Cells and Control: Synapses and Reflexes

Cells and Control: Synapses and Reflexes


  • A synapse is a tiny gap where information is transferred from one neurone to another.
  • Neurones are not directly linked: at the end of the neurone, neurotransmitters carry the nerve impulse across the synapse to the next neurone or muscle fibre.
  • Electrical signals can’t cross the synaptic gap, instead, chemicals (neurotransmitters) are released by the transmitting neurone into the synapse.
  • These chemicals diffuse across the synapse and bind to receptor molecules on the membrane of the other neurone. This causes the signal to continue its journey along the new neurone.
  • Neurotransmitters in the synapse are quickly broken down or taken back up by the transmitting neurone to stop the signal being transmitted indefinitely.


  • Reflexes are rapid, automatic responses to certain stimuli that can involve the brain, but often happen before the information gets to the brain (reflex action).
  • They are a defensive mechanism designed to prevent injury.
  • The path taken by the nerve impulses in a reflex action is called a reflex arc.
  • A simple reflex arc goes through the following steps: stimulus, receptor, sensory neurone, relay neurone in the central nervous system, motor neurone, effector muscle or gland, response.
  • An example of a reflex arc is the blink reflex. When an object comes too close to your eye, your nervous system automatically closes the eyelids to protect the eye from potential damage.

Mitosis and Meiosis:

  • Mitosis is a process of cell division that results in two genetically identical daughter cells developing from a single parent cell, and is used for growth and repair.
  • It goes through phases known as interphase, prophase, metaphase, anaphase, and telophase.
  • Meiosis, on the other hand, is a form of cell division that produces four daughter cells, each with half the number of chromosomes of the parent cell. It is used in sexual reproduction for the formation of gametes.
  • Meiosis ensures genetic variation because the four daughter cells are all genetically different.

Cell Specialisation and Differentiation:

  • All cells originate as stem cells, which have the potential to become any type of cell in the body.
  • As the cells grow and mature, they undergo cell differentiation: the process by which a cell changes from one cell type to another, more specialised cell type.
  • Specialization allows cells to perform different functions. For example, nerve cells transmit electrical impulses while red blood cells transport oxygen.

Remember, it’s also important to understand how cells communicate, control, and coordinate for efficient function of a biological system. So keep revising these key concepts!