nervous system

• stimulus: is a change in the environment that can be detected by organism
• external stimuli: such as noise or smell

  internal stimuli: changes in body temperature and carbon dioxide levels in the blood
• nervous system is an organ system that allows humans and other animals to detect stimuli and respond to them
• nerves carry electrical impulses from the central nervous system (brain + spinal cord) to all part parts of the body; this makes the mucles contract and glands produce enzymes or hormones
• electrical impulses are electrical signals that pass along the nerve cells (neurones)
• glands and muscles are called effectors because they og into action when they recieve nerve impulses or hormones
• the nerves also carry impulses back to the central nervous system from receptors in the sense organs of the body. This makes us aware of the changes in our surrounding
• nervous from sense organs to the CNS are called sensory impulses
• from the CNS, to the resulting effectors are called motor impulses which result in actions being performed
• the nerves that connect the body to the CNS make up the peripheral system
• sensory neurones help carry impulses from the receptor (sense organs) to the CNS are
• motor neurones help carry impulses from the CNS to the effector
• each neurone has a cell body consisting of a nucleus surrounded by a little cytoplasm
• dendrites: branching fibred from the cell body make contact with other neurones
• nerve fibre: filament of cytoplasm surrounded by an insulating sheath
• the cells bodies of the neurones are mostly located in the brain and spinal cord and is the nerve fibres that run in the nerves
• a nerve mostly contains sensory and motor fibres
• these impulses travel in one direction in sensory fibres and in the opposite direction in the motor fibres
• nerve fibres do not carry sensations, these are only felt when a nerve impulse reaches the brain
• when nerve impulses are recieved from the eyes, they travel to the brain which the brain recognises and signals that something is being seen