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The NERVOUS System Functions of the Nervous System Sensory senses stimuli from both within the body and from the external environment Integrative analyzes, interprets, and stores information about the stimuli it has receives from the sensory portion of the nervous system Motor responds to stimuli by some type of action muscular contraction glandular secretion Divisions of the Nervous System Central Nervous System (CNS) Peripheral Nervous System (PNS) Somatic Nervous System (SNS) Autonomic Nervous System (ANS) Sympathetic Division Parasympathetic Division Nervous System Schematic Nervous System Schematic Nervous System Schematic The Central Nervous System Consists of the brain and the spinal cord Sorts incoming sensory information Generates thoughts and emotions Forms and stores memories Stimulates muscle contractions Stimulates glandular secretions The Brain We’ll talk about it more later… The Spinal Cord The spinal cord is the main pathway for information connecting the brain and peripheral nervous system The length of the spinal cord is about 45 cm in men and 43 cm in women. The spinal cord is shorter than the vertebral column Nerves that extend from the spinal cord from the lumbar and sacral levels must run in the vertebral canal for a distance before they leave the vertebral column. This collection of nerves in the vertebral canal is called the cauda equina horse tail The Spinal Cord The Peripheral Nervous System Connects sensory receptors, muscles, and glands in the peripheral parts of the body to the central nervous system Consists of spinal and cranial nerves Afferent Neurons (Sensory) conduct nerve impulses from sensory receptors toward the CNS Efferent Neurons (Motor) conduct nerve impulses from the CNS to muscles and glands Consists of the somatic and autonomic systems Spinal Nerves Also called nerve roots Branch off the spinal cord and pass out through the vertebral foramen Carry information from the spinal cord to the rest of the body, and from the body back up to the brain. 31 pairs total Four main groups of spinal nerves, which exit different levels of the spinal cord: Cervical Nerves "C" : (nerves in the neck) supply movement and feeling to the arms, neck and upper trunk. Also control breathing. Thoracic Nerves "T" : (nerves in the upper back) supply the trunk and abdomen. Lumbar Nerves "L" : (nerves in the lower back) supply the legs, the bladder, bowel and sexual organs Sacral Nerves "S" : (nerves in the lower back) supply the legs, the bladder, bowel and sexual organs Spinal Nerves Cranial Nerves I-XII 12 pairs Lead directly from the brain to various parts of the head, neck, and trunk Some involved in the special senses (such as seeing, hearing, and taste) Others control muscles in the face or regulate glands The nerves are named and numbered (according to their location, from the front of the brain to the back) Cranial Nerves Cranial Nerves Need more help? On Old Olympus Towering Top A Famous Vocal German Viewed Some Hops olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, spinal accessory, hypoglossal Divisions of the PNS Somatic Nervous System Autonomic Nervous System Sympathetic Parasympathetic The Somatic Nervous System Made up of sensory neurons that convey information from the cutaneous and special sense receptors in the head, body wall, and extremities to the CNS Also contains the motor neurons from the CNS that conduct impulses to the skeletal muscles The Autonomic Nervous System Contains sensory neurons mainly from the viscera that convey information to the CNS Contains the efferent neurons that conduct impulses to smooth muscle, cardiac muscle, and glands Unconscious control Divisions include: Sympathetic nervous system Parasympathetic nervous system Sympathetic Division Sympathetic Division— “Fight or Flight” Cope with stress or emergency situations Increase in heart rate, blood glucose levels, breathing rate Pupils dilate Increased blood flow to muscles, lungs, heart Reduced digestive activity due to decreased blood flow to visceral organs Parasympathetic Division Parasympathetic Division— “Rest and Relaxation” Helps body return to homeostasis Decrease in heart rate, breathing rate, and blood glucose levels Reduced blood flow to skeletal muscle Increased digestive activity due to increased blood flow to visceral organs Activity Directions: Choose the responses that best correspond to the descriptions provided in the following statements. Insert the appropriate letter in the answer blanks. A. Autonomic Nervous System C. Peripheral Nervous System B. Central Nervous System D. Somatic Nervous System ________________1. Nervous System subdivision that is composed of the brain and spinal cord. ________________2. Subdivision of the PNS that controls voluntary activities. ________________3. Nervous system subdivision that is composed of the cranial and spinal nerves. ________________4. Subdivision of the PNS that regulates the activity of the heart and smooth muscle (involuntary). Neurons The nerve cells responsible for the special functions of the nervous system sensing remembering thinking controlling muscle activity controlling glandular secretions Synapse - the functional relay points between two neurons or between a neuron and an effector organ Neuromuscular Junction Neuroglandular Junction Parts of A Neuron Cell Body (Soma or Perikaryon) nucleus, cytoplasm, organelles of a neuron Dendrites - tapered, highly branched processes protruding from the cell body usually very short AFFERENT FUNCTION Axons - long, thin, cylindrical process usually myelinated EFFERENT FUNCTION Neuron Neurons Neuroglia Nervous system cells that support, nurture and protect the neurons Not actual neurons Do not conduct electrical impulses Types of Neuroglia found in the CNS Astrocytes Oligodendrocytes Microglia Ependymal Cells Types of Neuroglia found in the PNS Satellite Cells Neurolemmocytes (Schwann Cells) Neuroglia of the CNS Astrocytes Star-shaped cells with many processes Participate in metabolism of neurotransmitters Maintain K+ balance for generation of nervous impulses Participate in brain development Help form the blood brain barrier Provide a link between neurons and blood vessels Astrocyte Oligodendrocytes Small cells with few processes Form a supporting network around the neurons by twining around neurons and producing a lipid and protein wrapping around the neurons (myelin sheath) Microglia Small phagocytic cells that protect the central nervous system by engulfing and invading microbes Clears away debris from dead cells Ependymal Cells Neuroglia cells that line the brain ventricles Line the central canal of the spinal cord Helps form and circulate cerebral spinal fluid Help form the blood-CSF barrier (different from the blood-brain barrier) Ependymal Cells Neuroglia of the PNS Satellite Cells Provide physical support to neurons in the peripheral nervous system Neuroglia of the PNS Schwann Cells Neurolemmocytes Cells responsible for producing the myelin sheaths around the PNS neurons Can also wrap thinly around bundles of axons without wrapping multiple layers around each axon Unmyelinated neurons Schwann Cell (Neurolemmocyte) Neuroglia Overview Myelination The process of developing or producing a Myelin Sheath Insulates the axon of a neuron Increases the speed of nerve impulse conduction CNS - oligodendrocytes PNS - neurolemmocytes (Schwann Cells) Diseases such as Tay-Sachs disease and Multiple Sclerosis involve destruction of the myelin sheaths around the nerve Myelination Myelinated Axon Unmyelinated Axon Activity Match the anatomical terms that best correspond to the following statements. Place the correct letter in the answer blanks. A. Axon D. Myelin Sheath B. Axon Bulb E. Cell Body C. Dendrite __________1. Releases neurotransmitters __________2. Directs messages toward the cell body __________3. Increases the speed of the message __________4. Location of the nucleus __________5. Long extension that takes messages to the target Neurophysiology The transmission of nerve (electrical) impulses from nervous tissue to other nervous tissue, organs, glands, and muscles. Transmission of Nerve Impulses Nerve Impulse: An electrical event due to movement of ions across a membrane Also called an action potential Lasts about 1 msec (1/1000 of a second) Dependent upon diameter of the axon larger diameter axons - 0.4 msec (1/2500 sec) 2500 impulses per second smaller diameter axons - 4 msec (1/250 sec) 250 impulses per second All or None Principle If depolarization reaches a threshold, an action potential (impulse) is conducted Each action potential (impulse) is conducted at maximum strength unless there are toxic materials within the cell or the membrane has been disrupted Neuron Membrane Potential Neuron Action Potential Action Potential Resting phase (polarization) The axon is not actively conducting nerve impulses. Sodium is the ion found in the greatest concentration in the extracellular fluid. Potassium is the ion found in the greatest concentration in the intracellular fluid. The outside charge of the polarized membrane is positive while the inside charge of the polarized membrane is negative. Depolarization phase As the action potential propagates down the length of the axon, the sodium channels open in the axon membrane. Sodium, which is found in greater concentration in the extracellular fluid, rushes through the protein channels creating a negative charge in the extracellular fluid and a positive charge in the intracellular fluid. Repolarization phase Just split seconds after the opening of the sodium channels, the potassium channels in the axon membrane open. Since potassium is found in greater concentration within the cell, potassium ions rush outward. This flow of positively charged ions restores the positive charge outside of the cell and the negative charge inside of the cell. Refractory period During this period of time, no nerve impulses (action potentials) can be sent. The sodium-potassium pump (using ATP) functions to restore the ion concentration of the polarized cell by pumping sodium ions out of the cell and bringing potassium ions into the cell. Neuron Impulse Neuron Action Potential Types of Impulse Conduction Continuous Conduction - step by step depolarization of each sequential, adjacent area of of the nerve cell membrane typical of unmyelinated nerve fibers type of action potential in muscle fibers Saltatory Conduction - the jumping of an action potential across specialized neurofibril nodes along the axon Nodes of Ranvier Nerve Conduction Nerve Conduction—Myelinated Axon Transmission of Nerve Impulses at Synapses Most nervous conduction is from neuron to neuron (interneurons - 90%) Types of Synapses Axon to dendrite Axon to soma Axon to axon Two ways to transmit impulses across a synapse Electrical Synapses Chemical Synapses Reflexes Fast, predictable, automatic responses to changes in the environment that help maintain homeostasis Somatic Reflexes - involve skeletal muscles Visceral (Autonomic) Reflexes - involve responses of smooth muscles, the heart, and glands Involve the spinal nerves The Reflex Arc A response by the body involving only the body segment being affected and the spinal cord Brain does not have to be involved Receptor - the distal end of a sensory neuron (dendrite) Responds to a specific stimulus a change in internal or external environment Triggers a nerve impulse Receptor - the distal end of a sensory neuron (dendrite) Responds to a specific stimulus a change in internal or external environment Triggers a nerve impulse Sensory Neuron - the neuron located in the gray matter of the spinal cord conducts impulses from the receptor to the spinal cord Integrating Center - a region within the CNS (spinal cord or brain) that interprets the information from the sensory neuron and initiates an appropriate response Motor Neurons - the neurons arising from the integrating center that relay a nerve impulse to the part of the body that will respond to the stimulus Effector - the part of the body that responds to the motor nerve impulse (usually a muscle or a gland) Effector - skeletal muscle - somatic reflex Effector - cardiac, smooth muscle, or gland -visceral reflex The Reflex Arc Reflex Arc Examples Stretch Reflex - results in the contraction of a muscle if it has been stretched suddenly Tendon Reflex - results in the contraction of a muscle when a tendon is stretched suddenly Flexor (Withdrawal) Reflex - sudden contraction and removal of a body segment as a result of a pain stimulus Tendon Reflex Withdrawal Reflex Also called the Flexor/Withdrawal Reflex The BRAIN The BRAIN One of the largest organs in the body Controls all mental functions Component of the CNS Composed of over 100 billion neurons Comprises 2-3% of body weight Utilizes over 20% of body’s energy Brain Video The Brain Gray and White Matter White Matter - the aggregation of myelinated processes from many neurons Visible upon freshly dissected brain or spinal tissue White color is due to myelination Gray Matter - unmyelinated nerve cell bodies, axons, dendrites, ganglia, and axon terminals Appears gray because of lack of myelin Gray and White Matter Ventricles Cavities within the brain Lateral ventricles (2) - located within each hemisphere in the cerebrum Third ventricle - a vertical slit between the lateral ventricles and inferior to the right and left halves of the thalamus Fourth ventricle - space between the brainstem and the cerebellum Ventricles of the Brain Choroid Plexus Network of capillaries in the walls of the ventricles Formation of CSF by the choroid plexus is facilitated by the very high rates of blood flow to the choroid plexus Covered with ependymal cells that form the cerebrospinal fluid In the choroid plexus the ependymal cells are, in contrast to elsewhere in the brain, tightly bound by tight junctions That means, these ependymal cells are so close together they form the blood-CSF barrier (different than the blood-brain barrier). Selectively permeable barrier White cells are capillary endothelial cells Blue cells are ependymal cells The structure of cell layers in the choroid plexus/BCB (blood-CSF barrier) is shown in the top of the figure. The structure of cell layers elsewhere in the brain/BBB (blood-brain barrier) is shown in the lower part of the figure. Blood-CSF vs Blood-Brain Barriers Protection and Coverings of the Brain Protected by the cranial bones and the cranial meninges Dura Mater - outer layer Arachnoid - middle layer Pia Mater - inner layer Also protected by cerebrospinal fluid fluid that nourishes and protects the brain and spinal cord continuously circulates through the subarachnoid space around the brain and throughout the cavities within the brain Spinal Cord Protective Coverings Dura Mater Arachnoid Pia Mater Meninges Connective tissue covering found around the brain and spinal cord Three layered membrane Dura Mater - outer most layer dense irregular connective tissue Arachnoid - middle layer spider web arrangement of collagen fibers Pia Mater - inner most meninges very delicate layer of thin tissue Meninges of the Brain Subarachnoid Space Wide space between the arachnoid and pia mater Contains Cerebrospinal Fluid (CSF) Spinal cord ends at about the level of the L2 vertebra but the subarachnoid space continues to S2 making it possible to access CSF fluid with needle puncture (lumbar puncture) Cerebrospinal Fluid Mechanical Protection Serves as a shock absorbing medium Buoys the brain so it literally floats within the cranial cavity Chemical Protection Provides an optimal chemical environment for neural signaling Circulation Acts as a medium for exchange of nutrients and waste products between the blood and nervous tissue Flow of CerebroSpinal Fluid Flow of CerebroSpinal Fluid Blood Supply to the Brain One of the most metabolically active organs in the body Makes up only 2-3% of body weight but uses about 20% of available O2 at rest Well supplied with O2 and nutrients Only nutritional source for brain metabolic activity is glucose Capillaries in the brain are much less leaky than other capillaries in the body and form a blood brain barrier Major Divisions of the BRAIN CEREBRUM - occupies most of the cranium and is divided into right and left halves called hemispheres CEREBELLUM - the posterior-inferior portion of the brain BRAIN STEM - consists of the medulla oblongata, the pons, and the midbrain it is continuous with the spinal cord DIENCEPHALON - located above the brainstem, composed primarily of the: Thalamus Hypothalamus The Brain Stem The most inferior portion of the brain Connects the brain to the spinal cord Composed of Three Areas The Medulla Oblongata The Pons The Midbrain The Medulla Oblongata Most inferior portion of the brain stem Connects the brain stem to the spinal cord Respiratory Center Adjusts rhythm and depth of breathing Cardiovascular Center Regulates heart rate and contraction force Influences vasoconstriction and vasodilation Also controls coughing, vomiting, swallowing, and hiccupping The Medulla Oblongata The Medulla Oblongata The Pons Lies superior to the medulla oblongata Together with the respiratory center in the medulla helps control respiration The Midbrain Superior to the pons Connects the brain stem to the diencephalon Pons and Midbrain The Diencephalon Area of the brain containing the: Thalamus Hypothalamus The Thalamus Oval structure that makes up 80% of the diencephalon Comprised of a pair of oval masses (mostly gray matter) Principle relay station between the various sections of the brain The Hypothalamus A small portion of the diencephalon located below the thalamus One of the main regulators of homeostasis in the body Lacks a blood brain barrier Partially protected by the sella turcica of the sphenoid bone Functions of the Hypothalamus Coordinates nervous system and endocrine system activities to maintain homeostasis Thirst, Hunger, Satiety Sleep Patterns and Waking States Temperature regulation Sex Drive, Maturation, Aggression, and Rage Influences movement of food through the Gastrointestinal Tract production and secretion of hormones that control other Endocrine Glands Hypothalamus The Cerebrum Largest division of the brain Occupies most of the cranium Accounts for 85% of brain mass Divided into right and left hemispheres Longitudinal Fissure Corpus Callosum Connects the two hemispheres Cerebral cortex - the outer surface area of the cerebrum Composed mainly of gray matter Contains billions of neurons The Cerebrum Terms associated with the Cerebrum Gyri A series of folds in the cortex that increase surface area Sulci A groove or furrow that separates the gyri of the brain Lobes of the Cerebrum Named after the bones that cover them Frontal Lobe Parietal Lobe Temporal Lobe Occipital Lobe A Note about the Cerebral Cortex The cerebral cortex is the most highly developed part of the human brain and is responsible for thinking, perceiving, producing and understanding language It is also the most recent structure in the history of brain evolution Frontal Lobe Motor Areas Controls movement of voluntary skeletal muscles Association Areas Carry on high level intellectual processing Problem Solving Reasoning Planning Concentration Memory Behavior Emotions Expressions Broca’s area One of the main areas responsible for speech production Parietal Lobe Sensory Areas Interprets sensations from the skin such as: touch temperature pressure pain Association Areas Understanding of speech Using words to express thoughts and feelings Temporal Lobe Sensory Areas Hearing and balance Association Areas Interpret sensory experiences Memory of visual scenes - music - smells and other complex sensory patterns Wernicke’s Area region of the brain where spoken language is understood (speech comprehension) Occipital Lobe Sensory Areas Visual processing and interpretation Association Areas Combines visual images with sensory experience Left Brain vs Right Brain Right side of brain controls left side of body Left side of brain controls right side of body New research at the U of U indicates left and right brain attributes aren’t as clear cut as once thought A little rap to help you remember… The occipital lobe controls your sight. Why it does, we don’t know why. The temporal lobe controls how you hear, like the clucking of a chicken or the stomping of a deer. The parietal lobe processes what you touch whatever you can squeeze or grab or clutch. The frontal lobe helps you think and memorize so you can process what you need right before your eyes. These are the lobes of the brain and now you know them so call up all your friends and don’t forget to show em’ WORD! The Cerebellum Second largest portion of the brain Occupies the inferior and posterior aspects of the cranial cavity Processes sensory information Balance Coordination Maintains postural equilibrium Cerebellum and Brainstem Nervous System Disorders and Homeostatic Imbalances Alzheimer’s Disease (AD) Disabling neurological disorder that effects about 11% of the population 6th leading cause of death in the U.S. It is the only cause of death among the top 10 in America without a way to prevent it, cure it or even slow its progression. A chronic, organic, mental disorder, a form of pre-senile dementia due to atrophy of neurons of the frontal and occipital lobes AD patients usually die from complications due to being bedridden Alzheimer’s vs. Dementia Dementia is not a disease itself, it is the symptoms language difficulty, loss of recent memory poor judgment Alzheimer’s accounts for 60-70% of dementia cases Other types of dementia include: Vascular dementia Parkinson's disease dementia with Lewy Bodies Frontotemporal dementia. Amyotrophic Lateral Sclerosis (ALS) Also known as Lou Gehrig’s Disease A relatively rare neurological disorder A syndrome marked by muscular weakness and atrophy with spasticity and hyperflexion due to degeneration of the motor neurons of the spinal cord, medulla, and cortex A degenerative disease No known cure Bacterial Meningitis Infection of the meninges by the bacterium Haemophilus Influenzae Usually affects children under age 5 Symptoms include severe headaches and fever Can lead to brain damage and even death if not treated Cerebral Palsy (CP) A group of motor disorders due to loss of muscle control Caused by damage to the motor areas of the brain during fetal development, birth, or infancy About 70% of CP individuals are somewhat mentally retarded due to the inability to hear well or speak fluently Not a progressive disease but the symptoms are irreversible Epilepsy Short, recurrent, periodic, attacks of motor, sensory, or psychological malfunction Characterized by seizures which can result in involuntary skeletal muscle contraction, loss of muscle control, inability to sense light, noise, and smell, and loss of consciousness Most epileptic seizures are idiopathic Multiple Sclerosis (MS) The progressive destruction of the myelin sheaths of neurons of the CNS The sheaths deteriorates to scleroses hardened scars or plaques “short circuits” nerve transmission Cause is unknown May be a type of an autoimmune disease No known cure Progressive loss of function with intermittent periods of remission Parkinson’s Disease (PD) A chronic nervous disease characterized by a fine, slowly spreading tremor, muscle weakness and rigidity, and a peculiar gait Usually affects people over 60 Cause is unknown but a toxic environmental factor is suspected Chemical basis of the disease appears to be too little dopamine and too much Ach Treatment includes increasing levels of dopamine and decreasing Ach Difficult because dopamine does not cross the blood brain barrier Usually can be controlled with drug therapy GABA - gamma aminobutyric acid Attempting to transplant fetal nervous tissue into the damaged area of the brain of some Parkinson’s Disease patients Guillan-Barré Syndrome Rare disorder in which a person’s own immune system damages their nerve cells Causes muscle weakness and sometimes paralysis Symptoms that usually last for a few weeks Most people recover fully from GBS, but some people have long-term nerve damage Risk factors Infection with Campylobacter jejuni (diarrhea) People can develop GBS after having the flu or other infections (such as cytomegalovirus and Epstein Barr virus) On very rare occasions, they may develop GBS in the days or weeks after getting a vaccination Guillan-Barré Syndrome Cerebral Vascular Accident (CVA) - Stroke The most common brain disorder Characterized by slurred speech, loss of or blurred vision, dizziness, weakness, paralysis of a limb or hemiplegia, coma, and death Ischemic CVA - due to lack of blood supply to a particular area of the brain Hemorrhagic CVA - due to the rupture of a blood vessel in the brain Risk Factors for Stroke hypertension heart disease smoking diabetes atherosclerosis hyperlipidemia obesity excessive alcohol intake Symptoms of a Stroke Sudden numbness, tingling, weakness, or loss of movement in your face, arm, or leg, especially on only one side of your body (facial drooping) Sudden vision changes. Sudden trouble speaking. Sudden confusion or trouble understanding simple statements. Sudden problems with walking or balance. A sudden, severe headache that is different from past headaches. Is it a stroke? Reye’s Syndrome Acute childhood illness that causes fatty infiltration of the liver and brain, encephalopathy, and increased intracranial pressure Almost always follows within 1 to 3 days of an acute viral infection, flu, or chicken pox Common in infants and children. The incidence often arises during flu outbreaks May be linked to aspirin use Symptoms include vomiting, mood changes, confusion, tachycardia, and tachypnea Treatment involves treating the symptoms Hydrocephalus Excessive accumulation of cerebrospinal fluid within the ventricles of the brain. Occurs most often in newborns The head is enlarged and the brain may be compressed causing brain damage Early detection and surgical intervention improves the prognosis Complications of the surgery include infection of the shunt. Hydrocephalus Spina Bifida Congenital defect where the neural arch fails to unit Usually involves the lumbar vertebrae Symptoms may be mild to severe usually results in paralysis partial or complete loss of bladder control absence of reflexes Can be diagnosed during pregnancy by sonography, amniocentesis, blood tests Spina Bifida Spina Bifida Spina Bifida Spina Bifida Headaches Most commonly begins as a patient complaint, but is usually a symptom of an underlying disorder Ninety percent are caused by vascular problems or muscle contractions Tension headaches mild, dull pressure without other accompanying symptoms Cluster headaches severe pain (sometimes described as “stabbing” pain) behind one eye, and may be accompanied by redness and nasal congestion Sinus headaches pain and pressure behind the brow and cheek bones Migraines pounding headache, nausea, vomiting, and light sensitivity Headaches Concussion Most common head injury resulting from a blow to the head – a blow hard enough to jostle the brain and make it hit against the skull causing temporary neural dysfunction. Precipitating causes include a fall to the ground, a punch to the head, automobile accidents and child abuse Most victims recover within 24 to 48 hours after the injury Symptoms a loss of consciousness vomiting possible amnesia dizziness headache Lethargy Treatment Monitoring vital signs, mental status, level of consciousness, and pupil size Whiplash Results from a sharp hyperextension and flexion of the neck that damages the muscles, ligaments, disks and nerve tissue Common after rear-end automobile accidents. Padded headrests and shoulder harnesses reduce the risk of this type of injury. Symptoms can include: pain in the interior and posterior neck dizziness headache neck rigidity numbness in the arms Treatment includes: immobilizing the neck at the scene of the accident ruling out spinal cord injury analgesics warm compresses a cervical collar possible physical therapy Whiplash Spinal Cord Injury (SCI) Commonly referred to as a broken neck Involves injury to the spinal cord The more superior the injury, the more permanent damage results to the patient Causes of the injury include: motor vehicle accidents falls sporting injuries (football, skiing) diving into shallow water gunshot wounds. Paralysis of the body may occur Paraplegia: lower half of the body is paralyzed Quadriplegia: body from the neck down is paralyzed Treatment: maintaining vital functions and rehabilitation to maintain the use of muscles. Depression This is a sad mood, which may be a primary disorder, a response to a disease process or a drug reaction. Causes include: Genetic Familial Biochemical Physical and physiological processes The person may have feelings of helplessness, anger, hopelessness, low selfesteem, and pessimism Other symptoms include weight loss or weight gain, sleep disturbance, depressed mood most of the day, energy loss, fatigue, difficulty thinking or concentrating Treatment may involve: Psychotherapy drug therapy Counseling Light therapy Sensations and Special Senses Senses Specialized structures of the nervous system which provide information about the environment in which we live to help maintain homeostasis Functions of Special Senses Sensory - monitoring the body and the external environment for changing conditions Sensory Pathways All pathways begin with a receptor and the sensory information is transmitted to the CNS Always begins with a stimulus change in the environment Receptors Structures which provide feedback about the environment Are impulse specific—Only respond to one type of stimulus Mechanoreceptor Any information about mechanical changes in its environment, such as movement, tension and pressure. Photoreceptor able to detect, and react to light Chemoreceptor Sense organ, or one of its cells (such as those for the sense of taste or smell), that can respond to a chemical stimulus Thermoreceptor sensitive to changes in temperature Nociceptor sends signals that cause the perception of pain in response to a potentially damaging stimulus. Many have sensory function adaptations May end as bare dendrites or be a complex organ Vision The most complex of the special senses Over 70% of the sensory receptors in the body are photoreceptors for sight Visual organs, the eyes are supported by a number of accessory structures and internal organs Dependent upon photoreceptors in the eyes The Eye Accessory Structures of the Eye Eyelids - protects the anterior surface Conjunctiva - the mucous membrane of the eyelid Helps moisten and lubricate the eyeball Lacrimal Apparatus - secretes tears lacrimal gland lacrimal sac lacrimal canals nasolacrimal duct moistens and lubricates the eyeball fights against infection (enzymes in tears) Extrinsic Muscles of the Eyeball (6) skeletal muscles that move the eyeball Accessory Structures of the Eye Structure of the Eye The wall consists of three layers of tissue or tunics Fibrous Tunic - outer layer Vascular Tunic - middle layer Nervous Tunic - inner layer Fibrous Tunic Thick, outermost layer of the eyeball Sclera - the posterior “white” portion Forms most of the fibrous tunic The “whites” of the eye Cornea - the anterior transparent portion of the fibrous tunic Bulges outward slightly Fibrous Tunic Vascular Tunic Extremely vascular Supplies blood to numerous structures of the eye Choroid Ciliary Body Iris Lens Vascular Tunic Choroid - posterior, thin portion of the vascular tunic A thin, dark brown membrane that lines most of the internal surface of the sclera Ciliary Body - anterior, thick portion of the vascular tunic Thickest part of the vascular tunic Consists of smooth muscle fibers Attaches to the lens by ligaments Changes the thickness and shape of the lens. Ciliary Body Iris - anterior, colored portion of the Vascular Tunic contraction of it’s smooth muscle accounts for dilation or constriction of the Pupils (openings to the inner cavities of the eyes) Lens - special tissue which focuses and directs light entering the eye suspended by the Ciliary Body located behind the Iris alteration of the shape of the lens to accommodate for near or far vision focusing (Accommodation) The Lens Iris – Pupil Diameter Nervous Tunic The inner layer of the eye Retina - a thin fragile layer of neurons that forms the inner lining of the eyeball’s posterior wall Lines the posterior cavity and contains the photoreceptor cells (rods and cones), bipolar neurons, and ganglion cells Optic Nerve - axons and ganglion cells Transmits images to the occipital lobe of the brain for interpretation of what we see Nervous Tunic Rods and Cones Rods - elongated cylindrical dendrites that are sensitive to varying light conditions Allows us to see under varying light intensities (night vision) Cones - dendrites with tapered ends Color sensitive Determines the “sharpness” of vision Rods and Cones Rods and Cones Other Structures of the Nervous Tunic Optic Disc - blind spot where the optic nerve exits the retina Fovea Centralis - an area of the retina containing many cone cells the area of sharpest vision Retina Elements of Vision in the Eye Vision spectrum of the eye only detect three colors Red Green Blue Aspects of vision of the eye color motion form depth Refraction the “bending” of light rays as it travels through the eye the pathway of light as it travels through the eye influenced by: shape of the lens shape and thickness of the cornea amount and consistency of the Aqueous and Vitreous Humor Refraction Vision Abnormalities related to Refraction Physiology of Vision Rods and cones convert light waves into a series of signals that results in the generation of an action potential in the ganglion cells Both rods and cones contain pigments that decompose when exposed to light The decomposition of the pigments is what generates the action potential Visual Pathways From the rods and cones, the nervous impulse is passed on to bipolar neurons and then on to ganglion cells Axons from the ganglion cells extend out of the eye and converge to from the optic nerve The optic nerves cross behind the eye at an area known as the optic chiasma The optic nerve terminates at the thalamus Visual impulses from the thalamus are transmitted by other neurons to the occipital lobe of the cerebral cortex where the impulses are interpreted as the sense of sight. Visual Pathway Hearing Dependent upon special organs within the ear The ears are also associated with maintaining equilibrium and balance Three Regions of the Ears Outer Ear Middle Ear Inner Ear The Ear The Ear Outer Ear Direct sound waves toward the eardrum Auricle - the outer appendage Auditory Canal - a tube that extends into the temporal bone The Outer Ear Middle Ear Middle Ear An air-filled space within the temporal bone Tympanic Cavity - contains the auditory ossicles Smallest bones in the body Malleus (hammer) Incus (anvil) Stapes (stirrup) Auditory (Eustachian) Tube - a tube from the middle ear to the pharynx Allows for pressure equalization between the middle ear and the atmosphere Tympanic Membrane (Eardrum) - thin, semitransparent membrane separating the outer and the middle ear Vibrates in response to sound waves striking it The vibrations are then transmitted to the auditory ossicles Middle Ear Structures The tympanic membrane and auditory ossicles convert sound waves into mechanical movement within the middle ear and then transmit that motion to the “oval window” The oval window opens into the cochlea of the inner ear Within the inner ear the vibrations of the stapes causes the fluid within the inner ear to move stimulating the receptors for hearing The Three Regions of the Inner Ear Formed by the canals of the bony labyrinth and the series of sacs of the membranous labyrinth Involved in both the sense of hearing and the maintenance of balance and equilibrium Cochlea Vestibule Semicircular Canals The Inner Ear Inner Ear Structures Inner Ear Structures The Semicircular Canals - three loops that lie at right angles to each other The Vestibule - the chamber between the cochlea and the semicircular canals Both the semicircular canals and the vestibule are involved with maintaining balance or equilibrium The Cochlea - shape resembles a snail shell Contains the organs of hearing (Organ of Corti) Receptor cells that move in response to endolymph motion Releases neurotransmitters that stimulate nerve impulses The Cochlea The Cochlea Organ of Corti Cross Section of Cochlea Inner Ear (Labyrinth) Consists of a winding, complicated series of passageways or canals Bony Labyrinth - a series of canals within the temporal bone Contains perilymph Membranous Labyrinth - an internal series of sacs and tubes Contains endolymph Conforms to the bony labyrinth shape Also helps form the shape of the three regions of the inner ear Vestibulocochlear Nerve Nerve Pathways Sound waves cause the tympanic membrane to vibrate The vibration of the tympanic membrane causes the stapes to move back and forth Movement of the stapes back and forth pushes the oval window in and out producing waves in the perilymph of the inner ear Pressure waves in the perilymph push the vestibular membrane inward increasing the pressure of the endolymph within the cochlear duct The hair cells in the Organ of Corti convert the motion of the endolymph to the release of neurotransmitters These neurotransmitters stimulate a nerve impulse in a sensory branch of the Vestibulocochlear Nerve (CN #VIII) The impulse is then transferred through the midbrain and the thalamus and finally terminates in the temporal lobe of the cerebral cortex where the sound is interpreted Physiology of Hearing Physiology of Hearing Nervous System Disorders Homeostatic Imbalances Clinical Terms Diseases and Disorders Ametropia Myopia - nearsightedness Imaged focused in front of the retina Presbyopia A defect in vision in advancing age involving loss of accommodation or recession of near point (results in farsightedness) Hyperopia - farsightedness Image focused in back of the retina Cataracts Abnormal loss of transparency of the lens Vision becomes blurry or cloudy Can be removed and have an artificial lens inserted Most often occurs to individuals over the age of 50. Exposure to sunlight and smoking increases the risk. Conjunctivitis Inflammation of the conjunctiva, the mucous membrane that lines the eyelid and is reflected to the eyeball. Also known as “Pink Eye” Strabismus Disorder in which the two eyes do not line up in the same direction, and therefore do not look at the same object at the same time. Also known as "crossed eyes." Glaucoma A group of eye diseases characterized by elevated intraocular pressure in the eye resulting in atrophy of the optic nerve which may lead to blindness Caused by an obstruction of the outflow of the aqueous and vitreous humor Minor cases can be treated with eye drops More severe cases may require a surgical incision into the iris of the eye Macular Degeneration The destruction or tearing away of the retina from the back of the eye Commonly occurs in the region of the retina known as the macula lutea Can be caused by: Vascular diseases (diabetes) Chronic increased pressure (glaucoma) Sudden blow or impact to the head or eye (Detached Retina) Vertigo A condition of dizziness and spatial disorientation A spinning sensation that may result in loss of balance and equilibrium In some individuals it is due to heights or fear of high places Tinnitus Ringing or tinkling sounds or sensations in the ear Middle Ear Infection Infection of the tympanic membrane or other structures associated with the middle ear (Otitis Media) Deafness Loss of the ability to hear Conductive Deafness: deafness resulting from any condition that prevents sound waves from being transmitted to the auditory receptors Sensorineural Deafness: deafness due to defective function of the cochlea, organ of Corti, or the auditory nerve