Chapter 11: Peripheral Nervous System Flashcards

1
Q

what is peripheral nervous system

A
  • includes all neural tissue outside the CNS
  • provides communication between the CNS and the rest of the body
  • has two divisions: efferent (motor) and afferent (sensory)
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2
Q

what are the parts of the efferent division?

A

1) autonomic nervous system
2) somatic nervous system

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3
Q

what is the autonomic nervous system?

A
  • acts largely unconsciously to regulate involuntary processes including heart rate, blood pressure, respiration, digestion
  • innervates most effector organs (i.e cardiac muscle, smooth muscle, glands)
  • works with endocrine and behavioural state system to maintain homeostasis
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4
Q

two divisions of the autonomic nervous system

A

1) sympathetic nervous system = fight or flight
2) parasympathetic nervous system = rest and digest

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5
Q

what is the somatic nervous system?

A
  • associated with the voluntary control of skeletal muscles and skin
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6
Q

what is the goal of the autonomic division?

A
  • to ensure homeostasis is maintained
  • one system always predominates depending on the state the body is in

at rest = the parasympathetic nervous system dominates.
body is excited or stressed = sympathetic nervous system dominates

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7
Q

describe the concept of dual innervation of the autonomic nervous system

A
  • some effector organs are innervated by both divisions of the autonomic nervous system
  • results in opposing antagonistic effects between the two autonomic divisions
  • primary function is to help regulate organs and MAINTAIN HOMEOSTASIS
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8
Q

where does dual innervation not occur?

A
  • sweat glands
  • blood vessels
  • adrenal medulla
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9
Q

what is the role of antagonistic control?

A
  • necessary for homeostasis because it allows a physiological variable to either increase or decreases
  • depends on dual innervation of a organ
  • is used in autonomic branch of nervous system (one is excitatory and one is inhibitory)
  • controls most internal organs
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10
Q

what does “fight or flight” mean?

A
  • the sympathetic nervous system is most active during periods of excitation or physical activity
  • the body prepares to cope with threatening situations
  • heart rate increases, blood pressure increases, dilate pupils, energy stores are mobilized etc
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11
Q

what does “rest and digest” mean?

A
  • the parasympathetic nervous system is most active during resting conditions
  • both stimulates the digestive organs (digestion & absorption of nutrients) and inhibits the cardiovascular system (decreasing heart rate)
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12
Q

how does the autonomic nervous system maintain homeostasis?

A
  • balances the activity levels of the parasympathetic and sympathetic nervous system

–> at low energy demands, heart doesn’t need to work hard because the body doesn’t demand blood = parasympathetic dominates
–> when body is active, energy demand increases and heart works harder = sympathetic dominates

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13
Q

how does the central nervous system regulate the autonomic nervous system?

A
  • sensory information about the state of an organ or tissue is continuously relayed to homeostatic control centres in brain stem (hypothalamus, pons, medulla)
  • the hypothalamus, pons and medulla act as an integrating centre. they take info and illicit a response
  • the control centres tightly regulate bodily functions and regulate autonomic output (via sympathetic and parasympathetic systems) to maintain systemic homeostasis
  • this means that heart rate, blood pressure, temperature etc are controlled and adjusted depending on the state of the body
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14
Q

what areas of the brain (CNS) regulate autonomic function?

A
  • mainly the hypothalamus (known as “centre for homeostasis”), the pons and medulla
  • these are called the integrating centre
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15
Q

anatomy of the autonomic nervous system

A
  • consists of two efferent pathways containing 2 types of neurons (pre-ganglionic and post-ganglionic) that communicate between CNS and effector organs
  • the neurons communicate via synapses in peripheral structures called autonomic ganglia
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16
Q

what is a visceral reflex?

A
  • automatic changes in the functions of organs in response to changing conditions in the body
  • the motor response of the body can be modified, facilitated, or inhibited by the CNS (hypothalamus, medulla, pons)
17
Q

what is the concept of autonomic regulation (tone)?

A
  • autonomic tone refers to the ongoing activity of the ANS when the body is at rest
  • is the balance between sympathetic and parasympathetic activity
  • tone can increase or decrease depending on the activity of the effector organ
18
Q

what is the function of pre-ganglionic and post-ganglionic neurons?

A
  • pre-ganglionic neurons travel from the CNS to the ganglia
  • post-ganglionic neurons travel from the ganglia to the effector organs
    –> usually a single pre-ganglionic neuron synapses with 8-9 post-ganglionic neurons
19
Q

what is the autonomic ganglia?

A
  • a cluster of synapses between pre-ganglionic and post-ganglionic neurons
  • in each ganglion, there are axon terminals of pre-ganglionic neurons
  • in each ganglion, there are cell bodies and dendrites of post-ganglionic neurons
20
Q

how do sympathetic and parasympathetic neuron pathways differ?

A

1) the pathways point of origin within the CNS
2) location of the autonomic ganglia

in sympathetic division:
- most pathways originate in thoracic and lumbar regions of spinal cord
- ganglia is proximal to spinal cord
- short pre-ganglionic neurons that synapse with ganglia
- long post-ganglionic neurons that go to effector tissue
- stimulates tissue metabolism and alertness

in parasympathetic division:
- pathways originate in brain stem and leave via cranial nerves
- ganglia is proximal to effector/target organs
- long pre-ganglionic neurons to synapse with ganglia
- short post-ganglionic neurons to effector organs
- stimulates digestion and lowers HR

21
Q

what is the role of the vagus nerve in the parasympathetic nervous system?

A
  • about 75% of all parasympathetic neurons are running through the vagus nerve
  • most parasympathetic innervation is to the head, neck and internal organs via the vagus nerve (originates in brain stem)
  • sensory info comes from internal organs to brain and parasympathetic info goes brain to internal organs
22
Q

what other nerves play a role in the parasympathetic nervous system?

A
  • cranial nerve III (occulomotor)
  • cranial nerve VII (facial)
  • cranial nerve IX (glossopharyngeal)
  • sacral spinal nerves
23
Q

what are the 2 primary neurotransmitters in the peripheral nervous system?

A
  • acetylcholine
  • norepinephrine
24
Q

what are neurons that releases neurotransmitters referred to as?

A

release acetylcholine = cholinergic
release norepinephrine = adrenergic

25
Q

what specific neurons release acetylcholine and norepinephrine?

A

acetylcholine is released by:
- pre-ganglionic and post-ganglionic neurons of parasympathetic branches
- pre-ganglionic neurons of sympathetic branch

norepinephrine is released by:
- all post-ganglionic neurons in sympathetic branch

26
Q

what are the two classes of cholinergic receptors? where are they located?

A

1) nicotinic receptors
- located on cell bodies and dendrites of sympathetic and parasympathetic post-ganglionic neurons
2) muscarinic receptors
- located on effector organs of parasympathetic nervous system (heart, smooth muscle of eye, digestive tract)

27
Q

what are the two pathways of chemical signalling in the autonomic nervous system?

A

in SYMPATHETIC nervous system:
- ACh released from the pre-synaptic neuron binds to nicotinic cholinergic receptors on the postsynaptic membrane
- it is excitatory and depolarizes the post-synaptic neuron
- NE released from the post-ganglionic binds to the adrenergic receptors on the effector/target tissue

in PARASYMPATHETIC nervous system:
- ACh released from the pre-synaptic neuron binds nicotinic cholinergic receptors on the post-synaptic membrane
- it is excitatory and depolarizes the post-synaptic neuron
- then the post-ganglionic neuron releases ACh, which binds to muscarinic cholinergic receptors on the effector organ or target tissue.
- this action can either be excitatory or inhibitory

28
Q

what is the difference between parasympathetic and sympathetic signalling pathways?

A
  • parasympathetic pathways only use acetylcholine as the neurotransmitter
  • sympathetic pathways use both acetylcholine and norepinephrine as the neurotransmitter
29
Q

what if a neuron doesn’t secrete NE or ACh?

A
  • it is called a non-adrenergic, non-cholinergic neiron
  • the neuron secrete adenosine, ATP, NO or somatostatin instead
  • the secretion depends on where their pre-ganglionic fibres leave the spinal cord
30
Q

what are the receptors on effector tissues in the sympathetic nervous system?

A
  • NE binds with adrenergic receptors
  • all adrenergic receptors act via G-proteins

1) there is an alpha class of adrenergic
–> a1 = excitatory effect
–> a2 = inhibitory effect

2) there is a beta class of adrenergic
–> b1 = excitatory effect
–> b2 = inhibitory effect
–> b3 = stimulates fat cell lipolysis

31
Q

what are the receptors on effector tissues located in the parasympathetic nervous system?

A
  • ACh binds with cholinergic receptors
  • all cholinergic receptors are G-protein coupled

–> muscarinic receptors are located on effector organs
–> the receptor is inhibitory or excitatory depending on the subtype

32
Q

what is a neuroeffector junction?

A
  • the synapse between an efferent neuron and its effector organ
  • is the target region
33
Q

how does a neuroeffector junction differ from a typical synapse?

A
  • the post-ganglionic neuron do not have discrete axon terminals
  • instead, neurotransmitters are released from several swellings along the axons called varicosities
  • the varicosities contain vesicles with the neurotransmitter
34
Q

how is a neurotransmitter released from a variscositie?

A
  • when an action potential arrives at the varicosity, depolarization occurs and causes a voltage gated calcium channel to open
  • this causes calcium to enter the cytosol and stimulate the release of the neurotransmitter via exocytosis
  • the neurotransmitter is released over the surface of target cells and binds with its receptor on the target cell
  • the neurotransmitter is terminated and removed from the synapse via diffusion away from the receptor, re-uptake or degradation by an enzyme
35
Q

what enzymes can eliminate neurotransmitters?

A

1) acetylcholinesterase acts on acetylcholine to break down into acetate and choline
2) monoamine oxidase acts on catecholamines

36
Q

what is the adrenal medulla?

A
  • the inner part of the adrenal gland
  • releases hormones (epinephrine and norepinephrine) that regulate your autonomic nervous system
  • is the endocrine component of the sympathetic nervous system
37
Q

how does the adrenal medulla secrete epinephrine into the blood?

A
  • pre-ganglionic neurons innervate the adrenal medulla (located above the kidney) instead of synapsing on post-ganglionic neurons
  • the medulla consists of modified sympathetic post-ganglionic cells (called chromaffin cells)
  • when stimulated by the SNS, the adrenal medulla releases 80% epinephrine and 20% norepinephrine, and very small amount of dopamine
  • these are secreted directly into the bloodstream to function as hormones and sent to target tissues