Exam 2: Ch 9 ANS Flashcards
Autonomic nervous system (ANS)
manages our physiology by regulating cardiac & smooth muscles & glands that are not under voluntary control
Neurons that conduct impulses away from CNS =
= motor = efferent
2 types of Efferent neurons
- somatic pathway
2. autonomic pathway
somatic pathway
have cell bodies in CNS and send axons to skeletal muscle for voluntary control
Somatic = skeletal muscle
The pathway
(sensory neuron → CNS → motor out put neurons→ effector organ)
autonomic pathway =
sensory neuron → CNS → preganglionic neuron → postganglionic neuron → effector organ)
Autonomic ganglion
collection of cell bodies outside of CNS; located in head, neck, abdomen, and parallel to the spinal cord
Preganglionic fibers
originate in midbrain, hindbrain, upper thoracic to 4th sacral level of spinal cord
ANS Control of Muscle:
Skeletal muscle
Skeletal muscle is paralyzed without innervation,
ANS Control of Muscle:
smooth muscle and cardiac muscle
maintains resting tone (tension or contracts) in absence of nerve stimulation; ex. Heart
denervation hypersensitivity
Smooth & cardiac muscle become more sensitive when ANS input is cut
Some types of muscle are spontaneously active & contract rhythmically without ANS input
ANS input simply increases or decreases intrinsic activity but recall that ACh always excites skeletal muscle
Feature: effector organs:
- somatic and Autonomic motor?
somatic motor: skeletal muscles
autonomic motor: cardiac muscle, smooth muscles, and glands
Feature: presence of ganglia
- somatic and Autonomic motor?
somatic motor: no ganglia
autonomic motor: cell bodies of postganglionic autonomic fibers located in paravertebral (collateral) and terminal ganglia
Feature: number of neurons from CNS to effecgtor
- somatic and Autonomic motor?
somatic motor: One
autonomic motor: two
Feature: type of neuromuscular junction
- somatic and Autonomic motor?
somatic motor: specialized motor end plate
autonomic motor: none; all areas of smooth muscle cells contain receptor proteins for neurotransmitters
Feature: effect of nerve impulse on muscle
- somatic and Autonomic motor?
somatic motor: excitatory only
autonomic motor: either excitatory or inhibitory
Feature: type of nerve fibers
- somatic and Autonomic motor?
somatic motor: fast-conducting and myelinated
autonomic motor: slow-conductin: preganglionic fibers lightly myelinated but thing: postganglionic fibers unmyelinated and very thin
Feature: effect of denervation
- somatic and Autonomic motor?
somatic motor: flaccid paralysis and atrophy
autonomic motor: Muscle tone and function persist: target cells show denervation hypersensitivity
2 divisions of ANS
sympathetic & parasympathetic divisions
- usually have antagonistic effects and coordinate physiology
Both sympathetic and parasympathetic systems
• Consist of preganglionic neurons originating in CNS
- Preganglionic sympathetic fibers
* Preganglionic parasympathetic fibers
Both sympathetic and parasympathetic systems
• Consist of postganglionic neurons originating outside the CNS in ganglia
- Postgagnlionic sympathetic fibers
* Postgagnlionic parasympathetic fibers
Preganglionic fibers of sympathetic division
originate in the spinal cord between thoracic and lumbar levels
Sympathetic division mediates
“fight, flight, & stress” reactions mostly through the release of norepinephrine from postganglionic fibers and epinephrine from the adrenal medulla
Preganglionic fibers of parasympathetic division
originate in the brain and in the sacral levels of the spinal cord
Parasympathetic division mediates
“rest & digest” reactions through the release of Ach from postganglionic fibers
The 2 divisions must be balanced to
maintain homeostasis
Sympathetic Division of the ANS is also called
thoracolumbar division because its preganglionic neurons exit spinal cord from T1 to L2
Most sympathetic fibers then separate from somatic motor neurons and synapse on
postganglionic neurons within a double row of ganglia called the paravertebral ganglia
sympathetic chain of ganglia
chain of interconnected ganglia paralleling spinal cord formed by paravertebral ganglia
• Mylenated preganglionic sympathetic axons exit the
the spinal cord in the ventral roots of spinal nerves but diverge within short pathways called white rami communicantes
• Axons within each ramus enter
sympathetic chain of ganglia where they travel to ganglia at different levels and synapse with postganglionic symapthetic neurons
Axons of postganglionic neurons are
unmylenated and form the gray rami communicates as they return to spinal nerves
Since sympathetic axons form a component of spinal nerves they are
widely distributed to skeletal muscles and skin where they innervate blood vessels and other involuntary effectors
Divergence
occurs in the sympathetic chain of ganglia as preganglionic neurons branch to synapse with postganglionic neurons located in ganglia at different levels in the chain
Convergence
occurs where a postganglionic neuron receives input from a large number of preganglionic neurons
Divergence & convergence together cause
the sympathetic division to mostly act as a unit (mass activation)
Some preganglionic neurons that exit the spinal cord below the diaphram
do not synapse in the symapthetic chain of ganglia
Beyond the sympathetic chain these preganglionic fibers form
splanchnic nerves and synapse in collateral ganglion (preventral ganglia)
Postganglionic fibers that arise from collateral ganglia innervate
organs of the digestive, urinary, and reproductive systems
Sympathoadrenal System
Paired adrenal glands located on top of the
Paired adrenal glands located on top of the kidneys are composed of 2 parts:
- outer adrenal cortex (secretes steroid hormones) and
2. inner adrenal medulla (mostly secretes epinephrine 85% (adrenaline) and norepinephrine (less ~ 15%))
The adrenal medulla appears to be
a modified symapthetic ganglion because it has the same embryonic origin as the postganglionic sympathetic neurons
Cells of adrenal medulla are innervated by
by preganglionic sympathetic fibers
Cells of adrenal medulla are Stimulated during
mass activation of sympathetic division of ANS
Parasympathetic Division of the ANS is also called
because long preganglionic parasympathetic fibers originate in midbrain, medulla, pons, & 2nd – 4th sacral region of spinal column
Preganglionic parasympathetic fibers synapse on
postganglionic parasympathetic fibers in parasympathetic ganglia called terminal ganglia located next to or within target organ
Postganglionic fibers have
short axons that innervate targets
Most parasympathetic fibers do NOT
do NOT travel with spinal nerves as do the sympathetic fibers thus, cutaneous effectors (blood vessels, sweat glands, arrector pili muscles) receive sympathetic but NOT parasympathetic innervation
The long vagus nerve carries most
most parasympathetic fibers
The long vagus nerve innervates
Innervates heart, lungs, esophagus, stomach, pancreas, liver, small intestine, and upper half of the large intestine
Preganglionic fibers from S2-4
innervate lower half of large intestine, rectum, urinary & reproductive systems
4 of 12 pairs of cranial nerves contain
preganglionic parasympathetic fibers.
Oculomotor (III), facial (VII), and glossopharyngeal (IX) synapse with ganglia located in the head.
Fibers in the vagus nerve (X) synapse in terminal ganglia spread throughout
the body (heart, lungs, esophagus, stomach, pancreas, liver, small intestine, and upper ½ of large intestine
ANS Neurotransmitters
Both sympathetic & parasympathetic preganglionic fibers release ACh
Parasympathetic postganglionic fibers also
ACh
Called cholinergic synapses = all preganglionic fibers
Most postganglionic sympathetic fibers release
norepinephrine (noradenaline); called adrenergic synapses
A small number release Ach
Where postganglionic autonomic neurons enter into their target organs they have
have many swellings called varicosities, which release NTs along a length of axon
This forms unusual synapses synapses en passant
Adrenergic stimulation
by epinephrine release into the blood or norepinephrine release at a synapse
Adrenergic stimulation causes
causes both excitation & inhibition depending on tissue
Because of different subtypes of receptors for same NT
Many useful drugs have been developed to
affect ANS receptors
agonists
Drugs that promote actions of a NT
antagonists
Drugs that inhibit actions of a NT
ACh is used at
all motor neuron synapses (excitatory) on skeletal muscle, all preganglionic neurons (excitatory), & parasympathetic postganglionic neurons (usually excitatory)
Cholinergic Stimulation
Cholinergic receptors have 2 subtypes:
Nicotinic
muscarinic
Nicotinic receptors are stimulated by
by nicotine and Ach and are always excitatory; located in NMJs and autonomic ganglia (released by preganglionic neurons); blocked by curare
Muscarinic receptors are stimulated by
by ACh and muscarine (from poisonous mushrooms) and can be excitatory or inhibitory; released by postganglionic parasympathetic neurons;
Muscarinic receptors are blocked by
atropine = belladonna
“nonadrenergic, noncholinergic fibers”
Some postganglionic neurons do not use norepinephrine or Ach
nonadrenergic, noncholinergic fibers”
Appear to use
ATP) adenosinetriphosphate, (VIP) vasoactive intestinal peptide, or (NO) nitric oxide as NTs
• NO produces smooth muscle relaxation in many tissues (stomach, urinary bladder, small intestine)
Most visceral organs receive
dual innervation (supplied by both sympathetic & parasympathetic fibers)
2 branches are usually antagonistic
effects on heart rate (sympathetic innervation ↑ HR and parasympathetic innervation ↓HR) or digestive tract where sympathetic innervation inhibits movement and parasympathetic innervation increases movement and secretions
Can be complementary (cause similar effects) such as with
such as with salivation
• parasympathetic fibers cause watery saliva secretion and secretions of other glands in the digestive tract
sympathetic nerves stimulate constriction of blood vessels throughout the digestive tract thus there is a decrease blood flow to salivary glands causing thicker saliva
Or cooperative or synergistic
(produce different effects that work together to cause desired effect)
eg., reproductive system: erection and vaginal secretions are stimulated by the parasympathetic division and orgasm and ejaculation are cause by sympathetic division
Organs Without Dual Innervation
Most organs receive dual innervation but some only receive sympathetic innervation and regulation is achieved by
increasing or decreasing firing rate
Adrenal medulla, arrector pili muscle, sweat glands, & most blood vessels receive only
sympathetic innervation
Medulla oblongata most directly controls activity of
ANS by receiving afferent information via CNX (vagus)
Medulla oblongata has centers for control of
of cardiovascular, pulmonary, urinary, reproductive, & digestive systems
Hypothalamus has centers for control of
body temperature, hunger, thirst, the pituitary gland, the cerebral cortex and limbic system (emotions), & can regulate medulla oblongata!!
Limbic system is responsible for
visceral responses that reflect emotional states
Cerebral cortex & cerebellum
also influence ANS
