Chapter 8 Part 1: Nervous System PDF

1 Chapter 8 Part 1: The Nervous System / Part 2: Special Senses Chapter 8 Part 1: Nervous System (This system is the primary controlling system of the body. It uses electrochemical impulses to communicate.) Functions of the Nervous System 1. Detection of internal and external changes –...

1 Chapter 8 Part 1: The Nervous System / Part 2: Special Senses Chapter 8 Part 1: Nervous System (This system is the primary controlling system of the body. It uses electrochemical impulses to communicate.) Functions of the Nervous System 1. Detection of internal and external changes – receptors do this job o Changes = stimuli 2. Analysis and organization of the information received – control center does this (brain and spinal cord) 3. Initiation of the appropriate actions – brain sends this message out to effectors (muscles and glands) Divisions of the Nervous System 1. Central nervous system (CNS) – brain and spinal cord; control center 2. Peripheral nervous system (PNS) – nerves outside the CNS; carry impulses formed by receptors to the CNS and then carries them back out to effectors (muscles and glands) Divisions of the PNS (pathway into the CNS and out of the CNS 1. Sensory (afferent) division – nerves that carry impulses to the CNS; “IN DOOR” 2. Motor (efferent) division – nerve fibers that carry impulses away from the CNS; “OUT DOOR” o Two subdivisions of Motor Division: 1. Somatic nervous system (SNS) – voluntary responses from skeletal muscles 2. Autonomic nervous system (ANS) – involuntary responses from smooth muscle, cardiac muscle and glands Divided into two divisions: 1. Sympathetic – “fight – or – flight” – takes over to increase activities. Activated during exercise, excitement, emergency, embarrassment 2. Parasympathetic – “resting and digesting” – concerned with normal digestion, elimination of feces and urine, and with conserving body energy – “Housekeeping system”  2 Neurons Neuron – delicate cell that is specialized to transmit neural impulses; they are the structural and functional unit of the nervous system Major regions of neurons 1. Cell body – contains nucleus and all other organelles except centrioles 2. Processes – fibers that extend from the cell body o Dendrites – short branched processes extending from the cell body that conduct impulses toward the cell body o Axons (nerve fiber) – long thin process that conduct impulses away from the cell body 3. Myelin sheath – outer insulating covering of the axon formed from neuroglial cells; neurons that have a myelin sheath conduct impulses faster 4. Nodes of Ranvier – tiny spaces between the myelin sheath where the axon is exposed Saltatory conduction – the process by which an impulse jumps from node to node on the myelin sheath; allows for the fastest conduction 5. axon terminals – ends of an axon 6. synaptic knob – enlarged tips at the axon terminal Types of neurons based on function: 1. Sensory (afferent) neurons – carry impulses from sensory receptors to CNS; cell bodies are located outside CNS in clusters called ganglia 2. Interneurons – located entirely in the CNS and function to process and interpret impulses received from sensory neurons 3. Motor (efferent) neurons – carry impulses from CNS to effectors (muscles and glands); cell bodies in CNS  3 Neuroglia of Nerve Tissue (Supporting cells that protect the neurons) (Neuroglia never lose their ability to divide (unlike neurons); most brain tumors are gliomas) 1. Astrocytes – abundant star-shaped cells; primary supporter of neurons; form a barrier between capillaries and neurons to protect neurons 2. Microglia – spider-like phagocytes that dispose of debris, including dead brain cells and bacteria 3. Ependymal cells – line cavities of brain and spinal cord; ciliated to circulate CSF (cerebrospinal fluid) 4. Oligodendrocytes – produce a myelin sheath (protective covering) around nerve fibers in the CNS 5. Schwann cells – form the myelin sheath around neurons in PNS Nerve Impulses Properties of Neurons 1. Irritability – ability to detect and respond to stimuli 2. Conductivity – ability to transmit an impulse An un-stimulated neuron uses the sodium-potassium pump to actively pump sodium out and potassium ions in. This results in more positively charged ions outside. (for every 3 sodiums that are pumped out, 2 potassiums enter). This results in a resting potential – unequal distribution of electrical charges on each side of the plasma membrane At rest, the plasma membrane is polarized – more positive ions outside the cell and more negative ions inside the cell In order for an impulse to be generated, the charges outside and in must swap…sodium enters and potassium leaves. When stimulated, neurons exhibit an all-or none response. There is no such thing as a weak impulse or a strong impulse. They are all the same. There can, however, be a difference in the stimulus (weak stimulus and strong stimulus). The weakest stimulus that will activate a neuron is called a threshold stimulus. Impulse Formation: The nerve impulse begins when a stimulus occurs. The stimulus causes the plasma membrane to instantly become very permeable to sodium. Sodium floods the cell and causes the cell to become positively charged. This is depolarization. The depolarization of the cells initiates an action potential or impulse.  4 Immediately after depolarization, potassium channels reopen and sodium channels close allowing potassium to diffuse out to re-establish the resting potential – more positive ions outside than inside. This is called repolarization. With sodium still inside the cell and potassium now outside the cell, the sodium potassium pump is used to re-establish resting-state distribution of ions….sodiums outside and potassiums inside. All this takes place in about 1/1000 of a second!!! Synaptic Transmission Synapse – a junction of an axon with either another neuron or an effector cell (muscle or gland). Synaptic cleft – the tiny gap between adjacent neurons The synaptic knobs at axon terminals contain vesicles with neurotransmitters – chemicals that cross the synaptic cleft to stimulate an adjacent neuron or effector Protection for the Central Nervous System - Meninges Meninges of the brain – 3 connective tissue membranes covering and protecting the CNS structures 1. Dura mater – tough, fibrous outermost layer 2. Arachnoid layer – middle web-like layer 3. Pia mater – innermost membrane attaching to brain Cerebrospinal Fluid – watery cushion that protects nervous tissue; found within ventricles (cavities within the brain), central canal of spinal cord and meninges The Brain 4 Regions of the Brain Cerebrum Diencephalon Brain Stem Cerebellum  5 Cerebrum Cerebrum – largest portion of the brain; performs higher brain functions involved with sensations, voluntary actions, reasoning, planning and problem solving The cerebrum consists of 2 hemispheres – right and left – joined together by a mass of neuron process called the corpus callosum – allows right side to communicate with left side The surface is described as convoluted because it has numerous folds and grooves o Gyri (gyrus) – ridges o Sulci (sulcus) – shallow grooves o Fissures – deeper grooves that divide the cerebrum into lobes Cerebral Cortex – surface of the cerebrum that is most densely packed with neurons Lobes of the Cerebrum 1. Parietal lobe - sensory region of skin and sense of taste 2. Occipital lobe - vision 3. Temporal lobe – auditory area 4. Frontal lobe – motor area that controls skeletal muscles and sense of smell Hemisphere specialization – in most (about 90% of people), each hemisphere is specialized to perform different functions. The left hemisphere is specialized for analytical and verbal skills such as math, reading, writing, and speech. The right hemisphere controls musical, artistic, imagination and insight. Diencephalon – thalamus and hypothalamus Thalamus – relay station for sensory impulses passing to the cerebral cortex (director of traffic) Hypothalamus – major control center for the autonomic nervous system; it controls all internal organs and is the connecting link between the brain and endocrine system; regulates body temp, water and mineral balance, appetite and digestion, heart rate and blood pressure, sleep and wake cycle Limbic system – composed of parts of the thalamus, hypothalamus, and deep matter of the cerebrum; involved in memory and emotions. Mood disorders such as depression are usually a result of malfunction of the limbic system  6 Brain Stem – midbrain, pons, medulla oblongata Midbrain – contains reflex centers for head, eye, and body movements in response to visual and auditory stimuli Pons – works with the medulla oblongata in the control of breathing Medulla oblongata – linked with the spinal cord. This is where ascending and descending fibers between the brain and spinal cord cross over. Contains 3 control centers vital for homeostasis: 1. Respiratory control center – works with the pons to regulate the depth and rate of breathing; contains reflexes for coughing and sneezing 2. Cardiac control center – regulates the rate of heart contractions 3. Vasomotor center – regulates blood pressure and blood flow by controlling the diameter of blood vessels Cerebellum Cerebellum – coordinates skeletal muscle activity that controls posture, balance, and coordination (fibers reach the cerebellum from the inner ear, the eye, and proprioceptors) Nerves Nerve – axons and dendrites that are bundled together by connective tissue in much the same way as muscle fibers Neuron fibers are bundled by connective tissue: 1. Endoneurium – surrounds a neuron 2. Perineurium – surrounds a fascicle of neurons 3. Epineurium – surrounds many fascicles; outside of nerve Classification of Nerves: 1. Mixed nerves – both sensory and motor; all spinal nerves are mixed 2. Afferent (sensory) nerves – carry impulses toward CNS 3. Efferent (motor) nerves – carry impulses away from CNS Cranial Nerves – 12 pairs of nerves that mostly serve the head and neck; most are mixed nerves, but three are sensory only Spinal Nerves – There are a total of 31 pairs of spinal nerves, all mixed.  7 Disorders of the Nervous System Inflammatory Disorders: Neuritis – inflammation of nerves; caused by infection, compression of nerves, or trauma Sciatica – form of neuritis that involves the sciatic nerve (affects the thigh and leg) Shingles – infection of one or more nerves caused by the reactivation of the chickenpox virus Noninflammatory Disorders Alzheimer’s disease (AD) – progressive deterioration of brain neurons; results in loss of memory, disorientation, and mood swings Cerebral palsy – partial paralysis and sometimes a degree of mental retardation; caused by damage to the brain during prenatal development often from viral infections such as measles or maybe caused by trauma during delivery Cerebrovascular accidents (CVAs) – disorders of blood vessels to the brain…include blood clots, aneurysms or hemorrhage; They are commonly referred to as strokes Coma – state of unconsciousness; usually caused by altered functioning of the reticular formation Concussion – caused by severe jarring of the brain; potentially could result in unconsciousness, confusion, and amnesia Dyslexia – malfunctioning of the language center in the cerebrum causes an individual to reverse letters or syllables within words Epilepsy – could be genetically caused or result from trauma, infection, or tumors; leads to seizures or momentary loss of consciousness Fainting – brief loss of consciousness due to decreased blood flow to the brain Headaches – often result from dilation of blood vessels within the meninges which leads to pressure on the brain; could also result from sinus pressure, tension in head and neck muscles o Migraine headaches have visual or digestive side effects; may result from stress, allergies, surges in hormones, or fatigue Mental illness – broadly categorized as neuroses or psychoses o Neuroses – mild adjustment problems to life situations such as anxiety or depression that can interfere with normal behavior o Psychoses – serious mental disorders that sometime causes delusions, hallucinations or withdrawal from reality  8 Multiple sclerosis – progressive degeneration of the myelin sheath surrounding neuron processes in the CNS; results in the formation of hardened sheaths called scleroses; this destruction results in damaged neural pathways Neuralgia – pain arising from a nerve, regardless of cause Paralysis – permanent loss of motor control of body parts; results from injury to the CNS Parkinson’s disease – caused by an insufficient production of dopamine by neurons within the basal nuclei (deep region of the cerebrum); produces tremors and impairs normal skeletal muscle contractions Chapter 8 Part 2: Special Senses The senses are subdivided into two broad categories: 1. General Senses – cutaneous senses such as pain, touch, pressure, cold, heat 2. Special Senses – taste, smell, vision, hearing, and equilibrium Sensations – an interpretation of impulses generated by various sensory receptors and reaching sensory areas of the cerebral cortex General Senses – Temperature, Pressure and Touch, Pain Temperature – receptors are called thermoreceptors; there are receptors for heat and cold Pressure and Touch – receptors are called mechanoreceptors – sensitive to movement (the displacement of tissues) o Pacinian corpuscles – pressure receptors located deep in the dermis and in ligaments and tendons o Meissner’s corpuscles – located in the superficial layer of the dermis, most often in the dermal papillae; very sensitive to light stimuli such as the motion of objects that barely touch the skin Pain – receptors are called free nerve endings – found in many body tissues and especially abundant in the skin; they are stimulated whenever tissue is damaged  9 Special Senses – Taste, Smell, Hearing and Vision Taste – receptors are called chemoreceptors – stimulated by chemicals Taste buds – groups of taste cells on the tongue. The taste cells function as the chemoreceptors that are sensitive to chemicals dissolved in saliva. Taste hairs are found on each cell and are exposed to the chemicals on the tongue Taste buds are found within papillae – small raised structures on the surface of the tongue Taste Sensations 1. Sweet receptors – sugars 2. Sour receptors – acids 3. Salty receptors – metal ions 4. Bitter receptors – alkaloids (bases) Smell – receptors are also chemoreceptors Olfactory receptors – receptors for the sense of smell; found in roof of nasal cavity. Olfactory receptors are neurons with long cilia (hairs) that are covered in a layer of mucus. Chemicals must be dissolved in mucus for detection. Hearing – receptors are mechanoreceptors – stimulated by sound vibrations The ear is divided into three areas – Outer, Middle, and Inner The Outer Ear Auricle (pinna) – visible part of ear External auditory (acoustic) meatus – canal entering the middle ear § ceruminous glands – exocrine glands that secrete cerumen (wax); sticky trap for foreign particles – bugs, bacteria, etc. The Middle Ear Tympanic membrane (Eardrum) – covers opening into middle ear; vibrates when exposed to sound waves Auditory tube (Eustachian tube) – connects middle ear to throat (normally its collapsed, but swallowing and yawing opens it to equalize pressure)  10 Ossicles – smallest bones in the body; transfer and amplify sound to the inner ear through the oval window 1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup) Vibrations from eardrum move the malleus, then the vibrations are transferred through the incus and stapes to the inner ear through the oval window Inner Ear Within the inner ear are 2 chambers: a bony labyrinth on the outside and a membranous labyrinth on the inside. The space between the 2 chambers is filled with a plasma-like fluid called perilymph. Inside the membranous labyrinth is a thicker fluid called endolymph. Cochlea (shell-shaped bone) – contains structure for hearing o Organ of Corti – inside the cochlea and contains the hearing receptors; Structures of the Organ of Corti include: § Basilar membrane – lines the bottom of the organ of corti and receives vibrations from the oval window § Tectorial membrane – gel-like membrane that receives vibrations from the basilar membrane and capable of bending the hair cells § Hair cells – located below the tectorial membrane  11 Mechanism of Hearing o Sound waves enter the external auditory canal and reach the tympanic membrane. The tympanic membrane begins to vibrate and these vibrations are transferred through the ossicles to the inner ear by the oval window. The vibrations now travel through the perilymph and stimulate the basilar membrane which, in turn, vibrates the tectorial membrane. The bouncing of the tectorial membrane bends the hair cells and this stimulation generates an impulse. Organs of Equilibrium – Vestibule and Semicircular canals Equilibrium has two functional parts: 1. Static equilibrium – at rest; the head is motionless 2. Dynamic equilibrium – angular or rotary movements; the head is moving Static Equilibrium (Vestibule) Enlarged structures within the vestibule called the utricle and saccule contain the macula – organ for static equilibrium. Each macula is made up of hair cell receptors that are embedded in a otolithic hair membrane. In this membrane are tiny stones called otoliths. Movements cause the otoliths to bend the hair cells thus generating an action potential which is sent to the brain. (cerebellum) Dynamic Equilibrium (Semicircular canals) At the base of each semicircular canal is a swollen region called the ampulla. Within the ampulla, is a receptor region called a crista ampullaris which consists of a tuft of hair cells covered by a gelatinous cap called the cupula. Angular head movements results in the cupula bending; the cupula stimulates the hair cells; and impulse is generated  12 Vision – receptors are photoreceptors – stimulated by light and found within the retina of the eye The eye is composed of three tunics (layers): 1. Fibrous tunic – outside layer 2. Choroid – middle layer 3. Sensory tunic – inside layer The Fibrous Tunic Sclera – white of the eye Cornea – transparent; allows light to pass through; repairs itself easily; only human tissue that can be transplanted without fear of rejection Choroid Layer – blood-rich layer; has a dark pigment (melanin) to prevent light from scattering Ciliary body – smooth muscle that holds the suspensory ligament suspensory ligament – attaches the lens; contraction causes the lens to change shape (focus) Lens – biconvex structure that focuses light on the retina iris – smooth muscle fibers that contain eye pigments pupil – rounded opening in iris through which light passes Sensory Tunic (Retina) Contains receptor cells (photoreceptors) – stimulated by light 1. Rods – black and white vision 2. Cones – color vision Fovea centralis – located within the macula and is the area of greatest visual acuity (sharpest vision) because it has only cones Optic disk – area with no photoreceptors – blind spot  13 Internal chambers of the eye are filled with 2 fluids (humors): 1. Aqueous humor – watery fluid between lens and cornea; maintains pressure, provides nutrients to lens and cornea 2. Vitreous humor – behind the lens; thick gel-like substance forming the body of the eye Accommodation Lens Accommodation – ability of the eye to focus (lens changes shape The resting eye is set for distance vision (over 20 feet away) – this means that no change in shape of the lens is necessary. To focus closer objects, the lens changes shape (accommodation) to refract (bend) the light to properly focus light on the retina. Mechanism of Vision 1. Light rays are bent as they pass through the cornea. The iris controls the amount of light passing through the pupil 2. Light passes from the pupil through the lens. The ciliary body adjusts the shape of the lens (accommodation) to focus the light rays on the retina. 3. Light absorbed by the rods and cones causes the formation of nerve impulses. Impulses travel through neurons that converge at the optic disk to form the optic nerve which carries the impulse to the thalamus then on to the vision center in the occipital lobe Disorders of the Ear Deafness – partial or total loss of hearing; can be neural deafness – damage to cochlea or cochlear nerve or conduction deafness – damage to the tympanic membrane or ossicles Labyrinthine disease – inner ear disorders that produce symptoms of dizziness, nausea, ringing in the ears (tinnitus), and hearing loss; may be caused by excess endolymph, infection, allergy, trauma, circulation disorders or aging Motion sickness – functional disorder in which the repetitive stimulation of the equilibrium receptors in the inner ear causes nausea Otitis media – inflammation of the middle ear; common in young children Disorders of the eye Blindness – partial loss or lack of vision; caused by many things…cataract, glaucoma, detachment or deterioration of the retina, damage to optic nerve or visual centers in the occipital lobe  14 o Cataract – cloudiness or opacity of the lens which impairs vision; common in older people; leading cause of blindness o Glaucoma – aqueous humor is produced faster than it is removed and intraocular pressure rises; the rise in pressure compresses blood vessels nourishing the retina and the receptor cells die; second leading cause of blindness Myopia – near sighted – light converges in front of retina, can’t see far objects Hyperopia – farsighted – light converges behind retina, can’t see close Astigmatism – unequal focusing of light rays on the retina; causes part of an image to appear blurry Presbyopia – diminished ability of the lens to accommodate due to a decrease in elasticity; natural result of aging Retinoblastoma – cancer of immature retinal cells Strabismus – disorder of the extrinsic eye muscles in which the eyes are not directed toward the same object simultaneously Chapter 8 Medical Terminology astr- star-shaped astrocyte - astr/o/cyte: a star-shaped cell aur and oto- ear auricle - aur/i/cle: the projecting part of the ear lying outside the head parotid - par/ot/id: situated near the ear (the parotid salivary gland is near the ear) dacry- tear (dacry is typically used with conditions related to tear production) dacryoadenitis - dacry/o/aden/itis: inflammation of a lacrimal or tear gland dendr- tree; branching dendrite - dendr/ite: name for the nerve fibers that extend from a nerve cell dura- hard; used principally as a shortened form of the dura mater (outer layer of meninges) epidural - epi/dur/al: pertaining to the space upon or exterior to the dura mater gangli- swelling; knotlike mass; denotes a relationship to ganglion (mass of nerve cells outside the brain and spinal cord) gangliocytoma - gangli/o/cyt/oma: a tumor containing ganglion cells  15 iris- rainbow iris - name of the colored membrane of the eye lacrim- tear (lacrim is typically used to denote the body parts or structures of tear production) lacrimotomy - lacrim/otomy: incision of the lacrimal duct macul - spot macula - macul/a: a spot or blotch mani- madness, mental disturbance megalomania - megal/o/mani/a: delusion of having extreme greatness or power myring- eardrum myringoscopy - myring/o/scop/y: inspection of the eardrum using a myringoscope ocul/opt/opthalm - eye oculopathy - ocul/o/path/y: any disease or disorder of the eye olfact- smell, to smell olfactophobia - olfact/o/phobi/ia: morbid aversion to odors palpebr- eyelid palpebration - palpebr/ation: abnormally frequent winking phot- light photoallergy - phot/o/allergy: an allergic sensitivity to light -plexus - braid, an interweaving network subplexal - sub/plex/al: beneath a plexus or network of vessels or nerves psycho- mind; mental processes psychic - psych/ic: pertaining to the mind scler- hard or "white of the eye" sclerosis - a condition of the hardening of a structure  16 thalam- inner chamber thalamus - thalam/us: name for the large gray mass in the brain tympan- eardrum tympanic membrane - tympan/ic: name for the eardrum