Chapter 06 Neuronal Signaling and the Structure of the Nervous System Flashcards
The Nervous System Two major divisions:
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
Nervous System Composed of the brain and spinal cord
Central Nervous System (CNS)
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)
Cell types in Nervous System
Neuron
Nuclei
Glial cells
Cell types in Nervous System
Basic cell type of CN and PN systems
Functional unit
Neuron
Cell types in Nervous System
Clusters of cell bodies in the CNS
Nuclei
Cell types in Nervous System
Most numerous cell in the CNS
Glial cells
Glial Cells of the CNS
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
Glial Cells of the CNS
Support cells, control extracellular environment of neurons
Astrocytes
Glial Cells of the CNS
“Immune system” of the CNS
Microglia
Glial Cells of the CNS
Ciliated, involved with production of the cerebrospinal fluid (CSF) and CSF movement
Ependymal cells
Glial Cells of the CNS
Responsible for the myelin
Oligodendrocytes
Glial Cells of the PNS
Satellite cells
Schwann cells
Glial Cells of the PNS
surround neuron bodies located in the PNS
Satellite cells
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
Functional Classes of Neurons
Interneurons
Afferent Neurons
Efferent Neurons
Functional Classes of Neurons
Transmits neuron to neuron
Interneurons
Functional Classes of Neurons
Away from the receptors towards the brain
Afferent Neurons
Functional Classes of Neurons
From the brain to the receptors / effectors
Efferent Neurons
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
Different cells have different resting membrane potentials.
true
Neurons have a resting membrane potential generally in the range of
-40 to -90 mV
which is more negative? the inside or the outside of the cells?
Inside is more negative
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.
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.
AP
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
- Acetylcholine (ACH)
- Biogenic amines
Catecholamines
Dopamine (DA)
Norepinephrine (NE)
Epinephrine (Epi)
Serotonin
Histamine - Amino acids
Excitatory amino acids; glutamate
Inhibitory amino acids; gamma aminobutyric acid (GABA) and glycine
- Neuropeptides
endogenous opioids
oxytocin
tachykinins - Gases
nitric oxide, carbon monoxide, hydrogen sulfide - 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.
