A&P1 Exam 4 Notes - Professor Amatuli PDF

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Anatomy & Physiology 1 – Exam 4 Notes Chapter 13: The Peripheral Nervous System – Part 1: -*KNOW THE NAME, NUMBER, AND FUNCTION OF ALL 12 CRANIAL NERVES* Peripheral Nervous System (PNS): - Provides links from and to world outside body - All neural structures outside brain - Sensory receptors - Peripheral nerves and associated ganglia - Efferent motor endings

From Sensation to Perception: -Survival depends upon sensation and perception - Sensation = the awareness of changes in the internal and external environment - Perception = the conscious interpretation of those stimuli Sensory Integration: -Somatosensory system  part of sensory system serving body wall and limbs - Receives inputs from: - Exteroceptors, proprioceptors, and interoceptors - Input relayed toward head, but processed along way - Levels of neural integration in sensory systems: 1. Receptor level  sensory receptors 2. Circuit level  processing in ascending pathways 3. Perceptual level  processing in cortical sensory areas Sensory Receptors: -Specialized to respond to changes in environment (stimuli) - Activation results in graded potentials that trigger nerve impulses - Sensation (awareness of stimulus) and perception (interpretation of meaning of stimulus) occur in brain

Classification of Receptors: -Based on: 1. Type of stimulus they detect: - Classification of Stimulus Type: 1. Mechanoreceptors – respond to touch, pressure, vibration, and stretch 2. Thermoreceptors – sensitive to changes in temperature - Cold receptors (10-40 degrees Celsius); in superficial dermis - Heat receptors ( 32-48 degrees Celsius); in deeper dermis - Outside of those temperature ranges, nociceptors are activated  pain 3. Photoreceptors – respond to light energy (ex: retina) 4. Chemoreceptors – respond to chemicals (ex: smell, taste, changes in blood chemistry) 5. Nociceptors – sensitive to pain-causing stimuli (ex: extreme heat or cold, excessive pressure, inflammatory chemicals) - Player in detection – vanilloid receptor - Ion channel opened by heat, low pH, chemicals, ex: capsaicin (red peppers) - Respond to pinching, chemicals from damaged tissue, capsaicin 2. Location in body - Classification by Location: 1. Exteroceptors - Respond to stimuli arising outside body - Receptors in skin for touch, pressure, pain, and temperature - Most special sense organs 2. Interoceptors (visceroceptors) - Respond to stimuli arising in internal viscera and blood vessels - Sensitive to chemical changes, tissue stretch, and temperature changes - Sometimes cause discomfort, but usually unaware of their workings - ex: visceral organs, blood vessels, hunger/thirst 3. Proprioceptors - Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles - Inform brain of one’s movements - Restricted location; help make sure we don’t overstretch 3. Structural complexity - Classification by Receptor Structure: 1. Simple receptors for general senses - Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense

- Modified dendritic endings of sensory neurons - Either nonencapsulated (free) or encapsulated 1. Nonencapsulated (free) nerve endings: - Abundant in epithelia and connective tissues - Most are nonmyelinated, small-diameter, group C fibers; distal ending have knoblike swellings - Respond mostly to temperature and pain; some to pressure-induced tissue movement; itch - Ex: Nociceptors; light touch receptors (Tactile/Merkel discs and hair follicle receptors) 2. Encapsulated Dendritic Endings - ~All mechanoreceptors in connective tissue capsule - Tactile (Meissner’s) corpuscles – discriminative touch - Lamellar (Pacinian) corpuscles – deep pressure and vibration - Bulbous corpuscles (Ruffini endings) – deep continuous pressure - Muscle spindles – muscle stretch - Tendon organs – stretch in tendons - Joint kinesthetic receptors – joint position and motion 2. Receptors for special senses - Vision, hearing, equilibrium, smell, and taste Cranial Nerves: -12 pairs of nerves associated with brain - 2 attach to forebrain; rest with brain stem - Most mixed nerves; two pairs purely sensory - Each numbered (I through XII) and named from rostral to caudal I: The Olfactory Nerves: -Sensory nerves of smell - Run from nasal mucosa to olfactory bulbs - Pass through cribriform plate of ethmoid bone - Purely sensory (olfactory) function

II: The Optic Nerves: -Arise from the retinas; really a brain tract - Pass through optic canals, converge, and partially cross over at optic chiasma - Optic tracts continue to thalamus, where they synapse - Purely sensory (visual) function

III: The Oculomotor Nerves: -Fibers extend from ventral midbrain through superior orbital fissures to four of six extrinsic eye muscles - Function in raising eyelid, directing eyeball, constricting iris (parasympathetic), and controlling lens shape - Motor function

IV: The Trochlear Nerves: -Fibers from dorsal midbrain enter orbits via superior orbital fissures to innervate superior oblique muscle - Primarily motor nerve that directs eyeball

V. The Trigeminal Nerves: - Largest cranial nerves; fibers extend from pons to face - 3 Divisions: 1. Ophthalmic (V1) passes through superior orbital fissure 2. Maxillary (V2) passes through foramen rotundum 3. Mandibular (V3) passes through the foramen ovale - Convey sensory impulses from various areas of face (V1) and (V2) - Supply motor fibers (V3) for mastification

VI: The Abducens Nerves: -Fibers from inferior pons enter orbits via superior orbital fissures - Primarily a motor nerve, innervating lateral rectus muscle

VII: The Facial Nerves: -Fibers from pons travel through internal acoustic meatuses, and emerge through stylomastoid foramina to lateral aspect of face - Chief motor nerves of face with 5 major branches - Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands - Sensory function (taste) from anterior two-thirds of tongue

VIII: The Vestibulocochlear Nerves: -Afferent fibers from hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from inner ear through internal acoustic meatuses, and enter brain stem at ponsmedulla border - Mostly sensory function; small motor component for adjustment of sensitivity of receptors - Formerly called auditory nerve

IX: The Glossopharyngeal Nerves: -Fibers from medulla leave skull via jugular foramen and run to throat - Motor functions  innervate part of tongue and pharynx for swallowing, and provide parasympathetic fibers to parotid salivary glands

- Sensory functions  fibers conduct taste and general sensory impulses form pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors

X: The Vagus Nerves: -Only cranial nerves that extend beyond head and neck region - Fibers from medulla exit skull via jugular foramen - Most motor fibers are parasympathetic fibers that help regulate activities of heart, lungs, and abdominal viscera - Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

XI: The Accessory Nerves: -Formed from ventral rootlets from C1-C5 region of spinal cord (not brain) - Rootlets pass into cranium via each foramen magnum - Accessory nerves exit skull via jugular foramina to innervate trapezius and sternocleidomastoid muscles - Formerly called spinal accessory nerve

XII: The Hypoglossal Nerves: -Fibers from medulla exit skull via hypoglossal canal - Innervate extrinsic and intrinsic muscles of tongue that contribute to swallowing and speech

Chapter 13: The Peripheral Nervous System – Part 2: Reflex and Senses: Reflexes: -Functional classification: 1. Somatic Reflexes  activate skeletal muscle 2. Autonomic (Visceral) Reflexes  activate visceral effectors (smooth or cardiac muscle or glands) - Can be in-born or learned - Can override a somatic reflex Spinal Reflexes: -Spinal somatic reflexes - Integration center in the spinal cord - Effectors are skeletal muscle - Testing of somatic reflexes important clinically to assess condition of nervous system

- If exaggerated, distorted, or absent  degeneration/pathology of specific nervous system regions Stretch and Tendon Reflexes: -To smoothly coordinate skeletal muscle, nervous system must receive proprioceptor input regarding: 1. Length of muscle spindles - Muscle Spindles: - Excited in 2 ways: 1. External stretch of muscle and muscle spindle 2. Internal stretch of muscle spindle - Activating motor neurons stimulates ends to contract, thereby stretching spindle - Stretch causes increased rate of impulses to spinal cord 2. Amount of tension in muscle - From tendon organs

The Stretch Reflex: -Maintains muscle tone in large postural muscles, and adjusts it reflexively - Makes sure muscle length and tone stay in tact - Causes muscle contraction in response to increased muscle length (stretch) - How it works: 1. Stretch activates muscle spindle 2. Sensory neurons synapse directly with  motor neurons in spinal cord 3.  motor neurons cause stretched muscle to contract - All stretch reflexes are monosynaptic and ipsilateral - Reciprocal inhibition also occurs – Ila fibers synapse with interneurons that inhibit  motor neurons of antagonistic muscles - ex: in patellar reflex, stretched muscle (quadriceps) contracts and antagonists (hamstrings) relax - Positive reflex reactions indicate: - Sensory and motor connections between muscle and spinal cord intact

- Strength of response indicates degree of spinal cord excitability - Hypoactive or absent if peripheral nerve damage or ventral horn injury - Hyperactive if lesions of corticospinal tract

The Tendon Reflex: -Produces muscle relaxation (lengthening) in response to tension - Contraction or passive stretch activates tendon reflex - Afferent impulses transmitted to spinal cord - Contracting muscle relaxes; antagonist contracts (reciprocal activation) - Information transmitted simultaneously to cerebellum and used to adjust muscle tension The Flexor and Crossed-Extensor Reflexes: -Flexor (withdrawal) reflex: - Initiated by painful stimulus - Causes automatic withdrawal of threatened body part - Ipsilateral and polysynaptic - Protective; important - Brain can override - ex: finger stick for blood test - Crossed-extensor reflex: - Occurs with flexor reflexes in weight-bearing limbs to maintain balance - Consists of ipsilateral withdrawal reflex and contralateral extensor reflex - Stimulated side withdrawn (flexed) - Contralateral side extended - ex: step barefoot on broken glass

Superficial Reflexes: -Elicited by gentle cutaneous stimulation - Depends on upper motor pathways and cord-level reflex arcs - Best known: - Plantar reflex: - Test of integrity of cord from L4 through S2 - Stimulus = stroke lateral aspect of sole of foot - Response = downward flexion of toes - Damage to motor cortex or corticospinal tracts  abnormal response = Babinski’s sign - Hallus dorsiflexes; other digits fan laterally - Normal in infant to ~1 year due to incomplete myelination - Abdominal reflex - Test integrity of cord from T8 through T12 - Causes contraction of abdominal muscles and movement of umbilicus in response to stroking of skin - Vary in intensity from one person to another - Absent when corticospinal tract lesions present Special Senses: -Special sensory receptors - Distinct, localized receptor cells in head - Vision - Taste - Hearing - Equilibrium The Eye and Vision: -70% of body’s sensory receptors are in the eye - Visual processing by ~ half cerebral cortex - Most of eye protected by cushion of fat and body orbit

Accessory Structures of the Eye: - Eyebrows - Eyelids (palpebrae) - Conjunctiva - Lacrimal apparatus - Extrinsic eye muscles

Structure of the Eyeball: -Wall of eyeball contains 3 layers: 1. Fibrous: - Outermost layer; dense avascular connective tissue - Two regions: 1. Sclera - Opaque posterior region - Protects, shapes eyeball; anchors extrinsic eye muscles - Continuous with dura mater of brain posteriorly 2. Cornea - Transparent anterior 1/6 of fibrous layer - Bends light as it enters eye - Sodium pumps of corneal endothelium on inner face help maintain clarity of cornea - Numerous pain receptors contribute to blinking and tearing reflexes - “Window” that light enters; first place light bends - Regenerates self quickly - Can be transplanted between people without being rejected because no access to immune system 2. Vascular: - Uvea - Middle pigmented layer - Three regions: 1. Choroid region - Posterior portion of uvea

- Supplies blood to all layers of eyeball - Brown pigment absorbs light to prevent light scattering and visual confusion - Serves everything in sclera and retina; nutrients to all 3 regions - Brown pigment = melanocytes 2. Ciliary body: - Ring of tissue surrounding lens - Smooth muscle bundles (ciliary muscles) control lens shape - Capillaries of ciliary processes secrete fluid - Ciliary zonule (suspensory ligament) holds lens in position 3. Iris: - Colored part of eye - Pupil = central opening that regulates amount of light entering eye - Close vision and bright light sphincter pupillae (circular muscles) contract; pupils constrict - Distant vision and dim light dilator pupillae (radial muscles) contract; pupils dilate – sympathetic fibers - Changes in emotional state  pupils dilate when subject matter is appealing or requires problem-solving skills - Iris only contains brown pigment; less brown pigment = blue, green, gray; more = brown/black - Constriction = parasympathetic - Dilate = sympathetic

3. Inner Layer: - Retina - Deepest layer - Outpocketing of the brain - Delicate 2-layered membrane: 1. Outer pigmented layer: - Single-cell-thick lining - Absorbs light and prevents its scattering - Phagocytosis of photoreceptor cell fragments - Stores vitamin A

2. Inner neural layer - Transparent - Composed of 3 main types of neurons: - Photoreceptors, bipolar cells, ganglion cells - Signals spread from photoreceptors to bipolar cells to ganglion cells - Ganglion cell axons exit eye as optic nerve - Internal cavity filled with fluids called humors - Lens separates internal cavity into anterior and posterior segments (cavities) The Retina: - Optic disc (blind spot): - Site where optic nerve leaves eye - Lacks photoreceptors - Quarter-billion photoreceptors of two types: 1. Rods 2. Cones

Photoreceptors: -2 types: 1. Rods: - Dim light, peripheral vision receptors - More numerous, more sensitive to light than cones - No color vision or sharp images - Numbers greatest at periphery 2. Cones: - Vision receptors for bright light - High-resolution color vision - Macula lutea exactly at posterior pole  mostly cones; “yellow spot” - Fovea centralis  tiny pit in center of macula with all cones; best vision; only cones

Internal Chambers and Fluids: -The lens and ciliary zonule separate eye into 2 segments: 1. Anterior segment: - Contains 2 chambers: - Anterior chamber = between cornea and iris - Posterior chamber = between iris and lens - Contains aqueous humor that: - Plasma-like fluid continuously formed by capillaries of ciliary processes - Drains via scleral venous sinus (canal of Schlemm) at corneoscleral junction - Supplies nutrients and oxygen mainly to lens and cornea but also to retina, and removes waste - Glaucoma = blocked drainage of aqueous humor increases pressure and causes compression of retina and optic nerve  blindess 2. Posterior segment: - Contains vitreous humor that: - Transmits light - Supports posterior surface of lens - Holds neural layer of retina firmly against pigmented layer - Contributes to intraocular pressure - Forms in embryo; lasts lifetime

Lens: -Biconvex, transparent, flexible, and avascular - Changes shape to precisely focus light on retina - 2 regions: 1. Lens epithelium anteriorly 2. Lens fibers form bulk of lens - Lens fibers filled with transparent protein crystallin - Lens becomes more dense, convex, less elastic with age - Cataracts = clouding of lens; consequence of aging, diabetes mellitus, heavy smoking, frequent expose to intense sunlight Light and Optics: Wavelength and Color:

-Eyes respond to visible light - Small portion of electromagnetic spectrum - Wavelengths of 400-700 nm - Light = packets of energy (photons or quanta) that travel in wavelike fashion at high speeds - Color of light that an object reflects determines what color the eye perceives - Red waves = longest - Purple = shortest; most energetic Refraction and Lenses: -Light passing through convex lens (as in eye) is bent so that rays converge at focal point - Image formed at focal point is upside down and reversed right to lef - Concave lenses diverge light; prevent light from focusing - Lens = biconvex  curved on both sides; light bends 2 times (enter and exit) - A thicker lens bends more easily; image called a real image Focusing Light on the Retina: -Pathway of light entering eye: Cornea  aqueous humor  lens  vitreous humor  entire neural layer of retina  photoreceptors - Light refracted 3 times along pathway: 1. Entering cornea 2. Entering lens 3. Leaving lens - Majority of refractory power in cornea - Change in lens curvature allows for fine focusing Focusing for Distant Vision: -Eyes best adapted for distant vision - Far point of vision = distance beyond which no change in lens shape needed for focusing - 20 feet for emmetropic (normal) eye - Cornea and lens focus light precisely on retina - Ciliary muscles relaxed - Lens stretched flat by tension in ciliary zonule - Sympathetic activation Focusing for Close Vision: -Light from close objects (...