FPP

Stimulation byt the ANS either excites or inhibits visceral effectors; SNS stimulation always excites its effectors

A body organ innervated by the ANS receives both sympathetic and parasympathetic fibres.

It was thought to function autonomously or in a self-governing manner, without control by the CNS. However, the ANS is regulated by centres in the brain, mainly in the hypothalamus and brain stem, that receive input from the limbic system and other regions of the cerebrum.

Visceral sensory (afferent) and motor (efferent) neurons, both sympathetic and parasympathetic.

A cluster of sympathetic or parasympathetic cell bodies located outside the central nervous system.

The portion of the peripheral nervous system consisting of somatic sensory (afferent) neurons and somatic motor (efferent) neurons.

One of two subdivisions of the ANS, having cell bodies of preganglionic neurons in the lateral gray columns of the thoracic segment and the first two or three lumbar segments of the spinal cord: primarily concerned with processes involving the expenditure of energy ("fight or flight"). Also called the thoracolumbar division.

One of two subdivisions of the ANS, having cell bodies of preganglionic neurons in nuclei in the brain stem and the lateral gray matter of the sacral protion of the spinal cord: primarily concerned with activities that conserve and restore energy ("rest & relax"). Also called the craniosacral division.

Mainly from interoceptors: some from special senses and somatic senses.

Involuntary control from limbic system, hypothalamus, brain stem, and spinal cord; limited control from cerebral cortex.

Two-neuron pathway: preganglionic (pre-g) neurons extending from CNS synapse with postganglionic (post-g) neurons in an autonomic ganglion, and post-g neurons extending from ganglion synapse with a visceral effector. Also, pre-g neurons extending from CNS synapse with cells of adrenal medulla.

Pre-g axons release acetylcholine (ACh); post-g axons release ACh (parasympathetic division and sympathetic fibres to sweat glands) or norepinephrine (NE; remainder of sympathetic division); adrenal medulla releases epinephrine and norepinephrine.

Smooth muscle, cardiac muscle, glands.

Contraction or relaxation of smooth muscle; increased or decreased rate and force of contraction of cardiac muscle; increased or decreased secretions of glands.

Most parasympathetic pre-g axons are longer than most sympathetic pre-g axons because most parasympathetic ganglia are in the walls of visceral organs, whereas most sympathetic ganglia are close to the spinal cord in the sympathetic trunk.

Branches of a spinal nerve.

• S: bodywide: skin, sweat glands, arrector pili muscles of hair follicles, adipose tissue, smooth muscle of blood vessels.
• P: limited mainly to head and to viscera of thorax, abdomen, and pelvis; some blood vessels.

• S: close to CNS and distant from visceral effectors.
• P: typically near or within wall of visceral effectors.

• S: short pre-g fibres synapse with many long post-g neurons that pass to many visceral receptors.
• P: Long pre-g fibres usually synapse with four to five short post-g neurons that pass to a single visceral effector.

• S: both present; white RC contain myelinated pre-g fibres, and gray RC contain unmyelinated post-g fibres.
• P: neither present

• all sympathetic and parasympathetic pre-g neurons
• sympatheitc post-g neurons that innervate most sweat glands
• all parasympathetic post-g neurons

• nicotinic receptors
• muscarinic receptors

Adrenergic (bind to norepinephrine and epinephrine).

• Blood vessels to non-essential organs (e.g. GI tract, kidneys) constrict
• Blood vessels to skeletal muscles, cardiac muscle, liver and adipose tissue dilate

• Heart rate, force of heart contraction, and blood pressure increase
• The airways dilate

• Blood vessels to the liver dilate
• Increase in breakdown of glycogen to glucose (glygogenolysis)
• Releases glucose to increase blood sugar level

• Pupils dilate
• Non-essential processes (e.g. muscle movements of GI tract and digestive secretions) slow down or even stop

• Widespread as post-g fibres diverge extensively so many tissues activated simultaneously
• Long-lasting as norepinephrine not inactivated quickly

• Salivation
• Lacrimation
• Urination
• Digestion
• Defecation

• heart rate
• diameter of airways
• diameter of pupils