Chapter 10c

Sensory Physiology

The Ear: Equilibrium

• Vestibular apparatus• Semicircular canals• Otolith organs• Equilibrium pathways

The Vestibular Apparatus

• Vestibular apparatus• A series of interconnected fluid-filled

chambers• Provides information about movement and

position in space

Cochlea

(a)

Saccule

UtricleCristae within

ampulla

Maculae

SEMICIRCULAR CANALS

Superior

Horizontal

Posterior

Anatomy Summary: The Vestibular Apparatus

Figure 10-25a

Anatomy Summary: The Vestibular Apparatus

Figure 10-25b

Vestibularapparatus

Superior canal(nod for “yes”)

Horizontal canal(shake head

for “no”)

Posterior canal(head tilt)

Left right

(b)

Anatomy Summary: The Vestibular Apparatus

Figure 10-25c

(c)

Cupula

Haircells

Supportingcells

Nerve

Endolymph

Anatomy Summary: The Vestibular Apparatus

Figure 10-25d

Nerve fibers

Gelatinousotolith

membrane

Hair cells

Otoliths are crystalsthat move in responseto gravitational forces.

(d) Macula

Transduction of Rotational Forces in the Cristae

• The semicircular canals sense rotational acceleration

Figure 10-26

Stationaryboard

Bristlesbend left

Brush movesright

Direction of rotation of the head

Endolymph

Bone

Bone

Cupula

Hair cells

When the head turns right, endolymph pushes the cupula to the left.

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

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,

Meniere's disease

Central Nervous System Pathways for Equilibrium

Figure 10-28

Vestibular apparatus

Vestibular branch ofvestibulocochlearnerve (VIII)

Reticularformation

Cerebralcortex

Somaticmotor neuronscontrolling eye

movements

Thalamus

Cerebellum

Vestibularnuclei ofmedulla

The Eye and Vision

• Light enters the eye • Focused on retina by the lens

• Photoreceptors transduce light energy • Electrical signal

• Electrical signal • Processed through neural pathways

External Anatomy of the Eye

Figure 10-29

Lacrimal glandsecretes tears.

Uppereyelid

Lowereyelid

Pupil

Iris

Sclera

Muscles attached toexternal surface of eyecontrol eye movement.

The orbit is a bonycavity that protectsthe eye.

Nasolacrimal ductdrains tears intonasal cavity.

Anatomy Summary: The Eye

Figure 10-30

Vitreous chamber

Aqueoushumor

Cornea

Fovea

Macula

Optic nerve

Iris

Pupil

Retina

Sclera is connective tissue.Ciliary muscle

Central retinalartery and vein

Canal ofSchlemm

(a) Sagittal section of the eye

(b)

Optic disk(blind spot)

LensZonules

Anatomy Summary: The Eye

Figure 10-30a

Vitreous chamber

Aqueoushumor

Cornea

FoveaOptic nerve

Iris

Pupil

Retina

Sclera is connective tissue.Ciliary muscle

Central retinalartery and vein

Canal ofSchlemm

(a) Sagittal section of the eye

Optic disk(blind spot)

LensZonules

Anatomy Summary: The Eye

Figure 10-30b

Fovea

Macula

Central retinalartery and vein

(b)

Optic disk(blind spot)

Neural Pathways for Vision and the Pupillary Reflex

Figure 10-31a

Optic tract

Eye Optic chiasm

Optic nerve

(a) Dorsal view

Neural Pathways for Vision and the Pupillary Reflex

Figure 10-31b

Optictract

Eye

Lateral geniculatebody (thalamus)

Opticchiasm

Opticnerve

Visual cortex(occipital lobe)

(b) Neural pathway forvision, lateral view

Neural Pathways for Vision and the Pupillary Reflex

Figure 10-31c

Optictract

Eye

Lateral geniculatebody (thalamus)

Opticchiasm

Opticnerve

Visual cortex(occipital lobe)

Midbrain

Cranial nerve III controlspupillary constriction.

Light

(c) Collateral pathwaysleave the thalamusand go to themidbrain.

The Pupil

• 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

Figure 10-34a

Cornea

Iris

Lens

Ligaments

Ciliary muscle

(a) The lens is attached to the ciliarymuscle by inelastic ligaments (zonules).

Accommodation

Figure 10-34b

Cornea

Ligamentspulled tight

Lens flattened

Ciliary musclerelaxed

(b) When ciliary muscle is relaxed, theligaments pull on and flatten the lens.

Accommodation

Figure 10-34c

Ligamentsslacken

Lens rounded

Ciliary musclecontracted

(c) When ciliary muscle contracts, itreleases tension on the ligamentsand the lens becomes more rounded.

Common Visual Defects

Figure 10-35a

Common Visual Defects

Figure 10-35b

The Electromagnetic Spectrum

Figure 10-36

Anatomy Summary: The Retina

Figure 10-37d

Rod (monochromatic vision)

Cone (color vision)Bipolar

cell

Ganglioncell

Amacrinecell

Horizontalcell

(d) Retinal photoreceptors are organized into layers.

Neurons where signalsfrom rods and cones

are integrated

Light

Phototransduction

Figure 10-38

Photoreceptors: Rods and Cones

Figure 10-39

Melanin granules

OUTER SEGMENTVisual pigments inmembrane disks

INNER SEGMENT

SYNAPTIC TERMINALSynapses withbipolar cells

PIGMENTEPITHELIUM

Bipolar cell

Location of majororganelles and metabolicoperations such asphotopigment synthesisand ATP production

Disks

Connectingstalks

Mitochondria

Cone Rods

LIGHT

Old disks at tip arephagocytized bypigment epithelial cells.

Retinal

Rhodopsinmolecule

Disks

Opsin

Photoreceptors: Rods and Cones

Figure 10-39 (1 of 2)

Melanin granules

OUTER SEGMENTVisual pigments inmembrane disks

PIGMENTEPITHELIUM

Disks

Connectingstalks

Old disks at tip arephagocytized bypigment epithelial cells.

Disks

Photoreceptors: Rods and Cones

Figure 10-39 (2 of 2)

INNER SEGMENT

SYNAPTIC TERMINALSynapses withbipolar cells

Bipolar cell

Location of majororganelles and metabolicoperations such asphotopigment synthesisand ATP production

Mitochondria

Cone Rods

LIGHT

Retinal

Rhodopsinmolecule

Opsin

Light Absorption of Visual Pigments

Figure 10-40

Phototransduction in Rods

Figure 10-41a

cGMPlevels high

Transducin(G protein)

Membrane potentialin dark = –40mV

Pigment epithelium cell

Inactiverhodopsin

(opsin and retinal)

Na+Ca2+

(a) In darkness, rhodopsin isinactive, cGMP is high, andCNG and K+ channels are open.

Disk

CNG channelopen

K+

Tonic release ofneurotransmitter

onto bipolar neurons

Rod

Phototransduction in Rods

Figure 10-41b

Ca2+

Neurotransmitter releasedecreases in proportion

to amount of light.

Membranehyperpolarizes

to –70 mV

Activatedretinal

Na+CNG channel

closes

DecreasedcGMP

Opsin (bleachedpigment)

Activatestransducin

Cascade

(b) Light bleaches rhodopsin. Opsindecreases cGMP, closes CNGchannels, and hyperpolarizes the cell.

K+

Light

Phototransduction in Rods

• When light activates rhodopsin, a second-messenger cascade is initiated through transducin

Figure 10-41c

(c) In the recovery phase, retinalrecombines with opsin.

Retinal converted toinactive form

Retinal recombineswith opsin to

form rhodopsin.

Ganglion Cell Receptive Fields

Figure 10-42

Visual Fields and Binocular Vision

Figure 10-43

Opticchiasm

Optic nerve

Lateralgeniculate body

(thalamus)

Visual cortex

Leftvisualfield

Rightvisualfield

Binocularzone

Visual field

Optic tract

Summary

• General properties• 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

Summary

• Chemoreception• Olfaction and taste

• The ear: hearing and equilibrium• The eye and vision• Retina, pupil, ciliary muscle, and

photoreceptors