Putting It All Together.

After a brief, painful hiatus in the form of Ironman Texas, we’re back, exploring to tracking the pathway a karate front kick takes through the nervous system all the way from inception through completion. How do we take in all the sights, smells, and tastes around us and decide what to do with it? In our case,we are tracking the signals that drive a frontal kick through our nervous system. If we were sparring, how would we see our our partner has dropped their guard, and decide the best option is to kick her?

So far, we tracked the signal through much of our visual system, from our eyes, to the back of our brain in our occipital lobes, where much of early visual processing takes place. We do not yet have a meaningful image of our situation, opponent, or the dojo, at this point. We have yet to layer on our other senses, the sounds of our opponent taunting us, the smells of the dojo, the feel of the mat under our feet. The images have no meaning either until we can recognize what is going on, for this we need to access memories.

That raw visual information splits into two parallel streams, called the dorsal and ventral streams, and travels forward again from our occipital lobes for further processing and integration (fig 1). Parallel processing decreases processing times, so for our kick, it decreases reaction times.  The dorsal stream is the ‘where’ stream- distance, movement, spatial awareness, which is important for us as our kick is primarily visually guided. The ventral stream is the ‘what’ stream- information like color and basic image recognition (like recognizing our sparring partner) are processed via this pathway. The information in this area comes predominantly from the fovea. This pathway will travel forward and is important in memory and emotion, which will be play into our kick later.

Fig 1. Dorsal and ventral visual streams. Remember, these parallel streams are paired, the same thing is happening in the right cerebral hemisphere as well. By OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30148013

 This integration happens in the creatively named, multimodal sensory association areas. Three pairs of these areas layer on our other senses, emotions, and memories. The posterior multimodal sensory association area, at the junction between the parietal, occipital, and temporal lobes (fig 2) receives input from the dorsal stream, and is important in visuospatial organization, attention, adding other senses- figuring out distances like how far our opponent is, are they moving away or closer, is their front guard arm dropping, where are we in relation to the boundaries of the sparring mat, lots of stuff we need to know to place an effective front kick. The limbic association area, by the temporal lobe is where memories and emotion are integrated and receives input from the ventral stream (fig 3). Now, we can identify what we are looking at and add context- we’re sparring, have done this a hundred times before, but still nervous. And lastly the anterior multimodal motor association area in the frontal cortex, is important in early motor planning and judgement. In our case, should we kick or punch, if so, how hard, or maybe just run away. It is right about here, halfway through our paper, or 100-150 msec in real time, that we have finally started planning our front kick.

fig 2. Lateral view of the brain. By BruceBlaus - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=31118589

So we have a fairly complete understanding of the situation at this point.  We know that we are sparring and have created an exploitable opening in partner’s midsection.  We know how far away we are, that our left leg is forward, and maybe we are maybe a little annoyed at all the jabs to the shin and the fact that she left her cereal bowl out this morning, again.  We know from memories of previous sparring sessions that she will keep backing up rather than move to the side.

Each step along this pathway added a more complex layer of processing to our sensory input, but we have finally neared the end. It is probably also worth mentioning that while the more basic sensory processing is unilateral, it becomes more bilateral (uses both sides of the brain) as becomes more complex. The reverse will hold true for the execution phase of our kick.  

fig 3. The Limbic system functions in memory and emotion. Injury and illnesses involving limbic system result in some interesting and tragic disorders that fundamentally change our sense of self and will be the topic of a future post. By BruceBlaus. :Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=31118604

So how does that sensory picture get converted into a front kick? Via a process creatively named sensorimotor transformation which we will talk about next time.     

What’s Back There. The Story of a Front Kick. Part D.

Week 4 already! Time flies when you getting your learning on and having fun. So far in our brief history, we have been tracking the neural pathways involved in a karate kick. Basically, how do you see something, decide ‘gosh, that really needs to be kicked’, and then, well, kick it. We took a look at that in broad terms the first week, but for the last several weeks, we have put that aside to cover some basics about the nervous system. Week two (Starting Small) we covered how neurons use electrical impulses to transmit information. Last week, (It’s All in Your Head), we talked about some of the basic anatomy and function of the brain. This week, we’re going to finish up our basic anatomy review of the central nervous system with the spinal cord. Next week we will cover the peripheral nervous system, so we can start back to our original topic.

Fig 1. The spinal cord showing 31 pairs of nerves exiting the cord. By BruceBlaus - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=27796969

 We probably should quickly define some terms. Axons frequently travel in bundles. A bundle of axons (the wiring) in your brain is called a fasicle, those some bundles in our spinal cord are called tracts (and are named for where they are coming from to where they are going, and once they leave the spinal cord they are called nerves. Okay, back to the spinal cord.

Fig 2. Cross section of the spinal cord. The gray matter is central with the white matter surrounding the outside. The cells that will form the motor component of the peripheral nervous system are located in the ventral horn of the gray matter, their axons travel out through the ventral root to join with axons from sensory neurons that enter the spinal cord through the dorsal root to make a spinal nerve as part of the peripheral nervous system. Cell bodies (soma) for sensory nerves are located not in the spinal cord, but in what is called the dorsal root ganglion. Tracts of axons running to and from the brain travel through the white matter. Not pictured are cell bodies for the sympathetic nervous system. http://cnx.org/contents/GFy_h8cu@10.53:rZudN6XP@2/Introduction

The spinal cord (fig 1) is the second part of central nervous system (the other being the brain). It is an elongated structure also made of nerves and neuroglia running down the spinal canal of the vertebra from the medulla (the last part of the brainstem) to the lumbar region. (the bones that make up the spine). Like the brain, it has a hard candy shell for protection in the form of the spine. It also has gray and white matter with neuron cell bodies making up the center gray portion, and axons going to and from the brain and nerves around the outside making up the white matter (fig 2). Three segments (fig 3) called the cervical, lumbar, and thoracic make up the spinal cord. Information is carried from the spinal cord to and from the body via 31 pairs of spinal nerves which we will discuss in more detail next week.  Those nerves are named by what vertebral body they exit above in the cervical spine, and below in the thoracic and lumbar (more on that next week). Spinal cord levels are identified by where their nerve roots exit, which does not always correlate to the vertebral level by that part of the cord. (T1 would be the part of the thoracic cord that has its nerve root exiting below the first thoracic vertebra). This gets a little more confusing further down in the spinal cord as the actual spinal cord ends by the first lumbar vertebra, but there are nerve roots that come off of the cord that exit through lumbar vertebra, and even the sacrum.

The spinal cord has several functions; it transmits information to and from the brain, controls part of the autonomic nervous system (the part of the nervous system that controls bodily functions, even the gross ones), and coordinates some reflexes.

There are two basic types of information the spinal cord carries to and from the brain, motor and sensory. There are multiple white matter tracts that run almost the entire length of the spine, carrying sensory information cephalad (towards the brain), and motor commands caudad (away from the brain) The tracts are named by where the come from to where they are going. For example, one of the main motor tracts is called the corticospinal tract because it comes from the cortex and terminates at different levels along the spinal cord (we will talk about this more later). From the spinal cord, the motor signals that travel along that pathway exit the spinal cord via nerves bound for muscles. Sensory information travels in to opposite direction. It travels to the spinal cord through nerves, up tracts through the spinal cord to the brain.

Fig 2. Cervical, thoracic, and lumbar segments of the spinal cord.

Adapted from Andrewmeyerson - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49411614

Reflexes coordinated at the level of the spinal cord, creatively named ‘spinal reflexes’ are yet another function of the spinal cord. A reflex is a nearly instantaneous involuntary movement in response to a stimulus. One of the most famous spinal reflexes is the knee jerk, or patellar reflex, where the doctor taps you knee and you kick. There are more complicated movements controlled by the spinal cord, like… walking! Yep, the basic rhythmic action of walking is coordinated at the level of the spine (much of it still requires some higher input, like stepping around obstacles).

The last major function of the spinal cord is control of part of the autonomic nervous system (fig 4). The autonomic nervous system regulates many bodily functions, controls heart rate, digestion, sweating, etc. It can be further subdivided into the sympathetic (fight or flight), or parasympathetic (rest and digest or feed and breed, hehe) nervous system. Anyway, cell bodies for the sympathetic nervous system can be found at most thoracic and some lumbar levels of the spinal cord (T1-L2).

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Fig 4. Summary of the sympathetic nervious system as mediated by the spinal cord.

Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=28086441

Well, that is it for this week. Next week we will cover the peripheral nervous system, so we can get back to the fun stuff. As always please send questions or ideas to frontal.lobe@duramatters.com. Thanks!

It’s All in Your Head. The Story of a Front Kick. Part C.

Welcome to week 3 of looking at the neural pathways involved in a karate front kick. We have taken a little diversion from that to cover some basics about the nervous system is and how it works, which we started into last week, (Starting Small. The Story of a Front Kick. Part B) with a discussion on neurons and how they communicate. (To recap, neurons, or nerve cells, form the basis of our nervous system. They transmit information with their target (be it other neurons or another type of cell) via electrical impulses called action potentials.)

Fig 1. A posterior view of the nervous system. A, The cerebral hemispheres. B. The cerebellum. C. I can’t really tell what that is pointing at, maybe the hip? (okay, per the author, it is pointing at the sciatic nerve, but it could be labeled better).

Title: Elementary anatomy, physiology and hygiene for higher grammar grades Year: 1900 (1900s) Authors: Hall, Winfield Scott, b. 1861

This week, we will talk about neuroanatomy and functional divisions of the nervous system, so that next week we can start looking at our karate kick, hooray!

The nervous system (fig 1) is the system responsible for sending to and receiving information from all areas of the body. It has two major divisions, central and peripheral. The central nervous system, CNS, is made of the brain and spinal cord. It processes incoming sensory information and generates a response. The peripheral nervous system, PNS, is made of all the nerves in the body, sending information to the CNS via sensory nerves and carries information from the CNS to the body via (predominately) motor nerves. Say you happen to do the most painful think known to humankind, and step on a lego. The pain sensation is carried by sensory nerves from your foot to your spinal cord and on to your brain. Your brain and spinal cord process that on different levels and generate a response which is carried by motor nerves if you’re like me, your mouth, but also back down to your leg so you pick your foot up. Simple, right?

We can go into a little more detail than that though (actually, we could go into a lot more detail… later). For the most part, our nervous system is symmetric, meaning you could draw a line down the center of your body, and the left side of your nervous system- the left side of your brain, the left side of your spinal cord, the nerves running down your left arm and leg, are similar in function and a mirror image of the right side. The major exception to that is in our brains. Superficially our brains are symmetric, but each side has some specialized functions. The average adult brain weighs about 3 pounds, contains about 86 billion neurons and roughly the same number of support aka glial cells (Azevedo et al). For scale, it is thought there are about 200-400 billion stars in the Milky Way.

So what does this 3 lb mass of 180 billion cells do? Lots of stuff.  It processes incoming sensory information, plans and initiates movement, regulates other systems in the body, and most of that it does on a subconscious level, constantly in the background, only occasionally reaching conscious awareness. If you had to think about every breath or every step, there would be no time to do anything else. It is the seat of consciousness and cognition, generator of emotions and dreams, and creator of memories. Some of this we understand very well, and some not so well.

Fig 2. A lateral view of the brain. The cerebrum is made up of the paired cerebral hemispheres. The midbrain, pons, and medulla oblongata make up the brainstem. A sulcus is a fissure on the surface of the brain, and separates the surface into ridges called gyri. The cerebellum plays a role in initiation and control of movement among other things. The diencephalon is a collection of midline nuclei that serve many functions, the hypothalamus is involved in regulation of different systemic processes like sleep and temperature, and the thalamus is involved in sensory processing among other things.

Blausen.com staff (2014) ). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

Figure 3. A lateral view of the brain. The frontal lobe, parietal lobes, temporal lobes, and occipital lobes make up the cerebral hemispheres. The central sulcus is the fissure that separates the frontal and parietal lobes, the frontal gyrus is involved in control of movement, the post central gyrus is where sensory information is processed. The cerebellum plays a role in initiation and control of movement among other things. The midbrain (not shown), pons, make up the brainstem.

Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436

The brain is made up of substructures, the major ones being the paired cerebral hemispheres, the cerebellum, and brainstem. (Fig 2&3). The cerebral hemispheres are where we do our ‘thinking’, and play a role in most higher order functions, which are responses that are more complicated. Each cerebral hemisphere is divided into four lobes called the frontal, parietal, temporal, and occipital lobes.  The surface of each lobe (called the cortex) has a special function, occipital lobes process visual information, parietal lobes process sensory and some language (on the dominant side and serve other functions on the non-dominant), temporal lobes are involved in memory and some emotion, and frontal lobes have a dominant role in movement, speech output, emotion, and decision making. Most sensory and motor functions are crossed, meaning the right side of the brain is responsible for the left side of the body.  

The cortex and some of the deep structures (collectively called deep gray nuclei) are made up mostly of neuronal cell bodies and are called gray matter (fig 3). The deep gray nuclei, have wide spread connections, and are involved in many processes. The area below the cortex, called sub-cortical, is called the white matter and is made of axons and glial cells. It is basically the wiring in the brain, transmitting information (in the form of action potentials) via bundles of axons called tracts, to different areas in the brain and spinal cord.

Figure 3. MRI showing the gray matter and white matter. Adapted from Coronal T2 (grey scale inverted) MRI of the brain at the level of the the caudate nuclei. Image from Radiopaedia.org Dr Frank Gaillard.

The brainstem (fig 2, fig 4, fig 5) is made of 3 parts, the midbrain, pons, and medulla. This part of the brain controls our facial movements, chewing, eye movements, and processes special senses- vision, hearing, taste, smell via 12 pairs of cranial nerves, and regulates some other systems. It also has multiple white matter tracts running through it from other parts of our brain heading down to our bound via our spinal cord and vice versa. It also multiple nuclei both for the cranial nerves that arise from it, and nuclei that are involved in other processes.

Fig 4.Human brain as viewed from the bottom showing 12 pairs of cranial nerves coming off the brainstem and their functions. As an aside, in medical school there is a mnemonic we learned the memorize the pairs of nerves. There are two, actually, one clean one that we were taught by the anatomy professor, and a less clean one that is passed on from other students. I do not remember the clean one. The other one, well, maybe after we get to know each other better.

Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436

The cerebellum is the last major division of the brain. Most of the neurons in the brain, about 3/4, are actually in the cerebellum, it is just packed with neurons. Like the cerebral hemispheres it has paired lobes, sulci and gyr (called folia)i, a gray matter cortex, white matter, and nuclei. Initiation and control of movement (coordination), are the most well understood functions of the cerebellum, but it also has roles in several cognitive functions, that are not yet as clear.  

That is probably enough for now. Next week we will finally finish up our neuroanatomy primer so we can get back to talking about our karate kick. Please email with questions or comments to frontal.lobe@duramatters.com.