Nervous System

• Nervous System

  The nervous system is made up of nerve cells known as neurones
• Central Nervous System (CNS)

  • Allows us to think, plan and learn from our experiences
  • Receives information from our sense organs, so we are aware of changes in the environment and can react to them
  • Made up of the brain and the spinal cord
• Peripheral Nervous System (PNS)

  • Made up of spinal and cranial nerves which are further divided into motor neurons and sensory neurons
  • Spinal nerves originate from spinal cords and spread throughout the entire body while cranial nerves emanate from the brain
  • Connects the CNS with the other parts of the body and the environment, and it receives all stimuli
  • Forms a vast communication network linking the reception of a stimuli to a response
• The CNS processes information and decide what kind of reaction the body will have to a given stimuli


  The PNS can execute the action/reaction deemed fit by the CNS
• The CNS and PNS

  Work together to process information and execute a reaction
• Brain

  The largest part of the nervous system, with two hemispheres
• Cerebrum

  • The main controlling centre for the whole body
  • Allows us to think, plan and remember
  • Controls voluntary movement, speech, intelligence, memory, emotion, and sensory processing
• Cerebellum

  • Helps coordinate and fine-tune movement, balance and coordination
• Medulla Oblongata

  • Controls automatic responses such as regulating vital functions like heartbeat, digesting food, circulating blood, controlling body temperature and breathing
• Spinal Cord

  • Connects the brain with nerves going to the rest of the body
  • Carries sensory information and information from the brain to the muscles and organs
• How the brain works

  1. Sensory nerves from the sense organs take their impulses to the brain

  2. Different parts of the brain control different body functions- sight, hearing, touch

  3. The brain interprets the information received from the sense organs and decides how to respond
• Neurones

  • The basic structural and functional unit of the nervous system
  • Specialized cells adapted to rapidly carry electrochemical changes (nerve impulses or messages) from one part of the body to another
• Parts of a neurone

  • Dendrites - receive signals from other cells or organs
  • Axon - carries the signal from the dendrite end to the axon terminal end
  • Axon terminal - delivers the signal to the final location that it was sent to
• Electric signals always move from the dendrites to the axon terminal
• The 3 different types of neurons (sensory, relay, motor) work together
• Nerve cells or neurones

  Cells that transmit information through electrical and chemical signals
• Sensory neurone

  • Carries information from the receptor to the CNS
• Motor neurone

  • Carries information from the CNS to the effector
• Parts of a neuron

  • Dendrites
  • Axon
  • Cell body
• Dendrites

  Nerve fibres which conduct impulses towards the cell body
• Cell body (soma)

  Contains nucleus, nucleolus, lysosomes, mitochondria and large amounts of endoplasmic reticulum
• Myelin sheath

  Fatty material that wraps around the axon to insulate and increase the speed of electrical signal conduction
• Nodes of Ranvier

  Periodic gaps in the myelin sheath where the signal is "recharged" as it travels along the axon
• Axon

  Nerve fibres that conduct impulses AWAY from the cell body
• Synapses

  Gaps between the end of an axon and the next nerve cell, where neurotransmitters pass to stimulate the next cell
• Types of neurones

  • Sensory neurone
  • Motor neurone
  • Relay/Interneurone
• Sensory neurone

  • One end is in receptors, the other end is in the CNS, carries nerve impulses to the spinal cord and brain
• Relay neurone

  • Connects sensory neurons to motor neurons, found in the brain and spinal cord
• Motor neurone

  • One end is in the CNS, the other end is in an effector (muscle or gland), controls muscle movements or hormone secretion
• Location of neurons

  • Sensory neuron: Dendrites in sensory receptor, axon terminals in spinal cord/CNS
  • Relay neuron: Brain and spinal cord
  • Motor neuron: Axon terminal of interneuron, effector
• Reflex action

  Automatic (involuntary) and rapid response to a stimulus, minimizes damage to the body
• Reflex arc

  1. Receptor detects stimulus

  2. Sensory neuron sends impulses to relay neuron in spinal cord

  3. Relay neuron connects to motor neuron

  4. Motor neuron sends impulses to effector

  5. Effector produces response
• The reflex arc is the simplest circuit of neurons arranged to produce a reflex action
• Synapse

  Junction between two neurons where electrical signals pass via neurotransmitters
• Nerve impulses are converted back into electrical impulses as they pass across the synapse
• Voluntary and involuntary actions are coordinated by the nervous system