Nerves Flashcards
Where are cell bodies for sympathetic neurons found?
T1-L3, thoracolumbar region
Where are cell bodies for parasympathetic neurons found?
In the cranial and sacral regions
Define: chronotropic
An effect that changes heart rate
Define: inotropic
An effect that changes the strength of muscular contraction
Are autonomic preganglionic axons of small/large diameter? Are they myelinated/unmyelinated? Do they conduct impulsues fast/slow?
Small, myelinated, slow
Are postganglionic axons of small/large diameter? Are they myelinated/unmyelinated? Do they conduct impulsues fast/slow?
Small, unmyelinated, slow
Are somatic axons of small/large diameter? Are they myelinated/unmyelinated? Do they conduct impulsues fast/slow?
Large, myelinated, fast
Do sympathetics or parasympathetics have greater divergence?
Sympathetics- contact 100 postganglionic neurons. Paras contact about 15
Define: en passant synapses
When a neuron makes multiple synapses. This is common for ANS neurons
What are three ways in which the sympathetic NS has broad effects?
- Divergence
- En passant synapses
- Stimulation of chromaffin cells in the adrenal medulla causing the release of epi/norepi into the bloodstream
Preganglionic symps and paras signal with this neurotransmitter which acts on this receptor (and it is ionotropic/metabotropic)
Acetylcholine, N2 nicotinic cholinergic receptor, ionotropic
Somatic neurons signal with _____ neurotransmitter on ______ receptors which are (ionotropic/metabotropic)
Acetylcholine, N1 nicotinic cholinergic receptors, ionotropic
Postganglionic paras signal with _____ neurotransmitter on ______ receptors which are (ionotropic/metabotropic)
Acetylcholine, M muscarinic cholinergic receptors, metabotropic
Postganglionic symps signal with _____ neurotransmitter on ______ receptors which are (ionotropic/metabotropic)
Epininephrine and norepinephrine, a1, b1 and b2 adrenergic receptors, metabotropic
What are chromaffin cells?
Cells in the adrenal medulla with N2 receptors that release epinephrine and norepinephrine into the blood upon stimulation from preganglionic sympathetic neurons
Where are a1 adrenergic receptors found? What neurotransmitter preferentially binds them?
In the vasculature. Norepinephrine
Where are B adrenergic receptors found? What neurotransmitter preferentially binds them?
In the heart, lungs and liver. Epinephrine
What innervates eccrine sweat glands? What receptor do they have?
Postgang symps via acetylcholine. Muscarinic receptors
What do a1 adrenergic receptors cause release of in a cell?
Calcium (cytoplasmic concentration increases)
What do B1 and B2 adrenergic receptors cause production of in a cell?
cAMP
What do nicotinic cholinergic receptors cause in a cell?
Influx of sodium, efflux of potassium
What do M1, M3, M5 muscarinic cholinergic receptors cause in a cell?
Increased cytoplasmic calcium concentration
What do M2, M4 muscarinic cholinergic receptors cause in a cell?
Decreased cAMP production
What is a N1 receptor antagonist?
d-tubocurarine
What is a N2 receptor antagonist?
hexamethonium
What is an M receptor antagonist?
Atropine
What is a propranolol?
A B1 adrenergic receptor antagonist
What are the four phases of an action potential?
Rising (depolarizing) phase, overshoot phase, falling (reporlarizing) phase, undershoot phase
Which ion is essential for the generation of an action potential (in most neurons)?
Sodium
What ion causes the undershoot phase of the action potential?
Potassium
What is the absolute refractory period? What creates it?
A period when no action potentials can be conducted in response to stimuli. Inactivation of Na+ channels.
What is the relative refractory period? When does this occur?
When a cell can conduct an action potential but needs greater stimulation to do so because it is hyperpolarized. During the undershoot phase.
Explain voltage clamp recording
A negative feedback loop prevents voltage from changing across a cell membrane by injecting a current equal and opposite to the current flowing through the voltage-gated channels.
What two currents are involved in an action potential?
An early inward Na+ current and a late outward K+ current
How does an action potential propagate?
Na+ ions entering a neuron passively flow down an axon, depolarizing different parts of the membrane and opening Na+ channels there
How does myelination change action potential propagation?
Increased insulation and diameter and decreased capacitance all speed propagation. Potentials jump between nodes of ranvier in saltatory conduction
What are dendrites specialized for?
Receiving synaptic signals
What goes on in the cell soma of a neuron?
Housekeeping functions i.e. protein synthesis and degradation
What does an axon do?
Transmits all-or-none action potentials
What happens at the presynaptic terminal?
An electrical signal (action potential) is converted into a chemical one (neurotransmitter)
Kinesin is a (+ or -) directed motor that moves along microtubules in a/an (anterograde/retrograde) fashion
+-end directed, anterograde transport of mitochondria and vesicles
Dynein is a (+ or -) directed motor that moves along microtubules in a/an (anterograde/retrograde) fashion
(-)- end directed, retrograde transport of degraded vesicular membranes and toxins/viruses/growth factors
What are some advantages and disadvantages of electrical synapses?
They are fast and synchronous. However, there is no directionality of transfer, little inhibitory signaling, and the mode is not very selective.
What are the 7 steps for synaptic transmission at a chemical synapse
Neurotransmitter is made and packaged into vesicles-> an action potential arrives at the presynaptic terminal-> Voltage-gated Ca2+ channels open and Ca2+ enters the cell-> Neurotransmitter vesicles fuse with the presynaptic cell membrane-> neurotransmitters bind to receptors on the postsynaptic cell-> response in the postsynaptic cell-> neurotransmitter taken up or degraded
Name a V-SNARE involved in vesicular fusion at the nerve cell membrane
Synaptobrevin
Name two T-SNAREs involved in vesicular fusion at the nerve cell membrane
SNAP-25 and Syntaxin
Define: ionotropic receptor
A ligand-gated ion channel
Define: metabotropic receptor
A G-protein coupled receptor
Which receptor initiates a more rapid response, an ionotropic or a metabotropic receptor?
Ionotropic
How does glutamate create excitatory post-synaptic potentials? (2 ways- fast and slow)
Fast- AMPA channels mediate Na+, K+ flow down their gradients, depolarizing the cell
Slow- In addition to AMPA, NMDA receptors allow Na+, K+, and Ca2+ to flow down their gradients, depolarizing the cell.
How does GABA create inhibitory post-synaptic potentials?
GABA binding opens Cl- channels, allowing Cl- into a neuron and hyperpolarizing the cell
Define summation as it relates to action potentials
If a neuron is stimulated at the end of an action potential by either the same neuron that caused the first action potential (temporal) or a different neuron (spatial), the depolarizations are additive and can create an action potential.
What is pheochromocytoma? What are some effects of having this disease?
A tumor of the adrenal medulla (usually) that causes increased norepi (or epi or both) secretion. Can cause hypertension, heart palpitations, flushing, cold hands and feed, nausea, headaches.
What is Horner’s syndrome? What are three effects of this disease?
A loss of sympathetic innervation of one side of the face. Ptosis (eyelid drooping), anhidrosis (lack of sweating) and miosis (partial constriction of the pupil).
What are some examples of parasympathetic activation in the body?
Pupillary constriction, glandular secretion, decreased heart rate, bronchioconstriction, GI motility, erection, bladder/rectal emptying
Where does the vagus nerve (Cr X) originate?
Dorsal motor nucleus of the vagus nerve and the nucleus ambiguus. Both are in the medulla (brain stem)
What is the nucleus tractus solitarius?
The major regulator of mean arterial pressure
What does the myenteric plexus control?
GI motility
What does the submucosal plexus control in the gut?
Secretion
How does the sympathetic nervous system maintain homeostasis during exercise?
It redistributes blood by causing vasoconstriction of some capillary beds and vasodilation of others (i.e. heart, muscle)
How does the parasympathetic nervous system maintain homeostasis during digestion?
It enhances motility by increasing wall muscle tone and decreasing sphincter tone. It also increases secretion from the stomach and pancreas.
How does descending cortical control influence the autonomic nervous system?
Certain higher order functions are controlled by nuclei in the brain. Additionally, emotions or certain situations can cause autonomic responses (i.e. fear initiates the fight-or-flight response)
What are some examples of when visceral afferents can overwhelm cortical function?
Hunger, nausea, dyspnea, visceral pain, bladder/bowel distension, hypothermia, hyperthermia
