the peripheral nervous system- efferent division: the autonomic nervous system

what does the autonomic nervous system do

• all the motor outputs from the CNS apart form those to skeletal muscle

• provides motor control of the heart, smooth muscles and glands

are the actions voluntary or involuntary

involuntary

what is the autonomic nervous system divided into

• sympathetic

• parasympathetic

what do the sympathetic and parasympathetic nervous system have a primary role in

• regulating the internal environment

• functions to maintain homeostasis

what are the main functions of the ANS

• contraction and relaxation of smooth muscle

• control of exocrine and some endocrine glands

• control of cardiac function

• regulation of energy metabolism

what do the sympathetic and parasympathetic systems usually produce

• producing opposing physiological effects

• dual innervation

what does the autonomic nervous system pathway consist of

2 neurons in series

where do the 2 neurons in series synapse

at. the autonomic ganglia

where does the pre-ganglionic neuron have its cell body

• in the CNS

• synapses in the autonomic ganglion

where does the post-ganglionic neuron have its cell body

• in the autonomic ganglion

• synapses with the effector organ

pre-ganglionic sympathetic neurons

• leave from thoracic and lumbar regions of the spinal cord (thoracolumbar system)

• synapse at ganglia close to spinal cord (sympathetic chain)

• innervate the adrenal medulla causing release of adrenaline into the bloodstream

post-ganglionic sympathetic neurons

• they are noradrenergic

• the NT released at the neutron-effector organ synapse is noradrenaline (NA)

pre-ganglionic parasympathetic neurons

• leave from brain stem and the sacral region of the spinal cord (craniosacral system)

• synapse at ganglia close to effector organ

post-ganglionic parasympathetic neruons

• they are cholinergic

• acetylcholine is released at the neurone-effector organ synapse

heart

• sympathetic
  increased heart rate
  increased force of contraction

• parasympathetic

  decreased heart rate

blood vessels (arterioles)

• sympathetic
  constriction (skeletal muscle-dilation)

• parasympathetic
  no effect/dilation (via NO)

bronchi

• sympathetic
  dilation

• parasympathetic
  constriction

GIT (gut motility)

• sympathetic
  decreased motility (sphincter contraction)

• parasympathetic
  increased motility (sphincter relaxation)

bladder

• sympathetic
  relaxation (sphincter contraction)

• parasympathetic
  contraction (sphincter relaxation)

pupil

• sympathetic
  dilation

• parasympathetic
  contraction

glands

• sympathetic
  no effect (except for sweat gland secretion)

• parasympathetic
  secretion

kidney (renin secretion)

• sympathetic
  increased

liver

• sympathetic
  increased glucose

adipose tissue

• lipolysis

what are the 2 major NT of the PNS

• acetylcholine

• noradrenaline

where do the acetylcholine and noradrenaline act at

• act at receptors

• mediate their responses in the post-synaptic cell

what are the 2 receptor subtypes in the ANS that acetylcholine acts as

• nicotinic receptors

• muscarinic receptors

nicotinic receptors

ligand-gated ion channels activated by acetylcholine

muscarinic receptors

G-protein coupled receptors activated by acetylcholine

acetylcholine in the ANS acting at nicotinic receptors

• acetylcholine released from both sympathetic and parasympathetic pre-ganglions as well as synapses with adrenal medulla

• acts at nicotinic receptors at the synapses in the autonomic ganglia and adrenal medulla

• rapid responses

• stimulates AP in the post-ganglionic neurons

• stimulate adrenaline release

what are the different subtypes of nicotinic receptors

• skeletal muscle

• ganglionic

• CNS

acetylcholine in the ANS acting at muscarinic receptors

• acetylcholine released from parasympathetic post-ganglionic neurons

• acts at muscarinic receptors at the synapses with the target organ

• stimulates the response in the target cell

what are the different subtypes of muscarinic receptors

• M1

• M2

• M3

• M4

• M5

Noradrenaline in the ANS

• released from post-ganglionic neurons of the sympathetic nervous system

• noradrenaline acts at receptors at the synapse with the target organ

• n noradrenaline acts at adrenoceptors

• all adrenoceptors are GPCR

what are the 2 major subtypes of adrenoreceptor

• alpha

• beta

targets for drug action at the synapse

1. uptake of precursors

2. synthesis of transmitter

3. storage of transmitter in vesicles

4. degradation of surplus transmitter

5. AP

6. influx of Ca2+

7. release of NT

8. diffuson to post-synaptic membrane

9. interaction with postsynaptic receptor

10. inactivation of transmitter

11. reuptake of NT

12. uptake of NT by non-neuronal cells

13. interaction with pre-synaptic receptors