ANS - autonomic nervous system

describe the anatomy of the nervous system - 2 parts and nerves

• CNS = central nervous system = brain and spinal cord

• PNS = peripheral nervous system = nerves that leave the brain and spinal cord (everything else basically)

• nerves leaving brain = cranial nerves

• nerves leaving spinal cord = spinal nerves

structure of the nerves in the PNS

• many individual neurones

• bundles of axons - wrapped in connective tissue

• arteries and veins

structural organization of the nervous system

• information coming in to CNS travels through PNS - neurons are part of sensory division - sensory neurons - information relating to changes on skin - pressure receptors etc.

• motor division - information out of CNS towards muscle and glands

• motor division:

• somatic division - controls skeletal muscles - voluntary

• and ANS = controls smooth muscle and glands - sympathetic and parasympathetic division

what are the 2 types of neurotransmitters that responsible for the diverse effects of the ANS

• Ach and noradrenaline

describe Ach and its receptors

• Nerve fibres that release ACh are called cholinergic fibres

• Receptors that bind to ACh are call cholinergic receptors:
  • Nicotinic receptors
  • Muscarinic receptors

describe noradrenaline and its receptors

• Nerve fibres that release NA are called adrenergic fibres

• Receptors that bind to NA are call adrenergic receptors:
  • Alpha: 1 and 2 receptors
  • Beta: 1 and 2 receptors

comparison of the somatic and ANS

• in ANS = always 2 neurons - one pre ganglion neuron and one post ganglion neuron // whereas in somatic only 1 neuron (motor neuron)

comparison of parasympathetic and sympathetic nervous system

what are the effects of the sympathetic AND parasympathetic divisions on the heart

• P effect = decreases heart rate - slows heart

• S effect = increase heart rate and force of contraction

what are the effects of the sympathetic AND parasympathetic divisions on the lungs

• P effect = constricts bronchioles

• S effect = dilates bronchioles

what are the effects of the sympathetic AND parasympathetic divisions on the adrenal medulla

• P effect = no effect - no innervation

• S effect = stimulates the medulla cells to secrete adrenaline and noradrenaline

what are the effects of the sympathetic AND parasympathetic divisions on the gastrointestinal tract/digestive tract organs

• P effect = increases motility and amount of secretion by digestive organs; relaxes sphincters to allow movement of food along tract

• S effect = decreases activity of muscles and glands of digestive system and constricts sphincters

what are the effects of the sympathetic AND parasympathetic divisions on the blood vessels

• P effect = little/no effect

• S effect = constricts most vessels BUT dilation of blood vessels to cardiac and skeletal muscle via adrenaline* = *Action via Adr release from adrenal medulla

patterns of innervation of sympathetic division

• Wide field of innervation due to division in ganglion cells

• Activity has wide spread effects & provokes a mass
  response

summarise the activity of the sympathetic pathway (5)

– increase in activity in cardiac and skeletal muscle
– decrease in activity in all the viscera organs (except the heart)
– resulting in the fight or flight response
• The result is to increase the blood supply of the active
skeletal muscle and cardiac muscle.
• The blood will contain oxygen and glucose to meet the
demands of increased muscle activity.

patterns of innervation of parasympathetic divisions

• Narrow fields of innervation as ganglia are located in target organs

• Effects are local & related to activities of the respective organs

summarise parasympathetic division activity (3)

• decrease in activity in cardiac and skeletal muscles

• increase in activity in the visceral organs (except the heart)

• promotes body maintenance activities “rest and digest”

what is the dual reciprocal innervation rule

• idea that in the ANS muscles (smooth and cardiac) are innervated/controlled by parasympathetic AND sympathetic nerves which have opposing effects

• opposing muscle groups (like flexors and extensors) are controlled by paired, opposite nerve signals — when one is stimulated, the other is inhibited.

exceptions to the dual reciprocal innervation rule in terms of arterioles and veins / sweat glands / salivary glands (3)

• arterioles and veins most receive only sympathetic nerve fibers (arteries and capillaries are not innervated)

• sweat glands: most are innervated only by sympathetic nerves - But they are cholinergic fibers

• salivary glands:
  − innervated by both ANS divisions but activity is not
  antagonistic – both stimulate salivary secretion
  − Sympathetic - small amount of thick viscous saliva
  − Parasympathetic - copious amounts of watery
  saliva

summary of the cholinergic & adrenergic receptors table - receptor type / NT / synapse / response / excitatory or inhibitory / location

define agonist and antagonist in terms of drugs

• agonist = drug that binds to the same receptor as the neurotransmitter (NT) and produces the same response as the NT

• antagonist = An antagonist binds to the same receptor as the NT and blocks the NTs response

2 drugs we need to know about

salbutamol and atropine

explain how salbutamol can selectively alter autonomic response (4)

• is an agonist

• causes dilation of the bronchioles - so used to treat asthma - to increase diameter and allow more air into lungs

• does not stimulate the heart

• acts on the beta 2 receptors

explain how atropine can selectively alter autonomic response (5)

• is an antagonist

• causes dilation of the pupil - because the parasympathetic action is being inhibited

• causes inhibition of salivary and bronchial secretions

• acts on muscarinic receptor

• used in eye drops to dilate the eyes by optometrists

what is the hierachy/level of control of the ANS - in the frontal levels of the brain (2)

• The hypothalamus stands at the top of the control hierarchy as the integrator of the ANS

• However, subconscious cerebral inputs via the limbic
  lobe connections influence hypothalamic functioning

what functions of the body does the ANS control

visceral functions of the body - life-sustaining body processes that happen without you thinking about them.

like - heart rate, blood pressure, breathing, digestion, pupil dilation etc.