ANS

Question 1

Describe the sensory arm of the ANS, noting the general types of receptors supplying input.

Answer 1

• Sensory arm of ANS allows motor arm to function
• Input comes from interoceptors in visceral organs (blood vessels, walls of heart, GI tract, and bladder)
• Interoceptors include mechanoreceptors (respond to changes in stretch) and chemoreceptors (sense changes in oxygen, pH, and carbon dioxide levels)
• Important because allows a person to unconsciously sense a change in internal and external environments

Question 2

Identify and describe the 5 components of the visceral reflex arc.

Answer 2

Receptor - in viscera

Sensory neuron

• Visceral sensory neurons - send information about chemical changes, stretch, and irritation of viscera
• Found in sensory ganglia of cranial nerves or in dorsal root ganglia of spinal cord or sympathetic ganglia where preganglionic neurons synapse

Integration center

• May be preganglionic neuron
• May be a dorsal horn interneuron
• May be within walls of GI tract

Motor neuron
- 2 consecutive neurons (preganglionic neuron and postganglionic neuron)

Effector

Question 3

What effectors can be activated by a visceral reflex arc?

Answer 3

Smooth muscle, cardiac muscle, or glands

Question 4

Compare and contrast the motor pathways of the somatic nervous system (SNS) and the autonomic nervous system (ANS)

Answer 4

Similarities

• Higher brain centers regulate and coordinate activities of SNS and ANS
• Most spinal nerves contain somatic nerve fibers and autonomic nerve fibers
• Most homeostasis regulations involve both skeletal muscles and visceral organs

Contrasts

• SNS stimulates skeletal muscles; ANS innervates cardiac and smooth muscle and glands
• Somatic motor fibers are typically thick, heavily myelinated group A fibers that conduct nerve impulses rapidly. ANS motor fibers are thinner and less myelinated.
• SNS motor neuron cell bodies (single lower motor neuron) are in the CNS and their axons extend in spinal or cranial nerves all the way to the skeletal muscles they activate. ANS uses two-neuron chain to reach its effectors — preganglionic nerve and postganglionic nerve.
• All somatic motor nerves release ACh at their synapses, and the effect is always excitatory. Autonomic postganglionic fibers release two neurotransmitters: norepinephrine (secreted by most sympathetic fibers) and ACh (secreted by parasympathetic fibers); depending on the type of receptors on the target organ, the effect can be excitatory or inhibitory.

Question 5

What is a preganglionic neuron? a postganglionic neuron?

Answer 5

Preganglionic neuron - resides in the brain or spinal cord. Its axon, the preganglionic axon, synapses with the second motor neuron. This is probably the first motor neuron. Preganglionic axons are thin, lightly myelinated fibers.

Postganglionic neuron - second motor neuron, its cell body is in an autonomic ganglion outside the CNS. Its axon, the postganglionic axon, extends to the effector organ. Postganglionic axons are even thinner than preganglionic axons and nonmyelinated.

Question 6

Which division of the ANS is sometimes called the thoracolumbar division? the craniosacral? Explain these designations.

Answer 6

Thoracolumbar division - sympathetic division; the sympathetic fibers originate in the thoracic and lumbar regions of the spinal cord

Craniosacral division - parasympathetic division; the parasympathetic fibers originate in the brain (cranium) and sacral spinal cord

Question 7

Contrast the sympathetic and parasympathetic motor pathways, noting differences in origin, length of preganglionic and postganglionic fibers, location of ganglia, and neurotransmitter profiles.

Answer 7

Origin

• Parasympathetic fibers - craniosacral part: brain stem nuclei of cranial nerves III, VII, IX, and X; spinal cord segments S2 - S4
• Sympathetic fibers - thoracolumbar part: lateral horns of gray matter of spinal cord segments T1 - L2

Length of preganglionic fibers and postganglionic fibers

• Parasympathetic division - long preganglionic fibers, short postganglionic fibers
• Sympathetic division - short preganglionic fibers, long postganglionic fibers

Location of ganglia

• Parasympathetic ganglia - in or near the visceral effector organs
• Sympathetic ganglia - close to the spinal cord: alongside vertebral column and anterior to vertebral column

Neurotransmitter profiles

• Parasympathetic division - all preganglionic and postganglionic fibers release ACh (cholinergic fibers)
• Sympathetic division - all preganglionic fibers release ACh. Most postganglionic fibers release norepinephrine (adrenergic fibers). Postganglionic fibers serving sweat glands release ACh. Neurotransmitter activity is augmented by release of adrenal medullary hormones (NE and epinephrine)

Question 8

8. Which of the above neurons (#7) releases neurotransmitter at a synapse within a ganglion? at the neuroeffector synapse?

Answer 8

Releases NT at a synapse within a ganglion - preganglionic neuron

Releases NT at the neuroeffector synapse - postganglionic neuron

Question 9

There are three types of autonomic ganglia. Identify them, tell the ANS division with which they are associated, and describe the location of each.

Answer 9

Terminal ganglia

• Division: parasympathetic nervous system
• Location: within wall of organ served or close to organ

Sympathetic trunk ganglia/paravertebral ganglia

• Division: sympathetic nervous system
• Location: paired, beside spinal cord

Collateral ganglia (prevertebral ganglia)

• Division: sympathetic nervous system
• Location: unpaired, anterior to spinal cord

Question 10

What are the CNS origins of the parasympathetic division?

Answer 10

Brainstem and the sacral region of the spinal cord

Craniosacral part: brainstem nuclei of cranial nerves III, VII, IX, and X; spinal cord segments S2 - S4

Question 11

Which body regions and organs are served by parasympathetic preganglionic fibers originating with CNs III, VII, and IX?

Answer 11

CN III - smooth muscles in the eyes that cause the pupils to constrict and the lens to bulge

CN VII - many large glands in the head including the nasal glands, lacrimal glands, submandibular and sublingual salivary glands

CN IX - the parotid salivary glands

Question 12

Which body regions and organs are served by parasympathetic preganglionic fibers originating with CN X?

Answer 12

Serve virtually every organ in the thoracic and abdominal cavities

Heart (fibers to the heart), lungs and bronchi, esophagus

Also innervates the liver, gallbladder, stomach, small intestine, pancreas, and the proximal half of the large intestine

Question 13

Name the nerves that carry parasympathetic preganglionic fibers originating at the S2-S4 level of the spinal cord.

Answer 13

Pelvic splanchnic nerves

Question 14

Which body regions and organs are served by sacral parasympathetic outflow?

Answer 14

Distal half of the large intestine, urinary bladder, ureters, and reproductive organs

Question 15

Where specifically does the sympathetic division arise?

Answer 15

All preganglionic fibers of the sympathetic division arise from cell bodies of preganglionic neurons in spinal cord segments T1 through L 2

The numerous cell bodies of preganglionic sympathetic neurons in the gray matter of the spinal cord form the lateral horns

Question 16

Trace the pathway of sympathetic preganglionic fibers from the spinal cord to a paravertebral ganglion.

Answer 16

The preganglionic sympathetic fibers leave the spinal cord via the ventral root. Then, the fibers pass through a white ramus communicans to enter an adjoining paravertebral ganglion/sympathetic trunk ganglion and form part of the sympathetic trunk that flanks each side of the vertebral column.

Leave ventral roots of spinal cord –> go to white rami communicans –> paravertebral ganglion

Question 17

What are the three things that can happen to a preganglionic fiber in a paravertebral ganglion?

Answer 17

Synapse at the same level
- In this case, the synapse is in the same paravertebral ganglion

Synapse at a higher or lower level
- The preganglionic axon ascends or descends the paravertebral ganglion to another paravertebral ganglion

Synapse in a distant collateral ganglion
- The preganglionic axon passes through the trunk ganglion and emerges from the sympathetic trunk without synapsing. These preganglionic fibers help from several splanchnic nerves and synapse in collateral/prevertebral ganglia located anterior to the vertebral column.

Question 18

Which is more numerous –white rami communicantes or gray rami communicantes? Explain your answer.

Answer 18

Gray rami communicantes - white rami communicantes are found only in the T1 - L 2 cord segments, regions of sympathetic outflow. Gray rami communicantes are found from the cervical to the sacral region

Question 19

What organs of the head and neck are innervated by sympathetic postganglionic fibers? What is the effect of increased sympathetic outflow on these organs?

Answer 19

Skin, blood vessels, dilator muscles of the irises, inhibit nasal and salivary glands (the reason your mouth goes dry when you are scared), and innervates smooth muscle that lifts the upper eyelids

Question 20

Describe the pathway of the sympathetic preganglionic fibers that synapse with catecholamine-secreting cells in the adrenal medulla.

Answer 20

Some fibers traveling in the thoracic splanchnic nerves continue through the celiac ganglion without synapsing and terminate by synapsing with the hormone producing medullary cells of the adrenal gland (adrenal medulla) and stimulates the release of catecholamines (norepinephrine and epinephrine)

Question 21

Explain why the epinephrine- and norepinephrine-secreting cells of the adrenal medulla are correctly classified as modified sympathetic postganglionic neurons.

Answer 21

The epinephrine- and norepinephrine-secreting cells of the adrenal medulla are classified as this because they have the same embryological origin.

Question 22

Name and describe the synaptic terminals of sympathetic postganglionic fibers.

Answer 22

Varicosities - swelling of network on surface containing many NT vesicles. NT vesicles near receptors/effectors not directly in synaptic knobs

Question 23

What is a cholinergic fiber? an adrenergic fiber?

Answer 23

Cholinergic fibers - release ACh

Adrenergic fibers - release norepinephrine

Question 24

Which fibers of the ANS are cholinergic? Which are adrenergic?

Answer 24

Cholinergic

• All ANS preganglionic axons
• Parasympathetic postganglionic axons

Adrenergic

• Most sympathetic postganglionic axons
• *except postganglionic axons that secrete ACh to sweat glands

Question 25

Identify the two types of cholinergic receptors. What is the general effect of activation (by ACh binding) of each receptor type.

Answer 25

Cholinergic Receptors

• Nicotinic - respond to nicotine; stimulatory (excitatory) effect
• Muscarinic - respond to muscarine; inhibitory or excitatory effect (depends of subclasses of muscarinic receptor

Question 26

Identify the classes and subclasses of adrenergic receptors.

Answer 26

Alpha receptors

• Alpha-1
• Alpha-2

Beta receptors

• Beta-1
• Beta-2
• Beta-3

Question 27

When activated, which of the adrenergic receptor subclasses generally produce excitation of the target cell? which generally cause inhibition?

Answer 27

Alpha receptors

• Alpha-1 - excitatory
• Alpha-2 - inhibition

Beta Receptors

• Beta-1 - excitatory
• Beta-2 - inhibitory (mostly)
• Beta-3 - excitatory

Question 28

Explain why sympathetic activation vs. parasympathetic produces effects that are longer lasting and more widespread throughout the body.

Answer 28

In sympathetic activation, all portions discharge at the same time and act as a single unit which leads to a wider, longer-lasting response

Question 29

Many visceral organs have both parasympathetic and sympathetic innervation. However, there are 3 structures in the body that have only sympathetic innervation. What are they?

Answer 29

The adrenal medulla, sweat glands and arrector pili muscles of the skin, the kidneys, and most blood vessels receive only sympathetic fibers

Question 30

Describe the physiologic effects of sympathetic activation.

Answer 30

• Constriction of cutaneous blood vessels
• Increased heart rate and force of constriction
• Arrector pili muscles and sweat glands
• Increased blood flow to skeletal muscles and away from viscera
• Increased lipolysis, which makes more E available to working muscles
• Dilation of pupils and respiratory passages

Question 31

Describe the physiologic effects of parasympathetic activation.

Answer 31

SLUDD (Salivation, Lacrimation, Urination, Digestion, Defecation)

• Decreased heart rate
• Bronchoconstriction
• Constriction of pupils

Question 32

What is meant by the term agonist? Antagonist?

Answer 32

• Agonist - the effect that is dominant (in effect) at the moment
• Antagonist - the effect that is counteracting (resisting) the agonist
• Heart rate is increased by the sympathetic division (agonist) and is brought back to resting levels by the parasympathetic division (antagonist)

Question 33

Explain why blood vessels are said to exhibit sympathetic (vasomotor) tone.

Answer 33

Blood vessels are always partially constricted due to innervation by sympathetic fibers; this allows the body to manipulate blood pressure (stronger constriction or weaker constriction) and adjust the speed in which blood travels to necessary target areas

Question 34

Explain why the heart at rest is said to exhibit parasympathetic (vagal) tone.

Answer 34

Parasympathetic fibers innervate the heart and smooth muscles of the digestive and urinary organs; these fibers slow the heart and help determine the normal activity of the urinary and digestive systems

Question 35

Which ANS division, parasympathetic or sympathetic, produces a more diffuse response when activated? Which produces a more localized effect when activated?

Answer 35

Diffused response when activated - sympathetic division

Localized effect when activated - parasympathetic division

Question 36

Explain why sympathetic activation produces longer-lasting effects than does parasympathetic activation.

Answer 36

The parasympathetic division produces localized effects when activated; the preganglionic neuron synapses with only one to a few postganglionic neurons. The parasympathetic is shorter-lasting because the ACh (the neurotransmitter for all parasympathetic terminals) is also broken down quickly by ACh-ase.

The sympathetic division produces a more diffuse effect when activated; the preganglionic neurons are long (further away from the cell body) and synapse at many different levers, creating a diffuse effect. The adrenal medullary cells secrete NE and epinephrine into the blood and it lasts minutes before the liver gets a chance to break them down. Also, the effects of the hormones released last a while.

Question 37

What part of the CNS performs overall integration of ANS activity?

Answer 37

Hypothalamus (primary control), brain stem & spinal cord, and cerebral cortex

Question 38

Identify the main components of the ANS hierarchy of control. Describe the role played by each component.

Answer 38

Brain Stem & Spinal Cord
- Motor centers in the ventrolateral medulla reflexively regulate heart rate and blood vessel dilation
- Some medullary regions - oversee GI activities
- Midbrain centers - control muscles of pupil diameter and
lens focus

Hypothalamus

• Anterior Regions - parasympathetic control
• Posterior Regions - sympathetic control
• Coordinates heart activity, blood pressure, body temp., water balance, and endocrine activity
• Implements sympathetic system (activates sympathetic division to fight or flight status) after receiving emotional response of the limbic system

Cortical Controls (Cerebral Cortex)
- Remembering a frightening event (sympathetic activation) or thinking of a favorite food (parasympathetic activation)