Exam 2 Signal Transmission Flashcards
▪A ____ is a junction between two neurons, or between a neuron and an effector (muscle or gland)
synapse
▪Synapses contribute to ______ by providing for evaluation and integration of stimuli
homeostasis
▪____ are physically changed with repeated use (which includes learning)
Synapses
▪Some diseases and disorders result from synaptic _____, and many therapeutic and addictive chemicals have their sites of action at synapses
disruptions
▪At a synapse between neurons . . .
– The neuron sending the signal is the ___
– The neuron receiving the message is the ____
▪Most neurons, including all interneurons, function as both presynaptic and postsynaptic neurons, receiving information from some neurons and conveying information to others
presynaptic neuron
postsynaptic neuron
Synapses (chemical synapses) are most
commonly . . .
– ___, from axon to dendrite
– ____, from axon to soma
– _____, from axon to axon
– Axodendritic, from axon to dendrite
– Axosomatic, from axon to soma
– Axoaxonic, from axon to axon
Two Types of synapses?
Electrical and Chemical
▪_____ synapses
– The cells on each side of the synapse are in physical contact
– Action potential moves from one cell to the other as a flow of ions through gap junctions
Electrical
▪_____ synapses
– The cells on each side of the synapse are not in physical contact
– Action potential moves from one cell to the other by means of a neurotransmitter that bridges the gap between the two cells
Chemical
Electrical synapses
▪Action potentials (impulses) are conducted between adjacent cells by _____
▪Hundreds of _____ per gap junction connect the cytosol of the adjacent cells
▪Ions flow from one cell to the other, conveying the ____
gap junctions
connexons
action potential
Electrical synapses
▪Electrical synapses or chemical synapses are faster?
▪Electrical synapses can synchronize groups of?
▪Locations include ?
▪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
visceral smooth muscle
First Event at a chemical synapse
- Increased intercellular Ca++ level within the presynaptic neuron triggers exocytosis of some of the synaptic vesicles, releasing neurotransmitter into the synaptic cleft
Second Event at a chemical synapse
- Neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the post-synaptic neuron’s plasma membrane
Third Event at a chemical synapse
- Ligand-gated channels open, allowing ions to cross the membrane (here, Na+), changing the voltage and creating a postsynaptic potential
Fourth Event at a chemical synapse
- Threshold depolarizing postsynaptic potential triggers one or more nerve impulses
Explain or draw the Four events at a chemical synapse
- Increased intercellular Ca++ level within the presynaptic neuron triggers exocytosis 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 post-synaptic neuron’s plasma membrane
- Ligand-gated channels open, allowing ions to cross the membrane (here, Na+), changing the voltage and creating a postsynaptic potential
- Threshold depolarizing postsynaptic potential triggers one or more nerve impulses
Postsynaptic potentials
▪Neurotransmitters that depolarize the postsynaptic membrane cause an excitatory graded potential because ___
▪Neurotransmitters that cause hyperpolarization (further polarization) of the postsynaptic membrane are ___
it brings the membrane closer to threshold
inhibitory
Excitatory postsynaptic potential
▪Abbreviated _____
▪Typically result from opening of ______, the three most common cations being Na+, K+, and Ca++
▪A single EPSP does not normally _____, but the neuron does become more excitable, and being partially depolarized is more likely to reach threshold at future EPSP arrival
EPSP
ligand- gated cation channels
initiate a nerve impulse
Inhibitory postsynaptic potential
▪Abbreviated ____
▪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 ______
IPSP
the inside becoming more negative (hyperpolarized)
Typically result from opening of ligand- gated cation channels, the three most common cations being Na+, K+, and Ca++
Excitatory postsynaptic potential (EPSP)
Neurotransmitter removal
▪Neurotransmitters must be removed from the synaptic cleft for _____
▪If neurotransmitters were not removed, they would ___
normal synaptic function
continue to influence the postsynaptic neuron, muscle fiber, or gland indefinitely
Mechanisms of neurotransmitter removal
▪Diffusion
▪Enzymatic degradation (acetylcholinesterase breaks
down acetylcholine into acetyl and choline)
▪Uptake by the cells
Explain uptake and reuptake
– 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
Summation of postsynaptic potentials
▪Central nervous system neurons typically receive input from between 1,000 and 10,000 synapses
▪The synaptic input is integrated (evaluated) by a process known as _____, which occurs at the trigger zone
▪The greater the summation of EPSPs, the greater the chance that threshold will be reached, and that a nerve impulse will arise
summation
What are the two summation types?
Spatial summation
Temporal summation
______ results from buildup of neurotransmitter released simultaneously by several presynaptic end bulbs
▪Spatial summation
______results from buildup of neurotransmitter released by a single presynaptic end bulb many times in rapid succession
▪Temporal summation
Postsynaptic neuron response to summation
▪If the total excitatory effects are greater than total
inhibitory effects, but still less than threshold the
result is a sub-threshold EPSP, ______, but
partial depolarization may make a nerve impulse
easier with additional stimuli
no nerve impulse
Postsynaptic neuron response to summation
▪If the total excitatory effects are greater than total
inhibitory effects, and threshold is reached, the result
is ________
generation of one or more nerve impulses
Postsynaptic neuron response to summation
▪If the total inhibitory effects are greater than the
excitatory effects, the membrane hyperpolarizes,
thereby _________
inhibiting the ability of the postsynaptic neuron to generate a nerve impulse
▪ Presynaptic neurons _____ release excitatory neurotransmitters that generate EPSPs
▪Presynaptic neurons _____ release inhibitory neurotransmitters that generate IPSPs
1, 3, and 5
2 and 4
▪ Presynaptic neurons ______ release excitatory neurotransmitters that generate EPSPs
1, 3, and 5
▪Presynaptic neurons _____ release inhibitory neurotransmitters that generate IPSPs
2 and 4
odd presynaptic neurons 1, 3, and 5
odds EXCITE - ESPSs
even presynaptic neurons 2 and 4
evens INHIBIT - ISPSs
Neurotransmitters
▪Many neurotransmitters are also hormones, and are produced by
– Endocrine glands in various parts of the body
– Neurosecretory cells, which are certain neurons in the brain
▪Neurotransmitters are divided into two classes based primarily on size`
– Small-molecule neurotransmitters
– Neuropeptides
Small molecule neurotransmitters
▪Acetylcholine ▪Amino acids ▪Biogenic amines ▪ATP and other purines ▪Nitric oxide
▪Best studied neurotransmitter
▪Commonly abbreviated ACh
▪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
▪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. [Endogenous biogenic amines are formed by decarboxylation of amino acids or by amination of aldehydes and ketones] -brackets untestable this block
▪As neurotransmitters, think BRAIN
▪Depending on the type of receptor, biogenic amines may cause either excitation or inhibition (there are multiple receptor types for each
biogenic amine)
Biogenic amines
▪Classical monoamine neurotransmitters
Biogenic amines
– Histamine – Serotonin – Catecholamine neurotransmitters (subsequent slide) • dopamine • norepinephrine (noradrenaline) • epinephrine (adrenaline)
Biogenic amines
– ______, 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
Catecholamine neurotransmitters
- dopamine
- norepinephrine (noradrenaline)
- epinephrine (adrenaline)
▪______, 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
▪______ is used by some neurons of the brain, and is also an adrenal medulla hormone
Epinephrine
▪Chemical formula NO Gas
▪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
▪ These are neurotransmitters that comprise 3 to 40 amino acids (i.e. short chain amino acids) linked by peptide bonds
▪They are widespread in both the CNS and PNS
▪Have both excitatory and inhibitory actions
▪They are formed in the neuron cell body, packaged
into vesicles, and transported to axon terminals
▪Many of them also serve as hormones, regulating
physiological responses elsewhere in the bod
Neuropeptides
Neuropeptides
▪Naturally occurring neuropeptides that use those
receptors are called opioid peptides, and include . . .
– Enkephalins
– Endorphins
– Dynorphins
▪Opioid peptides are thought to be the body’s natural painkillers
Neuropeptides
▪Opioid peptides are thought to be the body’s natural painkillers
Neuropeptides
Neural circuits
▪The billions of neurons in the central nervous
system are organized into networks termed neural
circuits
▪A neural circuit is a functional group of neurons that
processes a specific kind of information
▪There are a number of such neural circuits, among which are the ones we will discuss: – Simple series circuit – Diverging circuit – Converging circuit – Reverberating circuit – Parallel after-discharge circuit
▪ One presynaptic neuronstimulates 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
▪ 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
▪ 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)
▪ This imposes varying synaptic delays, so the last neuron
exhibits multiple EPSPs or IPSPs
▪ 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 plasticity, which is the ability to change based on experience and need
▪Individual neurons can sprout new dendrites, synthesize new proteins, and change the nature and number of synapses
Nervous system plasticity
▪Neurons are generally not able to regenerate, that is to undergo mitosis and replicate, or to repair themselves to any great extent
Regeneration
▪PNS dendrites and myelinated axons may be repaired if the cell body remains intact, and Schwann cells remain active…. T or F
True
▪Little or no repair of damage to neurons occurs in the CNS; generally even a severed axon can not be repaired or regrown…. T or F
True
Neuronal Regeneration In the PNS
▪ The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath, is the _____
(sheath of Schwann).
– When an axon is injured, the neurolemma aids regeneration by forming a ______ that guides and stimulates regrowth of the axon.
neurolemma
regeneration tube
Neuronal Regeneration
▪ To d o any regeneration, neurons must be located in the ____, have an intact ____, and be myelinated by
functional Schwann cells having a _____.
– Demyelination 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.
• Any single episode of demyelination may cause deterioration of affected nerves.
PNS
cell body
neurolemma
Demyelination
Loss or destruction of myelin sheaths around axons in the CNS or PNS
In axons that are normally myelinated, voltage-gated channels are concentrated (or exclusively present) only at nodes of Ranvier. 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
Multiple sclerosis and Guillain-Barré Syndrome are demyelinating diseases
All true sensei
is an autoimmune disease that causes progressive destruction of myelin sheaths in the CNS
– 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
Multiple Sclerosis
______ is a demyelinating disorder in which macrophages strip myelin from axons in the PNS.
– May result from the immune system’s response to a….
Guillain-Barré syndrome
bacterial infection
▪Manifests in epileptic seizures, which are commonly described “an electrical storm in the brain”
▪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
▪Most common cause is brain damage at birth, other causes have been identified, but many have no identifiable underlying cause
Epilepsy
▪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
▪Local anesthetics block pain and other somatic sensations, and are commonly used to produce anesthesia in the skin during suturing, or in the mouth during \dental work
▪Examples are Novocaine and Lidocaine
▪They act by blocking the opening of voltage-gated Na+ channels, thereby preventing transmission of pain signals
Local anesthetics
MS or Multiple Sclerosis is a ____ disease in the ____
autoimmune disease in the CNS
Guillain-Barre Syndrome is a _____ disorder found in the _____
demyelinating disorder in the PNS
rabies travels by….
fast axonal transport
