Introduction to Neurobiology Flashcards
Ganglia
clusters of neurons
CNS
brain and spinal cord
PNS
rest of body
Excitable cells
neurons and muscle cells
Supporting cells
glia
Types of neurons
- sensory
- interneurons
- motor
Components of spinal cord
gray matter, white matter, dorsal root, dorsal horn, ventral horn, ventral root
neuron anatomy
-dendrites
-cell body
-axon hillock
-axon (output)
-axon termini
-synapse
Functions of glia
-structural support and insulation
-nutrient support
-blood-brain barrier
-neurotransmitter uptake
-ion homeostasis
Schwann cells and oligodendrocytes
-Schwann = PNS
-oligodendrocytes = CNS
-produce myelin sheaths to insulate neurons
Resting membrane potential is a consequence of:
- concentration differences of ions across membrane
- differential membrane permeability to ions
What is the equilibrium potential?
It is the membrane voltage where the electrical gradient is “strong enough” to attract ions back across the membrane, stopping the net flow of ions driven by the concentration gradient of that ion
What is driving force?
The difference between E for that ion and the membrane potential
-Ca2+ = very strong (ECF>ICF)
-Na+ = strong (ECF>ICF)
-K+ = moderate (ICF >ECF)
-Cl- = moderate (ECF>ICF)
Sodium-potassium pump
maintains ion concentration gradients, 3 Na+ out and 2 K+ in
What happens if sodium-potassium pump is poisoned?
The ionic concentration gradients last for a long time before they start to run down
Phase of an Action Potential at one point along an axon
- Resting condition at one point in an axon
- Depolarization to threshold opens voltage-gated Na+ channels
- Na+ rushes in and depolarizes
4a. Na+ channel inactivation gates close, voltage-gated K+ channels open
4b. K+ rushes out and repolarization occurs
4c. Near Vm all voltage-gated channels close - 1-2 msec later, Na+ channel inactivation gates reset
The speed of conduction in an action potential is determined by:
- speed of current flow in the axoplasm
- leakage of ions across the plasma membrane
- kinetics of channel opening and closings
Why are larger dm axons faster than smaller ones?
Large diameter axons have lower resistance and current can propagate more quickly and farther in cytoplasm. Ion channels regenerate current and lower resistance allows for less frequent opening and closing of channels
Why are myelin sheaths beneficial?
they reduce ion leakage and insulate axons to make action potentials more efficient (saltatory conduction)
Where are ion channels clustered?
at the nodes of Ranvier
Why is saltatory conduction fast?
- Electrical (ionic) current travels quickly through the cytoplasm if there are no leakages
- Fewer ion channels are opening and closing (less time is required for ion channels to open and close)
Types of synapses
- Electrical
- Chemical
Electrical synapses
mediated by gap junctions
Chemical synapses
chemical neurotransmitter released from presynaptic cleft to the postsynaptic cell
Important neurotransmitters
- acetylcholine
- serotonin
- dopamine
- glutamate
- norepinephrine
- glycine
- GABA
- neuropeptides
- nitric oxide
Excitatory neurotransmitters
acetylcholine, dopamine, glutamate, norepinephrine
Inhibitory neurotransmitters
serotonin, norepinephrine, glycine, GABA
Neuromuscular junction
- Action potential arrives at axon terminus
- Depolarization (must exceed threshold) at terminus opens voltage-gated Ca2+ channels
- Synaptic vesicles fuse w/ membrane
- NT is released
- Triggers action potential in postsynaptic cell (elicit contraction in muscle cell)
Ligand-gated channels (ACh)
- ACh opens Na+ channel on postsynaptic membrane
- Vm across the postsynaptic membrane depolarizes
- ACh in the cleft is degraded by acetylcholinesterase
- Signal is terminated
Synapses between neurons
- Excitatory postsynaptic potential
- Inhibitory postsynaptic potential
EPSP
-depolarize postsynaptic cell
-might not be strong enough to single-handedly elicit an action potential
IPSP
-hyperpolarize cell
Where is the critical area for the “decision” to fire an action potential?
axon hillock
Spatial summation
several weak signals from different locations are converted into a single larger one
Temporal summation
converts a rapid series of weak pulses from a single source into one large signal
Types of chemical synapses
- Ionotropic receptors
- Metabotropic receptors
Ionotropic receptors
bind a NT and cause a direct change in ion movements
Metabotropic receptors
GPCRs
ex: cardiac adrenergic receptor in heart cells
Process of Synaptic Signal Termination
- NT is released from presynaptic termini as very brief bursts, so channels in postsynaptic membranes are open for very brief intervals. When channels close, the Vm rapidly returns to the resting Vm that is largely determined by the K+ electrochemical gradient.
- NT is rapidly removed from synaptic cleft by:
a) degradation in synaptic cleft
b) diffusion
c) being taken up by transporters in membrane’s presynaptic cell and repackaged/recycled adjacent glial cells
