Ch5 THE AUTONOMIC NERVOUS SYSTEM Flashcards
The autonomic nervous system (ANS)
independently functioning systems that helps maintain homeostasis in the body by controlling involuntary muscles and glands.
small sensory aspect to the ANS that consists of sensory neurons
Composed of sympathetic and parasympathetic
always two neurons between the CNS and the effector. The first neuron is called the preganglionic neuron and is myelinated, whereas the second is called the
postganglionic neuron and is unmyelinated
The peripheral nervous system
incoming or afferent division that is sensory and sends messages to the brain and spinal cord
outgoing or efferent division that is motor and sends messages away from the brain and spinal cord
motor division
controls two parts of the peripheral nervous system: the somatic motor division, which controls the voluntary muscles, and the autonomic system, which is
involuntary
parasympathetic
SLUDD (Salivation, Lacrimation, Urination, Digestion, and Defecation)
Rest and Digest
The ganglia are close to the organs, and the axons of the preganglionic neurons are long, allowing organs to be stimulated individually as it would be inconvenient if they were all activated simultaneously. The neurotransmitter of the postganglionic neurons of the parasympathetic nervous system is ACh, and the receptors are muscarinic-cholinergic.
sympathetic
flight, fight, or fright
ganglia are close to the CNS; so the axons of the preganglionic neurons are short. Beneficial when a message has to be distributed quickly, because
the postganglionic neurons can branch extensively and spread to
numerous organs, and the target organs are stimulated simultaneously.
The neurotransmitter in the ganglia is ACh, and the receptor is nicotiniccholinergic.
The neurotransmitter of the postganglionic neuron is norepinephrine; the
receptors are α- or β-adrenergic receptors. The widespread activation
of the sympathetic nervous system is necessary to allow a coordinated
response to the sympathetic stimulus. To ready the body for the “flight
and fright” response, bronchioles need to be dilated, the heart has to
increase both its rate and force, and blood has to be moved from the skin
and viscera to be available for the anticipated exertions. These changes
must occur at the
somatic motor nerve
under voluntary control
has only one neuron originating in the central nervous system (CNS) and sends one heavily myelinated axon directly to a striated muscle (the effector). There are no ganglia, and the only neurotransmitter used is acetylcholine (ACh), which interacts with a nicotinic receptor
Why is a newborns HR thchychardic?
sympathetic input into the heart is not moderated yet as the parasympathetic input is not fully developed.
chronotropic effect
Something effecting the rate of contractions
sympathetic input of the heart speeds up the heart rate - a positive chronotropic effect
parasympathetic input slows the heart rate - a negative chronotropic effect
Inotropic effect
something effecting the force of contractions
sympathetic input of the heart increases the force of heart contractions - a positive inotropic effect
parasympathetic input decreases the force of contractions - a negative inotropic effect
How many typed of receptors are in the ANS?
2
Cholinergic receptors and Adrenergic receptors
Cholinergic receptors
There are two types of cholinergic receptors.
Nicotinic receptors, found in sympathetic and parasympathetic ganglia (ACh [or nicotine] stimulation leads to both sympathetic and parasympathetic effects)
Muscarinic receptors, found in all parasympathetic target organs
short time of activation because ACh breaks down rapidly due to the acetylcholinesterase in the synapse.
Adrenergic Receptors
There are two subtypes of adrenergic receptors.
α-receptors, which generally stimulate contractions
β-receptors, which generally inhibit contractions (except for
heart contractility)
2 types of receptors are necessary so the widespread activation of the SNS can constrict in some areas while dilating in others
Stimulation leads to relatively long-term activation of the neurons, and the breakdown or removal of the neurotransmitter is slow compared
to ACh. The lengthy activation of the neurons, combined with the large
spread of the SNS stimulation, means that sympathetic effects last a
relatively long time.
α-receptors
α1 - causes smooth muscle contractions and found mostly in blood vessels (but not heart)
α2 - presynaptic receptors and promote clotting
β-receptors
β1 - increases rate and force of heart contractions and causes relaxation in blood vessels of the heart (need more space for that extra blood) (β1 - one heart)
β2 - relaxed bronchioles, uterus and other sympathetic target organs (β2 - two lungs)
β3 - Increases lipolysis (break down fat for energy)
visceral afferents / referred pain
visceral afferents are all sympathetic nerves; thus, they enter the spine at the thoracic and lumbar levels like the sympathetic motor nerves.
They sending information about mechanical, chemical, and thermal stimuli to the CNS, particularly when these stimuli are likely to cause tissue damage.
The visceral afferents travel in close proximity with somatic sensory afferents, and the pain message will often be interpreted as arising from the area innervated by the somatic nerve. Because the visceral pain is detected at a site remote to the actual site of stimulation, it is called referred pain.
