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Flashcards in Autonomic nervous system lecture 1 week 3 Deck (24):
1

True or false: The ANS innervates every organ in the body. It thereby helps to control arterial pressure, GI motility and secretions, urinary bladder emptying, sweating, body temperature, and other fxns.

True.

2

How/what activates the ANS?

The ANS is activated by centres in the spinal cord, brain stem and hypothalamus. The hypothalamus provides the ANS with its greatest level of integration. The cerebral cortex and the limbic system (which includes olfactory areas, amygdylate, hippocampus and other areas) regulate the hypothalmus by transmitting impulses to it. Higher centers thus influence autonomic control and are critical for emotional expression.

3

What are the 2 main functions of the ANS? What fxns fall under those categories?

1. Basic metabolic or vegetative functions:

  • a. energy storage and release.
  • b. control of endocrine and neuroendocrine release.
  • c. control of exocrine secretion.

2. Role in behavior.

4

The somatic nervous system is largely subject to conscious and voluntary control. The ANS is normally not subject to voluntary control and therefore ___ ___ are extremely important in the functioning of the ANS.

reflex arcs

5

True or false: Reflex arcs are voluntary.

False. A reflex arc does not require voluntary decisions.

6

What are reflex arcs? Why do they exist? Explain the reflex arc that occurs when a person touches a hot object. What kind of reflex is this (autonomic or somatic)?

A reflex arc does not require voluntary decisions. Reflex arcs monitor the environment and information is fed back to effector organs. In general, reflex arcs are restorative-they try to keep something constant. As an example of a somatic reflex, consider a hand accidentally placed against a hot object - the hand is automatically withdrawn within a fraction of a second (Figure 3). The heat stimulates receptors in the skin, producing receptor potentials which generate action potentials. The action potentials propagate within the afferent fiber, from the hand to the spinal cord. This incoming information is communicated across synapses to motoneurons in the spinal cord. Action potentials are then propagated within efferent motoneurons. Synaptic transmission across the neuromuscular junction causes muscle contraction. In everyday language, the hand is withdrawn. In this case, the body withdraws the hand to keep the temperature of the hand constant. 

7

What are the lengths of the pre and postganglionic fibers of the sympathetic and parasympathetic NS?

Sympathetic: short preganglionic fiber, long postganglionic fiber

Parasympathetic: long preganglionc fiber, short postganglionic fiber (have terminal ganglia close to/on effector organ)

8

What are the properties of sympathetic preganglionic fibers (size, myelination, propagation speed)? Where do they synapse? What parts of the body do the preganglionic fibers in the upper region of the spinal cord control vs those in the lower region?

Most sympathetic preganglionic fibers are small, myelinated, and propagate APs at less than 20 m/s.

The short preganglionic fibers either terminate and synapse with postganglionic fibers close to the spinal cord or within outlying ganglia. Because they have the option to synapse in ganglia at levels above and below where they originated, this creates a sympathetic ganglionic chain that runs parallel on each side of the spinal cord from the base of the skull to the sacrum.

Preganglionic fibers in the upper parts of the spinal cord effect/control innervation to upper parts of the body. Preganglionic fibers from lower parts of the spinal cord effect/control innervation to lower parts of the body.

9

What is the difference in the right and left sympathetic chain as it pertains to innervation of the heart?

The right sympathetic chain innervates the SA node and the left and right atria.

The left sympathetic chain innervates the left and right ventricles. 

10

What is convergence? What is divergence? Where do these processes occur and what are the reasons?

Much convergence and divergence occurs within the sympathetic chains. Divergence occurs when an axon of a preganglionic fiber subdivides into several or many branches to form synapses with several or many postganglionic neurons. Through divergence, a relatively small number of preganglionic fibers connects to a large number of postganglionic fibers. Convergence occurs when a postganglionic fiber receives synaptic input from many preganglionic neurons. Convergence and divergence leads to neuronal integration. Convergence and divergence result in: 

i. This integration results in global action.
ii. It also provides an important safety factor guaranteeing synaptic transmissions. That is, the synaptic inputs onto post-ganglionic fibers exceeds that minimally required to elicit a physiological response.
iii. The utility of this integration is illustrated by the observation that as animal size increases from small (e.g. a mouse) to large (e.g. human), the ratio of preganglionic fibers does not increase as much as the ratio of postganglionic fibers, and for both fibers, the increase in ratio is less than the increase in ratio of animal size. Increasing the degree of convergence and divergence has been an evolutionary strategy for increasing body and organ size without having to proportionally increase the number of neurons.

 

11

Instead of dircetly passing out as a sympathetic nerve to an effector, some postganglionic neurons pass through gray rami andn into a tract of spinal nerves. What do these nerves innervate?

These postganglionic fibers extend to all parts of the body and control blood vessels, sweat glands, and piloerector muscles of hairs. 

12

What chemicals are secreted by the sympathetic branch of the ANS? From where are these chemicals released and onto what?

Sympathetic: ACh is released from preganglionic fibers onto postganglionic fibers. NE is released from postganglionic fibers onto effector organs. E is predominantly secreted by the adrenal medulla (but some NE is also released). ACh is secreted by postganglionic nerves innervating sweat glands and some blood vessels. Note that the adrenal medulla secretes E/NE into bloodstream: hormone

13

What are the properties of sympathetic postganglionic fibers (size, myelination, propagation speed)? What do postganglionic fibers receiving synaptic inputs from preganglionic fibers originating in the thoracic region of the spinal cord innervate? The lumbar region?

Postganglionic sympathetic fibers are long, very thin, and unmyelinated (propation 1 m/s). Postganglionic fibers that receive synaptic inputs from preganglionic fibers originating from the throracic region of the spinal cord innervate the head, thorax, abdomen and upper extremities. Those postganglionic fibers that receive synaptic inputs form preganglionic originating in the lumbar region innervate the pelvis and lower ext. 

14

Where do parasympathetic preganglionic fibers exit? What nerves do preganglionic fibers innervate viscera through and what parts of the body do these nerves innervate?

What are the properties of preganglionic nerves (size, myelination)? Where do they synapse and what NT do they relase?

What fxns are associated with the parasympathetic NS?

 

Parasympathetic fibers leave the CNS through cranial nerves and the sacral regions of the spinal cord.

About 3/4 of the preganglionic fibers are in the vagus nerve, the 10th cranial nerve. The vagus nerve innervates the thorax and adomen. Fibers that leave from the sacral spinal cord are in the pelvic nerve.

Parasympathetic preganglionic neurons are usually myelinated and long and terminate in a synaptic connection with the postganglionic fiber close to the effector organ or even within the wall of the target organ (parasympathetic ganglia are located here). They release ACh onto the postganglionic neurons. 

Parsympathetic NS is associated with local protective reflexes. All of vegetative, non-stress, restorative fxns are associated with parasympathetic NS.

 

15

How may sympathetic innervation impact long QT syndrome?

Most, but not all, inflicted individuals of long QT syndrome encoutner cardiac events during increased sympathetic activity. In addition to physical exercise, stress, or emotional excitement, drugs can induce the increased sympathetic activity. 

16

How do stimuli lead to information being sent to the body? Include a discussion of receptors, receptor potentials, and APs. Be sure to state what a receptor is. 

An incoming signal stimulates a receptor which transforms the stimulus into an electrical potential (attached figure). NOTE: The term “receptor” is used in many contexts, but always refers to a system that receives something. Receptors can refer to membrane-bound macromolecules that receive incoming sensory information (e.g. receptors in olfactory epithelial membranes.) The word receptor is also used to describe other types of membrane proteins that receive chemical messages such as the nicotinic ACh channel and receptors within cells that are innervated by the autonomic nervous system. As discussed below, these latter receptors are G-protein coupled receptors. The word receptor is also used to refer to sensory organs. 

A receptor is both a transducer and a translator. It converts one form of energy, the stimulus, into a second form of energy, an electrical receptor potential. In turn, the receptor potential generates action potentials (APs). As a result, the receptor converts the information-containing signal to APs, altering the information itself.

The transduced potential is known as a receptor potential or generator potential. The receptor potential is the intermediate link between the stimulus and the action potential. Receptor potentials are local potentials. They are graded, not all-or-none, do not have a threshold, are non-propagated, electrotonic, and are summing. These are the same properties exhibited by EPSPs. 

Information is coded in frequency of firing action potentials (AP). For any given nerve cell, all APs have the same amplitude and shape (all-or-none). That is, information for the intensity of the stimulus is carried as a frequency code.

SEE SLIDE 13 OF NOTES

 

17

What are mechanoreceptors, chemoreceptors, thermoreceptors, and osmoreceptors? Give examples in the body along with their fxns.

taken from pg 47 of notes

18

The simplest connection btwn afferents and autonomic efferents is at the segmental level of the spinal cord and is known as what?

an autonomic reflex arc

19

True or False: The simplest reflex arc in the ANS has an interneuron btwn the afferent fiber and the pre-ganglionic fiber. In contrast, and interneuron is not present for teh simplest reflex arc of the somatic NS.

True. 

20

List and describe the processes that occur in the carotid baroceptor relex.

See pg 49 of course notes for in depth explanation

21

What does the output of a baroreceptor depend on? 

The baroreceptor output depends on both the rate of change of blood pressure and the magnitude of the pressure. In different terms, the baroreceptor exhibits both phasic and tonic components. A phasic component reports changes in stimulus; a tonic component reports the magnitude of the stimulus. A receptor that exhibits both phasic and tonic components is said to be a mixed receptor. 

22

Blood pressure is constantly changing. The _____ component of the baroreceptor reflex arc responds to increases in pressure but not to decreases. If the systolic upstroke quickens, the number of receptors and their discharge increases. The ____ component becomes more prominent as the mean arterial pressure increases.

1. phasic

2. tonic

23

Because baroreceptors are sensitive to rapid changes in blood pressure,tehy are very responsive to beat-to-beat changes in blood pressure and tend to opose changes in pressure that occur over minutes or hours. What happens to the sensivity of these receptors to blood pressure after several days? What receptors then become responsible for controlling blood pressure?

After several days of altered mean arterial pressure, they adapt and so other control systems, notably those that regulate body fluid balance, are responsible for controlling sustained changes in blood pressure (e.g. as occurs in hypertension).

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