autonomic nervous system

  • ANS: autonomic nervous system

  • innervate: connect to an organ or tissue with functional nerves

  • emotions depends on body states
    • the vice verse is also true

  • some parts of the body states are voluntarily produced, while others are automatically produced

  • consider a panic attack
    • the body first response,
    • reactions are all about protecting are the body
    • followed by the emotions that result from that body state
    • the one example of when the emotion and body state are out not working together
      • there is a phase difference between the two
  • in most other cases
    • emotion and body state work together as one unit
  • this post will explore the automatic (involuntary) body states
    • primarily on the sympathetic and parasympathetic nervous system
    • they give rise to automatic body states that affect emotion

three parts

  1. sympathetic
  2. parasympathetic
  3. enteric

enteric nervous system

  • shared by all vertebrates
  • lines up with the digestive tract
    • mouth to anus
  • there are intrinsic neurons
    • 100 million neurons
    • they form the enteric nervous system
  • the form two different plexuses
    • one is responsible for pumping food in the digestive system
    • the other one is responsible for section of stuff
      • eg. secretion that regulates the wateriness of poop

automatedness

  • this is the most automated of the autonomic nervous system
    • pushing food though digestive system happens automatically
      • “peristalsis’
    • needs no conscious effort from the organism
  • disease: Hirschsprung’s disease (megacolon)
    • found in children
    • a section of the gastro-intestinal (GI) tract is aganglionic
      • i.e. neurons of the enteric nervous system are missing
    • so the food until this section is pushed through
      • but then, the GI tract in the aganglionic section is contracted
      • nothing is pushed through the contraction
    • this is fixed surgically by placing an innervated piece of digestive tract
      • having removed the aganglionic section

influence on mood and emotion

  • the enteric nervous system communicates with the central nervous system (CNS)

  • a lot of information is sent to the central nervous system
    • receives info from the central nervous system
      • through the sympathetic and the parasympathetic nervous system
    • sends ten time more info to the CNS than it receives from the CNS
  • so, a lot info from the digestive tract is sent to the CNS
    • the state of digestive tract influence a person’s mood a lot
  • going the other way, a person’s emotions affects bowel movement
    • how we feel influences the gastrointestinal tract
  • so, many psychiatric diseases are associated with the certain GI issues

parasympathetic and sympathetic nervous system

  • parasympathetic and sympathetic (PS/S) nervous system is a subset of the autonomous nervous system (ANS)

  • two different systems, working together through two-chain neurons
  • they’re both automatic

  • both are motor systems

  • they target three different types of tissues
    • smooth muscle
    • cardiac muscle
    • glands
  • the sympathetic system is the fight-or-flight system
  • parasympathetic the rest and digest, sleep and heal injury type system

location

  • the sympathetic system comes entirely from neurons in the thoracic cord

  • the parasympathetic system from two places
    • from the cranium through cranial nerves
    • from the sacral cord (bottom of the spinal cord)
  • so, parasympathetic system is often called the “cranio-sacral” system

function

  • they work in opposition, to produce different functional ends

  • example: heart
    • both innervate the heart
    • parasympathetic system drives the heart rate down
    • sympathetic system drives the heart rate up
  • example: eyes
    • both innervate the eyes
    • parasympathetic system makes the pupil small
    • sympathetic system makes the pupil big
  • both the sacral cord and the thoracic innervates
    • bladder
    • colon
    • sexual organs
  • but they do different non-opposing things
    • parasympathetic is critical for sexual arousal
    • sympathetic is critical for sexual climax

sympathetic system only

  • some organs and tissues are innervated only the sympathetic system
    • no innervation by the parasympathetic system
  • example: sweat glands
    • sympathetic system turns on the sweat glands
  • example: piloerection
    • getting ready to hunt, focussing on something
    • only affected by the sympathetic system
  • example: cutaneous (skin) blood vessels
    • restricted vs dilated blood vessels
    • when exercising, skin blood vessels dilate to release heat to the environment
    • this is handled only by the sympathetic system
    • consequently, blood pressure will go up or down
      • more blood to the skin leads to lower pressure, as it fills a larger volume
      • constricted flow at the skin leads to high pressure
  • example: adrenal medulla
    • gland that pumps out cortisol
    • cortisol is a stress hormone
      • lacking in case of addison’s disease

sympathetic-parasympathetic balance

  • parasympathetic - fight or flight

  • sympathetic - rest or digest

  • instantaneous control:
    • not 100% parasympathetic mode or 100% sympathetic mode all the time
    • surrounding events change the amount of control exercised by either system
    • a well designed control system that responds to stimuli
      • disregarding disorders and diseases
  • lifetime trend:
    • young beings are parasympathetically dominated
    • with ageing, there is increase in sympathetic domination
  • sympathetic domination leads to
    • increased heart rate and increased blood pressure
    • leads to hypertension

closer look at autonomic system

  • all motor neurons use acetylcholine (ACh) to realize muscle contraction

  • all motor neuron receptors are nicotinic ACh
    • regardless of whether post-synaptic is a skeletal muscle or a ganglion cell
  • nicotinic type ACh receptors are fast ionotropic receptors
    • their response is fast
  • to draw contrast consider a motor neuron
    • it innervates a skeletal muscle
    • it does so via a single neuron
    • a single neuron connection exists with a skeletal muscle for its operation
chained system
  • both sympathetic and parasympathetic systems together are chained systems
    • both finally actuate either a smooth muscle, cardiac muscle or a gland
    • however, unlike a motor neuron, they get to the target via two neurons
  • they both target three different types of tissues
    • smooth muscle
    • cardiac muscle
    • glands
  • the first stage neuron sits in the CNS
    • called the pre-ganglionic motor neuron
    • it connects to a ganglionic neuron outside the CNS in the PNS
    • so the first neuron is a ganglionic neuron

  • the second stages neuron in the PNS then bridges this first ganglionic neuron to the target

  • CNS to PNS is fast response
    • this is neuron to neuron communication
    • myelinated axon
    • fast nicotinic post-synaptic receptors
  • PNS to target is slow response
    • neuron to organ communication
    • unmyelinated axon
    • slow metabotropic post-synaptic receptors
  • both parasympathetic and sympathetic ganglionic neurons both use acetylcholine (ACh)
  • they both go to ganglionic cells that express nicotinic ACh receptors
  • however, the two systems diverge at what happens after the chain connection
parasympathetic divergence
  • the chain ganglion that innervates the parasympathetic to its target
    • sends a post-ganglionic, unmyelinated axon
    • this releases ACh at the target
  • the post-synaptic of parasympathetic targets express muscarinic ACh receptors
    • each target has its own signature muscarinic receptor
    • in contrast with the fast ionotropic response of nicotinic receptors,
      • muscarinic ACh receptors display metabotropic behavior
    • metabotropic: response takes own sweet time (slow)
sympathetic divergence
  • the chain ganglion that innervates the sympathetic to its target
    • sends an post-ganglionic, unmyelinated axon
    • this releases norepinephrine (NE) at the target
  • the post-synaptic of sympathetic targets express adrenergic receptors
    • adrenergic receptors receive messages from norepinephrine (NE)
    • metabotropic: response takes own sweet time (slow)
    • there are two kinds of adrenergic receptors
      • alpha adrenergic receptors and
      • beta adrenergic receptors

balance restoration

  • there are several conditions that cause imbalance in the sympathetic/parasympathetic system
  • if nothing else, aging generally caused sympathetic system domination
    • rest and digest events reduce while fight or flight events increase
  • this necessitates pharmacological aid (drugs) in the body
    • agonists - drugs that work like a neurotransmitter
      • used in cases of degraded neurotransmitter release
    • antagonists - drugs that inhibit a neurotransmitter
      • used in cases of over active neurotransmitter
  • treatment of imbalance is by imitation or blocking of ACh or NE
    • to imitate parasympathetic effects, use drug that acts like ACh at muscarinic receptors
    • to stop parasympathetic effects, block muscarinic ACh receptors
  • example: to reduce secretions
    • antagonize muscarinic ACh receptors with appropriate pharmacological aid
  • example: to treat hypertension
    • use beta-blockers to block beta version of adrenergic receptors
effect on CNS
  • drugs that act on the parasympathetic system either mimic it or block, stay in the PNS
    • do not affect the CNS
    • they have no direct effect on the brain
    • they may cause side effects dry mouth, dry eyes, bad mood etc, but do not have psychotropic effects
  • drugs that act of the sympathetic system also act in the CNS
    • they demonstrate psychotropic effects
    • they directly affect mood and motivation

spinal cord injury

  • the location of the pre-ganglionic neurons is another feature of the PS/S system
  • the parasympathetic and sympathetic system cores both sit in the spinal cord
    • the PS sits at the top (cranial nerves) and bottom (sacral cord) of the spinal cord
    • the S sits in the lower middle spinal cord
  • parasympathetic innervation is the most vulnerable to spinal cord injuries

  • the sacral cord is isolated in injuries

  • the sacral cord does not make decisions
    • depends on input from the brain
  • example: when an individual wants to urinate
    • a whole part of the prefrontal cortex runs an algorithm to check for
      • safety
      • socially appropriate etc
    • then it signals the sacral cord to the program for urination
    • the actual program for urination is run in the sacral cord
    • the sacral cord does not run the algorithm to initiate the urination
    • the bladder is a smooth muscle
      • it is contracted by the neurons in the sacral cord
      • it is a parasympathetic event
    • in addition there is an external urethral sphincter that lets the urine out
      • that is a voluntary muscle
      • it has to be relaxed to let out urine
    • in the case of a spinal cord injury
      • when the bladder fills up it contracts
      • but the urethral sphincter never opens
    • this condition is bladder dyssynergia
      • it is a problem in the case of spinal cord injuries
      • one of the first things that physicians test for
  • in the topmost part of the thoracic region of the sympathetic part of the spinal cord
    • there are pre-ganglionic cells that go to the eye pupil
    • they are also go to the eyelid
    • the eyelid has two muscles
      • levator palpebrae: innervated skeletal voluntary muscle
      • superior tarsus: other one in the back is a smooth muscle
    • superior tarsus is innervated my the sympathetics
      • while asleep, low sympathetic
      • while awake, comes up to a minimum waking state level
        • including a contraction of the superior tarsus
        • which makes the eyelid come up
    • so some people can sleep with their eyes open
      • due to a sympathetic mal-condition

embodied emotion

  • different emotions are associated with particular body states
  • body state is crucial to feel the accompanying emotion
    • else body falls out of sync with the emotion appropriate for the environment
  • body’s emotion is regulated a lot by the ANS
  • body experiences influences our emotions via the ANS
    • ANS is an involuntary response to body experience
    • it communicates to the conscious about how to feel about body experiences

treatment of PTSD

  • under normal circumstances, memories are made primarily of emotional events
  • for example, the location of keys is not particularly an emotional event
    • so it is hard to remember where it was last placed
    • so most people form a habit of putting it in the same place
    • so they can find it again easily without thinking about it

  • but everyone remembers what they were doing while watching the 9/11 attack news

  • every time we remember something, the memory gets reconsolidated and re-experienced

  • PTSD is a high sympathetic arousal state of the body
    • a particular memory triggers an sympathetic system dominant imbalance
  • so one way PTSD is treated is by triggering PTSD memory in the presence of beta-blockers
  • the idea is to stop the violent body triggers if this procedure is repeated several times
    • and provide some relief to PTSD sufferers
  • the negative body response to PTSD is pharmacologically prevented with beta-blockers
    • during this particular reconsolidation of the memory, the body response doesn’t get included
    • only the non-body response is reconsolidated

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