Neuroanatomy (College Board AP® Psychology): Revision Note

The structure & function of neurons

• Neurons are individual nerve cells that transmit information throughout the nervous system

  • They are the fundamental building blocks of all behavior and mental processes

• The human nervous system contains billions of neurons that communicate with one another via electrical and chemical signals

• Neurons fire in only one direction — from dendrites through the cell body and down the axon toward the next neuron

Structure of a typical neuron

• Dendrites are branch-like extensions that receive incoming signals from other neurons and transmit them toward the cell body

• The cell body (soma) contains the nucleus and sustains the life of the neuron

  • It also integrates incoming signals from the dendrites

• The axon is a long, tube-like structure that carries the electrical signal away from the cell body toward the terminal buttons

• The myelin sheath is a fatty coating surrounding the axon of some neurons that insulates the axon and speeds up the transmission of electrical signals

  • Gaps in the myelin sheath, known as nodes of Ranvier, further accelerate signal transmission

  • When the myelin sheath deteriorates — as in the disorder multiple sclerosis — signal transmission slows or fails, disrupting movement and sensation

• The terminal buttons are branched endings at the tip of the axon that release chemical messengers (neurotransmitters) into the gap between neurons

• The synapse is the gap between the terminal buttons of one neuron and the dendrites of the next neuron, across which chemical communication occurs

Glial cells

• Glial cells are non-neuronal cells found throughout the nervous system that support the function of neurons

• Glial cells provide:

  • structure — forming the physical scaffolding that holds neurons in place

  • insulation — producing the myelin sheath that coats axons

  • communication — facilitating signaling between neurons

  • waste transport — clearing debris and dead cells from the nervous system

• Glial cells do not transmit information themselves but are essential to the functioning of neurons

  • Without them, neural communication would break down

• Glial cells and neurons together form the basis of the nervous system and are the building blocks of all behavior and mental processes

Three types of neurons

• Three types of neurons work together in the nervous system, each with a distinct function:

  • Sensory neurons

  • Interneurons

  • Motor neurons

The reflex arc

• The reflex arc demonstrates how sensory, motor, and interneurons work together within the CNS and PNS to produce a rapid, automatic response to a stimulus

  • The brain does not need to be involved for the reflex to occur, as the spinal cord coordinates the response and informs the brain afterward

• The reflex arc is an adaptive response

  • Its speed protects the body from harm

• The sequence of a reflex arc:

  • A sensory receptor detects a stimulus, e.g. intense heat from touching a hot surface

  • A sensory neuron carries the signal from the receptor toward the spinal cord

  • An interneuron in the spinal cord processes the signal and relays it to the appropriate motor neuron

  • A motor neuron carries the signal from the spinal cord out to the relevant muscle

  • The muscle contracts, producing the reflex response, e.g. pulling the hand away

• Conscious awareness of the stimulus (e.g. feeling pain) follows the reflex response

  • The brain is informed after the protective action has already occurred

• The reflex arc illustrates how the CNS and PNS work together

  • the spinal cord (CNS) coordinates the response while sensory and motor neurons (PNS) carry signals to and from the body