Autonomic Nervous System Flashcards
1 anatomical organization of the autonomic nervous system: sympathetic vs parasympathetic divisions 2 neurotransmission of the sympathetic and parasympathetic divisions of the autonomous nervous system 3 functional role of the sympathetic and parasympathetic nervous systems in organ system coordination and regulation
Describe anatomical differences between sympathetic and parasympathetic NS
- P: LONG preganglionic fibers S: short preganglionic fibers
- P: short post-ganglionic fibers S: long post-ganglionic fibers
- P: pre:post innvervation = 1:1; S pre:post innervation = 1:20
Anatomical similarities between sympathetic and parasympathetic NS
- Both 2-neurons systems
- Preganlionic cell body in spinal cord or brainstem
- Post-ganglionic cell body in ganglia
- Myelinated preganglionic neuron, unmyelinated post-ganglionic neuron
- How was acetylcholine discovered?
Guy with the dream. 1st heart was innervated by vagus, second heart bathed with solution of 1st heart. Stimulating vagus slowed down heart 1 and after some time, heart 2, showing that there is a molecule in the solution that translates neural activity into heart activity.
What is the neurotransmitter used in the 1st synapse?
Acetylcholine in BOTH sympathetic and parasympathetic
What is neurotransmitter in 2nd synapse of sympathetic NS?
Norepinepherine
What is neurotransmitter released by adrenal medulla? Which NS?
Sympathetic NS.
Epinepherine and Norepinepherine
What is the neurotransmitter used in 2nd synapse of parasympathetic NS?
Acetylcholine
What is the sympathetic NS exception?
Sweat glands have cholinergic 2nd synapses (they are in the sympathetic NS so technically should be norepi)
all summarized in slide 14 and 15
What are the receptors of the ANS?
- PARA: 1st: cholinergic nicotinic; 2nd: adrenergic
- SYMP: 1st: cholinergic nicotinic; 2nd: cholinergic muscarinic
slide 16, 18, 19 and 20
How does atropine help in reversing the effects of Ache inhibitors?
Blocks muscarinic receptors
Is Ach mostly reuptaken or degraded? Is dopamine mostly reuptaken or degraded?
Ach mostly degraded.
Dopamine mostly reuptaken (more difficult to break up)
What do para and sympa NS do to the heart?
PARA: Stimulation of parasympathetic NS causes a DECREASED HR, force
SYMPA: stimulation of sympathetic NS causes an INCREASED HR, force
Describe heart rate as a function of atropine injected
- At LOW atropine levels, HR decreases probably because of its effect in CNS (not important here)
- At HIGH atropine levels, HR increases b/c atropine BLOCKS parasympathetic muscarinic receptors, which increases HR
Which NS is dominant in the heart? What happens when both pathways are blocked?
Paraympathetic NS is dominant so it is more affected. HR increases.
What happens to the pupil when atropine (from the flower) is ingested?
The sphincter of the eye is innervated only by the parasympathetic ANS. Atropine acts on parasympathetic ANS by being a muscarinic receptor antagonist. So parasympathetic activity is lowered, which causes a dilation of the eye.
3 properties of fight/flight response
- Increased HR and force
- Relaxation of trachea and bronchii to improve breathing
- Decreased motility in stomach
Describe baroreceptor reflex
BP increases > stretch receptors in aortic arch fire more > PARA increased, SYMPA decreased > HR decreases
BP decreases > stretch receptors in aortic arch fire less > PARA decreases, SYMPA increases > HR increases
from the lecture:
→ Is a homeostatic mechanism for maintaining blood pressure.
→ Provides a negative feedback loop, in which an elevated blood pressure reflexively causes heart rate to decrease , therefore causing blood pressure to decrease.
→ To prevent postural hypotension, reduced blood flow to the brain, and fainting. When BP falls, the sympathetic nerves turn ON, and the parasympathetic nerves turn OFF.
→ Baroreceptors are located in the carotid sinuses and transverse aortic arch.
→ Are stretch receptors that are stimulated by distortion of the arterial wall when pressure changes.
→ An increase in the mean arterial pressure increases depolarization of these sensory endings, which results in action potentials.
- organization flow
brain and spinal cord -> motor pathways -> autonomic nervous system (involuntary) (and somatic nervous system, voluntary) -> sympathetic/parasympathetic/enteric
compare somatic motor neurons vs autonomic motor neurons pathway
slide 3
organization of the parasympathetic system
1. Long preganglionic fibers →Myelinated →Few branches →Release ACh 2. Postganglionic ganglia resides near end effector organs. Ganglia sometimes organized cluster of postsynaptic neurons. 3. Short postganglionic axon →Unmyelinated →Release ACh 4. The ratio of pre- to post- ganglionic fibers is close to 1:1 →more localized and discrete response
organization of the sympathetic system
1. Short preganglionic axon
→ Myelinated
→Many branches
→ Release ACh
2. Postganglionic nerve cell body in pre- and para-vertebral ganglia
3. Long postganglionic axon
→ Unmyelinated
→Many branches
→ Release NE/EPI (most)
4. The ratio of pre- to post- ganglionic fibers is over 1:20
→Coordinated, diffuse
→One turns on, all are ondescribe adrenal medulla
● Composed principally of chromaffin cells;
● Are similar to embryonic undifferentiated neurons;
● When cultured in vitro these cells can be induced to grow long neuron-like processes;
● Could be considered similar to postganglionic neurons;
● Innervated by cholinergic preganglionic neurons which release ACh and acting on Nicotinic receptor (N1);
● Cholinergic stimulation of chromaffin cells evokes secretion of epinephrine and norepinephrine into the circulation, where they act as neurohormones.
describe pheochromocytoma
→ A neuroendocrine tumor of the adrenal medulla; Originating in the chromaffin cells;
→ Secreting excessive amounts of NE and EPI;
→ Elevated HR, Elevated BP, Palpitations, Anxiety, Diaphoresis (excessive sweating), Headaches, Pallor, Weight loss; Malignant hypertension, can be fatal;
→ Surgical resection of the tumor, the treatment of first choice;
→ Alpha adrenoceptor blocker Phenoxybenzamine.
general feature of autonomic neurotransmission
slide 11
pathway of ACh transmission cholinergic terminal and norepinephrine at adrenergic terminal
slide 21 and 23
pathway of autonomic transmission for both sympathetic and parasympathetic
slide 25
comparison of sym and parasym
Similarities
a. Involuntary;
b. Two-neuron systems;
c. Location of preganglionic neurons;
d. Location of postganglionic neurons;
e. Neurotransmitter of preganglionic neurons;
f. Principal receptor type on postganglionic neurons;
Differences
a. Origination:
b. Length of preganglionic axon:
c. Length of postganglionic axon:
d. Locations of ganglia:
e. Neurotransmitter of postganglionic neurons:
f. Ratio of pre- to post-ganglionic innervations:
g. Inactivation of neurotransmitter:
h. Function:
physiology of ANS
- Controls smooth muscle (visceral and vascular); exocrine (and some endocrine) secretions; rate and force of the heart; certain metabolic processes such as glucose utilization.
- Paraympathetic and sympathetic systems have opposing actions in many situations (heart rate, GI smooth muscle).
- Parasympathetic activity predominates during satiation and repose (Rest and Digest, Breed and Feed) → Energy Conservation
- Sympathetic activity increases in stress (Fight or Flight response) →Energy Expenditure.
dual innervation
→ Generally, the dual innervations usually cause opposite physiological effects.
→ Both systems are not quiet, normally active at all the times.
→ level of function depends on the balance between the two systems.
→ One branch is usually dominant, That is, one branch provides the most important functional control under resting conditions.
→ Removal of all autonomic innervations will have different influences on different tissues, depending on which system is dominant.
level of ANS control
slide 41
