Autonomic Nervous System Flashcards
Why is it important to study the autonomic nervous system?
It’s very important in homeostasis (there’s a tightly controlled internal environment), drug actions (some classes of drugs work on the ANS) and drug side effects (over 200 drugs that don’t work primarily at this site have side effects due to activation of the ANS
What are the two main systems that control body functions?
The endocrine system (hormones, e.g., insulin, are released into the blood)
The nervous system (electrical transmission with chemical “links”, i.e., neurotransmitters)
Explain how the peripheral nervous system is organized/divided?
The PNS has motor nerves and sensory nerves (efferent and afferent, respectively). There are two kinds of two kinds of PNS motor nerves: somatic and autonomic. Within the autonomic nervous system, there is sympathetic nerves, enteric nerves and parasympathetic nerves
How do sensory nerves work?
They are also known as the “afferent” division (flows to the CNS)
Information from the periphery (sensory) goes to the spinal cord and/or to the central nervous system
How do motor nerves work?
They are also know as the “efferent” division (flows to the CNS)
Information from the CNS or spinal cord goes to the periphery. This results in some peripheral change (motor), such as altered muscle activity, somatic (skeletal muscles), autonomic (smooth muscles, i.e., gut, bronchiolar; cardiac muscle i.e., atria ventricles)
What makes the somatic nervous system different form the autonomic nervous system?
Largely not automatic
Consciously controlled functions
Movement - locomotion, respiration, posture
Involves electrical and chemical transmission
What makes the autonomic nervous system different from the somatic nervous system?
“Automatic” and involuntary (you process information and the ANS response accordingly)
It controls organs and glands
It involves electrical and chemical transmission
Control of the internal environment/milieu (Heart, blood vessels, salivation, digestion, muscle tone (intestinal, urinary, bronchioles), accommodation of the eye (near/far vision, etc.)
There are two main divisions: sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS)
What do the SNS and the PNS have in common?
Both are efferent (motor) systems (visceromotor)
Both involve regulation of the “internal” environment generally outside of our conscious control: “autonomous”
Both involve 2 neutrons that synapse in a peripheral ganglion
They innervate glands, smooth muscle, cardiac muscle
What is unique about the basic function of SNS?
It is widespread of local
It’s “ergotropic”, meaning leading to energy expenditure
It’s involved in the fight or flight response
It causes cardiac stimulation, increases blood sugar, causes cutaneous vasoconstriction
The preganglionic axons are short and the postganglionic axons are long (when the SNS fires, it affect pretty much all the organs)
What is unique about the basic function of the PNS?
It’s “trophotropic”, meaning leading to growth
It is energy conserving; slows the heart rate, stimulates digestion
The preganglionic axons are long and the postganglionic axons are short (allows the PNS to control organs separately)
Where are the preganglionic cell bodies of the PNS and SNS found? Why is this important?
The sympathetic preganglionic cell bodies are in the thoracolumbar segments of the spinal cord.
The parasympathetic preganglionic cell bodies are in the brain (CN III, VII, IX, X) and the sacral sacrel segments of the spinal cord.
This is important because it has implications for spinal cord injury (e.g., spinal cord injury in the lower thoracic region could result in a loss of SNS function in the digestive system but not PNS, leading to an overactive digestive system)
What neurotransmitters do the preganglionics of the SNS and the PNS release?
All preganglionics release acetylcholine (ACh) and are excitatory
What neurotransmitters do postganglionics of the SNS and the PNS release?
Sympathetic postganglionics release norepinephrine and they are excitatory or inhibitory
Parasympathetic postganglionics release ACh and are excitatory or inhibitory
Excitation or inhibition is a receptor-dependent and receptor-mediated response
What are the target tissues of the SNS?
Organs of the head, neck, trunk and external genitalia Adrenal medulla Sweat glands in the skin Arrector muscles of hair ALL vascular smooth muscle
The SNS is distributed to essentially all tissues (because of vascular smooth muscle)
What are the target tissues of the PNS?
Organs of the head, neck, trunk and external genitalia
The PNS never reaches the limbs or body wall (except for external genitalia)
