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1.1 The structure of the central nervous system

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1.1 The structure of the central nervous system

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the central nervous system is the controller of the body's voluntary and involuntary functions. it is responsible for sending, receiving, and interrupting information from all part of the body.
it consists of two major
structures:
1. the brain
2. the spinal cord
the brain is responsible for coordinating consciously and unconsciously body functions
the spinal cord works as a conduit for signals between the brain and the rest of the body. it also controls simple reflexes without an input from the brain

both brain and spinal cord are consisted of nervous tissue, which it has a consistency of jelly. Therefore, a special protection is required to prevent any physical damage.
The whole central nervous system is sheathed with bones. the spinal cord runs within a canal  through the vertebrae and it called the vertebral column. in the other hand, the brain is within unmovable bones called the cranium.
A colourless liquid is found within the bony case and it is called The Cerebrospinal fluid. it is produced by special structures of the brain and provides extra protection to the CNS as it is bathed in that fluid. it also provides a special chemical environment for nervous tissues.
The central nervous system is made up of two general types of tissues.
1.The white matter: is mostly consists of axons, which is the reason for the whiteness, because of the myelin sheathing of the axons.
2. The grey matter: consists of axons, nerve cell bodies, and dendrites. It is rich in cell bodies, therefore it earned that grey colour, which is fairly pink-grey in a clear vision.

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1.1 The structure of the central nervous system 

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1.1 The structure of the central nervous system 

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I found this video is straight forward and has a detailed description of the central nervous system, however I found it too long and gone into further details that are not needed for an introduction video for the structure of the central nervous system.
This video is reliable because it is produced with a series of educational video by Khan academy, which is a non-profit educational organization based in the United States.
Jensen, M., 2014. Structure of the nervous system | Organ Systems | MCAT | Khan Academy [On Line]. Available at: https://www.youtube.com/watch?v=jmD0LBdAvlE&t=5s .
Accessed at: 20/10/18

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Structure of the nervous system | Organ Systems | MCAT | Khan Academy

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1.1 the structure of sensory, relay, and motor neurones 

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1.1 the structure of sensory, relay, and motor neurones 

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Neurons are the basic building block of the nervous system.
human body is made up of three main types of neurons.
All three types are made up of similar parts, however each one of these neurons has different function and structure in the body. the location of the neuron and the role that it has in the body are the main two factors that can identify the type of the neuron.
the three main types are: The sensory neuron, the motor neuron, and the relay or the connector neuron.
The simple structure of a neuron is sectioned into three main compartments: the cell body or the soma, the dendrites, and the axon.
1.The cell body is found in each three neurons and is consists of cytoplasm and the nucleus, however the size of the cell body can differ from type to type.
2. The dendrites are short projections that extend from the cell body and they can be found in both connector and motor neurons only. The dendrites in the connector neuron are more slender, short, and numerous, compared to the dendrites in the connector neuron.
3.The axon is  a long narrowed, thread-like projection of the neuron. It carries nerve impulses away from the cell body towards the axon terminals where the neuron ends. There are nodes on the axon called nodes of Ranvier and can be found in both sensory and motor neurons only. A myelin sheet covers the whole axon which insulate the axon and it helps the electrical impulse to travel faster along the axon, yet it is not existed in the sensory neurones.
The axon terminal connects the neuron with other neuron or directly to organs.

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1.1 The structure of sensory, motor, and relay neurons.

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1.1 The structure of sensory, motor, and relay neurons.

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It is clear picture that demonstrates the different structures of the three types of neurons, however it is missing some details.
This picture is provided by Tutor2u, which is a company that provides a number of free  educational materials.
Sparks, J., 2018. Biopsychology: Sensory, Relay and Motor Neurons. [On Line] . Available at: https://www.tutor2u.net/psychology/reference/biopsychology-sensory-relay-and-motor-neurons
Accessed at 21/ 10/2018

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1.2 The role of sensory and motor neurons in a reflex arc

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1.2 The role of sensory and motor neurons in a reflex arc

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a reflex is an unconscious, quick response from the body toward any unexpected harm.
There are two types of reflexes. A simple reflex is when the brain is not aware of the initial response, however a signal will be sent to the brain after the initial response to prosses if there is any action needed after. Conditioned reflex involve prior thought or learning, but the body still respond subconsciously.
A simple reflex arc happens for example when a person touches a hot surface. The fingers are stimulated by the heat causing a pain sensor to create a nerve impulse. The nerve impulse travels along the dendrite of the sensory neuron to reach a physical gap called synapse. The nerve impulse then is transmitted through the synapse by chemical transmitter and reach the relay neuron. Here, the relay neuron takes the nerve impulse through the grey matter of the back of the spinal cord. then, the impulse reaches the ventral surface of the spinal cord, which is the front pat of it. The last step has been reached, when the impulse arrived at the cell body of a motor neuron, then to the axon of the motor neuron where the pathway of the axon is covered with Schwann cells and myelin sheaths which what makes the impulse travel faster. The last stop is the muscle where the motor neuron is terminated. the motor end bulbs release acetylcholine and diffuse across into the surface of the muscle, causing the muscle to depolarize and contract.
During this whole procedure, another component from the sensory neuron synapses with an ascending neurons, which take the information to the brain in order to alert the brain about the surrounding actions that have been taken, however, it reaches the brain after the reflex is happened so the brain can prosses all the information and work out if there is any further action is needed

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2.1 The role of autonomic nervous system

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2.1 The role of autonomic nervous system

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This video demonstrates the role of the autonomic nervous system and the two main parts of it and the function of both of them. the video provide good quality drawing that helps to understand the video.
This video seemed to be trustworthy as it is one of a number of videos by a junior doctor called Armando Hasudungan.
Hasudungan, A., 2015. Neurology - Autonomic Nervous System. [On Line]. Available at : https://www.youtube.com/watch?v=3a_aLsFvNWs
Accessed at 26/10/18

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1.3 The mechanism of an impulse transmission

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1.3 The mechanism of an impulse transmission

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Neurons are the passage network for impulse to travel along the organism to reach its destination. When a stimulus triggers the neuron's cell membrane, an action potential process start to occur within the neuron. At this stage, the cell membrane is  polarized and become penetrable to sodium ions. The sodium ion electrochemical gradient start to open and allow more sodium ions to diffuse into the neuron, and that makes the interior of the neuron les negative, but not completely positive either. If the different charge is enough, then the potential difference will reach the threshold, where the neuron reach is
--55mV. that will trigger the voltage gated channels of sodium ions to open and allow more sodium ions to diffuse. This stage is called depolarization and at this stage the neuron is positive in the inside. Sodium ion voltage gated channels close and the cell membrane start to be more permeable to potassium, that leads the potassium ion voltage gated channels to open and allow potassium ions to diffuse out of the neurone down the potassium ion concentration gradient. That happens through the repolarization. Potassium channels take more time to close, that cause to have slightly more potassium ions on the outside than it has sodium on the inside This causes the membrane potential to drop slightly lower than the resting potential, that effects the membrane to be hyperpolarization. This period does not last for a long time. At this stage, the impulse has arrived to its destination and the action potential process is finished and the cell membrane returns to the rest potential.

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The autonomic nervous system is a functional division of the peripheral nervous system. It regulates involuntary, internal body functions without any conscious or effort by the organism. It also controls the smooth, cardiac, and also gland cells, and reacts toward the external changes of the body such as, breathing, digestion, or feeling scared.
There are two main divisions of the autonomic nervous:
The sympathetic division preforms in cases of danger or threat. It responses in a statue called flight or fight, where in this case, the body choose to either react to the danger and fight it , or running way from it. number of changes take place, such as speeding the heart rate, relaxing the bladder, and raising the blood pressure.
The parasympathetic division is the rest and digest system .it controls the homeostatic of the body, and conserves body energy. it slows the heart rate, stimulates an increase in alimentary glandular secretion, and digesting food.
Both sympathetic and parasympathetic divisions work in a reverse, but complementary order to maintain the survival of the organism

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1.3 The mechanism of transmission of a impulse along a neuron

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1.3 The mechanism of transmission of a impulse along a neuron

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A clear description of the process of an impulse transmission along a neuron.
This video is obvious to be reliable as it is produced by a nurse teacher and A and E nurse based in England
Campdell, J., 2015. Nervous system 4, Nerve impulses. [On Line] Available at: https://www.youtube.com/watch?v=J1abk-ecsEs&t=2s
Accessed at 22/10/18

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1.2 the role of sensory and motor neurons in a reflex arc

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1.2 the role of sensory and motor neurons in a reflex arc

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A simple picture that shows the role of both neurons. However, there is a lack of information that would make the picture more helpful if they were existed.
The picture appears to be reliable, because it is produced by Austin Peay state university as part of educational resources for its students.
Cummings, B., 2004 . Proprioception and Types of Reflexes. [On Line] Available at: http://www.apsubiology.org/anatomy/2010/2010_Exam_Reviews/Exam_4_Review/CH_13_Proprioception_and_Types_of_Reflexes.htm
Accessed at :28/10/18

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A reflex action is an automatic response toward an unexpected, specific stimulus. It occurs unconsciously, and initiates at the spinal cord without any prior plan, or involvement from the brain.
The response is very quick and involves a minimum member of nervous cells.
A voluntary action occurs consciously due to a prior thought from the brain. It requires more nervous cells, because the impulse reaches the brain.
The needed time for the response to be developed can vary, depending on the action itself.
The pathway of a reflex action is shorter than a voluntary action's pathway, where the sensory and motor neurons are directly linked together to the spinal cord. In the other hand, a voluntary action requires several neurons to transmit the impulse from the brain which makes the pathway longer, and a sensory impulse that trigger a voluntary response can deal with more than one part of the brain and that is on of the factors that make a voluntary action slower than a reflex action