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HLSC-126 > Module 7 - PNS Efferent Division > Flashcards

Module 7 - PNS Efferent Division Flashcards

1
Q

What are the neurotransmitters used by the efferent division of the PNS?

A

Acetylcholine and norepinephrine

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2
Q

Describe the autonomic nervous system

A

• Part of PNS
• Controls automatic or involuntary functions
• Major function is homeostasis
• Responsible for fight or flight response
• Sends messages from the brain to the glands for hormonal secretion
• Sends messages from the brain to the smooth and cardiac muscles
• Can also be subdivided
o Sympathetic Nervous System
o Parasympathetic Nervous System
o Two systems work in opposition of each other to be able to respond to stimuli and then return to homeostasis

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3
Q

Describe the basic nerve pathway of the efferent division of the autonomic nervous system

A 
•	Uses a 2-neuron chain
•	First neuron
o	Cell body located within CNS
o	Preganglionic fibre
	Axon that reaches the ganglion where it synapses with the second neuron
•	Second neuron
o	Cell body located within ganglion 
o	Postganglionic fibre
	Axon of second order neuron 
	Innervates effector organ
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4
Q

What neurotransmitters are used by the sympathetic and parasympathetic nervous systems?

A

All preganglionic neurons use acetylcholine as neurotransmitter

Postganglionic neurons in sympathetic system use norepinephrine

Postganglionic neurons in parasympathetic system use acetylcholine

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5
Q

Where do the nerves originate and where are the ganglia for the sympathetic nervous system? What is another name for most of the postganglionic neurons?

A

• Nerves originate in the thoracic and lumbar regions of the spinal column
• Sympathetic ganglion chain
o Ganglia located in chains on either side of vertebral column
o Most preganglionic fibers are short with long postganglionic fibers
• Collateral ganglia
o Ganglia located halfway between CNS and effector organ
o Some preganglionic fibers synapse here rather than in the chain
• All preganglionic neurons use acetylcholine as neurotransmitter
• Adrenergic fibers
o Common name for most postganglionic fibers
o Use norepinephrine (also called noradrenaline) as a neurotransmitter

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6
Q

Where do the nerves originate and where are the ganglia for the parasympathetic nervous system? What is another name for most of the postganglionic neurons?

A

• Nerves originate in brain and sacral region of the spinal column
• Ganglia located next to or within the innervated organ
o Long preganglionic fibers and very short postganglionic fibers
• First and second neurons use acetylcholine as neurotransmitter
• Cholinergic fibers
o Common name for postganglionic fibers
o Due to use of acetylcholine as a neurotransmitter

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7
Q

What is sympathetic dominance?

A
  • Sympathetic fiber firing rate goes above the tonic level
  • Parasympathetic fibers firing rate goes below the tonic level
  • Fight or Flight
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8
Q

What is parasympathetic dominance?

A
  • Parasympathetic fiber firing rate goes above the tonic level
  • Sympathetic fibers firing rate goes below the tonic level
  • Rest and Digest
  • Works in direct opposition of the sympathetic
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9
Q

What is dual innervation of the autonomic nervous system and how does it work?

A

• Like operating the gas and brake using only one foot
• Tonic control
o Like slowing down by just taking your foot off the gas
• Antagonistic control
o Like slowing down by taking your foot off the gas and applying the break
• Reciprocal control
o Increased activity in one division happens with decreased activity in the other division

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10
Q

What are some exemptions to the reciprocal control of the autonomic nervous system?

A

• Innervated blood vessels
o Most arterioles and veins have only sympathetic control
• Sweat glands
o Only sympathetic have acetylcholine for neurotransmitter
• Salivary glands
o Innervated by both sympathetic and parasympathetic fibers
Both sides stimulate secretion but composition and volume changes

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11
Q

Describe the adrenal medulla and its role in the autonomic nervous system

A 
•	Inner portion of the adrenal gland
•	Modified sympathetic ganglion 
•	Stimulation by the preganglionic fiber causes hormone secretion 
o	80% epinephrine
o	20% norepinephrine
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12
Q

What are the two types of cholinergic receptors?

A

Nicotinic and muscarinic

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13
Q

What are the 2 types of the adrenergic receptors?

A

alpha and beta

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14
Q

Describe nicotinic receptors of the autonomic nervous system

A
  • Type of cholinergic receptor
  • Activated by nicotine
  • Found on postganglionic cell bodies in all autonomic ganglia
  • Respond to acetylcholine from sympathetic and parasympathetic preganglionic fibers
  • Binding opens Na+ and K+ channels resulting in depolarization and subsequent action potential of the postganglionic cell
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15
Q

Describe muscarinic receptors of the autonomic nervous system

A
  • Type of cholinergic receptor
  • Activated by mushroom poison muscarine
  • Found on effector cell membranes
  • Bind to acetylcholine from parasympathetic postganglionic fibers
  • 5 subtypes linked to G proteins that activate a second-messenger system leading to target cell response
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16
Q

What is another term for adrenergic receptors of the autonomic nervous system?

A

Catecholamine receptors

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17
Q

Describe alpha receptors of the autonomic nervous system

A
  • Have a 1 and 2 subclassifications
  • Both have greater affinity for norepinephrine than epinephrine
  • Both use the Ca2+ second-messenger system but α1 blocks cAMP production
  • α1 is usually excitatory and present in most sympathetic target tissues
  • α2 is usually inhibitory
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18
Q

Describe the various beta receptors of the autonomic nervous system

A 
Beta Receptors
•	Have a 1, 2, and 3 subclassifications
•	β 1 receptors
o	Have equal affinity for epinephrine and norepinephrine 
o	Uses cAMP system
o	Primarily excitatory and located in the heart
•	β2 receptors 
o	Uses cAMP system
o	Generally inhibitory 
o	Causes dilation in lungs and blood vessels
o	Salbutamol uses these receptors 
•	β3 receptors
o	Less common in the body 
	Is located in adipose tissue 
o	Primarily bind to epinephrine
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19
Q

What are agonist drugs?

A
  • Binds to the same receptor as the neurotransmitter

* Mimics the effect of the neurotransmitter

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20
Q

What are antagonist drugs?

A
  • Binds to the same receptor as the neurotransmitter

* Block the neurotransmitters response

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21
Q

Where are the cell bodies of the motor neurons located?

A
  • Axons extend from motor nuclei of cranial nerves in the brain stem for face and head
  • Axons extend from anterior (ventral) gray horns at all levels of spinal cord for limbs and trunk
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22
Q

What neurotransmitter is used by the somatic motor neurons?

A

Acetylcholine

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23
Q

What happens with polio virus?

A

Cell bodies of crucial motor neurons selectively destroyed resulting in paralysis of the muscles they control

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24
Q

What is ALS?

A

Amyotrophic lateral sclerosisAmyotrophic Lateral Sclerosis (ALS)
• Also called Lou Gehrig’s disease
• Progressive degenerative disease that attacks motor cortex regions of
o Cerebrum
o Axons of upper motor neurons in lateral white funiculi
 Corticospinal and rubrospinal tracts
o Lower motor neuron cell bodies
o Most common motor-neuron disease
• Actions include
o Neurofilaments blocking axonal transport
o Extracellular accumulation of glutamate at toxic levels
 Excitatory neurotransmitter
o Aggregation of misfolded intracellular proteins
o Mitochondrial disfunction
• Causes progressive muscle weakness and atrophy
• Often begins in hands and arms, but rapidly spreads
• Does not affect intellect or sensations
• Death typically occurs in 2 – 5 years
• Causes
o Gene mutation
o Mutation to protein that breaks down glutamate
o Free radical damage
o Autoimmune response
o Viral infections
o Deficiency of nerve growth factor
o Apoptosis
o Environmental toxins
o Trauma
• Treatment
o Riluzole
o Medications to help with symptoms
o Physical, occupational, and speech therapy
o Nutritionists
o Social workers
o Home care
o Hospice care

25
Q

What is the terminal button?

A

Axon terminal enlarged into a knob like structure that fits into a cleft of underlying muscle (called the motor end plate)

26
Q

Where on the muscle fiber is the neuromuscular junction located?

A

The middle

27
Q

What is the motor end plate?

A

o Shallow depression, or cleft, in the muscle below the terminal button

28
Q

What neurotransmitter is used at neuromuscular junctions and what is the enzyme that breaks it down?

A

• Acetylcholine (ACh) is the neurotransmitter used
o Enzyme acetylcholinesterase (AChE)
 Quickly breaks down ACh at motor end plate

29
Q

What type of receptors are neuromuscular junctions?

A

• Nicotinic cholinergic receptors

30
Q

Describe the end-plate potential

A

• End-plate potential (EPP)
o Graded potentials similar to EPSP
o Larger than EPSP because
 More neurotransmitter released from terminal button than other cell types
 Motor end plate larger surface area with more densely packed receptors
 More ion channels opened as a response
o Results in action potential initiated in the muscle fibre
 Usually each action potential from a nerve result in an action potential of the muscle fibre

31
Q

What is a depolarization block?

A

Sodium channels trapped in an inactivated state prohibiting initiation of new action potential

32
Q

How does black widow venom affect the neuromuscular junction?

A

Triggers explosive release of ACh from storage vesicles in all cholinergic sites including neuromuscular junctions. This causes prolonged depolarization, the most dangerous of which is respiratory failure. Prolonged depolarization can cause depolarization block where sodium channels are stuck inactive and cannot be stimulated resulting in failure to contract the diaphragm

33
Q

How does botulinum toxin affect the neuromuscular junction?

A

Blocks release of ACh from the terminal button; this can cause death via respiratory failure due to inability to contract the diaphragm

34
Q

How does the curare toxin affect the neuromuscular junction?

A

Antagonist found in plants. Binds to ACh receptor sites on the motor end plate but does not initiate and action potential and is not broken down by AChE; prevents depolarization by ACh and results in paralysis, which if occurring to the diaphragm can cause death

35
Q

How do organophosphates affect the neuromuscular junction?

A

Irreversible inhibits AChE so ACh is not broken down and continuous muscular contraction occurs. Death results due to respiratory failure as the diaphragm cannot repolarize and return to resting potential as normal to allow for breath intake

36
Q

Describe Myasthenia Gravis and how it affects the neuromuscular junction

A

Myasthenia Gravis
• Autoimmune condition involving neuromuscular junctions
• Destroys ACh receptors at motor end plates
o AChE has chance to break it down before ACh can stimulate action potential
• Symptoms
o Extreme muscle weakness
• Treatment
o Neostigmine
 Inhibits AChE to allow ACh a longer time to stimulate contraction

37
Q

Which one of the following is caused primarily by parasympathetic stimulation?

a) dilation of pupil
b) constriction of bronchioles
c) decreased gastric motility
d) increased heart rate

A

B

38
Q

The influx of which ion triggers the release of vesicles from the terminal button of a motor neuron?

a) CA2+
b) Cl-
c) K+
d) Na+

A

A

39
Q

Where are the parasympathetic ganglia found?

A

Close to the effector organs

40
Q

What is the primary neurotransmitter at neuromuscular junctions?

A

Acetylcholine

41
Q

Which type of nerve fiber innervates the ventricles of the heart to increase contractility?

a) sympathetic preganglionic
b) sympathetic postganglionic
c) parasympathetic preganglionic
d) parasympathetic postganglionic

A

B

42
Q

Using your knowledge of neuromuscular junctions, identify the correct channels that depolarize the motor end plate

a) calcium channels
b) cation channels
c) potassium channels
d) sodium channels

A

B

43
Q

Explain what is meant by sympathetic or parasympathetic tone

A

Usually both systems are partially active on any organ at any particular time. Under certain circumstances, either system may increase its done and become dominant

44
Q

Describe how olfactory receptor cells are activated

A

Following the binding of an appropriate scent signal to a receptor on an olfactory receptor cell, G-protein activation leads to the production of cAMP, which in turn leads to the opening of Na+ channels. The inward flux of Na+ depolarizes the receptor cell and generates an action potential in the afferent fiber

45
Q

If a person is unable to sweat, which one of the following is a likely reason?

a) parasympathetic postganglionic neurons are not secreting norepinephrine
b) parasympathetic postganglionic neurons are not secreting acetylcholine
c) sympathetic postganglionic neurons are not secreting norepinephrine
d) sympathetic postganglionic neurons are not secreting acetylcholine

A

D

46
Q

What do most sympathetic postganglionic neurons release? What are the exceptions to this?

A

Norepinephrine

Sweat glands and some blood vessels in skeletal muscle

47
Q

If a person sustained damage to their hypothalamus, which of the following autonomic activities would be most impacted?

a) regulation of heart rate
b) regulation of urination
c) regulation of defecation
d) regulation of fine motor control

A

A

48
Q

Describe how destruction of motor neurons by poliovirus or amyotrophic lateral sclerosis (ALS) can be fatal?

A

If the motor neurons that control the respiratory muscles, especially the diaphragm, are destroyed by poliovirus or ALS, the person is unable to breathe and dies (unless breathing is assisted by artificial means)

49
Q

Explain why epinephrine, which causes arteriolar constriction in most tissues, is frequently administered with local analgesics?

A

By promoting constriction, epinephrine reduces blood flow to the region of the injection, helping the analgesic to stay localized instead of being washed away

50
Q

Predict what would happen if acetylcholinesterase was not present in neuromuscular junctions

A

Without AChE to remove ACh from the neuromuscular junction, ACh would continuously evoke end-plate potentials and, therefore, cause continuous, incontrollable muscle contractions

51
Q

Illustrate the origin, termination, fiber length, and neurotransmitter released for parasympathetic and sympathetic preganglionic fibers and post ganglionic fibers

A

Sympathetic - origin in thoracolumbar regions of spinal column, short cholinergic (acetylcholine-releasing) preganglionic fibers, long adrenergic (norepinephrine-releasing) postganglionic fibers; terminate in the effector organs or the adrenal medulla (modified sympathetic ganglion releasing epinephrine and norepinephrine

Parasympathetic - origin is brain and sacral region of spinal column, long cholinergic preganglionic fibers, short cholinergic postganglionic fibers; terminate in the effector organs

52
Q

Illustrate the origin, termination, fiber length, and neurotransmitter released for parasympathetic and sympathetic preganglionic fibers and post ganglionic fibers

A

Sympathetic - origin in thoracolumbar regions of spinal column, short cholinergic (acetylcholine-releasing) preganglionic fibers, long adrenergic (norepinephrine-releasing) postganglionic fibers; terminate in the effector organs or the adrenal medulla (modified sympathetic ganglion releasing epinephrine and norepinephrine

Parasympathetic - origin is brain and sacral region of spinal column, long cholinergic preganglionic fibers, short cholinergic postganglionic fibers; terminate in the effector organs

53
Q

Compare the times of sympathetic and of parasympathetic dominance

A

Sympathetic dominates in emergency or stressful situations preparing body for strenuous physical activity

Parasympathetic dominates in quiet, relaxed situations and promotes good housekeeping activities

54
Q

Discuss the relationship of the adrenal medulla to the autonomic nervous system

A

A modified sympathetic ganglion that does not give rise to postganglionic fibers but instead, when stimulated, secretes the hormones epinephrine and norepinephrine into the blood

55
Q

Compare the effector organs innervated by the autonomic nervous system and by the somatic nervous system

A

Autonomic - innervates cardiac and smooth muscles, most exocrine glands, some endocrine glands, and adipose tissue

Somatic - innervates skeletal muscle

56
Q

Explain why motor neurons are considered the final common pathway

A

The only way any other parts of the nervous system can influence skeletal muscle activity is by acting, in common, on these motor neurons

57
Q

Discuss the role of ACh and AChE at a neuromuscular junction

A

ACh - neurotransmitter which results in an action potential at the end-plate of the muscle fiber

AChE - enzyme in the membrane of the motor end plate and inactivates ACh, removing ACh allows for relaxation

58
Q

Compare the magnitude of an EPP and an EPSP, and explain the functional significance of this difference

A

EPP is larger
EPP usually large enough to bring end-plate to potential for one-to-one transmission
EPSP not enough to bring about an action potential, needs summation to initiate and action potential

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