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Janelle Leboutillier

PSYB64: Introduction to Physiological Psychology Lecture 2: The Anatomy and Evolution of the Nervous System Lecture Overview  Anatomical Directions and Planes of Section  Protecting and Supplying the NS  The CNS  The PNS  Evolution of the Brain and Nervous System Anatomical Directions (Planes of reference to a specific point)  Rostral or anterior = Head end of four legged animal  Caudal or posterior = Tail end of four legged animal  Inferior or ventral = Towards the belly  Superior or dorsal = Towards the back Anatomical Directions (Figure 2.1)  Human being, we are bipedal  There is a 90 degree turn at the top of the spine where the brain comes in  90 degree twist where the brain is; different from when we look at a rodent, which we would look straight across the spinal cord and the brain would be lined up  Using the 90 degree twist at the brain for humans: o Ventral/inferior = base of the brain o Dorsal/superior = top of the brain o Rostral/anterior = towards the eyes o Caudal/posterior = towards the back  Proximal = close to  Distal = far away (e.g. fingers are distal to the spinal cord)  Lateral =toward the sides  Medial = toward the middle Three Customary Orientations for Viewing the Brain and Body (3 cuts made to the brain) 1. Horizontal plane o aka transverse cut o Cutting the brain in half o Cut in terms of the long-length 2. Sagittal plane o Cut right through the centre along the longitudinal fissure o Cut from top to bottom o Para-sagittal: cut off- centre 3. Coronal plane o aka frontal cut o Cutting from the front to the back of the brain Protecting and Supplying the Nervous System  Meninges o Three distinct layers of meninges provide protection of the brain  Cerebrospinal Fluid o Secreted in hollow spaces in the brain known as ventricles o Circulates through ventricles, subarachnoid space, and central canal of the spinal cord  Blood Supply o Brain receives nutrients through the carotid arteries and vertebral arteries The Skull and Three Layers of Membrane Protect the Brain (Figure 2.3) 1. DURA MATER o Underneath the hair o Tough, rigid layer o Thick layer withhold damage 2. ARACHNOID MEMBRANE o Typically includes the subarachnoid space o Spongy layer o Arachnoid trabeculae: web-like structure o Full of cerebrospinal fluid o Blood vessels found here that supply nutrient to this region 3. PIA MATER o Light purple layer in diagram o Follows all the convolution of the brain o Not tough, not rigid o Follows every gyri and sulci in the brain o Easily damaged o Protects the cortex o Brain adheres closely to pia mater Cerebrospinal Fluid Circulates Through the Ventricles, Spinal Cord and Subarachnoid Space (Figure 2.5)  Cavities in the brain where there are no brain tissue  Flowing through the ventricular system is cerebrospinal fluid which carries nutrients and helps buffer the brain  Ventricular system highlighted in grey/blue in left image  2 large lateral ventricles, 1 found in each hemisphere in the brain  There is a 3rd ventricle and 4th ventricle which connect with the central canal  All comprise the ventricular system, filled with fluid,  We have approx 120 ml of cerebrospinal fluid in our brain; it changes over 3x a day o Roughly 300-500 ml change-over each day o Constantly being changed over o Sometimes there is a blockage, where one of the ventricles gets blocked, so a shunt is needed to allow the flow o A back-up of fluid can cause an enlargement and damage the brain  Lateral ventricles are also known as ventricles 1 and 2  CSF is produced in these ventricles, produced in a structure referred to as choroid plexus (black gummy structure) o This produces CSF o CSF flows through these ventricles and down through the spinal cord region in the meninges and through the arachnoid membrane and subarachnoid o Providing nutrients and buffering throughout the brain  The spinal cord, there are 3 layers of meninges as well (dura mater, arachnoid membrane, and pia mater) found in the CNS  The PNS doesn't have 3 layers, it only has 2, because the arachnoid membrane is missing (only seen is the dura and pia mater) The Ventricular System  Abnormalities: 7. Brain Anomaly and Plasticity: Hydrocephalus  Hydrocephalus, a childhood disorder of excess fluid in the brain (large ventricles), illustrates brain plasticity — the brain's amazing ability to rebound after injury. While patients with this disorder experience compression and destruction of brain tissue early in life, many are able to function normally later in life, after their brains have compensated for the loss  Dr. John Lorber (University of Sheffield, England) compares the brain of a normal child with that of a hydrocephalic to illustrate the enormous difference in the size of the ventricles. In the hydrocephalic, ventricular expansion compresses the cerebral cortex, which leads to a loss of brain mass. In the past, hydrocephalus was untreatable, but today infants can be helped through a shunting technique for draining excess fluid from the brain.  The main point of the video is that despite significant compression of the brain tissue, some patients, such as Sharon, are average to above-average in intellectual functioning and can lead normal lives. The program shows Sharon undergoing both a CAT scan and cerebral blood flow analysis, which reveal a severely distorted brain with activity focused mostly in the visual area of the brain. In the normal brain tasks are distributed more evenly. These differences are interpreted in terms of brain plasticity.  Nicole is introduced as another example of brain plasticity. Dr. Erin Bigler (Brigham Young University) describes Nicole's history of early hydrocephalus. The brain scans he shows indicate a loss of brain tissue due to a large expansion of the ventricles, primarily on the left side of her brain. Additionally, the occipital area of Nicole's brain is extensively damaged.  At the conclusion of this portion of the video, Nicole's attempt to perform certain tasks shows that although she is unable to do visual/perceptual motor tasks, she has developed normal language skills.  The cases of Sharon and Nicole dramatically demonstrate the brain's plasticity. Although they may raise more questions than answers, they provide a challenge for further research into the brain's remarkable ability to recover from injury.  The emphasis here is on plasticity more than on hydrocephalus. Two points require further clarification and explanation. First, brain injury that occurs early in life is different from brain injury experienced after maturity. This distinction is important to emphasize to students who may over-generalize from these cases to their ability to recover from accident and injury. Second, although their brains are distorted, both Sharon and Nicole have a cortex which is essential to normal human brain function. The Brain Has a Generous Supply of Blood (Figure 2.7)  Brain cannot store glucose or energy, so it needs blood for metabolic processes  Vertebral artery and carotid artery are the main arteries that let blood into the brain  Divided into 3 main arteries: 1. Anterior cerebral artery  Supplies blood to the front of the brain 2. Middle cerebral artery  Supplies blood to the middle of the brain 3. Posterior cerebral artery  Supplies blood to the back of the brain  We need a constant supply of blood to provide this energy  Cut off of blood to the brain for 3 minutes can cause damage The Organization of the Nervous System (Figure 2.8) Divisions of the Nervous System *Overview of The CNS*  The Spinal Cord o Extends from medulla to first lumbar vertebra  The Hindbrain o Myelencephalon (medulla) o Metencephalon (pons and cerebellum)  The Midbrain o Mesencephalon  The Forebrain o Diencephalon, Telencephalon The Anatomy of the Spinal Cord (Figure 2.9)  Spinal cord extends from medulla to the first lumbar vertebrae Hindbrain Structures of the Brain Stem (Figure 2.10)  Consists of the: o Myelencephalon (medulla) o Metencephalon (pons + cerebellum)  Control functions that allow us to survive (heart rate, breathing, blood pressure)  Damage often causes death SOME IMPORTANT STRUCTURES OF THE BRAINSTEM  RETICULAR FORMATION o Sleep and arousal o Temperature regulation o Motor control  MEDULLA (sustains life) o Regulation of breathing and heart rate o Tissue damage in this area often fatal The Internal Structure of the Midbrain (Figure 2.11)  Two structures known as the colliculi 1. Visual information processing  (superior colliculus) 2. Auditory information processing  (inferior colliculus)  Superior colliculus is above the inferior colliculus (point of reference) Forebrain  The Thalamus and Hypothalamus of the Diencephalon  The following structures of the Telecephalon o The Basal Ganglia o The Limbic System o The Cortex  Lobes of the cortex  Localization of function in the cortex The Thalamus and Hypothalamus of the Diencephalon (Figure 2.12)  Orientation: frontal/coronal plane (cut of the brain)  Surrounded by other brain material (telecephalon)  Thalamus and hypothalamus is in the diencephalon DIENCEPHALON  Thalamus o Relay Station  Hypot
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