Nervous System Lesson 9 & 10 PDF

NERVOUS SYSTEM Efreim Louie Sombillo Ilano, LESSON 9 RN, MSN, MD, FIAMS, MHA I. MORPHOLOGICAL DIVISONS: A. Central Nervous system 1. Brain 2. Spinal cord B. Peripheral Nervous System 🢝1. Cranial Nerves (12 pairs) 🢝2. Spinal Nerves ( 31 pairs) 🢝3. Autonomic Nervous System II. FUNCTIONAL...

NERVOUS SYSTEM Efreim Louie Sombillo Ilano, LESSON 9 RN, MSN, MD, FIAMS, MHA I. MORPHOLOGICAL DIVISONS: A. Central Nervous system 1. Brain 2. Spinal cord B. Peripheral Nervous System 🢝1. Cranial Nerves (12 pairs) 🢝2. Spinal Nerves ( 31 pairs) 🢝3. Autonomic Nervous System II. FUNCTIONAL DIVISIONS: A. Somatic Efferent - innervating somatic structures like skeletal muscles and skin. B. Visceral Efferent - innervating visceral or involuntary structures like smooth muscles, cardiac muscles and glands. This is the autonomic nervous system TYPES OF CELLS IN THE NERVOUS SYSTEM - The nervous system is composed of a special tissue containing two major Types of cells: 1. Neurons 🢝The active conducting elements 2. Neuroglia 🢝The supporting elements NEURON - basic unit of the nervous system which conducts electrical impulses from one part of the body to another. - consists of a cell body (perikaryon), containing a single nucleus, and processes transmitting impulses to and from the cell body. TWO TYPES OF PROCESSES A. Dendrites - group of short, unsheathed processes arranged like branches of a tree that transmit impulses toward the cell body B. Axons - a single, elongated sheathed process conducting impulses away from the cell body. ACCESSORY CELLS - The non nervous elements consist of blood vessels, connective tissue, and supporting cells known collectively as neuroglia. -Non neuronal cells that maintain homeostasis from myelin and provides support and protection for neurons in CNS and PNS SYNAPSE - Synapses are points of connection between neurons. The axon of one neuron make functional contact with dendrites of another neuron. Certain chemicals, called neurotransmitters are released from axonal endings for impulse to leap the synaptic junction: Main neurotransmitters: 1. epinephrine (adrenalin) 2. norepinephrine (nor adrenaline) 3. acetylcholine All are released by autonomic fibers. Acethylcholine released at neuromuscular junction. NERVE IMPULSE Cell membrane of an unstimulated neuron carries an electric charge. The inside of membrane is negative compared with the outside. A nerve impulse is a localized reversal in the charge of cell membrane and spreads there like an electric current. This sudden electric change in membrane is called ACTION POTENTIAL. A stimulus can start this action potential. This electric change is due to the rapid shifts in sodium and potassium ions across cell membrane. This occurs very rapidly and followed by rapid return of the membrane to its original state so it can be stimulated again A. MYELIN SHEATH - insulating material covering axons in central and peripheral nervous system - the thicker the myelin sheath is, the faster the passage of nerve impulse will be. - the electric impulse “jumps” from node to node in myelin sheath instead of traveling continuously along the nerve fiber. (SALTATORY CONDUCTION OF IMPULSES) CENTRAL NERVOUS SYSTEM - Central nervous system includes the BRAIN and SPINAL CORD. - Each division is further divided grossly into gray and white matter: A. Gray matter - so called because of its darker appearance and preponderance of nerve cell bodies. B. White matter - composed chiefly of myelinated nerve fibers - In the spinal cord an H-shaped central region of gray matter is surrounded by white matter. GRAY MATTER - In a surface layer (cortex) of the cerebrum and cerebellum. The brain the gray matter is broken into clumps or is present as - Nucleus designates a mass of gray matter in any part of the brain or spinal cord. - Ganglion also means cluster of nerve cell bodies and dendrites, but usually refers to those cells located outside the brain and spinal cord BRAIN - part of the central nervous system contained within the skull. - most complex and largest mass of nervous tissue in the body and contains literally billions of nerve cells. EMBRYOLOGICAL DIVISIONS OF THE BRAIN 1. Forebrain (Prosencephalon) a. Telencephalon (cerebrum with basal ganglia) b. Diencephalon ( thalamus,hypothalamus) 2. Midbrain (Mesencephalon) 3. Hindbrain (Rhombencephalon) a. metencephalon (cerebellum, pons) b. myelencephalon (medulla oblongata) 1. PROSENCEPHALON A. TELENCEPHALON (CEREBRUM) - represents seven-eight of weight of brain - surface layer of gray matter (cerebral cortex) greatly expanded by convolutions, or gyri. Internal to which is the white substance made up of nerve fibers. FISSURES OF CEREBRUM 1. Longitudinal Fissure - runs from the posterior to the anterior aspects almost completely dividing it into 2 hemispheres. - the hemispheres are connected in the midline by the corpus callosum (largest band of crossing or commisural fibers). This is found in the depths of longitudinal fissure. 2. Lateral Sylvian fissure - between the frontal and parietal lobes above and temporal lobe below. 3. Central of Sulcus (Rolandic Fissure) - between frontal and parietal lobes 4. Parieto - occipital fissure - between the occipital and parietal lobes. 5. Calcarine fissure - found in the occipital lobe perpendicular to parieto occipital fissure around which is the visual center. LOBES OF THE CEREBRAL CORTEX 1. Frontal Lobe - includes all the cortex lying anterior to the central sulcus of Rolando and above the lateral sulcus Sylvius - center for motor functions and personality. 2. Parietal Lobe - lies posterior to central sulcus of Rolando and above lateral Sylvian fissure. - center for ordinary sensory functions 3. Temporal Lobe - lies beneath the lateral sulcus of Sylvius - center for hearing and olfaction 4. Occipital Lobe - occupies the posterior extremity of the cerebral hemisphere behind parieto- occipital fissure - visual center 5. Insula ( Island of Reil) - exposed when the lips of lateral Sylvian fissure are separated FUNCTIONS OF THE CEREBRUM 1. seat of advanced intellectual functions like memory storage, recall, learning and reasoning for comprehension and execution of language. 2. perception of all sensations and sites where one modality of sensation can be integrated with others. 3. initiation of movements FUNCTIONAL AREAS OF THE CEREBRAL CORTEX 1. Primary Motor Area or Pre-central gyrus - lies in the frontal lobe immediately anterior to the central sulcus - controls voluntary movements in the opposite side of body. 2. Pre-frontal Area - concerned with behavior, character and emotional state of the individual. - concerned with foresight, good judgment, abstract thinking. 3. Primary sensory/Somesthetic Area or Post-central gyrus - lies behind the central sulcus of Rolando in parietal lobe - ordinary sensations of pain, temperature, pressure and touch, position and movement sensation from opposite side of body are received and interpreted here. 4. Motor speech area - lies in inferior frontal gyrus of dominant hemisphere (usually the left) - Broca’s area 5. Sensory speech area: - lies in temporal lobes posterior to auditory area of dominant hemisphere (usually the left) - Wernicke’s area 6. Auditory or Hearing Area (transverse gyri of Heschl) - lies below lateral sulcus within the temporal lobe - center for hearing 7. Visual area: - cortex around the calcarine fissure - found in occipital lobe 8. Olfactory or smell area - within the temporal lobe 9. Taste Area - above lateral sulcus into the deep layers of the sensory area BASAL GANGLIA - four paired masses of gray matter embedded in the white matter of the cerebral hemispheres - include the caudate nucleus(medial portion) and the putamen and globus pallidus(lateral portion) collectively called lentiform nucleus. - Basal ganglia play an important role in the control of motor function, and injury to them produces unitentional, unnecessary movements. B. DIENCEPHALON - located in the forebrain along with the cerebrum. - made up of: - 1. Thalamus - - paired mass of gray matter situated below corpus callosum. - - highest subcortical sensory integrating center - - all sensory impulses (ordinary and special ) should pass the thalamus first before going to cerebral cortex, except for smell - which can go directly to cerebral cortex. -2. Hypothalamus -- involved in the regulation of body temperature, feeding activities, -concentration and volume of extracellular fluid, autonomic -nervous system responses, endocrine functions. -- where pituitary gland is attached to. 2. MESENCEPHALON - connects the forebrain and hindbrain 3. RHOMBENCEPHALON CEREBELLUM ( Part of metencephalon ) - the constricted central portion is called the vermis(Latin of worm) and the lateral expanded portions the hemispheres. - resembles the cerebrum in structure, with the gray matter forming a layer of cortex placed on the surface - the cerebellum greatly aids the motor cortex of the cerebral hemispheres in the integration of voluntary movements. Injury does not result to paralysis of muscles but loss of coordination only of these motor activities. PONS ( Part of metencephalon ) - lies anterior to the cerebellum and between the midbrain and medulla. - bridge-like structure, consisting almost entirely of white matter linking the various parts of the brain. MEDULLA OBLONGATA ( myelencephalon ) - continuous with the spinal cord inferiorly and with the pons superiorly - lies ventral to the cerebellum - has a number of vital regulatory and reflex centers, including those controlling the circulatory system, breathing, swallowing, vomiting, coughing, sneezing. VENTRICLES OF THE BRAIN - spaces inside brain filled with cerebrospinal fluid. - the Ventricular System includes: 1. lateral ventricle - found inside the cerebral hemispheres - each lateral ventricle communicates with the third ventricle by way of an interventricular foramen(foramen of Monroe) 2. Third ventricle - small, slitlike cavity in the center of the diencephalon in between the 2 thalami. - continuous with the cerebral aqueduct of Sylvius, a canal which passes through the midbrain. 3. Fourth ventricle - lies between the cerebellum on the posteriorly side and the pons and medulla on the anterior side. - communicates with subarachnoid space through Foramen of Luschka and Magendie MENINGES -These are membranes collectively known as the meninges provide protection to the brain and spinal cord - from outside in, these are the: A. Pachymeninx 1. Dura mater B. Leptomeninges 1. Arachnoid mater 2. Pia mater 1. DURA MATER - the dura mater (latin for hard mother), the outer meninx, is made of dense, fibrous tissue. - There are 2 portions of the dura mater; 1. cranial 2. spinal - the cranial dura is arranged in two layers. (outer endosteal and inner meningeal) - the inner layer becomes continuous with the one layered dura mater. in the spinal cord. - the potential space between dura and bone is epidural space. The one between dura and arachnoid mater is subdural space filled with small amount of serous fluid. 2. ARACHNOID MATER - delicate serous membrane located between the dura and pia. - As the name implies, it has the microscopic appearance of a spider web. The subarachnoid space between the arachnoid and the pia is occupied by thin, delicate connective tissue trabeculae and intercommunicating channels in which cerebrospinal fluid is contained - the cranial portion invests the brain loosely 3. PIA MATER -The pia mater (gentle mother) is a vascular membrane consisting a plexus of fi ne blood vessels held together by areolar connective tissue. -The cranial portion invests the surface of the brain and dips down into the sulci. CEREBROSPINAL FLUID - colorless fluid similar to lymph circulating within the ventricles, the central canal of the spinal cord and also within the subarachnoid space. - the volume : about 150 ml. - serves as a water cushion to guard the brain and spinal cord against injury. - Cerebrospinal fluid is continuously formed in all four ventricles by active secretion, principally from the capillaries of the choroid plexus(pouch like projections of the pia mater into the ventricles covered with the ependymal lining of the ventricles CSF PATHWAY CSF from choroid plexuses in lateral ventricles interventricular foramen of Monroe third ventricle iter of aqueduct of Sylvius -- 4thventricle foramen of Luschka and Magendie subarachnoid space arachnoid villi absorbed in the venous circulation. CSF FLOW SPINAL CORD - the elongated and almost cylindrical part of the CNS - 45 cm long lying within the vertebral canal. - continuous with the medulla oblongata above and extends from the level of foramen magnum to the lower border of 1st lumbar vertebra in adult and level of L3 vertebra in children - 2 enlargements: 1. cervical enlargement (where nerve supply of upper extremities arises from) 2. lumbar enlargement (where nerve supply of lower extremities arises from) - narrows down as a conus medullaris, where it gives rise to the threadlike filum terminale that terminates in the first coccygeal vertebra. - the lumbar and sacral spinal nerves descend along the filum terminale in a bundle known as the cauda equina PERIPHERAL NERVOUS SYSTEM: SPINAL AND CRANIAL NERVES I. SPINAL NERVES - a bundle of nerve fibers attached to spinal cord - all are classified as mixed nerves – with sensory and motor fibers - 31 pairs of spinal nerves arise from the spinal cord along almost its entire length and emerge from the vertebral canal through the intervertebral foramina. - a spinal segment is the part of the spinal cord where a pair of spinal nerves is attached - attached to each spinal segment on either side are: 1. dorsal root - containing sensory fibers 2. ventral root - containing motor fibers - these 2 roots join together to from spinal nerve - 31 pairs of spinal nerves are named from the region of the vertebral column through which they exit. - There are 8 pairs of cervical spinal nerves, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal PLEXUSES - group of nerve fibers from ventral rami of cervical , lumbar and sacral spinal nerves. Posterior rami never form plexuses. 1. Cervical Plexus - formed by the first 4 cervical nerves (C1C2C3C4) - this supplies the back and sides of the head and the front of the neck with ordinary sensory fibers - most important branch is the phrenic nerve composed of motor fibers supplying the diaphragm 2. Brachial Plexus - lower 4 cervical (C5C6C7C8) nerves and 1st thoracic (T1) supplies the skin and muscles of the upper limb - with branches like radial, ulnar, median nerves 3. Lumbar Plexus - from L1 -L4 spinal nerves - one of its branches is: Femoral nerve - supplies muscles and skin on anterior aspect of the thigh Obturator nerve - supplies muscles and skin of medial aspect of thigh 4. Sacral Plexus - from L4L5S1S2S3 spinal nerves - the largest branch of which is the sciatic nerve (the largest nerve in the body divided into common peroneal nerve and tibial nerve) CRANIAL NERVES - The cranial nerves are 12 pairs of symmetrically arranged nerves attached to the brain. - The cranial nerve includes the following: 1. Olfactory (I) 2. Optic (II) 3. Oculomotor (III) 4. Trochlear (IV) 5. Trigeminal ( V) 6. Abducens (VI) 7. Facial ( VII) 8. Vestibulocochlear (acoustic) (VIII) 9. Glossopharyngeal (IX) 10. Vagus (X) 11. Accessory (XI) 12. Hypoglossal (XII) CLASSIFICATION OF CRANIAL NERVES PURELY SENSORY NERVES - carry impulses towards brain. Also called afferent fibers - cranial nerves I, II, VIII PURELY MOTOR NERVES - carry impulses away from the brain. Also called efferent fibers - cranial nerves III, IV, VI, XI, XII MIXED NERVES - carry both sensory and motor nerve fibers 2wsdeeeeeeeeeeeee AUTONOMIC NERVOUS SYSTEM - efferent peripheral nerve fibers distributed to smooth muscle, cardiac muscle, and glands AUTONOMIC SUBDIVISIONS - The autonomic nervous system may be divided, both functionally and structurally into sympathetic and parasympathetic nervous divisions. 1. Sympathetic or Thoracolumbar Divisions of the autonomic nervous system arises from all the thoracic and the first three lumbar segments of the spinal cord. - Generally actions are directed toward mobilizing the body’s energies for dealing with an increase in activity. - the more primitive, sometimes exerting a mass action fortified by epinephrine from the adrenal medulla. 2. Parasympathetic or Craniosacral Divisions of the autonomic nervous system arises from the third, seventh, ninth, and tenth cranial nerves and from the second, third, and fourth sacral segments of the spinal cord. - the actions of this division onserve body energies. - The parasympathetic system is more advanced structurally and functionally, and its actions are never as generalized as the sympathetic responses. Most visceral organs are supplied by both sympathetic and parasympathetic and their effects are usually are opposite NEUROCLINICAL CORRELATION 1. Cerebrovascular Accident (CVA) (STROKE) - injury to the brain due to involvement of its blood vessels, in conditions like tumor compressing on blood supply, or in obstruction or rupturing of these cerebral vessels. 2. Meningitis - infection of the meninges. 3. Seizure Disorders - manifestations of an abnormal discharge of nerve impulses from some parts of the brain. e.g. - Grand mal type of seizure with sudden loss of consciousness and a generalized convulsion 4. Hydrocephalus – increase in cerebrospinal fluid pressure - usually resulting from obstruction of the CSF pathway 5. Plegia - complete loss of voluntary motor function due to dysfunction of nervous system e.g. hemiplegia (one half of body is paralyzed) 6. Paresis - weakness of voluntary muscle activity due to dysfunction of nervous system 7. Infantile paralysis (poliomyelitis) - caused by a virus that damages the anterior horn cells of the cord and the motor nuclei of the cranial nerves. 8. Multiple Sclerosis - characterized by a patchy demyelinization in multiple areas of the nervous system involving sensory and motor fibers followed by replacement of the myelin by scarlike plaques. 9. Syringomyelia - cavitation of the central canal of the spinal cord and excessive multiplication of neuroglia in the gray substances around it. 10. Brown-Sequard Syndrome - injury to one half of the spinal cord and involving neuronal groups and nerve tracts. SPECIAL SENSE Efreim Louie Sombillo LESSON 10 Ilano,MSN, MD VISUAL SENSE - Each eyeball is positioned in a bony depression in the skull called orbit. - Only the anterior one-sixth of the eye’s surface can normally be seen. Accessory Structures of the eye: 1. extrinsic eye muscles 2. eyelids 3. conjunctiva 4. lacrimal apparatus EYELIDS - Anteriorly, the eyes are protected by the eyelids which meet at the medial and lateral corners of the eye, the medial and lateral canthus respectively. - Projecting from the border of each eyelid are the eyelashes. - Meibomian Glands- modified sebaceous glands associated with the eyelid edges; produce an oily secretion that lubricates the eye. - Ciliary Glands- modified sweat glands between the eyelashes CONJUNCTIVA - lines the eyelids and covers part of the white of the eye (sclera) infront. - secretes the mucus which helps to lubricate the eyeball and keep it moist LACRIMAL GLANDS: - located above the lateral ends of each eye. - Continually release a dilute salt solution (tears=”lacrimal fluid”) that drain into the nasal cavity through the inferior meatus - Lacrimal fluid not only moistens and lubricates conjunctival sac but also reduces eye infections because it contains bactericidal enzyme called lysozyme. TEAR DRAINAGE SYSTEM 1. Fibrous Coat a. Sclera- posterior 5/6; opaque, “white” of the eye b. Cornea- anterior 1/6; transparent 2. Vascular and Muscular Coat (UVEA) a. choroid b. ciliary body c. iris 3. Nervous coat a.retina COATS OF THE EYE SCLERA - the outermost coat - also called the fibrous tunic seen anteriorly as the “white of the eye” - covered in the anterior part by transparent conjunctiva CORNEA - the central transparent anterior portion of the eye covering the colored part of the eye which is the iris - the only tissue in the body that can be transplanted from one person to another without the worry of rejection because it has no blood vessels thus it is beyond the reach of the immune system CHOROID - middle coat of the eye - blood-rich nutritive tunic that contains a dark pigment that prevents light from scattering inside the eye CILIARY BODY - with ciliary muscle for accomodation - when ciliary muscle contracts, the lens become more convex - with ciliary processes producing aqueous humor IRIS - the colored part of the eye which is a membranous extension of the choroid - partially covers the lens, leaving a round opening at the center called pupil -with sphincter and dilator pupillae (to constrict and dilate pupil) - like the diaphragm of the camera; it can increase or decrease the diameter of its aperture (the pupil) to admit more or less light. - Constriction of the pupils is produced by contraction of the circularly arranged fibers within the iris supplied by parasympathetic, dilation is produced by contraction of the radially arranged fibers supplied by sympathetic RETINA - the nervous coat of the eyeball containing the photoreceptor cells: Photoreceptors: 1. rods – stimulated by low intensity light - for night vision (scotopic vision) 2. cones – stimulated by high intensity light - for day vision/color vision (photopic vision) Refractive Media of the eyes: 1. cornea 2. aqueous humor (in anterior and posterior chamber) 3. lens 4. vitreous humor - When light passes from one substance to another substance that has a different density, its speed changes and its rays are bent , or refracted. Light rays are bent in the eye as they encounter the cornea, aqueous humor, lens, and vitreous humor - The refractive or bending power of the cornea and humors is constant. However, that of the lens can be changed by changing its shape – that is by making it more or less convex, so that light can be properly focused on the retina. The greater the lens convexity, or bulge, the more it bends the light. On the other hand, the flatter the lens, the less it bends the light. - The resting eye is “set” for distant vision. In general, light from a distant source (over 20 ft) approaches the eye as parallel rays, and no change in lens shape is necessary for it to be focused properly on the retina. However, light from a close object tends to scatter and to diverge, or spread out, and the lens must bulge to make close vision possible. - To achieve this, the ciliary body contracts, allowing the lens to become more convex. This ability of the eye to focus specifically for close objects (those less than 20 ft away) is called accommodation. VISUAL PATHWAY Optic nerve has nasal fibers(from the medial side) and temporal fibers (from the lateral side) Nasal fibers receive impulse from the temporal visual field and the temporal fibers receive impulse from the nasal visual field Nasal fibers decussate at the level of the optic chiasm while temporal fibers leave the optic chiasm without decussating Fibers from the optic chiasm going to the lateral geniculate bodies are called optic tract Lateral geniculate bodies are the last relay station of the visual pathway Cells from the lateral geniculate bodies project fibers to the primary visual area and are called optic radiation or geniculocalcarine tract Termination of the visual pathway is at the calcarine area, the primary visual area (Brodmann’s Area 17 VISUAL PATHWAY AUDITORY SENSE OUTER (EXTERNAL) EAR 1. pinna or auricle - shell-shaped structure surrounding the auditory canal opening 2. External Auditory Canal - a short narrow chamber (about 1 inch long by ½ inch wide) - curved into temporal bone of the skull - skin of walls lined with ceruminous glands which secrete a waxy yellow substance called earwax, or cerumen 3. Tympanic Membrane or Eardrum - a thin membrane separating outer from middle ear 2. Middle Ear of Tympanic Cavity - a small, air-filled cavity within the temporal bone a. medial boundary a bony wall with 2 openings: -oval window - round window b lateral boundary tympanic membrane with handle of the malleus attached c. anterior boundary – Eustachian tube (connects middle ear and nasopharynx) d. posterior boundary – mastoid process Ossicles in the middle ear: - Malleus (hammer) – attached to tympanic membrane. - Incus (anvil) - Stapes (Stirrups) – presses on the oval window of the inner ear 3. Inner (internal) Ear - contains bony chambers called osseous or bony labyrinth enclosing the membranous labyrinth Bony Labyrinth Membranous Labyrinth Vestibule Saccule Utricle Cochlea Cochlear Duct Semicircular canals Semicircular Duets Bony Labyrinth - filled with plasma like fluid perilymph Membranous Labyrinth - contains a thicker fluid called endolymph Receptor for Hearing =” Organ of Corti” – found in the cochlea Mechanism of Hearing - within the membranes of the snail like cochlea is the organ of Corti containing the hearing receptors or hair cells - sound waves that reach the cochlea through the vibrations of the eardrum ossicles and oval window set the cochlea fluids into motion - receptor cells resting on the basilar membrane, the organ of Corti are stimulated when these “hairs” are bent or tweaked by the movement of the gel-like tectorial membrane that lies over them - once stimulated, the hair cells transmit impulses along the cochlear nerve to the auditory cortex in the temporal lobe the primary auditory area (Brodmann’s Area 41) MECHANISM OF HEARING Deafness - hearing loss of any degree 2 Types of Deafness: 1. Conduction Deafness - temporary or permanent - results when something interferes with conduction of sound vibrations to the fl uids of inner ear. Involves diseases of external and middle ear e.g. impacted cerumen otosclerosis – (fusion of ossicles) rupture of eardrum otitis media 2. Sensorineural Deafness - results from degeneration or damage to receptor cells, to cochlear nerve, or to neurons of auditory cortex - could be due to : a. old age (presbycusis) b. extended listening to excessively loud sounds c. intake of ototoxic drugs like streptomycin, quinine, aspirin etc TESTS TO DISTINGUISH SENSORINEURAL FROM CONDUCTION DEAFNESS: 1. Weber’s Test - the base of the vibrating tuning fork is applied to the forehead in the midline Result for: 1. normal individual - sound appears to be in the midline 2. conduction deafness - sound appears louder in the affected ear 3. sensorineural deafness - sound appears louder in the normal ear 2. Rinne’s Test - The base of the tuning fork is placed over the mastoid process of the skull - When it can no longer be heard, it is removed and then is held in front of the ear Result for: 1. normal individual - continues to hear by air conduction after bone conduction ceases - air conduction is greater than bone conduction 2. conduction deafness - bone is greater than air conduction 3. sensorineural deafness - both are diminished but air conduction remains better than bone conduction VESTIBULAR SENSE - consists of receptors located in the inner ear on both sides of the head - 8th cranial nerve transmits the vestibular information ( for equilibrium) from the receptors to the CNS FUNCTION: 1. maintains body balance 2. coordinates eye, head, and body movements 3. permits the eyes to remain fi xed on a point in space as the head moves RECEPTORS: Cristae Ampullaris - found in the dilatations of semicircular ducts called ampulla - stimulated by angular acceleration - contains gelatinous substance called cupula Macula - found in the vestibule - stimulates by linear acceleration - contains gelatinous substance called otolithic membrane containing otoconia, which are calcium carbonate crystals Dynamic Function - mediated largely by the semicircular canals - can detect motion of head in space Static Functions - mediated mostly by the utricle - allow detection of the position of the head in relation to gravity - important in control of posture VESTIBULAR NUCLEI: 1. Superior – vestibular nucleus of Bechterew 2. Inferior – descending spinal 3. Medial – vestibular nucleus of Schwalbe 4. Lateral – vestibular nucleus of Deither - will have ascending fibers synapsing with somatic motor neurons of cranial nerve III,IV and VI for movement of eyeballs - will have descending fibers to the spinal cord controlling the anti gravity muscle OLFACTION SENSE Receptor: olfactory epithelium located in the upper 1/3 of each nasal mucosa - When receptors are stimulated by chemicals (chemoreceptor) dissolved in the mucus, they transmit impulses along olfactory nerve to olfactory cortex in the temporal lobe (uncus- Brodmann’s Area 34). - olfactory pathway is closely tied with the limbic system (emotional- visceral part of the brain) thus, olfactory impressions are long-lasting and very much part of our memories and emotions. - for example, the smell of chocolate chip cookies may remind you of our grandmother or the smell of perfume may remind you of your boyfriend. - the olfactory receptors are exquisitely sensitive – just a few molecules can activate them. - just like the auditory receptors, the olfactory neurons tend to adapt rather quickly when they are exposed to an unchanging stimulus, in this case, an odor. - This is why a woman stops smelling her own perfume after a while but will quickly pick up the scent of another perfume on someone else. - Certain chemicals activate the trigeminal nerve (CN V) as well as the olfactory (CN I) nerves and cause a particular reaction. Pepper for example may cause sneezing, onions cause the eyes to water, and smelling salts (ammonium salts) initiate respiratory reflexes and are used to revive people who are unconscious. GUSTATORY SENSE TASTE BUDS - most are localized in the tongue - a few are found on the soft palate, inner surface of the cheeks, walls of oropharynx - cylindrical taste bud is composed of many sensory gustatory cells that are encapsulated by supporting cells. Taste pore - opening in the taste buds where the gustatory hairs(sensitive portion of receptor cell) pass through. - dorsal surface of tongue is covered with small peglike projections or papillae. 1. circumvallate papilla– with taste buds 2. fungiform papilla– with taste buds 3. foliate papilla- with taste buds 4. filiform papilla – no taste buds, only gustatory cells - taste buds are found on the sides of the circumvallate and on the more numerous fungiform papilla. - filiform papillae contain the gustatory cells which are not clustered into taste buds. - molecules dissolved in saliva at the surface of the tongue interact with the receptor molecule in the microvilli of the taste buds. - this interaction stimulates the release of neurotransmitter from the receptor cells, which in turn stimulates the sensory nerve endings that innervate the taste buds. - taste buds on the anterior 2/3 of the tongue are innervated by the facial nerve (CN VII). - taste buds on the posterior 1/3 of the tongue innervated by glossopharyngeal nerve (CN IX). - taste buds on the soft palate and the oropharynx are supplied by the vagus nerve (CN X). 4 Basic Modalities of Taste are sensed acutely in particular regions of the tongue: 1. sweet – tip of tongue 2. bitter – back of tongue 3. salty – over most of tongue 4. sour – sides of tongue * Sweet receptors respond to substances such as sugars, saccharine, and some amino acids. * Sour receptors respond to hydrogen ions (h+), or the acidity of the solution. * Bitter receptors respond to alkaloids. * Salty receptors respond to metal ions in solution. * Termination of the gustatory pathway is at the area located in the opercular part of the post central gyrus (Brodmann’s Area 43). QUESTION S?