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Question 1

Afferent, interneuron, efferent

Answer 1

Afferent nuroun
Sensory receptor = Generates an action potential in
response to a stimulus
Cell body: Adjacent to the spinal cord (no dendrites)
Note: axon terminals project slightly into CNS
Long peripheral axon = Afferent fibre (feedback to CNS)

Interneurons: 99% of our neurons (>100 billion!)
- link between afferent / efferent systems
- Important in integrating peripheral
responses to peripheral information

Efferent neuron crossing from CNS to PNS
Cell bodies are in CNS, axons in PNS.
Signal originates in brain or received from interneuron

Question 2

Ganglion

Answer 2

cluster of neuronal cell bodies outside of the CNS
Purpose: coordinate and relay signals from different neurons
Each autonomic neural pathway extending from the CNS to an innervated organ is a two-neuron chain
- Cell body of the presynaptic neuron => Located in the CNS
- Preganglionic fibre => Synapses with the cell body of the second neuron in a ganglion
- Axon of the second neuron => Postganglionic fibre

Varicosity: unlike synaptic knobs, postganglionic autonomic fibres end in terminal branches with numerous
swellings that simultaneously release neurotransmitters over large areas of target organ rather than single
cells.

Question 3

The sympathetic nervous system

Answer 3

(from the thoracic and lumbar regions
Short preganglionic fibres, synapse in the sympathetic ganglia chain (‘sympathetic trunk’) located along
the side of the spinal cord, and long postganglionic fibre => innervates effector organs
- Some pass through the ganglion without synapsing => They synapse in a sympathetic collateral
ganglia

Question 4

The parasympathetic nervous system (from the brain and sacral/lower spinal cord)

Answer 4

The parasympathetic nervous system (from the brain and sacral/lower spinal cord)
- Long preganglionic fibres that will reach a terminal ganglion in or near the effector organ
- Very short postganglionic fibres ending on cells of an organ itself

Question 5

what do they release at the end terminal

Answer 5

sympathetic: adrenergic fibres: norepinephrine, epinephrine
parasympathetic: cholinergic fibers: ACh

Question 6

Innervation of visceral organs

Answer 6

Very often, these systems have opposed
actions.
They are usually partially active =>
Parasympathetic and sympathetic ‘tones’
(tonic activity).
Sometimes one system will show Dominance
“Fight-or-flight“ (SNS) versus “rest-and-digest”
(PNS)
Innervation of visceral organs