Unit 4 Flashcards
CNS
- brain
- spinal cord
PNS
- voluntary
- involuntary
Involuntary
- sympathetic
- parasympathetic
2 efferent neurons
- preganglionic
- postganglionic
voluntary
skeletal muscle
1 efferent neuron
autonomic
- cardiac
- smooth
- glands
sensory neuron
to
somatic motor neuron
autonomic motor neuron
from
efferent division
from the CNS
afferent division
to the CNS
Autonomic Nervous System (ANS)
efferent system that governs fx w/o conscious effort
CNS to periphery
Branches of the ANS
- sympathetic nervous system (SNS)
- parasympathetic nervous system (PNS)
SNS
fight or flight
- increase HR, BP
- blood volume shifts to skeletal muscles
- bronchodilation
- increase blood glucose (liver)
PNS
rest and digest
- increase GI motility
- increase visceral blood flow
- decrease HR
Anatomy of ANS
2 neuron system
- Preganglionic and Postganglionic
- Pairs of neurons linked together
- Action potentials driven through sodium channels across synapses
- Chemical communication at ganglia and junction with target organ
sympathetic neurons
-Preganglionic neurons located in the thoracic and lumbar region
-Synapse in 2 cord-like chains of ganglia that run parallel
on each side of the spinal cord
-Long postganglionic neurons
Parasympathetic
Preganglionic neurons arise from cranial/sacral regions of spinal cord and synapse in ganglia near or on the effector organ (short postganglionics)
neurotransmitters
mediate signals // cell/targets
neurotransmitters received by down-stream cell and produce a response
ANS: 2 kinds of neurotransmitters
- Cholinergic
- Adrenergic
Acetylcholine
released by both PNS and SNS presynaptic neurons
-cholinergic
These receptor (at the ganglia) are called ________ (b/c they bind other chemicals as well…namely nicotine)
Nicotinic
nicotinic receptors
actually sodium channels, so when they open they stimulate an action potential to travel down the postganglionic neuron
Drugs that target nicotinic receptors essentially…
turn on ALL of the ANS
parasympathetic fibers release Acetylcholine (Ach) at the postganglionic target
called Cholinergic Neurons
Cholinergic Neurons
The receptors on targets are called
muscarinic receptors
Action of Ach is terminated quickly by:
acetylcholine esterase (enzyme)
Parasympathetic NS dominated by:
activity of muscarinic receptors interacting w/ Ach
Ach
very versatile neurotransmitter
- acts at all ganglia (bind nicotinic receptors)
- motor neurons release Ach
- Ach binds nicotinic receptors on skeletal muscle
- binds muscarinic receptors in PNS
Cholinesterases
get rid of Ach very quickly
when Ach is released from the receptors it is rapidly destroyed
pathway of Ach
- Ach is released
- Ach binds w/ its receptor
- action of Ach is terminated by AchE
- if AchE is inhibited. Ach is not broken down as quickly and produces a more dramatic effect
adrenergic receptors
Alpha
Beta
Alpha
smooth muscles in blood vessles
alpha 1 - post-synaptic and primarily found in the vasculature
alpha 2 - autoreceptors and found on the nerve terminal and in the brain
Beta
beta 1 - found in the heart (and in the kidney)
beta 2 - found in the lungs, also influence metabolic rate
Nor-epinephrine (NE)
released by sympathetic postganglionic neurons and generate response
NE will bind to ______ receptors
adrenergic
most NE gets pumped back into post-ganglionic neurons
re-uptake mechanism
takes longer to get rid of NE from synapse
receptors for Ach
- muscarinic
- nicotinic
receptors for Norepinephrine
- Alpha (1 and 2)
- Beta 1
- Beta 2
sympathetic nervous system
innervates most of the vascular smooth muscle
BP and peripheral resistance controlled by SNS
stimulation
vasoconstriction
not stimulated
vasodilation
cholinergic receptors
- muscarinic receptors are located at the parasympathetic postganglionic fibers (target organ)
- nicotinic receptors are found at the motor end plate (neuromuscular junction), in all autonomic ganglia and in adrenal medulla
Responses to PNS stimulation
Heart - decreases HR (SA node and AV node) - effects limited to the atria
Eye - contracts the sphincter of the iris and constricts the pupil, contracts ciliary muscle - accommodation for near vision
GI - increases secretions and peristalsis
Genitourinary - muscle in bladder wall contracts, sphincter relaxes
Where are Adrenergic receptors and what do they do when stimulated?
Alpha
peripheral blood vessels
contraction of constriction…mostly vasoconstriction
Where are Adrenergic receptors and what do they do when stimulated?
Beta 1
Heart
increase HR and contractility
Where are Adrenergic receptors and what do they do when stimulated?
Beta 2
smooth muscle
relaxes smooth muscle…bronchodilation, decrease secretion in bronchioles
increase metabolic rate
Responses to SNS stimulation
Heart - increase HR, contractility, cardiac output
Eye - innervates the radial muscles of iris (alpha receptors) dilating the pupil
GI - SNS diverts attention away from the GI tract decreasing secretions and motility
GU- relax bladder wall and contracts the sphincter
General Rules of Innervation
- many organs are innervated by both SNS and PNS
- most of the time the 2 systems have opposing effects
- important organs that receive innervation from both SNS and PNS - eye, heart, bronchial smooth muscle, GI, GU
- resting state, most dually innervated organs are controlled by PNS
drug design
we could effect neuronal conduction - stop conduction along axons
drug design
Ganglionic agonists (NICOTINIC):
will fire off ALL the ganglia and all the targets will get SNS and PNS stimulation at the same time. Also neuromuscular junction stimulation
drug design
Ganglionic (NICOTINIC) antagonists:
block PNS and SNS as well as neuromuscular junction
Nicotinic agonists
Will turn on all of the ANS – not clinically desirable
Toxicity: skeletal muscle contraction
REMEMBER: nicotinic receptors are the only receptor found in the voluntary nervous system
Nicotinic antagonists
trimethaphan
- Blocks the entire autonomic nervous system by blocking ganglionic transmission
- Used in hypertensive emergencies but with many side effects.
Decreases sympathetic tone
Rarely used due to side effects
But will block skeletal muscle contraction
Muscarinic agonists
located at the targets for the PNS
Turn on the receptors and produce a parasympathetic like response. “rest and digest”
inhibit the breakdown of Ach = Ach will be present in higher levels at the synapsis
Muscarinic agonist
pilocarpine, bethanechol
turns on muscarinic receptors at targets
Uses:
- Glaucoma: constricts pupil, increase drainage
- GI retention: post GI surgery
- Urinary retention: spinal cord problems
- Supraventricular tachycardia: SA node is setting the rate too fast. Pacing takes place in the atrium, SA node receives input fro the PNS.
- Atropine (muscarinic antagonist) poisoning: competition
Muscarinic antagonist
atropine, scopalamine
Blocks muscarinic receptors at targets – interferes with actions of PNS
Uses:
-Dilates eyes
- Problem w/ getting air into airways due to PNS constriction.
- Motion sickness: scopolamine. Can be delivered across the skin (patches & skin). Has nothing to do with ANS. Problem is in the brain, scopolamine blocks receptors in the brain.
Parkinson’s Disease: block the Ach to balance the dopamine deficiency
GI tract hyperactivity: interfere with peristalsis (usually preparations of atropine + opiate)
Insecticides that are Ach-esterase inhibitors (muscarinc agonists) can be blocked by atropine (also nerve gases)- think competition again.
Muscarinic antagonists
side effects
- Photophobia / blurred vision
- Glaucoma can be aggravated
- Tachycardia
- Inhibition of sweating (heat stroke)
- Urinary retention
- Gastric retention
Decrease the release or increase the re-uptake mechanism of nor-epi.
Adrenergic antagonists
Increase the release of catecholamines (epi and nor-epi)
Adrenergic agonists
Nor-Epi and Epi bind to alpha, beta 1 and beta 2 receptors
Alpha 1 agonist
(phenylephrine)
Uses:
- Dilation of the eyes
- Local anesthetic adjunct – vasoconstrict and leaves local anesthetic in area longer / also decreases bleeding from damaged vessels
- Decongestant: constrict vessels carrying fluid to the sinuses and decrease fluid delivery to the
sinuses - Increase blood pressure due to vasoconstriction, fluid doesn’t leak out of vessels
Alpha 1 agonist
(phenylephrine)
side effects:
- Increase BP
- reduction in perfusion = potential for tissue hypoxia and inflammation, more inflammation -> rebound congestion -> more nasal spray etc.
- photophobia
Beta agonists (isoproterenol)
Uses:
- CHF to increase HR and contractility
- dilate blood vessels in certain parts of the body…especially skeletal muscle beds (fight or flight mobilize blood to skeletal muscle)
- Treatment of asthma (B2 – bronchodilates) there are B2 selective agents
- Anaphalactic shock: hyperactive immune response with potential for airway collapse and circulatory collapse [epinephrine]
- B2 selective agonist can relax uterine smooth muscle to treat pre-term labor (prevent preterm birth)
Beta agonists (isoproterenol)
Side effects:
increase in BP
angina
tachycardia
Alpha 1 antagonist (prozasine)
Uses:
Blocks nor-epi binding
- HTN - block alpha 1 constriction
- hypersensitive emergency can cause blood vessel damage rapidly
- Pheochromocytoma: adrenal tumor
- Urinary obstruction with prostate enlargement. (alpha antagonist helps probably through changes in the prostate and the bladder.)
Alpha 1 antagonist (prozasine)
Side effects:
- hypotension
- tachycardia: reflex action through activation of SNS
- can induce nasal congestion
- impotence
- fluid retention
Beta antagonists
(propranolol)
Uses:
- decrease cardiac output and HR = decrease BP (decrease blood vessel resistance)
- Angina: ischemic heart disease
- Arrythmia: decreases heart rate
- Glaucoma: decreases formation of aqueous humor from the ciliary body
- Hyperthyroidism: not reverse hyperthyroidism, just treats the symptoms of too much thyroid.
- Tremors and anxiety: especially things like stage fright.
- Migraine headaches
Beta antagonists
(propranolol)
Side effects:
- May precipitate CHF – decrease contractility
hypotension - precipitate asthma – block the signals that are keeping the airways open
- rebound hypertension – especially if drug is D/C
Pupil - SNS
Contraction of the circular muscle
causes constriction
Pupil - PNS
Contraction of the radial muscle
causes dilation
Which type of drug is used topically to dilate the pupil during an eye exam?
alpha agonist
The neurotransmitter released at the preganglionic sympathetic nerve ending is:
acetylcholine
Which of the following kinds of drugs might be used to delay absorption of a local anesthetic?
alpha agonist
Drugs that have urinary urgency as a common side effect most specifically contain:
muscarinic agonist
A patient has been given medication which stimulates bladder contractions to increase urination. What type of receptors have been stimulated?
muscarinic
Where do the efferent pathways of the parasympathetic division originate from as they leave the CNS?
cranial and sacral regions
Which receptor when inhibited slows heart rate and decreases force of contraction?
beta 1
At times of stress, which of the following occur within the body?
glycogen is broken down and glucose is mobilized
The neurotransmitter released at voluntary nerve endings is:
acetylcholine
In the peripheral nervous system, which portion(s) send nerve fibers to smooth muscle?
sympathetic, parasympathetic but not voluntary
