Neurons Flashcards
Where are interneurons found? What do they do?
-in the CNS(brain and spinal cord)
-integrate the information, formulate a response
Where are efferent and afferent neurons found?
-in the PNS
What are afferent neurons?
sensory neurons; pick up stimulus via sensory receptors transmit this info to interneurons (usually) in CNS
What are efferent neurons?
carry response signal to the muscles, glands so that response can be carried out
What are motor neurons?
type of efferent neuron that carries signals to the skeletal muscle.
What is the basis of information processing in the nervous system?
-Sense, Integrate, Act
What do most neurons have in their structure?
an enlarged cell body, dendrites, axon
What is the difference between a neuron and a nerve?
- A neuron is a cell. A nerve is a cord-like structure that contains many axons; provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons.
What is contained in white matter?
-myelinated axons, glial cells
What is contained in grey matter?
-neuronal cell body
What does DAVE stand for in the context of PNS?
-Dorsal root-Afferent
-Ventral root-Efferent
What are glial cells?
-non-neuronal cells that provide nutrition and support to neurons
-ex. Ependymal cells produce cerebrospinal fluid
What is the Node of Ranvier
-gaps in the myelin that expose the axon membrane directly to extracellular fluid; speed the rate at which electrical impulses move along axons
What are the two types of signal conduction?
-Presynaptic (transmitting)
-Postsynaptic (receiving)
Define Synapse
The junction between the axon terminals of a neuron and the receiving cell
Where are electrical synapses found?
-found in pulp of tooth, heart muscle tissue and some smooth muscle
What are gap junctions in the context of electrical synapses?
-they allow current to flow directly between adjacent cells
What are connexons
protein tubes in the cell membrane
Action potential of one cell…
-causes action potential in the next cell, almost as if the tissue were one cell
How do chemical synapses work?
-Electrical impulse travels along the axon, arrives at the terminal
-neurotransmitter is released
-neurotransmitter diffuses across the synaptic cleft, bind to the receptor on postsynaptic cell
-New electrical impulse is generated if enough neurotransmitter is bound
Which type of synapse- electrical or chemical… enables faster conductance of an action potential?
-Electrical synapse is faster than chemical synapse
Which type of synapse-electrical or chemical is better modulated?
chemical synapse
Which type of synapse-electrical or chemical enables synchronized electrical activity?
Electrical synapse enabled synchronized electrical activity among populations of neurons.
Ions cross the cell membrane under two influences:
-diffusion(due to concentration gradient)
-electric fields
Define electrochemical gradient
net-driving force; consists of concentration gradient and electrical gradient
What voltage is the membrane potential at rest
70mV
Is the membrane more permeable to potassium or sodium?
-potassium
How does the sodium-potassium pump work
-3 sodium out, 2 potassium in
-higher sodium concentration outside
-higher potassium concentration inside
In a resting neuron..
-Na+ and K+ channels are closed
In a neuron membrane at rest, there are many more … leak channels open than there are ungated…. Leak channels open
-ungated potassium
-ungated sodium
Define action potential
the abrupt and transient change in membrane potential that occurs when a neuron conducts an electrical impulse
What is all or nothing in reference to action potential
once threshold is reached depolarization will occur and action potential will fire regardless of the strength of the stimulus
Define absolute refractory period
time when an excitable membrane cannot generate an action potential in response to any stimulus
Define relative refractory period
time during which excitable membrane will produce action potential but only to a stimulus of greater strength than the usual threshold strength
Which of the following is true regarding the refractory period?
-It only lasts for a few milliseconds
-During the relative refractory period, the threshold required for generated an action potential is much higher than normal
-It keep impulses from traveling in both direactipons in neurons
-All of the above
-None of the above
-All of the above
What would be the primary basis for the absolute refractory period?
-Not enough sodium ions left outside
-Sodium channels closed
-Sodium channels inactivated
-Voltage gated potassium channels open
Membrane is depolarized
Sodium channels inactivated
-Voltage gated potassium channels open
The absolute refractory period occurs when…
-the voltage gated sodium channels are either already open or have proceeded to the inactive state. Then once they have been closed, the channels can reopen to a second stimulus
What would be the basis for the relative refractory period (more than one answer)
-Not enough sodium ions left outside
-Sodium channels closed
-Some sodium channels still inactivated
-Voltage gated potassium channels open
-Membrane hyperpolarized
-Some sodium channels still inactivated
-Voltage gated potassium channels open
-Membrane hyperpolarized
Conduction velocity
-is how fast an action potential travels down an axon
-lower diameter- lower internal resistance, faster conduction
The intensity of a stimulus is indicated by
-the frequency of action potentials
What is cable theory?
-the neuron is treated as an electrically passive, perfectly cylindrical transmission cable. It uses mathematical equations to calculate the flow of electric current along axons. Takes into account capacitance and resistance.
The capacitances of a neuronal fiber is due to
electrostatic forces that act through the phospholipid bilayer
The resistance (Longitudinal or internal resistance) is due to the
cytosol’s significant resistance to movement of electric charge
The Nerst Equation
-predicts the equilibrium potential across the membraneof a cell for a singly charged positive ion
The Goldman Equation
-predicts the membrane potential when the membrane is permeable to more than one ion
Ependymal cells
produce cerebrospinal fluid
Microglia
phagocytic cells that ingest and break down pathogens and waste products in the CNS
Astrocyte
in CNS, cover the surfaces of blood vessels; for structural support, help maintain ion concentrations in the interstitial fluid surrounding them
Satellite cells
similar function to astrocytes but are in the PNS
Schwann cells
Form myelin sheath in PNS
Oligodendrocytes
form myelin sheath in CNS
Axon Hillock
Has an incredibly high concentration of voltage-activated sodium channels. Generally considered to be the spike initiation zone for action potentials. Multiple signals (from presynaptic neuronal terminals) are generated at the dendrites and transmitted by the soma. They all converge at the axon hillcock.
