potential of a cell?
the static membrane potential (voltage difference across the cell) of quiescent (resting) cells (cca. - 60 to 70 mV). Present in all cells (and neurons).
Name two excitable cells (wikipedia)
neurons, myocytes, (some glandular cells)
What are Nissl bodies?
discrete clumps of rough endoplasmatic reticulum and free ribosomes inside of nerves (they occur in the somata and dendrites, but not axons or axon hillock)
Name three types of proteins synthesised inside of a neuron
neurotransmitors, enzymes, membrane proteins
Two functions of an axon
- to conduct action potential (depolarisation (+) then repolarisation (-),
- transport of organels and vesicles containing proteins
Two proteins that are involved in transport thru the axon mycrotubules
Kinesin (+): positive (anterograde) axonal transport (from soma to axon terminal)
Dynein (-): negative (retrograde) axonal transport (from axon terminal to soma)
What are the functions (2) of the axon terminal?
secretion of neurotransmitters, reuptake of neurotransmitters
Two ways of neurotransmitter termination in the synapse?
reuptake, degradation
Structural classification of neurons (3)
Multipolar: >3 dendritic extensions, usually sensory neurons
Bipolar: one dendritic extension and one axon, retina and olfactory nerves and inner ear (special sensory organs)
Pseudounipolar: peripheral process and central process, mainly in the dorsal root ganglion or trigeminal ganglion
What is graded potential?
change in the membrane potential that vary according to the size of the stimulus (can be excitatory or inhibotory)
Functional classification (3) of neurons?
1) Sensory (afferent): general visceral afferent (GVA), general somatic afferent (GSA), special sensory afferent (SSA), special visceral afferent (SVA)
2) Motor (efferent): general visceral efferent (GVE), general somatic efferent (GSE), special visceral efferent (SVE)
3) Interneurons: between the sensory and motor neurons (dorsal column, thalamus, nuclei etc.)
How is the negative resting potential generated (3)
- Na/K ATPase (3Na+ out, 2K+ in),
- Leaky K+ channels (allow for passive/free movement of K in and out of cell),
- Leaky Na+ channels (allow for passive/free movement of Na in and out of cell).
The neurons are more permeabile to K then to Na (allow for more K to exit then Na to enter the cell thru leaky channels).
What is the action potential?
a brief reversal in membrane potential when membrane permeability of Na+ and K+ increases subsequent to activation of voltage‐gated Na+ and K+ channels
Which ion channels are responsible for hyperpolarisation?
voltage gated K+ channels (+30 to - 90 mV) or Cl- channels
Which ion channels are responsible for depolarisation?
voltage gated Na+ channels (-55 mV to + 30 mV)
Which ion channels are responsible for the neurotransmitter exocytosis at the end of an action potential?
voltage gated Ca++ channels
What is the threshold potential?
the critical level to which a membrane potential must be depolarised to initiate an action potential (-55 mV)
What is the refractory period?
the period of time it takes for an excitable membrane to be ready for a second stimulus once it returns to its resting state following excitation. In other words, the refractory
period represents the time period needed for the voltage‐gated Na+ channels to revert from the inactivated state to the resting state (can be absolute and relative)
What is the absolute, and what the relative refractory period?
When an action potential is initiated, a second action potential cannot be triggered for about 1 ms, regardless of how large a stimulus is applied to a neuron. This period, called the absolute refractory period, makes certain that a second action potential will not be initiated before the completion of the first action potential, preventing overlap of action potentials. The absolute
refractory period corresponds to nearly the entire duration of
the action potential. The period of time known as the relative refractory period follows the absolute refractory period. This time period starts when the membrane potential undergoes repolarization and approaches the threshold membrane voltage. It lasts until the
time when voltage‐gated K+ channels are closed. During the
relative refractory period, initiation of a second action potential is inhibited, but not impossible, as the much stronger depolarizing
current that shifts the membrane potential to the threshold can generate an action potential.
Name at least 5 neurotransmitters present in the CNS
1) ACh,
2) amines, (serotonin, dopamine,
norepinephrine, epinephrine)
3) amino acids (glutamate, aspartate, glycine, GABA)
4) peptides (endorphins, subst. P, enkephallin)
5) gases (nitric oxide)
Name 2 excitatory and 2 inhibitory NS of the CNS
Excit.: glutamate, aspartate
Inhib.: GABA, glycin
How are Ns removed from the synaptic cleft? (2)
1) enzymatic inactivation
2) diffusion
Name 3 NS of the CNS involved in pain mediation
Subspance P
endorphins
encephallins
Name two ionotropic receptors for glutamate
1) AMPA
2) NMDA
(both activated by glutamate, both depolarise the cell, both permeable to Na and K)
Name two specificities of the NMDA receptors
1) permeable also to Ca (with Na and K),
2) open only if the cell is already depolarised in the time glutamate is binding to the NMDA receptor,
3) at resting potential a Mg ion is blocking the channel
Name the receptor for GABA
Cl channels (Cl- ions are anions and cause hyperpolarisation of the postsynaptic call, thus having an inhibitory effect),
mainly found in the mammalian brain
Name two groups of drugs that activate the GABAa receptors
barbiturates
benzodiazepines
muscimol (in mushrums like Amaninta muscaria)
What are the glycin receptors?
ionotropic receptors Cl channels,
mainly found in the mammalian spinal cord,
Which receptors are blocked by strychnine?
the glycin receptors
Name 3 neurotransmitters present in the PNS
ACh
noradrenaline
adrenaline
Name two receptors for acetylcholine (ACh)
1) nicotinic cholinergic (ionotropic, NMJ),
2) muscarinic cholinergic (metabotropic, autonomic nervous system - mostly parasympathetic)
Which receptors are blocked by curare?
the nicotinic cholinergic receptors
Name two molecules that block the muscarinic AChR
atropine
scopolamine
Name two metabotropic (GPCR) receptors
- beta adrenergic receptors
- muscarinic AChR
Name two GABA receptors
GABAa
GABAb
Name two dopamine receptors
DA1 (excitatory)
DA2 (inhibotory)
Clinical implications of hyper- and hyopokalemia, in regards to the membrane potential:
1) Hyperkalemia - depolarisation
2) hypokalemia - hyperpolarisation
Which 2 factors determine the conduction speed of the action potential?
(1) the diameter of the
axon
(2) the resistance of the axonal membrane to the
current that leaks out
(larger diameter and myelination of axons effectively increase the conduction speed)
What is the node of Ranvier?
The myelinated portion of an axon (i.e., internode) has no voltage‐gated Na+ and K+ channels. These channels are located at the area of the node of Ranvier. As a result, passive current generated by an action potential must reach the adjacent node of Ranvier to generate a new action potential.
Name 2 types (classes) of synapses
1) electrical (ion channels connect the pre- and postsynaptic cell)
2) chemical (has a synaptic cleft, the most prevalent type of synapses)
What is a motor unit?
One motor neuron
forms a neuromuscular junction with a group of skeletal
muscle fibers. To do so, an axon of motor neurons branches at its terminus to innervate muscle fibers, all of which contract together as a unit. This unit of a motor neuron and the muscle fibers it innervates is known as a motor unit.
Classification of peripheral nerve fibers in regards to speed and myelination
