Nervous System 6.5

Here is a link to the SAT content: nervous system syllabus

This is the IB Core syllabus (6.5). There is no additional content for HL students. There is though a good Option, A, called NEUROBIOLOGY AND BEHAVIOUR, which contains considerably more syllabus

The topic of the nervous system should be seen in the context of the need for regulation and control systems, to manage all the organ systems and responses which the body can make. This is essentially called homeostasis. There are two control systems:

  1. The nervous system
  2. The endocrine system (of hormones)

Reading:intro p1 intro p2


The nervous system consists of:

  • The central nervous system (CNS) – the brain and spinal cord. The most important areas of the brain are:
    • cerebrum
    • cerebellum
    • medulla (brain stem)
    • hypothalamus
  • The peripheral (or lateral) nervous system of
    • sensory (afferent) neurons, bringing information into the CNS
    • motor (efferent) neurons conducting information away from the CNS

Motor neurons are of two types:

  • Somatic – controlling voluntary responses of the skeleton
  • Autonomic – controlling involuntary activities (such as heartbeat, digestion, etc.)

And the autonomic nervous system is itself divided into two divisions:

  • Sympathetic (fight and flight)
  • Para-sympathetic (rest and digest)

Division-of-nervous-systemnervous s

This shows how the divisions of the autonomic nervous system interact: 


There are basically three sorts of neuron:

  1. Sensory (afferent) neurons, bring information into the CNS from sensory receptors
  2. Intermediary (sometimes called Relay) neurons in the CNS
  3. Motor (efferent) neurons, carrying impulses out to create responses in motor organs or glands.

IB does not require that you differentiate between these three types – sensory neurons have a subtly different structure – so focus upon motor neurons.


neurone page 1 neurone page 2


The manner in which an electrical impulse (action potential) is fired along a neuron is due to a complex interaction between different transport proteins along the membrane, which control the movement of sodium and potassium ions. The presence of concentrations of these ions on one side or the other of the membrane allows the presence of voltage differences across the membrane. All of this is a nice cross-curricular link-up with cell membrane biology and membrane proteins (1.4 & 1.4).

Reading:nerve impulse context 1nerve impulse context 2

There are many, many images available to help understand the idea of an action potential:Blausen_0011_ActionPotential_Nerve image33 img015


When an action potential arrives at the far end of the neuron down which it has been travelling, it needs to be transmitted (or not) to another neuron. The electrical ‘signal’ becomes a chemical signal at the synapse between two neurons. These different chemicals or neurotransmitters may be excitatory or inhibitory.

(Mood would seem to result from an interaction between different neurotransmitters in the brain. Many drugs of abuse, such as alcohol, and psychoactive drugs like amphetamines, produce their effects by interfering with neurotransmitters. This is all a most interesting part of Option A.)

Reading:synapse context 1 synapse context 2 synapse context 3 synapse context 4

Here are some good links about the way in which synapses occur:

  1. Simple introduction:
  2. Synapses (from the point of view of insecticides):
  3. Good complete description:
  4. Animation – focussing on some different neurotransmitters:

A powerpoint about synapses: THE SYNAPSE oct 2015

EXTENSION STUFF (related to Option A, but interesting to look at here!)

The way in which neurons interact in order for decisions to be made: decision making neurones GOOD oct 2015

Drugs and the synapse: nervous-system-drugs oct 2015

Eyyy! left to right


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