Nervous System

Learning Outcomes

• Understand the role of the Nervous System• Understand what Stimuli, Receptors and Effectors are• Understand what the role of Motor and Sensory

Neurons are.• Understand the role of Axons and Impulses.

Nervous System

• Things are happening round you all the time. You have to detect and respond to many changes. But how does your body do this

• Your body responds to changes in ways• Nervous system• Hormonal system • Your nervous system sends electrical messages along your

nerves to and from different parts of your body.• Your hormonal system sends chemical messages around your

body in the blood.• The electrical messages and the chemical messages tell your

body what to do.

Getting a reaction

• All our reactions happen in the same way. There are always• Stimuli• Receptors • Effectors• Stimuli are changes that can be detected • Receptors detect the changes • Effectors bring about the responses What happens if you sit down on a drawing pin? The stimulus is the drawing pin The receptors are the pain receptors Your response is to get up quickly The Chain of events is:Stimulus Receptor Coordinator Effector ResponseThe coordinator is the part of the body that decides what to doWhat do you think the coordinator is in our example?

Your Nervous System

• The nervous system control your actions. It coordinates different parts of your body so that they work together and are able to bring about the correct responses

• Your nervous system coordinates your muscles, so that you can walk, run, write, read etc

• When you smile the nervous system coordinates the muscles in your face

• Your nervous system also coordinates things that you don’t even think about, like swallowing, blinking and breathing.

The main parts of the nervous system are the Brain and the Spinal Cord.Together they are called the Central Nervous System.The Brain is protected inside the skullThe Spinal Cord is protected inside your Backbone

The Central Nervous System is connected to different parts of the body by Nerves.Each Nerve is made up of lots of Nerve Cells or Neurons

Sense Organs are our receptors.They send messages to the Central Nervous System telling it what has happened.These messages are sent along Sensor Neurons

Muscles and Glands are our different effectors. The Central Nervous System sends messages telling them what to do.These messages are sent along Motor Neurons

The messages that Nerves carry are called Nerve Impulses. They carry electrical signals. They pass very quickly along the Axon of the NeuronAn Impulse travels along the Axon like a train along a track.

Each one is separate from the next. They travel along one after the other. Some Axons have a fatty sheath around them. This insulates the Axon and makes the Impulse travel along faster.

Sensory Neuron

Motor Neuron

Coordination

Your Nervous System helps you react to different situations.

What is the Stimulus?What is the Response?Which parts are the Receptors, the Effector and the Coordinator?

Synapses

• The end of one neuron is not connected to the next. There is always a small gap between them. The gap is called a synapse.

• When an impulse reaches the end of an axon, a chemical is produced. The chemical diffuses across the gap. It starts off an impulse in the next neuron .

• Only one end of a neuron can make this chemical. So synapses make sure an impulse can only travel in one direction.

• Synapses have two other functions: A Resistor- it may take a number of impulses before enough

chemical is made to start the impulse in the next neuron. A Junction Box- One neuron may pass on its impulse to a

number of other neurons. • Our synapses are easily affected by drugs. Some drugs can

block them. Others can make them work too quickly. Alcohol is thought to affect synapses in the brain. This can slow down people’s reactions.

Reflex arcs • What happens when you touch a hot object?• You take your hand away from a hot object very fast. You do it

automatically- without thinking. Why do you think this is?• Many reflexes protects you. They happen very quickly, so you don't harm

yourself.• The following diagram shows a picture of a reflex arc.

What’s going on!

Stimulus The stimulus is the flame

Receptor The receptor is the heat sensor in the skin

Sensory NeuronPasses along an impulse to the CNS

In the spinal cord the impulse is passed on to the relay neuron, it’s part of the co-ordinator

Relay Neuron

Motor Neuron This passes the impulse onto the effector

The motor neuron carries the impulse to a muscle in the arm. The muscle is the Effector.The muscle contracts to remove the hand from the hot object. This action is a Response.

H/W: 17th/1Draw a diagram of a neurone (motor, relay or sensory), and label it’s cellular components.