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C&M Neuroanatomy > Week 7 Lecture 14: Autonomic Nervous System > Flashcards

Week 7 Lecture 14: Autonomic Nervous System Flashcards

1
Q

Give three key features of the ANS

A
  • largely involuntary
  • monitors conditions in the internal environment to maintain homeostasis
  • influenced rostrally by the hypothalamus
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2
Q

How is the peripheral nervous system divided?

A
  1. Somatic (controls external actions of skin and muscles)
  2. Autonomic (controls internal activities of organs and glands)
    - sympathetic
    - parasympathetic
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3
Q

What is homeostasis?

A

a dynamic balance between the autonomic branches (parasympathetic and sympathetic)

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4
Q

What does the parasympathetic branch control?

A

“rest and digest” –> sustains normal bodily functions

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5
Q

What does the sympathetic branch control?

A

“fight or flight” –> prepares body for stress

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6
Q

What type of fibres are autonomic (visceral) motor?

A

efferent fibres to smooth muscles, cardiac muscles and glands

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7
Q

What type of fibres are autonomic (visceral) sensory?

A

afferent fibres from sensory receptors in an internal organ (conduct sensory impulses from viscera to CNS)

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8
Q

Where are the cell bodies of efferent fibres and in which spinal nerves are they found?

A

in the lateral grey horn of the spinal cord

ONLY carried within segmental spinal nerves T1-L2 and S2-S4

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9
Q

Explain what referred pain is

A
  • pain sensations from visceral organs often perceived as regions of the body surface innervated by the same spinal nerves
  • so the brain thinks this pain is coming from that area of the skin e.g in an MI, the pain is referred to the upper chest and limb on the left hand side
  • as parts of the arm and chest share the same spinal nerves as they enter so the brain interprets the information as though their coming from these regions of the skin
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10
Q

How do efferent fibres travel from the CNS to the PNS

A
  1. Efferent fibres leave the CNS to bring an effect to a target organ
  2. Two neurone chain: pre ganglionic and post ganglionic
  3. autonomic ganglion (located in PNS) connects the cell body of the pre ganglion (in the CNS) with the post ganglionic neurone (in the PNS)
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11
Q

What does the ANS innervate?

A 
smooth muscles (organs)
cardiac muscle (heart)
glands (e.g salivary, lacrimal, sweat)
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12
Q

What are the differences in outflow in the sympathetic and parasympathetic NS?

A

Sympathetic: thoracocolumbar outflow - only occurs between T1 and L2
Parasympathetic: cranialsacral outflow - brainstem CN III, VII, IX, X and S2-S4

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13
Q

What are the differences in organisation in the sympathetic and parasympathetic NS?

A

Sympathetic: organised ganglia called the sympathetic chain. Series of ganglia that extend throughout the whole length of the cord
Parasympathetic: occurs at the brain stem and then travel to the periphery via those specific nerves - and outflow to the S2-S4 levels of cord. ganglia near effector organ. not highly organised

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14
Q

What are the differences in size of effect in the sympathetic and parasympathetic NS?

A

Sympathetic: widespread effect –> sympathetic input can effect many target organs
Parasympathetic: localised effect

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15
Q

What does ‘cranio-sacral origin’ mean?

A

brainstem and S2-S4 –> where the cell bodies of the pre ganglionic neurones in the parasympathetic division will be located

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16
Q

In parasympathetic innervation, axons of the pre-ganglionic neurone leave the brain stem using which cranial nerves?

A

CN III, VII, IX or X

The axons leave using S2-S4 spinal nerves

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17
Q

Which neurotransmitter is secreted by pre ganglionic and post ganglionic in the parasympathetic division?

A

Acetylcholine (Ach)

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18
Q

Why is the effect of parasympathetic division localised?

A

1 pre: 1 post - equal ratio of neurones means the effect can be localised

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19
Q

Where do parasympathetic fibres travelling via CN III go?

A

to the pupil

20
Q

Where do parasympathetic fibres travelling via CN VII go?

A

To salivary and lacrimal glands

21
Q

Where do parasympathetic fibres travelling via CN IX go?

A

To salivary glands

22
Q

Where do parasympathetic fibres travelling via CN X go?

A

To cardiac, pulmonary and digestive systems

23
Q

What do cranial nerve parasympathetic fibres do to:

  1. Pupils
  2. Salivation and tears
  3. Heart rate and breathing
  4. Digestion
A
  1. constricts pupils
  2. decreases salivation and tears
  3. decreases heart rate and constricts bronchi (as we don’t need to breath that much)
  4. allows digestion - increases peristalsis
24
Q

Which cranial nerve is the main parasympathetic nerve of the viscera of the trunk?

A

vagus nerve

25
Q

what do the parasympathetic fibres from S2-S4 do?

A

leave as pelvic splanchic nerves to innervate distal large intestine, kidney, bladder and some reproductive organs. these fibres allow defaecation, urination and erection

26
Q

How is the trigeminal nerve involved in parasympathetic innervation?

A

Fibres pass from their ganglia to the respective organ by “piggy backing” onto branches of the trigeminal nerve (head and neck only) to reach target organs

27
Q

In the sympathetic division, which neurotransmitter is released in:

  1. pre ganglion
  2. post ganglion
A
  1. Ach

2. noradrenaline/norepinephrine

28
Q

How can the sympathetic division have widespread effects? (2 reasons)

A
  1. neuronal divergence
    - one pre ganglionic fibre can synapse and influence many post ganglionic neurones, therefore stimulating many effector organs
  2. adrenal medulla
    - some pre-ganglionic fibres travel directly to the adrenal medulla (they do not synapse with any ganglion)
    - adrenal medulla synthesises and releases norepinephrine and epinephrine into the blood stream (widespread release = widespread effect)
29
Q

Why is the sympathetic chain known as the ‘distribution hub’?

A
  • All preganglionic fibres leave cord in segmental spinal nerves – T1-L2 only (only exists at these levels)
  • Run to the sympathetic chains
  • From sympathetic chain distributed to the body
30
Q

What do sympathetic fibres do to:

  1. Pupils
  2. saliva and lacrimal glands
  3. heart rate
  4. breathing
  5. digestion
A
  1. dilates pupils
  2. inhibit secretions from saliva and lacrimal glands (as we do not want to be salivating and lacrimating during stress)
  3. heart rate increases
  4. bronchi dilate
  5. inhibit digestion
31
Q

What is the sympathetic trunk/chain?

A
  • interconnected chain of autonomic ganglia located on either side of the entire vertebral column
  • sites of synapse between sympathetic pre and post ganglionic neurones
32
Q

What are the three different roots a preganglionic neuron can take to find a ganglion to synapse

A
  1. Leaves cord and synapses at entry level in sympathetic trunk – paravertebral ganglia – post ganglionic neuron goes to thorax or skin of body wall
  2. Pass through sympathetic trunk without synapsing – so synapse in prevertebral (collateral) ganglia or adrenal medulla
  3. Ascend or descend - pre ganglionic neurone goes up or down a couple of levels instead of synapsing e.g to innervate head or pelvic organs
33
Q

What is the white ramus communicans?

A
  • in the sympathetic division
  • contains myelinated pre-ganglionic sympathetic fibres (myelinated is why we call it white–> appears white)
  • only between T1-L2
  • pre ganglionic are myelinated and use the white rami communicans to leave
34
Q

What is the grey ramus communicans?

A
  • contains unmyelinated post ganglionic fibres
  • all levels of the cord
  • post ganglionic fibres are not myelinated and they use gray ramus communicans to leave the cord and rejoin the spinal nerve
35
Q

How is oxygen in blood and bP monitored?

A
  • carotid body and sinus monitor blood pressure and oxygen
  • sensory visceral afferent fibres travel via the glossopharyngeal nerve toward the medulla oblongata giving information about state of oxygen in blood and BP which can then be controlled by the vagus nerve
36
Q

Explain the default state of the bladder

A

somatic innervation forms the default state. the external urethral sphincter is under constant contraction by the pudendal nerve so we are not urinating all the time

37
Q

What does the brain do when we want to urinate?

A

sends instructions voluntarily to relax the urethral sphincter
infants cannot hold urine because they have not acquired the voluntary contraction of the external urethral sphincter

38
Q

How is the sympathetic nervous system involved in mictuition?

A

prevents urination:

  • sympathetic NS relaxes detrusor muscle and contracts the internal urethral sphincter –> this allows us to fill the bladder with urine
  • stretch receptors in the bladder sense the level of distention of the detrusor muscle
39
Q

How is the parasympathetic nervous system involved in mictuition?

A
  • pre-ganglionic parasympathetic fibres contract detrusor muscle to compress it and allow urine to leave, as well as relaxing the internal urethral sphincter
  • however we do not urinate until we voluntarily tell our pudendal nerve to relax the internal sphincter
40
Q

Explain autonomic control of defecation

A
  • sympathetic prevents rectum emptying
  • parasympathetic induces rectum emptying
  • somatic voluntary inhibition of rectum emptying via pudendal nerve
41
Q

How is the Parasympathetic NS involved in rectal emptying?

A

Pre-ganglionic parasympathetic fibres leave via S2-4 to induce peristalsis and emptying of the rectum in situations when we are able to rest

42
Q

What is the default state of defaecation?

A

inducing contraction of external anal sphincter preventing defaecation

43
Q

What is Horner’s syndrome?

A
  • injury to sympathetic supply of head and neck

- characterised by ptosis, miosis, lack of sweating

44
Q

What might be a consequence of injury to cord or cauda equina?

A

disrupt sympathetic control to bladder

disrupt parasympathetic control of bladder, rectum, sexual functions

45
Q

What are the borders of the hypothalamus?

A

anterior: lamina terminalis
ventral: optic chiasma
inferior and posterior: brainstem

46
Q

What are 3 functions of the hypothalamus?

A
  1. controlling influence upon activity of the ANS –> exerts overall control and regulation of ANS
  2. central role in neuroendocrine function (via connections with pituitary) –> releases and synthesises some hormones
  3. important connections with the limbic system
47
Q

Explain the levels of ANS control of functioning

A
  1. cerebrum - emotional responses
  2. hypothalamus - overall control and regulation
  3. brainstem centres - cardiovascular, respiratory, swallowing
  4. spinal cord centres - urination, defaecation, erection, ejaculation

C&M Neuroanatomy (44 decks)

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