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Unformatted text preview: Psychology 170: Fundamentals of Neuroscience
Structure and Function of the Nervous System: Neuroanatomy Reading: Carlson, Chapter 3 Basic Features of the Nervous System Lecture Overview Central Nervous System Anatomical Terms The Brain's Protective Covering: Meninges The Brain's Nutrient Supply: The Ventricular System Development of the Brain The "5part" Brain The Peripheral Nervous System Spinal & Cranial Nerves The Autonomic Nervous System Basic Features of the Nervous System Rostral (Anterior) toward the front Caudal (Posterior) toward the back **Note that in humans, the Dorsal (Superior) toward the top neuraxis bends at the brainstem. Ventral (Inferior) toward the bottom Thus, the forehead is considered anterior, and the top of the head is Lateral away from the midline dorsal Medial toward the midline Relative to neuraxis Relative to midline **Note that in humans, the neuraxis bends at the brainstem. Thus, the forehead is considered anterior, and the top of the head is dorsal Transverse Sagittal Horizontal The nervous system is covered by a thick The Meninges outer layering called the meninges; there are 3 layers: 1) Dura mater thick leathery outer layer 2) Arachnoid membrane soft, spongy layer that gives rise to the subarachnoid space, which is filled with cerebrospinal fluid (CSF) 3) Pia mater thin inner layer that overlies every surface of the brain Contains many small blood vessels Many larger blood vessels run through arachnoid layer Dura Covering Brain The Brain's Blood Supply
Sagittal View Dorsal View **most of these large vessels are in the subarachnoid space The BloodBrain Barrier Experiment: The CNS thus contains a bloodbrain barrier that serves to protect the brain from chemicals that may interfere with its function The bloodbrain barrier is produced by capillaries in the CNS that are not "leaky" like other blood vessels The CNS therefore contains no blood instead, neurons and glia are bathed in cerebrospinal fluid (CSF) If you inject blue dye into blood vessel, everything turns blue except the brain and spinal cord No leaks! Typically, astrocytes take up appropriate substances from the blood and transfer them to the neurons The Ventricular System & Cerebrospinal Fluid (CSF) The adult human brain weighs about 1400 grams (~3 lbs) For protection, the brain literally floats in the CSF contained in the subarachnoid space Within the brain, there are also 4 CSFfilled spaces called ventricles: Lateral ventricles (largest) Third ventricle Fourth ventricle This reduces its net weight by about 95% and also provides shock absorption Sagittal View Anterior View Dorsal View Part I: The Central Nervous System Brain Development Day 8 after conception: On days 927, the neural plate elongates and folds in on itself, forming the neural tube By the 28th day, the neural tube is closed and the anterior end forms 3 interconnected chambers these will become the forebrain, midbrain, and hindbrain part of the embryonic ectoderm thickens and forms the neural plate gives rise to the brain and spinal cord Formation of the Neural Tube Anterior Neural plate somites Posterior Major 5 Embryonic Brain Divisions As development progresses, the forebrain splits in 3 parts; 2 become the lateral ventricles and 1 becomes the 3rd ventricle: The midbrain becomes narrow, forming the cerebral aqueduct, and is called the mesencephalon The hindbrain further splits into 2 divisions: Metencephalon Myelencephalon Telencephalon the region containing the lateral ventricles Diencephalon the region containing the 3rd ventricle The Fate of the 5 Divisions
1) Telencephalon Cerebral Cortex Basal Ganglia Limbic System 2) Diencephalon 3) Mesencephalon 4) Metencephalon 5) Meylencephalon FOREBRAIN Thalamus Hypothalamus Tectum/Tegmentum Cerebellum Pons MID BRAIN HINDBRAIN
Medulla Oblongata Neuron Birth & Migration The neural tube is initially just a tube filled with CSF; a group of stem cells lines this tube called the ventricular zone Founder cells of the ventricular zone divide The immature neuron then leaves the leaving one founder cell and one immature neuron ventricular zone and migrates to its target along radial glial cells these assist the newborn neurons in finding their targets Migrating Neurons In the cortex, which contains six layers, neurons migrate to the innermost layer first, then move progressively outward; thus, the cortex develops "inside out" Many more neurons are born than are needed When neurons reach their targets, they stop and start to sprout dendrites and axons The axons then elongate in order to find their targets; at the end of each axon is a structure called the growth cone Neurons secrete different types of chemicals that attract different types of axons About 50% of the neurons that are born fail to find their targets Those that do not find targets die in a process called apoptosis Connect...Or Die! At 24 Weeks At 24 weeks (6 months), the fetal human brain begins to resemble an adult human brain Note, however, that the cortex is still growing (it still lacks folds) ~2 inches The Cerebral Cortex The Cerebral Cortex The cerebral cortex is the outermost part of the brain Approx. 3 mm thick contains mostly cell bodies and dendrites that give it a gray appearance (gray matter) White matter is formed by the axons that leave the cortex In higher mammals, especially humans, the cortex is greatly convoluted: Sulci small grooves Fissures large grooves Gyri bulges between adjacent sucli & fissures Fissures & Gyri The function of sucli & gyri is to increase surface area; the human cortex, if stretched out flat, would be ~2.5 ft2 The rat cortex is the size of a postage stamp Comparative Cortices Regions of the Cortex The cortex is divided up into different areas that have different functions Many of these areas are involved in processing sensory information: Primary visual cortex (Visual) Primary auditory cortex (Auditory) Somatosensory cortex (Touch) Insular cortex (Taste) Primary motor cortex Others are involved in producing actions The central sulcus divides the primary sensory and motor cortices Medial Lateral Motor Cortex Representation Different regions of the body are also represented disproportionately in the primary motor cortex The face, including the tongue, and fingers have many muscles for control of fine movements Sensory & Motor Cortex Sensory information originating on one side of the body is sent to the contralateral primary sensory cortex Similarly, the primary motor cortex controls The olfactory and gustatory systems are the exception! the contralateral side of the body stimulation of the arm region of the right motor cortex will result in a movement of the left arm The cortex is roughly divided up into 4 areas or lobes: Lobes of the Cortex Some say there is a 5th area, called the Limbic lobe, which contains the cingulate cortex and is concerned with emotions 1) Frontal lobe includes everything in front of the central sulcus; concerned mostly with planning and actions 2) Parietal lobe located just behind the central sulcus; concerned mostly with perception 3) Temporal lobe ventral to the frontal and parietal lobes; concerned mostly with auditory processing and memory 4) Occipital lobe in the posterior part of the brain; concerned mostly with visual processing Lobes of the Cortex Ventral view
Rostral Caudal Sagittal view Association Cortex The areas of the cortex not devoted to processing sensory information are devoted to activities such as perceiving, learning, remembering, and planning These activities take place in association areas There are multiple association areas, each in close proximity to their primary sensory or motor area: Motor association cortex Somatosensory association cortex Auditory association cortex Visual association cortex Association Areas The brain contains 2 hemispheres The Hemispheres In most people, the left hemisphere is specialized more for things like language production and comprehension the right hemisphere is specialized for non verbal and spatial abilities This functional difference between the hemispheres is called lateralization Both hemispheres are connected by a large fiber (axon) bundle called the corpus callosum The SplitBrain Patient Lateralization effects are difficult to observe in healthy people because the 2 hemispheres talk to each other You can observe lateralization if the corpus callosum has been cut The SplitBrain Experiment The SubCortical Forebrain The limbic system is made up of many Limbic System brain regions The nuclei include: It is primarily thought to play a role in emotions and in memory formation Cingulate cortex emotions Amygdala plays a role in emotion and emotional memory formation Septum "rage" is produced after lesions Hippocampus plays a role in memory Basal Ganglia The basal ganglia are involved in the control of movement and consist of the: Caudate nucleus Putamen Globus pallidus
"Striatum" Lesions to the basal ganglia result in uncontrolled movements Diseases of the basal ganglia include Parkinson's disease and Huntington's Disease The diencephalon contains 3 important structures: The Diencephalon Thalamus a structure that relays sensory information from the brainstem to the forebrain and cortex Hypothalamus involved in controlling the endocrine and autonomic nervous systems Pituitary connected to the hypothalamus; the "master gland" that controls the endocrine system of the body controls the "4 F's" (fighting, fleeing, feeding, and...mating) Anterior & Posterior regions The Hypothalamus The hypothalamus is actually a collection of nuclei each with a distinct function; but all are involved in motivation (e.g. feeding, sex, etc) The hypothalamus contains neurosecretory cells that innervate the pituitary and result in the release of hormones from its two divisions
Adrenocorticotropic hormone Growth hormone Thyroid hormone FollicleStimulating hormone Luteinizing hormone Oxytocin Vasopressin The Midbrain, Hindbrain, & Spinal Cord Tectum (dorsal aspect) The Mesencephalon Tegmentum (ventral aspect) Superior colliculi involved in visual processing Inferior colliculi involved in auditory processing Reticular formation involved in arousal Periaqueductal gray involved in species typical behaviors, incl. fighting, mating, etc Red nucleus and substantia nigra both involved in motor control Metencephalon Metencephalon & Myelencephalon Myelencephalon Cerebellum "little brain" responsible for motor coordination Pons mostly composed of fibers that are relayed from the forebrain to the spinal cord Medulla oblongata base of brainstem; contains a number of nuclei that are important for vital functions, including breathing, cardiovascular function, etc 51.
**note that the brainstem is composed of everything but the telencephalon Functions to relay sensory information to The Spinal Cord the brain and to relay motor commands from the brain to the muscles Enclosed by vertebral column and surrounded by meninges Composed of 4 regions that control different parts of the body: Cervical controls the arms and hands Thoracic controls the trunk and upper body Lumbar controls the legs Sacral controls the feet Spinal Cord Anatomy Most of the spinal cord is composed of ascending and descending fiber (axon) tracts Unlike in the brain, most this "white matter" is located on the outside of the cord The inner portion of the cord contains collections of (mostly inhibitory) cells that serve to modulate incoming sensory signals or outgoing motor signals **note that the spinal cord is only about 2/3 of the length of the spinal column; the final 3rd is made up of descending nerve fibers called the cauda equina Part II: The Peripheral Nervous System The Peripheral Nervous System The PNS is made up of 2 divisions: The Somatic Nervous System sensory nerves originating in the body and motor nerves that innervate the muscles The Autonomic Nervous System nerves that innervate the internal organs and glands, including the heart, lungs, the gut, etc Spinal nerves Cranial nerves Spinal Nerves There are 31 pairs of spinal nerves The sensory fibers coming in from the periphery travel trough the dorsal roots Fibers that are leaving the cord The dorsal root ganglia contains cell bodies of unipolar sensory neurons that originate in the body (mostly motor) travel through the ventral roots There are 12 pairs The Cranial Nerves of cranial nerves Cranial nerves are similar to spinal nerves With 1 exception (the vagus nerve), most cranial nerves innervate the face and head I. Olfactory II. Optic III, IV,VI. V.
Spinal Accessory VIII.
Auditory X. Vagus IX. Glossopharyngeal The ANS is made up of 2 divisions: The Autonomic Nervous System (ANS) The Sympathetic System concerned with activities associated with energy expenditure in the body The Parasympathetic System concerned with vegetative states in the body Strongly activated during arousal, fight or flight Originates in the thoracic and lumbar portions of the cord and forms the sympathetic ganglia outside of the spinal column Strongly activated during digestion, relaxation, etc Originate from the cervical and sacral regions of the cord Sympathetic Parasympathetic Next Class
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This note was uploaded on 09/16/2008 for the course PSYC 170 taught by Professor Schafe during the Fall '08 term at Yale.
- Fall '08