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Chapter 16: Neural Integration 2: The autonomic nervous system and higher order functions
Fundamentals of Anatomy and Physiology, 7th edition by Martini
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It is the ANS that coordinates cardiovascular, respiratory, digestive, urinary, and reproductive functions
The ANS adjust internal water, electrolyte, nutrient, and dissolved gas concentrations in body fluids –
and it does so without instructions or interference from the conscious mind
An overview of the ANS
 Both are efferent divisions that carry motor commands; the SNS controls skeletal muscles and the ANS
controls visceral effectors
Divisions of the ANS
 The ANS contains two subdivisions: the sympathetic division and the parasympathetic division
The Sympathetic Division
 The sympathetic division prepares the body for heightened levels of somatic activity
 When fully activated, this division produces what is known as the “fight or flight” response, which
readies the body for a crisis that may require sudden, intense physical activity
The Parasympathetic division
 The parasympathetic division consists of preganglionic fibers that originate in the brain stem and the
sacral segments of the spinal cord and they synapse in ganglia very close to the target organs
 The parasympathetic division stimulates visceral activity;
o For example, it is responsible for the state of “rest and repose” that follows a big dinner
The Sympathetic division
 This division consists of preganglionic neurons that are located between segments T-1 and L-2 of the
spinal cord, and ganglionic neurons that are located in ganglia near the vertebral column
 The ganglionic neurons occur in three locations:
o Sympathetic chain ganglia
o Collateral ganglia
o The adrenal medullae
Organization and anatomy of the sympathetic division
 Each ganglion in the sympathetic chain innervates a particular body segment or group of segments
Sympathetic chain ganglia
 If a preganglionic fiber carries motor commands that target structures in the body wall or thoracic
cavity, or in the head, neck, or limbs, it will synapse in one or more sympathetic chain ganglia
o Post ganglionic fibers control visceral effectors in the body wall, head, neck, or limbs
o Sympathetic nerves
Collateral ganglia
 The abdominopelvic viscera receive sympathetic innervation by way of sympathetic preganglionic fibers
that pass through the sympathetic chain without synapsing. They synapse in separate collateral ganglia
 Postganglionic fibers leaving the collateral ganglia extend throughout the abdomiopelvic cavity,
innervating a variety of visceral tissues and organs
The Adrenal Medullae
 Preganglionic fibers enter in an adrenal gland proceed to its center, a region called the adrenal medulla
 The adrenal medulla is a modified sympathetic ganglion
 epinephrine (E) and norepinephrine (NE)
Sympathetic activation
 The sympathetic division can change the activities of tissues and organs by releasing NE at peripheral
synapses and by distributing E and NE throughout the body in the bloodstream
 The visceral motor fibers that target specific effectors, such as smooth muscle fibers in blood vessels of
the skin, can be activated in reflexes that do not involve other visceral effectors
 In a crisis the entire division responds
 Sympathetic activation
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When sympathetic activation occurs, an individual experiences the following changes:
o Increased alertness
o A feeling of energy and euphoria
o Increased activity in the cardiovascular and respiratory centers
o A general elevation in muscle tone
o The mobilization of energy reserves
Neurotransmitters and Sympathetic Function
Neurotransmitter release
 The stimulation of sympathetic preganglionic neurons leads to the release of ACh at synapses with
ganglionic neurons
 The stimulation of these ganglionic neurons leads to the release of neurotransmitters at specific target
organs
 Varicosity
 Most sympathetic ganglionic neurons release NE at their varicosities
 Adrenergic
The Parasympathetic division
 The parasympathetic division consists of:
o Preganglionic neurons in the brain stem and in sacral segments of the spinal cord
o Ganglionic neurons in peripheral ganglia within or adjacent to the target organs
Organization and anatomy of the parasympathetic division
 Parasympathetic preganglionic fibers leave the brain as components of cranial nerves: oculomotor,
facial, glossopharyngeal, and vagus
 Parasympathetic fibers in the oculomotor, facial, and glossopharyngeal nerves control visceral structures
in the head
 The vagus nerve provides preganglionic parasympathetic innervation to structures in the neck and in the
thoracic and abdomiopelvic cavity
 The preganglionic fibers in the sacral segments of the spinal cord carry the sacral parasympathetic
output
Parasympathetic activation
 The major effects produced by the parasympathetic division include the following:
o Constriction of the pupils
o Secretion by digestive glands
o The secretion of hormones
o Changes in blood flow
o An increase in smooth muscle activity along the digestive tract
o The stimulation and coordination of defecation
o Contraction of the urinary bladder during urination
o Constriction of the respiratory passageways
o A reduction in heart rate and in the force of contraction
o Sexual arousal and the stimulation of sexual glands in both genders
Neurotransmitters and parasympathetic functions
 All parasympathetic neurons release ACh as a neurotransmitter
Neurotransmitter release
 The neuromuscular and neuroglandular junctions of the parasympathetic division are small and have
narrow synaptic clefts
 The effects of the parasympathetic stimulation are localized, and they last a few seconds
Membrane receptors and responses
 Two types of Ach receptors occur on the postsynaptic membranes:
o Nicotinic receptors
o Muscarinic receptors
Interactions between the sympathetic and parasympathetic divisions
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The parasympathetic division innervates only visceral structures that are serviced by the cranial nerves
or that lie within the abdomiopelvic cavity
 Dual innervation
Autonomic tone
 Even in the absence of stimuli, autonomic motor neurons show a resting level of spontaneous activity.
The background level of activation determines and individual’s autonomic tone
Integration and control of autonomic functions
 The ANS is also organized into a series of interacting levels.
Higher Levels of Autonomic control
 The levels of activity in the sympathetic and parasympathetic divisions of the ANS are controlled by
centers in the brain stem that deal with specific visceral functions
 More complex sympathetic and parasympathetic reflexes are coordinated by processing centers in the
medulla oblongata
The Integration of SNS and ANS activities
 Integration occurs at the level of the brainstem, and both systems are under the control of higher centers
Higher order functions
 Higher order functions share the following characteristics:
o The cerebral cortex is required for their performance
o They involve both conscious and unconscious information processing
o The are not part of the programmed “wiring” of the brain
Memory
 Memories
 Fact memories
 Skill memories
 Two classes of memories are identified.
o Short term memories or primary memories & long term memories
 Memory consolidation
 There are two types of long-term memory
o Secondary memories
o Tertiary memories
 The amygdaloid body and the hippocampus
Cellular Mechanisms of memory formation and storage
 Memory consolidation at the cellular level involves anatomical and physiological changes in neurons
and synapses
 Mechanisms involved:
o Increased neurotransmitter release
o Facilitation at synapses
o The formation and additional synaptic connections
 These processes create anatomical changes that facilitate communication along a specific neural circuit
 Memory engram
 Amnesia
 Retrograde amnesia
 Anterograde
 Post-traumatic amnesia (PTA)
Consciousness
 A conscious individual is alert and attentive; an unconscious individual is not
 There are many gradations of both the conscious an unconscious states
 Healthy individual cycle between the alert, conscious state and the asleep state each day
 coma
Sleep
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Conscious implies a state of awareness of an attention to external events and stimuli
Unconscious can imply a number of conditions, ranging from the deep, unresponsive state induced by
anesthesia before major surgery to the light, drifting “nod” that plagues students
 Patterns of brain wave activity
o slow wave or non-REM (NREM)
o rapid eye movement (REM) sleep
 Periods of REM and deep sleep alternate throughout the night, beginning with a period of deep sleep
that lasts about an hour and a half
Arousal
 Or waking from sleep, appears to be one of the functions of the reticular formation
The reticular activating system
 Your state of consciousness is determined by complex interactions between your brain stem and cerebral
cortex
 reticular activating system (RAS)
Brain chemistry and behavior
Neurotransmitters and brain function
 Changes in the normal balance between two or more neurotransmitters can also profoundly affect brain
function
 The importance of a specific neurotransmitter has been revealed during the search for a mechanism for
the effects of administered drugs
Alzheimer’s disease
 Is a progressive disorder characterized by the loss of higher order cerebral functions. It is the most
common cause of senile dementia or senility
 Genetic factors play a major role
 There is no cure for Alzheimer’s