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1.1 Describe the structure of the central nervous system, sensory, connector and motor neurons.

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1.1 Describe the structure of the central nervous system, sensory, connector and motor neurons.

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This resource covers  assessment criteria (1.1) by briefly describing the structure of the central nervous system(CNS),
sensory,connector and motor neuron.The first  part of the criteria gives a brief description of the central nervous system with  the aid of a labelled diagram.
The second part of the criteria is covered through  three labelled diagrams of the sensory neuron, connector and motor neurons, together with a tabular representation of these three neurons based on length of their fibres ,location and function.

The central nervous system consists of the brain and spinal cord. The CNS processes and integrates sensory impulse.
The impulse received is either stored or immediately acted upon with one or more motor neurons.

The central nervous system can also be divided into functional units. An example of a  functional unit is the hypothalamus. Changes in  temperature sensation is  received and interpreted by the hypothalamus, where appropriate action is  initiated.

In terms of length of fibres,location and function, the sensory neuron has long dendrites and short axon. Its cell body and dendrite are located outside the spinal cord;the cell body is located in the dorsal root ganglion.The sensory neuron conducts electrical impulse from receptors to the brain or spinal cord. Connector neuron has short dendrites and short or long axon for functional adaptation. It is  entirely within in the spinal cord or CNS. The connector neuron connects the sensory neuron with appropriate motor neuron. A motor neuron has  short dendrites and long axons.The cell body and dendrites can be found  in the spinal cord; the axon is located outside the spinal cord. The motor neuron is responsible for conducting  impulse to an effector muscle or organ.

The website was informative and well presented. The language format was simple and clear . The website also provided a good analysis of many aspects of human anatomy and physiology, especially topics relating to the nervous system. The diagrams and illustrations on the website were simple, clear and easy to comprehend.

However, the website is too simplistic and lacks more in-depth analysis of topics. For example ,the diagrammatic illustration on the website could have gone a little further in explaining the many complex processes and structure about the central nervous system and neurons.

Biologymad.com. Nervous System Intro. [online] Available at: http://www.biologymad.com/nervoussystem/nervoussystemintro.htm [Accessed 28 Oct. 2018].

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

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

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This video covers assessment criteria (1.2) by providing brief explanation about the role of the sensory neuron and motor neuron in a reflex arc. The video also provided brief description of the reflex arc and reflex action with  examples.A reflex action is an automatic response to a stimulus. An example of the way in which  an organism respond to a stimulus is a human reaction to touching a hot object (candle flame). Very quickly, and without immediate thinking, the hands pull away.This sort of very fast, automatic response is called the reflex action. It shows the pathway taken by the nerve impulses in this reflex action. The stimulus here is the heat which is felt in the hand upon touching the candle flame.
This heat is sensed by a sensory receptor (thermoreceptor) in the hand.The receptor triggers an impulse in a sensory neuron, which transmits the message to the spinal cord. Here, the impulse is passed on to a relay neuron, which in turn, passes it to a motor neuron. The motor neuron relays the impulse to a muscle in the arm. The muscle then contracts and pulls our hand away from the candle flame. The muscle of arm is an effector because it responds to the stimulus. This pathway along which the impulse travels is called the reflex arc.This video clearly explains how electrical impulses travel through the different neurons to reach the nervous system and what impact this has in response to pain. It is clear and perfectly explained making it easy to comprehend. I find this video  reliable, clear and informative source, as it provides a lot of  information and examples on reflex actions and theories.

CBSE (2016). [video] Available at: https://www.youtube.com/watch?v=nOOLIM2JW0s, [Accessed 28 Oct. 2018].

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1.3 Explain the mechanism of transmission of an impulse along a neuron.

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1.3 Explain the mechanism of transmission of an impulse along a neuron.

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This video covers assessment criteria (1.3) by explaining the transmission of an impulse along a neuron. When a nerve cell is not stimulated, it is in a resting state. During this state, the inside of the axon is relatively more negative than outside of the axon, this is called the resting potential. The reason behind this negative charge is because of the distribution of the principal ions (Na+ and K+).    In reality, there is a higher concentration of sodium ions outside the neuron while there is a higher concentration of potassium inside the neuron. This allows an electrochemical gradient to be generated, which is crucial for an action potential (AP) to be generated. During the resting state, there is a larger amount of positive ions on the outside of the neuron compared to the inside, thus giving it a relatively negative charge inside the axon. When there is a stimulus, this causes the Sodium (Na+) channels located on the surface of the axon to open, causing an influx of sodium ions into the axon. This causes the charge within the axon to reverse and become positive, a process called depolarisation((from –70 to about +30 millivolts). . Once the axon has depolarised over a certain threshold, this causes an AP. The AP, a charge in the electrical potential associated with the propagation of an impulse along, in this case, the nerve cell, travels in one direction from the soma to the axon terminals. Thus, once the AP passes a certain area of an axon, that part must return back to its resting state. This is called re-polarisation. During this period, the sodium ion channels that were previously open during depolarisation start to close slowly and simultaneously the potassium ion channels open, causing an efflux of potassium ions from within the axon, causing the charge within the axon to become less positive (and therefore more negative - returning back to the resting potential).  In order to prevent a shortage of cations, there is a mechanism called the sodium potassium pump that is constantly working. It works by pumping 3 sodium ions out for every 2 potassium ions being pumped in, therefore maintaining and restoring the axon back to the resting potential.  Once the AP reaches the axon terminals, it must be converted into something else as an AP cannot cross interneuron space between the postsynaptic and presynaptic neuron, which is called the synaptic cleft. Thus, when the AP reaches the axon terminal, it releases a chemical messenger called a neurotransmitter (NT). This NT is released into the synaptic cleft and moves through diffusion from the presynaptic to the postsynaptic neuron where the NT binds to receptors on the postsynaptic neuron. Once they bind to receptors, this allows ion channels to open, causing an influx of sodium ions, which may initiate an action potential depending on the amount of receptors that have been activated.
The video is very informative ,clear, simple and a very reliable source as all study contents are written and narrated by real professors.

(Harvard Extension school (2015). [video] Available at: https://www.youtube.com/watch?v=oa6rvUJlg7o [Accessed 28 Oct. 2018].

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2.1 Compare voluntary and reflex actions and explain the role of the autonomic nervous system.

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2.1 Compare voluntary and reflex actions and explain the role of the autonomic nervous system.

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The Aviva medical encyclopaedia is a reliable source of medical knowledge. It provided a useful information that  cover assessment criteria (2.1).

The responses of the nervous system to stimuli may be voluntary or involuntary. Voluntary responses are mainly under conscious control, but some voluntary movements, such as walking, require less conscious attention. There are two types of involuntary response, autonomic and reflex. Autonomic responses regulate the body’s internal environment. Reflexes mainly affect those muscles that are normally under voluntary control. All voluntary activities involve the brain, which sends out the motor impulses that control movement. These motor signals are initiated by thought, and most also involve a response to sensory stimuli. For example, people use sight and sense of position to help them coordinate the action of walking. A reflex is an involuntary response to a stimulus, such as withdrawing your hand from a hot surface before you become aware of the heat. Most reflexes are processed in the spine, although some, such as blinking, are processed in the brain. In a spinal reflex, the stimulus signal travels along a sensory nerve to the spinal cord, and a response signal travels back by means of a motor nerve.The autonomic nervous system controls the body’s internal environment without conscious intervention and helps to regulate vital functions, such as blood pressure.The two types of autonomic nerves are parasympathetic and  sympathetic , have opposing effects but balance each other most of the time. At certain times, such as during stress or exercise, one system dominates."
Although the information from this website was clear ,simple and well written,more detailed analysis could have been explored.

Aviva.co.uk.  Medical Encyclopedia - Function: Voluntary and Involuntary Responses - Aviva. [online] Available at: https://www.aviva.co.uk/m/health-insurance/home-of-health/medical-centre/medical-encyclopedia/entry/function-voluntary-and-involuntary-responses/ [Accessed 28 Oct. 2018].

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Medical Encyclopedia - Function: Voluntary and Involuntary Responses - Aviva

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Questions about general health advice? Medical Encyclopedia - Function: Voluntary and Involuntary Responses