ANS
describe the structure of sympathetic pathway neurons
- short, myelinated preganglionic neurons
- long, myelinated postganglionic neurons
What two hormones are synthesizes in the hypothalamus and released by the posterior pituitary?
Oxytocin and vasopressin
what are hormones?
chemical messengers secreted into the bloodstream
What are contractile units of smooth muscle?
Actin and myosin form contractile units with more than skeletal muscle, smooth muscle not arranged into sarcomeres
Where do the cell bodies originate for preganglionic neurons and postganglionic neurons?
preganglionic cell bodies originate in CNS and project to ganglia, postganglionic cell bodies in ganglion, project to target tissues
what is the vagus nerve?
a parasympathetic nerve that runs from the medulla to vital organs
What is the feedback loop for GnRH or gonadotropin releasing hormone?
1. GnRH
2. Increase gonadotroph
3. Increase levels of LH and FSH
4. Increase activity of reproductive organs including ovaries, testes, and placenta
5. Hormone secretion, organ development, and reproduction
Is inhibited by PRL-prolactin
what are the two different types of hormone cell responses?
- protein activation
- genomic effect
What are phasic smooth muscle and tonic smooth muscle?
Phasic smooth muscle- alternate between periodic contraction and relaxation cycle ex: intestine
Tonic smooth muscle-always maintain some level of muscle tone ex: a sphincter that relaxes to allow material to pass
Where does the sympathetic nervous system and parasympathetic nervous system originate?
sympathetic-thoracolumbar
parasympathetic-craniosacral
what NT do all preganglionic neurons release?
acetylcholine
What are magnocellular neurons and parvocellular neurons?
Magnocellular neurons synthesize hormones released by the posterior pituitary while parvocellular neurons synthesize hormones that target the anterior pituitary such as releasing hormones and inhibiting hormones
what is the homeostatic reflex loop when there is an increase in blood glucose?
1. stimulus = increased blood glucose
2. sensor = pancreatic beta cells release insulin
3. targets = membrane-bound receptors on the liver
4. response = decreased blood glucose
What are the stages of a smooth muscle action potential?
1. Depolarization (not based on Na+)- L-type Ca2+ channels open->influx of Ca2+
2. K+ channels open
3. Ca2+ plateau- Ca2+ influx balanced out by K+ efflux
4. More K+ channels open
5. Repolarization as K+ efflux
During a fight-or-flight response, the activity of the sympathetic nervous system can lead to vasoconstriction of some blood vessels and vasodilation of others. What is a mechanistic explanation of this?
There are different membrane receptors for norepinephrine on different vascular smooth muscles. These receptors initiate different signal transduction cascades that lead to either contraction or relaxation of the muscle.
What is the sequence of events at the neuroeffector junction?
1. NTs synthesized and stored in synaptic vesicles in axon varicosities
2. AP in postganglionic neuron
3. Ca2+ dependent exocytosis
4. NT release
5. NT diffuses away from varicosities to receptors dispersed on target tissues
6. NT either binds at the target receptors for a response or are terminated
What is the sequence of cAMP signaling?
1. signal binds to GPCR
2. activation of G-proteins that regulate adenylyl cyclase
3. adenylyl cyclase converts ATP to cAMP
4. cAMP activates PKA
5. downstream phosphorylation of cellular proteins
what is the homeostatic reflex loop when there is a decrease in blood glucose?
1. stimulus = decreased blood glucose
2. sensor = pancreatic alpha cells release glucagon
3. target = membrane-bound receptors on the liver
4. response = increased blood glucose
how does smooth muscle contraction occur?
1. Intercellular Ca+2 concentrations increase when Ca+2 enters cell and is released from the L-type Ca2+ channels or sarcoplasmic reticulum
2. Ca+2 bind to calmodulin (CaM)
3. Ca+2-CaM activates myosin light chain kinase (MLCK)
4. MLCK phosphorylates light chains in myosin heads and increase myosin ATPase activity
5. Active myosin crossbridges slide along actin and create muscle tension
what is the sequence of phosphoinositol signaling?
1. GPCR-ligand binding
2. activation of Gq
3. phospholipase C (PLC) converts phospholipid -> DAG + IP3
4. DAG activates PKC
5. PKC phosphorylates cellular proteins
4. IP3 binds IP3 receptors on SR/ER
5. Ca2+ release
6. Ca2+ dependent enzyme activities-contraction in smooth muscle, exocytosis, etc
what is the sequence of a Gs protein?
1. NT binds
2. GPCR conformational change
3. Gs protein stimulates adenylyl cyclase
4. increased cAMP
5. activation of PKA
6. cellular proteins activated/inactivated
7. cellular response
what is the sequence of beta1 and beta2 receptors?
1. NE/E binds
2. GPCR conformational change
3. activation of Gs protein
4. adenylyl cyclase increases cAMP which activates PKA
5. cellular proteins activated/inactivated
6. cellular responses
What is the feedback loop when the stimulus is nursing/suckling?
Hormone: oxytocin
Target: breast
Response: milk ejection
Negative feedback: nursing reduces baby's suckling behaviors
What receptors in parasympathetic and sympathetic nervous system cause smooth muscle contraction/relaxation?
Parasympathetic-
- Acetylcholine, m3AChR-> contraction
Sympathetic
-Norepinephrine/epinephrine, a1->contraction, b2->relaxation
BAPTA-AM is a potent calcium buffering molecule that enters into cells and then binds calcium ions in the cytoplasm. If smooth muscle cells were filled with BAPTA-AM, how would this affect the muscle?
Calmodulin would be unable to activate myosin light chain kinase (MLCK)