2. RECEPTORS & EFFECTORS RECEPTORS Receptors are groups of specialized cells. They can detect changes in the environment, which are called stimuli, and turn them into electrical impulses. Receptors are often located in the sense organs, such as the ear, eye and skin. Each organ has receptors sensitive to particular kinds of stimulus.

3. SENSE ORGANRECEPTORS SENSITIVE TO SKIN TONGUE NOSE EYES EARS

4. Receptors SENSE ORGANRECEPTORS SENSITIVE TO SKINTouch, pressure, pain & temperature TONGUEChemicals in food NOSEChemicals in the air EYESLight EARSSound and head position

5. Effectors An effector is any part of the body that produces the response. Here are some examples of effectors: a muscle contracting to move the arm a muscle squeezing saliva from the salivary gland a gland releasing a hormone into the bloodhormone

7. The nervous system is divided into: Central nervous system: this includes the BRAIN and the SPINAL CORD. Peripheral nervous system: this includes the nerves that connect the spinal cord to the body. The brain, the spinal cord and the nerves are made of nerve cells or NEURONS.

8. Neurons are nerve cells. They carry information as tiny electrical signals. The diagram in the next slide shows a typical neuron - in this case, a motor neuron. It has tiny branches at each end and a long fiber carries the signals. NEURONES

10. Label the Neurons

12. DENDRITE  Fine hair-like extensions on the end of a neuron. Function: receive incoming stimuli. CELL BODY OR SOMA  The control center of the neuron. Function: Directs impulses from the dendrites to the axon. NUCLEUS  Control center of the Soma. Function: Tells the soma what to do. AXON  Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron. MYELIN SHEATH  An insulating layer around an axon. Made up of Schwann cells. NODES OF RANVIER  Gaps between schwann cells. Function: Saltatory Conduction (Situation where speed of an impulse is greatly increased by the message ‘jumping’ the gaps in an axon).

13. There are three different types of neurons, each with a slightly different function. Sensory neurons carry signals from receptors to the spinal cord and brain.receptors Relay neurons carry messages from one part of the CNS to another.CNS Motor neurons carry signals from the CNS to effectors.CNS

14. Types of neurons

15. TYPES OF NEURONS Based on: Mader, S., Inquiry Into Life, McGraw-Hill

16. Nerve fibers, Nerves and Tracts A nerve is a bundle of nerve fibers, located outside the brain and spinal cord, that connect various parts of the body. Sensory nerves carry messages to the CNS (brain) and the motor nerves carry messages away from the CNS. Groups of nerve fibers within the CNS are known as tracts.

17. Telling the difference How can your brain tell the difference between a strong chocolate smell and a faint chocolate smell? If a stimulus is strong, then a greater number of impulses will be sent out. This is because more nerve cells will be stimulated and transmit their messages to your brain. If the smell was faint, then fewer impulses would be sent out and fewer nerve cells would be stimulated. In this way the brain is able to detect differences.

18. What if a stimulus is applied for a long time? If you ate chocolate all day long, for example, the sensory receptors would stop reacting to it and eventually you would not taste it anymore. We say the sensory receptors have adapted. Similarly, when you put jeans on fi rst thing in the morning, you feel the material against your skin. But soon you don’t notice the material is there because your skin receptors have adapted to its presence.

19. SYNAPSES Where two neurons meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neuron releases the chemical into the gap. The chemical diffuses across the gap and makes the next neuron transmit an electrical signal.

20. Synapses Neurotransmitter being released into synapse and attaching to receptors on dendrite Based on Harvard Medical School Family Health Guide

21. 50 Known Neurotransmitters Examples include: Acetylcholine Dopamine Serotonin

22. Why do we need a neurotransmitter like dopamine?

23. Human behavior is controlled by natural chemical reward systems in the body For example, we like to eat fatty foods because it make us feel good It is the release of dopamine that is the chemical reward system responsible for the good feeling Dopamine “reinforces behaviors essential to our survival.” Importance of Dopamine

24. Dopamine is released by cells of the nervous system during pleasurable activities such as eating or having sex.cellssex Once released, dopamine travels across a gap between nerve cells, called a synapse, and binds to a receptor on a neighboring nerve cell (also called a neuron). This sends a signal to that nerve cell, which produces a good feeling. Under normal conditions, once the dopamine sends that signal it is reabsorbed by the neuron that released it. This reabsorption happens with the help of a protein called the dopamine transporter. Cocain interrupts this cycle. It attaches to the dopamine transporter, preventing the normal reabsorption process. As dopamine builds up in the synapse, it continues to stimulate the receptor, creating a lingering feeling of exhilaration or euphoria in the user. http://health.howstuffworks.com/wellness/drugs- alcohol/crack.htm/printable http://health.howstuffworks.com/wellness/drugs- alcohol/crack.htm/printable

26. (Somatic) REFLEX ACTIONS When a receptor is stimulated, it sends a signal to the central nervous system, where the brain co- ordinates the response. But sometimes a very quick response is needed, one that does not need the involvement of the brain. This is a reflex action.reflex action. Reflex actions are rapid and happen without us thinking. For example, you would pull your hand away from a hot flame without thinking about it. The animation below allows you to step through each stage of the reflex arc.