A recap of the Brain- Bio 230 This recap of the brain is to help you make sense of that 3 pound tofu blob that you carry around everyday. My hope is that if you get these basics, you can build and add the other information/structures that we will be covering. So sit back and relax have a cup of Joe and lets smell the coffee hello temporal lobe! (okay I ve been up way to late!) Here are three basic illustrations showing various views of the brain, to help you understand the information which follows. PS the brain powerpoints on your class website are awesome. Figure 1 Longitudinal fissure Figure 2 1
A corpus callosum 4 1 2 4 3 6 * 6a 5 5 5 7 ** * B 8 8 Brain Model (This is our class room model, we will go over all the structures you need to know that are on this view (mid sagittal) The surface of the brain consists of rounded ridges (gyrus - singular, gyri- plural), which are separated from one another by grooves (sulcus singular, sulci - plural). These structure give the surface of the brain more surface area! Why would we want more surface area? Also really deep grooves in the brain are called fissures. Be sure you know the difference between a sulcus and a fissure! The brain is divided into four major parts: 1. The cerebrum: The largest part of the brain. It controls movement, sensation (touch, feel, position, heat, cold, vision, hearing, etc.), as well as cognition, memory, reasoning and higher mental functioning. (Figure 1& Labeled A on the Brain model.) 2. The cerebellum: Primarily but not exclusively involved in coordination of muscle movement and balance. (Figure 1 & 2, and labeled B on the Brain model.) 2
3. The diencephalon: Involved in relaying information from the spinal cord to the cerebrum, connection to the endocrine system, and homeostasis. (brain model structures labeled 1,2,3 and 4 are in the diencephalon) 4. The brain stem (also called the primitive brain): Involved in relaying information from (and to) the cerebrum and cerebellum to the rest of the body through the spinal cord, as well as being involved in regulation of basic bodily functions like breathing, control of heart rate, control over blood pressure, and other functions. (figure 1, and structures labeled 6, 6a, 7 and 8 on Brain model) Lets start with our CEREBRUM The Cerebrum is divided into 2 hemispheres, called the right and left cerebral hemispheres. They are separated by the longitudinal fissure (figure 2- c). Connecting the 2 hemispheres is an arched bridge of myelinated nerve fibers (white matter tracts) called the corpus callosum, which allows the right and left sides of the brain to communicate. (See Part B of figure 1, and labeled on the Brain model.) The Cerebrums Lobes Each hemisphere consists of four lobes that are located at the front, middle, back and side. Their technical names are based on the part of the skull bone covering that particular area. The frontal lobe is located just where it sounds like, up front, just behind the forehead. The parietal lobe is in the central part of the brain. The occipital lobe is at the back of the head. The temporal lobe is on the side, near the ear. The frontal and parietal lobes are separated by the central sulcus (groove). The lateral sulcus (some call is the lateral fissure because it is a deeper groove than a sulcus) separates the frontal and parietal lobes from the temporal lobe. (figures 1 & 2.) While the functioning of the brain is very complex and specific functions are affected by input from other areas of the brain, the four lobes do have specific functions associated with each of them. (These lists are not intended to be all-inclusive.) 1. Frontal lobe: Largest lobe: abstract thought; problem solving; creative thought; emotions; judgment; inhibition (impulse control); initiative; sexual urges, control of voluntary and coordinated motor movements. Here is where you will find the precentral gyrus= primary motor cortex and in left hemisphere Broca s area (motor speech i.e. verbal communication.) 2. Parietal lobe: sensory interpretation (pain, pressure, heat, cold, touch); Here is the postcentral gyrus= primary sensory cortex. 3. Occipital lobe: Reading and vision, including an important visual center that is critical for the complex processing of vision and for relating vision to other sensory experiences. 4. Temporal lobe: Primary auditory (hearing) and olfactory (smelling) cortex. It is here we store our auditory and olfactory memories. I.e. that smell reminds me of The Cerebellum- ( little brain ) The cerebellum is located below the occipital lobe, separated from the occipital lobe by the Transverse Cerebral Fissure. It also has two hemispheres, which are connected by tissue called the vermis ( worm ). The cerebellum has a series of folds on its surface also. The cerebellum acts a reflex (unconscious) center that coordinates the movement of muscles. It is also the primary center for proprioception, which is another expensive word for position sense. It just means the ordinary, innate ability to know where your arms and legs are in space without having to see them. (These are tested if you ever have a sobriety test if you are stopped by the police) To understand better, just try this: Close your eyes, put your right arm out to the side and point your index finger, now bend your elbow and touch your nose with your finger. 3
You obviously knew where your hand/index finger, and nose was, even without looking at them. The cerebellum is critical for the coordinated movements required for fine motor skill, normal gait in walking or running, and balance. In a mid sagittal cut of the cerebellum, you will see the inner white matter. (see Brain model structure B). The white matter looks like a tree with branches, this white matter in the cerebellum is called Arbor Vitae (tree of life) Diencephalon The diencephalon sits between the mighty cerebral hemispheres and connects to the brain stem. The diencephalon is composed of gray matter (which is what?). This area is mid line, surrounded by the cerebral hemispheres, in the area of the third ventricle. Difficult to visualize I know. I will try to draw this for you! The 3 components of the diencephalon are the: Thalamus, hypothalamus, and epithalamus. Their names tell you where they are! The Thalamus (makes up 80% of the diencephalon) consists of paired (2) egg shaped like masses that are on either side of the third ventricle. These 2 egg shaped masses are connected to one another by a stalk called the interthalamic adhesion (structure 2 on Brain model), the brown dot represents the interthalamic adhesion, the bulge/swelling deep to this structure represents the thalamus I will show you.). The thalamus is a relay station for ALL the sensory impulses that come from other parts of the brain and spinal cord and then directs that information to the proper area in the cerebral cortex for interpretation. The thalamus is called THE GATEWAY TO THE CEREBRAL CORTEX, if information is coming up to the cerebral cortex for processing, this is the guy that directs it to where it needs to go. Can you imagine the responsibility of that job! The diencephalon also includes the hypothalamus (Brain Model structure #4), which plays a key role in regulation of heart rate, blood pressure, body temperature, control of fluids, hunger, thirst, respiration, metabolism, sexual response, emotional responses. I.E. this small area in your brain is responsible for maintaining homeostasis. What is also way cool about the hypothalamus, it sits below the thalamus, but just above the might pituitary gland (structure 5) It is connected to the pituitary gland by a little stalk called the infundibulum. Why is this connection important? Well the hypothalamus basically controls the pituitary gland and the release of a multitude of hormones! The hypothalamus is the relay station between the Nervous system and the Endocrine system. I like to think of the saying, Behind every great man (here the pituitary gland) is a great woman (the hypothalamus). I will include a diagram from the anatomy book to show you this relationship. Am I being sexist..again? Nah. So here you see the connection from Ms. Hypothalamus to Mr. Pituitary Who s your Daddy! (infundibulum) Sella turcica The last structure of the Diencephalon is the Epithalamus. (Brain model structures 1 & 3). What do you need to now about the epithalamus? Well it forms the roof of the 3 rd ventricle, and the 4
pink #1 structure represent the choroid plexus of the 3 rd ventricle. Remember what the choroid plexuses do? They are found in all 4 ventricles, our model only shows this one. Structure # 3, just posterior/inferior to structure 1 is a small endocrine gland called the Pineal Gland. This gland secretes the hormone melatonin, which helps regulate our sleep: wake cycles. Brain Stem The brain stem is located at the base of the brain inferior to the diencephalon and in front of (ventral) to the cerebellum. It consists of many fiber tracts (remember what nerve fibers are and what the term tracts means?) carrying nerve impulses from the brain to the spinal cord, and from the spinal cord to the brain: and the brain stem also has areas called nuclei. Remember, nuclei are clusters of cell bodies; these nuclei have specific functions that are primarily related to basic bodily functions and the senses. The brain stem consists of several distinct areas called the midbrain, pons, and medulla oblongata. (See Part B of figure 1, and structures 6,6a, 7and 8 on the Brain model) The Midbrain is a small area in the brain stem between the diencephalon and the pons. (See Part B of Brain Anatomy 1, and Part D of Brain Anatomy 2, and the Brain model shows you a mid sagittal cut of this area; structures 6 and 6a). The midbrain connects the brain stem and spinal cord with the cerebral cortex. It contains several important reflex (unconscious) centers. The only ones you need to know are the visual and auditory reflexes. The brain model structure 6a is a structure you need to know, it contains the areas for these reflexes. 6a represent ½ of a structure called the Corpora Quadrigemina. On this model you see 2 bumps, connect it to its other half of the model and you will have 4 bumps, hence the name quadrigemina. The upper 2 bumps (of the corpora quadrigemina) are called the superior colliculi (control visual reflexes) and the 2 bumps below are the inferior colliculi (control auditory reflexes). I will show you these in class and you will get it! Also in the midbrain, in the brain model between 6 and 6a is a *, this is the cerebral aqueduct (where CSF flows); it connects the 3 rd ventricle (the area of the thalamus) to the 4 th ventricle (** labeled) distally. The Pons is a round protuberance on the brain stem that lies between the midbrain and the medulla oblongata. (See Part B of Brain Anatomy 1, Part D of Brain Anatomy 2, and structure # 7 of the brain model.) The Pons relays information between the spinal cord, cerebrum and cerebellum. What to know about the pons.it is called the BRIDGE between the spinal cord, cerebellum and cerebrum. So the bulge in the middle of the brain stem is the Bridge that relays info between the major parts of the brain and spinal cord. No structures to know. The Medulla Oblongata (you will love how these words sound.a great band name..and yes I know Adam Sandler) is the last portion of the brain stem, and it connects to the spinal cord distally (when the medulla exits the foramen magnum it is now the spinal cord.) (See Part B of figure 1 1, Part D of figure 2, and structure #8 of the brain model.) All nerve impulses running up from and down to the body run through the medulla. The medulla contains vital clusters of nuclei (there s that word again, what does nuclei mean in the CNS?) that control basic (critical) body functions. The medulla has a respiratory center to regulate breathing, a cardiac center that can increase or decrease heart rate and a vasomotor center that regulates how blood vessels dilate and constrict, thereby affecting blood pressure. The possible consequences to damage to the medulla are obvious. This was the center that was put to sleep by the physician that was taking care of Michael Jackson. Michael s breathing center was put to sleep, and the reflexes to breath were stopped! Also, when the brain herniates because of pressure from above, this is the first region of the brain that goes through the foramen magnum.that is B.A.D. What else do you need to understand about the medulla? Well let s start with a structure 5
called the Pyramids (two longitudinal ridges). Here s a picture: medulla Spinal cord This is a posterior view of the medulla (and brain). Structures #4 on each side is the cerebellum, 1 is a median fissure that separates the two pyramids (structure 3 is one of the two pyramids). Why are these pyramids so important? Here you will find the secret to why the left side of your brain controls the right side of your body! In these pyramids we have something called the Decussation (crossing over) of Pyramids What is that you ask! Remember your precentral gyrus (motor cortex) in your frontal lobes that control motor movement? Well there are tracts (remember what a tract is?) called corticospinal tracts that connect the cerebral motor cortex to the skeletal muscles of the body. These corticospinal tracts travel down through the medulla into the spinal cord; hence the name corticospinal! (cortex + spinal cord). So we say: The decussation of the pyramids, or motor decussation, is the crossing over of cortical motor nerve fibers of the pyramidal tracts at the lower end of the medulla oblongata. Here is what it looks like. In the internal capsule. So we have motor fibers (tracts) coming down from the motor cortex with instructions for our skeletal muscles. These instructions are carried via these corticospinal tracts, down through the internal capsule (remember what the internal capsule is?) and when they reach the distal end of the medulla, they cross over (see the crossing in the diagram). So the information from your left side of the brain is passed over to the right side of the spinal cord. The right spinal cord will then deliver the information to the skeletal muscles on the right side via a right sided spinal nerves. Pretty cool! I hope this helps. You need to understand this information for any of this to make sense. If you don t understand try to find the answer yourself (you learn more that way), but if you just don t get it.ask! On to the Spinal cord! 6