Peripheral nervous system: efferent division

Question 1

what is the efferent division of the PNS?

Answer 1

the communication link by which the CNS controls the activities of the effector organs

Allows CNS to control muscles, glands, secretions, movement: homeostasis

Question 2

What nervous system is involved in the efferent PNS?

a. autonomic
b. somatic
c. both a and b

Answer 2

c

Question 3

What are the two branches of the autonomic nervous system?

Answer 3

sympathetic and parasympathetic

Question 4

What is the autonomic nervous system controlling?

Answer 4

involuntary responses of visceral organs(cardiac and smooth muscles) exocrine and some endocrine

Question 5

What does the somatic nervous system control?

Answer 5

voluntary e.g. skeletal muscles

Question 6

What are the two neurons in the autonomic nervous system?

Answer 6

preganglionic fiber

postganglionic fiber

Question 7

How many neurotransmitters are released by the autonomic nervous system on the structures it controls?
What are the two neurotransmitters?

Answer 7

Only two different neurotransmitters: acetylcholine and norepinephrine

Question 8

What is the significance of varicosity? (the postganglionic fiber terminates in a structure ) ** slide 5 listen

Answer 8

Affect all of the effector organs innervated at once. Helps the entire organ function together instead of separate units

Question 9

The following are characteristics of the sympathetic or parasympathetic nervous system?

a. nerve fibers originate from thoracic and lumbar regions of the spinal cord
b. preganglionic fibers: short, release Ach
c. postganglionic fibers: long, release norepinephrine (andrenergic)
d. synapse within the blank ganglion chain/collateral ganglion

Answer 9

Sympathetic nervous system

blank = sympathetic

Question 10

The following are characteristics of the sympathetic or parasympathetic nervous system?

a. nerve fibers originate from the cranial and sacral levels of the CNS
b. preganglionic fibers: long, release Ach
c. postganglionic fibers: short, release Ach (cholinergic)
d. most synapse at terminal ganglia near effector organs

Answer 10

parasympathetic nervous system

Question 11

If you want to walk, you think about it, but the actions to walk are via involuntary actions, what part of the PNS is involved with this?

Answer 11

The somatic nervous system

Question 12

What is true about the action of parasympathetic and sympathetic nervous systems?

Answer 12

They are both active at all times, but one may predominate at any given moment

Question 13

What is an example of sympathetic dominance?

Answer 13

Fight or flight response, prepares the body for stressful situations

• all responses are to protect the body
• perform functions more efficiently

Question 14

what is an example of parasympathetic dominance?

Answer 14

dominates in a quiet, relaxed situation

• low heart and respiratory rate
• promote digestion and urination
• responsible for house keeping activities (cook and clean, but don’t do it when you have an exam)
• conserves energy

Question 15

Does the autonomic nervous system have synapses?

Answer 15

No, only varicosity

Question 16

What are some involuntary functions the ANS is responsible for ?

Answer 16

circulation, digestion, sweating urination

Question 17

What organs receive dual/reciprocal innervation?

Answer 17

visceral organs

Question 18

What is the advantage of dual/reciprocal innervation?

Answer 18

It allows precise control over the activity of an effector organ

Question 19

What happens in the body during sympathetic dominance?

Answer 19

• dilate blood vessels supplying skeletal muscles
• increases heart and respiratory rate
• converts glycogen to glucose (needed by muscles) in liver
• promote sweating
• dilate pupils of the eye and bronchioles (far vision can see clearly ahead)
• inhibit digestion and urination (don’t want these to happen in emergency)

Question 20

What is sympathetic dominance aimed at?

Answer 20

increasing flow of oxygenated, nutrient rich blood to skeletal muscles: strenuous physical activity

Question 21

What are the exceptions of dual/reciprocal innervation?

Answer 21

• sympathetic only: arterioles and veins, sweat glands
• salivary glands: have both systems, but leads to increased salivation (thicker saliva sympathetic, parasympathetic saliva = more enzymes so it is thinner)

Question 22

When there are receptors present at different locations, the receptors are coupled to different signaling pathways, and different kinds of receptors have different sensitivity to the neurotransmitters, what is this called?

Answer 22

Target specificity

Question 23

The somatic nervous system signals what?

Answer 23

skeletal muscle via motor neurons

Question 24

What constitutes the somatic nervous system?

Answer 24

Axons and cell bodies

the cell bodies lie in the ventral horn

Question 25

How do the somatic nervous system and the autonomic nervous system differ?

Answer 25

In the somatic nervous system axons do not synapse in the ganglion, the SNS can only stimulate skeletal muscle contraction - cannot relax

Question 26

What diseases can result from disturbances in the somatic nervous system?

Answer 26

polio, lou gehrig's disease (ALS)

Question 27

Efferent motor neurons are also composed of two neuron chains. True or false?

Answer 27

False - they don't synapse or stop anywhere, they go directly to the fiber

Question 28

Why are the somatic motor neurons known as the final common pathway?

Answer 28

Because once the signal is transferred in a particular axon fiber, it will bring about skeletal muscle contraction and it cannot make the muscle relax

Question 29

What is the neuromuscular junction?

Answer 29

The point where the terminal branches (unmyelinated) terminate on the muscle fiber is known as the neuromuscular junction

Question 30

Efferent neuron (myelinated) -> terminal branches (unmyelinated) -> ?

Answer 30

neuromuscular junctions

Question 31

What is a neuromuscular junction made of?

Answer 31

terminal button: knob like terminal at muscle fiber | Motor end plate: muscle cell membrane below terminal button

Question 32

What chemical messenger (neurotransmitter) is released when an action potential reaches the terminal button?

Answer 32

acetylcholine

Question 33

In a neuromuscular junction what leads to the generation of end plate potential?

Answer 33

the release of Ach

Question 34

What is an end plate potential responsible for?

Answer 34

muscle contraction

Question 35

where is the action potential initiated?

Answer 35

axon hillock

Question 36

What happens when the action potential at the axon terminal reaches the terminal button?

Answer 36

it brings about a conformational change in the voltage gated calcium channels in the terminal button, therefore opening them

Question 37

When the VG calcium channels open as a result of the action potential what happens?

Answer 37

Calcium is usually more concentrated outside, so calcium rushes into the cell (influx) at the terminal button, when the calcium comes into the cell, exocytosis of Ach from the terminal button is initiated

Question 38

When Ach is released from the terminal button what happens?

Answer 38

Ach diffuses through the space between the nerve cell and muscle cell and binds to receptor sites on the motor end plate of the muscle cell, which produces a local current flow that opens adjacent sodium channels in the motor end plate, the electrical gradient of sodium favors the inside so it goes into the muscle cell resulting in initiation of a small depolarization (graded potential)

Question 39

After graded potentials in the motor end plate summate and cause an action potential through the muscle fiber, how is the process stopped?

Answer 39

acetylcholinesterase (AChe) terminate the activity of Ach at the nerumuscular junction (NMJ)

Question 40

How is the neuromuscular junction similar to synapses?

Answer 40

It is an important drug target because it is vulnerable to chemical agents and diseases

Question 41

What is acetylcholinesterase

Answer 41

a membrane bound enzyme that destroys floating Ach -> rapid hydolysis

Question 42

What are some things that affect neuromuscular junctions?

Answer 42

Toxins (black widow spider venom, botulinum toxin) Curare Organophosphates Myasthenia gravis

Question 43

What do toxins do?

Answer 43

they alter the release of Ach causing respiratory (diaphragm) failure

Question 44

What is the toxic effect of black widow spider venom?

Answer 44

explosive release of Ach (think spider man exploding web)

Question 45

What is the toxic effect of botulinum toxin?

Answer 45

Blocks release of Ach | - food poisoning - food not stored properly can create botulinum toxin

Question 46

What happens when Ach is explosively released?

Answer 46

too much Ach release can cause continuous influx of sodium ions, even though potassium is leaving the cell, sodium keeps coming in other channels, not allowing the membrane to get back to -70 mV making the muscle unresponsive

Question 47

What happens if there is too much ach in the diaphragm (respiratory muscle)?

Answer 47

the diaphragm stays in contraction

Question 48

What happens if Ach is released?

Answer 48

If the diaphragm does not receive Ach, it will be unable to contract, so inhalation and exhalation will not be possible

Question 49

How does curare effect the neuromuscular junction?

Answer 49

it blocks ach receptors at the motor end plate - if animals are shot with curare arrows they become immobile and are easily hunted - Ach receprots are blocked so even if Ach is released there is no action potential and one dies of respiratory failure

Question 50

How do organopohsphates effect neuromuscular junctions

Answer 50

organophosphates are insecticides and pesticides - they irreversibly inhibit acetylcholinesterase (AChE), so Ach levels will rise which has a similar effect as black widow spider venom

Question 51

What is myasthenia gravis?

Answer 51

loss of Ach receptors at motor end plate, so action potentials can't be generated - auto- immune disease, causes extreme muscular weakness