Autonomic and Somatic Nervous Systems

Autonomic Nervous System

• The autonomic nervous system (ANS) regulates internal body functions unconsciously, adjusting to meet needs like fight-or-flight or rest-and-digest.
• The ANS is typically divided into two parts that oppose one another: sympathetic and parasympathetic.
• Sometimes they work together to balance bodily functions.
• The sympathetic nervous system (SNS) prepares the body for action ("fight or flight").
• The parasympathetic nervous system (PNS) calms the body and helps with "rest and digest".

Neuron Chain

• The autonomic nervous system uses a two-neuron chain.
• The first neuron (preganglionic) has its cell body in the central nervous system (CNS).
• The preganglionic axon synapses with the second neuron (postganglionic) in an autonomic ganglion.
• The postganglionic axon synapses with the target organ.

Somatic Nervous System

• The somatic nervous system operates consciously by directly innervating skeletal muscle.
• It uses single neurons extending from the CNS to the muscle.
• It primarily uses acetylcholine (ACh).

Neurotransmitters

• Acetylcholine (ACh): a neurotransmitter used by both the parasympathetic and somatic systems.
• Norepinephrine (NE): a neurotransmitter used by the sympathetic system; effects depend on receptor type.
• Epinephrine (adrenaline): a neurotransmitter used by the sympathetic system; effects depend on receptor type.

Sympathetic Nervous System (Fight-or-Flight)

• Originates from thoracic and lumbar spinal cord.
• Short preganglionic neurons, long postganglionic neurons.
• Ganglia near spinal cord.
• Increases heart rate, blood pressure, respiration, and other functions associated with alertness and energy expenditure.
• Decreases digestion.
• Dilates pupils (mydriasis)

Parasympathetic Nervous System (Rest-and-Digest)

• Originates from the brain and sacral spinal cord.
• Long preganglionic neurons, short postganglionic neurons.
• Ganglia near effector organ.
• Decreases heart rate, blood pressure, respiration.
• Increases digestion.
• Constricts pupils (miosis).

Receptor Types

• Cholinergic receptors receive acetylcholine (ACh).
• Nicotinic receptors: always excitatory
• Muscarinic receptors: can be excitatory or inhibitory
• Adrenergic receptors bind norepinephrine (NE) and epinephrine (E).
• Alpha receptors, Beta receptors: effects vary.

Drugs and the ANS

• Drugs can alter ANS function for various needs (e.g., anesthesia, treating asthma).
• Drugs can be agonists (mimicking the effect of a neurotransmitter) or antagonists (blocking the receptor from engaging with a neurotransmitter).

Regulation/Control

• The autonomic nervous system regulates body temperature, blood pressure, heart rate, etc.
• It helps maintain homeostasis; a dynamic balance.
• Sympathetic and parasympathetic activities work together or oppose one another depending on the need.

Explore the intricacies of the autonomic and somatic nervous systems in this quiz. Understand how these systems regulate body functions, including the interplay between the sympathetic and parasympathetic divisions. Test your knowledge on neuron chains and muscle innervation.