DLA 29/Lecture 37: Autonomic Nervous system/Lecture 38 Flashcards
Characteristics of Autonomic Nervous System
- Visceral
- 3 innervates 3 target tissues = smooth muscle, cardiac muscle, glands
- Two divisions =
1) Sympathetic (stress)
2) Parasympathetic (Rest/digest)
(Enteric Nervous system = intestines)
Functions of Autonomic Nervous System
Sympathetic Nervous System:
- Fight/flight/fright
- Catabolic
- Increases HR, BP, blood sugar, cardiac contractions, sweat, ventilation, blood flow in skeletal muscles
Parasympathetic Nervous System:
- Rest & Digest
- Homeostatic or anabolic system
- Decreases BP and HR, respiratory rate
- Removal of waste
- Constricts pupils
Motor Pathways:
Somatic
Autonomic
Somatic:
- One Neuron
- Myelinated
- CNS –> effector
Autonomic: Two Neuron 1) Preganglionic neuron = -myelinated -cell body in CNS
2) Postganglionic neuron=
- unmyelinated,
- cell body in PNS (In autonomic ganglion)
Pre-ganglionic and post-ganglionic
Cell body locations
Preganglionic:
1) Parasympathetic Outflow:
- Cranial Nerves III, VI, IX, X
- Sacral spinal segments S2-S4
- longer than post-ganglionic neuron
2) Sympathetic Outflow:
- Thoracolumbar T1-L2
- Shorter than post-ganglionic neuron
Postganlionic:
1) Parasympathetic Ganglia:
- Near walls of target organs
- ONLY founds in head associated with parasympathetic cranial nerves
2) Sympathetic Ganglia:
- Sympathetic chain (trunk) ganglia: paravertebral ganglia, superior cervical ganglion (base of skull) –> coccyx, one pair per spinal nerve
-Preaortic ganglia: prevertebral ganglia, abdomen, branching
Adrenal Gland
- Preganglionic sympathetic axons synapse on chromaffin cells
- Chromaffin cells releases catecholamines (affect tissues)
One neuron
Uses hormones to affect rest of system
Cholinergic Transmission
Presynaptic nerve –> Synaptic cleft
Presynaptic nerve:
1) ) Acetyl Coa synthesized
2) Choline transported to neuron terminal by sodium-dependent carrier (CHT1)
3) Ach synthesized by acetyl-CoA and choline
4) ACh transported into vesicles by a the vesicular ACh transporter (VAChT)
Synaptic cleft:
1) Action potential
2) Release of ACh
3) Release of calcium
4) ACh binds to and activate ACh receptors
5) Acetylcholinesterase (AChE) splits ACh
into choline and acetate
(ACh release is inhibited by ACh acting on
presynaptic M2)
Adrenergic Transmission
Presynaptic nerve –> Synaptic cleft
Presynaptic nerve:
1) Tyrosine is transported into the adrenergic neuron by system L
2) Tyrosine –> L-DOPA by the enzyme tyrosine hydroxylase.
3) L-DOPA –> dopamine by DOPA decarboxylase
4) Vesicular monoamine transporter (VMAT)
translocate dopamine into synaptic vesicles
5) Intravesicular dopamine-β-hydroxylase
converts dopamine to NE.
Synaptic cleft:
1) NE binds adrenergic receptors
2) Diffusion away from the receptor site/Re-uptake into the nerve terminal = Termination of the action of NE
-(Reuptake is mediated by the Na+-dependent NE transporter (NET)
-NE release is inhibited by NE acting on presynaptic α-2 autoreceptors
Cholinergic Receptors:
Nicotinic receptor
1) Nicotinic muscle subtype (NM)
Location: Skeletal muscle
Function: Skeletal muscle contraction
2) Nicotinic neuronal channels subtype (NN)
Location: Autonomic ganglia, Adrenal medulla, brain
Function: Postganglionic neuron activation, Chromaffin cells releases catecholamines to bloodstream, Neuronal
development Learning and memory
-Ligand-gated sodium/potassium channels
Cholinergic Receptors:
Muscarinic receptor
“Qiq”
All parasympathetic
1) M1
Location: Brain, Autonomic ganglia
Function: Higher cognitive functioning, Stimulates enteric nervous system (digestive)
-Increases IP3, DAG, Ca++
2) M2
Location: Presynaptic nerve terminal, heart
Function: Inhibition of Ach release, decreases HR/Contractility of atria
-Decreases cAMP
3) M3
Location: Exocrine glands, pancreatic B glands, smooth muscle, endothelial cells
Function: Increases exocrine gland secretion, insulin release, Gut peristalsis, bladder contraction, Pupillary constriction/accommodation, Bronchial constriction
-Gq protein linked
α-receptors
α1 receptors
-Gq protein
-Vasoconstriction
-Sympathetic
Location: Vascular smooth muscle, eye, Intestinal and
bladder sphincter smooth muscle
Function: Vascular smooth muscle/Intestinal and
bladder sphincter contraction, Pupillary dilation
α2 receptors
-Gi protein
Location: Presynaptic nerve terminal neurons, Pancreatic β cells
Function: decrease of Norepinephrine and insulin release
ALL SYMPATHETIC
β-receptors
β1 receptors
- Gs Protein
- Location: Heart, kidney, adipocytes
- Function: Increases HR, contractility, renin release, Lipolysis
β2 receptors
-Gs Protein
-Vasodilation
-Location: Urine and bronchial smooth muscle, blood vessel skeletal muscle,
Function: Bronchial dilation, vasodilation, decrease uterine tone
β3 receptors
- Gs protein
- Location: Brown tissue
- Function: Makes heat, increase Lipolysis
ALL INCREASE CAMP
Sympathetic
ANTAGONISTIC CONTROL/ EFFECTS
-Involve both branches of autonomic nervous system = balanced responses
(Ex: increasing and decreasing HR)
-Most organs do this
Effector site
Predominant tone
Receptor type
Loss of predominant tone
Arterioles:
- Sympathetic,
- Alpha-1
- Hypotension
Veins:
- Sympathetic,
- Alpha-1
- Venodilation (dilation of blood vessels)
Heart SA Node:
- Parasympathetic
- M2
- ↑Heart Rate
Heart Ventricle:
- Sympathetic
- β1
- ↓Contractility
Iris:
- Parasympathetic
- M3
Autonomic Functions in the eye
1) Pupillary dilation/ contraction:
- mydriasis = Sympathetic = dilates eye
- miosis= parasympathetic = constricts eye
2) Lens less convex/ more convex
- More convex = parasympathetic (ciliary muscle)
ACCOMMODATION:
Miosis + Lens more convex = BETTER NEAR VISION
Baroreceptor Reflexes
Can inhibit cholinergic agonists
