Autonomic nervous system Flashcards
Compare and contrast the functions and structural organisation of the somatic and autonomic nervous systems
Subdivisions of the PNS
neuronal pathways
Compare and contrast the functions and structural organisation of the parasympathetic and sympathetic divisions of the autonomic nervous system
Both ANS divisions have preganglionic and postganglionic neurons.
The preganglionic neuron is the first neuron in the pathway, running from the spinal cord to an autonomic ganglion to synapse with the second neuron.
The postganglionic neuron is the second neuron in the pathway, running from the autonomic ganglion to the target/effector.
Note that most targets/effectors of the ANS receive dual innervation, meaning they receive innervation from both the parasympathetic and sympathetic divisions.
Sympathetic NS
Enables the body to cope with stress and is commonly described as being activated in conditions of ‘fight, flight or fright’.
Cell bodies of the preganglionic neurons are found only in the lateral horn of the spinal cord
Axons of these neurons (preganglionic fibres) leave the spinal cord via the ventral roots of the spinal nerves.
The preganglionic fibre then synapses in a sympathetic ganglion that contains the postganglionic cell body
In the sympathetic division, the ganglia tend to be relatively close to the spinal cord, located in either the sympathetic trunk (chain) or the prevertebral ganglia
The sympathetic division has short preganglionic fibres and long postganglionic fibres.
organisation of the sympathetic nervous system
Parasympathetic NS
Acts as the ‘housekeeper’ of the body. Most active when an individual is calm and relaxed - ‘resting and digesting’ commander
Cell bodies of the preganglionic neurons are found in the brainstem and in the lateral horn of the sacral segments of the spinal cord
The ganglia are located either near or directly within the wall of the target/effector.
The preganglionic fibres travel considerable distances before synapsing in the ganglia
Preganglionic = long, postganglionic = short
fibres arising from the brainstem innervate the viscera of the head and neck, thorax and abdomen, whereas those arising from the sacral spinal cord innervate the lower part of the gastrointestinal tract and the pelvic viscera.
organisation of parasympathetic nervous system
Physiological effects of the ANS
Both sympathetic and parasympathetic are antagonistic (opposite effects at their targets/effectors)
Many effectors have dual innervation (both sympathetic and parasympathetic neurons) - provides ‘break’ and ‘accelerator’
Some effectors only have sympathetic innervation e.g. sweat glands
Describe the effects of the parasympathetic and sympathetic divisions on organs and body systems (visceral reflex/sensory information)
