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Anatomy and Physiology 1 > Chapter 15: ... > Flashcards

Chapter 15: ... Flashcards

1
Q

Autonomic Nervous System (ANS)

A

Motor nervous system which innervates involuntary effectors
* Cardiac and smooth muscle, glands

Primary target organs:
* Thoracic viscera
* Abdominopelvic viscera
* Some body wall structures

  • Actions occur without voluntary input or conscious awareness

Effectors do not require ANS innervation for normal function
* ANS adjust organ function to meet changing needs of body

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2
Q

Notes on Reflexes

A

Any quick, involuntary, stereotyped reaction to stimulation
* Muscle OR gland

Characteristics
* Require stimulation
* Involuntary
* Quick
* Stereotyped

Two main categories
* Somatic reflexes involve skeletal muscle
* Visceral reflexes involve cardiac and smooth muscle or glands
* aka autonomic reflexes

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3
Q

Somatic Vs Visceral Reflexes

A

Somatic Reflexes
* Somatic receptors
* In skin, muscles, tendons
* Somatic effectors
* Skeletal muscle
* Faster

Visceral Reflexes
* Visceral receptors
* In organs
* Visceral effectors
* Cardiac and smooth muscle,
glands
* Slower

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4
Q

Components of a Reflex Arc

A

Receptor
* Detects stimulus

Sensory (afferent) neuron
* Carries information to integrating center

Integrating center
* Within gray matter of CNS
* Involves interneurons

Motor (efferent) neuron
* Carries commands to effector

Effector
* Carries out response

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5
Q

Divisions of the ANS

A

Two divisions
* Sympathetic
* Parasympathetic

  • Differ in structure and function

Typically organs innervated by both divisions
* May have opposing or cooperative effects

  • Some organs may be innervated by only one division
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6
Q

Sympathetic Vs Parasympathetic

A

Sympathetic Division
* Adapts body for physical activity
* “Fight or flight”
* More blood flow to cardiac and
skeletal muscle
* Response to stress, exercise,
danger, fear, anger, trauma, etc.
* Increased energy expenditure

Parasympathetic Division
* Calming effect on body
* “Rest and digest”
* More blood flow to skin and
digestive tract
* Reduced energy expenditure and
normal bodily maintenance
* Digestion and waste elimination

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7
Q

Autonomic Tone

A
  • Both divisions are usually active simultaneously

Autonomic tone is the background rate of ANS activity
* Balance between sympathetic and parasympathetic tone
* Shifts according to body’s needs

Neither division is exclusively excitatory or inhibitory
* Sympathetic division excites heart, inhibits digestive organs
* Parasympathetic division inhibits heart, excites digestive organs

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8
Q

Somatic Vs Autonomic Motor Division

A

Somatic
* One lower motor neuron
* No ganglia
* Acetylcholine (ACh)
* Axons end in neuromuscular
junctions
* Skeletal muscle
* Faster conduction
* Usually voluntary
* Always excitatory

Autonomic
* Two lower motor neurons
* Ganglia
* Either ACh or NE
* Axons end in varicosities
* Cardiac and smooth muscle,
glands
* Slower conduction
* Usually involuntary
* Can be excitatory or
inhibitory

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9
Q

Pre- and Postganglionic Neurons

A

Preganglionic neuron lies before autonomic ganglia
* Neurosoma in brain or spinal cord
* Myelinated
* Axon projects to autonomic ganglion
* Uses ACh exclusively

Postganglionic neuron lies after autonomic ganglia
* Neurosoma lies in autonomic ganglion
* Unmyelinated
* Axon projects to effector
* Uses either ACh or NE
* End in varicosities

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10
Q

ANS Division Structural Differences

A

Location of preganglionic neuron neurosoma
* SNS: spinal cord (T1-L2) = thoracolumbar
* PNS: brainstem and spinal cord (S2–S4) = craniosacral

Location of ganglia
* SNS: close to vertebral column
* PNS: close to or within target organs

Neurotransmitter utilized
* Both preganglionic: ACh
* SNS postganglionic: mostly norepinephrine (NE)
* PNS postganglionic: ACh

Length of pre- and postganglionic axons
* SNS: pre = shorter, post = longer
* PNS: pre = longer, post = shorter

Neural divergence
* SNS: extensive (many branches)
* PNS: minimal (fewer branches)

Effects
* SNS: more widespread, general
* PNS: more local, specific

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11
Q

Sympathetic Neurons

A

Preganglionic
* Neurosomas within thoracic and lumbar spinal cord
* Lateral horns and nearby gray matter
* Use ACh only
* Axons exit via spinal nerves (T1 – L2)

Postganglionic
* Neurosomas within autonomic ganglia
* Primarily use NE
* Axons innervate body wall structures and viscera

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12
Q

Sympathetic Ganglia

A

Sympathetic chain (paravertebral) ganglia
* Chains lateral to spinal cord
* Runs from cervical to coccygeal level
* Postganglionic axons innervate head, neck, thoracic cavity,
abdominopelvic cavity

Collateral (prevertebral) ganglia
* Anterior to vertebral column
* Named for nearby blood vessels
* Three in total
* Postganglionic axons innervate abdominopelvic structures
* Travel along with blood vessels to effectors

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13
Q

SNS Effector Innervation

A
  • Postganglionic fibers leave sympathetic chain to innervate effector\

Via spinal nerves
* Sympathetic axons travel within spinal nerves
* Overall: structures within muscles and body wall
* Sweat glands, piloerector muscles, blood vessels of skin and skeletal muscles

Via sympathetic nerves
* Heart, lungs, esophagus, thoracic blood vessels
* Form carotid plexus, fibers innervate effectors of head
* Overall: head and thoracic cavity

Via splanchnic nerves
* Preganglionic axons don’t synapse within sympathetic ganglia
* Form splanchnic nerves which synapse at collateral ganglia
* Overall: structures within abdominopelvic cavity

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14
Q

The Adrenal (Suprarenal) Glands

A
  • Positioned on top of kidneys

Divided into two regions
* Adrenal cortex: endocrine gland, secretes steroids
* Adrenal medulla: modified sympathetic ganglion

Medulla produces catecholamine hormones
* Epinephrine, norepinephrine, dopamine
* Also act as neurotransmitters

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15
Q

Selected Effects of Increased SNS Stimulation

A

Increased cardiac output
* Heart rate
* Contraction strength

Systemic vasoconstriction, raised blood pressure
* Vasodilation of coronary arteries

Increased airflow
* Bronchodilation

  • Increased metabolic rate and nutrient breakdown
  • Increased sweat secretion
  • Pupillary dilation
  • Inhibition of digestive and urinary activity

Increased secretion from medulla
* Hormones prolong SNS effects

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16
Q

Parasympathetic Neurons

A

Preganglionic
* Neurosomas within brainstem and sacral spinal cord
* Use ACh only
* Axons travel via cranial and sacral nerves

Postganglionic
* Neurosomas within autonomic ganglia
* Use ACh only
* Axons do not typically innervate body wall structures
* Some exceptions

17
Q

Parasympathetic Ganglia

A

Terminal ganglia
* Lie in or near target organ

Intramural ganglia
* Embedded within the wall of target organ
* Subtype of terminal ganglion

18
Q

PNS Effector Innervation

A
  • Parasympathetic axons travel via cranial or splanchnic nerves

Cranial nerves
* From neurosomas in brainstem
* CN III, VII, IX innervate structures of head
* CN X handles innervation to thoracic and abdominal cavities

Pelvic splanchnic nerves
* From neurosomas in the sacral spinal cord
* Give rise to pelvic nerves
* Innervate pelvic structures

19
Q

Cranial Nerves and the PNS

A

Oculomotor nerve III
* Innervates muscles of eye

Facial nerve VII
* Innervates lacrimal glands, salivary glands, nasal glands
* Splits, associated with two ganglia

Glossopharyngeal nerve IX
* Innervates salivary glands

Vagus nerve X
* Majority (90%) of parasympathetic axons
* Thoracic and abdominal organs
* Forms three plexuses

20
Q

Selected Effects of PNS Stimulation

A

Decreased cardiac output
* Decreased heart rate

Decreased airflow
* Bronchoconstriction

Decreased metabolic rate
* Increased nutrient digestion, synthesis, and storage

Pupillary constriction
* Stimulation of digestive and urinary activity

21
Q

ANS and Neurotransmitters

A
  • SNS and PNS typically have contrasting effects on target organs

How: postganglionic neurons release different NTs
* SNS: NE
* PNS: ACh

Same NT from the same division can have contrasting effects
* EX: vasoconstriction versus bronchodilation (both SNS NE)

How: different receptors for NTs exist
* Permits NTs to have varying effects based on which receptor is
present

22
Q

Acetylcholine (ACh)

A

Released by
* All preganglionic neurons
* All PNS postganglionic neurons
* Some of SNS postganglionic neurons
* Sweat glands, blood vessels

  • Neurons that release ACh named
    cholinergic neurons (fibers)
  • Receptors that bind ACh named
    cholinergic receptors
23
Q

Cholinergic Receptors

A

Muscarinic
* Smooth and cardiac muscle, gland cells
* Subtypes with excitatory and inhibitory effects
* Requires use of second messenger systems

Nicotinic
* Locations
* All autonomic ganglia synapses
* Adrenal medulla
* Neuromuscular junctions
* Always excitatory!
* Open gated ion channels, produces EPSPs

24
Q

Norepinephrine (NE)

A
  • Secreted by majority of sympathetic
    postganglionic neurons
  • Neurons that release NE named
    adrenergic neurons (fibers)
  • Receptors that bind NE named
    adrenergic receptors
25
Q

Adrenergic Receptors

A

Alpha (α) receptors
* Primarily excitatory
* Two subclasses permit contrasting effects on effectors
* Uses second messenger systems

Beta (β) receptors
* Primarily inhibitory
* Two subclasses permit contrasting effects on effectors
* Use second messenger systems

26
Q

Neurotransmitters and Effect Duration

A
  • Sympathetic effects last longer than parasympathetic effects

Acetylcholine
* Degraded by acetylcholinesterase enzyme

Norepinephrine
* Reabsorbed by neuron
* Diffuses into nearby tissues
* Enters bloodstream
* Ultimately degraded by enzymes or the liver

27
Q

Dual Innervation

A
  • Most organs innervated by both SNS and PNS

Antagonistic effects
* Divisions have opposing effects
* Target same or different effector cells
* Ex: heart, pupil, digestive organs

Cooperative effects
* Divisions work together to produce unified effect
* Divisions act on different effector cells
* Salivation, male sexual activity

  • Divisions may not innervate organs equally or have equal influence
28
Q

Control Without Dual Innervation

A
  • Organ receives innervation from either SNS or PNS

Changes occur due to alterations of autonomic tone
* Sympathetic tone
* Parasympathetic tone

Blood pressure regulation via vasomotor tone
* Increased SNS tone  vasoconstriction, raised blood pressure
* Decreased SNS tone  vasodilation, lowered blood pressure

Several organs receive only SNS innervation
* Many blood vessels, adrenal medulla, arrector muscles, sweat
glands

29
Q

CNS Control Over ANS

A

The autonomic nervous system is a division of the nervous
system
* Not fully independent

Activity of the central nervous system can adjust ANS activity
* Allows adjustments based on current body conditions

30
Q

CNS Structures Which Influence ANS

A

Cerebral cortex
* Sensory and emotional experiences to alter ANS activity
* Due to limbic system
* Features connections to hypothalamus

Hypothalamus
* Major control center for autonomic nervous system
* Houses nuclei which regulate specific functions
* Hunger, thirst, thermoregulation, emotion, sexuality, etc.
* Has connections to limbic system
* Has connections to brainstem

Brainstem
* House autonomic nuclei
* Cardiac center, vasomotor center, respiratory centers, salivation, etc.
* Reticular formation

Spinal cord
* Integrates some autonomic reflexes
* Micturition, defecation, erection, ejaculation
* Note: brain can consciously inhibit some of these reflexes

Anatomy and Physiology 1 (2 decks)

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