Nervous System Physiology Flashcards
bundles of peripheral nerve fibers held together by several layers of connective tissue
nerves
bundles of nerve fibers within the CNS
tracts
neurons exhibit both _____ and ______.
excitability and conductivity
signals initiated and conducted by neurons
nerve impulses
The difference in electrical charge due to excess of (+) ions on the outside of the membrane and an excess of (-) ions on the inside of the membrane
membrane potential
The membrane potential maintained by a non-conducting neuron’s plasma membrane
resting membrane potential (RMP)
The light excess of (+) ions on a membrane’s outer surface is produced by (2):
- ion transport mechanisms
2. selective permeability of the membrane
One mechanism that is very important in maintaining the RMP is the ____________.
Sodium-potassium pump
an active transport mechanism in the plasma membrane that transports sodium (Na+) and potassium ions (K+) in opposite directions and at different rates
sodium-potassium pump
the sodium-potassium pump transports ____ ions out of cells and ____ ions into cells
sodium (Na+), potassium (K+)
the sodium-potassium pump changes shape and releases # ____ to the outside of the cell, and attracts # ____ and releases them to the inside of the cell
3 Na+, 2 K+
a slight shift away from the RMP in a specific region of the plasma membrane
local or graded potentials
ion channels that open in response to a mechanical stimulus or a chemical stimulus located in dendrites and soma
stimulus-gated channels
When stimulus triggers the opening of stimulus-gated Na+ channels. More Na+ enters the cell allowing the potential to move towards zero.
excitation (depolarization)
When stimulus triggers the opening of stimulus gated K+ channels. More K+ exits the cell allowing the potential to move away from zero.
Inhibition (hyperpolarization)
The membrane potential of a neuron that is conducting an impulse; also known as a nerve impulse
action potential
A _____ is an all or none response.
action potential
Forced recall: Mechanism of the action potential
- Adequate stimulus triggers stimulus-gated Na+ channels to open, causing Na+ to diffuse rapidly into cell and producing a local depolarization
- When threshold potential is reached voltage-gated Na+ channels open. More Na+ enters cell, causing further depolarization
- As Na+ enters the cell membrane potential moves rapidly toward 0 mV. It continues in a positve direction until it peaks (30+mv)
- voltage gated Na+ channels stay open for 1 ms before they automatically close
- Repolarization
- K+ channels often remain open as membrane reaches RMP. Possible hyperpolarization may occur.
voltage-gated K+ channels open when threshold is reached, however, they open slowly and do not allow outward diffusion of K+ until peak is reached
repolarization
brief period during which a local area of the axon’s membrane resists restimulation
refractory period
about 0.5 ms after membrane surpasses threshold potential, it will not respond to any stimulus… no matter how strong
absolute refractory period
few ms after absolute refractory period - the time during which the membrane it repolarizing and restoring the RMP. Membrane will only respond to very strong stimuli.
relative refractory period
Conduction of an action potential: Reversal of _____ from RMP to peak of an action potential causes electrical current to flow between the site of reversal and adjacent regions of membrane
polarity
During a _________ the refractory period prevents restimulation of previous segments.
conduction of an action potential
In myelinated fibers electrical changes can only occur at gaps in the myelin sheath known as:
Nodes of Ranvier
action potential seems to leap from node to node. This is called:
Saltatory conduction
a place where signals are transmitted from one neuron to another neuron
synapse
A synapse could also be between a presynaptic neuron and a _____, such as a muscle gland
effector
The 2 types of synapses are:
- electrical synapse
- chemical synapse
cells joined end to end by gap junctions and allow action potential to simply continue along the postsynaptic membrane
electrical synapse
Presynaptic cell releases a chemical transmitter (neurotransmitters) to the postsynaptic cell
chemical synapse
a tiny bulge at the end of a terminal branch of a presynaptic neuron’s axon that contains vesicles housing neurotransmitters
synaptic knob
a very narrow space between a synaptic knob and the plasma membrane of a postsynaptic neuron
synaptic cleft
Structure of a chemical synapse (3):
- synaptic knob
- synaptic cleft
- the plasma membrane of a postsynaptic neuron
The axon of a presynaptic neuron may form a synapse at the: ____, ____ , or ____ of another neuron
dendrite, soma, axon
______ travel the length of an axon and stop at the axon terminals
action potentials
______ are released from the synaptic knob, cross the synaptic cleft, and bring about a response at the postsynaptic neuron
neurotransmitters
______ neurotransmitters depolarize the postsynaptic membrane
excitatory
_____ neurotransmitters hyperpolarize the postsynaptic membrane
inhibitory
Lots of terminal knobs synapse with a single postsynaptic neuron. One single synapse is not enough to generate an action potential, but the combined effects of multiple synapses can
summation of nerve transmission
2 main types of summation:
- spatial summation
- temporal summation
combined effects of several presynaptic knobs stimulating different locations on the postsynaptic membrane at the same time to produce an action potential
spatial summation
synaptic knobs stimulate a postsynaptic neuron in rapid succession, their effects add up over a brief period of time to produce an action potential
temporal summation
The means by which most neurons communicate. They act to facilitate, stimulate, or inhibit postsynaptic neurons and effector cells.
neurotransmitters
______ are classified by function or chemical structure
neurotransmitters
The function of a neurotransmitter is determined by the _______ receptor.
postsynaptic
The 2 major functional classifications of neurotransmitters:
- excitatory neurotransmitters
- inhibitory neurotransmitters
2 main groups of classification by chemical structure for neurotransmitters are:
- small molecule transmitters
- large molecule transmitters
acetylcholine (can be excitatory or inhibitory) is classified as what type of transmitter?
Class I
small molecule transmitter
Amines: monamine (serotonin, histamine) , catechlamine (dopamine, epinephrine, and norephrine) are classified as what type of transmitter?
Class II
small molecule transmitters
Amino acids (glutamate, gamma-aminobutyric acid) are classified as what type of transmitter?
Class III
small molecule transmitters
Nitric oxide are classified as what type of transmitter?
Class IV
small molecule transmitters
neuropeptides - enkephalins, endorphins, substance P are classified as what type of transmitter?
large molecule transmitters
