Chapter 10 - Autonomic Nervous System Flashcards
What are the two divisions of the Nervous System?
Central and Peripheral
What are the organs that make up the CNS?
Brain and Spinal Cord
What are the two subdivisions of the PNS?
Motor Neurons and Sensory Neurons
What are the two subdivisions of Motor Neurons?
Somatic Nervous System and Autonomic Nervous System
What are the subdivisions of the Autonomic Nervous System?
Sympathetic, Parasympathetic, and enteric branches
What are Motor Neurons?
CNS to muscles and glands; control skeletal muscle contraction
What are Sensory Neurons?
Sensory organs to CNS; collect info about environment (internal and external)
Somatic Nervous System
part of Motor Neurons; controls voluntary movements
Autonomic Nervous Systems
part of Motor Neurons; system controls involuntary responses (ex. smooth muscle, cardiac muscle, and glands)
Sympathetic Division
Part of ANS; “fight or flight”
Parasympathetic Division
Part of ANS; “rest or digest”
Where do ANS neurons originate?
in the spinal cord OR in the brainstem
Where does the ANS originate?
in spinal cord w/ sympathetic division (thoracolumbar division) or parasympathetic division (craniosacral division)
ANS is under _____________ control
unconscious/involuntary
SNS is under _____________ control
voluntary
SNS targets:
skeletal muscle
acronym for parasympathetic branch
SLUD
S.L.U.D.
S: salivation
L: lacrimation
U: urination
D: defecation
pre-ganglionic fibers of the parasympathetic ANS are:
craniosacral (arise from cell bodies of nuclei of the cranial nerves and sacral spinal cord segments)
Where do SNS neuronal bodies originate?
motor cortex
Neurons of the SNS project:
directly onto skeletal muscles that are a part of a motor unit
Neurons of the ANS synapse:
in ganglia (swellings) outside of the spinal cord
Where does the parasympathetic branch of the ANS originate?
in cranial nerves from the brainstem and sacral regions of the spinal cord
Pre-ganglionic fibers in parasympathetic branch:
long and myelinated, and they synapse in ganglia near the target tissue.
Post-ganglionic fibers in parasympathetic branch:
short and un-myelinated; receive messages from pre-ganglionic fibers and innervate target tissues;
Where do the synapses occur in parasympathetic branch?
in ganglia close to target tissues
Where do the synapses occur in sympathetic branch?
in sympathetic chain ganglia
Sympathetic branch pre-ganglionic fibers:
cell bodies located in thoracic and lumbar segments of spinal cord
Sympathetic branch post-ganglionic fibers:
innervate more organs than parasympathetic branch
Sympathetic _______________ fibers can take multiple pathways.
post-ganglionic
Steps of SOMATIC REFLEX
- proprioceptive receptors signal to dorsal root neuronal cell bodies
- afferent dorsal root sensory cells send information via the posterior grey matter of spinal cord/brainstem, where they synapse onto interneurons
- cells in motor cortex project to interneurons that synapse on an alpha-motor neuron in dorsal horn
- interneurons send signals through the thalamus to the motor cortex in the cerebral cortex
- the alpha-motor neuron synapses with skeletal muscle
Steps of AUTONOMIC REFLEX
- visceral sensory receptors signal to dorsal root neurons
- dorsal root neurons send sensory information directly to CNS (no interneuron)
- efferent information is sent to hypothalamus or cranial nerve nuclei in the brainstem, or into the lower cord to pre-ganglionic neurons
- pre-ganglionic neurons project out to ganglia and synapse onto post-ganglionic cells
- post-ganglionic cells project out and synapse onto target cells.
Stereotypic responses of sympathetic division of ANS
- increased heart rate, heart contraction force, blood pressure
- vasoconstriction of most blood vessels but vasodilation in skeletal muscle, heart and lung
- mobilization of energy sources from liver, skeletal muscles, and adipocytes
- increased sweat production
- decreased food digestion
Stereotypic responses of parasympathetic division of ANS
- increased mouth saliva
- swallowing reflex
- secretion of acid and enzymes in stomach for digestion of food; increased stomach wall tone and contraction strength
- secretion of enzymes and bicarbonate-rich buffers in small intestine; increased contractions in GI tract
- control of nausea, vomiting, abdominal cramps, and diarrhea
Raynaud’s syndrome
- transient vasospasm of arteries
- fingers, toes, nose, ears, and lips
- turn white then blue
- numbness and pain
- due to hyper-activation of sympathetic nervous system causing extreme vasoconstriction of some peripheral blood vessels causing hypoxia.
Sympathetic Chain Ganglion
chain ganglion carry sympathetic post-ganglionic fibers out to target tissues
Splanchnic nerve
formed from fibers that do NOT synapse in sympathetic chain; most important structure innervated by this nerve is ADRENAL MEDULLA, made up of modified post-ganglionic sympathetic cells (secretory portion of adrenal medulla)
Cells in Adrenal Medulla
are round, lack axons and dendrites, aka chromaffin cells (release about 80% epi and 20% norepin)
Sympathetic system =
entire body
parasympathetic system =
localized to a specific origin
Tissues can be innervated by:
parasympathetic division only/ sympathetic division only/ or both
When a tissue is innervated by both parasympathetic and sympathetic divisions:
they do it through a system of ANTAGONISTIC CONTROL
Antagonistic Control
regulators have opposite effects on their target tissue
Neurotransmitters work by:
physically interacting w/ receptors on the post-synaptic membrane; they are released by neurons
3 major receptors in ANS are:
acetylcholine, epinephrine, and norepinephrine
Receptor activated by acetylcholine
cholinergic receptor (if ionotropic (ion channel) then it’s nicotinic acetylcholine receptor; if metabotropic (signaling enzymes) then it’s muscarinic acetylcholine receptor)
Receptor activated by norepinephrine or epinephrine
Adrenergic Receptors; all adrenergic receptors are metabotropic and are located on target tissues
Agonist
chemical that can bind to same receptor as a particular neurotransmitter and have the same effect
Antagonist
can also bind to same receptor as a particular neurotransmitter either at same place of nearby, but blocks the effect of the neurotransmitter
Is the parasympathetic nervous system cholinergic or adrenergic?
cholinergic;
- pre-ganglionic neurons are cholinergic
- post-ganglionic neurons are nicotinic acetylcholine receptors
- target tissues are muscarinic acetylcholine receptors (M1-M5)
Is sympathetic nervous system cholinergic or adrenergic?
it’s mixed;
- pre-ganglionic neurons are cholinergic
- post-ganglionic neurons are adrenergic, and release norepinephrine/epi. onto target tissues
- 5 adrenergic receptor subtypes: alpha 1 and 2, and beta 1-3.
Activation of alpha 1 and beta 1 receptors
- stimulatory response
- directly stimulated by NE released from post-ganglionic sympathetic nerves
Activation of alpha 2 and beta 2 receptors
- variation between target cells
- do NOT associate w/ post-ganglionic sympathetic synapses and are activated by Epi. released from adrenal medulla
Autonomic Reflex Sensory Receptors
Baroreceptors, Chemoreceptors, Carotid Body, Osmoreceptors
Baroreceptors
specialized stretch receptors in walls of aorta and carotid sinuses. Sense the stretch of those organs when blood volume/pressure changes
Chemoreceptors
respond to chemical stimuli; found throughout body
Carotid Body
cluster of chemoreceptors near bifurcation of carotid artery that monitors arterial blood pH, CO2, and partial pressure of O2
Osmoreceptors
found in hypothalamus and detect changes in osmotic pressure and tonicity of CSF.
ANS Integration Centers
- scattered throughout brainstem, hypothalamus, and spinal cord
- important for homeostasis
- most important is hypothalamus
