Signal Flashcards
A ____ is a junction between two neurons, or between a neuron and an effector (muscle or gland)
synapse
Synapses contribute to homeostasis by providing for evaluation and integration of ____
stimuli
Synapses are physically ___ with repeated use (which includes learning)
changed
Some diseases and disorders result from synaptic disruptions, and many therapeutic and addictive chemicals have their sites of action at ___
synapses
The neuron sending the signal is the _____
presynaptic neuron
The neuron receiving the message is the ____
postsynaptic neuron
Most neurons, including all interneurons, function as both ___ and ____ neurons, receiving information from some neurons and conveying information to others
presynaptic
postsynaptic
from axon to dendrite
axodendritic (slide 4)
from axon to soma
axosomatic (slide 4)
from axon to axon
axoaxonic (slide 4)
The cells on each side of the synapse are in physical contact
Electrical synapses
Action potential moves from one cell to the other as a flow of ions through ___
(Electrical synapses)
gap junctions
Ions flow from one cell to the other, conveying the action potential
The cells on each side of the synapse are not in physical contact
Chemical synapses
Action potential moves from one cell to the other by means of a ____ that bridges the gap between the two cells
(chemical synapses)
neurotransmitter
Hundreds of ___ per gap junction connect the cytosol of the adjacent cells
(electrical synapse)
connexons
Electrical synapses are faster than chemical synapses
Electrical synapses can synchronize groups of neurons or muscle fibers
Locations include muscle fibers of the heart and ____
electrical synapse
visceral smooth muscle
Nerve impulse arrives at a synaptic end bulb of a presynaptic neuron
Depolarizing phase of the nerve impulse opens voltage-gated ___ channels, and Ca++ flows inward through the opened channels due to concentration differences
(Events at a chemical synapse pt. 1,2)
Ca++
Increased intercellular Ca++ level within the presynaptic neuron triggers ___ of some of the synaptic vesicles, releasing neurotransmitter into the synaptic cleft
Neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the _____ plasma membrane
(Events at a chemical synapse pt. 3,4)
exocytosis
post-synaptic neuron’s
Ligand-gated channels open, allowing ions to cross the membrane (here, Na+), changing the voltage and creating a postsynaptic ___
Threshold _____ postsynaptic potential triggers one or more nerve impulses
(Events at a chemical synapse pt. 5,6)
potential
depolarizing
Neurotransmitters that depolarize the postsynaptic membrane cause an excitatory ___ potential because it brings the membrane closer to threshold
graded
Neurotransmitters that cause hyperpolarization (further polarization) of the postsynaptic membrane are ____
inhibitory
Typically result from opening of ligand-gated cation channels, the three most common cations being Na+, K+, and Ca++
Excitatory postsynaptic potential
EPSP
A single EPSP does not normally initiate a nerve impulse, but the neuron does become more ____, and being partially depolarized is more likely to reach threshold at future EPSP arrival
excitable
Typically result from opening of ligand-gated anion channels for Cl- or ligand-gated channels for K+, which then diffuse according to concentration gradients resulting in the inside becoming more negative (hyperpolarized)
Inhibitory postsynaptic potential (IPSP)
Neurotransmitters must be ____ from the synaptic cleft for normal synaptic function
removed
If neurotransmitters were not removed, they would continue to ___ the postsynaptic neuron, muscle fiber, or gland indefinitely
influence
Diffusion
Enzymatic degradation
Uptake by the cells
Mechanisms of neurotransmitter removal
acetylcholinesterase breaks down acetylcholine into acetyl and choline
Enzymatic degradtion, e.g.
Termed reuptake if taken back up by the same cell that released the neurotransmitter
Termed uptake if taken up by a cell that did not actually release it in the first place
Neurotransmitter transporters are membrane proteins that accomplish the uptake
“uptake by the cells”
most common mechanism of neurotransmitter removal
The synaptic input is integrated (evaluated) by a process known as summation, which occurs at the ___
trigger zone
The greater the summation of ____, the greater the chance that threshold will be reached, and that a nerve impulse will arise
EPSPs
results from buildup of neurotransmitter released simultaneously by several presynaptic end bulbs
(summation type)
spatial summation
results from buildup of neurotransmitter released by a single presynaptic end bulb many times in rapid succession
(summation type)
Temporal summation
If the total excitatory effects are greater than total inhibitory effects, but still less than threshold the result is a sub-threshold EPSP, no ____, but partial depolarization may make a nerve impulse easier with additional stimuli
nerve impulse
If the total excitatory effects are greater than total ___ effects, and threshold is reached, the result is generation of one or more nerve impulses
inhibitory
If the total inhibitory effects are greater than the excitatory effects, the membrane ____, thereby inhibiting the ability of the postsynaptic neuron to generate a nerve impulse
hyperpolarizes
Neurotransmitters are divided into two classes based primarily on size
Small-molecule neurotransmitters
Neuropeptides
Acetylcholine
Amino acids
Biogenic amines
ATP and other purines
Nitric oxide
Small molecule neurotransmitters
Best studied neurotransmitter
Released by many PNS neurons and some CNS neurons
Excitatory at some synapses such as the previously-discussed neuromuscular junction where it opens ligand-gated cation channels
Inhibitory at other synapses (specifics to be covered later in the course)
Acetylcholine
Commonly abbreviated ACh
Associated with central nervous system
Most common excitatory examples are glutamate (glutamic acid) and aspartate (aspartic acid)
Most common inhibitory examples are gamma aminobutyric acid (GABA) and glycine
Amino acids
Nutritionally, they are found in a wide range of foods, and as exogenous amines they are directly absorbed in the intestine.
Biogenic amines
As neurotransmitters, they are generally associated with the brain
Depending on the type of receptor, biogenic amines may cause either excitation or inhibition (there are multiple receptor types for each biogenic amine)
Histamine
Serotonin
Classical monoamine neurotransmitters
as a neurotransmitter it mediates arousal and attention, also a pro-inflammatory signal released from mast cells in response to allergic reactions or tissue damage
Histamine
thought to be involved in sensory perception, temperature regulation, control of mood and appetite, and induction of sleep
Serotonin
dopamine
norepinephrine (noradrenaline)
epinephrine (adrenaline)
Catecholamine neurotransmitters (type of biogenic amine)
for brain neurons that are active during emotional responses, addictive behaviors, and pleasurable experiences, plus regulating skeletal muscle tone and skeletal muscle contractions
Dopamine
used by some neurons of the brain, has roles in awakening from deep sleep, dreaming, and regulating mood. It is also a hormone produced by the adrenal medulla
Norephinephrine
used by some neurons of the brain, and is also an adrenal medulla hormone
Epinephrine
Formed on demand, rather than being synthesized and stored in synaptic vesicles
Produced by endothelial cells in blood vessel walls, it is LIPID SOLUBLE and diffuses into neighboring smooth muscle cells causing them to relax, producing vasodilation
Nitric oxide
neurotransmitters that comprise 3 to 40 amino acids (i.e. short chain amino acids) linked by peptide bonds
widespread in both the CNS and PNS
excitatory and inhibitory actions
formed in the neuron cell body, packaged into vesicles, and transported to axon terminals
also serve as hormones, regulating physiological responses elsewhere in the body
Neuropeptides
Certain brain neurons have plasma membrane receptors for opiate drugs such as morphine and heroin
neuropeptides
Naturally occurring neuropeptides that use those receptors are called opioid peptides, and include . . .
Enkephalins
Endorphins
Dynorphins
A ___ is a functional group of neurons that processes a specific kind of information
neural circuit
Simple series circuit
Diverging circuit
Converging circuit
Reverberating circuit
Parallel after-discharge circuit
neural circuit type
One presynaptic neuron stimulates only a single postsynaptic neuron
The postsynaptic neuron then stimulates another, etc.
Most neural circuits are more complex than this
Simple series circuit
A nerve impulse from a single presynaptic neuron causes the stimulation of increasing numbers of cells along the circuit (i.e. the action potential diverges)
The effect is amplification of the original signal
Sensory signals often spread into diverging circuits that are relayed to different parts of the brain
Diverging circuit
slide 32
A postsynaptic neuron receives nerve impulses from several different sources (i.e. the action potentials converge)
The effect is more effective stimulation or inhibition of the postsynaptic neuron
Motor neurons that synapse with skeletal muscle fibers may receive input from several pathways that originate in different parts of the brain
Converging circuit
The incoming impulse stimulates the first neuron, which stimulates the second, which stimulates the third, etc
Branches from later neurons loop back to synapse with earlier neurons, sending impulses back through the circuit many times
Reverberating circuit
The reverberations may last seconds to hours
Thought to be used in breathing, waking up, and short-term memory
Reverberating circuit
One presynaptic input neuron has one output neuron with a variable number of intermediate neurons between input and output (and therefore variable number of synapses)
Parallel after-discharge circuit
This imposes varying synaptic delays, so the last neuron exhibits multiple EPSPs or IPSPs
Parallel after-discharge circuit
If the input is excitatory, the output neuron can send out a stream of impulses in quick succession
Parallel after-discharge circuit
The nervous system exhibits ___ which is the ability to change based on experience and need
plasticity
Individual neurons can sprout new dendrites, synthesize new proteins, and change the ___ of synapses
nature and number
Neurons are generally not able to ____, that is to undergo mitosis and replicate, or to repair themselves to any great extent
regenerate
___ dendrites and myelinated axons may be repaired if the cell body remains intact, and Schwann cells remain active
PNS
Little or no repair of damage to neurons occurs in the __; generally even a severed axon can not be repaired or regrown
CNS
The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath, is the ____ (sheath of Schwann).
neurolemma
When an axon is injured, the neurolemma aids regeneration by forming a \_\_\_\_ that guides and stimulates regrowth of the axon
regeneration tube
To do any regeneration, neurons must be located in the ___, have an INTACT CELL body, and be MYELINATED by functional Schwann cells having a neurolemma
PNS
refers to the loss or destruction of myelin sheaths around axons. It may result from disease, or from medical treatments such as radiation therapy and chemotherapy
Demyelination
Any single episode of demyelination may cause deterioration of affected nerves
In axons that are normally myelinated, voltage-gated channels are concentrated (or exclusively present) only at ____. Myelin insulates the neuron and allows the current to spread further before it attenuates. Destruction of myelin means the current does not spread as far, and therefore does not reach the next concentration of voltage-gated channels
nodes of Ranvier
an autoimmune disease that causes progressive destruction of myelin sheaths in the CNS
Multiple Sclerosis
Multiple regions of myelin sheaths deteriorate to scleroses (hardened scars or plaques)
Destruction of the myelin sheaths first slows, then short circuits nerve impulse propagation
demyelinating disorder in which macrophages strip myelin from axons in the PNS
Guillain-Barré syndrome
May result from the immune system’s response to a bacterial infection
The discharges stimulate neurons to send spontaneous impulses, resulting in the perception of lights, noises, and smells that do not exist and for which the corresponding sense organ has not been stimulated; skeletal muscles may also contract involuntarily; not all seizures are dramatic
Epilepsy
Manifests in epileptic seizures, which are commonly described “an electrical storm in the brain”
A fatal disease caused by a virus that reaches the CNS via fast axonal transport
Usually transmitted by the bite of a dog or other meat-eating animal
Symptoms are excitement, aggressiveness, and madness, followed by paralysis and death
Rabies
They act by blocking the opening of voltage-gated Na+ channels, thereby preventing transmission of pain signals
Local anesthetics
