Physical and Electrical Properties of Neurons Flashcards
What is the functional unit of the CNS?
neuron
What is the function of neurons?
to receive, integrate, and transmit information from thousands of other neurons using electrical signals and chemical messengers
How can you tell the difference between neurons and other types of cells?
Neurons have a rich diversity in shape, different bioelectrical properties and intracellular communications
What are the 4 components of neurons?
- Cell body/Soma
- Dendrites
- Axon
- Presynaptic terminals
What organelles are found in the cell body?
- nucleus
- Golgi apparatus
- mitochondria
- nucleic acids
- endoplasmic reticulum
What does the cell body do?
Synthesizes a large quantity and variety of proteins used as neurotransmitters
Do dendritic projections function as input or output units for neurons?
input
What are the beginning and ending structures of an axon?
Axons arise from axon hillock and end in presynaptic terminals
Which are longer dendrites or axons?
Dendrites are only about 100 microns
Axons can be longer than 1 meter
Do axon projections function as input or output units for neurons?
output
What are the 3 main elements of a synapse?
- Presynaptic terminals
- Synaptic cleft
- Post-synaptic terminals
2 Classifications of Vertebrae Neurons based on the number of processes that directly arise from the cell body
- Bipolar cells
- multipolar cells
Bipolar cells have ___ primary processes from the cell body. What are they?
Two:
- Dendritic root
- Axon
What is an example of a bipolar cell?
the retinal bipolar cell in the eye
What are pseudounipolar cells?
A subclass of bipolar cells that appear to have a single projection from the cell body that divides into 2 axonal roots (peripheral and central)
What are the most common pseudounipolar cells?
sensory neurons
What does the peripheral axon on a pseudounipolar cell do? What does the central axon do?
The peripheral axon conducts sensory information from the periphery to the cell body
The central axon conducts information from the cell body to the spinal cord
Multipolar cells have _____ dendrites arising from the cell body and a single axon
multiple
What is an example of a multipolar cell?
spinal motor neuron
What are the multipolar cells in the cerebellum called?
Purkinje cells
How is information transmitted through a neuron?
synapse –> dendrite –> cell body –> axon –> synapse
How do neurons function?
By undergoing rapid changes in the electrical potential across the cell membrane
What is an electrical potential?
a difference in electrical charge (+ or -) carried by ions on each side of the cell membrane
What are the 4 types of membrane channels that allow for ions to flow across a membrane? Which are gated and which are non-gated?
- Modality-gated channels
- Ligand-gated channels
- Voltage-gated channels
- Leak channels
The first 3 are gated while leak channels are non-gated
Describe leak channels
These channels allow diffusion of a small number of ions through the membrane at a slow, continuous rate
What do modality-gated channels open in response to?
Mechanical forces (stretch/touch/pressure), temperature changes, or chemicals
What do Ligand-gated channels open in response to?
A neurotransmitter binding to the surface of a channel receptor on a postsynaptic cell membrane
Ligand-gated channels are result in the generation of what type of potential?
local potentials
What do voltage-gated channels open in response to?
Changes in the electrical potential across the cell membrane
Voltage-gated channels are result in the generation of what type of potential?
action potentials
Three types of electrical potentials
- Resting membrane potential
- Local potential
- Action potential
Define resting membrane potential
The difference in electrical potential across the cell membrane of a neuron when the neuron is neither receiving nor transmitting information
What is the typical value of the resting membrane potential?
-40 mV to -80 mV
What are the 2 forces that act on ions to determine their distribution across the plasma membrane?
- Concentration gradient
- Electrical gradient
When the concentration and electrical gradients are balanced what occurs?
electrochemical equilibrium
In neurons, the proper electrochemical gradient and the resulting membrane resting potential are maintained by what 3 things?
- Negatively charged molecules (anions) trapped inside the neuron that are too large to diffuse through the channels
- Passive diffusion of ions through leak channels in the cell membrane
- The Na+/K+ pump
What does the Na+/K+ pump do?
It carries 2 K+ ions into the cell and 3 Na+ ions out of the cell, both against their electrochemical grradients
The membrane is ______ when the potential becomes less negative than the resting potential.
depolarized
Depolarization increases the likelihood that the neuron will do what?
generate a transmittable electrical signal
The membrane is ______ when the potential becomes more negative than the resting potential.
hyperpolarized
Hyperpolarization decreases the neuron’s ability to do what?
generate an electrical signal
A depolarized membrane is considered _____, while a hyperpolarized membrane is considered _____.
excitatory
inhibitory
Initial changes in membrane potential is called a ____ potential because it spreads only a short distance along the membrane
local
If the change in local potential results in sufficient depolarization of the cell membrane, then what type of potential occurs?
action potential
What are the 6 events following stimulation of a sensory receptor?
1) deformation of a peripheral pressure receptor
2) change in local membrane potential of the sensory ending
3) development of an action potential in the sensory axon
4) release of transmitter from the sensory neuron presynaptic terminal
5) binding of transmitter to the ligand-gated channel on the postsynaptic membrane
6) activation of synaptic potential in the postsynaptic membrane
Local potentials are categorized as either ____ potentials or _____ potentials
receptor
synaptic
Local receptor potentials are generated how?
By the mechanical change of a peripheral receptor of a sensory neuron
Local synaptic potentials are generated how?
By the release of chemical transmitters at the synapse with the second neuron
Because local potentials can spread only passively along their receptors or synaptic membranes, they generally travel how far?
only 1 to 2 mm and the amplitude decreases with distance traveled
Strength can be increased and potentials integrated via what 2 types of summation?
temporal and spatial summation
What is temporal summation?
The combined effect of a series of small potential changes that occur within milliseconds of each other
What is spatial summation?
The process by which either receptor or synaptic potentials generated in different regions of the neuron are added together
What is an action potential?
a large depolarizing signal that is actively propagated along an axon by repeated generation of a signal
Unlike local potentials (graded in amplitude and duration), action potentials are _______.
all-or-none
Do larger currents elicit larger action potentials than minimally sufficient stimuli?
No, the amplitude of the action potential is independent of the magnitude of the current used to evoke it
What is the threshold stimulus intensity?
the stimulus intensity that is just sufficient to produce an action potential
Typically, a __ mV depolarization is sufficient to trigger an action potential
15 mV
from -70 mV to -55 mV
An action potential is produced by the sequence of what three events?
1) Rapid depolarization sue to the opening of the voltage-gated Na+ channels
2) A decrease in Na+ conduction due to the closing of the channels
3) Rapid repolarization due to the opening voltage-gated K+ channels
What occurs immediately after an action potential?
Following the rapid repolarization due to the opening of voltage-gated K+ channels there is a period of hyperpolarization, during which the membrane potential is even more negative than during resting.
The membrane is refractory at this time.
How does this period of hyperpolarization (refractory period) take place?
Because the Na+ channels become inactivated immediately after opening for an action potential and require a specific amount of time before they can be activated again for a subsequent action potential
What are the 2 distinct states of the refractory period?
- Absolute refractory period in which the membrane is completely unresponsive to stimuli
- Relative refractory period in which a stimulus may activate the Na+ channels, but it must be stronger than normal
What does the refractory period promote?
forward propagation of an AP while preventing backward flow
How is an action potential propagated?
Once an AP is generated, the change in electrical potential spreads passively along the axon to the adjacent region of the membrane. The impulse is propagated by flipping of the polarity of the electric signal (like dominoes). When depolarization of the adjacent, inactive region reaches threshold, another AP is generated.
What are 2 structural adaptations that some axons have that allow them to propagate APs faster?
- Increased diameter of the axon
- Myelination
Myelinated axons have small patches that lack myelin called what?
Nodes of Ranvier
What is salutatory conduction?
The quick node-to-node jumping of an action potential down a myelinated axon
What are the 3 functional groups of neurons?
- Afferent neurons
- Efferent neurons
- Interneurons
The specificity and diversity of function within the nervous system can be attributed to neuronal ______ and ______.
Convergence
Divergence
What is neuronal convergence?
the process by which multiple inputs from a variety of cells terminate on a single neuron
What is neuronal divergence?
the process whereby a single neuronal axon may have many branches that terminate on a multitude of cells
