Chapter 14- The autonomic nervous system Flashcards
Somatic nervous system
Branch of the PNS, it’s a system responsible for voluntary muscle movements and reflex arcs. Mostly efferent.
Somatic refers to
Skeletal muscle tissue
Which neurotransmitter is released by the SNS?
Acetylcholine, it has an excitatory effect at is released at all synapses in the SNS
Autonomic nervous system
A branch of the PNS, almost all effectors are visceral (involuntary). Branches into the sympathetic and parasympathetic divisions
Autonomic nervous system function
Helps maintain a stable internal environment. Regulation of heart rate, blood vessel diameter, pupil size, body temperature, increases/decreases stomach secretions
Effector organs of the SNS
Skeletal muscle tissue
Effector organs of the ANS
Cardiac muscle, smooth muscle, and glands
SNS efferent pathways
A single neuron extends from CNS to effector. Motor neuron cell bodies are located in the CNS, axons in PNS extend to skeletal muscle. Thick and heavily myelinated fibers.
ANS efferent pathways
The ANS has a two neuron chain to reach effector, consists of preganglionic and postganglionic neurons.
Preganglionic neuron (ANS)
Cell body is located in the CNS, preganglionic axon synapses with second motor neuron. Thin, lightly myelinated fibers
Postganglionic neuron (ANS)
Cell body is located outside the CNS, postganglionic axon extends to effector organ. Thin, nonmyelinated fibers
ANS ganglia
Ganglia in the ANS are sites of synapse between the preganglionic neuron and the postganglionic neuron. Entirely motor ganglia.
Which neurotransmitters are released by the ANS?
Releases norepinephrine or acetylcholine- effect can be excitatory or inhibitory depending on receptors on the effector organ in ANS.
Parasympathetic division function
“Rest and digest”- keeps body energy use as low as possible when we are relaxed. Directs “housekeeping” activities- digestion, elimination of waste, low blood pressure and heart rate, constricted pupils.
Where do the fibers of the parasympathetic nervous system originate?
The brain and sacral spinal cord. Preganglionic fibers are long, postganglionic fibers are short. The ganglia will always be closer to the effector organ than they are to the nervous system
Cauda equina
Sacral spinal cord
Cranial portion of the parasympathetic nervous system
Will serve the head, neck, thorax, and abdomen. Preganglionic fibers run in oculomotor, facial, glossopharyngeal, and vagus cranial nerves
Oculomotor nerve
Innervates smooth muscle in the eyes and muscle associated with the lens. Effect- lens is stimulated to become thicker
Facial nerve
Stimulates large glands of the head (salivary glands, nasal glands, lacrimal glands)
Glossopharyngeal nerve
Activates parotid salivary gland. The parotid salivary gland is the largest one
Vagus nerve
Provide fibers to neck and almost every organ in the thoracic and abdominal cavities. The vagus nerve is large and complex, so we see plexus formation
Cardiac plexus
supplies fibers to the heart, division of the vagus nerve
Pulmonary plexus
supplies fibers to the lung, division of the vagus nerve
Esophageal plexus
Serves the esophagus. The fibers from the esophageal plexus also extend into the abdominal cavity- innervates liver, gallbladder, stomach, small intestine, pancreas, and proximal half of large intestine
When is the sympathetic nervous system activated?
“Fight or flight”: activated when we are excited/scared/embarrassed
Sympathetic nervous system function
Mobilizes the body- constriction of visceral blood vessels, dilates bronchioles of lungs, increases glucose release to blood, pupils dilate, etc.
Where do the fibers of the sympathetic nervous system originate?
Thoracolumbar region of spinal cord (T1-L2)
Preganglionic fibers are short, postganglionic fibers are long. Cell bodies of this division form lateral horns of spinal cord
Where are the ganglia of the SNS located?
Close to the spinal cord
What areas does the sympathetic nervous system innervate?
Innervates smooth muscle, cardiac muscle, and glands in body cavities. It also innervates smooth muscle and glands in superficial regions. Sweat glands, arrector pili, smooth muscle in blood vessel walls
Sympathetic trunk
Allows nerve fibers to travel to spinal nerves that are superior and inferior to the one in which they originated. Found on both sides of the spinal cord
What happens to preganglionic fibers when they leave the spinal cord (SNS)?
Fibers then pass through white ramus communicans, enter sympathetic trunk ganglion
White ramus communicans
White rami communicans carry preganglionic fibers to the sympathetic trunk
Sympathetic trunk ganglion
Sympathetic trunk ganglion are like a string of pearls going down both sides of the spinal cord
How can preganglionic and postganglionic fibers can form synapses at the trunk ganglion (3 possibilities)?
- Preganglionic neuron and postganglionic neuron synapse at the same level.
- Preganglionic neuron and postganglionic neuron synapse at a higher or lower level
- Preganglionic neuron and postganglionic neuron synapse at a distant collateral ganglion in the abdomen and pelvis
What happens when the preganglionic neuron and postganglionic neuron synapse at the same level?
Preganglionic neuron goes straight out through the side of the ventral root to synapse. This is the most simple way to form a synapse
What happens when the preganglionic neuron and postganglionic neuron synapse at a higher or lower level?
Travels through the spinal nerve and white ramus communicans, travels up or down to a higher or lower ganglion and forms a synapse there.
What happens when the preganglionic neuron and postganglionic neuron synapse at a distant collateral ganglion in the abdomen and pelvis?
At the sympathetic trunk, the fiber extends straight through the trunk to a distant location
Sympathetic pathways with synapses in trunk ganglia
If synapse forms in trunk ganglia, postganglionic fibers enter ventral or dorsal ramus of adjoining spinal nerves via gray rami communicans- travel to effectors from here.
Gray rami communicans
Carry postganglionic fibers from sympathetic trunk ganglion to periphery
Superior cervical ganglion function
Serves skin and blood vessels of the head, stimulate dilator muscles of eyes, inhibits nasal and salivary glands, innervates muscle to upper eyelid, sends branches to heart
Sympathetic pathways to the head
Preganglionic fibers emerge from T1-T4, synapse with postganglionic fibers at superior cervical ganglion
Sympathetic pathways to the thorax
Preganglionic fibers emerge from T1-T6. Most postganglionic axons pass through cardiac, pulmonary, and esophageal plexuses to the effector organ. These plexuses are formed from the parasympathetic division, the sympathetic division is hitching a ride
Sympathetic pathways with synapses in the collateral ganglia
Preganglionic fibers from T5-L2 synapse in collateral ganglia, form splanchnic nerves.
Splanchnic nerves function
Serve abdominal viscera. These ganglia usually reach the effector organ by traveling with a blood vessel.
Sympathetic pathways to the abdomen
Fibers T5-L2 innervate the abdomen. Function- serve the stomach, most of the intestines, liver, spleen, and kidneys
Sympathetic pathways to the pelvis
Fibers T10-L2 innervate the pelvis. Function- serves the bladder, reproductive organs, and the distal half of the large intestine
How does sympathetic innervation effect the abdominopelvic visceral organs?
The effect of sympathetic innervation on the abdominopelvic visceral organs is mostly inhibitory. Don’t want to digest things during the fight or flight response
5 components of visceral reflex arcs?
- Receptor in viscera
- Sensory neurons
- Integration center
- Motor neurons
- Visceral effector
Sensory neurons in visceral reflex arcs
These neurons are non-encapsulated nerve endings. Function- send sensory information about changes in chemical composition, stretch, temperature, and irritation of viscera.
Motor neurons in visceral reflex arcs
These neurons are preganglionic neurons and postganglionic neurons
What is the visceral effector in reflex arcs? (3)
Smooth muscle, cardiac muscle, and glands
How are the brain and spinal cord involved in visceral reflex arcs?
The brain and spinal cord aren’t really involved, GI tract is pretty independent.
Acetylcholine (ACh)
Effect is not entirely excitatory or inhibitory- depends on the receptor it binds. Released by cholinergic fibers at all ANS preganglionic axons and all parasympathetic postganglionic axons at synapse with effector.
Cholinergic receptors that bind ACh (2)
- Nicotinic receptors
2. Muscarinic receptors
Nicotinic receptors location
Found on all postganglionic neurons (sympathetic and parasympathetic), hormone producing cells of the adrenal medulla, and sarcolemma of skeletal muscle cells (skeletal muscle isn’t really part of the ANS).
What is the effect of ACh on nicotinic receptors?
Binding of ACh here is always stimulatory
Location of muscarinic receptors
Found on all parasympathetic effectors and some sympathetic effectors
Effect of ACh on muscarinic receptors
Binding of ACh here is stimulatory or inhibitory. Binding of ACh to muscarinic receptors of the heart is inhibitory, but binding of ACh to muscarinic receptors of the smooth muscle of the gastrointestinal tract is stimulatory
Where is norepinephrine released?
Released by adrenergic fibers at sympathetic postganglionic axons
Types of adrenergic receptors that bind NE (2)
- Alpha receptors
2. Beta receptors
Alpha receptors
Locations- all sympathetic target organs
Beta receptors
Locations- heart, adipose tissue, kidneys, lungs, blood vessels
Effect of NE and epinephrine
Binding of NE or epinephrine can be stimulatory or inhibitory. Example- NE binding at beta receptors of the heart increases activity, but epinephrine binding at beta receptors of bronchioles causes dilation
Antagonistic interactions of sympathetic and parasympathetic divisions
Divisions have opposite effects- whichever dominates will influence overall organ activity. Increased sympathetic activity= increased heart rate, dilated airways, decreased digestion and elimination. Increased parasympathetic activity= resting heart rate and airway diameter, increased elimination and waste.
Vasomotor (sympathetic) tone
Continuous partial constriction of blood vessels. Sympathetic fibers supply blood vessels and control blood vessels diameter
How does blood pressure influence the activity of vasomotor fibers?
If blood pressure is low, vasomotor fibers fire more rapidly, so blood vessels constrict to increase blood pressure. If blood pressure is high, vasomotor fibers fire less rapidly, so blood vessels dilate to decrease blood pressure
Parasympathetic tone
Present mostly in cardiac muscle tissue, smooth muscle tissue of digestive and urinary organs . Effect- slows heart rate, maintains normal activity of digestive and urinary organs. Sympathetic division can override parasympathetic tone, however.
Thermoregulatory response to heat
This is a unique role of the sympathetic division. In response to heat, blood vessels dilate and sweat glands are activated. Blood vessels will constrict in response to cold, so blood goes internally to warm the organs
Renin release from kidneys
This is a unique function of the sympathetic division. Renin is a hormone produced by cells in the kidneys that increases blood pressure.
How does the sympathetic division change the metabolism? (3)
- Increases metabolic rate of cells
- Raises blood glucose levels- to produce ATP and use skeletal muscle tissue
- Mobilizes fats used fuel use
How does the parasympathetic division exerts highly localized, short lived control?
One preganglionic neuron synapses with one (or a few) postganglionic neurons. In addition, all parasympathetic fibers release ACh- quickly broken down by acetylcholine esterase
How does the sympathetic division exert diffuse, long lasting control?
Preganglionic neurons synapse with multiple postganglionic neurons Also, NE and epinephrine prolong effects of sympathetic division activation. This is why is takes a while to come down from a stressful/traumatic event.
What area of the brain controls the ANS?
Hypothalamus
Anterior hypothalamic areas
Oversee parasympathetic division
Posterior hypothalamic areas
Oversee sympathetic division
What ANS functions does the hypothalamus control?
Coordinates heart activity, blood pressure, body temperature, water balance, endocrine activity
Why do emotional reactions activate the sympathetic division?
The hypothalamus is a part of the limbic system. Therefore, emotional reactions to fear, danger, and stress activate the sympathetic division
Hypertension is caused by
An overactive sympathetic vasoconstrictor response. This means that the heart must work harder to circulate blood through narrow blood vessels
What other health problems can be caused by hypertension?
Heart disease, enlarged arteries, and kidney failure. Kidneys filter your blood to produce urine. If you have a high pressure of blood going through the capillaries in the kidneys, it will rip them open and the kidney will lose function
How is hypertension treated?
Adrenergic receptor blocking drugs and diuretics (reduce blood volume). Adrenergic receptor blockers stop NE from binding from NE receptors at the heart, blocking sympathetic influence and lowering heart rate.
Raynaud’s disease is caused by
Caused by exaggerated vasoconstriction response due to cold or emotional stress
Effects of Raynaud’s disease
Effect- skin of fingers and toes becomes pale, skin can eventually become cyanotic and painful. Cyanotic tissue is not dead tissue- restoring blood flow will restore normal function. However, tissue will be black/necrotic if it goes without blood flow for too long. Severity can be minimal or more extreme
What group of individuals are affected by autonomic dysreflexia?
Affects individuals who are quadriplegic or have spinal cord injuries above T6
What causes autonomic dysreflexia?
Caused by uncontrolled activation of autonomic neurons. Usually triggered by some type of pain stimulus to the skin or overfilled visceral organ (like the bladder).
What is the effect of autonomic dysreflexia?
Arterial blood pressure skyrockets to the point that it can become deadly within minutes. Can rupture blood vessels in the brain, causing hemorrhagic stroke. Symptoms- headache, flushed face, sweating above injury, cold/clammy skin below injury.
