Neurons structure and function

• what does the nervous system communicate via?

  Billions of neurons
• How do nerve cells communicate with each other?

  through electrical (within each neuron) and chemical (between each neuron) messages within the body and brain.
• what is a neuron?

  The basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals.
• sensory neurons


  these carry messages from the peripheral nervous system to the central nervous system. They have long dendrites and short axons.
• relay neurons


  these connect the senory neurons to the motor or other relay neurons. They have short dendrites and short axons.
• motor neurons


  these connect the central nervous system to effectors such as muscle and glands. They have short dendrites and long axons.
• what is the signal or 'action potential.'?

  an explosion of electrical activity that always passes from the dendrites along the axon to the axon terminals.
• what are the main parts of the basic neuron structure?

  - dendrite

  - nucleus

  - cell body

  - myelin sheath

  - axon

  - node of ranvier

  - axon terminals
• how large are neurons?

  neurons can measure anywhere from less than a mm to around a metre.
• what is a dendrite?


  a short branched extension of a nerve cell body. It receives signals from other neurons or from sensory receptor cells.
• what is the nucleus?

  found within the cell body. Is the control centre of the cell which contains the cells chromosomal DNA.
• what is the Myelin sheath made up of?

  individual Schwann cells.
• what is the function of the Myelin sheath?

  insulates / protects the axon from external influences that might affect the transmission of the nerve impulse down the axon.
• What is the axon?

  The axon is a long slender fibre that carries nerve impulses, in the form of an electrical signal known as action potential, away from the cell body towards the axon terminals, where the neuron ends.
• what is the node of ranvier?

  gaps in the myelin sheath which speed up the transmission of impulse by forcing it to 'jump.
• what are the axon terminals?

  The axon terminal connects the neuron to other neurons (or directly to organs), using a process called synaptic transmission.
• Reflex arc (knee jerk example)


  A stimulus such as a hammer hits the knee. This is detected by sense organs in the peripheral nervous system which conveys a message along a sensory neuron. The message reaches the central nervous system, where it connects with a relay neuron. This then transfers the message to a motor neuron. This then carries the message to an effector such as a muscle, which then causes the muscle to contract, hence, causes the knee to move or jerk.