Chapter 06: Neuronal Signaling Flashcards
What are varicosities?
A series of bulging areas along the axon that release neurotransmitters
What are collaterals?
Branches that stem off of the axon
What are the myelin-forming cells of the CNS?
Oligodendrocytes
What are the myelin-forming cells of the PNS?
Schwann cells
How many axons can oligodendrocytes myelinate and connect to?
Up to 40
How may axons can Schwann cells myelinate and connect to?
Just one
What is the gap between areas of myelinated axon sheath called?
Nodes of Ranvier
Kinesin proteins bond __________ to the microtubule in the axon chain.
secretory vesicles
Dynein proteins bond _________ to the microtubule in the axon chain.
recycled membrane vesicles
Neurons make up _____% of the cells in the CNS but compose ____% of the volume.
10% of CNS cells, 50% CNS volume
What are the four types of neuroglial cells?
Oligodendrocytes, astrocytes, microglia, and ependymal cells
What are microglia?
Macrophage-like cells that perform immune function for CNS
What are the functions of astrocytes?
Regulate composition of extracellular fluid, stimulate formation of tight junctions that compose blood-brain barrier, provide glucose and remove ammonia for neurons
What are ependymal cells?
Producers and regulators of CSF that line the fluid filled cavities of the CNS
What is the growth cone?
Specialized enlargement that forms tip of extending axons that is involved in finding correct route and final destination
What are the growth factors for neural tissue called?
Neurotrophic factors
What is apoptosis?
Programmed self-destruction of cell
What percentage of newly formed neurons and synapses go through apoptosis?
50-70%
current (n.)
the movement of electric charge
resistance (n.)
hindrance to the flow of electric charge/current
What is the equation for Ohm’s Law?
I = V/R
membrane potential (n.)
the state of the negative charge of the inside of a cell relative to the outside
What is the range of resting membrane potentials for all cells?
-5 to -100 mV
What is the range for RMP in neurons?
-40 to -90 mV
What is average RMP for neurons?
-70 mV
What are the general permeabilities of K+, Na+, and Cl-?
P(K+) = 1 P(Na+) = 0.04 P(Cl-) = 0.45
What is the ionic flow of the Na+/K+ ATPase pump?
3 Na+ out, 2 K+ in
leak channel (n.)
open channel, the flow of which follows concentration gradient
What are the stages of the firing of an action potential?
Depolarization, overshoot, repolarization, hyperpolarization, afterhyperpolarization
What is plasticity?
The remodeling of neural tissue in response to stimulation or injury
What is the rate of axon regrowth?
1 mm/day
electrical potential (n.)
the potential of opposite, separated electrical charges to do work if brought together
Which ion has a high concentration intracellularly?
K+
Which ion has a high concentration extracellularly?
Na+ (also Cl-)
electrogenic pump (n.)
pump that moves net charge across a membrane and contributes directly to membrane potential
excitability (n.)
the ability of a cell to generate an action potential
inactivation gate (n.)
part of a voltage-gated Na+ channel that blocks flow shortly after the channel opens
What is the threshold level for most neurons?
-55 mV
relative refractory period (n.)
period during afterhyperpolarization in which only a very strong stimuli will generate an AP
graded potential (n.)
change in potential of variable amplitude and duration that is conducted incrementally (no threshold/refractory period) and has a decremental flow of current
What is a threshold stimulus?
A stimulus that generates a change in potential ~15 mV more positive than RMP
absolute refractory period (n.)
period in which the VG-Na+ channels are open or inactivated; during this period, no stimuli will generate an AP
equilibrium potential (n.)
the electrical potential at a membrane at which there is no net flux of the ion
What is equilibrium potential for Na+?
+60 mV
What does the Nernst equation calculate?
Equilibrium membrane potential for a single ion species based solely on concentration, measured in mV
What is the threshold level for most neurons?
-55 mV
What is the Nernst equation?
E = 60/Z * log (C(o)/C(i))
What is equilibrium potential for K+?
-90 mV
What percentage of RMP is contributed by the Na+/K+ATPase pump? What is the charge?
Up to 20%, about -15 mV
Where is the first place in the neuron that an action potential can occur?
Axon hillock
Where are action potentials found in the neuron?
The axon hillock and along the axon
anterograde conduction (n.)
conduction away from the soma/dendrite of the neuron towards the axon terminal
retrograde conduction (n.)
conduction away from the axon terminal towards the soma/dendrites
At what stage of the conduction of an action potential is the relative refractory period?
Afterhyperpolarization
reaction time (n.)
delay between stimulus and response (reflex or voluntary)
synaptic delay (n.)
the amount of time it takes to release and bind neurotransmitters and depolarize the membrane to threshold in the postsynaptic axon hillock
How large are neuronal synaptic clefts?
roughly 10-20 nm
How long is the synaptic delay?
~ 200 ms (0.2 sec)
What protein mediates final fusion of vesicles to the synaptic membrane?
Synaptotagmin
What does the Goldman equation calculate?
Equilibrium membrane potential for several ions based upon concentration and permeability, measured in mV
What is the signal pathway for all parasympathetic innervation?
Preganglionic neuron > nicotinic receptor > postganglionic neuron > muscarininc receptor > gland or smooth muscle
What is the signal pathway for most sympathetic innervation?
Preganglionic neuron > nicotinic receptor > postganglionic neuron > adrenergic receptor > glands and visceral organs
What is the less common signaling pathway for sympathetic innervation?
Preganglionic neuron > nicotinic receptor > postganglionic neuron > muscarinic receptor > sweat glands and blood vessels
What type of receptor is between the preganglionic and postganglionic neurons in the ANS?
Nicotinic receptors
What is the signaling pathway in somatic nervous innervation?
Lower motor neuron > nicotinic receptor > skeletal muscle
sensation (n.)
sensory information that reaches the consciousness
perception (n.)
a person’s understanding of the sensation’s meaning
sensory information (n.)
information process by the sensory system, regardless of whether the information reaches consciousness
What kind of receptor does norepinephrine bind to?
Adrenergic
What neurotransmitter is released by postganglionic sympathetic neurons?
Norepinephrine
What neurotransmitter is released by postganglionic parasympathetic neurons?
Acetylcholine
What neurotransmitter is released by preganglionic sympathetic neurons?
Acetylcholine
Which type of receptor that binds acetylcholine released by the parasympathetic system is commonly found on cells of effector organs?
Muscarinic
What do mechanoreceptors respond to?
Mechanical stimuli (e.g., touch-pressure)
What do thermoreceptors respond to?
Sensations of cold and warm
What do photoreceptors do?
Convert light energy into graded potentials
What do chemoreceptors respond to?
Respond to binding of chemicals to specific receptors on membrane (used in smell, taste, blood O2 and CO2)
What do nociceptors respond to?
Respond to a number of painful stimuli including heat and tissue damage
What are the five general classes of sensory receptors?
Mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors
stimulus transduction (n.)
transformation of energy into electrical signal
sensory adaptation (n.)
decrease in receptor sensitivity with constant stimulation
What do Meissner’s corpuscles sense?
Light touch
What do Merkle’s corpuscles detect?
Medium touch
What do free nerve endings detect?
Pain
What do lamellated (Pacinian) corpuscles detect?
Deep pressure
What do Ruffini corpuscles detect?
Warmth
What are nociceptors?
Unspecialized free nerve endings that detect various “painful” stimuli
What neurotransmitter would be increasingly released by post-ganglionic sympathetic cells in fight or flight?
Norepinephrine
What neurotransmitter would be increasingly released by pre-ganglionic sympathetic cells in fight or flight?
Acetylcholine
What does relative refractory period prevent?
Retrograde movement of action potentials
What does binding ACh to nicotinic receptors in a single synapse cause in a post-synaptic cell?
Excitatory Post-Synaptic Potential (EPSP)
What molecule directly causes GABA exocytosis from a pre-synaptic axon terminal?
Calcium
What type of ion channel is associated with the production of graded potentials?
Voltage-gated channel
