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Nervous System Northwest Rankin High School Human A&P Functions of the Nervous System Monitors changes inside and outside of the body. Changes are stimuli and gathered info is called sensory input Integration: processes the sensory input and makes decisions about what should be done Affects a response by activating muscles or glands, motor response Video Clip Structural Organization Central Nervous System (CNS) Brain and Spinal Cord Structural Organization Peripheral Nervous System (PNS) Nerves that extend from the brain and spinal cord Nervous System Overview Nervous System Composed of 2 types of neural tissue Neurons – are specialized to react to physical and chemical changes in their surroundings. Neuroglial cells – surround the neurons and nourish neurons and perhaps send and receive messages. Neuron Neurons Nerve cells that are highly specialized to transmit messages (nerve impulses) from one part of the body to another Video Clip Parts of a neuron Cell Body – contains nucleus 2 types of processes or fibers extending from the body 1. Dendrite – receives stimuli may have hundreds per neuron conduct currents toward the cell body Neurons Cont. 2. Axon neurons have only one Conduct nerve impulses away from the cell body Axons branch to form axonal terminals Neurotransmitters are released when impulses reach the terminals Synaptic cleft separates one neuron from the next THE NEURON d cb a d d The cell body is the portion of the nerve cell that surrounds the nucleus. Multipolar neurons have several branches arising form the cell body (cb). There is usually one axon (a) and many dendrites (d). Dendrites carry nerve impulses to the cell body. The axon is designed to carry nerve messages away from the cell body. Neurons cont. Myelin – mass of white lipid material that insulates the axon. These are called Schwann cells. Gaps between these cells are known as nodes of Ranvier. Disease Example Multiple Sclerosis – myelin sheaths are damaged and hardened which causes the person to lose the ability to control muscle movement. Neuron Classification Sensory (afferent) neurons – carry impulses from the sensory receptors in the organs and skin to the CNS Motor (efferent) neurons – carry impulses from the CNS to the muscles or glands Association (interneuron) neurons connect motor and sensory neurons 3 Neuron Structures Multipolar Neuron • Has many processes • • Including dendrites and axon most common type 3 Neurons Cont. Bipolar Neuron • Two processes – • • 1 axon and 1 dendrite Rare in adults, but found in some special sense organs Neurons Cont. Unipolar Neuron • Single process emerging from the cell body Neuroglia Many types of cells that support, insulate, and protect delicate neurons. Types of Neuroglia Astrocytes – form a barrier between capillaries and neurons Microglia – phagocytes that dispose of debris like dead brain cells and bacteria. Ependymal Cells – line the cavity of the brain and spinal cord. Oligodendrocytes – help to form the myelin sheath Neuroglia differs from Neurons Resemble neurons structurally, but are not able to transmit nerve impulses Never lose the ability to divide like neurons. Most brain tumors are formed by glial cells. Physiology of Nerve Tissue 2 types Nerve Impulses have 2 major functions 1. Irritability: ability to respond to a stimulus and convert it into a nerve impulse Conductivity: ability to transmit the impulse to other neurons, muscles, or glands. 2. Conductivity Neurotransmitters allow the impulse to continue between neurons Reflex Arc Reflexes are rapid, predictable, and usually involuntary responses to stimuli 2 types 1. 2. Autonomic - INVOLUNTARY Somatic - VOLUNTARY Pathway of Reflex Arc 1. 2. 3. 4. 5. Receptor – reacts to stimulus Afferent Neuron – carry impulse to CNS Integration – synapse between afferent and efferent neuron Efferent neuron – carry impulse to muscles or glands Effector – muscles or glands to be stimulated Central Nervous System Consists of the brain and spinal cord The brain weighs a little over 3 pounds and is about the size of two fists. It looks to be pinkish gray tissue, wrinkled like a walnut, with a cold oatmeal texture The Brains 4 Major Regions Cerebrum Cerebellum Brain Stem 1. 2. 3. Diencephalon 4. Midbrain pons medulla oblongata Thalamus Hypothalamus epithalamus Video Clip Cerebrum Largest portion of the brain Has 2 cerebral hemispheres (right and left) connected by the corpus callosum 4 Lobes of the Cerebrum 1. 2. 3. 4. Frontal Parietal Temporal Occipital The names of the lobes come from the skull bones that overlie them. Cerebral Cortex – Gray Matter Folded outer layer of the cerebral hemispheres Gray color because it contains cell bodies Cerebral Cortex – Gray Matter Covered by elevated ridges of tissue called gyri (gyrus – singular) and is the gray matter. Shallow grooves that separate the ridges are called sulci (sulcus – singular) Deep grooves are called fissures Cerebral Cortex - White Matter Lies below the cerebral cortex – gray matter Is composed of the axons of cortical neurons Parietal Lobe Interprets impulses sent from sensory receptors Speech and ability to use words Frontal Lobe Voluntary muscle control Problem solving and planning Occipital Lobe Area responsible for vision Temporal Lobe Hearing Auditory and visual memory Hippocampus – short term memory Cerebellum A region of the brain that plays a vital role in the coordination of muscle action Helps maintain normal muscle tone Brain Stem Midbrain Pons Important relay center for visual and auditory information Serves as a relay center between the neurons of the cerebral hemispheres and those of the cerebellum. Helps control breathing. Medulla Oblongata Serves as both a relay center and control center. Helps regulate heart rate, blood pressure, breathing, swallowing, and vomiting Diencephalon Thalamus – directs most incoming signals to the proper region of the cerebral cortex Hypothalamus – regulation of body temp, water balance, and metabolism directly and indirectly controls much of the body’s hormone production. (Pituitary gland of endocrine system) Part of limbic system - emotion Thirst, appetite, pain, sex, and pleasure centers Epithalamus – includes the pineal body ( endocrine system) and choroid plexus (makes CSF) Protection of the CNS Bones of the skull and vertebral column protect the CNS Meninges – membranes between bone and soft tissue. 3 Layers of Meninges Dura matter – tough outermost Arachnoid matter – middle, web like Pia matter – innermost delicate Cerebrospinal Fluid (CSF) A watery cushion around the brain and cord. Continually formed and drained to keep a constant rate. Any fluctuation in the in the pressure could indicate a disorder. Blood – Brain Barrier Neurons are kept separate from blood borne substances Metabolic wastes like urea, toxins, and proteins are prevented from entering brain tissue. Nutrients (like glucose), anesthetics, water, alcohol, and nicotine all easily pass through the barrier. Spinal Cord Reflex center and Conduction pathway Peripheral Nervous System Nerves and scattered groups of ganglia found outside the CNS. Functional Classification (PNS) Afferent (sensory) division: nerve fibers that convey impulses to the central nervous system from sensory receptors located in various parts of the body Efferent (motor) division: carry impulses from the CNS to effector organs, the muscles and glands Effector (motor) division Somatic Nervous system: allows conscious or voluntary control of skeletal muscles Autonomic Nervous system: regulates events that are autonomic or involuntary, such as the activity of smooth and cardiac muscles and glands Autonomic Nervous System Sympathetic Division activated by conditions of physical or emotional stress fight or flight division active when an emergency or threatening situation arises Parasympathetic Division deals with routine conditions most active when the body is at rest and not threatened in any way Structure of a Nerve Bundle of Neuron fibers outside the CNS Each fiber wrapped in a endoneurium Group of fibers in a perineurium All bound together by a epineurium Structure cont. Classified according to direction of impulse Mixed nerve – carry both sensory and motor fibers Afferent (sensory) – carry impulses to CNS Efferent (motor) – carry impulses away from CNS Cranial Nerves 12 pair that extend from the brain to serve the head and neck region. Only exception is the Vagus nerve which extends to the thorax and abdomen Spinal Nerves 31 pair of nerves formed by the dorsal and ventral roots of the spinal cord 4 Groups of Spinal Nerves Cervical: Diaphragm and muscles of neck Brachial: serves the arms Lumbar: serves the lower abdomen, buttocks, and thighs Sacral: serves the lower trunk, posterior surface of thighs, posterior and lateral aspect of leg and foot