For each fibre, say whether it is afferent or efferent, and which division it belongs to…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
For each fibre, say whether it is afferent or efferent, and which division it belongs to.
- A fibre from the skin of the foot to the spinal cord.
- A fibre from the spinal cord to a muscle of the leg.
- A fibre from the brain to the heart that makes it slow down.
- A fibre inside the spinal cord that joins two parts of it.
- A fibre from the wall of the stomach to the CNS.
Need a reminder? The key ideaShow
The CNS is the brain and the spinal cord. The PNS is the nerves. Afferent fibres bring impulses to the CNS, and efferent fibres carry them away. The somatic system serves skeletal muscles, and the autonomic system serves involuntary organs and smooth muscles. A multipolar neuron has one axon and two or more dendrites, a bipolar neuron has one axon and one dendrite, and a unipolar neuron has one axon only. Nodes of Ranvier lie between the parts of the myelin sheath.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The impulse goes to the CNS, so the fibre is afferent. It comes from the skin, so it is in the somatic part of the PNS.
Step 2. (b) The impulse goes from the CNS to a skeletal muscle. It is efferent and somatic.
Step 3. (c) The impulse goes from the CNS to an involuntary organ. It is efferent and autonomic. A signal that slows the heart belongs to the parasympathetic part.
Step 4. (d) The fibre stays in the CNS. It belongs to the CNS and not to the PNS, so it is neither afferent nor efferent in the sense of the PNS.
Step 5. (e) The impulse comes from an internal organ to the CNS. It is afferent, and it is a fibre of the visceral nervous system.
Answer: (a) afferent, somatic; (b) efferent, somatic; (c) efferent, autonomic (parasympathetic); (d) CNS; (e) afferent, visceral.
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