10: Spinal control of movement, brain control of movement

Motor control can be divided into two parts: the spinal cord’s command and the contraction of the muscles, and the brain’s control of the motor programs in the spinal cord. In the first chapter we discussed about the first type of motor control. 

There are smooth and striated muscles in out body. The striated muscles can be divided into cardiac muscle, which is the heart muscle, and the skeletal muscle, which enables us to move bones around our joints. The nervous system that controls our skeletal muscles is called somatic nervous system. Smooth muscles are found from digestive tract, arteries, and other structures that are innervated by the autonomic nervous system. Cardiac muscle is controlled by ANS as well. 

The motor neurons are divided into two categories; upper and lower motor neurons. The upper motor neurons of the brain supply input to the spinal cord, and the lower motor neurons initiate from the ventral horn and innervate the somatic musculature. These are called either alpha or gamma motor neurons. Alpha motor neurons generate the force in the muscles and make them contract, gamma neurons give input to the muscle spindle and innervate the intrafusal muscle fiber at the two ends of it instead. They play a role in contracting the muscles, keeping the muscle spindle taut.  

The upper motor neurons initiate from the motor cortex of the brain. Primary motor cortex is mostly responsible in initiating the movement, premotor area planning the movement and the posterior parietal motor cortex creates the idea of it. They leave the brain along different tracts. The descending pathways can be divided into the main pathways, which are lateral and ventromedial pathways. The first one includes mostly the tracts to do voluntary movements.

Alexandra & Alisa

 

9: The Resting Brain, Attention and Consciousness

One thing we learned this week was the activity of a resting state brain. Even though it said the ‘resting’ brain, there are several active areas during the resting state. These active areas include medial prefrontal cortex, posterior cingulate cortex, posterior parietal cortex, hippocampus and lateral temporal cortex. Together these areas are called the default mode network. So, this network is most active during rest. This ‘resting’ situation could happen e.g. when laying in bed and daydreaming, but what about if then suddenly someone shouts your name? This immediately catches our attention, even we were not “paying attention” to anything. At this moment, our brain shift from the resting state to an active state. 

About attention, we learned some of the concepts, disorders and principles such as the cocktail party effect, ADHD (attention-deficit hyperactivity disorder), bottom-up & top-down attention, effects of attention to our behaviour, areas and networks involved in attention as well as different research methods of attention such as PET and fMRI.

As last, we also learned about consciousness. Only defining consciousness is already challenging: are we conscious when we are awake and unconscious when we are asleep? Is consciousness the state where we are able to understand and realize things? One way to help this problem of consciousness is by dividing it to the easy problems of consciousness and the hard problem of consciousness. The easy problems of consciousness mean the mechanisms how certain functions are performed, whereas the hard problem of consciousness means how to explain the relationship between physical brain processes and the experiences: why and how does some physical process generate a specific experience?

Alexandra & Alisa

8: Wiring the Brain

This week we learned about wiring of the brain. It begins with the generation of neurons. The development can be split to three major phases: cell proliferation, cell migration and cell differentiation. One interesting thing regarding this is the “inside out development” of the cortex. It means that the cortical plate develops from the inner layer to outer. In other words, first cell layer to develop is the subplate and rest of the layers develop on top of that, finally forming layers I-VI on top of the white matter. 

We also learned about the genesis of connections. When neurons differentiate, their axons must find appropriate targets. The pathway formation can be divided to three phases: During pathway selection, the axon must choose the correct path, during target selection the axon must select the correct structure to innervate and the last phase is during address selection; choosing the correct cells to synapse with in the target structure.

While most of the connections form (find their way) before birth, the final refinement of the synaptic connection occurs mainly during infancy and is influenced by the sensory environment. However, also after infancy our brain keeps developing and forming: it is plastic. Thus, our brain is not only defined by our genes, but also by the world in which we grow up.

Alexandra & Alisa

 

7: The Auditory System

In lecture 7 we learned about the auditory system, i.e. how can we hear. So, as commonly known the tiniest bones in our body lie in the ear: the ossicles. From the ossicles, the tiniest one is stapes. Other ossicles are malleus and incus. The ossicles amplify the sound waves coming to the tympanic membrane (eardrum), that are originally collected by the auricle pinna of the outer ear and then channeled into the ear canal, where they end to the tympanic membrane. 

Even though it is commonly said, that the ossicles amplify the sound waves, the main amplification mechanism comes from the size difference between the eardrum and the oval window that connects the middle ear to the inner ear. Through this oval window, the amplified sound waves travel into the cochlea, which is a fluid-filled hearing organ. The Eustachian tube that opens up into the middle ear, equalizes the pressure between outside the ear and within the middle ear.

After the sound waves are in the cochlea, as the stapes moves in and out, the perilymph starts to flow, which then again generates a traveling wave in the basilar membrane. Depending on the frequency of the sound, the traveling waves differ: high-frequency sounds dissipate near the base of the basilar membrane, whereas low-frequency sounds dissipate in the apex of the basilar membrane. One very interesting thing we learned, related to these frequencies, is tonotopy. It is the systematic organization of sound frequencies within the auditory system. The tonotopic maps can be found the basilar membrane, and each auditory relay nuclei, medial geniculate nucleus (MGN) and auditory cortex.

Finally, the auditory receptor cells are located in the organ of Corti. They convert mechanical energy (bending of cilia) into a change in membrane polarization (neural signal). So e.g. when sound causes the basilar membrane to deflect upward, the reticular lamina moves up and cause the stereocilia to bend, which then generates a receptor potential. From the ear (from spiral ganglion), the neural signal travel via to the auditory cortex via numerous pathways, but the primary pathway is through ventral cochleae nucleus, superior olive, inferior colliculus, MGN and as last, auditory cortex.

Alexandra & Alisa

6: Chemical Control of the Brain and Behaviour

During past week and the lecture six we went through some important topics of chemical control of brain and behavior. The components of the nervous system that operate in expanded space and time are secretory hypothalamus (periventricular area of hypothalamus), autonomic nervous system (sympathetic and parasympathetic nervous systems) and the diffuse modulatory systems of the brain (cell groups that differ with respect to the neurotransmitter they use.)

Hypothalamus maintains the homeostasis of the body by regulating the temperature and blood consumption. The secretory hypothalamus affects their many targets by releasing hormones directly into the bloodstream. It is connected to the pituitary gland by a stalk. It controls the anterior and posterior pituitary gland different ways. Magnocellular cells in the periventricular area of hypothalamus extend axons down the stalk to pituitary and into the posterior lobe. It releases oxytocin and vasopressin. The anterior pituitary is an actual gland which secretes wide range of hormones that regulate secretion from other glands. The anterior lobe is controlled by the parvocellular cells of hypothalamus. There is no axons; they communicate via bloodstream, tiny vessels run down the stalk to anterior lobe where the hormones bind to specific receptors and secrete or stop secreting hormones into the general circulation. Anterior pituitary gland releases hormones such as ACTH, LS, FSH and GH.

In addition, we talked studied the structure and effects of sympathetic and parasympathetic nervous systems. Unlike somatic nervous system, autonomic nervous system is a disynaptic pathway, it contains two neurons from the beginning to the target. It innervates three types of tissues; glands, smooth muscles and cardiac muscles. It also regulates digestive, metabolic functions of the liver, functions of kidney, urinary bladder, large intestine and rectum. It is also essential to the sexual responses of the genitals and interacts with body’s immune system. Sympathetic NS is most active during stress and fight-or-flight situations and parasympathetic during rest.

The diffuse modulatory systems are cores, which each system has a small set of neurons. The neurons arise from the central core of the brain, most from the brain stem. The focus modulatory systems activate specific metabotropic receptors.They use neurotransmitters such as NE, 5-HT, DA and ACh. The neurons of NE arises from Locus Coeruleus and spread vast areas of CNS. Serotonergic nerves arise from Raphe Nuclei and innervates most of the brain. The cholinergic diffuse modulatory systems arise from Pontomesencephalotegmental complex and basal nucleus of Meynert and Medial septal nuclei. Substantia nigra innervates the striatum and Ventral tegmental area the frontal lobe. These use dopaminergic neurons. Many drugs affect on these pathways.

Alexandra & Alisa

 

5: The neurotransmitter systems

In the fifth lecture we talked about neurotransmitter systems. There are more than 100 different neurotransmitters and some neurotransmitter candidates. The major classes of these are amino acids, amines and peptides. To be called neurotransmitter, there are three conditions that has to be filled: it need to be synthesized and stored in presynaptic neuron, needs to be released from the presynaptic axon terminal following stimulation and need to produce a response in the postsynaptic cell.

We went a bit deeper in the function of synapses than previously in this course. The transmitter system can be divided into chain of events. The neurotransmitters are synthesized by the synthesizing enzymes and transferred to vesicles by vesicle transporters. This all happens in the presynaptic axon terminal. After releasing these neurotransmitters they can be reuptaken or degraded by degradative enzymes. In the postsynaptic membrane there are receptors, transmitter-gated receptors and G-protein-coupled receptors. They affect directly on the ion channels, either opening or closing them, or  they can work as a signal cascade through G-protein-coupled receptors. The G-protein-receptors activate the G-proteins, which then again activates the effector enzymes (like adenylyl cyclase in case of ACh). Effector enzymes use ATP to create second messenger cascade which leads to opening and closing many ion channels. This one G-protein-coupled receptors affecting on many ion channels is called signal amplification. These opening and closing of channels have an excitatory or inhibitory effect on the postsynaptic dendrite. Finally, we learned about the different types of neurons depending on which neurotransmitter they use:  catecholaminergic, amino acidergic, serotonergic, cholinergic neurons. 

 

 

4: Chemical Senses, Eye, Central Visual System

This week lecture was about the chemical senses (taste = gustatory and smell = olfactory), the eye and the central visual system. This week we learned a lot of new things, since each of these topics involve huge amount of information in order to understand their function. Especially, learning how our vision works was literally eye opening. 

However, regarding the chemical senses, what we found interesting was, how the information from the olfactory bulb to olfactory cortex differs from other sensory axons, since it doesn’t go through thalamus. It is also highly interesting how we detect all the different odors in our orbitofrontal cortex. It is discussed that the olfactory maps may be used the distinguish different chemicals, but there must be something that reads and understand it. Also the temporal coding in olfactory system might have a part in distinguishing the chemicals. From the side of gustatory sense, what we found most interesting, were the transduction mechanisms of the different tastes (sweetness, saltiness, bitterness, sourness and  umami). We learned that saltiness and sourness have similar transduction mechanism, whereas sweetness, bitterness and umami have similar transduction mechanisms.

Regarding our vision, there were very many new things we learned. Especially interesting was the whole process how the photoreceptors of our retina can convert light energy into neural activity. Other highly interesting thing was, how the image is then formed in our brain, and also more deeper, how we can for example recognize objects and movements (the dorsal and ventral streams). 

Alexandra & Alisa

3: Synaptic transmission

In the third lecture we talked about synapses and synaptic transmissions. There are two kind of transmissions, electrical and chemical. What was new, were especially the electrical synapses. They occur at gap junctions (which then again occur between cells in nearly every part of the body). The speciality of electrical synapses is, that they allow direct transfer of ionic current from one cell to the next and they function bidirectionally (to both directions, unlike chemical synapses). Also, transmission at these is very fast, which is logical since they don’t require the electrical-chemical-electrical transformation that chemical synapses do. For what are these then needed for? They are important in locations, where normal function requires synchronized activity of neighboring cells. 

The chemical synapses are only between neurons. Compared to electrical synapses, they are slow. It takes time to convert the electrical signal to a chemical signal in the synaptic cleft and then back to an electrical signal. In the chemical transmission the action potential opens Ca2+ channels in the axon terminals membrane which then again allows the vesicles to release the neurotransmitters to the synaptic cleft. These neurotransmitters either excite or inhibit the action potential in the postsynaptic cell depending on the neurotransmitter and the receptors of the postsynaptic membrane.  

Additionally, in the exercise session of this week, we learned about neuroanatomy, which was highly interesting!

Alexandra & Alisa

2: Neuronal membrane at rest & action potential

In the second lecture we learned about the neuronal membrane at rest, and about the action potential. The theory behind these focused on the intra- and extracellular fluids, the ions in them as well as on the phospholipid membrane (bilayer) in between of the intra- and extracellular fluids. Again, some things were already familiar to us, but many new findings came along. 

One thing that was quite familiar to us was that the basic structure of the neuronal membrane: it is formed of two molecules thick sheet of phospholipids and therefore called as the phospholipid bilayer. However, after studying the structure of the membrane more deeply we learned many new, especially electrochemistry related facts, that helped us understand more deeply the resting membrane and action potential. 

We learned also what different functions proteins have in the neuron: they distinguish neurons from other types of cells. Enzymes, cytoskeleton and receptors are all made up of protein molecules. One especially interesting part in this chapter was how the equilibrium potentials are established by the ionic concentrations and electrical forces between ions. Also, one new thing we learned was the importance of the astrocytes regulating extracellular potassium concentration in the brain which is called potassium spatial buffering.

Alexandra & Alisa

1: Introduction, Neurons and Glia

The first lecture was mainly an introductory lecture to the course, in which we went through all the practical matters of the course, motivational aspects and also some basics of the brain’s structure and functions.

Well, why is it important to study the brain? Two aspects were presented: first of all it is highly interesting how does the brain work (e.g. how can we store things in our memory or use languages). Secondly, the burden of brain disorders is huge. For example, alone dementia causes globally approximately $1000 billion costs to the society per year. Therefore, even a tiny achievement towards the cure of some brain disorder could have huge impacts.

After understanding the importance of studying the brain, we started to learn the basics about brain anatomy, neurons and glia, and the organelles inside the cells. Many of these things were already quite familiar, but some things were new. For example we learned how to classify neurons. They can be classified for example based on 1) the number of neurites (unipolar, bipolar, multipolar), 2) the dendrites (pyramidical/stellate & spiny/aspinous), 3) the connections formed (primary sensory neurons, motor neurons, interneurons), 4) axon length (golgi type I, golgi type II) and 5) gene expression (use of different neurotransmitters). Another relatively new thing we learned was the different glia types: astrocytes (most of the glia in brain are astrocytes) and myelinating glia (oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system).

Alexandra & Alisa