The Nervous System and The Heart

The Nervous System and The Heart

Central Nervous System

• Composed of the brain and spinal cord.

Peripheral Nervous System

• Encompasses everything outside the brain and spinal cord.

Peripheral Nervous System Details

• Somatic System: Controls voluntary movement.
• Autonomic System: Regulates vital functions and involuntary movements.

Autonomic Nervous System: Branches

• Sympathetic: Responsible for "fight or flight" responses.
• Parasympathetic: Responsible for "rest and relax" functions.

Sympathetic Nervous System: Specifics

• Originates from the thoracic and lumbar spinal cord.
• Neurotransmitters: Primarily uses epinephrine and norepinephrine.
• Effects: Includes pupil dilation, increased heart rate, bronchodilation, inhibited digestion, and stimulation of the adrenal medulla to secrete epinephrine and norepinephrine.

Autonomic Receptors: Nicotinic

• Nicotinic receptors: Ionotropic receptors.
• Common to both parasympathetic and sympathetic nervous systems.
• Acetylcholine binds to these receptors.
• Binding causes ion channels to open.

Sympathetic Nervous System Receptors

• Activated by adrenaline and noradrenaline.
• Includes Alpha and Beta receptors.

Beta Receptors

• B1: Found in the SA node, AV node, and atrial/ventricular cardiomyocytes in the cardiovascular system.
• B2: Located in vascular smooth muscle and coronary circulation.

Alpha Receptors

• A1: Found in vascular smooth muscle, causing vasoconstriction.
• A2: Found in vascular smooth muscle, causing vasodilation.

Parasympathetic Nervous System

• Activated by acetylcholine.
• Heart: M2 receptors.
• Lungs: M3 receptors.

Vagus Nerve

• An important parasympathetic nerve, also known as the "wandering" nerve.
• Cranial Nerve X: The 10th of the twelve cranial nerves.
• Runs from the brain to the large intestine.
• Innervates the sinoatrial (SA) node, atrioventricular (AV) node, and ventricular conduction system (Cleveland Clinic, 2024).

References

• Cleveland Clinic, (2025). Vagus Nerve.
• Gordan, R., Gwathmey, J., & Lai-Hua, X. (2015). Autonomic and Endocrine Control of Cardiovascular Function.
• Mastenbjork, M. & Meloni, S. (2024) Pharmacology Review