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Nervous System Part 2: Structures Central Nervous System Structures • Brain • Spinal cord The Brain • Operates the body and interprets vast amounts of information daily • The average adult human brain weighs 3.1 lbs • It contains about 100 billion neurons which function as a unit • The brain is one of the most mysterious organs of the body Parts of the Brain • • • • • • • Cerebrum Gyri Cerebral cortex Corpus callosum Diencephalon Brain Stem Cerebellum Cerebrum • Largest portion of the brain • Has a highly folded outer layer called the cerebral cortex • Underneath the cerebral cortex, are the ridges or convolutions, called gyri • It is divided into two hemispheres which are connected by the corpus callosum • The corpus callosum is a band of axons that lies deep in the central groove • The cerebrum is further divided into 5 distinct lobes Cerebral Cortex • Contains 10-20% of the brain’s total number of neurons • Its many folds allow the surface area of the cortex to fit within the skull • Different parts of it control information and sensations from the body and motor responses White Matter • Is the layer beneath the cerebral cortex • It is composed of myelinated axons – Myelin is an insulator of neurons • These axons link regions of the cortex with each other and with other neural centers • The crossover of these axons causes impulses originating in one hemisphere to be processes by the other half and vice versa Left Hemisphere • Rational & Sequential • Responds to verbal instructions • Problem solves by logically and sequentially looking at the parts of things • Looks at differences • Is planned and structured • Prefers established, certain information • Prefers talking and writing • Prefers multiple choice tests • Controls feelings • Prefers ranked authority structures • Is a splitter: distinction important • Is logical, sees cause and effect Right Hemisphere • Intuitive & Simultaneous • Responds to demonstrated instructions • Problem solves with hunches, looking for patterns and configurations • Looks at similarities • Is fluid and spontaneous • Prefers elusive, uncertain information • Prefers drawing and manipulating objects • Prefers open ended questions • Free with feelings • Prefers collegial authority structures • Is a lumper: connectedness important • Is analogic, sees correspondences, resemblances Lobes of the Brain • Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving • Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli • Occipital Lobe- associated with visual processing • Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech • Insula- (Island of Reil) is a lobe deep within the brain and covered by the other lobes. – It is believed to be involved with the consciousness and emotional homeostasis Diencephalon • Lies between the cerebrum and the brain stem • It contains relay centers from information entering and exiting the brain • It is divided into two distinct centers: – Thalamus – Hypothalamus • In addition, a set of brain structures called the limbic system incorporates parts of the thalamus and hypothalamus, centers in the temporal lobes and deeper parts of the cerebral cortex • The limbic system helps govern emotion, memory and motivation Thalamus • Is the uppermost relay center of the diencephalon • It directs most incoming sensory signals to the proper regions of the cerebral cortex Hypothalamus • Helps to maintain homeostasis • It also directly and indirectly controls much of the body’s hormone production Brain Stem • Located beneath the diencephalon • Has three main division: – Midbrain – Pons – Medulla oblongata • Lying throughout is a diffuse network of neurons called the reticular formation – Helps control respiration and circulation – Helps separate signals that demand attention from those that are unimportant Midbrain • Relays visual and auditory information Pons • Relays communications between the cerebral hemispheres and the cerebellum Medulla Oblongata • Serves as both a relay center and a control center for heart rate, respiration rate, and other homeostatic activities Cerebellum • • • • Lies below and behind the cerebral hemispheres Its surface is highly folded It helps coordinate muscle action It receives sensory impulses from muscles, tendons, joints, eyes and ears, as well as input from other brain centers • It processes information about body position • Controls posture by keeping skeletal muscles in a constant state of partial contraction • It coordinates rapid and ongoing movements Additional Structures • Cerebrospinal fluid: is a clear bodily fluid that surrounds the brain and spinal cord • Has three functions: – Delivers nutrients to the structures of the nervous system – Removes wastes from the brain and spinal cord – Protects the brain and spinal cord from trauma • Meninges: is a system of membranes which envelop the CNS • They are made up of three layers: pia mater, arachnoid mater, & dura mater Spinal Cord • Is a column of nervous tissue that starts at the medulla oblongata • It runs through the vertebral column • It carries nerve signals back and forth like a superhighway • It has an outer sheath of white matter • Its rigid inner core is made up of gray matter – Gray matter is composed of dendrites, unmyelinated axons and the cell bodies of neurons Peripheral Nervous System • Constantly interacts with the central nervous system via 12 pairs of cranial nerves and 31 pairs of spinal nerves • Nerves are the bundles axons and dendrites of many neurons • Each spinal nerve has a dorsal root and a ventral root Nerve Distinctions • Dorsal roots carry signals to the CNS from sensory receptors – Sensory receptors are specialized neurons that detect a stimulus such as light, pressure, or heat • Ventral roots contain the axons of motor neurons, which carry information from the CNS to muscles and glands – Motor neurons carry information from the CNS to muscles and glands – Interneurons relay information between other neurons