The Nervous System

  • Specialised network of cells and our primary communication system.
  • Two main functions; Collect,process and respond to information and the environment, and to co-ordinate the working of differenet organs and cells in the body.
  • Divided into the Central Nervous System (CNS) and Peripheral Nervous System (PNS)

Structure and functions of CNS

  • Made up of the brain and spinal cord, the brain being the centre of all conscious awareness
  • Spinal cord is an extension of the brain, responsible for reflex actions
  • Passes messages to and from the brain and connects nerves to the PNS

Structure and functions of PNS

  • Transmits messages via millions of neurons to and from the nervous system
  • Subdivided into the ; autonomic nervous sytem and the somatic nervous system
  • ANS- governs vital functions in the body such as breathing, heart rate, digestion 
  • SNS- controls muscle movement and receives info from sensory receptors.
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The Endocrine System

  • works alongside the nervous system to control vital functions in the body through actions of hormones
  • Works much more slower than the nervous system but has powerful effects.


  • Organs in the body that produce hormones
  • major endocrine gland is the pituitary gland, known as the 'master gland', located in the brain.


  • Secreted into the bloodstream and affect any cell in the body that has a receptor for that particular hormone

Endocrine system and the ANS work together

  • Sympathetic state; increase HR, increase BR, dilated pupils, inhibits digestion etc
  • Parasympathetic state; Decrease HR, decrease BR, constricts pupils, stimulates digestion.
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Structure and function of neurons

There are three types of neurons;

  • Motor neurons- connect the CNS to effectors (muscles and glands). They have short dendrites and long axons
  • Sensory neurons- Carry messages from the PNS to the CNS. They have long dendrites and short axons
  • Relay neurons- Connect sensory neurons to motor or other relay neurons. They have short dendrites and short axons.

Structure of Neurons

  • Cell body (soma)- Includes a nucleus which contains the genetic makeup of the cell
  • Dendrites- branch-like structures that protrude from the cell body. Carry nerve impulses
  • Axon- carries electrical impulse away from the cellbody down the length of the neuron
  • Myelin Sheath- Covers the axon to protect it
  • Nodes of Ranvier- Gaps in the axon that speed up the transmission of the impulse
  • Terminal button- end of axon, to communicate with the next neuron, across the synapse.
  • When a neuron is at resting state- inside is negative, when activated it is positive.
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Synaptic Transmission

Synapse- A tiny gap which separates each neuron

Chemical Transmission

  • Signals within neurons are transmitted electrically
  • Signals between neurons are transmitted chemically across the synapse
  • When the electrical impulse reaches the end of the neuron it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
  • Once the neurotransmitter crosses the gap it is taken up by the post-synaptic receptor
  • The chemical message is coverted back into an electrical impulse and the process of electrical transmission begins


  • Chemicals which diffuse across the synapse to the next neuron

Excitation and Inhibition- e.g adrenaline is excitatory and serotonin is inhibitory.

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