ESA 1 - ICPP > The ANS > Flashcards

The ANS Flashcards

(17 cards)

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1
Q

Describe the general organisation of the nervous system.

A
  • Consists of the central nervous system (CNS) - brain & spinal cord, and peripheral nervous system (PNS).
  • PNS has 2 branches:
    • somatic (conscious perception and voluntary movement)
    • autonomic (involuntary movement and functions)
  • ANS has 2 branches:
    • sympathetic (fight or flight)
    • parasympathetic (rest & digest)
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2
Q

What is the function of the ANS?

A
  • Regulates involuntary functions of internal organs (e.g. Heart and stomach).
  • Controls smooth & cardiac muscle, and glands.
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3
Q

How do sympathetic and parasympathetic nerves differ?

A
  1. Site of origin from CNS
    • Sympathetic: thoracolumbar nerves - originate in lateral horn of thoracic and lumbar spinal cord.
    • Parasympathetic: craniosacral nerves - originate in lateral horn of medulla (cranial) and sacral spinal cord.
  2. Ganglia location
    • Sympathetic: in paravertebral chain close to spinal cord - 1 signal can rapidly activate many effectors
    • Parasympathetic: further from spinal cord, even within innervated tissue - activate single organs
  3. Relative length of fibre
    • Sympathetic: short myelinated pre-ganglionic fibres -> long unmyelinated post-ganglionic fibres
    • Parasympathetic: long myelinated pre-ganglionic fibres -> short unmyelinated post-ganglionic fibres
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4
Q

Which neurotransmitters are used in the ANS?

A
  • All pre-ganglionic nerve fibres are cholinergic: release ACh and activate nAChRs on post-ganglionic cells.
  • Most sympathetic post-ganglionic nerve fibres are adrenergic: release NA and activate adrenoreceptors on post-ganglionic cells.
  • Some sympathetic post-ganglionic nerve fibres are cholinergic: release ACh and activate mAChRs on post-ganglionic.
  • Sympathetic post-ganglionic neurones in the medulla of adrenal glands differentiate to form neurosecretory chromaffin cells. Do not project into a target tissue but release adrenaline into the bloodstream.
  • Parasympathetic post-ganglionic nerve fibres are cholinergic: use ACh to activate mAChRs on post-ganglionic cells.
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5
Q

What type of NT receptors are found in the ANS?

A
  • Nicotinic ACh receptors (on post-ganglionic neurones) - ligand-gated ion channels
  • Muscarinic ACh receptors (in parasympathetic innervated tissues, in some sympathetic innervated tissues e.g. Sweat glands and piloerector muscles) - GPCRs
  • Adrenoreceptors (in most sympathetic innervated tissues) - GPCRs
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6
Q

Give examples of alternative NT used in the ANS.

A

In some situations (often co-released with ACh or NA) non-adrenergic, non-cholinergic (NANC) transmitters are used. E.g.

  • ATP
  • serotonin (5HT)
  • nitric oxide
  • several neuropeptides inc. neuropeotide Y, vasoactive intestinal peptide & substance P
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7
Q

Describe the changes occurring in the sympathetic ‘fight or flight’ response.

A

Activate ‘survival functions’:

  • Dilate pupils
  • Increase heartbeat
  • Relax airways
  • Stimulate release of glucose
  • Adrenaline and noradrenaline secretion

Deactivate non-essential functions:

  • Inhibit activity of stomach, intestines, gallbladder and saliva secretion
  • Relax bladder
  • Promote ejaculation/vaginal contraction
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8
Q

Describe the changes occurring in the parasympathetic ‘rest and digest’ response.

A

Deactivate ‘stress’ responses:

  • Constrict pupils
  • Slow heartbeat
  • Constrict airways
  • Inhibit release of glucose

Promote digestion:

  • Stimulate activity of stomach, intestines, gallbladder and saliva secretion
  • Contract bladder
  • Promote erection of genitals
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9
Q

What is the effect of sympathetic release of NA on the heart?

A
  • positive chronotropy (beta1 in SA node)

- positive inotropy (beta1 in ventricles)

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10
Q

What is the effect of sympathetic release of NA on adrenoRs throughout the body?

A
  • a1 (Gq): vasoconstriction (SM in vasculature), pupillary dilation (dilator pupillae in eye), continence (IUS of bladder)
  • a2 (Gi): CNS
  • B1 (Gs): increased HR (SAN) and inotropy (ventricles)
  • B2 (Gs): bronchodilation (lungs)
  • B3 (Gs): continence (detrusor relaxation)
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11
Q

What is the effect of sympathetic release of NA in the kidney?

A

Renin release from juxtaglomerullar cells (B1 R)

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12
Q

What is the effect of parasympathetic release of ACh on the heart?

A

Acts primarily in atria rather than ventricles as regulates rate rather than contraction force.

  • bradycardia (M2 in SA node)
  • decrease conduction velocity (M2 in AV node)
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13
Q

What is the effect of parasympathetic release of ACh on smooth muscle?

A
  • bronchoconstriction (M3 in lungs)
  • increased intestinal mobility/secretion (M3 in GI tract)
  • bladder contraction (detrusor) and relaxation (trigone/sphincter) (M3 in GU tract)
  • penile erection (NO generation)
  • ciliary muscle and iris sphincter contraction
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14
Q

What is the effect of parasympathetic release of ACh on glands?

A

Increase sweat, salivary and lacrimal secretion (M1 and M3)

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15
Q

Why does the sympathetic system increase vaso-/veno-constriction in some tissues but not others?

A

Prioritises blood flow:

  • Promotes vasodilation in the brain, skeletal muscle and heart
  • Promotes vasoconstriction of BVs to skin - minimises bleeding in injured
  • Promotes vasoconstriction to non-essential function organs (e.g. GI tract)
  • Promotes venoconstriction to increase cardiac return
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16
Q

What is dysautonomia?

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A

Malfunctions of the ANS

17
Q

Give examples of dysautonomias.

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A
  • Cathecolamine disorders
    E.g. Pheocromocytoma (constitutive A & NA release from cancerous adrenal cells)
  • Central autonomic disorders
    E.g. Multiple system atrophy (fatal, many commonalities with neurodegenerative conditions)
  • Peripheral autonomic disorders
    E.g. Guillain-Barre syndrome
    E.g. Familial dysautonomia
  • Orthostatic intolerance syndrome
    E.g. Postural orthostatic tachycardia syndrome (POTS)
  • Paroxysmal autonomic syncopes
    E.g. Neurocardiogenic syncope
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