Neurophysiology of the Autonomic Nervous System

Neurophysiology of the Autonomic Nervous System

• The autonomic nervous system (ANS) controls involuntary functions, like heart rate, digestion, and sweating.
• It's divided into two main branches: sympathetic and parasympathetic.
• Sympathetic: Prepares the body for "fight or flight" responses, mobilizing energy. It typically releases norepinephrine (NE) as a neurotransmitter.
• Parasympathetic: Rest and digest response. It typically releases acetylcholine (ACh) as a neurotransmitter.
• Acetylcholine often affects both branches.

General Organization of the Nervous System

• The nervous system is divided into central and peripheral branches.
• Central Nervous System (CNS): Composed of brain and spinal cord.
• Peripheral Nervous System (PNS): Consists of nerves branching off the CNS to reach all other parts of the body
• Somatic nervous system: Controls voluntary muscle movements.
• Autonomic nervous system (ANS): Controls involuntary functions like heart rate, digestion, and sweating.
  • The ANS is further divided into the sympathetic and parasympathetic nervous systems.

ANS Receptors

• Adrenergic receptors respond to norepinephrine and epinephrine, released during sympathetic stimulation. Subtypes include α1, α2, β1, and β2.
• Cholinergic receptors respond to acetylcholine, found in both sympathetic and parasympathetic branches, and have subtypes such as muscarinic (M1, M2, M3), and nicotinic (N1, N2).

Pheochromocytoma

• A tumor of the adrenal medulla that produces excessive catecholamines (primarily adrenaline/epinephrine and noradrenaline/norepinephrine).
• This can cause extreme sympathetic responses, resulting in high blood pressure, headache, sweating, anxiety.
• Diagnosed by elevated urine vanillylmandelic acid (VMA) levels and/or imaging.
• Treatment involves alpha-blockers to initially control blood pressure, then beta-blockers to control heart rate irregularities. Surgery (laparoscopic adrenalectomy) to remove the tumor is often necessary.
• The presented case study describes a patient with symptoms consistent with a pheochromocytoma, and confirms the diagnosis with diagnostic testing..

Horner's Syndrome

• A disorder causing a combination of signs (e.g., drooping eyelid, constricted pupil, decreased sweating on one side of the face ) due to damage to the sympathetic pathways in the head and neck.
• Causes include: carotid artery dissection, tumors in neck/chest cavity, lesions in the midbrain/spinal cord, or inflammation in the neck's lymph nodes.
• Diagnosis is clinical, often corroborated by imaging studies (e.g., X-rays, MRI, CT).
• Treatment focuses on addressing the underlying cause rather than the syndrome itself. Supportive care is common.

Explore the functions and organization of the autonomic nervous system (ANS) in this quiz. You'll learn about its two main branches, sympathetic and parasympathetic, and how they regulate involuntary bodily functions. Delve into the roles of key neurotransmitters like norepinephrine and acetylcholine.