Chapter 15: Flashcards
The nervous system has two main divisions
- the central nervous system (CNS)
- The PNS.
PNS has two major subdivisions:
- Somatic motor system
Controls voluntary
movement of muscles - Autonomic nervous system
Somatic motor system
Controls voluntary
movement of muscles
The autonomic nervous system is further subdivided into
- The parasympathetic nervous system and
- The sympathetic nervous system
The two subdivisions of the ANS regulate?
The two subdivisions of the autonomic nervous system regulate many involuntary processes
The autonomic nervous system has three principal functions:
- Regulation of the heart;
- Regulation of secretory glands
- Regulation of smooth muscles
Regulation of secretory glands
(salivary, gastric, sweat, and bronchial glands);
Regulation of smooth muscles
(muscles of the bronchi, blood vessels, urogenital system, and gastrointestinal [GI] tract).
The parasympathetic nervous system performs seven regulatory functions
Stimulation of appropriate parasympathetic nerves causes:
- Slowing of heart rate
- Increased gastric secretion
- Emptying of the bladder
- Emptying of the bowel
- Focusing the eye for near vision
- Constricting the pupil
- Contracting bronchial smooth muscle
Therapeutic agents that alter parasympathetic nervous system function are used primarily for
effects on the GI tract, bladder, and eye.
Occasionally, these drugs are also used for effects on the heart and lungs.
The sympathetic nervous system has three main functions:
- Regulating the cardiovascular system
- Regulating body temperature
- Implementing the acute stress response (commonly called a “fight-or-flight” reaction)
Stimulation of sympathetic nerves to the heart
Stimulation of sympathetic nerves to the heart increases cardiac output.
Stimulation of sympathetic nerves to arterioles and veins
Stimulation of sympathetic nerves to arterioles and veins causes vasoconstriction.
Release of epinephrine from the adrenal medulla results in
Release of epinephrine from the adrenal medulla results in vasoconstriction in most vascular beds and vasodilation in certain others.
By influencing the heart and blood vessels, the sympathetic nervous system can achieve three homeostatic objectives:
- Maintenance of blood flow to the brain
- Redistribution of blood flow during exercise
- Compensation for loss of blood, primarily by causing vasoconstriction
The sympathetic nervous system helps regulate body temperature in three ways:
- By regulating blood flow to the skin, sympathetic nerves can increase or
decrease heat loss. - Sympathetic nerves to sweat glands promote secretion of sweat, thereby helping the body cool.
- By inducing piloerection (erection of hair), sympathetic nerves can promote heat conservation.
When we are faced with an acute stress-inducing situation, the sympathetic nervous system orchestrates the fight-or-flight response, which involves:
- Increasing heart rate and blood pressure
- Shunting blood away from the skin and viscera and into skeletal muscles
- Dilating the bronchi to improve oxygenation
- Dilating the pupils (perhaps to enhance visual acuity)
- Mobilizing stored energy, thereby providing glucose for the brain and fatty acids for muscles
Agents that alter cardiovascular function are used to treat
- hypertension,
- heart failure,
- angina pectoris,
- and other disorders.
What happens in many organs that receive dual innervation
The influence of sympathetic nerves opposes that of parasympathetic nerves.
Example of influence of sympathetic nerves opposes that of parasympathetic nerves.
For example, in the heart, sympathetic nerves increase heart rate, whereas parasympathetic nerves slow heart rate
The effects of sympathetic and parasympathetic nerves are complementary, rather than opposite. What is an example?
In the male reproductive system, erection is regulated by parasympathetic nerves and ejaculation is controlled by sympathetic nerves.
A few structures under autonomic control receive innervation from only one division.
What is an example
Ex; blood vessels, which are innervated exclusively by sympathetic nerves.
There are three basic patterns of autonomic innervation and regulation:
- Innervation by both divisions of the autonomic nervous system in which the effects of the two divisions are opposed
- Innervation by both divisions of the autonomic nervous system in which the effects of the two divisions are complementary
- Innervation and regulation by only one division of the autonomic nervous system.
Feedback regulation
is a process that allows a system to adjust itself by responding to incoming information.
Synapse
junction (synapse) between these two neurons
Ganglion
a mass of nerve cell bodies.
Preganglionic neurons,
The neurons that go from the spinal cord to the parasympathetic ganglia
postganglionic neurons.
the neurons that go from the ganglia to effector organs
Neurons leading from ganglia to effector organs are termed
postganglionic neurons
The anatomy of the parasympathetic nervous system offers two general sites at which drugs can act:
- The synapses between preganglionic neurons and postganglionic neurons
- The junctions between postganglionic neurons and their effector organs.
Neurons leading from the spinal cord to the sympathetic ganglia are termed
preganglionic neurons
What does the medulla of the adrenal gland release for the sympathetic nervous system:
releasing epinephrine into the bloodstream,
As with the parasympathetic nervous system, drugs that affect the sympathetic nervous system have two general sites of action:
- the synapses between preganglionic and postganglionic neurons (including the adrenal medulla), and
- The junctions between postganglionic neurons and their effector organs.
How many neurons are involved for somatic nervous system
there is only one neuron in the pathway from the spinal cord to the muscles innervated by somatic motor nerves.
Having to do with administering drugs, how does having only 1 neuron involved in somatic motor nerves cause effects?
Because this pathway contains only one neuron, peripherally acting drugs that affect somatic motor system function have only one site of action: the neuromuscular junction (i.e., the junction between the somatic motor nerve and the muscle).
The PNS employs three neurotransmitters:
- Acetylcholine
- Norepinephrine
- Epinephrine
- Dopamine- may also serve as a PNS transmitter, but this role has not been demonstrated conclusively
What is the transmitter employed at most junctions of the PNS?
Acetylcholine
Acetylcholine is the transmitter released by (5 things)
- All preganglionic neurons of the parasympathetic nervous system,
- All preganglionic neurons of the sympathetic nervous system
- All postganglionic neurons of the parasympathetic nervous system,
- All motor neurons to skeletal muscles,
- Most postganglionic neurons of the sympathetic nervous system that go to sweat glands.
Norepinephrine
Norepinephrine is the transmitter released by practically all postganglionic neurons of the sympathetic nervous system.
What is the major transmitter released by the adrenal medulla?
Epinephrine
(The adrenal medulla also releases some norepinephrine.)
