U3 Topic 1: The Neuron



Role of the Neuron


o   Neurons are nerve cells with the primary function to receive, process and transmit information to communicate messages across the human nervous system in the brain and body


o   Synaptic Transmission is the process by which a neurotransmitter (a chemical messenger molecule) is released by a neuron and recieved by another


o   Neural Transmission is when a message, in the form of an electrical impulse, is sent to another neuron, muscle or gland


o   Neural Reception: is the process in which a neuron accepts or receives a message (the impulse)


o   Function: neurons are organised into pathways or “networks” within the nervous system and communication occurs within these networks to perform specific functions


   


Structure of the Neuron


Synapse: the space in between two neurons into which a message is sent

o  In the process of neural transmission from one neuron to another, the neural message is transmitted across the synapse


o   The neuron that fires the impulse into the synapse is known as the presynaptic neuron (before synapse). The neuron that receives this message is known as the postsynaptic neuron (after synapse)


Dendrites: are the bushy branches at the receiving end of a neuron. During neural communication, the end of dendrites, known as receptor sites, receive the electrical impulse before it is sent to the cell body (soma) for processing


Axon: is the long stick-like part of the neuron that extends down from the body of the cell to the end. It is responsible for transmitting the impulse down from the receiving end of the neuron to the sending end


Myelin Sheath: is the protein substance that looks like small fatty bubbles make up of glial cells along the axon. It functions to insulate the neuron, which helps to protect the axon and the messages from interference. The myelin is important to increase the speed of the electrical impulse as well.


Axon Terminals: are branches at the sending end of the neuron and responsible for the release of the neural message (in the form of chemicals) into the synapse. The very end of axon terminals, known as terminal buttons or synaptic buttons are where neurotransmitters are contained and then released from when the electrical impulse reached the end of the neuron




Glial Cells (glia)


Glial Cells (aka glia) are important cells in the nervous system that function to support and protect the neuron.

o   Primary roles of glia:

        o   Hold neurons in place

        o   Provide neurons with oxygen and nutrients

        o   Insulate neurons from one another

        o   Produce myelin

        o   Aid neurons in neurotransmission

        o   Repair neurons and eliminate diseased or damaged ones

     

They do not send electrochemical signals but rather support neurons to do so.

Estimated ratio of around one glial cell to one neuron


Glial cells exist in both the PNS and the CNS:


CNS glial cells: Astrocytes- most common, connect neurons to blood supply, remove waste


Oligodendrocytes: form myelin to insulate neurons, help with transmission


Microglia: tiny, remove waste and protect neurons from harmful substances



PNS glial cells: Schwann: form myelin for neurons in the PNS






Types of Neurons


There are three types of neurons, each with their own unique function

 

Motor Neurons (efferent neurons): specialise in communicating information about our movement.

                

o   CNS to PNS      -       Brain to Body


Sensory Neurons (afferent neurons): specialise in communicating about the body’s sensations (both from within the body and the external environment).

                

o   PNS to CNS      -       Body to Brain


Interneurons: function primarily to relay neural messages between motor and sensory neurons as they do not communicate directly with each other. Interneurons also communicate with each other. These neurons are particularly important for cognition and reflex actions (e.g. spinal reflex)

               

 o   Between sensory and motor neurons





Example 1

Q1.) What happens during neural transmission and in what form is the message sent? (approx. 2 marks)

A1.) Neural transmission is when a message is sent from one neuron to another neuron, muscle or gland (1 mark). This occurs in the form of an electrical impulse (1mark). 


Tips:

- Identify what the question is asking. There is no need to provide extra, elaborate information, as you will waste time and no extra marks are awarded for extra information.

- Make sure to answer all parts of the question. It is very easy to lose simple marks due to a simple misreading error.  



Q2.) Identify two types of neurons involved in the synaptic transmission process (approx. 2 marks)

A2.) The neuron that fires the impulse into the synapse is called the presynaptic neuron, and the neuron that receives this message is the postsynaptic neuron. 

Q3.) Describe the myelin sheath and its purpose. (6 marks)

A3.) The meylin sheath is a white, fatty, layer made up of protein and it surrounds the axon of a neuron. (1) It contributes to the protection and speed of the electrical impulse in neurons. (1) The myelin sheath acts as a an insulating layer around the axon, providing physical protection to the neuron. It helps prevent interference from external factors and maintains the structural integrity of the axon. (1) This insulation is crucial for safeguarding the delicate neural components from damage or degradation. (1) The myelin sheath significantly increases the speed of the electrical impulse (action potential) as it travels along the axon. (1) The myelin sheath is not continuous but is instead divided into segments with small gaps known as nodes of Ranvier. The electrical impulse "jumps" from one node to the next. This allows the nerve signal to propagate more rapidly compared to unmyelinated neurons, where the impulse would need to travel along the entire length of the axon. (1) As a result, myelinated neurons conduct nerve impulses with greater speed and efficiency.


Tips:

- For questions which require more content (are worth more marks) ensure that you format it so that your answer flows well. This will help the examiner understand your answer during marking. It will also help you keep note of aspects which you have already answered

- When answering longer questions, start with describing the key terms, for example, in this question a key word was "myelin sheath". This will set you up for the rest of your answer. 



Exercise &&1&& (&&1&& Question)

Q1.) Explain the primary function of neurons in the human nervous system and how it relates to the communication of messages. (approx 3 marks)


Sample Answer 1.)

Neurons serve as nerve cells (1) with the primary function of receiving, processing, and transmitting information to communicate messages throughout the human nervous system in both the brain and body (1). This facilitates the integration of complex signals and responses (1). 

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Exercise &&2&& (&&1&& Question)

Q2.) Discuss the role of the myelin sheath in neural communication, emphasising its impact on both speed and protection. (approx 3 marks)


Sample Answer 2.) 

The myelin sheath contributes to the protection of the axon by insulating it, preventing interference and maintaining the structural integrity of the neuron. Additionally, it enhances the speed of the electrical impulse through saltatory conduction, where the impulse jumps from one node of Ranvier to another. This results in faster transmission along the axon compared to unmyelinated neurons. 

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Exercise &&3&& (&&1&& Question)

Q3.) Elaborate on the significance of axon terminals, particularly the role of terminal buttons or synaptic buttons. (approx 3 marks)


Sample Answer 3.)

Axon terminals, located at the sending end of the neuron (1) play a crucial role in releasing neural messages in the form of chemicals into the synapse (1). The terminal buttons or synaptic buttons, at the very end, contain neurotransmitters that are released upon reaching the end of the neuron, facilitating interneuronal communication (1). 

 

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