Test One Study Guide
Describe the flow of Na+ and K+ ions in the process of an action potential (include depolarization, repolarization, and afterhyperpolarization).
-Opening of voltage gated Na+ channels --> increase Na+ conductance --> Na+ driven intocell --> increase (+) inside cell moves voltage towards battery --> membrane depolarization and overshoot -Na+ channels remain open for only a few msec. -Gradual opening of voltage gated K+ channels --> increase K+ conductance --> net K+ efflux --> repolarizes membrane -K+ channels open for a long time --> after hyperpolarization; membrane is refractory
During intense exercise, why does plasma K+ concentration go up?
When you exercise hard, there is an increase in plasma potassium this is because when you are active the concentration of Na+/K+ pumps increases and you lose a lot of the potassium to the plasma.
Define an action potential.
A transient reversal in the potential difference across the membrane that is transmitted rapidly along an excitable membrane.
For the neuromuscular junction, describe the role of calcium in the process of neurotransmitter release from a presynaptic membrane.
AP on presynaptic cell → (+) voltage gated Ca++ channels → Ca++ influx into presynapatic cell → (+) exocytosis of vesicles containing neurotransmitter (vesicles fuse with presynaptic membrane) → neurotransmitter diffuses across synaptic cleft → binds to receptors on postsynapatic membrane → activated receptors (ligand gated) (+) opening of ion channels → ∆ Vm.
Explain the difference between an electrical synapse and a chemical synapse.
An electrical synapse involves- -Direct flow of current between cells via gap junctions -Allow bidirectional ion flow -Fast -Rare in neuron -neuron communication in mammals A chemical synapse involves- -Neurotransmitter release by presynaptic cell binds to receptors associated with ligand -gated channels on postsynaptic membrane -Slow relative to electrical synapses -Neurotransmitter types -Small molecule neurotransmitters (acetylcholine, glycine, glutamate) -Neuroactive peptides (amino acid polymers)
Explain how neuron diameter affects the velocity of electrotonic conduction.
As the diameter increases, the velocity increases
Explain the role of the axon hillock in action potential formation in neurons. How does spatial and temporal summation affect the ability of an input to affect formation of an action potential.
Axon hillock Vm is the integration site for AP generation - trigger zone EPSP/IPSP effects on Vm at axon hillock depend on: -Spatial Summation - sum of inputs from multiple synapses -Temporal Summation - sum of multiple inputs at same synapse; "overlap of EPSP/IPSPs conducted via electrotonic transmission; therefore distance matters (λ). postsynaptic potentials produced by consecutive inputs from the presynaptic neuron". Trigger zone has high Na+ channel density; lower threshold for activation
Describe the process of axonal transport and discuss how this process can influence nerve and muscle characteristics.
Axonal transport effects on nerve and muscle cells -Nerve-muscle trophism (neurogenic) - e.g., changes in muscle cells when motor neuron connection is lost -Muscle-nerve trophism (myogenic) - e.g., changes in motor neuron when connection with muscle is lost
Under what conditions is neuromuscular transmission from the alpha motor neuron to the muscle cell potentially impaired? Include pharmacological, poisonous, and disease possibilities.
Can be impaired by pharmacological agents (diseases that affect the neuromuscular junction) or prolonged exercise -Myasthenia Gravis: an autoimmune disease that targets ACh receptors (decrease in autoimmune receptors decreases muscle activation) -Lambert Eaton myasthenic syndrome -Botulinum Toxin
Describe the structure of a cell membrane. How does this structure contribute to the development of the resting membrane potential?
Cell membranes are made of a phospholipid bilayer, each with a hydrophobic head and a hydrophilic tail. The membrane also has different gated channels that allows for the movement of different ions in and out of the cell. This structure means that ions can only through these channels and not through the membrane itself. The movement of these ions through channels creates the resting membrane potential where the inside of the cell is negative relative to the outside of the membrane.
What does the equilibrium potential calculated from the Nernst equation represent?
Chemical and electrical forces are balanced, there is no net flow of ions.
Describe factors that can influence the recording of EMG signals.
Crosstalk- signal from nearby muscle contaminates recording from muscle of interest- Mainly due to extinction phase of action potential -Can't filter out since both signals have information in same frequencies -Double differentiation: -2 pairs of electrodes (2 bipolar recordings) --> send the two differentiated signals into another differential amplifier -Differentiation attenuates information common in both electrodes. If double and single differentiated signals have similar amplitude, little cross talk.
Explain the role of ligand gated vs. voltage gated ion channels in the process of action potential generation at the neuromuscular junction.
Depolarization via ligand (ligand=ACh) gated ion channels stimulates voltage gated ion channels --> action potential Ligand gated channels are stimulated by alpha neuron --> depolarization Voltage gated channels propagate action potential down the muscle cell
Differentiate between depolarization, repolarization, and hyperpolarization.
Depolarization- membrane potential becomes less negative, this will lead to an action potential. Repolarization- membrane potential becomes more negative after depolarizing. Hyperpolarization- membrane potential becomes more negative.
Describe how a bipolar electrode system records muscle electrical activity.
EMG uses extracellular recordings; detect extracellular filed potentials associated with the currents that underlie muscle fiber action potentials. Bipolar recordings: two electrodes used to record the EMG -signal represents the difference in voltage between the two electrodes -overlapping action potentials from many muscle cells
Explain the role of EPSPs and IPSPs in affecting membrane potential, and how their information is integrated to determine whether an action potential will occur.
EPSP- excitatory postsynaptic potential, the response to a depolarizing current. IPSP- inhibitory postsynaptic potential, the response to a hyperpolarizing current.
Describe how electrode location relative to the innervation zone affects the amplitude of the EMG signal.
Electrode placement -Interelectrode distance -Position relative to innervation zone The greatest amplitude is recorded when the interelectrode distance is relatively large and the electrodes are placed on the same side of the innervation zone.If placed on the innervation zone the reading is 0.
Differentiate between high pass, low pass, bandpass, and notch filters.
High pass- allows high frequencies to pass Low pass- allows low frequencies to pass Band pass- allows frequencies in a specific range to pass Notch filters- rejects frequencies between two set values
State Ohm's law with respect to: a) resistance, and b) conductance.
I = gV or V = IR I- current g- conductance (reciprocal of resistance) V- voltage
How does neuron size affect input conductance of a neuron? How does the relationship between neuron size and input conductance affect the ease of changing the membrane potential? What is the importance of this in terms of generating action potentials?
Input conductance and neuron size are directly proportional. All else being equal a small neuron will have a smaller input conductance and vice versa. The voltage threshold is similar in neurons of all sizes meaning that the smallest neurons with the smallest input conductance will achieve threshold the quickest and in turn propagate an action potential the quickest.
Explain the difference between inotropic and metabotropic receptors.
Ionotropic Receptors- a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger. ACh receptors at neuromuscular junction are ionotropic receptors; receptor that contains ACh binding site AND ion channel Metabotropic Receptors- a type of membrane receptor of eukaryotic cells that acts through a secondary messenger. It may be located at the surface of the cell or in vesicles. Neurotransmitter binds to receptor --> (+) 2nd messenger system --> can affect ion channel gating, but slower than with ionotropic receptors
Define lambda (λ) in terms of electrotonic conduction. What factors affect the size of λ?
Lambda is the length constant, it is the distance the current will spread until the change in membrane potential is 37% that at current source. The better the axial conductance, the larger the lambda. The bigger the membrane conductance, the smaller the lambda.
In a myelinated axon, explain the role of electrotonic conduction in the transmission of an action potential from one node of Ranvier to the next.
Na+ current discharges membrane capacitance transmitted via electrotonic conduction along membrane; if myelinated, transmitted to next node of Ranvier --> AP at next node; repeat (Nodes of Ranvier have high density of ion channels) Refractory period prevents backward AP propagation
Explain how the chemical and electrical forces act on the following ions under typical conditions of an excitable membrane: Na+, K+, Cl-, Ca++.
Na+: chemical force driving Na+ inward electrical force driving Na+ inward Net force: IN K+: chemical force driving K+ outward electrical force driving K+ inward Net force: OUT Cl-: chemical force driving Cl- inward electrical force driving Cl- outward Net force: 0 Ca++ Both the chemical force and electrical force are trying to drive Ca++ from the outside to the inside of the cell
Explain the role of K+ in the formation of the resting membrane potential.
Potassium is a key ion in the resting membrane potential due to the Na+/K+ pump. Potassium inside the cell leaks out through the membrane via leak channels. There are more leak channels for K+ than there are for Na+ at rest and therefore potassium has greater conductance and resting membrane potential.
Define potential difference, current, conductance, and capacitance.
Potential difference- a measure of the potential energy that must be used to have a positive charge from one location to another Current- the rate at which positive charges move between the two locations that represent a potential difference Conductance- the capacity to conduct electrical current Capacitance- the ratio of charge stored to the potential difference
Differentiate between presynaptic inhibition and presynaptic facilitation, and describe how metabotropic neurons can influence these processes.
Presynaptic Inhibition- interneuron decreases amount of neurotransmitter released by innervated neuron; types: -Metabotropic neuron decreases Ca++ influx into presynaptic terminal --> decrease neurotransmitter exocytosis -Metabotropic neuron directly inhibits neurotransmitter release Presynaptic facilitation: mechanisms increase Ca++ influx
What is the relationship between conductance and resistance?
Resistance is the inverse of conductance. As conductance increases, resistance decreases. As resistance increases, conductance decreases. R = 1/g g = 1/R
Explain how the input conductance of a neuron affects the amount of current needed to change the membrane potential a given amount (hint - use Ohms law).
The input conductance reflects how much a change there will be for the amount of current injected; there needs to be enough to make the membrane potential exceed threshold in order to propagate an action potential.
For an excitable membrane, describe the process of events when an experimenter applies a current across the membrane and simultaneously measures the resulting membrane potential.
The membrane potential will increase (depolarization), voltage gated Na+2 channels open (influx of Na+2 due to chemical and electrical gradient), Efflux of K+ due to concentration gradient.
How does neuron size affect the input capacitance of a neuron? How does the relationship between neuron size and input capacitance affect the ease of changing the membrane potential? What is the importance of this in terms of generating action potentials?
The shift from a capacitive current to an ionic current depends on the size of the capacitor that has to be charged. Because large neurons require a greater amount of capacitive current to charge the capacitor, it takes them longer to realize a significant amount of ionic current and the corresponding membrane potential.
How does the cell maintain ionic gradients when ions leak across the membrane at rest and when generating action potential?
There is a larger net driving force for Na+ than for K+. But, there are more resting channels for K+ than for Na+, therefore, there is greater conductance for K+ than for Na+. On net, there are similar currents for K+ and Na+. When potassium "leaks" out of the cell (due to the concentration gradient), the anion that the K+ was originally paired with is left alone which generates a negative charge. When the inside of the cell is negative (membrane potential), the potassium is driven back into the cell.
Explain the difference between voltage and ligand gated ion channels.
Voltage gated channels open or close when there is a change in membrane potential. Hyperpolarization closes the gates and depolarization opens the gates. Ligand gated channels open when there is a chemical that binds to the receptor and close where there is no longer a chemical bound to the receptor. Acetylcholine is the chemical that muscles utilize to bind to the receptor.