The nervous system
Main Function: The Nervous System This communication system controls and coordinates functions throughout the body and responds to internal and external stimuli. Our nervous system allows us to feel pain.
What is the nervous system made up of? The brain The spinal cord The nerves (neurones) The central nervous system (or CNS for short) is made up of the brain and the spinal cord.
What is the job of the nervous system? Our survival depends on us being sensitive to our surroundings. We need to be able to detect any changes and be able to respond to them.
What are our sense organs? The sense organs are: The eyes The ears The nose Tongue skin These organs sense: Light Sound and balance Smell Taste Pressure, pain, temperature
The Nerve A nerve is an organ containing a bundle of nerve cells called neurons. Neurons carry electrical messages called impulses throughout the body. Picture shows hundreds of severed neuron axons
Basic nerve cell structure
3 main types of nerve cells sensory neurone relay neurone motor neurone
Because neurons never touch, chemical signalers called neurotransmitters must travel through the space called synapse between two neurons. Neurotransmitters (pink spheres) The message is transferred when RECEPTORS receive neurotrans-mitters. Synapse (gap)
Parts of a Neuron Cell body: contains nucleus & most of the cytoplasm Dendrites: projections that bring impulses into the neuron to the cell body. Axon: long projection that carries impulses away from cell body 1 3 2
Sensory Neuron Interneuron Types of Neurons Synapse Synapse Motor Neuron Interneuron Synapse Muscle Contracts Motor Neuron Sensory Neuron
Where can the largest cells in the world be found? Sensory Neuron carry impulses from sense organs to spinal cord & brain Fun Fact: Where can the largest cells in the world be found? The giraffe’s sensory and motor neurons! Some must bring impulses from the bottom of their legs to their spinal cord several meters away!!
Interneuron processes impulses in brain and spinal cord - connect sensory and motor neurons
carry impulses from the brain & spinal cord to muscles & glands Motor Neurons carry impulses from the brain & spinal cord to muscles & glands Axon End Axons branching out to muscle fibers
Communication with Neurons Nerves work together with muscles for movement. An impulse begins when one neuron is stimulated by another neuron or by the sense organs. The impulse travels down the axons of Sensory neurons to the brain cells called Interneurons. The brain will then send an impulse through motor neurons to the necessary muscle or organs, telling it to contract.
Reacting without thinking Sometimes a stimulus requires an immediate response. This is called a reflex action. It is an involuntary response and we do it without thinking. These automatic responses do not have to be learned. They can be very important in preventing injury to ourselves.
A reflex arc The nerve pathway taken in a reflex action is called a reflex arc. The nervous message goes to the spinal cord, then a message passes from the spinal cord directly to an effector to give an immediate response.
The knee jerk reflex action Sometimes called a relay or Connector neurone
Another reflex action
How does our nervous system work then? Our sense organs contain special receptor cells which will detect a change in our surroundings (a stimulus) The receptor cells will change the stimulus into an electrical impulse which is passed along nerve cells The message will usually go to the brain which will then process it The brain then sends a message along nerves to an effector organ (usually a muscle or a gland) The effector organ will then give a response (e.g. a muscle will move, or a gland will produce a hormone)
Response Stimulus Receptor Effector Motor neurone Sensory neurone Central Nervous system
Examples of responses Voluntary actions Eating a cake Riding a bicycle Walking Playing the piano Coming to school Involuntary actions Your heart beat Breathing Blinking Removing hand from hot object Choking Salivating