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NERVOUS SYSTEM NERVOUS TISSUE: SUPPORT CELLS FUNCTIONS OF THE NERVOUS SYSTEMS Support cells in the CNS are grouped together as “neuroglia” Sensory input—gathering information...

NERVOUS SYSTEM NERVOUS TISSUE: SUPPORT CELLS FUNCTIONS OF THE NERVOUS SYSTEMS Support cells in the CNS are grouped together as “neuroglia” Sensory input—gathering information General functions To monitor changes occurring inside and outside the body Support Changes = stimuli Insulate Protect neurons Integration To process and interpret sensory input and decide if action is needed Astrocytes Motor output - Abundant, star-shaped cells - Brace neurons A response to integrated stimuli - Form barrier between capillaries and The response activates muscles or glands neurons STRUCTURAL CLASSIFICATION OF THE - Control the chemical environment of the NERVOUS SYSTEM brain Central nervous system (CNS) Microglia - Organs - Spiderlike phagocytes Brain - Dispose of debris Spinal cord - Function Integration; command center Ependymal cells Interpret incoming sensory - Line cavities of the brain and spinal cord information - Cilia assist with circulation of cerebrospinal Issues outgoing instructions fluid Peripheral nervous system (PNS) - Nerves extending from the brain and spinal cord Spinal nerves—carry impulses to and from the spinal cord Oligodendrocytes Cranial nerves—carry impulses to and from the brain - Wrap around nerve fibers in the central - Functions nervous system Serve as communication lines - Produce myelin sheaths among sensory organs, the brain and spinal cord, and glands or muscles Satellite cells FUNCTIONAL CLASSIFICATION OF THE - Protect neuron cell bodies PERIPHERAL NERVOUS SYSTEM - Schwann cells - Form myelin sheath in the peripheral Sensory (afferent) division nervous system - Nerve fibers that carry information to the central nervous system NERVOUS TISSUE Motor (efferent) division : NEURONS - Nerve fibers that carry impulses away from the central nervous system Neurons = nerve cells two subdivisions - Cells specialized to transmit messages - Major regions of neurons - Somatic nervous system = voluntary Cell body—nucleus and metabolic Consciously controls skeletal center of the cell muscles Processes—fibers that extend from - Autonomic nervous system = involuntary the cell body Automatically controls smooth and cardiac muscles and glands Cell body Further divided into the sympathetic and parasympathetic nervous Nissl bodies systems - Specialized rough endoplasmic reticulum Neurofibrils - Intermediate cytoskeleton - Maintains cell shape  Nucleus with large nucleolus Sensory (afferent) neurons - Carry impulses from the sensory receptors to the CNS - Cutaneous sense organs - Proprioceptors—detect stretch or tension Motor (efferent) neurons - Carry impulses from the central nervous system to viscera, muscles, or glands Processes outside the cell body - Dendrites—conduct impulses toward the cell body Neurons may have hundreds of dendrites a. Free nerve endings (pain and temperature - Axons—conduct impulses away from the receptors) cell body b. Meissner’s corpuscle (touch receptor) Neurons have only one axon arising from c. Lamellar corpuscle (deep pressure the cell body at the axon hillock receptor) d. Golgi tendon organ (proprioceptor) Axons e. Muscle spindle (proprioceptor) - End in axon terminals Interneurons (association neurons) - Axon terminals contain vesicles with neurotransmitters - Found in neural pathways in the central - Axon terminals are separated from the next nervous system neuron by a gap - Connect sensory and motor neurons Synaptic cleft—gap between adjacent STRUCTURAL CLASSIFICATION OF NEURONS neurons Synapse—junction between nerve Multipolar neurons—many extensions from the cell body Myelin sheath—whitish, fatty material covering axons Schwann cells—produce myelin sheaths in - All motor and interneurons are multipolar jelly roll-like fashion around axons (PNS) - Most common structure Nodes of Ranvier—gaps in myelin sheath along the axon Bipolar neurons—one axon and one dendrite Oligodendrocytes—produce myelin sheaths around axons of the CNS NEURON CELL BOODY LOCATION - Located in special sense organs such as - Most neuron cell bodies are found in the nose and eye central nervous system - Rare in adults Gray matter—cell bodies and unmyelinated fibers Unipolar neurons—have a short single process Nuclei—clusters of cell bodies leaving the cell body within the white matter of the central nervous system Ganglia—collections of cell bodies outside the central nervous system Tracts—bundles of nerve fibers in the CNS Nerves—bundles of nerve fibers in the PNS - Sensory neurons found in PNS ganglia White matter—collections of myelinated fibers (tracts) Gray matter—collections of mostly unmyelinated fibers and cell bodies FUNCTIONAL CLASSIFICATION OF NEURONS FUNCTIONAL PROPERTIES OF NEURONS Repolarization Irritability - Ability to respond to stimuli - Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the Conductivity - Ability to transmit an impulse membrane NERVE IMPULSES - Repolarization involves restoring the inside of the membrane to a negative charge and Resting neuron the outer surface to a positive charge - The plasma membrane at rest is polarized - Fewer positive ions are inside the cell than Repolarization. Potassium ions diffuse out of the outside the cell cell as the membrane permeability changes again, restoring the negative charge on the inside of the Resting membrane is polarized. In the resting state, membrane and the positive charge on the outside the external face of the membrane is slightly surface. Repolarization occurs in the same direction positive; its internal face is slightly negative. The as depolarization. chief extracellular ion is sodium (Na+), whereas the chief intracellular ion is potassium (K+). The Repolarization membrane is relatively impermeable to both ions. - Initial ionic conditions are restored using the sodium-potassium pump. Depolarization - This pump, using ATP, restores the original - A stimulus depolarizes the neuron’s configuration membrane - Three sodium ions are ejected from the cell - The membrane is now permeable to sodium while two potassium ions are returned to the as sodium channels open cell - A depolarized membrane allows sodium Initial ionic conditions restored. The ionic (Na+) to flow inside the membrane conditions of the resting state are restored later by Stimulus initiates local depolarization. A stimulus the activity of the sodium-potassium pump. Three changes the permeability of a local "patch" of the sodium ions are ejected for every two potassium membrane, and sodium ions diffuse rapidly into the ions carried back into the cell. cell. This changes the polarity of the membrane (the TRANSMISSION OF A SIGNAL AT SYNAPSES inside becomes more positive; the outside becomes more negative) at that site. 1. When the action potential reaches the axon terminal, the electrical charge opens Action potential calcium channels 2. Calcium, in turn, causes the tiny vesicles - The movement of ions initiates an action containing the neurotransmitter chemical to potential in the neuron due to a stimulus fuse with the axonal membrane - A graded potential (localized depolarization) 3. The entry of calcium into the axon terminal exists where the inside of the membrane is causes pore like openings to form, releasing more positive and the outside is less the transmitter positive 4. The neurotransmitter molecules diffuse across the synapse and bind to receptors Depolarization and generation of an action on the membrane of the next neuron potential. If the stimulus is strong enough, 5. If enough neurotransmitter is released, depolarization causes membrane polarity to be graded potential will be generated completely reversed and an action potential is 6. Eventually an action potential (nerve initiated. impulse) will occur in the neuron beyond the synapse Propagation of the action potential 7. The electrical changes prompted by neurotransmitter binding are brief - If enough sodium enters the cell, the action 8. The neurotransmitter is quickly removed potential (nerve impulse) starts and is from the synapse propagated over the entire axon - Impulses travel faster when fibers have a THE REFLEX ARC myelin sheath Reflex—rapid, predictable, and involuntary Propagation of the action potential. Depolarization response to a stimulus of the first membrane patch causes permeability Occurs over pathways called reflex arcs changes in the adjacent membrane, and the events described in step are repeated. Thus, the action Reflex arc—direct route from a sensory neuron, to potential propagates rapidly along the entire length an interneuron, to an effector of the membrane. Somatic reflexes REGIONS OF THE BRAIN: CEREBRUM - Reflexes that stimulate the skeletal muscles Cerebral Hemispheres (Cerebrum) - Example: pull your hand away from a hot - Paired (left and right) superior parts of the object brain Autonomic reflexes - Includes more than half of the brain mass - The surface is made of ridges (gyri) and - Regulate the activity of smooth muscles, the grooves (sulci) heart, and glands - Example: Regulation of smooth muscles, Lobes of the cerebrum heart and blood pressure, glands, digestive - Fissures (deep grooves) divide the system cerebrum into lobes Five elements of a reflex: - Surface lobes of the cerebrum Frontal lobe Sensory receptor–reacts to a stimulus Parietal lobe Sensory neuron–carries message to the Occipital lobe integration center Temporal lobe Integration center (CNS)–processes information and directs motor output Motor neuron–carries message to an effector Effector organ–is the muscle or gland to be stimulated Specialized areas of the cerebrum Two-neuron reflex arcs - Primary somatic sensory area - Simplest type Receives impulses from the body’s - Example: Patellar (knee-jerk) reflex sensory receptors Three-neuron reflex arcs Located in parietal lobe - Primary motor area - Consists of five elements: receptor, Sends impulses to skeletal muscles sensory neuron, interneuron, motor neuron, Located in frontal lobe and effector - Broca’s area - Example: Flexor (withdrawal) reflex Involved in our ability to speak CENTRAL NERVOUS SYSTEM (CNS) - CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles Four chambers within the brain Cerebral areas involved in special senses Filled with cerebrospinal fluid Gustatory area (taste) Visual area Auditory area Olfactory area Interpretation areas of the cerebrum Speech/language region REGIONS OF THE BRAIN Language comprehension region - Cerebral hemispheres (cerebrum) General interpretation area - Diencephalon Layers of the cerebrum - Brain stem - Cerebellum - Gray matter—outer layer in the cerebral cortex composed mostly of neuron cell bodies - White matter—fiber tracts deep to the gray matter Corpus callosum connects hemispheres - Basal nuclei—islands of gray matter buried within the white matter REGIONS OF THE BRAIN: DIENCEPHALON Reticular Formation - Sits on top of the brain stem - Diffuse mass of gray matter along the brain - Enclosed by the cerebral hemispheres stem - Made of three parts: - Involved in motor control of visceral organs Thalamus - Reticular activating system (RAS) plays a Hypothalamus role in awake/sleep cycles and Epithalamus consciousness Thalamus - Surrounds the third ventricle - The relay station for sensory impulses - Transfers impulses to the correct part of the cortex for localization and interpretation Hypothalamus - Under the thalamus - Important autonomic nervous system center Helps regulate body temperature Controls water balance REGIONS OF THE BRAIN: CEREBELLUM Regulates metabolism - Two hemispheres with convoluted surfaces - Houses the limbic center for emotions - Provides involuntary coordination of body - Regulates the nearby pituitary gland movements Produces two hormones of its own PROTECTION OF THE CENTRAL NERVOUS Epithalamus SYTEM - Forms the roof of the third ventricle - Houses the pineal body (an endocrine gland) - Includes the choroid plexus—forms cerebrospinal fluid REGIONS OF THE BRAIN: BRAIN STEM - Attaches to the spinal cord - Parts of the brain stem Scalp and skin Midbrain Skull and vertebral column Pons Meninges Medulla Oblongata Cerebrospinal fluid (CSF) Blood-brain barrier Midbrain MENINGES - Mostly composed of tracts of nerve fibers Dura mater - Has two bulging fiber tracts— cerebral - Tough outermost layer peduncles - Double-layered external covering - Has four rounded protrusions— corpora Periosteum—attached to inner quadrigemina surface of the skull Reflex centers for vision and hearing Meningeal layer—outer covering of Pons the brain - Folds inward in several areas - The bulging center part of the brain stem Falx cerebri - Mostly composed of fiber tracts Tentorium cerebelli - Includes nuclei involved in the control of breathing Arachnoid layer Medulla oblongata - Middle layer - Web-like extensions span the subarachnoid - The lowest part of the brain stem space - Merges into the spinal cord - Arachnoid villi reabsorb cerebrospinal fluid - Includes important fiber tracts - Contains important control centers Pia mater Heart rate control - Internal layer Blood pressure regulation - Clings to the surface of the brain Breathing Swallowing Vomiting CEREBROSPINAL FLUID (CFS) Cerebrovascular Accident (CVA) or Stroke - Similar to blood plasma composition - Result from a ruptured blood vessel - Formed by the choroid plexus supplying a region of the brain - Choroid plexuses–capillaries in the - Brain tissue supplied with oxygen from that ventricles of the brain blood source dies - Forms a watery cushion to protect the brain - Loss of some functions or death may result - Circulated in arachnoid space, ventricles, Hemiplegia–One-sided paralysis and central canal of the spinal cord Aphasis–Damage to speech center in left hemisphere Cerebrospinal Fluid (CSF) Pathway of Flow - Transischemia-attack (TIA)–temporary 1. CSF is produced by the choroid plexus of brain ischemia -(restriction of blood flow) each ventricle. Warning signs for more serious 2. CSF flows through the ventricles and into CVAs the subarachnoid space via the median and Alzheimer’s Disease lateral apertures. Some CSF flows through the central canal of the spinal cord. - Progressive degenerative brain disease 3. CSF flows through the subarachnoid space. - Mostly seen in the elderly, but may begin in 4. CSF is absorbed into the dural venous middle age sinuses via the arachnoid villi. - Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons - Victims experience memory loss, irritability, confusion, and ultimately, hallucinations and death Hydrocephalus in a Newborn Hydrocephalus SPINAL CORD - CSF accumulates and exerts pressure on - Extends from the foramen magnum of the the brain if not allowed to drain skull to the first or second lumbar vertebra - Possible in an infant because the skull - Provides a two-way conduction pathway bones have not yet fused from the brain to and from the brain - In adults, this situation results in brain - 31 pairs of spinal nerves arise from the damage spinal cord BLOOD-BRAIN BARRIER - Cauda equina is a collection of spinal nerves at the inferior end - Includes the least permeable capillaries of the body - Excludes many potentially harmful substances - Useless as a barrier against some substances Fats and fat soluble molecules Respiratory gases Alcohol Nicotine Anesthesia SPINAL CORD ANATOMY TRAUMATIC BRAIN INJURIES - Internal gray matter is mostly cell bodies Concussion Dorsal (posterior) horns Slight brain injury Anterior (ventral) horns No permanent brain damages Gray matter surrounds the central canal Contusion - Central canal is filled with cerebrospinal - Nervous tissue destruction occurs fluid - Nervous tissue does not regenerate - Exterior white mater—conduction tracts Dorsal, lateral, ventral columns Cerebral edema - Swelling from the inflammatory response - May compress and kill brain tissue -  - Meninges cover the spinal cord - And – Abducens - Spinal nerves leave at the level of each - Feel – Facial vertebrae - Very – Vestibulocochlear - Dorsal root - Green – Glossopharyngeal Associated with the dorsal root - Vegetables – Vagus ganglia—collections of cell bodies - A – Accessory outside the central nervous system- - H – Hypoglossal - Ventral root PNS: CRANIAL NERVES Contains axons - I Olfactory nerve—sensory for smell - II Optic nerve—sensory for vision - III Oculomotor nerve—motor fibers to eye muscles - IV Trochlear—motor fiber to one eye muscle - V Trigeminal nerve—sensory for the face; motor fibers to chewing muscles - VI Abducens nerve—motor fibers to eye muscles - VII Facial nerve—sensory for taste; motor fibers to the face - VIII Vestibulocochlear nerve—sensory for balance and hearing - IX Glossopharyngeal nerve—sensory for taste; motor fibers to the pharynx - X Vagus nerves—sensory and motor fibers PERIPHERAL NERVOUS SYSTEM (PNS) for pharynx, larynx, and viscera - Nerves and ganglia outside the central - XI Accessory nerve—motor fibers to neck nervous system and upper back - Nerve = bundle of neuron fibers - XII Hypoglossal nerve—motor fibers to - Neuron fibers are bundled by connective tongue tissue PNS: SPINAL NERVES PNS: STRUCTURE OF A NERVE - There is a pair of spinal nerves at the level - Endoneurium surrounds each fiber of each vertebrae for a total of 31 pairs - Groups of fibers are bound into fascicles by - Formed by the combination of the ventral perineurium and dorsal roots of the spinal cord - Fascicles are bound together by - Named for the region from which they arise epineurium PNS: CLASSIFICATION OF NERVES Mixed nerves - Both sensory and motor fibers Sensory (afferent) nerves - Carry impulses toward the CNS Motor (efferent) nerves - Carry impulses away from the CNS PNS: CRANIAL NERVES - Twelve pairs of nerves that mostly serve the head and neck - Only the pair of vagus nerves extend to PNS: ANATOMY OF SPINAL NERVES thoracic and abdominal cavities - Spinal nerves divide soon after leaving the - Most are mixed nerves, but three are spinal cord sensory only - Ramus—branch of a spinal nerve; contains PNS: CRANIAL NERVES DEVICE both motor and sensory fibers Dorsal rami—serve the skin and - Oh – Olfactory muscles of the posterior trunk - Oh – Optic Ventral rami—form a complex of - Oh – Oculomotor networks (plexus) for the anterior - To – Trochlear - Touch – Trigeminal PNS: SPINAL NERVE PLEXUSES - Plexus–networks of nerves serving motor and sensory needs of the limbs - Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions - Four plexuses: Cervical Brachial Lumbar Sacral Cervical Plexus - Originates from ventral rami in C1 – C5 - Important nerve is the phrenic nerve - Areas served: Diaphragm PNS: ANATOMY OF THE PARASYMPATHETIC Shoulder and neck DIVISION Brachial Plexus - Preganglionic neurons originate from the craniosacral regions: - Originates from ventral The cranial nerves III, VII, IX, and X rami in C5 – C8 and T1 S2 through S4 regions of the spinal - Important nerves: cord Axillary - Due to site of preganglionic neuron Radial origination, the parasympathetic division is Median also known as the craniosacral division Musculocutaneous - Terminal ganglia are at the effector organs Ulnar - Neurotransmitter: acetylcholine - Areas served: shoulder, arm, forearm, and hand Lumbar Plexus - Originates from ventral rami in L1 through L4 - Important nerves: Femoral Obturator - Areas served: Lower abdomen Anterior and medial thighs Sacral Plexus - Originates from ventral rami in L4 – L5 and S1 – S4 - Important nerves: - Preganglionic neurons originate from T1 Sciatic through L2 Superior and inferior gluteal - Ganglia are at the sympathetic trunk (near - Areas served: the spinal cord) Lower trunk and posterior thigh - Short pre-ganglionic neuron and long Lateral and posterior leg and foot post-ganglionic neuron transmit impulse Gluteal muscles of hip are from CNS to the effector - Neurotransmitters: norepinephrine and PNS: AUTONOMIC NERVOUS SYSTEM epinephrine (effector organs) - Motor subdivision of the PNS PNS: AUTONOMIC FUNCTIONING Consists only of motor nerves - Also known as the involuntary nervous Sympathetic— “fight or flight” system Regulates activities of cardiac and - Response to unusual stimulus smooth muscles and glands - Takes over to increase activities - Two subdivisions - Remember as the “E” division Sympathetic division Exercise, excitement, emergency, and embarrassment Parasympathetic division PNS: DIFFERENCES BETWEEN SOMATIC AND AUTONOMIC NERVOUS SYSTEMS  Lacrimal apparatus Parasympathetic— “housekeeping” activites - Conserves energy - Maintains daily necessary body functions - Remember as the “D” division digestion, defecation, and diuresis EXTERNAL AND ACCESSORY STRUCTURES Eyelids - Meet at the medial and lateral commissure (canthus) Eyelashes - Tarsal glands produce an oily secretion that lubricates the eye DEVELOPMENT ASPECTS OF THE NERVOUS - Ciliary glands are located between the SYSTEM eyelashes - The nervous system is formed during the Conjunctiva first month of embryonic development - Membrane that lines the eyelids and eyeball - Any maternal infection can have extremely - Connects with the transparent cornea harmful effects - Secretes mucus to lubricate the eye and - The hypothalamus is one of the last areas keep it moist of the brain to develop - No more neurons are formed after birth, but Lacrimal apparatus = lacrimal gland + ducts growth and maturation continue for several years Lacrimal gland—produces lacrimal fluid (tears); - The brain reaches maximum weight as a situated on lateral end of each eye young adult - Tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity - Tears contain: Dilute salt solution Mucus Antibodies Lysozyme (enzyme that destroys bacteria) - Function of tears Cleanse, protect, moisten, lubricate SPECIAL SENSES the eye Special senses include: - Smell - Taste - Sight - Hearing - Equilibrium - Special sense receptors - Large, complex sensory organs - Localized clusters of receptors - Extrinsic eye muscles PART 1: THE EYE AND VISION Six muscles attach to the outer - 70 percent of all sensory receptors are in surface of the eye the eyes Produce gross eye movements - Each eye has over 1 million nerve fibers carrying information to the brain - Accessory structures include the: Extrinsic eye muscles Eyelids Conjunctiva  1. Outer pigmented layer absorbs light and prevents it from scattering 2. Inner neural layer contains receptor cells (photoreceptors) Rods Cones - Electrical signals pass from photoreceptors via a two- neuron chain: Bipolar neurons Ganglion cells - Signals leave the retina toward the brain through the optic nerve - Optic disc (blind spot) is where the optic nerve leaves the eyeball Cannot see images focused on the optic disc - Rods Most are found toward the edges of the retina INTERNAL STRUCTURES: THE EYEBALL Allow vision in dim light and - Three layers, or tunics, form the wall of the peripheral vision eyeball All perception is in gray tones Fibrous layer: outside layer Vascular layer: middle layer Sensory layer: inside layer - Humors are fluids that fill the interior of the eyeball - Lens divides the eye into two chambers - Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis–lateral to blind spot ✓ Area of the retina with only cones Fibrous layer = sclera + cornea ✓ Visual acuity (sharpest vision) is here - Sclera No photoreceptor cells are at the White connective tissue layer optic disc, or blind spot Seen anteriorly as the ―” white of - Cone sensitivity the eye” Three types of cones - Cornea Each cone type is sensitive to Transparent, central anterior portion different wavelengths of visible light Allows for light to pass through Repairs itself easily Lens The only human tissue that can be - Flexible, biconvex crystal-like structure transplanted without fear of rejection - Held in place by a suspensory ligament Vascular layer attached to the ciliary body - Lens divides the eye into two chambers - Choroid is a blood-rich nutritive layer that 1. Anterior (aqueous) segment contains a pigment (prevents light from Anterior to the lens scattering) Contains aqueous humor, a Choroid is modified anteriorly into clear, watery fluid two smooth muscle structures 2. Posterior (vitreous) segment - Ciliary body Posterior to the lens - Iris—regulates amount of light entering eye Contains vitreous humor, a Pigmented layer that gives eye color gel-like substance - Pupil—rounded opening Aqueous humor Sensory layer - Watery fluid found between lens and cornea - Retina contains two layers - Similar to blood plasma - Helps maintain intraocular pressure  - Provides nutrients for the lens and cornea Astigmatism - Reabsorbed into venous blood through the - Images are blurry scleral venous sinus, or canal of Schlemm - Results from light focusing as lines, not Vitreous humor points, on the retina because of unequal curvatures of the cornea or lens - Gel-like substance posterior to the lens - Prevents the eye from collapsing PHYSIOLOGY OF VISION - Helps maintain intraocular pressure Eye reflexes Ophthalmoscope - Convergence: reflexive movement of the - Instrument used to illuminate the interior of eyes medially when we focus on a close the eyeball and fundus (posterior wall) object - Can detect diabetes, arteriosclerosis, - Photopupillary reflex: bright light causes degeneration of the optic nerve and retina pupils to constrict - Accommodation pupillary reflex: viewing close objects causes pupils to constrict PHYSIOLOGY OF VISION PART II: THE EAR: HEARING AND BALANCE - Pathway of light through the eye and light - Ear houses two senses: refraction Hearing - Light must be focused to a point on the Equilibrium (balance) retina for optimal vision - Receptors are mechanoreceptors - Light is bent, or refracted, by the cornea, - Different organs house receptors for each aqueous humor, lens, and vitreous humor sense - The eye is set for distant vision (over 20 feet - The ear is divided into three areas: away) External (outer) ear - Accommodation—the lens must change Middle ear shape to focus on closer objects (less than 20 feet away) Internal (inner) ear - Pathway of light through the eye and light refraction (continued) Image formed on the retina is a real image Real images are: ✓ Reversed from left to right ✓ Upside down ✓ Smaller than the object Summary of the pathway of impulses from the retina to the point of visual interpretation 1. Optic nerve 2. Optic chiasma 3. Optic tract 4. Thalamus 5. Optic radiation 6. Optic cortex in occipital lobe of brain ANATOMY OF THE EAR External (outer) ear A CLOSER LOOK - Auricle (pinna) - External acoustic meatus (auditory canal) Emmetropia – eye focuses images Narrow chamber in the temporal correctly on the retina bone Lined with skin and ceruminous Myopia (nearsightedness) (earwax) glands - Distant objects appear blurry Ends at the tympanic membrane - Light from those objects fails to reach the (eardrum) retina and are focused in front of it - External ear is involved only in collecting - Results from an eyeball that is too long sound waves Hyperopia (farsightedness) Middle ear cavity (tympanic cavity) - Near objects are blurry, whereas distant - Air-filled, mucosa-lined cavity within the objects are clear temporal bone - Distant objects are focused behind the - Involved only in the sense of hearing retina - Located between tympanic membrane and - Results from an eyeball that is too short or oval window and round window from a ―”lazy lens” - Pharyngotympanic tube (auditory tube)  Links middle ear cavity with the - Hair cells are stimulated, and the impulse throat travels the vestibular nerve to the Equalizes pressure in the middle ear cerebellum cavity so the eardrum can vibrate HEARING - Three bones (ossicles) span the cavity Malleus (hammer) Spiral organ of Corti Incus (anvil) - Located within the cochlear duct Stapes (stirrup) - Receptors = hair cells on the basilar - Function membrane Transmit vibrations from tympanic - Gel-like tectorial membrane is capable of membrane to the fluids of the inner bending hair cells ear - Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Vibrations travel from the hammer → anvil → stirrup → oval window of inner ear - Internal (inner) ear Includes sense organs for hearing and balance Bony labyrinth (osseous labyrinth) consists of: ✓ Cochlea ✓ Vestibule ✓ Semicircular canals Bony labyrinth is filled with perilymph Membranous labyrinth is suspended in perilymph and contains endolymph EQUILIBRIUM Pathway of vibrations from sound waves - Equilibrium receptors of the inner ear are - Move by the ossicles from the eardrum to called the vestibular apparatus the oval window - Vestibular apparatus has two functional - Sound is amplified by the ossicles parts - Pressure waves cause vibrations in the Static equilibrium basilar membrane in the spiral organ of Dynamic equilibrium Corti - Hair cells of the tectorial membrane are STATIC EQUILIBRIUM bent when the basilar membrane vibrates Maculae—receptors in the vestibule against it - An action potential starts in the cochlear - Report on the position of the head nerve (cranial nerve VIII), and the impulse - Help us keep our head erect travels to the temporal lobe - Send information via the vestibular nerve - High-pitched sounds disturb the short, stiff (division of cranial nerve VIII) to the fibers of the basilar membrane cerebellum of the brain Receptor cells close to the oval window are stimulated Anatomy of the maculae - Low-pitched sounds disturb the long, floppy - Hair cells are embedded in the fibers of the basilar membrane otolithic membrane Specific hair cells further along the - (tiny stones) float in a gel around cochlea are affected hair cells PART III: CHEMICAL SENSES: SMELL - Movements cause otoliths to roll AND TASTE and bend hair cells - Chemoreceptors DYNAMIC EQUILIBRIUM Stimulated by chemicals in solution Crista ampullaris Taste has five types of receptors Smell can differentiate a wider range - Responds to angular or rotational of chemicals movements of the head Both senses complement each other - Located in the ampulla of each semicircular and respond to many of the same canal stimuli - Tuft of hair cells covered with cupula (gelatinous cap) OLFACTORY RECEPTORS AND THE SENSE OF - If the head moves, the cupula drags against SMELL the endolymph  - Olfactory receptors are in roof of nasal Five basic taste sensations cavity - Sweet receptors respond to sugars, Olfactory receptor cells (neurons) saccharine, some amino acids with long cilia known as olfactory - Sour receptors respond to H+ ions or acids hairs detect chemicals - Bitter receptors respond to alkaloids Chemicals must be dissolved in - Salty receptors respond to metal ions mucus for detection by - Umami receptors respond to the amino acid chemoreceptors called olfactory glutamate or the beefy taste of meat receptors - Impulses are transmitted via the olfactory filaments to the olfactory nerve (cranial nerve I) - Smells are interpreted in the olfactory cortex PART VI: DEVELOPMENTAL ASPECTS OF THE SPECIAL SENSES - Special sense organs are formed early in embryonic development - - Maternal infections during the first 5 or 6 weeks of pregnancy may cause visual abnormalities as well as sensorineural deafness in the developing child - Vision requires the most learning - The infant has poor visual acuity (is farsighted) - and lacks color vision and depth perception TASTE BUDS AND THE SENSE OF TASTE at Taste buds house the receptor organs birth - The eye continues to grow and mature until - Locations of taste buds age Most are on the tongue 8 or 9 Soft palate Age-related eye issues Superior part of the pharynx Cheeks - Presbyopia—―old vision‖ results from - The tongue is covered with projections decreasing lens elasticity that accompanies called papillae that contain taste buds aging Vallate (circumvallate) papillae Causes difficulty to focus for close Fungiform papillae vision Filiform papillae - Lacrimal glands become less active - Gustatory cells are the taste receptors - Lens becomes discolored Possess gustatory hairs (long - Dilator muscles of iris become less efficient, microvilli) causing pupils to remain constricted Gustatory hairs protrude through a - The newborn infant can hear sounds, but taste pore initial Hairs are stimulated by chemicals responses are reflexive dissolved in saliva - By the toddler stage, the child is listening critically and beginning to imitate sounds as language development begins Age-related ear problems - Presbycusis—type of sensorineural deafness that may result from otosclerosis - Otosclerosis—ear ossicles fuse - Congenital ear problems usually result from missing pinnas and closed or missing external acoustic meatuses - Impulses are carried to the gustatory - Taste and smell are most acute at birth and complex by several cranial nerves because decrease in sensitivity after age 40 as the taste buds are found in different areas number of olfactory and gustatory receptors Facial nerve (cranial nerve VII) decreases Glossopharyngeal nerve (cranial nerve IX) Vagus nerve (cranial nerve X) - Taste buds are replaced frequently by basal cells THE SKELETAL SYSTEM - Example: Carpals Parts of the skeletal system Tarsals Bones (skeleton) Flat bones Joints Cartilages - Thin, flattened, and usually curved Ligaments - Two thin layers of compact bone surround a layer of spongy bone Two subdivisions of the skeleton - Example: Axial skeleton Skull Appendicular skeleton Ribs Sternum FUNCTIONS OF BONES Irregular bones - Support the body - Protect soft organs - Irregular shape Skull and vertebrae for brain and - Do not fit into other bone classification spinal cord categories Rib cage for thoracic cavity organs - Example: - Allow movement due to attached skeletal Vertebrae muscles Hip bones - Store minerals and fats ANATOMY OF A LONG BONE Calcium and phosphorus Fat in the internal marrow cavity Diaphysis - Blood cell formation (hematopoiesis) - Shaft BONES OF THE HUMAN BODY - Composed of compact bone - The adult skeleton has 206 bones Epiphysis - Two basic types of bone tissue - Ends of the bone Compact bone - Composed mostly of spongy bone -Homogeneous Spongy bone Periosteum - Small needle-like pieces of bone - Outside covering of the diaphysis - Many open spaces - Fibrous connective tissue membrane Perforating (Sharpey’s) fibers - Secure periosteum to underlying bone CLASSIFICATION OF BONES ON THE BASIS Arteries OF SHAPE - Supply bone cells with nutrients Bones are classified as: Articular cartilage Long Short - Covers the external Flat surface of the Irregular epiphyses - Made of hyaline Cartilage CLASSIFICATION OF BONES - Decreases friction at joint surfaces Long bones - Typically longer than they are wide - Shaft with heads situated at both ends - Contain mostly compact bone - All of the bones of the limbs (except wrist, - ankle, and kneecap bones) - Example: Femur Epiphyseal plate Humerus Flat plate of hyaline cartilage seen in young, Short bones growing bone - Generally cube-shaped Epiphyseal line - Contain mostly spongy bone - Includes bones of the wrist and ankle Remnant of the epiphyseal plate - Sesamoid bones are a type of short bone Seen in adult bones which form within tendons (patella) Marrow (medullary) cavity  Cavity inside of the shaft - During development, much of this cartilage Contains yellow marrow (mostly fat) in is replaced by bone adults - Cartilage remains in isolated areas Contains red marrow for blood cell Bridge of the nose formation in infants Parts of ribs In adults, red marrow is situated in cavities Joints of spongy bone and epiphyses of some long BONE GROWTH (OSSIFICATION) bones Epiphyseal plates allow for lengthwise growth BONE MARKINGS of long bones during childhood - Surface features of bones - New cartilage is continuously formed Sites of attachments for muscles, - Older cartilage becomes ossified tendons, and ligaments Cartilage is broken down Passages for nerves and blood Enclosed cartilage is digested away, vessels opening up a medullary cavity - Categories of bone markings Bone replaces cartilage through the Projections or processes—grow out action of osteoblasts from the bone surface Terms often begin with “T” Bones are remodeled and lengthened until Depressions or cavities— growth stops indentations Terms often begin with “F” - Bones are remodeled in response to two factors MICROSCOPIC ANATOMY OF COMPACT BONE Blood calcium levels Osteon (Haversian system) Pull of gravity and muscles on the skeleton - A unit of bone containing central canal and matrix rings Bones grow in width (called appositional growth) Central (Haversian) canal - Opening in the center of an osteon - Carries blood vessels and nerves Perforating (Volkmann’s) canal - Canal perpendicular to the central canal - Carries blood vessels and nerves MICROSCOPIC ANATOMY OF BONE Lacunae - Cavities containing bone cells (osteocytes) - Arranged in concentric rings called lamellae Lamellae - Rings around the central canal - Sites of lacunae Canaliculi TYPES OF BONE CELLS - Tiny canals - Osteocytes—mature bone cells - Radiate from the central canal to lacunae - Osteoblasts—bone-forming cells - Form a transport system connecting all - Osteoclasts—giant bone-destroying cells bone cells to a nutrient supply Break down bone matrix for remodeling and release of calcium in FORMATION OF THE HUMAN SKELETON response to parathyroid hormone - Bone remodeling is performed by both - In embryos, the skeleton is primarily hyaline osteoblasts and osteoclasts cartilage BONE FRACTURES THE SKULL Fracture—break in a bone - Two sets of bones Cranium Types of bone fractures Facial bones - Closed (simple) fracture—break that does - Bones are joined by sutures not penetrate the skin - Only the mandible is attached by a freely - Open (compound) fracture—broken bone movable joint penetrates through the skin Bone fractures are treated by reduction and immobilization COMMON TYPES OF FRACTURES - Comminuted—bone breaks into many fragments - Compression—bone is crushed - Depressed—broken bone portion is pressed inward - - Impacted—broken bone ends are forced into each other - Spiral—ragged break occurs when excessive twisting forces are applied to a bone - Greenstick—bone breaks incompletely REPAIR OF BONE FRACTURES - Hematoma (blood-filled swelling) is formed - Break is splinted by fibrocartilage to form a callus - Fibrocartilage callus is replaced by a bony callus - Bony callus is remodeled to form a permanent patch THE AXIAL SKELETON - Forms the longitudinal axis of the body - Divided into three parts Skull Vertebral column Bony thorax  - Primary curvatures are the spinal curvatures of the thoracic and sacral regions PARANASAL SINUSES Present from birth - Hollow portions of bones surrounding the Form a C-shaped curvature as in nasal cavity newborns - Functions of paranasal sinuses - Secondary curvatures are the spinal Lighten the skull curvatures of the cervical and lumbar Give resonance and amplification to regions voice Develop after birth Form an S-shaped curvature as in adults THE HYOID BONE A TYPICAL VERTEBRAE - The only bone that does not articulate with Body another bone Vertebral arch - Serves as a moveable base for the tongue - Pedicle - Aids in swallowing and speech - Lamina Vertebral foramen Transverse processes THE FETAL SKULL Spinous process - The fetal skull is large compared to the Superior and inferior articular infant’s total body length processes Fetal skull is 1/4 body length SACRUM AND COCCYX compared to adult skull which is 1/8 body length Sacrum - Fontanels—fibrous membranes connecting - Formed by the fusion the cranial bones of five vertebrae Allow skull compression during birth Allow the brain to grow during later Coccyx pregnancy and infancy - Formed from the fusion of Convert to bone within 24 months after birth three to five vertebrae - “Tailbone,” or remnant of a tail that other vertebrates have THE BONY THORAX - Forms a cage to protect major organs - Consists of three parts Sternum THE VERTEBRAL COLUMN Ribs -True ribs (pairs 1–7) - Each vertebrae is given a name according - False ribs (pairs 8–12) to its location - Floating ribs (pairs 11–12) - There are 24 single vertebral bones - Thoracic vertebrae separated by intervertebral discs Seven cervical vertebrae are in the THE APPENDICULAR SKELETON neck - Composed of 126 bones Twelve thoracic vertebrae are in the Limbs (appendages) chest region Pectoral girdle Five lumbar vertebrae are Pelvic girdle associated with the lower back Nine vertebrae fuse to form two THE PECTORAL (SHOULDER) GIRDLE composite bones(Sacrum and Coccyx) - Composed of two bones Clavicle—collarbone -Articulates with the sternum medially and with the scapula laterally Scapula—shoulder blade - Articulates with the clavicle at the acromioclavicular joint - Articulates with the arm bone at the glenoid cavity - These bones allow the upper limb to have exceptionally free movement  BONES OF THE PELVIC GIRDLE BONES OF THE UPPER LIMB - Formed by two coxal (ossa coxae) bones - Composed of three pairs of fused bones - Humerus Ilium Forms the arm Ischium Single bone Pubis Proximal end articulation - Pelvic girdle = 2 coxal bones, sacrum -Head articulates with the glenoid - Bony pelvis = 2 coxal bones, sacrum, cavity of the scapula coccyx - Distal end articulation - The total weight of the upper body rests on Trochlea and capitulum articulate the with the bones of the forearm Pelvis - It protects several organs Reproductive organs Urinary bladder Part of the large intestine The forearm has two bones - Ulna—medial bone in anatomical position Proximal end articulation Coronoid process and olecranon articulate with the humerus - Radius—lateral bone in anatomical position Proximal end articulation Head articulates with the capitulum of the humerus BONES OF THE UPPER LIMBS Hand - Carpals—wrist Eight bones arranged in two rows of four bones in each hand GENDER DIFFERENCES OF THE PELVIS Metacarpals—palm - The female inlet is larger and more circular - Five per hand - The female pelvis as a whole is shallower, and the bones are lighter and thinner Phalanges—fingers and - The female ilia flare more laterally thumb - The female sacrum is shorter and less curved - Fourteen phalanges - The female ischial spines are shorter and in each hand farther apart; thus the outlet is larger - In each finger, there - The female pubic arch is more rounded are three bones because the angle of the pubic arch is - In the thumb, there are only two bones greater BONES OF THE LOWER LIMB Femur—thigh bone STRUCTURAL CLASSIFICATION OF JOINTS - The heaviest, strongest bone in the body Fibrous joints - Generally immovable - Proximal end articulation Cartilaginous joints - Immovable or slightly Head articulates with the moveable acetabulum of the coxal (hip) bone Synovial joints - Freely moveable Distal end articulation FIBROUS JOINTS - Lateral and medial condyles articulate with the tibia in the lower leg - Bones united by collagenic fibers - Types The lower leg has two bones Sutures – Immobile - Tibia—Shinbone; larger and medially Syndesmoses - Allows more oriented movement than sutures but still Proximal end articulation immobile Medial and lateral condyles Example: Distal end of tibia and articulate with the femur to form the fibula knee joint Gomphosis – Immobile - Fibula—Thin and sticklike; lateral to the CARTILAGINOUS JOINTS tibia Has no role in forming the knee joint - Bones connected by cartilage - Types The foot Synchrondrosis – Immobile - Tarsals—seven Symphysis - Slightly movable bones Example: Pubic symphysis, Two largest tarsals intervertebral joints - Calcaneus (heel bone) SYNOVIAL JOINTS - Talus - Metatarsals—five - Articulating bones are separated by a joint bones form the sole of the cavity - foot - Synovial fluid is found in the joint cavity - Phalanges—fourteen bones form the toes ARCHES OF THE FOOT - Bones of the foot are arranged to form three FEATURES OF SYNOVIAL JOINTS strong arches Two longitudinal - Articular cartilage (hyaline cartilage) covers One transverse the ends of bones - Articular capsule encloses joint surfaces and lined with synovial membrane - Joint cavity is filled with synovial fluid JOINTS - Reinforcing ligaments - Articulations of bones STRUCTURES ASSOCIATED WITH THE - Functions of joints SYNOVIAL JOINT Hold bones together - Bursae—flattened fibrous sacs Allow for mobility Lined with synovial membranes - Two ways joints are classified Filled with synovial fluid Functionally Not actually part of the joint Structurally - Tendon sheath FUNCTIONAL CLASSIFICATION OF JOINTS Elongated bursa that wraps around a tendon Synarthroses - Immovable joints Amphiarthroses - Slightly moveable joints Diarthroses - Freely moveable joints INFLAMMATORY CONDITIONS - 8 or 9 years old—skull is near adult size and proportion ASSOCIATED WITH JOINTS - Between ages 6 and 11, the face grows out - Bursitis—inflammation of a bursa usually from the skull caused by a blow or friction - Tendonitis—inflammation of tendon sheaths - Arthritis—inflammatory or degenerative diseases of joints Over 100 different types Curvatures of the spine The most widespread crippling disease in the United States - Primary curvatures are present at birth and Initial symptoms: pain, stiffness, are convex posteriorly swelling of the joint - Secondary curvatures are associated with a child’s later development and are convex CLINICAL FORMS OF ARTHRITIS anteriorly - Abnormal spinal curvatures (scoliosis and Osteoarthritis lordosis) are often congenital - Most common chronic arthritis Osteoporosis - Probably related to normal aging processes - Bone-thinning disease afflicting Rheumatoid arthritis 50 percent of women over age 65 - An autoimmune disease—the immune 20 percent of men over age 70 system attacks the joints - Disease makes bones fragile and bones - Symptoms begin with bilateral inflammation can easily fracture of certain joints - Vertebral collapse results in kyphosis (also - Often leads to deformities known as dowager’s hump) - Estrogen aids in health and normal density Gouty arthritis of a female skeleton - Inflammation of joints is caused by a deposition of uric acid crystals from the blood - Can usually be controlled with diet - More common in men DEVELOPMENTAL ASPECTS OF THE SKELETAL SYSTEM - At birth, the skull bones are incomplete - Bones are joined by fibrous membranes called fontanels - Fontanels are completely replaced with bone within two years after birth SKELETAL CHANGES THROUGHOUT LIFE Fetus - Long bones are formed of hyaline cartilage - Flat bones begin as fibrous membranes - Flat and long bone models are converted to bone Birth - Fontanels remain until around age 2 Adolescence - Epiphyseal plates become ossified and long bone growth ends Size of cranium in relationship to body - 2 years old—skull is larger in proportion to the body compared to that of an adult THE MUSCULAR SYSTEM Endomysium—encloses a single muscle fiber - Muscles are responsible for all Perimysium—wraps around a types of body movement fascicle (bundle) of muscle fibers - Three basic muscle types are Epimysium—covers the entire found in the body skeletal muscle Skeletal muscle Fascia—on the outside of the Cardiac muscle epimysium Smooth muscle SKELETAL MUSCLE ATTACHMENTS CHARACTERISTICS OF MUSCLES - Epimysium blends into a connective tissue - Skeletal and smooth muscle cells are attachment elongated (muscle cell = muscle fiber) Tendons—cord-like structures - Contraction and shortening of muscles is - Mostly collagen fibers due to the movement of microfilaments - Often cross a joint due to - All muscles share some terminology toughness and small size Prefixes myo and mys refer to Aponeuroses—sheet-like structures “muscle” -Attach muscles indirectly to bones, Prefix sarco refers to “flesh” cartilages, or connective tissue coverings - Sites of muscle attachment Bones Cartilages Connective tissue coverings SMOOTH MUSCLE CHARACTERISTICS COMPARISON OF SKELETAL, CARDIAC, AND SMOOTH MUSCLES - Lacks striations - Spindle-shaped cells - Single nucleus - Involuntary—no conscious control - Found mainly in the walls of hollow organs CARDIAC MUSCLE CHARACTERISTICS - Striations - Usually has a single nucleus - Branching cells - Joined to another muscle cell at an intercalated disc - Involuntary - Found only in the walls of the heart SKELETAL MUSCLE FUNCTION - Produce movement - Maintain posture - Stabilize joints - Generate heat MICROSCOPIC ANATOMY OF SKELETAL MUSCLE - Sarcolemma—specialized plasma membrane SKELETAL MUSCLE CHARACTERISTICS - Myofibrils—long organelles inside muscle cell - Most are attached by tendons to bones - Sarcoplasmic reticulum—specialized - Cells are multinucleate smooth endoplasmic reticulum - Striated—have visible banding - Voluntary—subject to conscious control CONNECTIVE TISSUE WRAPPING OF SKELETAL MUSCLE - Cells are surrounded and bundled by connective tissue - Myofibrils are aligned to give distinct bands  I band = light band THE NERVE STIMULUS AND ACTION -Contains only thin filaments POTENTIAL A band = dark band - Skeletal muscles must be stimulated by a -Contains the entire length of motor neuron (nerve cell) to contract the thick filaments - Motor unit—one motor neuron and all the skeletal muscle cells stimulated by that neuron - Sarcomere—contractile unit of a muscle fiber - Organization of the sarcomere - Myofilaments Thick filaments = myosin filaments Thin filaments = actin filaments Thick filaments = myosin filaments Neuromuscular junction - Composed of the protein myosin - Association site of axon terminal of the - Has ATPase enzymes motor neuron and muscle - Myosin filaments have heads (extensions, or cross bridges) - Myosin and actin overlap somewhat Thin filaments = actin filaments - Composed of the protein actin - Anchored to the Z disc Synaptic cleft - Gap between nerve and muscle - Nerve and muscle do not make contact - Area between nerve and muscle is filled with interstitial fluid - At rest, within the A band there is a zone that lacks actin filaments Action potential reaches the axon terminal of Called either the H zone or bare the motor neuron zone - Sarcoplasmic reticulum (SR) Calcium channels open and calcium ions enter the axon terminal Stores and releases calcium Surrounds the myofibril TRANSMISSION OF NERVE IMPULSE TO MUSCLE - Calcium ion entry causes some synaptic vesicles to release their contents (acetylcholine, a neurotransmitter) by exocytosis - Neurotransmitter—chemical released by nerve upon arrival of nerve impulse in the axon terminal STIMULATION AND CONTRACTION OF SINGLE - The neurotransmitter for skeletal muscle is SKELETAL MUSCLE CELLS acetylcholine (ACh) - Acetylcholine attaches to receptors on the - Excitability (also called responsiveness or sarcolemma of the muscle cell irritability)—ability to receive and respond to a stimulus - In response to the binding of ACh to a - Contractility—ability to shorten when an receptor, the sarcolemma becomes adequate stimulus is received permeable to sodium (Na+) - Extensibility—ability of muscle cells to be - Sodium rushes into the cell generating an stretched action potential and potassium leaves the - Elasticity—ability to recoil and resume cell resting length after stretching - Once started, muscle contraction cannot be Stopped  TYPES OF GRADES RESPONSES Twitch - Single, brief contraction - Not a normal muscle function Summing of contractions - One contraction is immediately followed by another - The muscle does not completely return to a resting state due to more frequent stimulations - The effects are added Unfused (incomplete) tetanus - Some relaxation occurs between contractions but nerve stimuli arrive THE SLIDING FILAMENT THEORY OF MUSCLE at an even faster rate than during summing CONTRACTION of contractions - Unless the muscle contraction is smooth - Activation by nerve causes myosin heads and sustained, it is said to be in unfused (cross bridges) to attach to binding