Week 38: Lecture 2

Signals in nerve cells  

Previously we got some information about neurons, the cells that are involved in carrying a signal (or information) to and from the brain. In this week’s blog we will briefly describe a part of this transmission process known as the action potential. We had some previous information about the process as a group but for some members the topic itself was completely unknown, so we made certain that everyone understood the topic correctly. The action potential takes place when a neuron is fired. During the potential, the neural membrane opens and allows ions to move through it causing a depolarization. This depolarization moves along the axon and carries the signal forward. 

Before the Action Potential: Neuronal membrane at rest 

Figure 1 The resting potential [1]

There are many charged ions inside and outside the neural membrane. A positively charged ion is known as cation and negatively charged ion is called anion. The cations calcium (Ca2+) and sodium (Na+have positive charges are mainly  present outside the nuclear membrane. A calcium ion contains 2 positive charges while a sodium and potassium ion have one positive charge. Chloride (Clis an anion and it has only one negative charge. The ions move to and from a cell through ion channels as most ions cannot pass the cell membrane with diffusion. 

When a neuron is at rest, i.e. not sending signals, it is slightly negatively charged has negative charged relative in comparison to the outside of the cell creating a potential difference. This electric potential difference is called the resting potential which is typically -70 mV. There are a high concentration of sodium ions outside the cell whereas inside the cell there are potassium ions and a high concentration of chloride ions. The ion channels are mainly closed, but some potassium ions move outside. This ion concentration is maintained by an ion pump that moves three sodium ions out and two potassium ions in by active transportation. This expends energy but allows for quick reaction to stimulus. 

Information Transmission: During the Action Potential  

Figure 2 The action potential [1]

When an impulse is sent out from a cell body, the sodium channels open and the sodium cations surge into the cell. Inside of the cell starts to become less negative, i.e. depolarize and once the cell reaches -55mV the neurons will fire an action potential sending the electrical signal down the axonDuring the action potential, the depolarization is so large that the potential difference briefly reverses polarity, which means inside of the cell becoming positively charged.  The action potential is always of same size i.e. there is no big or small action potential (this principle is also known as “All or None” law). The action potential is renewed in every Ranvier node. This ensures that full intensity of the signal is carried down the nerve fiber and hence the signal persists when it travels further from the source. 

After the Action Potential 

Figure 3: Hyperpolarization [1]

As more sodium ions enter the cell, the potassium ions start to move slowly outside the cell. This process continues until the cell reaches its peak action potential value which is about 40 mV. At peak action potential, the sodium channels close but potassium ions keep moving out of the cell and the membrane gets closer to the resting potential.  

Eventually, the membrane potential starts to turn negative again and briefly turns more negative than the resting potential before finally reaching it. This is called hyperpolarizationThe ion pump starts working and restores the membrane to resting potential. After the action potential there is a small refractory period, during which the cell resists new action potential. During the absolute refractory period, the membrane cannot create a new action potential. During the relative refractory period, the cell would need a bigger stimulus to cause another action potential. 

Figure 4: Summary of the stages of the action potential [2]

Sources: 

  1. Images   https://courses.lumenlearning.com/wmbiology2/chapter/resting-membrane-potential/ 
  2. Image http://faculty.washington.edu/chudler/ap.html#:~:text=The%20action%20potential%20is%20an,This%20is%20the%20threshold. 
  3. Text has been partially referenced from the book  and from the sources mentioned above 

Posted by Senni Selkama

NBE-E4210 Structure and Operation of the Human Brain D , Neuroscience - Leave a comment

Week 37: Introduction and Lecture 1

Introduction

The purpose of this blog is to work as a reflective tool for a group of three individuals on the course NBE-E4210 – Structure and operation of the human brain DWe will present here what we have learned on the lectures, exercises, and excursions and the observations we made during the learning process and if any questions arose while exploring the weekly topic. After each chapter we aim to reflect what we already knew about the topic in question and if there were any challenges when it came to understanding the concepts of the week in question. We use the coursebook Bear, Connors, Paradiso: Neuroscience: Exploring the Brain, 4th edition, Lippincott, Williams & Wilkins (2015as a source for information and sometimes external sources which are mentioned at the end of the post.

Neuroscience and nervous system 

Neuroscience is a field of science which researches the functions and structure of the nervous systems in general and it aims to understand the fundamental properties of these systems. When it comes to humans and their nervous system, the nervous system is defined as a perplexing system that controls and coordinates our actions by transmitting signals to and from different parts of our bodies. There are two main components of this system: 

  • The Central Nervous System (CNS) which consists of the central organ brain where all signals are processed and spinal cord that helps body and brain communicate.  
  • The Peripheral Nervous System which has all the other neural elements collectively known as neurons that conducts the transfer of signals to and from the central nervous system. 

Brain

Some fun facts: 

  • Brain is one of the largest organs of the human body and the most complex one. 
  • On average an adult brain weighs around 1.4kgs. Up to 60% of it is fat [1] cells while 73-75% of the brain is water [1, 2] 
  • It is a myth that humans use only 10% of their brain, (we apparently use more than 10% even when we are asleep). 
  • There are approximately 86 billion neurons in the brain. 

When it comes to the presented facts about the brain, it was surprising to discover that we use more than 1/10 of our brainPerhaps this is because the equipment and the technology we use nowadays have been improved enough so the scientists are able to detect more brain activity than before using modern technology. 

The lectures inspired us to search more information about the composition of the brain and it was fascinating to find out that around 73-75% of the brain consists purely of water, or perhaps better said, a water solution since we have e.g. different kinds of molecules in the fluid from which the brain consists of. So, based on this it can be stated that for example, dehydration will have an adverse effect not only on the human body in general but also on the proper functioning of the brain.

 Structure of the brain

Brain Structure from book

1a. Structure of Brain.

1b. Structure of the Cerebrum [5]

  1. The cerebrum is the uppermost section of the brain. It consists of two hemispheres, which are further classified into four lobes:  
    1. the frontal lobe (lobus frontalis),  
    2. the parietal lobe (lobus parietalis),  
    3. the occipital lobe (lobus occipitalis),  
    4. the temporal lobe (lobus temporalis).

The cerebrum is responsible for the initiation of the movement, coordination of the movement, temperature, touch, vision, hearing, judgment, reasoning, problem-solving, emotions, and learning

 2. The cerebellum (little brain) is found near the brain stems (Figure 1(a)). This part handles the coordination of the voluntary movements. The functions also include motor skills such as balance, coordination and posture. 

3. Brain Stems located in the hind position of the brain is made up of midbrain, pons and medulla oblongata. These parts have individual functions but together they help regulate breathing, heart rate, blood pressure and several other essential functions. 

Nerve cells 

There are two types of cells in the human nervous system: neurons and glia. Neurons are responsible for receiving sensory data and transmitting it to other neurons. They also transfer messages to muscle cells and enable movement. Neurons can be classified by the number of connections they have to other cells. Multipolar neurons are the most common type of brain cell. 

 

 

2. Types of neurons based on the number of neurites. [3]

Glia support neurons by filling the empty space, insulating and sustaining them. There are different types of glia which have different functions. Astrocytes regulate chemical content and remove waste. Microglia are part of the immune system and they remove waste, viruses and weak synapses from the brain. Oligodendrial and Schwann cells build the myelin layers which insulate axons and ependymal cells guide neuron migration during brain development. 

3. Types of glia in the nervous system. [4]

Neurons and their composition were familiar to most of the group at least when it came to the multipolar neurons, as they are the most common type of the neurons of the brain. The further classification of the neurons and different types of glia were new information for the group as a whole, except Schwann and Oligodendrial cells which construct the myelin layers of the axons. The myelin layer composition applies to multipolar neurons as well so at least most of the group had some information about them as a basis. 

Sources: 

  1. Santos-Longhurst, A. What Is the Physical Composition of the Human Brain? Available at: https://www.healthline.com/health/is-the-brain-a-muscle 
  2. USGS. The Water in You: The Water in Human Body. Available at: https://www.usgs.gov/special-topic/water-science-school/science/water-you-water-and-human-body?qt-science_center_objects=0#qt-science_center_objects 
  3. University of Queensland, Queensland Brain Institute. Types of Neurons. 2018. Available at: https://qbi.uq.edu.au/brain/brain-anatomy/types-neurons 
  4. Glial Cells. Available at: https://biologydictionary.net/glial-cells/ 
  5. NBIA. Structure and Function of the Human Brain. Available at: https://www.nbia.ca/brain-structure-function/ 

Posted by Rishabh Kapoor

Neurology , Structure and Operation Of Brain NBE-E4210 - Leave a comment