Chapter 18. The Nervous System. General and Special Senses. Lecture Presentation by Steven Bassett Southeast Community College

Chapter 18 The Nervous System General and Special Senses Lecture Presentation by Steven Bassett Southeast Community College

Introduction Every plasmalemma functions as a receptor for the cell Plasmalemma has receptors specific for: Chemical stimuli Electrical stimuli Mechanical stimuli Not all plasmalemmae have the same receptor sites

Introduction Sensory information arrives at the CNS Information is picked up by sensory receptors Sensory receptors are the interface between the nervous system and the internal and external environment

Introduction Categories of Senses General senses Refers to temperature, pain, touch, pressure, vibration, and proprioception Special senses Refers to smell, taste, balance, hearing, and vision Special sense receptors are located in complex sense organs Examples are: eyes, ears, and taste buds

Receptors Each receptor has a characteristic sensitivity This leads to receptor specificity Specificity is due to the structure of the receptor

Receptors Examples of Specificity Free nerve endings are the simplest receptors These respond to a variety of stimuli Receptors of the retina Very specific and only respond to light The area monitored by the receptor cell is the receptive field

Receptors Receptive Fields Large receptive fields have receptors spread far apart, which makes it difficult to localize a stimulus Small receptive fields have receptors close together, which makes it easy to localize a stimulus

Figure 18.1 Receptors and Receptive Fields Receptive field 1 Receptive field 2

Receptors Interpretation of Sensory Information Information is relayed from the receptor to a specific neuron in the CNS Each pathway carries information concerning a specific sensation The identity of the active neuron indicates: Location of the stimulus Nature of the stimulus

Interpretation of Sensory Information Classification of Receptors Tonic receptors Always active Photoreceptors of the eye and receptors that constantly monitor body position Phasic receptors Normally inactive but become active when necessary (for short periods of time) Touch and pressure receptors of the skin (for example)

Receptors Central Processing and Adaptation Adaptation Reduction in sensitivity due to a constant stimulus Peripheral adaptation Receptors respond strongly at first and then decline Central adaptation Adaptation within the CNS Consciously aware of a stimulus, which quickly disappears

The General Senses Classification of the General Senses One classification scheme: Exteroceptors Provide information about the external environment Proprioceptors Provide information about the position of the body Interoceptors Provide information about the inside of the body

The General Senses Classification of the General Senses Another classification scheme: Nociceptors Respond to the sensation of pain Thermoreceptors Respond to changes in temperature Mechanoreceptors Activated by physical distortion of cell membranes Chemoreceptors Monitor the chemical composition of body fluids

The General Senses Nociceptors Known as pain receptors Associated with free nerve endings and large receptor fields This makes it difficult to pinpoint the location of the origin of the pain There are three types Receptors sensitive to extreme temperatures Receptors sensitive to mechanical damage Receptors sensitive to chemicals

The General Senses Nociceptors Fast pain Sensations reach the CNS fast Associated with pricking pain or cuts Slow pain Sensations reach the CNS slowly Associated with burns or aching pains Referred pain Sensations reach the spinal cord via the dorsal roots Some visceral organ pain sensations may reach the spinal cord via the same dorsal root

Figure 18.2 Referred Pain Heart Liver and gallbladder Stomach Small intestine Appendix Ureters Colon

The General Senses Thermoreceptors Found in the dermis, skeletal muscles, liver, and hypothalamus Cold receptors are more numerous than hot receptors Exist as free nerve endings These are phasic receptors These are very active when the temperature changes, but quickly adapt to a stable temperature

The General Senses Mechanoreceptors Receptors that are sensitive to stretch, compression, twisting, or distortion of the plasmalemmae There are three types Tactile receptors Baroreceptors Proprioceptors

The General Senses Mechanoreceptors Tactile receptors Provide sensations of touch, pressure, and vibrations Unencapsulated tactile receptors Free nerve endings, tactile disc, and root hair plexus Encapsulated tactile receptors Tactile corpuscle, Ruffini corpuscle, and lamellated corpuscle

The General Senses Mechanoreceptors Unencapsulated tactile receptors Free nerve endings are common in the dermis Tactile discs are in the stratum basale layer Root hair plexus monitors distortions and movements of the body surface

Figure 18.3a Tactile Receptors in the Skin Hair Merkel cells and tactile discs Tactile corpuscle Free nerve ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Sensory nerves a Free nerve endings.

Figure 18.3b Tactile Receptors in the Skin Hair Merkel cells and tactile discs Tactile corpuscle Free nerve ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Merkel cells Tactile disc Sensory nerves b Merkel cells and tactile discs.

Figure 18.3c Tactile Receptors in the Skin Hair Merkel cells and tactile discs Tactile corpuscle Free nerve ending Ruffini corpuscle Lamellated corpuscle Root hair plexus c Free nerve endings of root hair plexus. Sensory nerves

The General Senses Mechanoreceptors Encapsulated tactile receptors Tactile corpuscle Common on eyelids, lips, fingertips, nipples, and genitalia Ruffini corpuscle In the dermis, sensitive to pressure and distortion Lamellated corpuscle Consists of concentric cellular layers / sensitive to vibrations

Figure 18.3d Tactile Receptors in the Skin Tactile corpuscle Epidermis Hair Merkel cells and tactile discs Tactile corpuscle Free nerve ending Dermis Ruffini corpuscle Lamellated corpuscle Root hair plexus Tactile corpuscle LM x 550 Capsule Accessory cells Sensory nerves Dendrites Sensory nerve fiber d Tactile corpuscle; the capsule boundary in the micrograph is indicated by a dashed line.

Figure 18.3e Tactile Receptors in the Skin Hair Merkel cells and tactile discs Tactile corpuscle Free nerve ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Collagen fibers Sensory nerve fiber Capsule Dendrites Sensory nerves e Ruffini corpuscle.

Figure 18.3f Tactile Receptors in the Skin Hair Merkel cells and tactile discs Tactile corpuscle Free nerve ending Ruffini corpuscle Lamellated corpuscle Root hair plexus Dermis Dendritic process Accessory cells (specialized fibrocytes) Concentric layers (lamellae) of collagen fibers separated by fluid Lamellated corpuscle LM x 125 Sensory nerves Concentric layers (lamellae) of collagen fibers separated by fluid Dendritic process f Lamellated corpuscle.

The General Senses Mechanoreceptors Baroreceptors Stretch receptors that monitor changes in the stretch of organs Location: Stomach Small intestine Urinary bladder Carotid artery Lungs Large intestine

Figure 18.4 Baroreceptors and the Regulation of Autonomic Functions Baroreceptors Baroreceptors of Carotid Sinus and Aortic Sinus Provide information on blood pressure to cardiovascular and respiratory control centers Baroreceptors of Lung Provide information on lung stretching to respiratory rhythmicity centers for control of respiratory rate Baroreceptors of Digestive Tract Provide information on volume of tract segments, trigger reflex movement of materials along tract Baroreceptors of Colon Provide information on volume of fecal material in colon, trigger defecation reflex Baroreceptors of Bladder Wall Provide information on volume of urinary bladder, trigger urinary reflex

The General Senses Mechanoreceptors Proprioceptors Monitor the position of joints Monitor tension in the tendons and ligaments Golgi tendon organs are the receptors in the tendons Monitor the length of muscle fibers upon contraction Muscle spindles are receptors in the muscles

The General Senses Chemoreceptors Detect small changes in the concentration of chemicals Respond to water-soluble or lipid-soluble compounds Found in respiratory centers of the: Medulla oblongata Carotid arteries Aortic arch

Figure 18.5 Chemoreceptors Chemoreceptive neurons Blood vessel Chemoreceptors Chemoreceptors In and Near Respiratory Centers of Medulla Oblongata Sensitive to changes in ph and P CO2 in cerebrospinal fluid Trigger reflexive adjustments in depth and rate of respiration Chemoreceptors of Carotid Bodies Sensitive to changes in ph, P CO2, and P O2 in blood Chemoreceptors of Aortic Bodies Sensitive to changes in ph, P CO2, and P O2 in blood Via cranial nerve IX Via cranial nerve X Trigger reflexive adjustments in respiratory and cardiovascular activity Carotid body LM x 1500

Olfaction (Smell) Olfaction The olfactory epithelium consists of: Olfactory receptors Supporting cells Basal cells Olfactory glands

Figure 18.6a The Olfactory Organs Olfactory Pathway Olfactory epithelium Olfactory nerve fibers (N I) Olfactory bulb Olfactory tract Central nervous system Cribriform plate Superior nasal concha Olfactory epithelium a The distribution of the olfactory receptors on the left side of the nasal septum is shown by the shading.

Figure 18.6b The Olfactory Organs Regenerative basal cell; divides to replace wornout olfactory receptor cells Olfactory gland To olfactory bulb Cribriform plate Lamina propria Olfactory epithelium Olfactory nerve fibers Developing olfactory receptor cell Olfactory receptor cell Supporting cell Mucous layer Knob Olfactory cilia; surfaces contain receptor proteins Substance being smelled b A detailed view of the olfactory epithelium.

Olfaction (Smell) Olfactory Pathways Axons leave the olfactory epithelium Pass through the cribriform foramina Synapse on neurons in the olfactory bulbs Impulses travel to the brain via CN I Arrive at the cerebral cortex, hypothalamus, and limbic system

Olfaction (Smell) Olfactory Discrimination The epithelial receptors have different sensitivities and we therefore detect different smells Olfactory receptors can be replaced The replacement activity declines with age

Gustation (Taste) Gustation The tongue consists of papillae Papillae consist of taste buds There are three types of papillae Filiform Fungiform Circumvallate Taste buds consist of gustatory cells

Figure 18.7ab Gustatory Reception Water receptors (pharynx) Umami Taste buds Sour Circumvallate papilla Bitter Salty Sweet a Gustatory receptors are found in taste buds that form pockets in the epithelium of the fungiform and circumvallate papillae. Fungiform papilla Filiform papillae b Papillae on the surface of the tongue.

Gustation (Taste) Gustatory Receptors Taste buds consist of gustatory cells Each gustatory cell has a slender microvilli that extends through the taste pore into the surrounding fluid Dissolved chemicals contact the microvilli This provides a stimulus that changes the transmembrane potential of the gustatory cell Information goes to the brain for the interpretation of taste

Gustation (Taste) Gustatory Pathways Dissolved chemicals contact the taste hairs (microvilli) Impulses go from the gustatory cell through CN VII, IX, and X Synapse in the nucleus solitarius of the medulla oblongata Synapse in the medial lemniscus Synapse in the thalamus Information arrives at the gustatory cortex

Figure 18.8 Gustatory Pathways Gustatory cortex Facial nerve (N VII) Nucleus solitarius Thalamic nucleus Medial lemniscus Glossopharyngeal nerve (N IX) Vagus nerve (N X)

Gustation (Taste) Gustatory Discrimination We begin life with more than 10,000 taste buds The number declines rapidly by age 50 Coupled with the decline in olfactory receptors, taste diminishes as we age Threshold level is low for gustatory cells responsible for unpleasant stimuli Threshold level is high for gustatory cells responsible for pleasant stimuli

Gustation (Taste) Gustatory Discrimination The are four (possibly six) primary tastes sensations Sweet Salty Sour Bitter Umami Taste that is characteristic of beef and chicken broth Water Located mainly in the pharynx region

Equilibrium and Hearing Equilibrium and Hearing Structures of the ear are involved in balance and hearing The ear is subdivided into three regions External ear Middle ear Inner ear

Figure 18.9 Anatomy of the Ear External Ear Middle Ear Inner Ear Elastic cartilages Auditory ossicles Auricle Oval window Semicircular canals Petrous part of temporal bone Facial nerve (N VII) Vestibulocochlear nerve (N VIII) Bony labyrinth of inner ear Tympanic cavity Cochlea To nasopharynx Auditory tube External acoustic meatus Tympanic membrane Round window Vestibule

Equilibrium and Hearing The External Ear Consists of: Auricle (pinna) External acoustic meatus Tympanic membrane Ceruminous glands Produces cerumen (earwax)

Equilibrium and Hearing The Middle Ear Consists of: Tympanic cavity Auditory ossicles Malleus, incus, and stapes Auditory tube (pharyngotympanic tube) Muscles: Tensor tympani Stapedius

Figure 18.10a The Middle Ear Auditory tube Auditory ossicles Tympanic membrane External acoustic meatus Tympanic cavity (middle ear) Inner ear a Inferior view of the right temporal bone drawn, as if transparent, to show the location of the middle and inner ear

Figure 18.10b The Middle Ear Temporal bone (petrous part) Malleus Stabilizing ligament Chorda tympani nerve (cut), a branch of N VII External acoustic meatus Tympanic cavity (middle ear) Tympanic membrane (tympanum) b Structures within the middle ear cavity Incus Base of stapes at oval window Tensor tympani muscle Stapes Round window Auditory tube Stapedius muscle

Figure 18.10c The Middle Ear Incus Malleus c The isolated auditory ossicles Points of attachment to tympanic membrane Stapes Base of stapes

Figure 18.10d The Middle Ear Malleus Tendon of tensor tympani muscle Malleus attached to tympanic membrane Inner surface of tympanic membrane Incus Base of stapes at oval window Stapes Stapedius muscle d The tympanic membrane and auditory ossicles as seen through a fiber-optic tube inserted along the auditory canal and into the middle ear cavity

Equilibrium and Hearing The Inner Ear Consists of: Receptors housed in membranous labyrinth (within the bony labyrinth) Bony labyrinth Vestibule Semicircular canals Cochlea Utricle Saccule

Figure 18.12a Semicircular Canals and Ducts Semicircular ducts Semicircular canal Anterior Lateral Posterior Vestibule Cristae within ampullae Maculae KEY Endolymphatic sac Membranous labyrinth Bony labyrinth Cochlea a Utricle Saccule Vestibular duct Cochlear duct Anterior view of the bony labyrinth cut away to show the semicircular canals and the enclosed semicircular ducts of the membranous labyrinth. Tympanic duct Organ of Corti

Equilibrium and Hearing The Vestibular Complex and Equilibrium The vestibular complex is the part of inner ear that provides equilibrium sensations by detecting rotation, gravity, and acceleration Consists of: Semicircular canals Utricle Saccule

Equilibrium and Hearing The Vestibular Complex and Equilibrium The semicircular canals Each semicircular canal encases a duct The beginning of each duct is the ampulla Within each ampulla is a crista with hair cells Each hair cell contains a kinocilium and stereocilia These are embedded in gelatinous material called the cupula The movement of the body causes movement of fluid in the canal, which in turn causes movement of the cupula and hair cells, which the brain detects

Equilibrium and Hearing The Vestibular Complex and Equilibrium When you rotate your head: The endolymph in the semicircular canals begins to move This causes the bending of the kinocilium and stereocilia This bending causes depolarization of the associated sensory nerve

Equilibrium and Hearing The Vestibular Complex and Equilibrium When you rotate your head: When you rotate your head to the right, the hair cells are bending to the left (due to movement of the endolymph) When you move in a circle and then stop abruptly, the endolymph moves back and forth causing the hair cells to bend back and forth resulting in confusing signals, thus dizziness

Equilibrium and Hearing The Vestibular Complex and Equilibrium The utricle and saccule The utricle and saccule are connected to the ampulla and to each other and to the fluid within the cochlea Hair cells of the utricle and saccule are in clusters called maculae Hair cells are embedded in gelatinous material consisting of statoconia (calcium carbonate crystals) Gelatinous material and statoconia collectively are called an otolith

Figure 18.14 The Function of the Semicircular Ducts, Part II Anterior semicircular duct for yes Lateral semicircular duct for no Posterior semicircular duct for tilting head a Location and orientation of the membranous labyrinth within the petrous parts of the temporal bones b A superior view showing the planes of sensitivity for the semicircular ducts

Figure 18.13a The Function of the Semicircular Ducts, Part I Semicircular ducts Anterior Posterior Lateral Ampulla Vestibular branch (N VIII) Cochlea Endolymphatic sac Endolymphatic duct Utricle Maculae Saccule a Anterior view of the maculae and semicircular ducts of the right side.

Figure 18.13ab The Function of the Semicircular Ducts, Part I Semicircular ducts Anterior Posterior Lateral Ampulla Vestibular branch (N VIII) Cochlea Endolymphatic sac Endolymphatic duct Utricle Maculae Saccule a Anterior view of the maculae and semicircular ducts of the right side. Ampulla filled with endolymph Cupula Hair cells Crista Supporting cells Sensory nerve b A section through the ampulla of a semicircular duct.

Figure 18.13b The Function of the Semicircular Ducts, Part I Ampulla filled with endolymph Cupula Hair cells Crista Supporting cells Sensory nerve b A section through the ampulla of a semicircular duct.

Figure 18.13c The Function of the Semicircular Ducts, Part I Direction of duct rotation Direction of relative endolymph movement Direction of duct rotation c Semicircular duct Cupula At rest Endolymph movement along the length of the duct moves the cupula and stimulates the hair cells.

Figure 18.13d The Function of the Semicircular Ducts, Part I Displacement in this direction stimulates hair cell Displacement in this direction inhibits hair cell Kinocilium Stereocilia Hair cell Supporting cell Sensory nerve ending d Structure of a typical hair cell showing details revealed by electron microscopy. Bending the stereocilia toward the kinocilium depolarizes the cell and stimulates the sensory neuron. Displacement in the opposite direction inhibits the sensory neuron.

Equilibrium and Hearing The Vestibular Complex and Equilibrium When you move up or down (elevator movement): Otoliths rest on top of the maculae When moving upward, the otoliths press down on the macular surface When moving downward, the otoliths lift off the macular surface When you tilt side to side: When tilting to one side, the otoliths shift to one side of the macular surface

Figure 18.15a The Maculae of the Vestibule Otolith Gelatinous material Statoconia Hair cells Nerve fibers a Detailed structure of a sensory macula

Figure 18.15ab The Maculae of the Vestibule Statoconia Otolith a Gelatinous material Statoconia Hair cells Nerve fibers Detailed structure of a sensory macula Otolith b A scanning electron micrograph showing the crystalline structure of otoliths

Figure 18.15c The Maculae of the Vestibule 1 Head in Neutral Position 2 Gravity Head Tilted Posteriorly Gravity Receptor output increases Otolith moves downhill, distorting hair cell processes c Diagrammatic view of changes in otolith position during tilting of the head

Equilibrium and Hearing Pathways for Vestibular Sensations Sensory fibers form the vestibular branch of the vestibulocochlear nerve Synapse within the vestibular nuclei Located between the pons and medulla oblongata

Figure 18.16 Neural Pathways for Equilibrium Sensations Semicircular canals Vestibular ganglion Red nucleus N III N IV To superior colliculus and relay to cerebral cortex Vestibular branch N VI Vestibular nucleus Vestibule To cerebellum Cochlear branch N XI Vestibulocochlear nerve (N VIII) Vestibulospinal tracts

Equilibrium and Hearing Pathways for Vestibular Sensations The vestibular nuclei: Integrate sensory information from each side of the head Sends information to: Cerebellum Cerebral cortex Motor nuclei within the brain stem and spinal cord Cranial nerves involved are: III, IV, VI, and XI

Equilibrium and Hearing Hearing The cochlea: Consists of snail-shaped spirals Spirals coil around a central area called the modiolus Within the modiolus are sensory neurons The sensory neurons are associated with CN VIII Organ of Corti

Equilibrium and Hearing The Cochlea (continued) Each spiral consists of three layers Scala vestibuli (vestibular duct): consists of perilymph Scala tympani (tympanic duct): consists of perilymph Scala media (cochlear duct): consists of endolymph / this layer is between the scala vestibuli and scala tympani

Equilibrium and Hearing The Cochlea (continued) There is a basilar membrane between each layer The scala vestibuli and scala tympani are connected at the apical end of the cochlea Sense organs rest on the basilar membrane within the scala media

Figure 18.17a The Cochlea and Organ of Corti Round window Stapes at oval window Cochlear duct Vestibular duct Tympanic duct Cochlear branch Vestibular branch Vestibulocochlear nerve (N VIII) a Structure of the cochlea in partial section KEY Semicircular canals From oval window to tip of spiral From tip of spiral to round window

Figure 18.17b The Cochlea and Organ of Corti Apical turn Vestibular membrane Tectorial membrane Basilar membrane From oval window Spiral ganglion Modiolus To round window Vestibulocochlear nerve (N VIII) Middle turn Vestibular duct (scala vestibuli contains perilymph) Organ of Corti Cochlear duct (scala media contains endolymph) Basal turn Tympanic duct (scala tympani contains perilymph) Temporal bone (petrous part) Cochlear branch b Structure of the cochlea within the temporal bone showing the turns of the vestibular duct, cochlear duct, and tympanic duct

Equilibrium and Hearing The Cochlea The Organ of Corti Also known as the spiral organ Rests on the basilar membrane between the scala media and the scala tympani Hair cells are in contact with an overlying tectorial membrane This membrane is attached to the lining of the scala media Sound waves ultimately cause a distortion of the tectorial membrane, thus stimulating the organ of Corti

Figure 18.17d The Cochlea and Organ of Corti Bony cochlear wall Vestibular duct Vestibular membrane Cochlear duct Tectorial membrane Spiral ganglion Basilar membrane Tympanic duct Organ of Corti d Three-dimensional section showing the detail of the cochlear chambers, tectorial membrane, and organ of Corti Cochlear branch of N VIII

Figure 18.17e The Cochlea and Organ of Corti Tectorial membrane Cochlear duct (scala media) Vestibular membrane Tectorial membrane Outer hair cell e Basilar membrane Inner hair cell Nerve fibers Diagrammatic and histological sections through the receptor hair cell complex of the organ of Corti Tympanic duct (scala tympani) Basilar membrane Hair cells of organ of Corti Spiral ganglion cells of cochlear nerve Organ of Corti LM x 125

Equilibrium and Hearing Sound Detection Sound waves enter the external acoustic meatus The tympanic membrane vibrates Causes the vibration of the ossicles The stapes vibrates against the oval window of the scala tympani Perilymph begins to move

Equilibrium and Hearing Sound Detection As the perilymph moves: Pressure is put on the scala media This pressure distorts the hair cells of the organ of Corti This distortion depolarizes the neurons Nerve signals are sent to the brain via CN VIII

Equilibrium and Hearing Auditory Pathways Stimulation of hair cells in the cochlea Sensory neurons carry the sound information from N VIII to the cochlear nuclei Information travels to the inferior colliculi of the midbrain

Equilibrium and Hearing Auditory Pathways (continued) The inferior colliculi causes the rotation of the head in the direction of the sound Information goes to the medial geniculate nucleus Information goes to the auditory cortex of the temporal lobe

Figure 18.18 Pathways for Auditory Sensations 1 Stimulation of hair cells at a specific location along the basilar membrane activates sensory neurons. To ipsilateral auditory cortex Thalamus Highfrequency sounds 6 Projection fibers then deliver the information to specific locations within the auditory cortex of the temporal lobe. Low-frequency sounds Cochlea Low-frequency sounds High-frequency sounds Vestibular branch 4 5 Ascending acoustic information goes to the medial geniculate nucleus. The inferior colliculi direct a variety of unconscious motor responses to sounds. 2 Sensory neurons carry the sound information in the cochlear branch of the vestibulocochlear nerve (N VIII) to the cochlear nuclei. Vestibulocochlear nerve (N VIII) Cochlear nucleus To reticular formation and motor nuclei of cranial nerves Superior olivary nucleus 3 Information ascends from the cochlear nuclei to the inferior colliculi of the midbrain. KEY First-order neuron Second-order neuron Third-order neuron Fourth-order neuron Motor output to spinal cord through the tectospinal tracts

Vision Accessory Structures of the Eye Palpebrae (eyelids) Medial and lateral canthus Connect the eyelids at the corners of the eye Palpebral fissure Area between the eyelid Eyelashes Contain root hair plexus, which triggers the blinking reflex

Vision Accessory Structures of the Eye (continued) Conjunctiva Epithelial lining of the eyelid Glands Glands of Zeis, tarsal glands, lacrimal gland, lacrimal caruncle

Figure 18.19a Accessory Structures of the Eye, Part I Eyelashes Palpebra Lateral canthus Sclera Corneal limbus Pupil Palpebral fissure Medial canthus Lacrimal caruncle a Superficial anatomy of the right eye and its accessory structures

Figure 18.19b Accessory Structures of the Eye, Part I Tendon of superior oblique muscle Lacrimal gland (orbital portion) Tarsal plates Levator palpebrae superioris muscle Orbital fat Palpebral fissure Lacrimal sac Orbicularis oculi (cut) b Diagrammatic representation of a superficial dissection of the right orbit

Figure 18.19c Accessory Structures of the Eye, Part I Superior rectus muscle Lacrimal gland ducts Lacrimal gland Lateral canthus Lower eyelid Inferior rectus muscle Inferior oblique muscle Tendon of superior oblique muscle Lacrimal punctum Superior lacrimal canaliculus Medial canthus Inferior lacrimal canaliculus Lacrimal sac Nasolacrimal duct Inferior nasal concha Opening of nasolacrimal duct c Diagrammatic representation of a deeper dissection of the right eye showing its position within the orbit and its relationship to accessory structures, especially the lacrimal apparatus

Vision Accessory Structures of the Eye Eyelids Also known as palpebrae Connected at the corners called medial and lateral canthus Eyelashes are along the palpebral borders Eyelashes are associated with sebaceous glands Tarsal glands are located along the inner lining of the eyelids They secrete lipid products that prevent the eyelids from sticking together

Vision Accessory Structures of the Eye Eyelids Conjunctiva Covers the inside lining of the eyelids and the outside lining of the eye Fluid production helps prevent these layers from becoming dry Palpebral conjunctiva (Inner lining of the eyelids) Ocular conjunctiva (Outer lining of the eyelids)

Vision Accessory Structures of the Eye Eyelids All of the glands are for protection or lubrication Glands of Zeis: sebaceous glands / associated with eyelashes Tarsal glands: secrete a lipid-rich product / keeps the eyelids from sticking together / located along the inner margin of the eyelids Lacrimal glands: produce tears / located at the superior, lateral portion of the eye Lacrimal caruncle glands: produce thick secretions / located within the canthus areas

Vision Accessory Structures of the Eye Eyelids An infection of the tarsal gland may result in a cyst An infection of any of the other glands may result in a sty

Vision Accessory Structures of the Eye The Lacrimal Apparatus Produces, distributes, and removes tears The lacrimal apparatus consists of: Lacrimal glands (produce tears) Lacrimal canaliculi Lacrimal sac Nasolacrimal duct

Vision Accessory Structures of the Eye The Lacrimal Apparatus Tears are produced by the lacrimal glands Flow over the ocular surface Flow into the nasolacrimal canal (foramen) This foramen enters into the nasal cavity Therefore, when you sob heavily, tears flow across your eye and down your face and also through the nasolacrimal canal into your nose and out, resulting in a runny nose

Vision The Eye Consist of: Sclera Cornea Pupil Iris Lens Anterior cavity Posterior cavity Three tunics: (1) fibrous tunic, (2) vascular tunic, and (3) neural tunic Retina

Figure 18.21b Sectional Anatomy of the Eye Posterior cavity (Vitreous chamber filled with the vitreous body) Fovea Ora serrata Fornix Palpebral conjunctiva Ocular conjunctiva Ciliary body Anterior chamber (filled with aqueous humor) Lens Pupil Central retinal artery and vein Optic nerve (N II) Optic disc b Retina Choroid Sclera Major anatomical landmarks and features in a diagrammatic view of the left eye Cornea Iris Posterior chamber (filled with aqueous humor) Corneal limbus Suspensory ligaments

Figure 18.21ab Sectional Anatomy of the Eye Fibrous tunic (sclera) Vascular tunic (choroid) Neural tunic (retina) Posterior cavity (Vitreous chamber filled with the vitreous body) Ora serrata Fornix Palpebral conjunctiva Ocular conjunctiva Ciliary body Fovea Anterior chamber (filled with aqueous humor) Lens a The three layers, or tunics, of the eye Central retinal artery and vein Pupil Cornea Iris Optic nerve (N II) Optic disc Retina Choroid Sclera Posterior chamber (filled with aqueous humor) Corneal limbus Suspensory ligaments b Major anatomical landmarks and features in a diagrammatic view of the left eye

Vision The Eyes The Fibrous Tunic (outermost layer) Makes up the sclera and cornea The cornea is modified sclera Provides some degree of protection Provides attachment sites for extra-ocular muscles Contains structures associated with focusing

Figure 18.22 The Lens and Chambers of the Eye Sclera Ciliary body Ciliary processes Canal of Schlemm Anterior cavity Anterior chamber Posterior chamber Posterior cavity Lens Pupil Iris Neural tunic (retina) Neural layer Pigmented layer Posterior cavity Vascular tunic Choroid Ciliary body Iris Anterior cavity Fibrous tunic Cornea Sclera Suspensory ligaments Pupillary sphincter muscle Pupillary dilator muscle Cornea Ciliary muscle a The lens is suspended between the posterior cavity and the posterior chamber of the anterior cavity. b Its position is maintained by the suspensory ligaments that attach the lens to the ciliary body.

Vision The Eyes The Vascular Tunic (middle layer) Consists of blood vessels, lymphatics, and intrinsic eye muscles Regulates the amount of light entering the eye Secretes and reabsorbs aqueous fluid (aqueous humor) Controls the shape of the lens Includes the iris, ciliary body, and the choroid

Vision The Eyes The Vascular Tunic The iris Consists of blood vessels, pigment, and smooth muscles The pigment creates the color of the eye The smooth muscles contract to change the diameter of the pupil

Vision The Eyes The Vascular Tunic The ciliary body The ciliary bodies consist of ciliary muscles connected to suspensory ligaments, which are connected to the lens The choroid Highly vascularized The innermost portion of the choroid attaches to the outermost portion of the retina

Vision The Eyes The Neural Tunic (inner layer) Also called the retina Made of two layers Pigmented layer outer layer Neural layer inner layer Retina cells Rods (night vision) Cones (color vision)

Figure 18.23a Retinal Organization Horizontal cell Cone Rod Choroid Pigmented layer of retina Rods and cones Amacrine cell Bipolar cells Ganglion cells LIGHT a Nuclei of ganglion cells Nuclei of rods and cones Nuclei of bipolar cells The retina LM x 75 Histological organization of the retina. Note that the photoreceptors are located closest to the choroid rather than near the vitreous chamber.

Figure 18.23b Retinal Organization PIGMENT EPITHELIUM Melanin granules OUTER SEGMENT Visual pigments in membrane discs INNER SEGMENT Location of major organelles and metabolic operations such as photopigment synthesis and ATP production Discs Connecting stalks Mitochondria Cone Golgi apparatus Nuclei Rods Synapses with bipolar cells b Bipolar cell Diagrammatic view of the fine structure of rods and cones, based on data from electron microscopy. LIGHT

Vision The Eyes The Neural Tunic (inner layer) Retinal organization There are rods and cones all over the retina 100% cones in the fovea centralis area The best color vision is when an object is focused on the fovea centralis 0% rods or cones in the optic disc area If an object is focused on this area, vision does not occur Also known as the blind spot

Vision The Chambers of the Eye Anterior cavity Anterior chamber Posterior chamber Filled with fluid called aqueous humor Posterior cavity Vitreous chamber Filled with fluid called vitreous body

Figure 18.21a-d Sectional Anatomy of the Eye Fibrous tunic (sclera) Vascular tunic (choroid) Neural tunic (retina) Posterior cavity (Vitreous chamber filled with the vitreous body) Fovea Ora serrata Fornix Palpebral conjunctiva Ocular conjunctiva Ciliary body Anterior chamber (filled with aqueous humor) Lens a The three layers, or tunics, of the eye Central retinal artery and vein Optic nerve (N II) Optic disc b Retina Choroid Sclera Major anatomical landmarks and features in a diagrammatic view of the left eye Pupil Cornea Iris Posterior chamber (filled with aqueous humor) Corneal limbus Suspensory ligaments Optic nerve (N II) Dura mater Retina Choroid Sclera c Pupillary dilator muscles (radial) Pupil Pupillary constrictor muscles (sphincter) Constrictors contract Dilators contract The action of pupillary muscles and changes in pupillary diameter d Posterior cavity (vitreous chamber) Sagittal section through the eye Ora serrata Conjunctiva Cornea Lens Anterior chamber Iris Posterior chamber Suspensory ligaments Ciliary body

Vision The Chambers of the Eye Aqueous humor Secreted by cells at the ciliary body area Enters the posterior chamber (posterior of the iris) Flows through the pupil area Enters the anterior chamber Flows through the canal of Schlemm Enters into venous circulation

Figure 18.24 The Circulation of Aqueous Humor Cornea Pupil Anterior cavity Anterior chamber Posterior chamber Ciliary process Suspensory ligaments Pigmented epithelium Lens Posterior cavity (vitreous chamber) Canal of Schlemm Body of iris Conjunctiva Ciliary body Sclera Choroid Retina

Vision The Chambers of the Eye Vitreous body Gelatinous material in the posterior chamber Supports the shape of the eye Supports the position of the lens Supports the position of the retina Aqueous humor can flow across the vitreous body and over the retina

Figure 18.21d Sectional Anatomy of the Eye Optic nerve (N II) Dura mater Retina Choroid Sclera Ora serrata Conjunctiva Posterior cavity (vitreous chamber) Cornea Lens Anterior chamber Iris Posterior chamber Suspensory ligaments Ciliary body d Sagittal section through the eye

Vision Aqueous Humor If this fluid cannot drain through the canal of Schlemm, pressure builds up This is glaucoma Vitreous Body If this fluid is not of the right consistency, the pressure is reduced against the retina The retina may detach from the posterior wall (detached retina)

Vision The Lens Focuses the image on the photoreceptors of the retina Consists of concentric layers of cells Changes shape due to: Tension in suspensory ligaments Contraction and relaxation of ciliary muscles

Vision Visual Pathways Light waves pass through the cornea Pass through the anterior chamber Pass through the pupil Pass through the posterior chamber Pass through the lens The lens focuses the image on some part of the retina This creates a depolarization of the neural cells Signal is transmitted to the brain via CN II

Figure 18.21e Sectional Anatomy of the Eye Visual axis Anterior cavity Posterior chamber Anterior chamber Edge of pupil Cornea Iris Suspensory ligament of lens Lacrimal punctum Lacrimal caruncle Nose Corneal limbus Conjunctiva Lower eyelid Medial canthus Ciliary processes Lens Lateral canthus Ciliary body Ora serrata Sclera Choroid Fovea Retina Ethmoidal labyrinth Posterior cavity Lateral rectus muscle Medial rectus muscle Optic disc Optic nerve (N II) Central artery and vein e Section through the eye Orbital fat

Vision Visual Pathways The retina (continued) The cones require light to be stimulated (that s why we see color) At night (still has to be at least a small amount of light), the cones deactivate and the rods begin to be activated (that s why we can see at night but we can t determine color at night)

Vision Visual Pathways Cortical Integration Information arrives at the visual cortex of the occipital lobes There is a crossover of information at the optic chiasm region

Figure 18.26 Anatomy of the Visual Pathways, Part II LEFT SIDE RIGHT SIDE Left eye only Binocular vision Right eye only Optic nerve (N II) Optic chiasm Optic tract Other hypothalamic nuclei, pineal gland, and reticular formation Suprachiasmatic nucleus Lateral geniculate nucleus Superior colliculus Lateral geniculate nucleus Projection fibers (optic radiation) LEFT CEREBRAL HEMISPHERE Visual cortex of cerebral hemispheres RIGHT CEREBRAL HEMISPHERE