Chapter 10c Sensory Physiology

Vestibular apparatus Semicircular canals Otolith organs The Ear: Equilibrium Vestibular apparatus Semicircular canals Otolith organs Equilibrium pathways

The Vestibular Apparatus A series of interconnected fluid-filled chambers Provides information about movement and position in space

Anatomy Summary: The Vestibular Apparatus SEMICIRCULAR CANALS (a) Superior Horizontal Posterior Cochlea Cristae within ampulla Utricle Saccule Maculae Figure 10-25a

Anatomy Summary: The Vestibular Apparatus Posterior canal (head tilt) Superior canal (nod for “yes”) Left right Horizontal canal (shake head for “no”) (b) Figure 10-25b

Anatomy Summary: The Vestibular Apparatus Cupula Endolymph Hair cells Supporting cells Nerve (c) Figure 10-25c

Anatomy Summary: The Vestibular Apparatus Hair cells Gelatinous otolith membrane Otoliths are crystals that move in response to gravitational forces. Nerve fibers (d) Macula Figure 10-25d

Transduction of Rotational Forces in the Cristae The semicircular canals sense rotational acceleration Brush moves right Cupula Bone Endolymph Stationary board Bristles bend left Hair cells Bone Direction of rotation of the head When the head turns right, endolymph pushes the cupula to the left. Figure 10-26

Otoliths Move in Response to Gravity or Acceleration Figure 10-27a

Otoliths Move in Response to Gravity or Acceleration Figure 10-27b

Dynamic Equilibrium and the crista ampullaris

Meniere's disease Vincent van Gogh, whose artistic brilliance and supposed madness have made him a focus of popular fascination, suffered not from epilepsy or insanity but from Meniere's disease,

Central Nervous System Pathways for Equilibrium Cerebral cortex Thalamus Reticular formation Vestibular branch of vestibulocochlear nerve (VIII) Cerebellum Somatic motor neurons controlling eye movements Vestibular apparatus Vestibular nuclei of medulla Figure 10-28

Photoreceptors transduce light energy The Eye and Vision Light enters the eye Focused on retina by the lens Photoreceptors transduce light energy Electrical signal Processed through neural pathways

External Anatomy of the Eye Muscles attached to external surface of eye control eye movement. Lacrimal gland secretes tears. Upper eyelid Sclera Pupil Iris Lower eyelid The orbit is a bony cavity that protects the eye. Nasolacrimal duct drains tears into nasal cavity. Figure 10-29

Anatomy Summary: The Eye Zonules Lens Optic disk (blind spot) Canal of Schlemm Aqueous humor Central retinal artery and vein Cornea Optic nerve Pupil Fovea Iris Macula Vitreous chamber (b) Retina Ciliary muscle Sclera is connective tissue. (a) Sagittal section of the eye Figure 10-30

Anatomy Summary: The Eye Zonules Lens Optic disk (blind spot) Canal of Schlemm Central retinal artery and vein Aqueous humor Cornea Optic nerve Pupil Fovea Iris Vitreous chamber Retina Ciliary muscle Sclera is connective tissue. (a) Sagittal section of the eye Figure 10-30a

Anatomy Summary: The Eye Optic disk (blind spot) Central retinal artery and vein Fovea Macula (b) Figure 10-30b

Neural Pathways for Vision and the Pupillary Reflex (a) Dorsal view Optic tract Eye Optic chiasm Optic nerve Figure 10-31a

Neural Pathways for Vision and the Pupillary Reflex (b) Neural pathway for vision, lateral view Eye Optic nerve Optic chiasm Optic tract Lateral geniculate body (thalamus) Visual cortex (occipital lobe) Figure 10-31b

Neural Pathways for Vision and the Pupillary Reflex (c) Collateral pathways leave the thalamus and go to the midbrain. Optic nerve Optic chiasm Optic tract Lateral geniculate body (thalamus) Visual cortex (occipital lobe) Eye Light Midbrain Cranial nerve III controls pupillary constriction. Figure 10-31c

Light enters the eye through the pupil Size of the pupil modulates light Photoreceptors Shape of lens focuses the light Pupillary reflex Standard part of neurological examination

Refraction of Light Figure 10-32a

Refraction of Light Figure 10-32b

Optics Figure 10-33a

Optics Figure 10-33b

Optics Figure 10-33c

Accommodation Accommodation is the process by which the eye adjusts the shape of the lens to keep objects in focus Cornea Iris Lens Ligaments Ciliary muscle (a) The lens is attached to the ciliary muscle by inelastic ligaments (zonules). Figure 10-34a

Accommodation Ciliary muscle relaxed Lens flattened Cornea Ligaments pulled tight (b) When ciliary muscle is relaxed, the ligaments pull on and flatten the lens. Figure 10-34b

Accommodation Ciliary muscle contracted Lens rounded Ligaments slacken (c) When ciliary muscle contracts, it releases tension on the ligaments and the lens becomes more rounded. Figure 10-34c

Common Visual Defects Figure 10-35a

Common Visual Defects Figure 10-35b

The Electromagnetic Spectrum Figure 10-36

Anatomy Summary: The Retina Horizontal cell Amacrine cell Light Ganglion cell Neurons where signals from rods and cones are integrated Cone (color vision) Bipolar cell Rod (monochromatic vision) (d) Retinal photoreceptors are organized into layers. Figure 10-37d

Phototransduction Figure 10-38

Photoreceptors: Rods and Cones PIGMENT EPITHELIUM Old disks at tip are phagocytized by pigment epithelial cells. Melanin granules OUTER SEGMENT Visual pigments in membrane disks Disks Disks Connecting stalks INNER SEGMENT Mitochondria Location of major organelles and metabolic operations such as photopigment synthesis and ATP production Rhodopsin molecule Cone Rods Retinal Opsin SYNAPTIC TERMINAL Synapses with bipolar cells Bipolar cell LIGHT Figure 10-39

Photoreceptors: Rods and Cones PIGMENT EPITHELIUM Old disks at tip are phagocytized by pigment epithelial cells. Melanin granules OUTER SEGMENT Disks Visual pigments in membrane disks Disks Connecting stalks Figure 10-39 (1 of 2)

Photoreceptors: Rods and Cones INNER SEGMENT Mitochondria Location of major organelles and metabolic operations such as photopigment synthesis and ATP production Rhodopsin molecule Cone Rods Retinal Opsin SYNAPTIC TERMINAL Synapses with bipolar cells Bipolar cell LIGHT Figure 10-39 (2 of 2)

Light Absorption of Visual Pigments Figure 10-40

Phototransduction in Rods (a) In darkness, rhodopsin is inactive, cGMP is high, and CNG and K+ channels are open. Pigment epithelium cell Disk Transducin (G protein) Inactive rhodopsin (opsin and retinal) cGMP levels high Ca2+ CNG channel open Na+ K+ Membrane potential in dark = –40mV Rod Tonic release of neurotransmitter onto bipolar neurons Figure 10-41a

Phototransduction in Rods (b) Light bleaches rhodopsin. Opsin decreases cGMP, closes CNG channels, and hyperpolarizes the cell. Activated retinal Opsin (bleached pigment) Activates transducin Cascade Decreased cGMP Ca2+ Na+ CNG channel closes K+ Membrane hyperpolarizes to –70 mV Light Neurotransmitter release decreases in proportion to amount of light. Figure 10-41b

Phototransduction in Rods (c) In the recovery phase, retinal recombines with opsin. When light activates rhodopsin, a second-messenger cascade is initiated through transducin Retinal converted to inactive form Retinal recombines with opsin to form rhodopsin. Figure 10-41c

Ganglion Cell Receptive Fields Figure 10-42

Visual Fields and Binocular Vision zone Left visual field Right visual field Optic chiasm Optic nerve Optic tract Lateral geniculate body (thalamus) Visual cortex Figure 10-43

General properties Somatic senses Summary Four types of sensory receptors Adequate stimulus, threshold, receptive field, and perceptual threshold Modality, localization, intensity, and duration Somatic senses Four modalities, second sensory neurons, and somatosensory cortex Nociceptors, spinal reflexes, and pain

The ear: hearing and equilibrium The eye and vision Summary Chemoreception Olfaction and taste The ear: hearing and equilibrium The eye and vision Retina, pupil, ciliary muscle, and photoreceptors