Chapter 14 ANS Flashcards
(13 cards)
The Autonomic Nervous System (Fig. 14.1)
Involuntary, general visceral motor system that innervates cardiac, smooth muscle, and glands
Differences from somatic nervous system (Fig 14.2):
Effector
Effector:
ANS innervates cardiac and smooth muscles and glands
Somatic system innervates skeletal muscle
Differences from somatic nervous system:
Motor unit:
Motor unit:
ANS = 2 motor neurons + effector
1st neuron = **pre-ganglionic neuron with cell body in **CNS
2nd neuron = **post-ganglionic neuron with cell body in **autonomic ganglion outside CNS
Somatic = 1 motor neuron with cell body in CNS + effector (skeletal muscle)
Differences from somatic nervous system:
Axon Fibers
Axon fibers:
ANS – 1st axon = myelinated but smaller diameter (Aβ), 2nd = unmyelinated (C fiber)
Somatic – large myelinated (Aα)
Differences from somatic nervous system:
Neurotransmitter
Neurotransmitter:
ANS – ACh and norepinephrine (NorEpi)
depending on receptor of effector tissue - can be excitatory or inhibitory
Somatic – ACh – always excitatory
ANS has two divisions:
Parasympathetic division
Sympathetic division
Parasympathetic division
Parasympathetic division
Promotes maintenance functions and conserves energy (rest and digest)
• reduces heart rate
• stimulates digestion, elimination of feces and urine
**craniosacral origins – cell bodies for preganglionic neuron in brain and sacral spinal cord
Fibers in cranial nerves:
III – oculomotor - supplies iris and ciliary bodies of eye
VII – facial – supplies nasal and lacrimal glands
IX – glossopharyngeal – supplies parotid and salivary glands
**X - right and left vagus nerves
- account for 90% of all preganglionic parasympathetic fibers
- supply almost every organ and gland in thoracic and abdominal cavities
Sacral nerves – supply pelvic organs and distal half of large intestine
Ganglion in or near effector organ:
Long pre-ganglionic **cholinergic fiber releases **ACh at ganglion
Excitatory at nicotinic receptors
Short post-ganglionic **cholinergic fiber releases **ACh at effector
**Muscarinic receptors – can be excitatory or inhibitory depending on receptor sub-type
Sympathetic division
Sympathetic division
Mobilizes the body during activity (fight or flight)
• temporally reduces nonessential activities
• increases both heart rate and force of its contraction
• constricts certain blood vessels allowing blood to be diverted to active tissues
• dilates bronchioles in lungs – increasing air flow
• stimulates release of glucose from liver
**Thoracolumbar origins – cell bodies for preganglionic neuron in thoracic and lumbar spinal cord
• cell bodies form **lateral horns of spinal cord
• nerves innervate more organs than parasympathetic division
• dilate smooth muscle of iris
• inhibit nasal and salivary glands
• supplies visceral organs
• supplies sweat glands and arrector pili muscles of skin
• supplies smooth muscle in walls of blood vessels
Sympathetic division
Sympathetic trunk ganglion
Sympathetic trunk ganglion close to spinal cord
•**collateral ganglia (prevertebral) – located anterior of vertebral column
preganglionic fibers form several **splanchnic nerves (greater, lesser, lumbar and sacral)
•short pre-ganglionic **cholinergic fiber releases **ACh at ganglion
**excitatory at **nicotinic receptors
• long post-ganglionic **adrenergic fiber **releases NorEpi at effector
**alpha and beta receptors – can be excitatory or inhibitory depending on sub-type
Sympathetic division
Adrenal Medulla
Adrenal medulla – center portion of the adrenal gland
• **modified sympathetic ganglion
• post-ganglionic fibers (Chromaffin cells) do not leave medulla
• releases **NorEpi and epinephrine (Epi) into the blood
Sympathetic division
Dual innervation
Dual innervation – when an organ innervated with both parasympathetic and sympathetic fibers
Actions antagonistic to one another – one divisions excites, one division suppresses activity
Visceral reflex arcs (Fig. 14.8)
Visceral reflex arcs – same components as somatic division but motor output involves pre and post ganglionic neurons
e.g. stretch of bladder initiating micturation reflex
**sympathetic reflexes – responsible for thermoregulatory responses to heat (sweating, vasodilation), release of renin from the kidneys, metabolic effects (increased rate and blood glucose levels, mobilization of fats) through activation of adrenal medulla
**enteric nervous system = **reflex arcs found completely within the walls of the gastrointestinal system
Hypothalamus (Check Fig 14.9)
Hypothalamus = primary controller of ANS
