 This video will cover the anatomy of the central nervous system, most of the material comes from chapters 12 through 16 of the open stacks anatomy and physiology text that is freely available online and additional content comes from Grey's Anatomy and the edition from 1918 which is in the public domain is also freely available online. As we go we will cover the following study objectives to describe the structure of the central nervous system and functions of the major structures. We will identify regions of the brain and provide functions for major regions within the cerebrum, diencephalon, cerebellum, and brainstem. Then we will identify regions of the spinal cord and provide functions for grey horns and white columns and last we will identify and describe the functions of the meninges. Here we see an image showing the brain with a section removed so that we can see the layers of the cerebrum. So the outer most portion of the brain, the large superficial portion of the brain that is very wrinkly is the cerebrum and the grey matter of the cerebrum is the cerebral cortex that contains the cell bodies of neurons and the dendrites and axon terminals. Then white matter deep underneath the cerebral cortex contains myelinated axons that are connecting from one region of the brain to another region of the brain. The folded outer surface of the cerebrum is called the cerebral cortex. There are two halves or left and right hemispheres of the cerebral cortex. Deep grooves between the folds of the cortex are called fissures. The longitudinal fissure separates the left and right hemispheres of the cerebral cortex. The corpus callosum is a tract that connects the left and right hemispheres. The transverse fissure is found on the posterior and inferior surface of the cerebrum where this red line was just placed. The transverse fissure separates the cerebrum from another major region of the brain called the cerebellum. The cerebral cortex can be divided into large areas known as lobes. The frontal lobe is on the anterior shown in red in the illustration. The parietal lobe is just posterior to the frontal lobe shown in purple in the illustration. Then the occipital lobe is on the posterior of the cerebrum. The temporal lobes are on the lateral surfaces of the cerebrum, just inferior to the frontal and parietal lobes. A shallow groove on the surface of the cerebral cortex is known as a sulcus, and the lateral sulcus forms the boundary between the temporal lobe and the parietal and frontal lobes. Then the central sulcus forms the boundary between the frontal lobe and the parietal lobe. A fold on the surface of the cerebral cortex that extends out opposite to a sulcus or fissure is known as a gyrus. The precentral gyrus is just anterior to the central sulcus and contains primary motor cortex, a region of the brain that sends out motor commands in order to excite our skeletal muscles. The postcentral gyrus is found just posterior to the central sulcus. This contains primary somatosensory cortex, a region of the brain that's receiving sensory information coming from the skin, including the sense of touch and beginning to process that information. Here we see an illustration of the sensory pathway bringing the sense of touch or temperature from our hand. In this case, it would be the right hand sensing the temperature of water in the shower. Those temperature sensors are neurons that have their dendrites in the skin. If the temperature is hot or cold, that can stimulate action potentials in an axon that travels from those dendrites in the skin all the way up to the spinal cord and then send that information through neurons found in the brain to the left side of the brain in the postcentral gyrus where the conscious perception of that information will be processed. You'll have a conscious perception of the temperature of the water. If that water is very hot, you'll want to withdraw your hand so it doesn't get burnt. The information can then be relayed to the motor neurons in the frontal lobe, in the precentral gyrus. The upper motor neuron will send the signal down through the spinal cord to excite a lower motor neuron in the spinal cord that extends its axon out to form a synapse with the skeletal muscles that are required to withdraw your hand from the water. Notice that the left side of the brain receives sensory information from the right side of the body and sends out motor commands to control the right side of the body. The opposite is also true. The right side of the brain controls the left side of the body and receives sensory information from the left side of the body. This is what we call the contralateral connections between the cerebral hemispheres and the body. Here we see an illustration representing the layout of sensory information in the postcentral gyrus within the primary somatosensory cortex. There are different regions along the postcentral gyrus that process sensory information coming from different regions in our body. If we're looking at the right hemisphere, these are regions in the skin on the left half of the body. There's a region that responds to touch on the hand on the left hand that would stimulate the neurons in the postcentral gyrus on the right hemisphere of the brain. There's a different region that would respond to the forearm or the elbow. This is a map. This map of the cerebral cortex was created by stimulating the brain during surgery when patients are awake. It's important to do brain mapping during neurosurgery to avoid cutting in a region of the brain that performs an essential function. But as these brain mapping experiments were performed, we acquired information as we stimulated or shocked a region of the brain in the postcentral gyrus. The patient would report that they felt a sense of touch on the surface of their body. Brodman's areas of the cerebral cortex are distinct regions based on the histology and cytology of the cerebral cortex. In many cases, these structural areas correspond to functional areas of the cerebral cortex. For example, Brodman's areas 1, 2, and 3 correspond to primary somatosensory cortex in the postcentral gyrus. Brodman's area 4 corresponds to primary motor cortex in the precentral gyrus. Brodman's area 17 corresponds to primary visual cortex in the occipital lobe. Brodman's area 22 corresponds to primary auditory cortex in the temporal lobe. Brodman's area 39 and 40 on the left hemisphere correspond to a region of the brain known as vernike's area. Damage to this area is associated with language impairments known as vernike's aphasia that involves impaired comprehension of language. Brodman's areas 44 and 45 in the left hemisphere correspond to Broca's area. Damage to this area is associated with language impairments known as Broca's aphasia that involves impaired language production. Here we see a coronal section of the brain. We can see the cerebral cortex folds deep to increase its surface area. Another lobe called the insula or insular lobe of the cerebral cortex is found deep under the posterior regions on the inferior of the frontal lobe and the anterior regions on the superior of the temporal lobe. The insula contains primary gustatory cortex, the first region of the cerebral cortex that processes information coming from the taste receptors of the tongue. Along the midline we can see the corpus callosum connecting the left and right hemispheres of the cerebrum. A space deep to the corpus callosum called the lateral ventricle is filled with fluid known as cerebrospinal fluid. In red we see the coroid plexus of the lateral ventricle. Coroid plexus is a specialized cluster of capillaries lined with epindymal cells responsible for the production of cerebrospinal fluid. Here we see the lateral ventricle and the coroid plexus is in red within the lateral ventricle. As we go on to the diencephalon we will see there is a third ventricle along the midline in the diencephalon. There is coroid plexus found within the third ventricle as well. And then in the medulla oblongata is the fourth ventricle and coroid plexus inside of the fourth ventricle as well producing cerebrospinal fluid. Here we see a midsaginal section of the brain. The corpus callosum is a large tract connecting the hemispheres. Septum pollucidum inferior to the corpus callosum is a membrane along the midline that forms the medial border of the lateral ventricles. The fornix is a tract found inferior to septum pollucidum that extends from the temporal lobe to the diencephalon. Here we see an inferior view of the surface of the brain. In yellow are the cranial nerves that are carrying information in and out of the brain. The olfactory bulb is found just inferior to the frontal lobe and receives and begins the processing of the sense of smell. So the olfactory nerves that travel in through the criberiform foramen of the ethmoid bone send information to the olfactory bulb. And then that information travels through a tract known as the olfactory tract that extends back to the temporal lobe and regions of the diencephalon. The optic nerve is a cranial nerve that travels through the optic foramen from the eye carrying visual information. The optic chiasm is where the optic nerve from the right and left come together and the fibers that come from the medial region of the eye cross over the midline so that information from the right visual field will be processed by the left half of the brain and information from the left visual field will be processed by the right half of the brain. And so from the optic chiasm axons extend on through a tract known as the optic tract that will then carry this information into the diencephalon. An interesting experiment was performed with patients that have undergone surgery to sever the corpus callosum. The corpus callosum is a large tract connecting the right and the half hemispheres of the cerebral cortex. This procedure is performed in order to treat epilepsy and the experiment involves having the patient that has had their corpus callosum severed known as a split brain patient, viewing a screen where images are presented to only one half of the visual field. And so information presented to the right half of the visual field will travel to the left half of the brain and be processed by the left half of the brain and information presented to the left half of the visual field will be processed by the right half of the brain. Here we can see that the split brain patient is presented with a heart in the right visual field and then the experimenter asks the subject, what did you see? And the patient can respond normally, I see a heart. However, on the right here we see a patient is being presented a face in the left half of their visual field. That information travels to the right half of the brain and is processed by the right half of the brain and then when the experimenter asks the patient, what do you see? The patient will respond, I see nothing. And so this shows us that the left half of the brain contains the network responsible for producing language to be able to respond appropriately with language. However, if the experimenter asks the patient who has been shown a face in the left visual field to make a drawing of what they saw and use their left hand to make the drawing, the patient can correctly draw a face. Similarly, if they were given several different images to pick from and they could point at the face with their left hand or if they were given cutouts of letters that were scrambled, they would be able to use their left hand to spell out the word face. And so while these experiments show us that there is something special about the left half of the brain required for responding with language, responding with verbal language, they also show us that the right hemisphere is capable of some type of language processing because when the experimenter asked, the patient was able to respond appropriately using the left hand. Here we see an illustration of the major regions of the cerebrum, major functional areas in the cerebral cortex. The frontal lobe contains the motor areas including the primary motor cortex as well as motor association areas and the frontal eye fields. Motor association areas are responsible for planning motor commands and then they will send those commands to the primary motor cortex where the upper motor neurons are located that extend their axons down to the spinal cord in order to stimulate lower motor neurons that extend axons out to the skeletal muscles to perform the action. The frontal eye fields are a specific type of motor association area that perform the planning of motor commands in order to direct our gaze, to move our eyes to direct our gaze. The prefrontal cortex is the anterior region of the frontal lobe. Regions within the prefrontal cortex are important for decision making, regulating our behavior for aspects of our personality, for long-term planning and judgments and decisions. The Broca's area is the region of the brain thought to be important for the motor commands required for speech. Planning speech and damage to Broca's area is associated with a loss of the ability to produce speech known as Broca's aphasia. In the parietal lobe shown in the darker pink color here we can see primary somatosensory cortex. Then just posterior to that is the sensory association area that receives sensory information from the primary somatosensory cortex and starts to make a bigger picture processing information coming from multiple regions of the body. On the posterior we can see within the occipital lobe is the primary visual cortex, this region of the cortex that receives the sense of vision as it's coming from the eyes. It travels first to a region in the diencephalon known as the thalamus, and then from the thalamus that information reaches the primary visual cortex, which begins to process that information. However, regions surrounding primary visual cortex known as visual association areas receive the information from the primary visual cortex and start to perform more complex processing of the visual information. In the temporal lobe there's primary auditory cortex that receives sensory information coming from the inner ear responsible for the sense of hearing, and then an auditory association area is surrounding primary auditory cortex. Nearby we see Vernike's area which is important for the comprehension of language and damage to Vernike's area is associated with an impairment in the comprehension of language known as Vernike's aphasia. Deep within the cerebrum there are collections of neuronal cell bodies, there's gray matter forming the basal nuclei. The basal nuclei of the striatum are known as the caudate nucleus and putamen. These nuclei are important for regulating motor commands. They adjust the stopping and starting as well as the intensity of movements. After they receive the motor commands from the cerebral cortex, lesions of these nuclei in the striatum lead to increased motor output and increased muscle tone, which makes difficulty initiating movement and can produce involuntary movements. Huntington's and Parkinson's disease result from dysfunction of the striatum. Here we see the amygdala, another basal nucleus that has an almond shape. It's found deep under the temporal lobe. It's important for responding to emotions and producing emotions, especially negative emotions like fear or disgust. The diencephalon is found deep underneath the cerebrum. Major regions of the diencephalon are the thalamus and the hypothalamus. The hypothalamus attaches to the pituitary gland through an extension known as the infundibulum. Then on the posterior and superior of the diencephalon, we'll see the pineal gland. Here we see a coronal section through the brain at the level of the diencephalon. The diencephalon is deep underneath the cerebrum. It's the middle region here and the large central region of the diencephalon is known as the thalamus. The thalamus is important for receiving sensory information, coming from the sensory receptors, and relaying that information to the primary sensory cortex. With one exception, the sense of smell or olfaction is not relayed through the thalamus before reaching the primary olfactory cortex. The intermediate mass is an extension of the thalamus across the midline. The intermediate mass connects the right and the left halves of the thalamus. There's space separating the left and the right halves of the thalamus, except for at the intermediate mass. This space is filled with fluid. The space along the midline separating the left and the right halves of the thalamus is known as the third ventricle. The lateral ventricles connect down to the third ventricle through an interventricular foramen. Then the third ventricle will then connect down to a fourth ventricle through a cerebral aqueduct. So cerebrospinal fluid is filling this third ventricle along the midline between the right and the left halves of the thalamus. On the inferior surface of the diencephalon are the mammillary bodies, which are two small rounded projections that connect to the medial temporal lobe through the fornix. These are important for memory. We know this because damage to the mammillary bodies, which results from deficiency of the B-vitamin thiamine, causes impairment in memory formation in a disease known as Vernike-Korsakov syndrome, which is a common result from long-term alcoholism. Alcoholism can lead to multiple nutrient deficiencies, but thiamine deficiency is especially common and leads to this memory deficit because the mammillary bodies become damaged. Here we have a transverse section through the brain with a superior view. Here we can see the thalamus, a large central region of the diencephalon. Then on the midline we can see here the pineal body or pineal gland, which is the major structure of the epithalamus. The pineal body is responsible for producing a hormone known as melatonin, which is a hormone that's released at night when we're sleeping. It's important for regulating the 24-hour, the day-night rhythm or the circadian rhythm. The limbic lobe or limbic system is a collection of structures in the cerebrum and diencephalon that is important for establishing emotional states and behavioral drives. It includes the hippocampus and amygdala. Regions of the medial temporal lobe, the hippocampus and amygdala are important for producing memories. The amygdala is important especially for emotional memories and emotional responses to memories that are triggering a negative emotion like fear. The cingulate gyrus is a region of the cerebrum found just superior to corpus callosum. The fornix connects from the hippocampus and surrounding regions of the temporal lobe to the mammillary bodies and the regions of the phalamus on the anterior as well as regions of the hypothalamus. The hypothalamus is the most anterior and inferior region of the diencephalon. The hypothalamus is a major regulator of the autonomic and endocrine systems, the autonomic branch of the nervous system as well as the endocrine system. The hypothalamus connects to the pituitary gland and the pituitary gland is regulated by the hypothalamus. As we study the endocrine system, we'll come back to revisit the role of the hypothalamus in regulating the pituitary gland. The brainstem has three major regions, the midbrain, the pons and the medulla. The hypothalamus, in addition to regulating the endocrine system, regulates the autonomic nervous system. The hypothalamus sends signals to the brainstem and nuclei within the brainstem are control centers for regulating the autonomic nervous system and controlling the visceral organs. Here we see a lateral view of the brainstem. On the anterior of the midbrain are the cerebral peduncles. These are tracts that contain axons connecting from the brainstem to the cerebrum. On the posterior of the midbrain are the corpora quadragemina. For round bodies on the posterior of the midbrain, the two superior bodies are the superior colliculi, which are responsible for coordinating visual reflexes. And then the inferior colliculi are responsible for coordinating auditory reflexes. The middle cerebellar peduncle is a tract connecting the cerebellum to the pons. Here we see transverse sections through the midbrain at the level of the superior colliculi and inferior colliculi. And there is a chamber that connects from the third ventricle down through the midbrain known as the cerebral aqueduct. The cerebral aqueduct will allow cerebrospinal fluid to flow through the ventricles from the third ventricle down to the fourth ventricle found in the medulla, oblongata. So here we have an anterior view of the brainstem showing the pons and the medulla oblongata. The pons is the middle region of the brainstem, and so the midbrain is not shown in this illustration. The pons is the middle region that connects to the cerebellum through the middle cerebellar peduncle. And then the medulla oblongata is the most inferior region of the brainstem. The medulla oblongata connects to the spinal cord and also contains the control centers for many vital reflexes regulating the visceral organs like the heart, the lungs, and the digestive system. The olives are nuclei that are important for relaying information to the cerebrum and the cerebellum. So the ascending sensory information coming up from the spinal cord is relayed through a nucleus in the olives to the cerebellum in order to help fine tune motor commands. And the sensory information coming from the inner ear is relayed through a nucleus in the olives of the medulla oblongata before traveling to the thalamus. The medullary pyramids are longitudinal ridges on the ventral surface that contain the motor tracks that are traveling down from the primary motor cortex in the precentral gyrus of the frontal lobe. And these tracks cross over from one side to the other at the pyramids. And so the information that's coming from the right precentral gyrus crosses over to the left half of the brainstem within the medulla oblongata and then will travel down the left half of the spinal cord. The cerebellum is a large structure on the posterior of the brainstem just inferior to the occipital lobe of the cerebrum. The cerebellum coordinates in time-skeletal muscle movements and also performs a feed-forward learning mechanism that corrects errors based on previous experiences and sensory information that travels up from the body is relayed through the cerebellum as well as motor commands that are coming down from the cortex are relayed through the cerebellum in order to fine tune and correct errors in our motor commands. Damage to the cerebellum leads to difficulty performing specific very precise coordinated movements. The folia are the folds on the outer surface of the cerebellum similar to the cerebral cortex. The outer layer of the cerebellum is grey matter that makes folds known as the folia. And there's white matter deep within the cerebellum known as the arborvita. And so the arborvita is literally translated as the tree of life and the branching structure of the arborvita looks similar to the branches of a tree that extend out to the grey matter of the folia. Folia literally means leaves and so the folia are the leaves on the arborvita, the tree of life within the cerebellum. Here we see an illustration showing the connections between the cerebellum and the brainstem known as the cerebellar peduncles. The inferior cerebellar peduncle connects between the medulla oblongata. The olives of the medulla oblongata connect to the cerebellum through the inferior cerebellar peduncle. There's a very large tract known as the middle cerebellar peduncle that connects between the cerebellum and the pons. And then the superior peduncle connects from the cerebellum to the midbrain. The cerebellum can be divided into two basic regions, the midline which is known as the vermis. The vermis literally means the worm shaped region and so there's a ridge along the midline, the central lobe of the cerebrum known as the vermis. And then on either side of the vermis there are hemispheres, a right and a left hemisphere of the cerebellum. There's also a region on the inferior of the cerebellum known as the flocculonadular lobe. The meninges are membranes that surround the brain and spinal cord. The outermost layer of protection around the brain is the bone of the cranium. And then just deep to the cranial bones is a layer of meninges known as the dura mater. The dura mater surrounding the brain forms two separate layers. There's the more superficial layer which is the periosteum of the cranial bones and then a deeper layer of the dura. And then deep underneath the dura, the middle layer of the meninges is known as the arachnoid mater and then the deepest layer of the meninges is known as the pia mater. The dura mater is a very tough, fibrous layer and dura literally is translated as the tough, and mater means mother, so the tough mother. Arachnoid, the arachnoid mater has a spider web-like appearance and so arachnoid means spider-like and the arachnoid mater has a spider web-like branching extensions and there's space underneath the arachnoid mater. And within this space is cerebrospinal fluid that surrounds the brain providing cushioning and then the pia mater, pia is literally translated as the gentle or delicate, pia mater is the delicate mother and pia mater covers the surface of the brain and follows all the contours of the sulci and fissures on the surface of the brain. There are extensions of the dura mater that help to stabilize the position of the brain. Within the longitudinal fissure, this region of the dura mater is known as the fox cerebri. So the fox cerebri extends into the longitudinal fissure and helps to anchor the brain by attaching to the crystal golly of the ethmoid bone and the internal occipital crest on the occipital bone. Then there are spaces inside of the dura mater that collect cerebrospinal fluid and blood from veins known as sinuses, dural sinuses. And so here we can see the superior sagittal sinus which is found at the superior of the fox cerebri. We can also see the arachnoid granulations also known as arachnoid villi that are extensions of the arachnoid mater that connect up into the dural sinuses. The function of the arachnoid villi is to allow cerebrospinal fluid to drain from the subarachnoid space into the dural sinus. So here we can see the dura mater forming the fox cerebri in the longitudinal fissure between the left and the right hemispheres of the cerebrum. Another extension of the dura mater that helps to stabilize the position of the brain is known as the tentorium cerebelli. This extends into the transverse fissure in order to separate the cerebrum from the cerebellum. So in between the occipital lobe of the cerebrum and the cerebellum is the tentorium cerebelli in the transverse fissure. Here we can also see the sinuses shown in blue. You can see the superior and inferior sagittal sinus which connect to a transverse sinus. Here we can see the dural sinuses that are draining blood and cerebrospinal fluid from the brain. So cerebrospinal fluid drains through the arachnoid villi into the sinuses. The superior sagittal sinus and inferior sagittal sinus connect to the transverse sinus and then drain into the sigmoid sinus that connects to the jugular vein. So as the sigmoid sinus exits the cranium at the jugular foramen, the vein that extends inferior is the internal jugular vein that is draining this blood and cerebrospinal fluid that has returned to the blood. Cerebrospinal fluid is first produced in the coroiplexus of the ventricles then it circulates through the ventricles. So from the lateral ventricles it can flow down through the interventricular foramen to the third ventricle. From the third ventricle it can flow down through the cerebral aqueduct to the fourth ventricle. Then at the fourth ventricle cerebrospinal fluid can either flow down into the central canal of space through the spinal cord or it can flow out through openings called apertures. The lateral and median apertures which allow the cerebrospinal fluid to flow out of the fourth ventricle into the subarachnoid space. Then this cerebrospinal fluid flows through the subarachnoid space around the brain and spinal cord and drains through the arachnoid granulations also known as arachnoid villi into the dural sinuses. Now we're going to move on to study the spinal cord. We can see here with a longitudinal view of the spinal cord major regions are the cervical enlargement which is a wider region of the spinal cord. It's wider as a result of numerous spinal nerves that are connecting to the arms from the spinal cord. Then the middle region is a little more narrow known as the thoracic region. And the inferior region where the spinal cord bulges out again is known as the lumbar enlargement. And this bulge is the result of many spinal nerves connecting from the spinal cord to the lower limbs. After the lumbar enlargement the spinal cord comes to a tapered end known as the conus medullaris. The conus medullaris is located at the border between L1 and L2 so the spinal cord does not continue all the way down through the vertebral foramen of the lower lumbar vertebrae. However, there is an extension of the meninges. The Pia matter of the spinal cord extends down as the philum terminale that attaches to the coccyx in order to stabilize the position of the spinal cord. Here we see another view of the spinal cord showing the three layers of meninges. The dura mater is the tough outer layer. Then the arachnoid mater is the middle layer. Underneath the arachnoid matter there is a subarachnoid space filled with cerebrospinal fluid. And then covering the surface of the spinal cord is the pia mater. Here we see the inferior end of the spinal cord with the dura mater retracted so that we can see the philum terminale. That is an extension of the pia mater past the conus medullaris down to anchor the spinal cord to the coccyx. And then just lateral to the philum terminale is the cauda equina. Cauda equina is a bundle of spinal nerves. The lower lumbar spinal nerves as well as sacral spinal nerves that extend down past conus medullaris. And so there is a cauda equina extending down inferior from the spinal cord. And you'll see that on either side of philum terminale are bundles of spinal nerves, known as the cauda equina, which is literally translated as horse's tail. Here we can see a transverse section through the spinal cord with the layers of the meninges shown. The outermost layer of meninges is the dura mater shown in black in the illustration. Then there's a small space known as the subdural cavity between the dura mater and the arachnoid matter shown in blue. And the arachnoid matter is just superficial to the subarachnoid cavity or subarachnoid space that contains the cerebrospinal fluid surrounding the spinal cord. And then the deepest layer of the meninges shown in red in the illustration is the pia mater. Here's another cross section or transverse section through the spinal cord showing the regions of gray matter and white matter in the spinal cord. So the tracts running through the spinal cord form larger collections known as columns. The posterior white columns or also known as the dorsal white columns contain numerous ascending tracts which are carrying sensory information up the spinal cord towards the brain. Then there are lateral white columns and anterior white columns. These contain a mixture of ascending and descending tracts, but the descending tracts, the motor tracts are all extending down through the lateral and anterior white columns. Then the gray matter in the spinal cord is organized in horns. The dorsal or posterior gray horns are clusters of neurons and the axons of sensory neurons that are extending in to the spinal cord, the dendrites of interneurons that are receiving information from those sensory neurons. And so the afferent axons that carry sensory information in to the spinal cord travel in through the dorsal root to the dorsal or posterior gray horn. Then on the anterior is the anterior or ventral gray horn. Inside of the anterior gray horn are the motor neurons, the lower motor neurons that extend their axons out in order to excite skeletal muscles. So the somatic motor neurons have their cell bodies in the anterior gray horn. The lateral gray horn contains the cell bodies of the autonomic motor neurons. The lateral and anterior gray horns, neurons, both extend their axons together out through a structure known as the ventral root or anterior root. Then we can see in the center of the gray matter is a space filled with fluid known as the central canal. So the central canal of the spinal cord is continuous with the fourth ventricle in the medulla oblongata. Cerebro spinal fluid will flow down into the central canal. So here we can see an illustration showing the major tracks of white matter in the posterior white column or dorsal column is the ascending sensory tracks carrying sensory information up towards the brain. And then in the lateral and anterior white columns we see the corticospinal tracks that are the descending motor commands coming down from the brain. And those axons will then synapse with neurons that are found in the anterior gray horn that then extend their axons out the ventral side of the spinal cord into a spinal nerve that will travel to skeletal muscles to regulate the activity of skeletal muscles.