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2 categories of cells in the nervous system
- neurons
- glia (glial cells)
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__, or nerve cells, are excitable - They generate & transmit electrical signals called __
Neurons; action potentials
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cells that provide support in the nervous system & maintain extracellular environment
Glia (glial cells)
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contains the nucleus & majority of cell organelles; is the site of synthesis of most of the proteins, carbs, & lipids in the neuron
cell body
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receive the signals & transmit them toward the cell body
dendrite
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conduct signals away from the cell body to another neuron or effector
axon
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Ligand-gated ion channels are at __ (part of the neuron).
dendrites
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Voltage-gated ion channels are found at __ (part of the neuron).
axon terminals
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In __, the plasma membranes of the presynaptic & postsynaptic cells are in direct contact & communication across such synapses occurs by the direct flow of an __
electrical synapses; electrical signal
- allow the most rapid conduction
- found in cardiac muscle & retina of the eye
(page 13 on slide)
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When an electrical impulse arrives at the axon terminal, __ allow ions to flow directly between the 2 cells, leading to unbroken transmission of electrical signal
gap junctions
(page 13 on slide)
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In __, the plasma membranes of the presynaptic & postsynaptic cells are separated by a narrow gap called the __. Communication across such synapses occurs by means of a __
- chemical synapses;
- synaptic cleft;
- neurotransmitter
(page 11 & 12 on slide)
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bundle of axons from different neurons
nerve
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structural classification of neurons
- multipolar: possess more than 2 processes (numerous dendrites, 1 axon. most common. all motor are multipolar)
- bipolar: possess 2 processes (rare, found in some special sensory organs. i.e. retina)
- unipolar (pseudounipolar): possess 1 short, single process (dorsal root ganglia)
(page 17 & 18 on slide)
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functions of glial cells
- release & re-uptake neurotransmitter
- support neurons (provide nutrients & maintain the extracellular environment)
- immune functions
- contribute to the blood-brain barrier
- myelinate axons in the CNS (oligodendrocytes) & PNS (schwann cells)
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the electrical potential, the charge difference across the membrane
membrane potential
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Outside the cell, the net charge is __ & the inside of the cell is __
positive; negative
This charge separation produces voltage
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the membrane potential of a resting neuron
resting membrane potential
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An __, or nerve impulse, is a rapid, large change in membrane potential
action potential
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Action potentials are generated by __
openings & closings of ion channels
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changes from the resting potential; a means of integrating input - the membrane can respond proportionally to depolarization or hyperpolarization
graded membrane potential
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EPSP (excitatory postsynaptic potential) & IPSP (inhibitory postsynaptic potential) are types of __ potentials
graded
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The direction & size of ion movement depends on the __ & __ of the membrane. These 2 forces acting on an ion are its __
- concentration gradient;
- voltage difference;
- electrochemical gradient
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If a membrane were permeable to only K+ or Na+ then..
K+ or Na+ would diffuse down its concentration gradient until the electrical potential across the membrane countered the diffusion
(page 37 & 41 on slide)
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The electrical potential that counters net diffusion of K+ or Na+ is called the __
- K+ equilibrium potential (Ek = -90 mV)
- Na+ equilibrium potential (ENa = +55 mV)
(page 38, 41, & 43 on slide)
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Why are cells negative?
- DNA
- Na+/K+ pump
- K+ leak channels
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Why is Vm (resting membrane potential) so close to Ek (K+ equilibrium potential)?
The membrane is far more permeable to K than Na
(page 45 on slide)
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If an equilibrium potential is close to the resting potential, there will be __
little ion movement even if the membrane is freely permeable to the ion
(See example on page 889 in book)
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driving force =
Vm (membrane/resting membrane potential) - Eion (equilibrium potential of ion)
ex. If the driving force = +70 mV (RMP) minus -90 mV (EK+), the driving force is +20mV
(In this case, K+ will leave the cell.)
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If the driving force = -70mV (RMP) minus +55mV (ENa+), the driving force = -125 mV. What happens to the ionic flow Na+?
Since the driving force is negative, there is inward movement of positive current.
(negative driving force = more negative inside the cell, so + ions will enter)
Therefore, Na+ will enter the cell.
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If the driving force = +75mV (MP) minus +55mV (ENa+), the driving force is +15mv. What happens to the ionic flow of Na+?
Since the driving force is positive, there is an outward movement of positive current.
(positive driving force = more positive inside the cell, so + ions will leave)
Therefore, Na+ will leave the cell.
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