recap

44.4 recap

Nervous systems are composed of neural networks that include afferent neurons, interneurons, and efferent neurons. Nervous systems range in complexity from simple nerve nets to the human brain. The spinal knee-jerk reflex is an example of a simple neural network, but networks that control more complex behavior are much more complicated.

learning outcomes

You should be able to:

  • Distinguish the central from the peripheral nervous system and recognize how these systems range in complexity among different species.

  • Analyze a simple circuit and map the communication between afferent and efferent neurons.

Question 1

What are ganglia, and why are they concentrated in the anterior region of many invertebrates?

Ganglia are collections of nerve cell bodies. They tend to be concentrated in the anterior region of many invertebrates because that is where large numbers of sense organs are located.

Question 2

Draw or describe the flow of information from stimulus to response in the knee-jerk reflex circuit.

See Figure 44.14.

Question 3

In the knee-jerk reflex circuit, how can the same stimulus cause contraction in one muscle and relaxation in another?

In the knee-jerk reflex the same stimulus can cause contraction of a muscle through an excitatory synapse and relaxation of the antagonist muscle because of an inhibitory interneuron.

Question 4

When considering fish, then reptiles, then mammals, which part of the vertebrate brain increases most in size?

The part of the vertebrate brain that increases the most in going from fish to reptiles to mammals is the most anterior part of the brain, the cerebrum.