Neuron’s and The Nervous System

1. Neuron’s and The Nervous System Created by Stella Thalluri 2013 www.beaconmedia.com.au

2. Neuron’s and The Nervous System Humans are created in the image of God before birth. God is the Life behind and beyond the simple flickering of biological cells, systems and processes. “For you formed my inward parts; you knitted me together in my mother's womb. I praise you, for I am fearfully and wonderfully made. Wonderful are your works; my soul knows it very well. My frame was not hidden from you, when I was being made in secret, intricately woven in the depths of the earth. Your eyes saw my unformed substance; in your book were written, every one of them, the days that were formed for me, when as yet there was none of them”. Psalms 139:13-16 “Before I formed you in the womb I knew you, and before you were born I consecrated you”. Jeremiah 1:5

3. Contents: • The Stimulus Response Model • CNS AND PNS • ANS: Sympathetic and Parasympathetic • Signal Transduction • Myelin Sheath • Motor Neurons • Sensory Neurons • Interneurons • How does a electric signal move from neuron to neuron. • Toxins and Neuron Transmission

4. Motor Neurons • A Motor Neuron is a specialised nerve cell that has the main purpose to carry a message from the CNS to a muscle cell. • Motor Neurons send short pulses which produce a twitch in the body, if these twitches become so fast, they produce smooth movement of the body which is known as Tetanus. • Motor Neurons are part of the PNS and are very important in movement, homeostasis and practically every other system in the body from digestions, to making the heart beat at a constant and steady rate.

5. Sensory Neurons • Sensory Neurons are a part of the bodies nervous system that are responsible for detecting external signals. • These neurons are rather important and special as they do not receive signals from the body, but from external sources like sound, light and temperature. • In complex organisms like Humans, most signals travel through the CNS to the brain but some reaction signals do not need to be processed by the brain and can be sent directly to the appropriate motor neuron.

6. Interneurons • Interneurons are a specific type of neuron that is generally small and only connects to other neurons. They are neither sensory or motor and have the primary goal to send a message. They are primarily found in the CNS (Brain and spinal cord)

7. Myelin Sheath • Some important nerve cells have an axon that is covered in Myelin. • Myelin is a fatty substance that acts as an insulator and allows an nerve impulse to travel very quickly. • Multiple Sclerosis is a disease where the Myelin Sheath is damaged causing some signals to ‘short-circuit’.

8. How does a electric signal pass from neuron to neuron • When an electrical signal travels down an axon it must cross over a gap between cells called the ‘synapse’. This occurs with a special kind of signaling molecule called a ‘neurotransmitter’. • Neurotransmitters are sent across the synapse and bind onto the surfaces of special protein receptors. Once they reach the next cell they are able to either inhibit or provoke the cell

9. The Stimulus Response Model • The stimulus response model is a visual way to communicate how the nervous system causes a response to a specific stimulus. If the response directly affects the stimulus, it is known as feed back.

10. Signal Transduction • Signal transduction occurs when a cell converts one type of signal, into a different type that the cell can understand. • In the nervous system, this involves the conversion of an electric signal to a chemical signal that can move across the synapse between neurons to be converted back into an electric signal. • This process is split into three different sections which are known as Reception, Transduction and Induction. Reception: When a signaling molecule binds to its specific receptor on a cell. Transduction: Through a reaction with the receptor and its signaling molecule, a ‘second messenger’ is created which enters the cytosol of a cell. Induction: The second messenger reaches its specific target and the activation of specific cellular processes occurs. Through signal transduction, a relatively small signal can eventually cause a large response through the replication of the ‘second messengers’.

11. CNS and the PNS • The nervous system can be split into two distinct sections. The CNS (Central Nervous System) and the PNS (Peripheral Nervous System). • The CNS includes the Brain and Spinal cord and generally processes nearly all sensory inputs and outputs in our body. • The PNS is generally responsibly for acting out messages from the brain including regulating systems and moving the body. • Some reactions from the body do not need to be processed via the brain and can be directly sent through the peripheral nervous system to the correct neuron.

12. The ANS: Sympathetic and Parasympathetic • The sympathetic and parasympathetic systems form the Autonomous Nervous System (ANS) which is responsible for controlling and regulating the body below a conscious level. While it was originally considered the sympathetic was ‘excitory’ and the parasympathetic ‘inhibitory’, this has since been over-turned as there are far too many exceptions for this. Both of these systems have many different roles but they both go together to form the ANS. • This is a simpler way to think of it… (but there are some exceptions) • Parasympathetic: “Rest and Digest” • Sympathetic: “Fight or Flight”

13. Toxins and Neuron Transmission • Many animals and bacteria contain toxins in their venom or body and when these interact with the human body, they can potentially cause devastating effects. This is especially true for toxins that target the nervous system. • Some toxins are small enough to enter the axon and interfere with the electrical pathway, causing paralysis which can quickly result in death if the victim cannot breathe. • Larger toxins often affect neurotransmitters crossing the synapse causing a loss of nervous control. • One animal that can cause severe paralysis is the Blue Ringed Octopus. This octopus can quickly inhibit a victims breathing and death can occur within minutes. There is no anti-toxin and artificial breathing must be used until the toxin has been excreted from the body.

14. References • http://txtwriter.com/Backgrounders/Drugaddiction/synapse.jpg • http://upclose.unimelb.edu.au/sites/upclose.unimelb.edu.au/files/images/myelin_sheath.jpg • http://upclose.unimelb.edu.au/sites/upclose.unimelb.edu.au/files/ • http://upclose.unimelb.edu.au/sites/upclose.unimelb.edu.au/files/http://txtwriter.com/Backgrounders/Drugaddiction/synaps • http://upclose.unimelb.edu.au/sites/upclose.unimelb.edu.au/files/ • http://encyclopediascience.files.wordpress.com/2011/05/sensory_neuron.gif • http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/autonomic.gif • http://visual.merriam-webster.com/images/animal-kingdom/reptiles/snake/morphology-venomous-snake-head.jpg • http://marinebio.org/upload/_cephs/Hapalochlaena-maculosa/3.jpg •  Nature of Biology Book 1 4E by Judith Kinnear and Marjory Martin