CHAPTER 16

Autonomic Nervous System (ANS)

Part of the peripheral nervous system that regulates involuntary functions of the body.

Homeostasis

The process of maintaining a stable internal environment in the body.

Sympathetic division

Part of the ANS that prepares the body for physical activity and stress; known as the fight-or-flight response.

Parasympathetic division

Part of the ANS that supports rest, digestion, and energy conservation; known as the rest-and-digest response.

Skeletal muscles

Muscles that are under voluntary control by the somatic nervous system.

Acetylcholine (ACh)

A neurotransmitter released by somatic motor neurons at the neuromuscular junction.

Receptor

A protein that detects or responds to a specific chemical messenger.

Effector

The structure that produces a response after receiving a signal from a receptor.

Nicotinic receptors

Type of acetylcholine receptor found in autonomic ganglia and neuromuscular junctions.

Muscarinic receptors

Type of acetylcholine receptor found on many parasympathetic target organs and sympathetic sweat glands.

Adrenergic receptors

Receptors activated by norepinephrine or epinephrine, with various types such as alpha and beta.

Preganglionic neuron

The first neuron in the autonomic pathway, originating in the CNS and synapsing in a ganglion.

Postganglionic neuron

The neuron that originates in the ganglion and innervates the target organ.

Thoracolumbar division

Refers to the sympathetic division of the ANS; neurons originate from T1-L2.

Craniosacral division

Refers to the parasympathetic division of the ANS; neurons originate from the brainstem and sacral spinal cord.

Sympathetic effects on heart

Increased heart rate and force of contraction during stress or physical activity.

Parasympathetic effects on heart

Decreased heart rate, primarily controlled by the vagus nerve.

Sympathetic fight-or-flight response

Physiological changes in the body, such as increased heart rate and blood flow to skeletal muscles.

Parasympathetic rest-and-digest response

Physiological changes that promote digestion and energy conservation.

Neurotransmitter

Chemical messenger that transmits signals across a synapse.

Autonomic reflex arc

Automatic response to a stimulus that helps regulate functions such as heart rate and digestion.

Integration center

The part of the CNS that processes sensory information and determines an appropriate response in a reflex arc.

Sweat glands and sympathetic stimulation

Sympathetic postganglionic neurons typically release ACh instead of NE, causing increased sweating.

Agonist

A chemical that binds to a receptor and activates or stimulates its normal response.

Antagonist

A chemical that binds to a receptor and blocks its activation, preventing the normal response.

Hypothalamus

A control center for the ANS that coordinates autonomic and endocrine activity, regulating homeostasis.

Autonomic tone

The continuous level of activity maintained by the ANS in organs, allowing for homeostasis.

Blood vessel sympathetic effects

Sympathetic stimulation causes vasoconstriction in many blood vessels and changes in blood distribution.

Epinephrine and norepinephrine

Hormones released from the adrenal medulla during sympathetic stimulation to amplify the fight-or-flight response.

Muscarinic ACh receptors

Receptors activated by acetylcholine in target organs of the parasympathetic division.

Adrenergic agonist

A drug that mimics the effects of sympathetic neurotransmitters.

Cholinergic antagonist

A drug that blocks the effects of acetylcholine.

Reflex arc components

Includes receptor, sensory neuron, integration center, motor neuron, and effector.

Major exception in sympathetic postganglionic neurons

Most sweat glands release ACh rather than norepinephrine, using muscarinic receptors.