The peripheral nervous system Flashcards
What are the functions of the autonomic nervous system ?
Controls:
- Smooth muscle (git and vascular)
- Exocrine function
- Rate (chronotropic) and force (inotropic) of heart
- Metabolic processes (glucose use)
Where in the spinal cord to sympathetic neurons originate ?
What about parasympathetic neurons ?
Sympathetic region = T1 - L2
Parasympathetic region = cranial nerves + S2 - S4
What are the characteristics of sympathetic Vs parasympathetic fibers ?
Sympathetic fibers :
- short pre-ganglionic neurons, clustered in paravertebral ganglionic chain, long post-ganglionic neurons
Parasympathetic fibers :
- all cranial nerves (except vagus X) –> short pre-synaptic neurons and long postsynaptic neurons
- S2-S4 region + vagus nerve –> long pre-ganglionic neurons, ganglion often in the wall of the innervated organ
What are the effects of parasympathetic stimulation ?
- salivary flow
- slowing of heartbeat
- constriction of bronchi
- stimulation of peristalsis and secretion
- release of bile
- contraction of bladder
What are the effects of sympathetic stimulation ?
- pupil dilation
- inhibition of saliva flow
- acceleration of heartbeat
- dilation of bronchi
- inhibition of peristalsis and secretion
- conversion of glycogen to glucose
- secretion of AD and NA
- inhibition of bladder contraction
What are the consequences pf the activation of the myenteric plexus ?
- increase in tonic contraction
- increase in intensity of rhythmic contractions
- increase in rate of rhythmic contractions
- increases velocity of conduction
What are the consequences of the activation of the submucosal plexus ?
- increase in secretory activity
- modulation of intestinal absorption
What are the NTs used in the ANS ?
PNS = ACh on nAChRs –> ACh on mAChRs
SNS = ACh on nAChRs –> NA or
ACh on nAChRs –> AD (in adrenal medulla)
What receptor are present in the parasympathetic system ?
- ACh at ganglion
- Fast nicotinic
- ACh at target
- Slow muscarinic receptors
What receptor are present in the sympathetic system ?
- ACh at ganglion
- Fast nicotinic
- NA at target
- Slow alpha & beta receptors
What molecules are co-transmitted along with ACh at the ganglia ?
ACh causes fast depolarization
LHRH can be co-released to cause slow depolarization
Opioid peptides can be co-released can be c-released to cause slow hyper-polarization
In the parasympathetic system, what receptors are found in :
- the GI tract ?
- the bladder ?
- on the X nerve ?
- at sweat glands ?
What effect do they have when stimulated ?
M1 –> GI tract + bladder, +ve effect
M2 –> Vagus X nerve, autoreceptor, -ve effect
M3 –> Sweat glands, +ve effect
What molecules can be co-transmitted along w/ ACh at parasympathetic targets ?
peptides, such as VIP (Vasoactive Intestinal Peptide), SP (Substance P)
In the sympathetic system, what receptors are found in :
- the GI tract ?
- blood vessels ?
- the bladder ?
- the CNS ?
- the heart ?
What effect do they have when stimulated ?
GIT --> alpha-1 (+ve) and beta-2 (-ve) Blood vessel --> alpha-1 (+ve) Bladder --> alpha-1 (+ve) CNS --> alpha-2 (autoreceptor, -ve) Heart --> beta-1 (+ve)
What molecule can be co-released along with NA at sympathetic targets ?
ATP, causes fast depolarization.
How is NO synthesized ?
How is it used in different tissues ?
In the endothelium, arginine is converted to NO by NOS (NO synthase), then :
- in the platelets, NO contributes to platelet inhibition (GTP in converted to cGMP by guanylyl cyclase, which is activated bu NO)
- in red blood cells, NO is metabolized in the reaction NO + Hb-O2 –> metHb + NO3-
- NO also contributes to the formation of peroxynitrite in the reaction NO + O2- –> ONOO-
- in smooth muscle NO activates sGC which converts GT to cGMP, which causes relaxation
What are the NT released in the enteric nervous system ?
5-HT, DA, GABA and SP
