second test lectures

* Please note: these notes are not "all you need" to prepare for the test, but will give an outline of the material that was covered in lecture
 
 
 

Chapter 10 Function of Muscles • Produce movement • Maintain posture • Stabilize joints • Support soft tissue • Guard openings to the internal body • Generate heat Types of Muscles • Skeletal muscle • Cardiac muscle • Smooth muscle Skeletal Muscle Anatomy • Definition of a skeletal muscle – Thousands of muscle fibers – Connective tissue – Blood vessels – Nerve fibers Connective Tissue of Muscles • Endomysium – Areolar connective – Around each muscle fiber • Perimysium – Sheath around fascicle • Fascicle = bundle of muscle fibers Connective Tissue of Muscles • Epimysium – Sheath around group of fascicles  • Fascia  – Covering outside epimysium • The function of these tissues is protection Muscle Attachments • Tendon – Connective tissue layers come together at end of muscle – Attaches to bone Muscle Attachments • Origin – Attachment to an immovable bone • Insertion – Attachment to a moveable bone Nerves • Each muscle has many nerves  • Each fiber has a nerve connection • Transmissions cause muscles to contract Function of Blood Vessels • Supply Oxygen • Supply ATP or other nutrients • Remove wastes • Muscles usually have high metabolism Microscopic Muscle Anatomy • Multiple nuclei • Sarcolemma  – Cell membrane – Contains myoglobin for O2 storage • Sarcoplasmic Reticulum – Type of smooth endoplasmic reticulum – Releases ionic calcium – Surrounds myofibrils Microscopic Muscle Anatomy • Myofibrils – Organelles  – Contractile element – Units = sarcomeres – A band • Dark, thick filament • Myosin  – I band • Light, thin filament • Actin  – Z-line • Midpoint of I band • Defines sarcomere Microscopic Muscle Anatomy • T-tubule – Transverse tubule – Runs between sarcoplasmic reticulum – Channels extracellular fluid – Acts as telegraph to myofibril • Mitochondria are very abundant Muscle Contraction • Shortening of sarcomeres • Sliding filament theory – Actin slides past myosin – Cross bridges cause movement • Mysoin head attracts to progressive sites on actin • Works like a ratchet – Contraction occurs as long as Ca++ and ATP are present Muscle Fiber Types • Most skeletal muscles are a mixture of muscle fiber types – Red  • Slow twitch • Abundant myogolbin – White • Fast twitch • Little myoglobin – Intermediate  Cardiac Tissue • T-Tubules are short and broad • Single, central nuclei • Cardiac cells attached to cardiac cells at intercalated disc Cardiac Tissue • Totally anaerobic – Abundant myoglobin – Large numbers of mitochondria • Contract by stimulation from pacemaker cells Smooth Muscle • Cause constriction of hollow organs – Peristalsis = squeezing rhythmically • Controlled by autonomic nervous system Smooth Muscle • No sarcomeres – Actin & myosin fibers are present • No T-tubules • Spindle shaped cells with 1 nucleus • Sarcoplasmic reticulum reduced • Ca++ from extracellular fluid Smooth Muscle • Very slow contraction • Mainly anaerobic • Has muscle tone • Stretching muscle causes slower contractions – No expulsive contractions Muscle Cell Replacement • All types originate from myoblasts • Skeletal muscle – Do not divide – Myoblast-like cells produce some new cells – Satellite cells help repair injured muscle – Repair is slow Muscle Cell Replacement • Smooth muscle – Cells can divide – Hyperplasia • Divide rapidly in uterus during pregnancy and puberty – Smooth muscle cells secrete their own connective tissue • Cardiac muscle – Cells are not replaced or repaired Muscle Tissue Disorders • Muscular Dystrophy – Muscle fibers degenerate – Fat and connective tissue replaces muscle Muscle Tissue Disorders • Fibromyalgia – Chronic pain syndrome – Severe musculoskeletal pain – Widespread in body – Cause is unknown Related Clinical Terms • Spasm – Sudden involuntary muscle twitch – Often due to chemical imbalance • Strain – Tearing of a portion of a muscle

Chaptera 10 Organization of Skeletal Muscles • Parallel • Convergent  • Pennate  • Circular • Parallel – Fascicles run parallel to long axis of muscle – Strap-like or spindle-shaped muscles – Great shortening ability (large movement) – Little power • Convergent – Muscles converge toward tendon – Broad origin – Powerful muscles • Pennate – Fascicles are obliquely attached – Several forms • Unipennate • Bipennate • multipennate • Circular – Arranged in rings – Sphincters or squeezers Tension Relationship of Muscles • Most skeletal muscles work like lever systems • Lever = rigid structure – Bone in human body • Fulcrum = fixed point of movement – Joint in human body • Muscle apply force to bones Tension Relationship of Muscles • Mechanical advantage – Less effort is needed to lift weight – Not very common in the human body Tension Relationship of Muscles • Mechanical disadvantage – More force than the weight to be lifted – This action increases speed  – Common in human muscles Muscle Terminology • Insertion – Attachment to moveable bone • Origin – Attachment to fixed, immovable bone • During contraction, insertion moves towards origin Actions of Muscles • Muscles can be classified by their movement – Agonist – Antagonist  – Synergist – Fixator  • Agonist – Prime mover – Provides major force for a specific movement – Ex: biceps brachii • Antagonist – Reverse action of agonist – Often stretched in the relaxed state – Ex: triceps brachii • Synergist – Aids in action of an agonist – Can prevent other actions like rotation – Many small muscles that span joints are examples • Fixator  – Immobalizes a bone – Ex.:  subscapularis Naming of Skeletal Muscles • Location of a muscle • Ex.: temporalis – Overlies temporal bone • Relative size of muscle – Ex: gluteus maximus            gluteus medius            gluteus minimus • Shape of muscle – Ex.:  deltoid • Direction of muscle fibers – Ex: external oblique • Number of origins • Ex.: biceps brachii • Location or origin and/or insertion – Origin listed 1st if both are used – Ex.: sternocleidomastoid • Origin = sternum • Origin = clavicle • Insertion = mastoid • Action of muscle • Ex.: extensor carpi radialis longus – Extension of wrist (carpals) – Lies close to radius – Longer than other wrist muscles Muscles of the Human Body • Over 600 muscles present Related Clinical Terms • Charley Horse – Tearing of a muscle followed by bleeding into the muscle – Severe pain • Shin Splint – Swelling of the anterior tibialis muscle – Muscle swells and cuts off its own circulation – Pressure against nerve causes pain  Chapter 12 Nervous System • Neurons – Nerve cells • Neuroglia – Nerve support cells • Connective tissue • Blood vessels Functional Units of Nervous System • Central Nervous System – Brain  – Spinal cord • Peripheral Nervous System – Afferent = sensory neurons – Efferent = motor neurons Neurons • Soma  – Cell body – Large central nucleus – “owls eye” nucleolus – Perikaryon surrounds nucleus • Organelles • Cytoskeleton • Dendrites – Sensitive processes – Areas stimulated to produce nerve transmission • Axon – May be mylenated – Carries transmission away from soma – Ends in telodendria Telodendria • Have synaptic knobs at the end • Found at the synaptic cleft • Contains and produces neurotransmitters Types of Neurons • Anaxonic – Small – Cannot distinguish axon from dendrite – Located in brain and sense organs – Function is poorly understood • Bipolar  – One dendrite and one axon – Rare type – Only in sense organs • Unipolar – Dendritic and axonal processes are continuous – Most sensory neurons – Allows accurate location of stimuli • Multipolar – Several dendrites – One axon – Most common type of neuron – Includes all motor neurons Functional Classification of Neurons • Sensory neurons – To central nervous system • Motor neurons – From central nervous system • Interneurons  – Within central nervous system Neuroglia • Astrocytes – Star cells – Most abundant glial cell – Controls chemical environment – Braces neurons – Links neurons to blood capillaries  • Microglia – Act as macrophages • Ependymal cells – Squamous to columnar – Many are ciliated – Line cavities of brain and spinal cord – Circulate and contain spinal fluid • Oligodendrocytes – Look like astrocytes with fewer branches – Produce myelin sheaths in central nervous system • Satellite cells – Surround neuron cell bodies in ganglia • Schwann cells – Form myelin sheath around peripheral axons – Form sheath around unmyelinated axons Myelin Sheath • Protein-lipid covering • Insulates and increases speed of impulses • Formed by Schwann cell in jelly-roll fashion • Nodes of Ranvier  – Gaps in myelin sheath The Synapse • Point where two nerves come together – Axon meets dendrite • Nerves do not physically touch Transmission at the Synapse • Impulses cross the synapse in two ways – Electrical synapse • Ionic current jumps gap – Chemical synapse • Chemicals released by one cell received by the next cell Nerves • Nerves are more than just nervous tissue – Connective tissue – Blood vessels • These structures are more commonly seen away from the central nervous system Connective Tissue Coverings • Myelin sheath – Covers axons – Produced by Schwann cell Connective Tissue Coverings • Endoneurium – Surrounds myelin sheath • Perineurium – Surrounds fascicle of nerves • Epineurium – Outside covering of nerve Related Clinical Term • Rabies – Virus that affects the nervous system – Usually transmitted by bite from infected animal

 

Chapter 13 Brain Embryonic Development of the Central Nervous System • 3 week embryo – Formation of neural plate – Next the neural fold develops – Plate invaginates • This is the beginning of the nervous system • Neural tube is formed by the 4th week – Stretches from anterior to posterior – Anterior develops faster • Becomes brain • Constrictions appear to make 3 primary brain vessicles – Prosencephalon – Mesencephalon – Rhombencephalon  • By 5 weeks the brain has 5 regions – Forebrain • Telencephalon  • Diencephalon – Midbrain  • Mesencephalon – Hind brain • Metencephalon  • Mylencephalon • Growth continues to be accelerated anteriorly Regions of Adult Brain • Cerebrum • Diencephalon • Brain Stem • Cerebellum Ventricles of the Brain • Lateral ventricles – One in each hemisphere – Separated by septum pellucidum (thin membrane) • Third ventricle • Fourth ventricle – Connected to subarachnoid space Brain Protection and Support • Bones of the cranium • Meninges • Cerebrospinal fluid Cranial Meninges • Continuous with spinal meninges • Dura mater – Double layer • Periosteal layer – Outer – Attached to skull • Meningeal layer – Inner  – Collects venous blood from brain • Arachnoid layer – Middle layer – Contains largest blood vessels • Pia mater – Next to brain – Contains small blood vessels • Dura speta – Folds of dura mater that dips inward into brain – Protects and supports brain Cerebrospinal Fluid • Floats free • Moved by microvilli of ependymal cells • Replaced 3 times per day • Has distinct circulation • Hydrocephalus – Obstruction – Build-up of cerebrospinal fluid Blood-Brain Barrier • Least permeable capillaries are around the brain • Maintains stable environment • Aided by astrocytes • Barrier is incomplete in newborns Blood-Brain Barrier • Ineffective against – CO2 – Fats  – Fat soluble molecules – Alcohol – Nicotine – Anesthetics • Part of the brain stem does not have a blood-brain barrier – Includes vomit reflex center Cerebrum • Each cerebral hemisphere has 3 regions – Cortex • Outer gray matter – White matter • Internal to cortex • Mylenated axons – Basal nuclei • Islands of gray matter Areas of Cerebral Cortex • Broadman areas – Some areas have special functions – Some functions are derived from several areas – Each hemisphere deals with functions of the opposite side of the body • Three kinds of functional areas – Motor areas – Sensory areas – Association areas • Lateralization  – Two hemispheres are not equal • Motor & sensory areas – Most are in frontal and parietal lobes – Broca’s area • Motor speech area – Visual cortex is in occipital lobe Cerebral white matter • Allows for communication between cerebral hemispheres – Commisures • Connects areas of hemispheres – Association fibers • Transmits impulses within a given hemisphere – Projection fibers • Fibers entering from lower brain or spinal cord Basal Nuclei • Some role in motor control • Some role in cognition • Allows us to perform several activities at once Diencephalon Thalamus • 80% of diencephalon • Bilateral masses of gray matter • Functions – Acts as relay station – Sorts and edits sensory inputs – All ascending impulses to cortex are funned through here Hypothalamus • Below thalamus • On top of brain stem • Includes mammillary bodies – Olfactory relay stations • Pituitary is attached by infundibulum • Main visceral control center of body • Important for homeostasis – Regulates involuntary nervous system – Center for emotional response – Body temperature regulation – Regulation of food intake – Regulation of water balance and thirst – Regulation of sleep-wake cycles – Control of endocrine functioning Epithalamus Brain Stem • Midbrain  • Pons  • Medulla Mid Brain • = Mesencephalon • Between diencephalon & pons • Pathway between higher & lower brain • Visual reflex center • Auditory reflex center Pons • Bulging part of brain stem • Mostly conduction tracts • Maintains normal breathing – Rate  – Depth  Medulla Oblongata • Connects with spinal cord • Many conduction tracts • Fiber tracts that connect medulla to cerebellum • Olives • Relay sensory information on joint & muscle stretch • Autonomic reflex center – Cardiovascular center • Force & rate of contractions – Respiratory centers • Maintains rhythm  • Rate & depth – Other regulatory centers • Vomiting • Hiccupping  • Coughing • Sneezing  • Swallowing Cerebellum • 11% of total brain mass • Rests in posterior cranial fossa of skull • Entire function is coordination • 2 symmetrical hemispherees • Connected medially by wormlike vermis • Heavy surface convolutions • Fissures are all transverse = floia – Divide into 3 lobes • One is deep • Organization – Outer gray matter – Internal white matter – Small, deep paired gray masses • Function – Anterior & posterior lobes control body movement – Deep lobe maintains balance & controls eye movement (coordination) Cranial Nerves • 1.  Olfactory nerve – To olfactory bulb  – Sensory for smell • 2.  Optic nerve – From retina of eye – Sensory for vision • 3.  Oculomotor nerve – To eye muscles – Motor function only •4.  Trochlear nerve –Superior eye muscles –Motor function only •5.  Trigeminal nerve –Chewing muscles mostly –Sensory & motor to face •6.  Abducens nerve –To eye muscles –Motor function only •7.  Facial nerve –Sensory & motor to face –Senses taste –Several motor functions •8.  Vestibulocochlear –To ear –Sensory for balance & hearing •9.  Glossopharyngeal –To head and neck –Senrory and motor •10.  Vagus nerve –“the wanderer” –To most major body organs –Few branches to neck & back –Sensory & motor •11.  Accessory –To muscles of neck & back –Motor function only •12.  Hypoglossal –To tongue –Motor function only Spinal Cord Gross Anatomy • Externally – Posterior median sulcus – Anterior median fissure • White matter – Outside layer of spinal cord – Myelinated axons • Gray matter – Central region of spinal cord – Nerve cell bodies Location of Spinal Cord • From foramen magnum to L1 • Cauda equina – Cluster of nerves below L1 Enlargements of the Spinal Cord • Spinal cord is larger in two regions – Cervical enlargement – Lumbar enlargement • Enlargement is due to association with limbs – More nerves associated with these regions Spinal Nerves • Several spinal nerves are associated with each vertebrae region – Dorsal root • Nerves coming to the spinal cord – Ventral root • Motor neurons Spinal Meninges • Provide protection to spinal cord • Carry blood vessels • Continuous with cranial meninges • Infection can cause spinal meningitis • Three layers – Dura mater – Arachnoid – Pia mater • Dura mater – Outermost layer – Dense collagen fibers – Outside is epidural space • Areolar connective tissue • Adipose tissue • Arachnoid – Narrow subdural space separates it with dura mater – Surface of simple squamous epithelium – Subarachnoid space filled with spinal fluid – Spinals taps taken from lower lumbar • Pia mater – Innermost layer – Meshwork of elastic and collagen fibers – Contains blood vessels servicing spinal cord Sectional Anatomy of Spinal Cord • White matter is superficial – Mylenated and unmylenated axons • Grey matter is central – Cell bodies of neurons – Projections towards outer surface are called horns • Central canal in middle Organization of Gray Matter • Nuclei  – Functional groups • Sensory nuclei • Motor nuclei • Posterior horns – Somatic and visceral sensory nuclei • Anterior horns – Motor nuclei • Lateral horns – Visceral motor nuclei Organization of White Matter • Divided into three columns – Posterior column – Anterior column – Lateral column • Each column is a bundle of axons Structure of Spinal Nerves • Mostly mylenated axons • Blood vessels • Surrounded by connective tissue – Endoneurion • Around axon – Perineurion • Surrounds fassicle of axons – Epineurion • Surrounds entire nerve Distribution of Spinal Nerves • Many spinal nerves go a short distance to a ganglion – Ganglion  • Collection of cell bodies outside the central nervous system • Spinal nerves synapse at ganglion Spinal Rami • Sensory and motor neurons associated with spinal cord – Dorsal Rami • Goes to skin and muscles of back – Ventral Rami • Ventrolateral body and limbs – Rami communicantes • Vertebral area Pathways of Spinal Tract  • Most cross to opposite side – Nerves on left side originate from gray matter on right side • All paths are paired – Matching left and right Problems of the Spinal Cord • Polio – Caused by poliovirus – Destruction of anterior horn – Begins with loss of somatic reflexes – Eventual paralysis – Death from paralysis of respiratory muscles or heart • Amyotrophic lateral sclerosis (ALS) – Lou Gerhig’s disease – Progressive destruction of anterior horn motor neurons – Loss of ability to speak, swallow, then breath • Spinal cord trauma – Paralysis • Loss of motor function – Parasthesia  • Sensory loss – Flaccid paralysis • Damage to ventral root or anterior horn • No voluntary or involuntary movement – Spastic paralysis • No voluntary movement  • Spinal reflexes work • Paralysis – Paraplegia • Damage between T1 & L1 • Upper body paralysis – Quadriplegia • Damage in cervical area • All limbs are paralyzed – Hemiplegia • Paralysis to one side • Usually caused by brain injury – Spinal shock • Functional loss for some time after injury

Chapter 14 Nervous System Pathways • Nuclei & tracts that link the brain with the rest of  the body • Sensory Pathways • Motor Pathways Sensory Pathways • Ascending pathways – Begin with sensory receptor • Monitor conditions in body or external environment • Can be classified by what they monitor Sensory Receptors • Nociceptors – Stimuli associated with tissue damage – Sensation of pain • Thermoreceptors – Respond to temperature change • Mechanoreceptors – Respond to physical stimuli • Chemoreceptors – Respond to changes in composition of body fluids Organization of Sensory Pathways • 1st order neuron – Delivers sensation to central nervous system • 2nd order neuron – In spinal cord or brain – Transfer within central nervous system • 3rd order neuron – Synapse in thalamus – Takes impulse to cortex Major Somatosensory Pathways of the Spinal Cord • Posterior column  – Sensations of localized sensation • Touch  • Pressure  • Vibration  • Position  Motor Pathways • Travels by one of two pathways – Pyramidal system • Conscious  – Extrapyramidal system • Subconscious  Pyramidal system • Voluntary control of skeletal muscle • Begins with pyramidal cells of primary motor cortex • Travels via descending paths – One of three pair Extrapyramidal System • Can modify direct skeletal contractions – Stimulate – Inhibit  – Facilitate  • Travels by one of four pair of spinal tracts Aging of the Nervous System • Reduction in brain size & weight • Reduction in number of neurons • Decrease in blood flow to brain • Changes in synaptic origin of brain impulses Related Clinical Terms • Shingles – Caused by Herpes zoster • Also causes chicken pox – Rash of scaly, painful blisters – Virus remains dormant – When the immune system is stressed, shingles can occur • Migraine headaches – Extremely painful, episodic headaches – Pain relates to sensory innervations of the trigeminal nerve • Myasthenia gravis – Autoimmune disease – Body defenses destroy neurotransmitter receptors on muscle – An impulse is sent but not received   Chapter 15  Autonomic Nervous System • Involuntary Nervous System • Motor neurons only • Innervates mostly smooth muscle, cardiac muscle, and glands Organization of Autonomic Nervous System • Two neuron chain delivers message from central nervous system to effector • Synapse is at ganglion – Preganglionic neuron – Postganglionic neuron Preganglionic Neuron • Soma in brain or spinal cord • Synapse at autonomic ganglion • Lightly myelinated – Not as fast as heavily myelinated somatic nerves Postganglionic Neuron • Soma at ganglion • Less myelin than preganglionic – Some are not myelinated • Axons to effector Neurotransmitters • Somatic  – Acetylcholine  • Autonomic – Acetylcholine  – Norepinephrine  – Epinephrine Divisions of Autonomic Nervous System • Parasympathetic – Non-stressful situations – “housekeeping”  – Keeps energy use low • Sympathetic – Reaction to unusual stimulus – Fight or flight – Rapid heart, deep breathing, …. Differences Between Divisions • Origin – Parasympathetic • Brain & sacral spine – Sympathetic • Thoracolumbar spine • Neuron lengths – Parasympathetic  • Long preganglionic  • Short postganglionic – Sympathetic  • Short preganglionic • Long postganglionic • Location of ganglia – Parasympathetic • Near visceral effector organs – Sympathetic • Near spinal cord – Sympathetic truck Parasympathetic Division • Includes 4 cranial nerves – Occulomotor  – Facial  – Glossopharyngeal  – Vagus  • Also has sacral outflow • Ganglia at adjacent organs Visceral Reflexes • 4 neuron chain – Sensory neuron – Interneuron – Preganglionic neuron – Postganglionic neuron • In given situations one division takes over • Most functions result from new internal stimulus Interaction of Divisions • Parasympathetic & sympathetic innervate most organs • Depending on situation, one division takes over • Sympathetic – Parasympathetic tone Some Functions are Uniquely Sympathetic • Thermoregulatory response to heat – Blood vessel dilation – Activation of sweat glands • Release of renin – Promotes increase in blood pressure • Metabolic stimulation – Enhance metabolism – Increase blood glucose – Mobilization of fats – Increase mental alertness Sympathetic Division Effects • Much longer lasting – Epinephrine and epinephrine are inactivated more slowly than acetylcholine • Secreted into blood Related Clinical Terms • Chagas’ Disease – Caused by a protozoan Trypanosoma cruzi – Tramsitted by kissing bug Damages organs and parasympathetic neurons

Chapter 16   Sense Organs Sensory Function • Each receptor has a characteristic sensitivity = receptor specificity – Information is routed to site in central nervous system – Stimulation continues to be analyzed Adaptation • Reduction in sensitivity in presence of constant stimuli  – Peripheral adaptation • Happens quickly in temperature receptors • Works slowly in pain receptors – Central adaptation • Inhibition of nuclei • Ex: turning off smell Location of Receptors • Scattered throughout the body – Exteroceptors • External stimuli receptor – Interoceptor  • Monitors visceral organs – Proprioceptors • Monitors skeletal muscles and joints Types of Excitation Stimulus  • Thermoreceptors • Mechanoreceptors • Chemoreceptors • Nociceptors Special Senses • Smell  • Taste • Vision • Hearing  • Equilibrium Olfaction • Sense of smell – Human nose is better than any machine • Not as keen as many animals • We can distinguish about 10,000 chemicals Olfaction • Sense of smell – Sensory portion is found in olfactory epithelium Olfactory Epithelium • Pseudostratified epithelial tissue • On roof of nasal cavity • Air swirls in eddies of nasal cavity Anatomy of Olfactory Epithelium • Receptor cells are bipolar neurons – Olfactory hairs • Cilia at end of cell • Non-motile – Only neurons in the body that are replaced • Support cells – Most of the olfactory epithelium – Includes short mitotic epithelial basal cells • Olfactory glands – Found in underlying connective tissue – Produce mucus • Solvent for airborne molecules Olfactory Pathway • Receptor cells synapse in overlying olfactory bulbs • Impulse travels along olfactory nerve – Receptor cells synapse with mitral cells in olfactory bulb • Easily inhibited • Mitral cells to thalamus or hypothalamus via olfactory tract – Thalamus interprets smell – Hypothalamus gives emotional aspect Gustation • Sense of taste • Most of what we call taste is 80% smell • Sensory structures – Taste buds (on lingual papillae) • Tongue • Soft palate • Inner cheeks • Pharynx • Epiglottis Types of Lingual Papillae • Fungiform – Mushroom shaped – Most common type – Over all tongue • Most common at tip – Taste buds found on the side • Circumvallate – Inverted V at back of tongue – Taste buds on top of papilla • Filiform – Contain no or few taste buds – Provide friction against objects Anatomy of Taste Buds • 40-60 epithelial cells – Gustatory cells • Sensory cells • Have long microvilli – Gustatory hairs – Support cells • Insulate receptor cells Taste Sensations • Sweet – Sugars, alcohol, some amino acids, lead salts • Sour  – Acids • Salty – Metal ions • Bitter  – Alkaloid • Also water receptors • Different areas are more sensitive to some sensations Gustatory Pathway • Dendritic endings are part of two cranial nerves – Facial nerve – Glossopharyngeal – A few in the esophagus use the vagus nerve • Cranial nerves to medulla • Medulla to thalamus • Thalamus to gustatory complex in parietal lobe • A few fibers go to the limbic system Vision  • 70% of all sensory receptors are in the eye • Optic tracts have over 1 million nerve fibers •Eyebrows –Shade eyes –Hold perspiration •Eyelids –Skin over flap of connective tissue – Contain sebaceous & sweat glands –Muscles activated voluntarily or automatically •Blink every 3-7 sec. •Reflex protects eye  –Can be activated by eyelashes •Conjunctiva –Mucous membrane that lines eye –Produces lubricating mucous –Gives some protection –Conjunctivitis = pink eye •Infection of conjunctiva • Lacrimal apparatus – Lacrimal gland • In upper lateral orbit • Continuous release of saline solution • Blinking spreads fluid – Lacrimal canals • Drains fluid to nose • Entry is at lacrimal punctum – Lacrimal sac • Empties fluid into nasal cavity • Extrinsic eye muscles – Six muscles that move eye – Origin = orbit – Also help maintain shape of eye Structures of eye • Three tunics for the wall of the eyeball – Fibrous tunic – Vascular tunic – Sensory tunic Fibrous Tunic Cornea • Collagen fibers arranged to make it clear • External sheath of simple squamous epithelium • Supplied with nerve endings for reflex blinking – Reflex also increases lacrimal fluid • Can be transplanted without danger of rejection Vascular Tunic Choroid Layer • Highly vascularized dark membrane • Provides nutrition to all tunics • Continuous with ciliary body anteriorly Ciliary Body • Ciliary muscles – Control lens shape • Suspensory ligament – Attaches to lens • Allows for focus Iris • Colored part of eye – Pigments are all brown – Amounts yield different colors • Between cornea and lens • Pupil = round central opening • Reflex regulates smooth muscles Sensory Tunic • Innermost tunic • Two layered retina – Outer pigmented layer – Inner neural layer • Optic disc – Exit area for optic nerve • No photreceptors Pigmented Layer of Retina • Single cell thick lining • Absorbs light  • Acts as phagocyte • Stores vitamin A Neural Layer of Retina • Transparent  • Out pocketing of brain • Millions of photoreceptors • Types of photoreceptors – Rods  • Dim-light receptors • Peripheral vision • Do not provide sharp images – Cones  • Bright light receptors • High accuracy color vision • Macula lutea – Lateral to blind spot – Center = fovea centralis – Contains only cones – Light passes directly to photoreceptors – Gives fine focus to small area of vision • Detached retina – Pigmented and nervous layers separate  – Causes blindness if not reattached • Laser surgery  Internal Eye Chambers • Anterior chamber – Filled with aqueous humor • Similar to blood plasma • Supplies nutrients to lens • Replaced constantly – Glaucoma = blocked drainage » Compression of retina » Pain and blindness Lens  • Biconvex flexible structure • Changes shape for focusing • Enclosed in thin elastic capsule Lens Problems • Gradually becomes less elastic & more convex – Impairs vision • Cataract – Clouding of lens – Some congenital, some age related – Can be surgically removed Visual Pathway • Thalamus to primary visual cortex in occipital lobes • Some fibers form optic chiasm to midbrain – Control eye muscles – & pupil • Some fibers to hypothalamus to set daily biorhythms  Hearing and Equilibrium The Ear • Contains sensory organs for hearing and balance • Three distinct regions – External ear – Middle ear – Inner ear The External Ear • Auricle or Pinna – Projection to direct sound – Elastic cartilage and skin – Muscles for movement are vestigial • External auditory canal – From auricle to tympanic membrane – Lined with skin – Accessory structures • Hair  • Sebaceous glands • Ceruminous glands • Tympanic membrane – Eardrum – Boundary between outer & middle ear – Connective tissue membrane – Flattened cone with apex towards middle ear – Vibrations transferred to associated bones Middle Ear •Called tympanic cavity •Air filled cavity •Lined with mucosa •Pharyngotympanic tube links middle ear with nasopharynx –Closed except when swallowing and yawning •Tympanic cavity is spanned by 3 bones –Malleus = hammer –Incus = anvil –Stapes = stirup –Ligaments suspend bones –Joined by synovial joints –Two muscles have attachments to ear bones Inner Ear • Called the labyrinth • Within temporal bone • Two divisions – Bony labyrinth • Filled with perilymph • Creates 3 regions – Vestibule – Semicircular canals – Cochlea – Membranous labyrinth • Interconnecting sacs and ducts • Vestibule  – Central egg-shaped cavity – Two membranous sacs • Saccule • Utricle  – Houses equilibrium receptors • Hair cells • Otoloiths • Semicircular canals – Attach to posterior vestibule – 3 canals in each ear – Ampulla = enlarged swelling at one end • Equilibrium receptor • Cochlea – Houses organ of Corti • Receptor for sound Auditory Pathways • Impulses sent to thalamus • Thalamus to auditory complex in temporal lobe Equilibrium Pathway •Impulses go directly to reflex centers –Ex: stumbling –Route is to brain stem and cerebellum •Motion sickness –Due to sensory mismatch Developmental Aspects • Smell & taste are sharp at birth • If you live to age 140 all hair cells will have been lost Developmental Aspects • Vision takes time to develop  – Gray tones at first – Eye movements are uncoordinated – Tearless until 2 weeks – Color vision by age 5