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What is the primary function of the thoracolumbar system?
How do postganglionic fibers reach effector organs?
Which of the following organs is controlled solely by the sympathetic division?
What is the role of the adrenal medulla in the sympathetic system?
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What is the precursor molecule for the production of neurotransmitters in the sympathetic system?
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What is the term for the basal rates of the sympathetic and parasympathetic systems?
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What happens to blood vessels when there is a decrease in sympathetic stimulation or tone?
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What happens to the pupil when there is a decrease in parasympathetic tone?
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What is the effect of stimulating Beta 2 and Beta 3 receptors?
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What is a characteristic of the parasympathetic system?
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What is the function of parasympathetic tone in relation to heart rate?
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What is NOT a function of parasympathetic tone in relation to digestion?
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What is the enteric nervous system responsible for?
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What is a component of the enteric nervous system?
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What is the effect of stimulating Alfa 1 receptors?
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What is the parasympathetic system also known as?
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What type of sensory information do nerve endings in the gut wall and mucosa convey to the intrinsic neural network?
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What is the function of NANC fibers in the GI tract?
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What is the role of mechanoreceptors in blood pressure control?
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Which of the following is an autonomic reflex activity controlled by the parasympathetic system?
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What is the function of the ANS in homeostatic reflexes?
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What is the importance of maintaining sufficient brain blood flow?
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Which of the following is NOT a part of the PLR reflex arc?
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What is the function of the parasympathetic nucleus of the oculomotor nerve (CN3) in the PLR reflex arc?
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What is the difference between direct PLR and consensual PLR?
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What is the cause of Horner's syndrome?
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What is the role of baroreceptors in the baroreceptor reflex?
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What is the effect of a decrease in sympathetic stimulation on the pupillary sphincter muscle?
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Which of the following is NOT a brainstem center for integration in the PLR reflex arc?
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What is the term for the PLR response that occurs in the non-illuminated eye?
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What is the common site of injury for Horner's Syndrome?
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Which type of Horner's Syndrome is caused by damage between the brain and spinal cord?
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What is the 2nd order neuron responsible for in Horner's Syndrome?
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What is the most common form of Horner's Syndrome in dogs and cats?
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What can cause 2nd order Horner's Syndrome?
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What is the 3rd order neuron responsible for in Horner's Syndrome?
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Study Notes
Sympathetic System: General Info
- The sympathetic system prepares the body for emergency situations, known as the "fight or flight" system, and is composed of the thoracolumbar system.
- Postganglionic fibers reach effector organs by accompanying the vasculature supplying them and are widely distributed as blood vessels.
- Some effector organs are controlled solely by the sympathetic division, such as sweat glands, piloerector muscles, and most blood vessels.
- The adrenal medulla is essentially a postganglionic ganglia/neuron of the sympathetic system that secretes neurotransmitters (epinephrine/adrenaline and norepinephrine/noradrenaline) into the bloodstream.
- Neurotransmitters are produced by the chromaffin cells from the amino acid tyrosine and bind to adrenergic receptors.
Sympathetic and Parasympathetic Tone
- The sympathetic and parasympathetic systems are continually active, with basal rates known as "tone".
- Tone allows a single nervous system to both increase and decrease the activity of a stimulated organ.
- For example, most blood vessels lack parasympathetic innervation, and their diameter is regulated by sympathetic nervous system input, so they have a constant state of sympathetic tone.
- A decrease in sympathetic stimulation or tone allows vasodilation.
Receptors
- Stimulation of Beta 2 and Beta 3 receptors causes stimulated lipolysis in adipose tissue, increasing fatty acid availability.
- Stimulation of Alfa 1 receptors causes dilated pupils.
Parasympathetic System
- The parasympathetic system is known as the "rest and digest" system, and it involves the craniosacral system which conserves and restores energy sources of the body.
- Preganglionic fibers are relatively long, projecting to ganglia located in the vicinity of or in the wall of their target tissues.
- Postganglionic neurons have short axons.
- The parasympathetic system does not innervate structures of the body wall and extremities.
- The parasympathetic system has a greater degree of independent control as well as more precise control of tissues and organs, compared to the sympathetic division.
Parasympathetic Tone
- Parasympathetic tone is generally concerned with restorative aspects of daily living.
- For example, parasympathetic tone lowers blood pressure by slowing down the heart rate and decreasing the force of contraction of the heart.
- Parasympathetic tone enhances digestive activity by:
- Increasing blood flow to the GI tract
- Increasing intestinal motility
- Stimulating secretion of digestive systems
- Relaxing the pyloric sphincter
Enteric Nervous System
- The enteric nervous system is an intrinsic nervous system located in the walls of the GI system that mediates the regulation of GI physiology (secretion, motility, nutrient absorption).
- The enteric nervous system contains sensory and motor components, and has a complex network that includes the myoenteric plexus and submucosal plexus.
- The enteric nervous system has nerve endings in the gut wall and mucosa that convey chemical, mechanical, and stretch sensory information to the intrinsic neural network.
- The PSNS and SNS innervation appear to modulate the enteric nervous system in a regulatory manner.
NANC Fibers
- NANC (non-adrenergic, non-cholinergic) fibers do not exhibit the histochemical characteristics of cholinergic or adrenergic fibers.
- The enteric nervous system is extensively innervated by NANC fibers, which are very important in the physiological regulation of the GI tract, genitourinary tract, and selected blood vessels.
- A good example of NANC fibers are those producing nitric oxide (NO).
Autonomic Reflexes
- The ANS participates in many homeostatic reflexes such as blood pressure control and PLR.
- Blood pressure control is very important to maintain sufficient brain blood flow.
- Stretch receptors in the internal carotid artery and aorta detect systemic blood pressure.
- Mechanoreceptors (like baroreceptors) act as physiological receptors.
Pupillary Light Reflex (PLR)
- PLR is an autonomic reflex activity controlled by the parasympathetic system.
- The PLR is a reflex arc composed of:
- Receptors for light (located in the retina) which act as photoreceptors
- Afferent neurons such as the optic nerve (CN2)
- Brainstem centers for integration, such as the pretectal nucleus and parasympathetic nucleus of the oculomotor nerve (CN3)
- Efferent neurons such as the oculomotor nerve (CN3)
- Effector organs such as the pupillary sphincter muscle contracting (miosis) under bright light
- Direct PLR leads to miosis in the illuminated eye.
- Consensual/Indirect PLR leads to miosis in the eye that is not illuminated.
Baroreceptor Reflex
- The baroreceptor reflex is a reflex arc composed of:
- Baroreceptors which are receptors for blood pressure
- Afferent neurons which carry information to the medulla oblongata
- Brain stem centers (medulla) which process information and coordinate an appropriate response
- Efferent neurons which have sympathetic and parasympathetic innervation
- Effector organs which direct changes in the heart and blood vessels to increase or decrease blood pressure
Horner's Syndrome
- Horner's syndrome is due to decreased sympathetic stimulation of smooth muscle of the eye and periorbita.
- Horner's syndrome can also be caused by a middle ear issue or even otitis.
- Horner's syndrome is ultimately caused by damage or dysfunction of the sympathetic pathway as it runs through the neck or chest.
- The common site of injury for Horner's Syndrome are the cervical intumescence (and brachial plexus), and the cervical cranial ganglion (medial to middle ear).
- Issues with the following sympathetic innervations to the eye can result in Horner's Syndrome:
- Damage within the brain and spinal cord is known as 1^st^ order Horner's syndrome (central).
- 1^st^ order neuron: Hypothalamus to T1-T3
- Damage between the chest cavity and the base of the skull is known as 2^nd^ order Horner's syndrome (preganglionic).
- 2^nd^ order neuron: T1-T3 to the cervical cranial ganglion
- Damage between the base of the skull and the eye is known as 3^rd^ order Horner's syndrome (postganglionic), and is the most common form within dogs and cats.
- 3^rd^ order neuron: Cervical cranial ganglion to the eye.
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Description
Test your knowledge of the sympathetic nervous system, including its functions, anatomy, and neurotransmitters. This quiz covers the thoracolumbar system, postganglionic fibers, and the role of the adrenal medulla.
