Phys 2 Flashcards
Small molecule neurotransmitters
-3 main groups
- Amino acids- glutamate, GABA, glycine
- Acetylcholine (ACh)
- Monoamines- Norepinephrine (NE), Epinephrine (E), Dopamine (DA), serotonin
Large molecule neurotransmitters
-4 main groups
- Substance P
- Enkephalin
- Endorphins
- Releasing hormones such as TRH and LHRH
ACh is synthesized in the…
nerve terminal from choline and acetyl-coA by choline acetylcholase (ChAT)
ACh is transported into…
vesicles by vesicle associated transporter (VAT)
ACh is stored in…
vesicles in cholinergic fiber termini
ACh is released via… as a response to…
exocytosis as a response to calcium influx with axonal depolarization
Which complex enables ACh exocytosis?
- SNARE complex enables exocytosis
- SNAPS on cytosolic face of PM
- VAMPS on vesicular membrane
Elimination of ACh from the synaptic cleft
- ACh has a short 1/2 life
- it is bound to post synaptic membrane
- acetylcholinesterase comes in an hydrolyzes ACh into choline and acetate
- choline and acetate can then be recycled or eliminated
Examples of cholinergic fibers are:
-5
- Somatic motor neurons
- ANS preganglionic neurons
- PSNS postganglionic neurons
In CNS:
- Basal forebrain complex (septal nuclei & nucleus basalis)
- Pontomesencephalic cholinergic complex
ACh nicotinic receptors
- location
- action
location:
- neuromuscular junction (Nm)
- CNS and ANS ganglia (Nn)
action:
- ligand-gated ion channels
- 5 subunits surround a central channel
- allows influx of cations (i.e. Na) which results in depolarization of the membrane: response is usually excitatory to cell
ACh muscarinic receptors
-location
-M1-M5 subtypes based on activity: all five are found in the CNS, while
M1-M3 are also found in various tissues
- M1 AChRs: ANS ganglia and GI
- M2 AChRs: cardiac tissue
- M3 AChRs: smooth muscles and glands
ACh muscarinic receptors
-action
form G-protein coupled receptor (GPCR) complexes, you can think of this as a 2 messenger system:
- the first messenger is a ligand that binds receptor causing conformational change
- the second messenger utilizes a G-protein second messenger system
Activation of G-protein for ACh muscarinic receptors
the G protein binds GTP dissociating subunits for further signaling:
- excitation or inhibition of adenylate cyclase to increase of decrease cAMP
- phospholipase C activation which cleaves membrane bound PIP2
Membrane-bound PIP2 can be cleaved into…
- IP3 (inositoltriphosphate): R on ER, release of Ca2+ to cytoplasm
- DAG (diacylglycerol): which activates protein kinase C
- PKC actions: contraction, vasoconstriction, secretion, etc.
ACh muscarinic receptor action
-M1, M2, M3
M1:
- Gastric glands, excitatory
- Phosphotidylinositol pathway
M2
- Heart
- Inhibitory to adenyl cyclase, decreasing cAMP
M3
- Glands and smooth muscle, excitatory
- Increase gastric motility and secretions
- Phosphotidylinositol pathway
Norepinephrine synthesis
- Tyrosine
- DOPA
- Dopamine is transported into vesicle
- It is hydroxylated to form NE
Norepinephrine release
- Depolarization of adrenergic fiber causes exocytosis of granules, releasing NE to synaptic cleft
- NE has longer half life than Ach
- Diffuses from cleft
Norepinephrine elimination
- Diffusion
- Binding postsynaptic membrane
3, Catabolism
for example by MAO - Reuptake into presynaptic fiber
–Accomplished by NET
(NE transporter)
–About 90% is reabsorbed
–Located away from synapse
–Removes diffused NE
Adrenergic fibers release…
Norepinephrine and epinephrine
The norepinephrine adrenergic fibers are:
- Postganglionic SNS fibers
2. Adrenal medulla
Norepinephrine adrenergic fibers
-adrenal medulla
- Releases more E than NE
- NE is transported out of vesicle
- Methylated to form E
- E is transported back to vesicle
Adrenergic fibers - G protein coupled Receptors
-Alpha 1
Alpha1
- Smooth muscle and heart
- IP3 and DAG
Adrenergic fibers - G protein coupled Receptors
-Alpha 2
Alpha2
- CNS and pancreas
- Inhibitory to AC (adenylate cyclase)
Adrenergic fibers - G protein coupled Receptors
-Beta 1
Beta1
- Heart, JGA
- Activates AC (adenylate cyclase)
Adrenergic fibers - G protein coupled Receptors
-Beta 2
Beta2
-Bronchial sm, myocardium, veins, GI organs, etc.
Adrenergic fibers - G protein coupled Receptors
-Beta 3
Beta3
-Adipose
Adrenergic receptors
-alpha 1 action
- vasoconstriction
- increased peripheral resistance
- increased blood pressure
- mydriasis
- increased closure of internal sphincter of the bladder
Adrenergic receptors
-alpha 2 action
- inhibition of norepinephrine release
- inhibition of ACh release
- inhibition of insulin release
Adrenergic receptors
-beta 1 action
- tachycardia
- increased lipolysis
- increased myocardial contraction
- increased release of renin
Adrenergic receptors
-beta 2 action
- vasodilation
- slightly decreased peripheral resistance
- bronchodilation
- increased muscle and liver glycogenolysis
- increased release of glucagon
- relaxed uterine smooth muscle
Interactions of Divisions - Antagonistic
- Clearly seen in dual innervation systems (i.e. Heart, respiratory, and GI systems)
- SNS increases HR, RR and decreases GI motility and secretions
- PSNS decreases HR, RR and increases GI motility & secretions
Interactions of divisions
-Sympathetic Tone
- With few exceptions CVS is entirely innervated by SNS
- Keep a continual partial contraction to maintain vasomotor tone
- Can quickly respond for adaptation
Interactions of Divisions
-parasympathetic tone
effects dominate the heart, smooth muscle of GI, and urinary tracts
Interactions of divisions
-cooperative effects
Pupils
- control of pupil diameter
- SNS widens (mydriasis)
- PSNS constricts (miosis)
External genitalia
- PSNS erection
- SNS ejaculation
One division innervation via SNS seen in:
- adrenal medulla
- arrector pili muscles
- sweat glands
- kidneys (renin release, which increases vasoconstriction, blood volume, BP)
- most blood vessels
unique role of SNS
- thermoregulation (3)
Local heat to skin SNS creates local vasodilation.
Elevated systemic body temperature
- -Widespread vasodilation to skin
- -Skin flushes
- -Dissipates heat
Depressed body temperature
- -Widespread vasoconstriction of vessels to skin
- -Shunts blood to core
unique role of SNS
-metabolic effects (6)
-Either via direct innervation or increased adrenal medulla secretion of E
-Creates diffuse effects by circulating NE and E
Increased MR of body cells
-Increased blood sugar
-Mobilization of fats for fuel use
-Increased mental alertness by RAS stimulation
What is the main integration center of ANS?
Hypothalamus
- PSNS: medial and anterior hypothalamus
- SNS: lateral and posterior
The integration centers in the hypothalamus exert effects via…
the reticular formation which then stimulates preganglionic ANS motor neurons in brain stem and spinal cord
What 6 things do the hypothalamus centers coordinate?
- Cardiac activity
- BP
- Body temp
- Water balance
- Emotional stages i.e. rage, pleasure
- Biological drives i.e. thirst, hunger, sex
What has the most influence over ANS function?
Reticular formation of brain stem appears to have the most influence over ANS function
What are the 2 arms of the reticular system?
- RAS (Reticular Activating System)
2. Reticular Formation Motor Arm
RAS (Reticular Activating System)
- projects to
- receives
Projects widely to:
- Hypothalamus
- Thalamus
- Cerebellum
- Spinal cord
Receives sensory info to maintain arousal
- Reticular Formation Motor Arm
- characteristics
-Somatic to cerebellum for tone and coordinated skeletal movements
Autonomic motor centers:
- Vasomotor center-medulla
- Cardiac center-medulla
- Respiratory center- pons and medulla
What reflex arcs does the brainstem receive info from?
from the reflex arcs for defecation and micturition
Where is the oculomotor reflex?
In the midbrain
Enteric nervous system
-location
Located in wall of digestive tract from esophagus to anus
Enteric nervous system
-afferents
Receptors in mucosa sense chemical, mechanical, osmotic changes
Enteric nervous system
-motor
Controls motility, arteriole diameter, secretion and absorption
*ANS nerves connect ENS to CNS to allow for coordination
What are the 2 neural plexuses of the ENS?
- Myenteric (Auerbach’s) plexus
2. Submucosal (Meissner’s) plexus
Myenteric (Auerbach’s) plexus
- location
- control
- Located in between long and circular smooth muscle layers
- Controls motility
Submucosal (Meissner’s) plexus
- location
- regulates
- Located between circular muscle and luminal mucosa
- Regulates GI blood flow
