Chapter 9

What is the reflex arc

Nerve pathway from a sensory neuron to the spinal cord and then to muscles, bypassing the brain.

Identify the advantages of a reflex arc.

No conscious thought is required for this type of action. The impulse follows a direct route from the receptor to the effector with an interconnecting link in the spinal cord. Additional impulses are sent to the appropriate part of the brain to keep it 'informed' of what happened. The reflex arc can be described in terms of a stimulus-response model. The stimulus may be the heat from a candle and our response may be to move away from the candle quickly.

Describe how a neuron works and identify the role of a synapse in message transmission.

The gaps between the neurons, called synapses, have to be crossed by the impulse. Chemical compounds called neurotransmitters are produced in little pockets at the end of a neuron's axon. They carry the impulse across the synapse to the next neuron. The message is then converted back into an electrical impulse, which continues down that axon until it reaches the next synapse or finishes its travels at the effector.

Describe the endocrine system.

Uses chemical messengers called hormones. They are produced in your endocrine glands and are released directly into your bloodstream. Although hormones are carried to all parts of your body, only particular cells are targeted. It is a little like radio signals that are sent out in all directions, but picked up only by radios attuned to a particular signal. These target cells are attuned to the hormones carried through your body and respond in a particular way.

Neurons

cells that are part of the nervous system and designed to carry electrical impulses

Synapses

junctions between the axon of one neuron and the dendrite of the neuron receiving the electrical impulse