Glial cells also called neuroglia are non-neuronal cells that maintain homeostasis, form myelin and provide support and protection for the brain’s neurons.
There are two types:
Microglia – protect the neurons of the central nervous system. They are capable of phagocytosis (meaning they are phagocyte). They are found in all regions of the brain and spinal cords. Their main role is to multiply when the brain is damaged.
– contains 4 different types of cells from the central nervous system:
astrocytes
oligodendrocyts
ependymal
radial glia
-contain 3 types of cells from the peripheral nervous system
Astrocytes:
- they have a very important role in the central nervous system
- are star shaped
- they are the most numerous cells in the central nervous system
- they can be found at the exterior of the brain and spinal cord
-they give biochemical support of endothelial cells that form the blood-brain barrier
-during brain damage or radiation they are the first affected cells
Oligodendrocyts:
-their main function is to form and maintain myelin
Schwann Cells
-they have a similar function to oligodentrocytes
-their main function is to produce myelin
-between two cells there is a gap which formes the node of Ranvier
-their role is also to regenerate destroyed neurons (the broken part of the axon is destroyed and the one from the cell body forms a structure that will be the next axon)
Satellite cells:
-surround neurons in sensory, sympathetic and parasympathetic ganglia
The main function of neuroglia or glial cell is to repair injuries of the central nervous system. Some will occupy the space left by injured neurons, like astrocytes while others will help repair the neuron, like oligodendrocytes. Schwann cells help the nerve regenerate. So you can see that all these cells have a very important role in neuronal organization.
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.
There are many ways you can classify neurotransmitters. The easiest way to remember them is by dividing them into two groups: excitatory and inhibitory. Excitatory neurotransmitters stimulate the brain while inhibitory neurotransmitters create balance when excitatory neurotransmitters are overactive.
They can also be divided intosmall molecule neurotransmitters and neuropeptide neurotransmitters. Small molecule neurotransmitters are more rapid and they are involved in the central nervous system prompt feedback like sensorial and motor signals.
I’ll just talk about a few of these neurotransmitters but I’ll give links to some resources if you want more.
Serotonin or 5-hydroxytryptamine (5-HT) plays an important role in a range of brain functions. It is derived from tryptophan and it is primarily found in the gastrointestinal tract, platelets and the central nervous system.
Low serotonin levels lead to insomnia, anxiety, depression, panic attacks, obesity, eating disorders, chronic pain, migraines and alcohol abuse. Also, negative thoughts correlated with low self esteem or obsessive thoughts and behaviors could be symptoms of low serotonin levels.
On the other hand, high serotonin levels could lead to Serotonin syndrome which has the following symptoms: hypomania, hallucinations, shivering, sweating, nausea, tremor, etc.
Noradrenalin or norepinephrine has a double role: as a neurotransmitter and as a hormone. It is synthesized from dopamine. The release of noradrenaline increases the level of excitatory activity in the brain and the noradrenergic pathways are involved in the control of attention and arousal functions. Along with epinephrine it underlines the fight or flight response which directly increases the heart rate, increases blood flow to skeletal muscle and releases glucose from energy stores.
Dopamine is a key neurotransmitter that has important roles in behaviour and cognition, movement, motivation, sleep, mood, attention, memory, and even learning. It helps us with our motivation and our desire to get tasks done. ADD/ADHD or even caffeine are stimulants that help us focus more by manipulating dopamine levels.
Acetylcholineis a neurotransmitter in the peripheral nervous system and the central nervous system. It is very important for proper functioning of the nervous system and muscle functioning.
If you would like to read more, check out this amazing website.
I want to make a few posts that will help psychology students or other people interested in the brain and how it works. These are just basic so don't expect them to be extremely detailed because they are only meant for beginners (like me); also, they are not meant for learning brain surgery :) When I will finish the neuron series I will also post a map that will help you even more with your recap.
The neuron is the core component of the nervous system. It is an electrically excitable cell that processes and transmits the information through chemical and electrical signaling. It is formed of a cell body and protoplasmic processes that extend from that cell body.
There are three types of neuron: unipolar, bipolar, and multipolar.
Unipolar neurons (sensory neurons which conduct impulses into the central nervous system) have one process from the cell body which splits into longer processes. They are found in the spinal ganglia and cranial nerves.
Bipolar neurons (also sensory neurons) have two processes: one axon and one dentrite. For example, bipolar neurons are found in the retina of the eye, the ganglia of the vestibulocochlear nerve and bipolar cells that transmit motor signals to control muscles.
Multipolar neurons have multi processes and they have many dentrites and a single axon. Their function is motor or as associations (they conduct impulses and permit communications between neurons in the central nervous system)
-cytoplasm (a thick liquid between cell membrane holding all the cell’s internal sub structures which are called organelles) which contains mitochondria, Golgi apparatus, lysosome, rough and smooth endoplasmic reticulum, vacuole, vesicle and cytoskeleton.
-cell membrane
The protoplasmatic processes have dentrites and axons. Dentrites are short and transport the impulses to the cell body.
Axons have varied length to a few nanometers to 1 meter (like the axons of the sciatic nerve); they make contact with other cells like other neurons, but also muscles or gland cells through synapses.
There are two types of axons:
-myelinated axons and unmyelinated axons
Myelin is a dielectric material composed of 40 % water; however the dry mass is about 70-85% lipids and 15%-30% proteins. If the myelin layer is think the transport is faster.
Axons contain two types of axoplasmic transport:
-anterograde transport (from the cell body to the synapse)
-retrograde transport (sends chemical messages and endocytosis products headed to endolysosomes from the axon back to the cell) is practically the way toxins and vitamins are transported to the central nervous system
Neuron Part 2 – Synapses
A synapse is a junction that permits a neuron to pass an electrical or chemical signal to another cell.
Two neurons are connected through a synapse. The synaptic cleft is what separates the presynaptic neuron and the postsynaptic one. Synthesized neurotransmitters are sent in the synaptic cleft and this produces feedback at a postsynaptic level. When there is an action potential at the synaptic terminal (a bulb at the end of an axon in which neurotransmitter molecules are stored and released), it releases neurotransmitters into the synaptic cleft. The receptors in the membrane or the cell body of the postsynaptic neuron receive the neurotransmitters from the synaptic cleft.
The axon terminal contains synaptic vesicles (about 39.5 nanometers) that play an important role for propagating nerve impulses between neurons and are constantly recreated by the cell.
In most synapses the presynaptic part is located on the axon but there are some presynaptic parts located on a dendrite or soma.
Excitatory Ion Channel Synapses – synapses with neurorecepters that are sodium channels.
Inhibitory Ion Channel Synapses – synapses with neuroreceptors with chloride channels/ typical neurotransmitters are glucine or GABA
Non Channel Synapses – neuroreceptors that are not channels but are membrane- bound enzymes
Neuromuscular Junctions – synapses formed between motor neurons and muscle cells
Electrical Synapses – the membranes of the two cells actually touch and share proteins in these synapses so the action potential passes directly from one membrane to the next (can only be found in the heart and eye)
Tomorrow we'll learn about neurotransmitters and I will post the final recap map.
