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The Nervous System Chapter 7 Organization Objectives: List the general functions of the nervous system. Explain the structural and functional classification of the nervous system. Define central nervous system and peripheral nervous system and list the major parts of each. What is the nervous system? The master control and communication system for the body All thoughts, actions, and emotions Uses electrical impulses to direct activity and communicate It monitors the entire body… maintains homeostasis Sensory input: gather stimuli from environment Homeostasis 1. 2. 3. Sensory receptors collect and monitor stimuli (sensory input) Control center processes and interprets sensory input and makes decisions about what to (integration) Sends a response by activating a system to take care of business, usually muscles or glands (motor output) The team Nervous system works with all systems to regulate functions Endocrine system especially, by releasing hormones into the blood stream to change things gradually Nervous system on the other hand, makes rapid changes occur Nerves and more nerves Two basic subdivisions: Central nervous system (CNS) which contains the brain and spinal cord (command center) Peripheral nervous system (PNS) which contains spinal nerves and cranial nerves (support center) MORE TO COME… Function The PNS has two basic functions Sensory (afferent) division Sends impulses to the CNS from sensory receptors Motor (efferent) division 1. 2. Sends impulses from the CNS to the effector organs (muscles and glands) Somatic nervous system: skeletal muscles Autonomic nervous system: cardiac muscles and glands Nervous Tissue: Structure and Function Two types of nervous tissue Supporting cells: Who and what depend on which system; PNS or CNS Neurons: Basic function and some difference in structure CNS: Supporting Cells Neuroglia “nerve glue” Astrocytes: barrier between capillaries and neurons, control chemical environment in brain Microglia: phagocytes>eat dead brain cells, bacteria Ependymal: line cavities of brain and spinal cord, moves cerebrospinal fluid around Oligodendrocytes: wrap around nerve endings and produce myelin sheath (fatty insulation) PNS: Supporting Cells Schwann cells: Form the myelin sheaths around nerve fibers Satellite cells: Protection and cushion Anatomy of Neurons These are common to ALL neurons: Cell body: contains nucleus Dendrites: impulses move toward cell body Axons:impulses move away from cell body Axonal terminals: branches at end of axon Neurotransmitters: chemicals released at axon Synaptic cleft: tiny gap between neurons (synapse) Myelin: fatty insulation that increases nerve impulse rates Let’s DRAW… YEAH! The Myelin Sheath Called the neurilemma sometimes “neuron husk” Spaces between myelin are called nodes of Ranvier, regular spacing MULTIPLE SCLEROSIS: a disease in which the myelin sheaths around the fibers are destroyed and converted to hard shells, this short circuits the impulse and muscle control is effected greatly….AUTOIMMUNE DISEASE… no cure, but some treatment Sensory Receptors Naked nerve endings (pain and temperature) Meissner’s corpuscles (touch) Pacinian corpuscle (deep pressure) Golgi tendon organ (proprioceptor) Muscle spindle (proprioceptor) *proprioceptor: detect stretch, tension in skeletal muscles, tendons, joints Classification of Neurons Multipolar: all motor neurons Bipolar: two processes, an axon and a dendrite (long in both directions) Unipolar: single process that is very short and divided into proximal and distal fibers (PNS ganglia neurons) See page 202 for a picture…ADD to notes Physiology of Neurons What makes a nerve go? 1. 2. Stimuli and conductivity… movement of ions across a membrane Polarized: resting stage (More sodium outside) Depolarization: causes a nerve impulse to be sent through a neuron (More sodium inside) 3. All or none response Repolarization: neuron becomes polarized again, back to resting stage (Sodium moves back inside) Nerve Impulses Myelin sheaths cause impulses to travel faster because they jump from node to node Alcohol, sedatives, and anesthetics all block nerve impulses by reducing membrane permeability to sodium ions… no sodium entry equals no action potential Cold temperatures and continuous pressure mess with impulses because of blood flow, like sitting on your foot or cold fingers Reflex Arc Reflexes are rapid, predictable, and involuntary responses to stimuli. Autonomic reflexes: regulate smooth muscles, the heart, and glands Somatic reflexes: regulate skeletal muscle (moving hand from hot pan) All contain 5 basic things in pathway Pathway for Arc 1. 2. 3. 4. 5. Sensory receptor: reacts to stimulus Afferent neurons: message carrier CNS integration center: synapse between afferent and efferent neurons Efferent neurons: message carrier Effector organ: muscle or gland that is stimulated *Most reflexes only involve the spinal cord and occur before the brain “notices” Central Nervous System CNS: The control center Development of CNS 1. 2. 3. Neural tube: a simple tube that extends down the dorsal median plane (center of back) During the 4th week, brain begins to form The tube expands and forms four chambers called ventricles (regions in the brain) Anatomy of Brain Cerebral Hemispheres Diencephalon Brain Stem Cerebellum Cerebral Hemispheres Most superior part, largest region of brain Folded shaped, wrinkles caused by gyri, sulci, and fissures Speech, memory, logical and emotional response Consciousness, interpretations of sensation, and voluntary movements Main lobes: parietal, occipital, temporal, frontal Parietal Lobe Interprets sensory input from somatic areas (not special senses like hearing, smell, taste) Recognize and process pain, coldness, light touch Input registered by lips, fingertips and other areas with lots of sensory receptors Occipital and Temporal Lobe Input from special sense organs are interpreted here Think occipital…eyes…vision Think temporal…ears… hearing Think temporal…nose…smell Frontal Lobe Primary motor area: Deal with movement of skeletal muscles Broca’s area: Deal with speech development and the ability to speak Speech area: located at junction of temporal, parietal and frontal lobes… allows us to sound out words What’s all the Matter? Gray matter: neurons involved in the cerebral hemisphere, make up the cerebral cortex (outermost layer of cerebrum) White matter: deeper, under the gray matter Bundles of nerve fibers Corpus callosum: connects two hemispheres Parkinson’s disease Basal nuclei: regulate voluntary motor activity by modifying instructs sent to he skeletal muscle by the primary motor cortex Symptoms: trouble initiating movements and mild/severe hand tremors Caused by a lack of dopamine (neurotransmitter) Some drug therapies are proving to benefit individuals with Parkinson's disease Diencephalon Sits on top of brain stem, surrounded by the cerebral hemispheres Major structures: thalamus, hypothalamus, and the epithalamus Thalamus Relay station for sensory impulses passing upward to the sensory cortex Briefly senses pleasant or unpleasant Hypothalamus Located under the thalamus (hypo is under) Regulates body temperature, water balance, and metabolism Makes up the limbic system: Thirst, appetite, pain/pleasure center Regulates pituitary gland (hormones) Regulates reflex areas for smell Epithalamus Pineal body (part of endocrine system) Choroid plexus: knots of capillaries in each ventricle that create the cerebrospinal fluid Brain Stem Size of thumb, 3 inches long Three structures: midbrain, pons, and medulla oblongata Reticular Activating System (RAS): consciousness and the awake/sleep cycle Damage to this area may cause permanent unconsciousness Midbrain Small part of brain stem Involved in reflex centers for vision and hearing Pons Area that that bridges between the midbrain and medulla oblongata Nerve tracts involved in breating Medulla Oblongata Merges into the spinal cord Regulates heart rate, blood pressure, breathing, swallowing, and vomiting Cerebellum Outer cortex (layer) made of gray matter Inner cortex made of white matter Located at back of head, under cerebrum Regulates timing of muscle movements Controls balance and equilibrium Monitors what is going on and what the brain wants the body to do Ataxia If the cerebellum is damaged by stroke, blow to the head, tumor or other means, body movements can become clumsy and disorganized Individuals cannot keep balance, may appear intoxicated CNS Protection Nerve tissue is very soft Protected by Bones (vertebral column, skull) Membranes (Meninges) Water cushion (cerebrospinal fluid) Meninges Three layers that protect the CNS Dura mater: outer, leathery, dbl layer Arachnoid mater: Middle, cobweb appearance Pia mater: inner layer, follows every fold, covers brain and spinal cord Meningitis Inflammation of the Meninges Can be bacterial or viral which could spread throughout nervous system Diagnosis can be made by taking a sample of the cerebrospinal fluid Causes brain swelling (encephalitis) Cerebrospinal Fluid Watery “broth” that surrounds the brain and spinal cord Very similar to blood plasma Can be sampled by a lumbar tap (spinal tap) After sampling, patient must stay lying down or a headache may result because of decrease fluid pressure Hydrocephalus: water on the brain…can cause brain damage due to increased pressure, can be controlled by shunts that drain excess fluid into neck vein Blood Brain Barrier Brain needs a special constant environment Blood changes in consistency and make up Capillaries in the brain are only allowed to pass water, glucose, and essential amino acids Barrier cannot protect against fats, respiratory gases, blood-borne alcohol, nicotine, and anesthetics Brain Dysfunctions Traumatic Brain Injuries (TBIs) Concussion Contusion Cerebral edema Degenerative Brain Disease (DBDs) Cerebrovascular accident Alzheimer’s disease Spinal Cord Approximately 17 inches long Provides two-way communication to and from brain Major reflex center Protected by vertebral column 31 pairs of spinal nerves Explore Spinal Cord injuries: Look up the following injuries and summarize your findings: Spastic paralysis Quadriplegic Paraplegic Peripheral Nervous System PNS: Spinal Nerves and Cranial Nerves Structure of a Nerve Nerve: Bundle of neuron fibers found outside the CNS Endoneurium: protective covering on a nerve Mixed nerves: have both sensory and motor fibers, contains all spinal nerves Cranial Nerves 12 pairs of cranial nerves that serve the head and neck region Only one pair serves the thoracic/abdominal cavities (Vagus Nerves) Olfactory, Optic, Oculomotor, Trochlear, Abducens, Trigeminal, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, and Hypoglossal Spinal Nerves and Plexuses 31 pairs of human spinal nerves that form the ventral and dorsal roots Damage to a spinal nerve effects both sensation and movement, causing paralysis in a specific region of the body Intercostals nerves: supply the muscle between the ribs and skin/muscles of trunk Nerve plexuses serve the motor and sensory nerves of the limbs Autonomic Nervous System Subdivision of the PNS Controls body functions automatically Regulates: Cardiac muscle (heart tissue) Smooth muscle (visera of organs, blood vessels Breathing, pupil dilatation, blood pressure Hugh player in homeostasis Two subdivisions: Sympathetic, parasympathetic Sympathetic Division of ANS “fight or flight” system Rapid heart beat, deep breathing, hair standing on end, dilated pupils, increased blood flow to the skeletal muscles Adrenal glands are a major player Hormones are released for a short time but have lasting effects, you have to “come down” Parasympathetic Division Does most work while you are sleeping and not threatened “resting and digesting” system Works for normal digestion and fecal removal, conserving body energy Assignment List each Cranial Nerve and the function of the nerve On page 229, for each organ or system, make a table like the one shown, summarize the points so you can remember Use the WS as your guide