A learning objective merges required content with one or more of the seven science practices. The AP ® Learning Objectives listed in the Curriculum Framework provide a transparent foundation for the AP ® Biology course, an inquiry-based laboratory experience, instructional activities, and AP ® exam questions. Information presented and the examples highlighted in the section support concepts outlined in Big Idea 3 of the AP ® Biology Curriculum Framework. Many drugs, including both pharmaceuticals and drugs of abuse, can induce changes in synaptic transmission for example, tetrahydrocannabinol (more commonly known as THC) in marijuana binds to a naturally occurring neurotransmitter important to short-term memory. Neurotransmitters may be either excitatory (such as acetylcholine or epinephrine) or inhibitory (such as serotonin or GABA) as they either increase or decrease the change of an action potential in the postsynaptic neuron. Synaptic vesicles at the axon terminal of the presynaptic neuron release chemical messengers called neurotransmitters into the junction neurotransmitters then bind to receptors embedded in the membrane of the postsynaptic neuron. Transmission of a nerve impulse from one neuron to another or to another type of cell such as a muscle cell occurs across a junction called a synapse. In myelinated neurons, action potentials “jump” between gaps of unmyelinated axons (nodes of Ranvier), a phenomenon called saltatory conduction. Repolarization occurs when K + flows across the membrane to the outside. In depolarization, the inside of the membrane becomes more positive than the outside as Na + flows to the inside. In response to a stimulus, such as an odorant molecule, membrane potential changes, and an action potential is generated along the membrane as the voltage-gated Na + and K + channels open sequentially, causing the membrane to depolarize. It is also important to recall that ions cannot diffuse across the lipid bilayer of the cell membrane and must use transport proteins in this case, the transport proteins are voltage-gated Na + and K + channels.Īt rest, the Na +/K + pump, powered by ATP, maintains this gradient, known as resting membrane potential. The neuron, however, uses Na + and K + to establish a gradient. We explored the formation of electrochemical gradients using H + when we studied photosynthesis and cellular respiration.
When an axon is at rest, the membrane is said to be polarized that is, there is an electrochemical gradient across it, with the inside of the membrane being more negatively charged than the outside. Action potentials propagate impulses along neurons. Like other eukaryotic cells, neurons consist of a cell membrane, nucleus, and organelles, including mitochondria. Information flow along a neuron is usually from dendrite to axon and from neuron to neuron or from neuron to a cell of a target organ.
The neuron is a great example of a structure-function relationship at the cellular level.
In this section, you will explore the following questions:
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