cns and pns Flashcards
(124 cards)
1
Q
central nervous system consists of
A
the brain and spinal cord
2
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the peripheral nervous system consists of
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sensory afferent neurons and efferent neurons
3
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enteric nervous system
A
located in the walls os the digestive tract (can function autonomously OR under the control of the autonomic nervous system)
4
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autonomic
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divided into parasympathetic, sympathetic branches
5
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motor neuron
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all efferent neurons but is often used specifically for physical motor neurons
6
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efferent neurons
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carry output signals from CNS to target muscles and gland
7
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afferent neurons
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carry sensory information from receptors to CNS (towards)
8
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what are efferent neurons divided into
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somatic motor division (controlling skeletal muscles) and the autonomic division (smooth and cardiac muscles, glands, etc)
9
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what are the two cell types of the nervous system
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neurons and support cells (glial cells)
10
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neurons
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are functional units of the nervous system, capable of performing the system’s functions
11
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glial cells
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communicate with neurons and offer crucial biochemical and structural support
12
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dendrites
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receiving signals (branched processes and serves as the template for protein synthesis
13
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multipolar neurons
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have many dendrites and branched axons
14
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pseudounipolar neurons
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have a single long process with the cell body off to one side
15
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bipolar neurons
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have one axon and one dendrite
16
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anaxonic neurons
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lack an axon but have numerous branched dendrites
17
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interneurons
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located entirely within the CNS and have complex branching processes for communication
18
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dendritic spines
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further expand the surface area of dendrites and play a role in receiving and processing information
19
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dendrite function in CNS
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more complex, and act as independent compartments, capable of sending signals and synthesizing proteins due to the presence of polyribosomes
20
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axon hillock
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where the axon originates
21
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collaterals
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structures where axons branched sparsely
22
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function of axon
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transmit electrical signals form the neuron’s integrating center to target cells
23
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axons convey chemical and electrical signals but lack
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ribosomes and endoplasmic reticulum
24
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axonal transport
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where proteins for the axon are synthesized and travel down
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anterograde transport
moves vesicles and mitochondria from the cell body to the axon terminal (forward)
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retrograde transport
returns old cellular components to the cell body for recycling
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nerve growth factors and viruses use which transport?
retrograde
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motor proteins
bind and unbind to microtubules with the help of ATP, stepping up their cargo along the axon
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fast axonal transport
moves materials in both directions at rates up to 400m
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slow axonal transport
moves soluble and cytoskeleton proteins from the cell body to the axon terminal at rates of 0.2-8 mm per day
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microcephaly and fragile X syndrome is associated with
axonal transport
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synapse
the region where an axon terminal meets its target cell, consisting of the presynaptic cell and postsynaptic cell
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synaptic cleft
filled with extracellular matrix (between post/pre synaptic cell
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chemical synapses
where the presynaptic cell releases a chemical signal that binds to receptors on the postsynaptic cell
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electrical synapses
allow bidirectional and faster communication through gap junction channels
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neurotrophic factors
chemicals secreted by schwann cells that keep damaged neurons alive
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schwann cells
support and insulate axons by forming myelin (PNS)
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oligodendrocytes
support and insulate axons by forming myelin (CNS)
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myelin
composed of multiple concentric layer of phospholipid membrane, acts as insulation and speeds up signal transmission along axons
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gap junctions
allow the flow of nutrients and information between membrane layers
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difference between oligodendrocytes and schwann cells
oligodendrocytes: can myelinate portions of several axons
schwann cells: associated with only one axon
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nodes of ranvier
tiny gaps between myelinated segments in the PNS, where the axon membrane is in direct contract with ECF
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PNS has two types of glial cells
schwann cells and satellite cells
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CNS has four types of glial cells:
microglia, astrocytes, ependymal cells, and oligodendrocytes
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ganglia
clusters of nerve cell bodies found outside CNS and appear as knots or swellings along a nerve
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how do glial cells communicate with neurons
primarily through chemical signals
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glial cells respond to
neurotransmitters and neuromodulators secreted by neurons
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what happens if the axon is severed
the cell body and attached axon segment survive but the separated axon segment degenerates
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what happens if a neuron's cell body dies
the entire neuron dies
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what happens if there is damage to somatic motor neurons
permanent paralysis of the innervated muscles
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damage to the sensory cells causes
loss of sensation
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resting membrane potential difference (Vm)
representing the separation of electrical charge across the cell membrane
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what is more concentrated in the ECF
Na+, Cl-, and Ca2+
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what is more concentrated in the cytosol & the major ion contributing to the resting membrane potential
K+
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nernst equation
describes the membrane potential if the membrane were permeable to only one ion
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equilibrium potential
is the membrane potential at which electrical and chemical forces on the ion are equal and opposite
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neurons at rest leak what into the cell?
leak Na+, making the resting membrane potential slightly more positive than if the cell were permeable only to K+
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goldman-hodgkin (GHK) equation
calculates the membrane potential by considering the contributions of multiple ions that can cross the membrane
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P
relative permeability of the membrane to the ion
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what happens is the membrane is not permeable to an ion
its permeability values is zero and doesn't affect the membrane potential
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cells at rest are not permeable to
Ca2+
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hyperpolarization
occurs if the membrane becomes more permeable to K+, causing a loss of positive charge inside the cell and Cl- enters the cell
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ion channels
they allow Na+, K+, Ca2+, and Cl- to pass
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channels conductance (G)
indicate how easily ions flow through a channel and varies with the gating state and channel protein isoform
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mechanical ion channels
open in response to physical forces
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chemically gated ion channels
response to ligands like neurotransmitters and intracellular signals
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voltage gated ion channels
respond to changes in membrane potential, crucial for electrical signal conduction
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channel activation
refers to the opening of channels to allow ion flow
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channel inactivation
mechanisms vary
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graded potentials
are changes in membrane potential that occur in dendrites, cell body or near the axon terminals of neurons
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local current flow
a wave of depolarization caused by sodium ion entry
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trigger zone
is the integrating center with a high concentration of voltage gated Na+ channels and initiates an action potential
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action potentials
are uniform electrical signals that travel from a neuron's trigger zone to the end of its axon without losing strength (100mv)
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what are the three phases of the action poential
the rising phase, the falling phase, and the after hyper-polarization phase
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rising phase
begins when a grade potential depolarizes the membrane to -55mV, then to 0mV, then to 60mV. the action potential peaks at +30mV
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falling phase
increased K+ permeability and reaches 30mV, K+ exits the cell and the membrane potential rapidly drops reaching -70mV but K+ permeability is still high, leading to hyper polarization of -90mV called undershoot. returns back to -70mV
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how many gates due voltage gated Na+ channels have?
two gates: inactivation and activation
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when is the activation gate closed?
at resting membrane potential, preventing Na+ movement
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what happens during the reset of Na+ channel gates
the activation gate is closing, and the inactivation gate is opening
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absolute refractory period
lasts about 1-2 milliseconds, a second action potential can not be triggered allows the Na+ channel gates to reset
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relative refractory period
follows the absolute refractory period K+ channels remain open; a stronger than normal graded potential can reopen Na+ channels
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conduction
maintains the strength of action potentials from the trigger zone to the end of the axon
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where does the action potential travel
travels in both directions: towards the axon terminal and towards the cell body
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why do unmyelinated axons travel slower?
have low resistance to current leak due to their entire membrane being in contact with extracellular fluid and having ion channels
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saltatory conduction
in myelinated axons where action potentials jump from node to node
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nodes of ranvier have high concentration of?
voltage-gated Na+ channels
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capacitance
the ability of the cell membrane to store charge, affecting how fast voltage changes across the membrane (myelinated have decreased capacitance)
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hyperkalemia
high levels of K+, making neurons more excitable
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hypokalemia
low levels of K+, causing muscle weakness
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neurohormones
are secreted into the blood and distributed throughout the body
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neurotransmitters
act as synapses, eliciting rapid responses; bind to specific receptor types
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neuromodulators
act as both synaptic and non-synaptic sites and have slow effects
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receptor channels (neurocrine receptors)
are ligand-gated ion channels that mediate rapid responses by altering ion flow across the membrane
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G protein-coupled receptors
mediate slower responses through a second messenger system and can regulate ion channel activity (involved in neuromodulation)
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what are the 7 types of neurocrine molecules
acetylcholine, amines, amino acids, peptides, purines, gases, and lipids
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CNS neurons release a variety of chemical signals including:
polypeptides: hypothalamic releasing hormones, oxytocin, and vasopressin
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PNS secretes three main neurocrine molecules:
acetylcholine, norepinephrine, and the neurohormone epinephrine
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acetylcholine
is synthesized from choline and acetyl coenzyme A in the axon terminal
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choline
found in membrane phosholipids
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cholinergic receptors
classified into two main subtypes: nicotinic and muscarinic
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nicotinic receptors
are monovalent cation channels allowing both Na+ and K+ to pass, with Na+ entry exceeding K+ exit due to a stronger electrochemical gradient, leading to depolarization and increased likelihood of action potential firing
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muscarinic receptors
are G-protein coupled receptors linked to second messenger systems and come in 5 subtypes (targets parasympathetic) (CNS)
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adrenergic
(adrenaline) have alpha & beta subtypes; linked with G-proteins and use different second messenger pathways
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norepinephrine
is the primary neurotransmitter of the PNS autonomic sympathetic division (neurons secreting norepinephrine are called adrenergic or noradrenergic
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where does neurotransmitter synthesis occur
in both nerve cell body and the axon terminal
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where are polypeptides synthesized
in the cell body because axon terminals lack the necessary organelles for protein synthesis
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propeptide
resulted from the synthesis of polypeptides; packaged into vesicles along with modifying enzymes and transported to the axon terminal via fast axonal transport
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what is require for the synthesis of smaller neurotransmitters
enzymes
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where are neurotransmitters stored
in vesicles in the axon terminal and released into the synaptic cleft via exocytosis
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how does the process of the release of neurotransmitters begin?
when an action potential depolarizes the axon terminal, opening voltage gated Ca2++ channels, then calcium enters the cell due to their higher extracellular concentration, binding to regulatory proteins and triggering exocytosis, synaptic vesicle membranes fuse with the cell membrane, releasing neurotransmitters into the synaptic cleft
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why are vesicle membranes recycled?
they are recycled by endocytosis to prevent an increase in membrane surface area
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why is neural signaling brief
due to the rapid removal or inactivation of neurotransmitters in the synaptic cleft
107
how can unbound transmitters be removed?
by diffusion away from the synapse, enzymatic inactivation, or reuptake into cells
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short term synaptic plasticity
can either enhance (facilitation) or decrease (depression) synaptic activity
108
what was does the duration and strength of a stimuli tell you?
stronger stimuli result in more action potentials per second, increasing neurotransmitter release
109
process of acetylcholine
it's broken down by acetylcholinesterase (AChE) into choline and acetyl CoA. choline is then transported back into the presynaptic terminal via Na+ dependent co-transporter and reused to synthesize new ACh
110
what does increased strength of graded potentials do?
leads to more frequent action potentials
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synaptic plasticity
refers to the nervous system[s ability to change synaptic activity, occurring mainly in the CNS
112
second messengers
can open or close ion channels from the cytoplasmic side, leading to changes in membrane potential known as slow synaptic potentials
113
GPCR activated neurotransmitters
can modify existing cell proteins or regulate the production of new proteins, influencing neuron growth, development, and long-term memory
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postsynaptic potentials (EPSPs)
increase the likelihood of an action potential, they are depolarizing synaptic potentials
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inhibitory postsynaptic potentials (IPSPs)
decrease the likelihood of an action potential, they are hyper polarizing synaptic potentials
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spatial summation
graded potentials from different locations on the neuron combine, lead to an action potential if the combine excitatory EPSPs exceed threshold
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what happens when inhibitory postsynaptic potential (IPSP) counteracts the EPSPs
prevents the action potential, and can result in postsynaptic inhibition if inhibitory neurotransmitters are involved
