Chapter 06 Neuronal Signaling and the Structure of the Nervous System Flashcards by Miyaki Jan Lim

The Nervous System Two major divisions:

Central Nervous System (CNS)
Peripheral Nervous System (PNS)

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Nervous System Composed of the brain and spinal cord

Central Nervous System (CNS)

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Nervous System Composed of the nerves that connect the brain or spinal cord with the body’s muscles, glands, and sense organs

Peripheral Nervous System (PNS)

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Cell types in Nervous System

Neuron
Nuclei
Glial cells

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Cell types in Nervous System
Basic cell type of CN and PN systems
Functional unit

Neuron

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Cell types in Nervous System
Clusters of cell bodies in the CNS

Nuclei

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Cell types in Nervous System
Most numerous cell in the CNS

Glial cells

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Glial Cells of the CNS

Astrocytes
Microglia
Ependymal cells
Oligodendrocytes

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Glial Cells of the CNS
Support cells, control extracellular environment of neurons

Astrocytes

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Glial Cells of the CNS
“Immune system” of the CNS

Microglia

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Glial Cells of the CNS
Ciliated, involved with production of the cerebrospinal fluid (CSF) and CSF movement

Ependymal cells

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Glial Cells of the CNS
Responsible for the myelin

Oligodendrocytes

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Glial Cells of the PNS

Satellite cells
Schwann cells

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Glial Cells of the PNS
surround neuron bodies located in the PNS

Satellite cells

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Glial Cells of the PNS
surround and form myelin sheaths around the larger nerve fibers - vital to regeneration and proper
nerve signal conduction

Schwann cells

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Functional Classes of Neurons

Interneurons
Afferent Neurons
Efferent Neurons

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Functional Classes of Neurons
Transmits neuron to neuron

Interneurons

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Functional Classes of Neurons
Away from the receptors towards the brain

Afferent Neurons

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Functional Classes of Neurons
From the brain to the receptors / effectors

Efferent Neurons

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refers to the electrical charge difference across a cell membrane, resulting from the combined forces of ions and their permeability. It plays a crucial role in cellular communication and overall body functions.

Membrane Potentials

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Different cells have different resting membrane potentials.

true

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Neurons have a resting membrane potential generally in the range of

-40 to -90 mV

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which is more negative? the inside or the outside of the cells?

Inside is more negative

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why is the inside of the cell more negative than the outside?

the cell membrane is more permeable to potassium ions (K+) which tend to leak out of the cell, leaving behind a net negative charge inside, while larger negatively charged molecules like proteins and DNA are primarily located within the cell and cannot easily cross the membrane.

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Distribution of Major Mobile Ions Across the Plasma Membrane of a Typical Neuron Na+ Cl− K+

Extracellular Intracellular 145 15 100 7* 5 150

Action of the Na+/K+ -ATPase pump sets up the concentration gradients for Na+ and K+

Establishing Membrane Potential

Establishing Membrane Potential why does it have a Greater flux of K+ out of the cell than Na+ into the cell

A significant negative membrane potential develops, with the value approaching that of the K+ equilibrium potential

Establishing Membrane Potential what happens in a steady state

there is a small but steady leak of Na+ into the cell and K+ out of the cell

in membrane potentials it is the potential moving from RMP to less negative values

Depolarization

in membrane potentials it is the potential moving back to the RMP.

Repolarization

in membrane potentials is the potential moving away from the RMP in a more negative direction.

Hyperpolarization

⚫ changes in membrane potential that are confined to a relatively small region of the plasma membrane the magnitude of the potential change can vary (is "graded")

Graded potentials

Graded potentials have been given various names related to the location or the function, examples

receptor potential, synaptic potential, and pacemaker potential

generally very rapid (as brief as 1-4 milliseconds) and may repeat at frequencies of several hundred per second ⚫ a large change in membrane potential ⚫ an "all or none" response

Action Potentials

the ability to generate action potentials

Excitability

Types of Ion Channels

Ligand-gated Channels Voltage-gated Channels mechanically gated channels voltage-gated ion channels

Types of Ion Channels often serve as the initial stimulus for an action potential.

Ligand-gated channels and mechanically gated channels

Types of Ion Channels give a membrane the ability to undergo action potentials by allowing the rapid depolarization and repolarization phases of the response.

Voltage-gated channels

Types of Ion Channels types of __________________ vary by which ion they conduct (e.g., Na+, K+, Ca2+, or Cl) and in how they behave as the membrane voltage changes

voltage-gated ion channels

postive feedback mechanisms

Start Depolarizing stimulus Opening of voltage-gated Na+ channels Increase Pna Increased flow of Na+ into the cell Depolarization of membrane potential Opening of voltage-gated Na+ channels Stop Inactivation of Na+ channels

negative feedback mechanisms

Depolarization of membrane by Na+ influx Opening of voltage-gated K+ channels Increased PK Increased flow of K* out of the cell Repolarization of membrane potential -Negative feedback

* Generation of AP is prevented by local anesthetics such as procaine and lidocaine by blocking __________.

voltage-gated Na+ channels

Without ________, graded signals generated in the periphery cannot reach the brain and give rise pain sensation.

Some animals produce __________ that interfere with nerve conduction like local anesthetics do.

toxins

For example, the puffer fish produces ______________, that block voltage-gated Na+ channels.

tetrodotoxin

Two types of refractory:

Absolute and Relative

a period of time immediately following an action potential during which the neuron cannot fire another action potential

refractory period

types of refractory period - a second stimulus, no matter how strong, will not produce a second action potential - Occurs when the voltage-gated Na+ channels are either already open or have proceeded to the inactivated state during the firs action potential

Absolute refractory period

the period of time after an action potential when a neuron can only generate another action potential with a stronger stimulus.

relative refractory period

Following the absolute refractory period, there is an interval during which a second action potential can be produced, but only if the stimulus strength is ____________

considerably great

limit the number of action potentials an excitable membrane can produce in a given period of time

Refractory period

contribute to the separation of action potentials so that individual electrical signals pass down the axon

Refractory period

key in determining the direction of action potential propagation

Refractory period

Action Potential Propagation direction

unidirectional

the process by which a nerve impulse, or action potential, travels along a neuron

Action Potential Propagation

Action Potential Propagation In skeletal muscle cells initiated near the middle of the cells and propagate toward the ________

two ends

velocity of AP propagation depends upon

fiber diameter and fiber myelination

Larger the fiber diameter, _____________ the action potential propagates

faster (less resistance to local current)

__________ makes it difficult for charge to flow between intracellular and extracellular fluid compartments.

Myelin

____________ axons are metabolically more efficient than ____________ ones.

Myelinated , unmyelinated

Action potentials occur only at the ___________ (concentration of voltage-gated Na+ channels is high)

nodes of Ranvier

Thus, action potentials jump from one node of ranvier to the next as they propagate along a ____________ (saltatory conduction)

myelinated fiber

Differences Between Graded Potentials and Action Potentials in Amplitude

Graded Potential Amplitude varies with size of the initiating event Action Potential All-or-none. Once membrane is depolarized to threshold, amplitude is independent of the size of the initiating event. Cannot be summed.

Differences Between Graded Potentials and Action Potentials in being summed

Graded Potential Can be summed. Action Potential Cannot be summed.

Differences Between Graded Potentials and Action Potentials in thresholds

Graded Potential Has no threshold. Action Potential Has a threshold that is usually about 15 mV depolarized relative to the resting potential.

Differences Between Graded Potentials and Action Potentials in refractory period

Graded Potential Has no refractory period. Action Potential Has a refractory period.

Differences Between Graded Potentials and Action Potentials in conduction

Graded Potential Is conducted decrementally; that is, amplitude decreases with distance. Action Potential Is conducted without decrement; the depolarization is amplified to a constant value at each point along the membrane.

Differences Between Graded Potentials and Action Potentials in duration

Graded Potential Duration varies with initiating conditions. Action Potential Duration is constant for a given cell type under constant conditions.

Differences Between Graded Potentials and Action Potentials in depolarization or a hyperpolarization

Graded Potential Can be a depolarization or a hyperpolarization Action Potential Is only a depolarization.

Differences Between Graded Potentials and Action Potentials in depolarization or a hyperpolarization

Graded Potential Initiated by environmental stimulus (receptor), by neurotransmitter (synapse), or spontaneously. Action Potential Initiated by a graded potential.

Differences Between Graded Potentials and Action Potentials in Mechanism

Graded Potential Mechanism depends on ligand-gated channels or other chemical or physical changes. Action Potential Mechanism depends on voltage-gated channels.

types Synapses

Electrical Chemical

* junctions between two neurons can be chemical or electrical

Synapses

types Synapses the electrical activity of the presynaptic neruon affects the electrical activity of the postsynaptic neuron

Electrical synapse

types Synapses utilize neurotransmitters

Chemical synapses

functional Anatomy of Synapses - Pre- and post-synaptic cells are connected by this gap junctions

Electrical

type of Synapses that have this functional Anatomy: Pre- and post-synaptic cells are connected by gap junctions

Electrical

type of Synapses that have this functional Anatomy: Pre-synaptic neurons release neurotransmitter from their axon terminals Neurotransmitter binds to receptors on post-synaptic neurons

Chemical

Docking of Vesicles and Release of Neurotransmitters

Neurotransmitters are produced and stored in vesicles at the axon terminal. When the cell is stimulated the intracellular Ca2+ levels increase and stimulate the vesicles to translocate and bind to the plasma membrane via the SNARE proteins. The neurotransmitter is then released via exocytosis.

Removal of Neurotransmitter

To terminate the signal in a chemical synapse the neurotransmitter must be removed. This is accomplished by: 1. Diffusion of the transmitter from the cleft 2. Degradation of the transmitter by enzymes 3. Reuptake into the pre-synaptic cells for reuse Receptors in the post-synaptic cell are removed from the membrane.

Activation of Post-synaptic Cells

* Excitatory chemical synapses generate an excitatory postsynaptic potential (EPSP). * EPSPs serve to bring the membrane potential closer to threshold for generating an action potential. * Inhibitor chemical synapses generate an inhibitory postsynaptic potential (IPSP). * IPSPS make the cell's membrane potential more negative, making it harder to generate an action potential.

Axo-axonic Synapse

The neurotransmitter released by A binds with receptors on B results in change in the amount of neurotransmitter released by B Neuron A has no direct effect on neuron C, but has influence on ability of B to influence C.

How the Modification of Synaptic Transmission by Drugs happen?

Drugs act by interfering with or stimulating normal processes in the neuron involved in neurotransmitter synthesis, storage, and release, and in receptor activation.

toxin that interferes with actions of SNARE proteins at excitatory synapses that activate muscles; botulism is characterized by muscle paralysis.

Clostridium botulinum bacilli toxin (botulism)

modify both the presynaptic and the postsynaptic cell's response to specific neurotransmitters, amplifying or dampening the effectiveness of ongoing synaptic activity.

Neuromodulators

part of neurotransmitters that affect ion channels that directly affect excitation or inhibition of the postsynaptic cell, and these mechanisms operate within milliseconds.

Receptors for neurotransmitters

part of neurotransmitters that bring about changes in metabolic processes in neurons, and these changes can occur over minutes, hours, or even days, include alterations in enzyme activity or, through influences on DNA transcription, in protein synthesis.

Receptors for neuromodulators

involved in rapid communication chemical messengers that carry signals between nerve cells, glands, and muscles

Neurotransmitters

chemicals that alter the way neurons communicate with each other. They can be released from neurons or non-neural sources. associated with slower events such as learning, development, motivational states, and some types of sensory or motor activities.

Neuromodulators

Classes of Some of the Chemicals Known or Presumed to Be Neurotransmitters or Neuromodulators

1. Acetylcholine (ACH) 2. Biogenic amines Catecholamines Dopamine (DA) Norepinephrine (NE) Epinephrine (Epi) Serotonin Histamine 3. Amino acids Excitatory amino acids; glutamate Inhibitory amino acids; gamma aminobutyric acid (GABA) and glycine 4. Neuropeptides endogenous opioids oxytocin tachykinins 5. Gases nitric oxide, carbon monoxide, hydrogen sulfide 6. Purines For example, adenosine and ATP

Classes of Some of the Chemicals Known or Presumed to Be Neurotransmitters or Neuromodulators found in PNS and CNS. acts at muscarinic (G protein coupled) or nicotinic (ion channels) receptors. Nicotininic receptors are found at the neuromuscular junctions of skeletal muscles.

Acetylcholine

Neurons that use Acetylcholineas the primary neurotransmitter are known as

cholinergic neurons

in acetochline, Muscarinic receptors (M-receptor) are found in

smooth muscle, gland and cardiac muscle M-smooth muscle gland M1-ganglia, gland M2-heart

in acetochline, Muscarinic receptors (M-receptor) have effects such as

inhibiting the cardiac muscle, exciting the smooth muscle & gland

in acetochline, nicotinic (ion channels) receptors have effects such as

N2:exciting skeletal muscle, N1 exciting the postsynaptic neuron in ganglia

in acetochline, nicotinic (ion channels) receptors are located at

skeletal muscle--motor ending-plate (N2 N2) ganglia-postsynaptic membrane(N1)

Acetylcholine or ACh is produced in the presynaptic axon by the ____________

enzyme choline acetyl transferase (CAT)

equation of Acetylcholine production

Acetyl CoA + choline → acetylcholine + COA

Degradation of ACh occurs in synaptic cleft and is done by the enzyme

acetylcholinesterase (AChE)

equation of Acetylcholine Degradation

Acetylcholine → acetate + choline

Biogenic Amine Neurotransmitters that are synthesized from tyrosine by a process of hydroxylation and decarboxylation

Catecholamines

Biogenic Amine Neurotransmitters Made from tryptophan

Serotonin

Biogenic Amine Neurotransmitters Made from histidine

Histamine

Receptors utilized by the neurotransmitters Norepinphrine (NE) and Epinephrine (Epi). are G protein coupled that are generally linked to second messenger signal transduction pathways.

Adrenergic Receptors

Enzymes which degrade the biogenic amine neurotransmitters

Monoamine oxidase (MAO) Catechol-o-methyltransferase

NE is found in both the CNS and PNS but Epi is found mainly in the PNS.

true

Alpha adrenergic receptors:

Alpha, (α1), Alpha2,

Beta adrenergic receptors:

Beta, (B1), Beta2, Beta,

Main CNS location of serotnin

Brainstem

Biogenic Amine Neurotransmitters Also known as 5-hydroxytryptamine or 5-HT * CNS neurotransmitter and is also made by enterochromaffin cells in the gut Regulating sleep Emotions Involved in the vomiting reflex Regulates cell growth Vascular smooth muscle cell contraction

Serotonin

Biogenic Amine Neurotransmitters CNS neurotransmitter whose major location is the hypothalamus commonly known for paracrine actions found in the peripheral system. It is involved in allergic reactions, nerve sensitization, and acid production in the stomach.

Histamine

Amino acid neurotransmitters at excitatory synapses

* Aspartate * Glutamate

Amino acid neurotransmitters at inhibitory synapses

* Glycine * GABA

Amino acid neurotransmitters primary neurotransmitter in 50% of the excitatory synapses in the CNS

Glutamate

Glutamate is sensed by two types of receptors

Metabotropic glutamate receptors Ionotropic glutamate receptors

ligand-gated ion channels that are activated by glutamate, a neurotransmitter

Ionotropic glutamate receptors

types of Ionotropic glutamate receptors

* AMPA receptors (identified by their binding to a-amino-3 hydroxy-5 methyl-4 isoxazole proprionic acid) * NMDA receptors (which bind N-methyl-D-aspartate)

G-protein Coupled receptors

Metabotropic glutamate receptors

in Glutamate the activity of _________ and ________ receptors has been implicated in long-term potentiation (LTP) phenomenon frequent activity across a synapse are coupled with lasting changes in the strength of signaling across that synapse, thought to be a cellular process underlying learning and memory

AMPA and NMDA

receptor implicated in mediating excitotoxicity

NMDA Receptors

implicated in mediating excitotoxicity igand-gated cation channels activated by glutamate, an excitatory neurotransmitter. These receptors are located mostly at excitatory synapses and, thereby, participate in excitatory neurotransmission in the central nervous system.

NMDA Receptors

a phenomenon in which the injury or death of some brain cells rapidly spreads to adjacent regions

excitotoxicity

When glutamate-containing cells die and their membranes rupture, the flood of glutamate excessively stimulates AMPA and NMDA receptors on nearby neurons. may be involved in stroke, traumatic brain injury and neurodegenerative diseases

excitotoxicity

excitotoxicity causes the accumulation of toxic levels of which in turn kills those neurons, and the wave of damage progressively spreads.

intracellular Ca2+

Amino acid neurotransmitters at inhibitory synapses the major inhibitory neurotransmitter in the brain * a modified form of glutamate. Postsynaptically, may bind to ionotropic or metabotropic receptors.

GABA (gamma-aminobutyric acid)

_______ neurons in the brain are small interneurons that dampen activity within neural circuits.

GABA

receptor that increases Cl flux into the cell, resulting in hyperpolarization of the postsynaptic membrane.

ionotropic receptor

alcohol that stimulates GABA → inhibits excitatory glutamate synapses

Ethanol

the overall effect is of alcohol and GABA is the

global depression of the electrical activity of the brain

As a person's blood alcohol content ____________, there is a progressive reduction in overall cognitive ability, along with reduced sensory perception (hearing and balance in particular), motor incoordination, impaired judgment, memory loss, and unconsciousness.

rises

* the major neurotransmitter released from inhibitory interneurons in the spinal cord and brainstem * binds to ionotropic receptors on postsynaptic cells that allow Cl to enter.

Glycine

neurons that are essential for maintaining a balance of excitatory and inhibitory activity in spinal cord integrating centers that regulate skeletal muscle contraction.

glycinergic neurons

short chains of amino acids with peptide bonds physiological roles are not all known peptidergic neurons are co-secreted with another type of neurotransmitter and act as neuromodulators

Neuropeptides

Neurons that release one or more of the peptide neurotransmitters are collectively called

peptidergic

Neuropeptides Endogenous opioids

* Enkephalins * Endorphins * Morphine and codeine

Endogenous opioids that are synthetic opioids that are used as analgesics (pain reducers).

Morphine and codeine

* a neuropeptide that acts as a neurotransmitter and neuromodulator * Released by afferent neurons that relay sensory information into the central nervous system. * It is known to be involved in pain sensation

Substance P

* Neurotransmitters that are produced by enzymes in axon terminals (in response to Ca* entry) * simply diffuse from their sites of origin in one cell into the intracellular fluid of other neurons or effector cells, where they bind to and activate proteins

Gas Neurotransmitters

Examples Gas Neurotransmitters

* Nitric oxide (NO)

* produced by nitric oxide synthetase (eNOS, NOS, iNOS) and undergoes very rapid degradation * activates cGMP signaling pathways

* Nitric oxide (NO)

* nontraditional neurotransmitters Still an active area of research

Purine Neurotransmitters

Purine Neurotransmitters include the purines, _____________ , which act principally as neuromodulators

ATP and adenosine

Purine Neurotransmitter that is present in all pre-synaptic vesicles and is co-released with other classical neurotransmitters in response to Ca?+ influx into the terminal.

ATP

How Neuroeffectors Communicat

* Many neurons also synapse on muscle and gland cells * The events that occur at neuroeffector junctions are similar to those at synapses between neurons. * The receptors on the effector cell may be either ionotropic or metabotropic.

Chapter 06 Neuronal Signaling and the Structure of the Nervous System Flashcards

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