A&P Chapter 14

• Both sympathetic and Parasympathetic have unmylenated postganglionic axons.
• The parasympathetic postganglionic axons are shorter than the sympathetic. Moreover, some of the parasympathetic Post GA are on the organ.

motor neurons

ACh; the effect is always excitatory

Norepinephrine (NE)

ACh

Preganglionic axons are lighly mylenated while postganglionic axons are unmylenated

• Origin site: Parasympathetic fibers emerge from the brain and spinal cord
• Relative length of fibers: The parasympathetic has long pre ganglionic and short post ganglionic fibers
• Location of the Ganglia: Parasympathetic ganglia are located in the visceral effector organs.

• Origin site: Sympathetic fibers emerge from the thoracolumbar region of the spinal cord.
• Relative length of fibers: The sympathetic has short pre ganglionic and long post ganglionic fibers.
• Location of the Ganglia: Sympathetic ganglia lie close to the spinal cord

• The axon can synapse with a ganglionic neuron in the same trunk ganglion
• The axon can ascend or descend the sympathetic trunk to synapse in another trunk ganglion
• The axon can pass through the trunk ganglion and emerge from the sympathetic trunk with out synapsing.

• White rami are mylenated preganglionic
• Gray rami are unmylenated postganglionic

only in the T₁- L₂ cord segments

sympathetic division only

• Pain felt at a site other than the area of origin
• Pain stimuli arising in the viscera are perceived as somatic in origin

• All ANS preganglionic axons
• All paraympathetic post ganglionic axons at synapses with their effector

Cholinergic fibers

• Nicotinic: excitation
• Muscarinic: excitation in most cases. Inhibition in cardiac muscle

• B₁, B₂, B₃, a₁, a₂aera
• The neurotransmitter released is norepinepherine (and epinephrine by the adrenal medulla).

• Location: Heart predominantly, but also kidneys and adipose tissue
• Effect: Increases heart rate and strength; stimulates renin release by kidneys

• Location: Lungs and most other sympathetic target organs; abundant on blood vessels serving the heart, liver and skeletal muscle
• Effect: effects mostly inhibitory; dilates blood vessels and bronchioles; relaxes smooth muscle walls of digestive and urinary visceral organs; relaxes uterus

• Location: Adipose tissue
• Effect: Stimulates lipolysis by fat cells

• Location: Most importantly blood vessels serving the skin, mucosa, abdominal viscera, kidneys, and salivary glads; also virtually all sympathetic target organs except heart
• Effect: constricts blood vessels and visceral organ sphincters; dilates pupils of the eyes

• Location: membrane of adrenergic axon terminals; pancreas; blood platelets
• Effect: inhibits NE release from adrenergic terminals; inhibits inulin secretion by pancreas; promotes blood clotting

the vascular system is entirely innervated by sympathetic fibers that keep the blood vessels in a continual state of partial constriction

• Increase metabolic rate of body cells
• raises blood glucose levels
• mobilizes fats for use as fuels

• Only one preganglionic neuron that synapses with generally only one ganglionic neuron
• ACh is quickly destroyed by acetylcholinesterase
• Exerts are short lived, highly localized control over its effectors

• Synapse with ganglionic neurons at several levels
• The response is a diffused and highly interconnected
• Effects are more pronounced and longer lasting because NE is not quickly removed

• Hypothalamus through the reticular formation
• Parasympathetic: anterior hypothalamic regions
• Sympathetic: Posterior hypothalamic regions