Autonomic Nervous System

Question 1

Describe anatomical differences between sympathetic and parasympathetic NS

Answer 1

1. P: LONG preganglionic fibers S: short preganglionic fibers
2. P: short post-ganglionic fibers S: long post-ganglionic fibers
3. P: pre:post innvervation = 1:1; S pre:post innervation = 1:20

Question 2

Anatomical similarities between sympathetic and parasympathetic NS

Answer 2

1. Both 2-neurons systems
2. Preganlionic cell body in spinal cord or brainstem
3. Post-ganglionic cell body in ganglia
4. Myelinated preganglionic neuron, unmyelinated post-ganglionic neuron

Question 3

• How was acetylcholine discovered?

Answer 3

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.

Question 4

What is the neurotransmitter used in the 1st synapse?

Answer 4

Acetylcholine in BOTH sympathetic and parasympathetic

Question 5

What is neurotransmitter in 2nd synapse of sympathetic NS?

Answer 5

Norepinepherine

Question 6

What is neurotransmitter released by adrenal medulla? Which NS?

Answer 6

Sympathetic NS.

Epinepherine and Norepinepherine

Question 7

What is the neurotransmitter used in 2nd synapse of parasympathetic NS?

Answer 7

Acetylcholine

Question 8

What is the sympathetic NS exception?

Answer 8

Sweat glands have cholinergic 2nd synapses (they are in the sympathetic NS so technically should be norepi)

all summarized in slide 14 and 15

Question 9

What are the receptors of the ANS?

Answer 9

1. PARA: 1st: cholinergic nicotinic; 2nd: adrenergic
2. SYMP: 1st: cholinergic nicotinic; 2nd: cholinergic muscarinic

slide 16, 18, 19 and 20

Question 10

How does atropine help in reversing the effects of Ache inhibitors?

Answer 10

Blocks muscarinic receptors

Question 11

Is Ach mostly reuptaken or degraded? Is dopamine mostly reuptaken or degraded?

Answer 11

Ach mostly degraded.

Dopamine mostly reuptaken (more difficult to break up)

Question 12

What do para and sympa NS do to the heart?

Answer 12

PARA: Stimulation of parasympathetic NS causes a DECREASED HR, force
SYMPA: stimulation of sympathetic NS causes an INCREASED HR, force

Question 13

Describe heart rate as a function of atropine injected

Answer 13

1. At LOW atropine levels, HR decreases probably because of its effect in CNS (not important here)
2. At HIGH atropine levels, HR increases b/c atropine BLOCKS parasympathetic muscarinic receptors, which increases HR

Question 14

Which NS is dominant in the heart? What happens when both pathways are blocked?

Answer 14

Paraympathetic NS is dominant so it is more affected. HR increases.

Question 15

What happens to the pupil when atropine (from the flower) is ingested?

Answer 15

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.

Question 16

3 properties of fight/flight response

Answer 16

1. Increased HR and force
2. Relaxation of trachea and bronchii to improve breathing
3. Decreased motility in stomach

Question 17

Describe baroreceptor reflex

Answer 17

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.

Question 18

• organization flow

Answer 18

brain and spinal cord -> motor pathways -> autonomic nervous system (involuntary) (and somatic nervous system, voluntary) -> sympathetic/parasympathetic/enteric

Question 19

compare somatic motor neurons vs autonomic motor neurons pathway

Answer 19

slide 3

Question 20

organization of the parasympathetic system

Answer 20

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

Question 21

organization of the sympathetic system

Answer 21

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 on

Question 22

describe adrenal medulla

Answer 22

● 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.

Question 23

describe pheochromocytoma

Answer 23

→ 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.

Question 24

general feature of autonomic neurotransmission

Answer 24

slide 11

Question 25

pathway of ACh transmission cholinergic terminal and norepinephrine at adrenergic terminal

Answer 25

slide 21 and 23

Question 26

pathway of autonomic transmission for both sympathetic and parasympathetic

Answer 26

slide 25

Question 27

comparison of sym and parasym

Answer 27

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:

Question 28

physiology of ANS

Answer 28

• 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.

Question 29

dual innervation

Answer 29

→ 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.

Question 30

level of ANS control

Answer 30

slide 41