Revision Notes

14.1.1 Nervous Control in Humans

The Nervous System

  • The human nervous system consists of the:
    • central nervous system (CNS) – the brain and the spinal cord
    • peripheral nervous system (PNS) – all of the nerves in the body
  • It allows us to make sense of our surroundings and respond to them and to coordinate and regulate body functions
  • Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
  • A bundle of neurones is known as a nerve

The human nervous system, IGCSE & GCSE Biology revision notesThe human nervous system

Types of Neurone

  • There are three main types of neurone: sensory, relay and motor
    • Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord)
    • Relay neurones are found inside the CNS and connect sensory and motor neurones
    • Motor neurones carry impulses from the CNS to effectors (muscles or glands)
  • Neurones have a long fibre (axon
  • This means that less time is wasted transferring the impulse from one cell to another
  • The axon is insulated by a fatty sheath with small uninsulated sections along it (called nodes)
  • This means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next
  • Their cell body contains many extensions called dendrites
  • This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication

A neurone, IGCSE & GCSE Biology revision notesA neurone


Identifying the types of neurone:

The three types of neurone, IGCSE & GCSE Biology revision notesThe three types of neurone


  • Sensory neurones are long and have a cell body branching off the middle of the axon
  • Relay neurones are short and have a small cell body at one end with many dendrites branching off it
  • Motor neurones are long and have a large cell body at one end with long dendrites branching off it
Extended Only

Voluntary & Involuntary Responses

  • A voluntary response is one where you make a conscious decision to carry out a particular action therefore it starts with your brain
  • An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out
  • Involuntary actions are usually ones which are essential to basic survival and are rapid, whereas voluntary responses often take longer as we consider what the response might be before doing it

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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