Study Notes on Neurons and Neurotransmission

Mod 9

Neurons and the Nervous System

• Neuron

  • Definition: A nerve cell; the basic building block of the nervous system.

Structure of Neurons

• Cell Body

  • Definition: The part of a neuron that contains the nucleus; the cell's life-support center.

• Dendrites

  • Definition: A neuron's often bushy, branching extensions that receive and integrate messages, conducting impulses toward the cell body.

• Axon

  • Definition: The neuron extension that passes messages through its branches to other neurons or to muscles or glands.

• Myelin Sheath

  • Pronunciation: [MY-uh-lin]

  • Definition: A fatty tissue layer segmentally encasing the axons of some neurons; enables vastly greater transmission speed as neural impulses hop from one node to the next.

• Glial Cells (Glia)

  • Definition: Cells in the nervous system that support, nourish, and protect neurons; they also play a role in learning, thinking, and memory.

Neural Impulses

• Action Potential

  • Definition: A neural impulse; a brief electrical charge that travels down an axon.

• Threshold

  • Definition: The level of stimulation required to trigger a neural impulse.

• Refractory Period

  • Definition: In neural processing, a brief resting pause that occurs after a neuron has fired; subsequent action potentials cannot occur until the axon returns to its resting state.

• All-or-None Response

  • Definition: A neuron's reaction of either firing (with a full-strength response) or not firing.

Synapse and Neurotransmission

• Synapse

  • Pronunciation: [SIN-aps]

  • Definition: The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.

  • Important Note: The tiny gap at this junction is called the synaptic gap or synaptic cleft.

• Neurotransmitters

  • Definition: Chemical messengers that cross the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.

• Reuptake

  • Definition: A neurotransmitter's reabsorption by the sending neuron.

Types of Neurotransmitters

• Endorphins

  • Pronunciation: [en-DOR-fins]

  • Definition: "Morphine within"; natural, opiate-like neurotransmitters linked to pain control and to pleasure.

• Agonist

  • Definition: A molecule that increases a neurotransmitter's action.

• Antagonist

  • Definition: A molecule that inhibits or blocks a neurotransmitter's action.