Unit 1 Flashcards
What is the neuron doctrine?
Ramon y Cajal: nerve cells are discrete entities
What are the four major parts of a neuron?
soma, axon, dendrite and synapses
What are the 4 types of glial cells
- Astrocytes
- Oligodendrocytes
- Microglial cells
- Glial stem cells
what are the types of the component neurons in neural circuits?
Afferent neurons, efferent neurons and interneurons
What are the components of the CNS and PNS?
CNS: Brain and spinal chord
PNS: sensory ganglia and nerves, sensory receptors, somatic motor division, and visceral or autonomic motor division
Neurons constitute ______ which constitute _______.
Neurons constitute neural circuits which constitute neural systems.
Neural circuits
neurons organized into ensembles to process specific kinds of information
Who coined the term “synapse”?
Charles Sherrington
What are two major cell types in the nervous system?
Nerve cells (neurons) and supporting glial cells
Input v Output in neuron
input: dendrite
output: axon
Synaptic Cleft:
extracellular space between pre and post synaptic elements
What happens with the function of a neuron with multiple, highly branched dendrites and one axon?
It integrates information from many neurons
Astrocytes
Maintain appropriate chemical environment for neuronal signaling, including the blood brain barrier
Oligodendrocytes
lay down a laminated, lipid rich wrapping called myelin around some CNS axons
What is myelin provided by in the PNS
schwann cells
Microglial cells
derived from hematopoietic precursor cells
- share many features with macrophages and are primarily scavenger cells that remove myelin and cellular debris from injury sites or normal cell turnover
Reside in the CNS
Glial stem cells
retain capacity to proliferate and generate additional precursors or differentiated glia and sometimes neurons
Neuropil
dense tangle of dendrites, axon terminals, and glial cell processes
- the regions between nerve cell bodies where most synaptic connectivity occurs
Afferent neurons
nerve cell that carry form periphery TOWARD brain or spinal chord
Efferent neurons
nerve cells that carry info AWAY from brain or spinal chord
Interneurons
** Only in CNS
Participate in local aspects of a circuit
Sensory systems
acquire and process information from environment
Motor systems
response to information by generating movements and other behavior
Associational systems
in between; mediate the most complex brain functions
Ganglia
nerve cell bodies that reside in the PNS
Nerves
bundles of peripheral axons
How are nerve cells in the CNS arranged?
Nuclei and cortex
Cortex:
sheet like array of nerve cells
Tracts
gathering of CNS axons
Commissures
tracts that cross the midline of the brain
- how left and right brain communicate with each other
Gray matter
any accumulation of cell bodies and neuropil in the brain and spinal chord
White matter
axon tracts and commissures in the CNS
Why is white matter lighter than the gray matter?
White matter is richer in myelin, which reflects more light than gray matter
Name some sensory ganglia and nerves
cranial nerve ganglia, dorsal root ganglia (spinal ganglia), cranial nerves, and spinal nerves
what do autonomic ganglia and nerves innervate
cells that innervate smooth muscles, cardiac muscle, and glands
enteric nervous system
small ganglia and neurons throughout the wall of the gut; control gastric motility and secretion
Parts of CNS
Brain: cerebral hemispheres, diencephalon, cerebellum, and brainstem
Spinal chord
motor neuron cell bodies
Parts of PNS
-Sensory ganglia and nerves
-sensory receptors
-somatic motor division (ONLY MOTOR NERVES NOT NEURON CELL BODIES)
-Visceral and autonomic motor division
What are some effectors in the nervous system?
smooth, skeletal, and cardiac muscles, and glands.
Define action potential
all or nothing change in the electrical potential across the nerve cell membrane that conveys information from one point to another
Define synaptic transmission
the information encoded by action potentials is passed on at synapses to a target cell
Synaptic vesicles
the secretory organelles in the presynaptic terminals of chemical synapses, filled with NT molecules
How is current determined?
by the number of electrons passing through a cross section of a conductor in one second
What is current measured in?
amperes (amps; A)
What is voltage
the force required to make current flow through a conductor
another name for voltage
potential
Movement of positive of negative charges to generate:
electrical currents
Separate positive and negative charges to generate:
electrical potentials
Why are electrical potentials generated?
1) differences in the concentrations of specific ions across neuronal membrane (ion concentration gradients)
2) membranes are selectively permeable to certain ions (selective permeability)
Neurons use ____ to produce electrical signals
ion movements
What are active transporters?
Actively move ions into or out of cells against their concentration gradient to establish ion concentration gradients
What are ion channels?
Creates the selective permeability for membrane and allow only certain kind of ions to cross the membrane in the direction of their concentration gradients **Passive movement
Channels and transporters work _____ each other to generate _____
against; resting potential, action potentials, synaptic and receptor potentials that trigger action potentials
Electrochemical equilibrium
a state in which the electrical effect causes diffusion in one direction and the concentration effect causes diffusion of equal magnitude in the opposite direction
Electrophysiological recordings
measures the electrical activity of a neuron
Extracellular recordings
an electrode is places near the neuron of interest to detect its activity
**Only detects temporal patterns of several action potentials but not the smaller, graded changed in electrical signals (only spikes)
Intracellular recording
the electrode is places inside the neuron of interest
**detects smaller, graded changes of electrical potential
What are the major functional features of neurons and how do neurons transmit signals within the circuit?
- specialized for intracellular communication
- moment to moment electrical signaling
- neurons send electrical signals through long distance through the action potential
How do neurons move ions across their membrane?
through ion movements
- active transporters and ion channels
What are the differences in how ions move across their membrane
active transporters: actively move selected ions against concentration gradient and create ion concentration gradients
ion channels: allow ions to diffuse down concentration gradient and are selectively permeable to certain ions
Neurons can generate electrical potentials across their membrane because…
1.ion concentration gradients
2. selective permeability
How do we measure electrical signals of neurons?
Through extracellular and intracellular recordings
What does intracellular recording detect
resting membrane potential
receptor potential
synpatic potential
wave form of single action potential
What is the resting potential
no action potential firing
-around -70 mV but can range from -40 to -90 mv
What are the different types of neuronal electrical signals and what are the differences among them?
Receptor potential
Synaptic potential
Action potential
Define receptor potential
shape of Pacinian corpuscle changed - Na+ chennel open
Synaptic potential
NT binds to post synaptic receptors
cation channel open
What is electrochemical equilibrium
balance between chemical force and electrical force
What is the equilibrium potential and how do we calculate it
electrical potential generated across the membrane at electrochemical equilibrium
Calculate it through the Nernst Equation
What is the Nernst equation
V = 58log [ion] outside / [ion]inside
relation of equilibrium potential to the concentration gradient
Goldman Equation
equilibrium potential when the membrane is permeable to several different ions
How does resting or action potential depend on relative permeability of the membrane to K+ and Na+?
at resting state: K+ is more permeable than Na+
during AP: Na+ permeability increases and becomes more permeable than K+
What did Hodgkin and Katz conclude?
- the membrane of the resting neuron is more permeable to K+ than to other ions
- There is more K+ inside the neuron than outside
How is the resting membrane potential of a squid giant axon determined
by the K+ concentration gradient and the selective permeability of it
What causes the membrane potential of a neuron to depolarize during an action potential?
increase Na+ permeability
Hodgkin anf Katz showed that the action potential arises because…
the neuronal membrane becomes temporarily permeable to Na+
Describe rising and overshoot phase of action potential:
membrane becomes extraordinarily permeable to Na+
- causes membrane potential to depolarize
Describe falling phase of AP
membrane potential rapidly repolarizes due to inactivation of Na+ permeability and increase in K+ permeability
Describe undershoot phase of AP
membrane potential is transiently hyperpolarized bc K+ permeability becomes even greater at rest
Why is the resting potential of a cell negative?
at rest there is an excess K+ inside the cell and the membrane is permeably chiefly to K+
In a two compartment model of a cell with a K+ permeable membrane, at equilibrium potential, there is _______ flux of K+ ions
no net
How does membrane permeability of K+ and Na+ change during an AP?
Pk exceeds Pna at rest; Pna temporarily increases during the AP
What is the voltage clamp method?
allows experimenters to control membrane potential and simultaneously measure the permeability changes
Current clamp method
records the membrane potential by injecting current into a cell through the recording electrode
What can the voltage clamp method measure?
membrane potential at any desired level
Define inward current
positive charge entering the cell (graph going below 0)
Negative ions moving out of the cell
Depolarization if on voltage trace
Define outward current
positive charge moving OUT of the cell (above 0)
Hyperpolarization on voltage trace
What are the two types of membrane permeabilities activated by changes in membrane potential during generation of an action potential?
Describe the time- dependent membrane conductance changes underlying the action potential
Na+ and k+ require for to activate
** K+ conductance has a pronounced time delay
What are the four phases of an action potential
- Rising and overshoot phase
- Falling phase
- Undershoot
- Refractory period
Describe the voltage- dependent membrane conductance changes underlying the action potential
The speed of both activation and inactivation increasing at more depolarizing potentials
What does depolarization cause Na conduction to do
Depolarization = Na+ conductance to activate AND inactivate over time
**K conductance does NOT inactivate like this
Explain rising and overshoot phase
selective increase in voltage dependent Na+ conductance is responsible for action potential initiation
Explain falling phase
depolarization slowly activates voltage dependent K+ conductance
causes K+ to leave cell and repolarize membrane potential
Explain undershoot phase
K+ becomes temporarily higher
hyperpolarization – more negative
What does hyperpolarization cause?
the voltage dependent K+ conductance to turn off
explain refractory period
**follows an action potential
a new action potential cannot be fired
Leak channels:
constantly open K+ channel
*not voltage dependent
Why is there a refractory period following an action potential?
(1) slow time course of turning off the K+ conductance
(2) persistence of Na+ conduction inactivation
Why do action potentials have a treshold?
so Na+ entering the neuron is exactly equal to the K+ current that is flowing out from the leak K+ channel
What kind of a feedback loop is an action potential?
positive feedback
Action potentials serve as a _____ that allows neurons to transmit signals over ______ distances
booster system; long
What does refractoriness prevent?
backward propagation
Why does myelination increase conduction velocity?
by insulating the axonal membrane to increase passive current flow and saltatory conduction
causes saltatory conduction
What can the patch clamp method measure
currents flowing through single channels
Define macroscopic currents
current flowing through large number of channels
Define microscopic currents
current flowing through single channeld
What are functional properties of single Na+
-inward
-inactivated during depolarization
-voltage dependent
- open probability increases when depolarized
What are functional properties of single K+
- outward
- not inactivated during depolarization
How can ion channels be classified?
ion selectivity and gating mechanisms
name two gating mechanisms of ion channels
- Non gated or leak channels
- voltage gated channels
- ligand gated channels
- mechanically gated channels
- temperature gated channels
which ions are used in non gated or leak channels?
Na, K, Cl
*small current going back and forth to maintain homeostasis
ions used in voltage gated channels
H, Na, K, Ca, Cl
extracellular ligands
**most common
many are NT: ACh, NMDA, AMPA, glycine, GABA, 5-HT
intracellular ligands
secondary messengers: Ca, cGMP, cAMP, or cyclic- nucleotide-gated channels
extraordinary ligand
light/photons
what is the least common gating mechanism?
mechanically - gated channels
how do ion channels generate diversity
- different selectivity and gating mechanisms
- alternative splicing of ion channels genes
- changing a single amino acid
- posttranslational modifications
- channels are often made up of subunits encoded by different genes
what are channelopathies
genetic diseases result from small but critical mutations in ion channel genes ex cystic fibrosis
Cystic fibrosis
mutatiosn in conductance regulator (CFTR) gene encoding a Cl- channel
What are the molecular properties of different voltage gated ion channels?
Na and Ca channels: 6 repeating membrane spanning motif
What are the two classes of neuronal transporters and what are their differences?
ATPase pump: acquire energy directly from hydrolysis of ATP
Ion exchangers and co-transporters: don’t use ATP but use electrochemical gradient of other ions as an energy source
Why is Na+/K+ pump electrogenic
pump generates an electrical current that can hyperpolarize the membrane potential by causing a net loss of one positively charged ion from inside of the cell during each round of pumping
Which which toxin can be used to block Na/K pump?
tetrodotoxin and tetraethylammonium ion
TTX
tetrodotoxin
selective Na+ channel blocker blocks early current
TEA
Tetraethylammonium ion
selective K+ channel blocker blocks late current
What are structural and functional properties of the electrical synapse?
current flows through connexons, which as specialized membrane channels that connetc two cells at gap junction
minority but in all nervous systems
permit direct, passive flow of current
function:
(1) synchronize electrical activity among population of neurons
(2) coordinate intracellular electrical signaling and metabolism of coupled cells
What are major differences between electrical and chemical synapses
enable cell to cell communication via the secretion of neurotransmitters
Describe the sequence of events involves in signal transmission at chemical synapses
- action potential arrives at axon terminal
- voltage gated ca channels open
- ca enters the presynaptic neuron
- ca signals to NT vescicles
- Vescicles move to the membrane and dock
- NT released via exocytosis i
- NT bind to receptors
- Signal initiated in post synaptic cell
What are co-transmitters
when more than one transmitter is present within a nerve terminal
What are two majoe categories of neurotransmitters?
small molecule neurotransmitters and neuropeptides
What are the criteria that define a nuerotransmitter
- substance must be present within the presynaptic neuron
2.substance must be released in response to presynaptic depolarization and release MUST be Ca dependent
- specific receptors for the substance must be present on the post synaptic cell
What is the role of Ca in synaptic transmission
causes NT to be released
What are the conclusions from Bernars Katz experiments that defines quantal release of NT?
**studied transmissions at the NMJ
conclusion: NT is released in multi-molecular packets (quanta)
What are EPP and MEPP
End plate potential and Mini end plate potential
End plate potential
a transient depolarization at the postsynaptic muscle fiber elicited by an AP from the presynaptic motor neuron
Miniature end plate potential
spontaneous changes in muscle cell membrane without stimulation from the presynaptic motor neuron
How is the fused vesicle membrane
retrieved after transmitter release?
with SNARES
What are the two types of neurotransmitter receptors
ionotropic receptors and metabotropic receptors
Ionotropic receptors
ligand gates ion channels
combine transmitter-binding and channel functions into a single molecular activity
Metabotropic receptors
g -coupled receptors
movement of ions through a channel depends on intervening metabolic steps
**NO CHANNEL as a part of the receptor structure
Explain reversal potential
direction of EPC reverses or the membrane potential at which there is no net flow of ions
What are PSC
post synaptic current
currents generated from opening of ion channel by transmitter binding to postsynaptic receptor in chemical synapse
What is PSC called in NMJ
EPC
What are PSP
changes of postsynaptic membrane potential due to PSC in chemical synapse
Relationship between PSC and PSP
How do you use the reversal potential to determine the direction of the PSC and polarity?
- channels depolarizing when postsynaptic membrane is more negative
-channels hyperpolarizing when post synaptic membrane is more positive than reversal potential
What are EPSP and IPSP
excitatory and inhibitory post synaptic potentials
How do you determine whether a postsynaptic response is excitatory or inhibitory
type of channel and concentration of permanent ions inside and outside the cell
How to determine PSC
PSC = Vm - Erev
Erev > threshold
excitation
Erev < threshold
inhibition
What is the summation of synaptic potentials?
- PSP at brain synapses are smaller than PSP at NMJ
CNS neurons are typically innervated by thousands of neurons and PSPs produced by each active synapse can sum together in time and in space to determine the behavior of the postsynaptic neuron
