Nervous System Flashcards
Neural signaling has four components, what are they?
reception, transmission, integration, response
Reception
detection of a stimulus (performed by neurons and by specialized sensory receptors
Transmission
the sending of a message along a neuron to another neuron or to a muscle or gland
Integration
the sorting and interpretation of neural messages and determination of the appropriate response
Response
the “output” or action resulting from the integration of neural messages
Afferent neurons
(sensory neurons) transmit stimuli from their sensory receptors to interneurons
Interneurons
integrate the information to formulate an appropriate response
Efferent neurons
carry signals indicating a response away from the interneuron to the effectors (muscles and glands)- motor neurons are efferent neurons that carry signals to skeletal muscle
Interneurons are part of…
CNS
Afferent and efferent neurons are part of…
PNS
Neurons are made up of an enlarged ______ and two types of processes _________ and _______
cell body, dendrites, and axons
The cell body of a neuron contains ______ and _____
the nucleus and most organelles
________ receive signals and transmit them toward the cell body
dendrites
A single ____, arising from the ________ conducts signals away from the cell body to another neuron or effector
axon; axon hillock
Electrical signals carried by dendrites and axons are produced by ___ flowing down concentration gradients through channels in the plasma membrane of the neuron
ions
The tip of the axon has branches that end as small, buttonlike swellings called…
axon terminals
Connections between axon terminals of one neuron and the dendrites or cell body of a second neuron contribute to the formation of…
neural circuits
What does a neural circuit normally contain?
afferent (sensory) neurons, one or more interneurons, and an efferent neuron
Ganglion
a group of neurons lying outside of CNS
Nucleus
a concentration of cells within the CNS
______ include several types of non-neuronal cells that provide nutrition and support to neurons
glial cells
Astrocytes
(in the vertebrate CNS) closely cover the surfaces of blood vessels, providing physical support and maintaining concentrations of ions in the interstitial fuid
_________ in the CNS and ________ in the PNS wrap around axons to form insulating myelin sheaths
Oligodendrocytes; Schwann cells
gaps between Schwann cells or ______ speed signal transmission
nodes of Ranvier
A _______ is where a neuron makes a communicating connection with another neuron, or with an effector
synapse
On one side of the synapse is an axon terminal of the _________, the neuron that transmits the signal
presynaptic cell
On the other side of the synapse is the dendrite or effector cell that receives the signal (the ________)
postsynaptic cell
In _______ synapses, the plasma membranes of the presynaptic and postsynaptic cells are in DIRECT contact
electrical synapses
When an electrical impulse arrives at the axon terminal, _______ allows ions to flow directly between the two cells
gap junctions
Characteristics of electrical synapses…
rapid signal conduction; essentially “on” or “off” and are unregulated
Where are electrical synapses found?
cardiac muscle, the retina of the eye, and the pulp of the tooth
In _________ synapses, the presynaptic and postsynaptic cells are separated by a narrow synaptic cleft
chemical synapses
When an electrical impulse arrives at an axon, a _____ is released into the synaptic cleft (in chemical synapse)
neurotransmitter
Characteristics of chemical synapse
more than a simple on-off switch; neurotransmitters used
All animal cells have a _____, a separation of positive and negative charges across a plasma membrane that produces an electrical potential (voltage)
membrane potential
Membrane potential is the result of ________ of the plasma membrane to charged molecules and ions
selective permeability
Na+/K+ pump
removes Na+ from the cytoplasm and bring in K+- producing separate concentration gradients
What two factors establish the resting membrane potential?
1) the membrane is more permeable to K+ than to Na+; 2) large anionic molecules in the cytoplasm cannot cross the cell membrane
The membrane of a neuron that is NOT conducting an impulse is POLARIZED, with a _________ of -50 to -70 mV
resting membrane
____________ open and close when a neuron is stimulated, causing membrane potential changes
voltage-gated Na+ and K+ channels
The electrical potential necessary to balance the tendency of a particular ion to diffuse across the membrane is its ________
equilibrium potential (+50)
Equilibrium potentials predict _________
ion movement across the cell membrane
If a Na+ channel opens, large amounts of Na+ enter and _____ the cell
depolarize
When a neuron transmits an electrical impulse, an abrupt change in membrane potential occurs called…
the action potential
An action potential begins when a stimulus causes positive charges outside the membrane to flow inward, making the cytoplasmic side less negative- this is called
depolarization
Depolarization proceeds slowly until it reaches ________, typically 10-20mV more positive than resting potential
threshold potential
What happens once threshold is reached?
the action potential fires and the membrane potential suddenly increases; the inside of the plasma membrane momentarily becomes positive from an influx of positive ions (+30mV or more)
When the potential falls against, dropped below the resting value to about -80 mV this is…
hyperpolarization
An action potential is produced only if…
a stimulus is strong enough to cause a depolarization that reaches the threshold
all-or-nothing principle
once triggered, the changes in membrane potential take place independently of the strength of the stimulus
Beginning at the peak of an action potential, the membrane enters a ______ that consists of two phases
refractory period
Voltage-gated Na+ channels have two gates, ________ and _________
activation gate; inactivation gate
Voltage-gated K+ channels have one gate _______
activation gate
An action potential is initiated at the ______ end of the neuron, then travels away from the stimulation point as a wave of depolarization along the surface of the cell
dendrite
In the _____, local current flow between the area undergoing an action potential and then adjacent inactive areas depolarizes the downstream membrane to threshold
axon
The _______ keeps an action potential from reversing direction along an axon
refractory period
only _____ voltage-gated ion channels are able to open, ensuring one-way movement
downstream
The ____ of an action potential stays the same as it travels along an axon
magnitude
The intensity of a stimulus is reflected in the _________ of action potentials- the greater the stimulus, the more action potentials per second
frequency
In an unmyelinated axon, the rate of conduction increases with…
the diameter of the axon
____ increases the rate of conduction in smaller axons
myelin
In complex vertebrates, _______ allows action potentials to “hop” rapidly along myelin-coated axons
saltatory conduction
Communication through chemical synapses allows neurons to…
receive inputs from hundreds to thousands of axon terminals at the same time
Where are neurotransmitters stored?
synaptic vesicles in the cytoplasm of an axon terminal
arrival of an action potential at the terminal releases the neurotransmitters by ______
exocytosis (active transport)
______ open or close ligand-gated ion channels that conduct Na+, K+, or Cl- across the postsynaptic membrane
neurotransmitters
Excitatory postsynaptic potential
a change in membrane potential that pushes the neuron closer to threshold; occurs when a ligand-gated Na+ channel opens and Na+ enters the cell (causes depolarization)
Inhibitory postsynaptic potential
a change in membrane potential that pushes the neuron farther from threshold; occurs when a ligand-gated ion channel opens that allows Cl- to flow in and K+ to flow out (hyperpolarization)
EPSPs and IPSPs are _______ in which membrane potential increases or decreases without necessarily triggering an action potential
graded potentials
The sum of all EPSPs and IPSPs at a given time determines the _______ in the postsynaptic neuron, and therefore, how that neuron responds
total potential
