CH15: The Autonomic Nervous System Flashcards
What are the two divisions of the autonomic nervous system and what do they each do?
The ANS consists of two main divisions, the sympathetic nervous system and the parasympathetic nervous system. Most organs receive nerves from both these divisions, and arrangement known as dual innervation.
The sympathetic nervous system promotes the flight-or-fight response, which prepares the body for emergency situations. The flight or fight response is named so because because its stimulation leads to increased alertness and metabolism to be ready for an emergency
For example, the neurons of the parasympathetic division increase heart
The parasympathetic nervous system enhances rest-and-digest activities, which conserve and restore body energy during times of rest or digesting a meal
For example, neurons of the sympathetic nervous system slow the heart rate down conserve energy
What are the main input and output components of the autonomic nervous system
the axon of a single myelinated somatic neuron extends from the CNS all the way to skeletal muscle fibers in its motor unit. By contrast, most autonomic motor pathways consist of two motor neurons in series, one following the other.
The first neuron, the preganglionic neuron, has its cell body in the CNS; its myelinated axon extends from the CNS to an autonomic ganglion (recall that a ganglion is a collection of neuronal cell bodies In the PNS)
The second neurons, the postganglionic neuron, has its cell body in the ganglionic neuron, where it can synapse with the preganglionic neuron, and its axon extends from the autonomic ganglion to the effector.
Where are the cell bodies of preganglionic nerves of the sympathetic and parasympathetic region located? What names arise from these locations?
In the sympathetic division the preganglionic neurons have their cell bodies in the lateral horns of the gray matter in the 12 thoracic segment (T1-T12) and first 2 or 3 lumbar segments (L1-L3). For this reason, the sympathetic division is known as the thoracolumbar division and the axons of the sympathetic preganglionic neurons are known as the thoracolumbar outflow
Cell bodies of preganglionic neurons of the parasympathetic division are located in the nuclei of four cranial nerves in the brainstem (II,VII,IX and X) and in the gray matter of the second through fourth sacral segments. Hence, the parasympathetic division is known as the craniosacral division, and the axons of the parasympathetic preganglionic neurons are referred to as the craniosacral outflow.
What are the regions where sympathetic ganglion are lcoated.
There are two major types of sympathetic ganglia:
Sympathetic trunk ganglia and prevertebral ganglia.
Sympathetic trunk ganglia, also called vertebral chain ganglia, lie in a vertical row on either side of the vertebral column. These ganglia extend from the base of the skull to the coccyx to the coccyx (remember, this is called the thoracolumbar division).
What do the sympathetic trunk ganglia inerrvate? Name the ones that have names lol
Postganglionic axons from sympathetic trunk ganglia primarily innervate organs above the diaphragm, such as the head, neck, shoulders, and heart.
Sympathetic trunk ganglia in the neck have specific names. They are the superior, middle, and inferior cervical ganglia.
The remaining sympathetic trunk ganglia do not have individual names.
What do the prevertebral ganglia innervate? Name the ones that have names
The second group of sympathetic ganglia, the prevertebral ganglia, lies anterior to the vertebral column and close to the large abdominal arteries.
In general, the postganglionic axons of prevertebral ganglia innervate organs below the diaphragm
There are 5 major prevertebral ganglia.
The celiac ganglion inferior to the diaphragm
The superior mesenteric ganglion, near upper abdomen
The inferior mesenteric ganglion, near middle of abdomen
The aorticorenal ganglion
The renal ganglion, along with the aorticorenal ganglion, both are near the kidney
What are the location of parasympathetic ganglia and name some common ones.
Preganglionic axons of the parasympathetic division synapse with postganglionic neurons in parasympathetic ganglia. Most of these ganglia are located close to or actually in the wall of a visceral organ. Parasympathetic ganglia in the head (recall this is the craniosacral division) have specific names, they are:
The ciliary ganglion
The pterygopalatine (ter′-i-gō-PAL-a-tīn)
The submandibular ganglion
The otic ganglion
Which neurons in the ANS release ACh and which release NE and epinephrine
All parasympathetic and sympathetic preganglionic neurons release Ach, while most sympathetic postganglionic neurons release NE and all parasympathetic postganglionic neurons release Ach
Sympathetic postganglionic neurons that innervate most sweat glands release Ach
Chromaffin cells of suprarenal medullae release both epinephrine and norepinephrine
Where are the types of cholinergic receptors found and what are their main functions.
The two types of cholinergic receptors, both of which bind ACh, are nicotinic receptors and muscarinic receptors
Nicotinic receptors are present in the plasma membrane of dendrites and cell bodies of both sympathetic and parasympathetic postganglionic neurons, the plasma membranes of chromaffin cells and in the motor end plate at the neuromuscular junction
Muscarinic receptors are present in the plasma membranes of all effectors (smooth/cardiac muscle and glands) innervated by postganglionic axons. In addition, most sweat glands receive their innervation from cholinergic sympathetic postganglionic neurons and possess muscarinic receptors
Activation of nicotinic receptors by ACh causes depolarization and thus excitation of the postsynaptic cell, which can be a postganglionic neuron, an autonomic effector, or a skeletal muscle fiber. Because acetylcholine is quickly inactivated by the enzyme acetylcholinesterase (AChE), effects triggered by cholinergic neurons are brief
Where are the types of adrenergic receptors found and what are their main functions.
In the ANS, adrenergic neurons release norepinephrine (NE), also known as noradrenaline. Most sympathetic postganglionic neurons are adrenergic
Adrenergic receptors bind both norepinephrine and epinephrine. The norepinephrine can either be released as a neurotransmitter by sympathetic postganglionic neurons or released as a hormone into the blood by chromaffin cells of the suprarenal medullae. Epinephrine is released as a hormone
Two main types of adrenergic receptors are found in the body, 𝛼-receptors and β-receptors which are found on visceral effectors innervated by most postganglionic axons
These receptors are further classified into subtypes, 𝛼1, 𝛼2, β1, β2 and β3
Although there are some exceptions, activation of 𝛼1 and β 1 receptors generally produces excitation and activation of 𝛼2 and β2 receptors causes inhibition of effector cells
β3 receptors are present only on cells of brown adipose tissue, where their activation causes thermogenesis (heat production).
Cells of most effectors contain either alpha or beta receptors; some visceral effector cells contain both. Norepinephrine stimulates alpha receptors more strongly than beta receptors; epinephrine is a potent stimulator of both alpha and beta receptors
What are the primary functions of the sympathetic system?
During physical or emotional stress, the sympathetic division dominates the parasympathetic division. High sympathetic tone favors body functions that can support vigorous physical activity and rapid production of ATP. At the same time, the sympathetic division reduces body functions that favor the storage of energy
Besides physical exertion, various emotions, such as fear, embarrassment, or rage, stimulate the sympathetic division. Visualizing body changes that occur during “E situations” such as exercise, emergency, excitement, and embarrassment will help you remember most of the sympathetic responses
Activation of the sympathetic division and release of hormones by the suprarenal medullae set in motion a series of physiological responses collectively called the fight-or-flight response, which includes the following effects
Pupils dilate
Heart rate, force of heart contraction, and blood pressure increase
Airways dilate, allowing faster movement of air into and out of lungs
The blood vessels that supply the kidneys and gastrointestinal tract constrict, which decreases blood flow through these tissues. The result is a slowing of urine formation and digestive activities, which are not essential during exercise
Blood vessels that supply organs involved in exercise or fighting off danger—skeletal muscles, cardiac muscle, liver, and adipose tissue—dilate, allowing greater blood flow through these tissues
Liver cells perform glycogenolysis (breakdown of glycogen to glucose), and adipose tissue cells perform lipolysis (breakdown of triglycerides to fatty acids and glycerol)
Release of glucose by the liver increases blood glucose level.
Processes that are not essential for meeting the stressful situation are inhibited. For example, muscular movements of the digestive canal and digestive secretions slow down or even stop.
What are the major functions of the parasympathetic system?
In contrast to the flight or fight responses of the sympathetic division, the parasympathetic division is characterized by rest-and-digest activities. Parasympathetic responses support body functions that conserve and restore body energy during times of rest and recovery. In the quiet intervals between periods of exercise, parasympathetic impulses to the digestive glands and the smooth muscle of the digestive canal predominate over sympathetic impulses. This allows energy-supplying food to be digested and absorbed. At the same time, parasympathetic responses reduce body functions that support physical activity.
The acronym SLUDD can be helpful in remembering 5 parasympathetic responses. It stands for salivation, lacrimation (flow of tears), urination,digestion and defecation
In addition to the increasing SLUDD responses, other important parasympathetic responses are “three decreases”: decreased heart rate, decreased diameter of airways (bronchoconstriction), and decreased diameter (constriction) of the pupils
What are the components of an automatic reflex arc? Describe their functions
Sensory receptor: Like the receptor in a somatic reflex arc, the sensory receptor in an autonomic reflex arc is the distal end of a sensory neuron, which responds to a stimulus and produces a change that will ultimately trigger nerve impulses. These sensory receptors are mostly associated with interoceptors (which respond to internal stimuli such as stretching of a visceral wall or chemical composition of a body fluid).
Sensory neuron: Conducts nerve impulses from receptors to the CNS.
Integrating center: Interneurons within the CNS relay signals from sensory neurons to motor neurons. The main integrating centers for most autonomic reflexes are located in hypothalamus and brain stem. Some autonomic reflexes, such as those for urination and defecation, have integrating centers in the spinal cord
Motor neurons: Nerve impulses triggered by the integrating center propagate out of the CNS along motor neurons to an effector. In an autonomic reflex arc, two motor neurons connect the CNS to an effector 😋😝, the preganglionic neuron conducts motor impulses from the CNS to an autonomic ganglion motor impulses from an autonomic ganglion to an effector
Effector: In an autonomic reflex arc, the effectors are smooth muscle, cardiac muscle, and glands, and the reflex is called an autonomic reflex
