Life Sciences Term 2

Structure and function of a simple reflex arc

A reflex arc

• The simplest form of nervous activity is the reflex action, which are actions you do without thinking
• The nerve pathway taken in a reflex action is called a reflex arc
  
• The nervous message goes to the spinal cord, and then a message passes from the spinal cord directly to an effector to give an immediate response.

Significance of a reflex arc

• A reflex action is involuntary or automatic
• Simple reflexes are inborn safety mechanisms to protect the body by producing immediate responses to the changes in the external and internal environments.

A synapse

• A synapse is the point where an impulse passes from the terminal branch of the axon of the one neuron to the dendrite of the next neuron
• The neurons NEVER touch each other
• The gap between the two neurons is called the synaptic gap
• Chemical neurotransmitters such as acetylcholine/dopamine/serotonin help to transmit the impulse from one neuron to the next across the synaptic gap.

Significance of a synapse

• Ensures that the impulse travels in one direction
• At the synapse a nerve impulse can either be speeded up or slowed down or blocked
• Therefore, it enables unnecessary or unimportant background stimuli to be filtered out
• Channels impulses so that reactions are integrated and become part of learning and memory.