Question

Horner's syndrome is an autonmoic disorder that is characterized by constricted pupils, bradycardia, and excess GI secretions. Horner's generally manifests when someone (or something; cats, dogs, and even horses can get it) suffers damage to one of the sympathetic trunk ganglia. You are seeing a patient who was in a recent automobile accident. Their eyes are constricted, and they are complaining that they are easily fatigued. A chest x-ray rules out pulmonary edema, so you start to test for Horner's.

A). Clearly explain how the autonomic nervous system might play a role. What pathways, transmitters, and receptors might be involved? How does this explain her symptoms?

B). Your patient asks "could atropine help me?" You frown because your last bit of atropine as used to treat another patient and it will take a bit of time to replenish your hospital's supply.

i. Answer YES it will help or NO it will not help

ii. Explain why or why not

iii. In one sentence, explain what you would prescribe for your patient instead of atropine and why it would work to help your patient.

Answer 1

Here whatever syndrome is present like constrict pupil(m3), bradicardia (B2)and excess GI secretion(m3 ) all are due to parasympathetic effect. and cholinergic transmission. Details regarding receptors present at particular organ and its action is explained below.

Autonomic nervous system

The autonomic nervous system (ANS) is part of the peripheral nervous system and regulates involuntary, visceral body functions in different organ systems. It is divided into the sympathetic and parasympathetic nervous systems. The sympathetic nervous system has a thoracolumbar outflow and is activated during fight or flight response, while the parasympathetic nervous system has a craniosacral outflow and is activated during digestion and rest.

The sympathetic and parasympathetic nervous systems consist of preganglionic and postganglionic neurons. The preganglionic fibers of both ANS divisions and the postganglionic fibers of the parasympathetic division are cholinergic fibers (release acetylcholine) that act on cholinergic receptors (nicotinic or muscarinic). All postganglionic fibers of the sympathetic division are adrenergic fibers (release norepinephrine) that act on adrenergic alpha or beta receptors for neurotransmission, with the exception of the fibers innervating the sweat glands, which are cholinergic. The adrenal medulla does not have a postsynaptic neuron. The sympathetic preganglionic fibers stimulate the chromaffin cells of the adrenal medulla directly via acetylcholine on nicotinic receptors, which results in the release of norepinephrine and epinephrine mediating the fight or flight response. The sympathetic and parasympathetic nervous systems have antagonistic effects in some organ systems.

Types of receptors

there are 2 types of parasympathetic receptor is present. They are muscarinichaving subtype m1 to m5 and nicotinic receptor having subtype Nm and Nn.

Nicotinic acetylcholine receptors

Ligand-gated Na+/K+ channels

NN subtype: autonomic ganglia and adrenal medulla

NM subtype: neuromuscular junction of skeletal muscle (somatic nervous system)

Muscarinic acetylcholine receptors

• The M1 (neural muscarinic receptors): CNS excitation, autonomic ganglia, parietal cells (increase gastric acid release)
• M2 (cardiac muscarinic receptors): cardiac inhibition effect. These are located in the heart, and act to bring the heart back to normal after the actions of the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the sinoatrial node and atrioventricular node. They have a minimal effect on the contractile forces of the ventricular muscle due to sparse innervation of the ventricles from the parasympathetic nervous system.
• M3 (glandular/smooth muscle muscarinic receptors): increase secretion of exocrine glands. miosis, bronchoconstriction, bladder contraction. located at many places in the body, such as the endothelial cells of blood vessels, as well as the lungs causing bronchoconstriction. The net effect of innervated M3 receptors on blood vessels is vasodilation, as acetylcholine causes endothelial cells to produce nitric oxide, which diffuses to smooth muscle and results in vasodilation. They are also in the smooth muscles of the gastrointestinal tract, which help in increasing intestinal motility and dilating sphincters. The M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other glands of the body. They are also located on the detrusor muscle and urothelium of the bladder, causing contraction
• M4 muscarinic receptors: Postganglionic cholinergic nerves, possible CNS effects
• The M5 muscarinic receptors: Possible effects on the CNS

Target organ             Parasympathetic nervous system

Brain             

M1 receptor is present

action :   CNS (increase memory, attention)

Eye                            M3    receptor is present

action :       Miosis

Salivary glands                     M3 receptor is present

action : increase serous secretion

blood vessels

• Most blood vessels in the body do not have parasympathetic                                                                        innervation

• Vasodilation Via M3

heart                       B2 receptor is present

action : decrease Heart rate (negative chronotropic)

decrease Contractility (negative inotropic)

  decrease  Conduction velocity (negative dromotropic

Lungs             M3 receptor is present

                    action :   : bronchoconstriction

Digestive system      Stomach, intestine

•           M1: increase gastric acid release

      •     M3: sphincter dilation, increase motility

                                        Pancreas                M3: increase  insulin secretion, increase exocrine secretion

                                           Liver:               M3: increase gluconeogenesis  

Bladder                        M3      receptor is present

                                         action :   Relaxation of vesical sphincter muscle

                                                             Contraction of detrusor muscle