A&P Chapter 14
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Why are the postganglionic axons of the ANS slower in conduction?
- 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.
What type of ganglia are associated with the autonomic system?
What is released by somatic motor neurons and what is its effect?
ACh; the effect is always excitatory
What neurotransmitter is released by most sympathetic fibers?
What neurotransmitter is submitted by most parasympathetic fibers?
What is the major anatomical differences between preganglionic axons and post ganglionic axons?
Preganglionic axons are lighly mylenated while postganglionic axons are unmylenated
What are the major anatomical aspects of the parasympathetic division?
- 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.
What are the major anatomical aspects of the sympathetic division?
- 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
Once a preganglionic axon reaches a trunk ganglion, one of three things can happen to the axon, what are they?
- 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.
What is the differences between white and gray rami?
- White rami are mylenated preganglionic
- Gray rami are unmylenated postganglionic
Where are white rami found?
only in the T1- L2 cord segments
Which division are the white rami communicantes associated with?
sympathetic division only
What is referred pain?
- Pain felt at a site other than the area of origin
- Pain stimuli arising in the viscera are perceived as somatic in origin
In the ANS, where is ACh released?
- All ANS preganglionic axons
- All paraympathetic post ganglionic axons at synapses with their effector
What are ACh releasing fibers called?
What are the classifications and effect of cholinergic receptors?
- Nicotinic: excitation
- Muscarinic: excitation in most cases. Inhibition in cardiac muscle
What are the Adrenergic receptors?
- B1, B2, B3, a1, a2aera
- The neurotransmitter released is norepinepherine (and epinephrine by the adrenal medulla).
What is the location and effect of B1 receptors?
- Location: Heart predominantly, but also kidneys and adipose tissue
- Effect: Increases heart rate and strength; stimulates renin release by kidneys
What is the location and effect of B2 receptors?
- 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
What is the location and effect of B3 receptors?
- Location: Adipose tissue
- Effect: Stimulates lipolysis by fat cells
What is the location and effect of a1 receptors?
- 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
What is the location and effect of a1 receptors?
- Location: membrane of adrenergic axon terminals; pancreas; blood platelets
- Effect: inhibits NE release from adrenergic terminals; inhibits inulin secretion by pancreas; promotes blood clotting
What is vasomotor tone?
the vascular system is entirely innervated by sympathetic fibers that keep the blood vessels in a continual state of partial constriction
What metabolic effects promoted by the sympathetic division are not reversible by the parasympathetic division?
- Increase metabolic rate of body cells
- raises blood glucose levels
- mobilizes fats for use as fuels
Describe the general effects of the parasympathetic nervous system
- 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
Describe the general effects of the sympathetic nervous system
- 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
What is the control center for the ANS
- Hypothalamus through the reticular formation
- Parasympathetic: anterior hypothalamic regions
- Sympathetic: Posterior hypothalamic regions
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