Chapter 7: The Peripheral Nervous System: Efferent Division

Question 1

PNS: Efferent Division

Answer 1

• communication link by which the CNS controls the muscles and glands and the effector organs that carry out intended effects or actions
• CNS regulates these effectors by initiating action potentials in the cell bodies of efferent neurons whose axons terminate on these organs

Question 2

Autonomic and Somatic Nervous Systems

Answer 2

Autonomic Nervous
- involuntary branch of the peripheral efferent division
Somatic Nervous
- branch of the efferent division subject to voluntary control

Question 3

Pathways and Divisions of the ANS

Answer 3

• an autonomic nerve pathway consists of a two-neuron chain
  Preganglionic Neuron
• synapses with the cell body of postganglionic fiber in a ganglion outside the CNS
  Postganglionic Neuron
• sends axons that end on the effector organ
  Autonomic nervous system has two subdivision
• sympathetic and parasympathetic

Question 4

Parasympathetic Postganglionic

Answer 4

• fibers release acetylcholine

- cholinergic fibers

Question 5

Sympathetic Postganglionic

Answer 5

• fibers release norepinephrine

- adrenergic fibers

Question 6

Dual Innervation

Answer 6

• sympathetic and parasympathetic nervous systems dually innervate most visceral organs
  Dual Innervation: innervation of a single organ by both branches of the autonomic nervous system
  Times of sympathetic dominance: fight or flight response
  Times of parasympathetic dominance: rest and digest response

Question 7

Advantage of Dual Autonomic Innervation

Answer 7

• reciprocally controlled
• increased activity in one division is accompanied by a corresponding decrease in the other
• the adrenal medulla is a modified part of the sympathetic nervous system
• adrenal glands are endocrine glands
• adrenal medulla secretes catecholamine hormones on stimulation

Question 8

Adrenal Medulla

Answer 8

• is a modified part of the sympathetic nervous system
• adrenal glands are endocrine glands
• adrenal medulla secretes catecholamine hormone on stimulation

Question 9

Receptors of the ANS

Answer 9

• several receptors are available for each autonomic neurotransmitter
  Cholinergic Receptors: nicotinic and muscarinic receptors
  Adrenergic receptors: alpha and beta receptors
  Autonomic Agonists and Antagonists: agonist bind to the neurotransmitter’s receptor and an antagonist binds with the receptor

Question 10

ANS and CNS

Answer 10

• many regions are involved in the control of the autonomic activities
• some autonomic reflexes are integrated at the spinal-cord level
• medulla within the brain stem is the region most directly responsible for autonomic output
• hypothalamus plays a role in integrating autonomic, somatic, and endocrine responses
• autonomic activity can be influenced by the prefrontal association cortex

Question 11

Somatic Nervous System

Answer 11

• motor neurons supply skeletal muscle
• bring about movement
• axons of motor neurons originate in the CNS and end on skeletal muscle
• motor-neuron axon terminals release ACh to stimulate muscle contraction
• motor neurons are the final common pathway

Question 12

Neuromuscular Junction

Answer 12

• motor neurons and skeletal muscle fibers are chemically linked at neuromuscular junctions
• each muscle cell has only one neuromuscular junction
  Muscle Fiber: single, long, and cylindrical muscle cell
  Terminal Button: enlarged knoblike structure at the end of axon terminal branches
  Motor End Plate: shallow depression where axon terminals end

Question 13

ACh and the Neurotransmitter Junction

Answer 13

• ACh is the neuromuscular junction neurotransmitter
• release of ACh at the neuromuscular junction
• each terminal button contains thousands of vesicles that store ACh
• formation of an end-plate potential
• collective potential change resulting from ion movements across all of the terminal buttons withing a neuromuscular junction

Question 14

Action Potential and the Neuromuscular Junctions

Answer 14

• initiation of an action potential
• EPP brings about an action potential in the muscle fiber
• acetylcholinesterase ends ACh activity at the neuromuscular junction
• enzyme in the motor end-plate membrane that turns off muscle cell’s electrical response

Question 15

The Impact of Agents/Disease on the Neuromuscular Junction

Answer 15

• is vulnerable to several chemical agents and diseases
• black widow spider venom causes explosive release of ACh
• botulinum toxin blocks release of ACh
• curare blocks action of ACh at receptor-channels
• organophosphates prevent inactivation of ACh
• Myasthenia gravis inactivates ACh receptor-channels

Question 16

How does the central nervous system cooperate with the autonomic nervous system to maintain you body temperature?

Answer 16

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Question 17

Compare and contrast “fight-or-flight” vs. “rest-and-digest.”

Answer 17

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Question 18

How might the “fight-or-flight” response help you in this course?

Answer 18

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