automomic nervous system

Question 1

what is the ANS

Answer 1

• responsible for regulation of visceral functions and maintenance of homeostasis of the internal environment
• is not under conscious control

Question 2

General organisation of ANS

Answer 2

• Consists of a two neuron chain
• First neuron -cell body in the central nervous system (Preganglionic Neuron)
• Synapse in ganglia where second order neurons originate from and which innervate effectors
(Postganglionic Neuron)

Question 3

organisation of SANS (sympathetic)

Answer 3

• Preganglionic neurons lie in the intermediolateral cell column between T1-L2 (i.e. thoracolumbar outflow)
• Preganglionic fibres synapse in paired paravertebral ganglia (22 of these on either side of the spinal cord extending from cervical to sacral region)
• Preganglionic fibres may pass up/down the paravertebral ganglia before synapsing

Question 4

exceptions for SANS organisation

Answer 4

• Some preganglionic neurons pass through the paravertebral ganglia without synapsing
• These preganglionic neurons eventually synapse with postganglionic neurons in the prevertebral ganglia
• These postganglionic neurons innervate the glands, blood vessels and smooth muscles of the abdominal and pelvic viscera
• Some preganglionic fibres directly innervate the adrenal gland
• Adrenal gland may be considered to be a specialized sympathetic ganglia
• The effect of stimulation is to release adrenaline and nor adrenaline into the blood resulting in a diffuse, wide ranging sympathetic response

Question 5

SANS neurotransmitters

Answer 5

• Between pre and postganglionic neurons the neurotransmitter is acetylcholine -the receptor subtype is nicotinic (cholinergic)
• Between postganglionic neuron and effector the neurotransmitter is noradrenalin -the receptor subtype is adrenergic

Question 6

Organisation of PANS

Answer 6

• Cell bodies of preganglionic neurons lie in the brainstem and intermedioalateral cell column of the sacral spinal cord (Cranio-sacral outflow)
• The ganglia of the PANS are located in close proximity to the effector structure. In some case the ganglia (and postganglionic neuron) are part of the effector structure

Question 7

neurotransmitters of the PANS

Answer 7

• Between pre and postganglionic neurons the neurotransmitter is acetylcholine -the receptor subtype is nicotinic
• Between postganglionic and effector the neurotransmitter is acetylcholine -the receptor subtype is muscarinic

Question 8

patterns of innervation

Answer 8

• dual antagonistic innervation (e.g. heart - SANS: cardiac accelerator nerve + PANS: vagus nerve)
• single innervation (e.g.
• dual non-antagonistic innervation (e.g. male genitalia - SANS: ejaculation + PANS: erection)

Question 9

ANS higher brain centres

Answer 9

• Visceral afferents enter spinal cord via dorsal horn
• Second order neurons terminate in various brainstem nuclei and thalamus and hypothalamus
• Activation of these afferents generates autonomic reflexes e.g. baroreceptors (afferents reach brainstem via vagus)
• In response to danger -defence reaction -normal reflex control overridden, increases in HR, BP, CO