Neurones

• What are neurons?

  Nerve cells
• How many neurons are in the human nervous system?

  100 billion
• What percentage of neurons are located in the brain?

  Around 80%
• What is the purpose of neurons and how do they function?

  Purpose: Communication

  Function: Transmit electrical + chemical signals
• What are the three types of neurones?

  Sensory, relay, and motor
• Where are relay neurones located?

  Central nervous system
• What are relay neurones also known as?

  Interneurones (because they are in between sensory and motor neurones)
• Neurone diagrams

  They all have an axon, dendrites, a cell body, nodes and axon terminals

  A) Axon

  B) Cell body

  C) Dendrites

  D) Myelin sheath

  E) Nodes of Ravier

  F) Receptor cell

  G) Sensory

  H) Relay

  I) Motor

  
• Where are axon terminals located?

  On the end of dendrites
• What is the difference between an axon and the nodes of ravier?

  Axon: the long, primary extension of a neuron responsible for carrying electrical impulses

  Nodes of Ravier: A small gap in the myelin sheath that surrounds the axon, where the electrical signals can be regenerated for faster transmission
• What is the myelin sheath?

  Fatty layer that forms around and insulates nerve cells, speeding up electrical impulses

  • Made up of protein and fat
  • Wraps around the axon
• What are the characteristics of a sensory neurone?

  Short axons and long dendrites
• What are the characteristics of a relay neurone?

  Short axons and short dendrites
• What are the characteristics of a motor neurone?

  Long axons and short dendrites
• Where do motor neurones take electrical impulses to?

  Muscles / glands (effectors)
• What does the process of electrical impulses travelling look like?

  Diagram below:

  A) Receptor

  B) Sensory

  C) Relay / interneuron

  D) Spinal

  E) Motor

  F) Muscle

  
• Knee-jerk reflex

  This is an example of a reflex arc.

  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 causes the muscle to contract and, hence, causes the knee to move or jerk.