Download Dr. Cam Perkins - BIOL 2210

PowerPoint Lecture Outlines
to accompany
Hole’s Human
Anatomy and Physiology
Tenth Edition
Shier w Butler w Lewis
Chapter
11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
11-1
Chapter 11
Nervous System II
Meninges
• membranes
surrounding CNS
• protect CNS
• three layers
• dura mater – outer,
tough
• arachnoid mater weblike
• pia mater – inner,
delicate
11-2
Meninges of the Spinal Cord
11-3
The Spinal Cord & Spinal Nerves
• Together with brain forms the CNS
• Functions
– spinal cord reflexes
– integration (summation of inhibitory and
excitatory) nerve impulses
– highway for upward and downward travel of
sensory and motor information
Meninges
• The meninges are three coverings that run
continuously around the spinal cord and brain
(Figures 13.1a, 14.4a).
– The outermost layer is the dura mater.
– The middle layer is the arachnoid.
– The innermost meninx is the pia mater, a thin,
transparent connective tissue layer that adheres to the
surface of the spinal cord and brain
• Denticulate ligaments are thickenings of the pia
mater that suspend the spinal cord in the middle of
its dural sheath.
Structures Covering the Spinal Cord
• Vertebrae
• Epidural space filled with fat
• Dura mater
– dense irregular CT tube
• Subdural space filled with
interstitial fluid
• Arachnoid = spider web of
collagen fibers
• Subarachnoid space = CSF
• Pia mater
– thin layer covers BV
– denticulate ligs hold in place
Ventricles
• interconnected cavities
• within cerebral
hemispheres and brain
stem
• continuous with central
canal of spinal cord
• filled with cerebrospinal
fluid (csf)
• lateral ventricles
• third ventricle
• fourth ventricle
• cerebral aqueduct
11-4
Cerebrospinal Fluid
• secreted by choroid
plexus
• circulates in ventricles,
central canal of spinal
cord, and subarachnoid
space
• completely surrounds
brain and spinal cord
• clear liquid
• nutritive and protective
• helps maintain stable ion
concentrations in CNS
11-5
Spinal Cord Structure
• extends foramen magnum to 2nd lumbar vertebra
11-6
Cross Section of Spinal Cord
11-7
Reflex Arcs
Reflexes – automatic, subconscious responses to stimuli
11-9
Tracts of the Spinal Cord
• Ascending tracts conduct sensory impulses to the brain
• Descending tracts conduct motor impulses from the brain to
motor neurons reaching muscles and glands
11-13
Ascending Tracts
• fasciculus cuneatus
• lateral spinothalamic
11-14
Corticospinal Tract
11-15
Brain
Functions
Major Parts
• interprets sensations
• cerebrum
• two cerebral hemispheres
• determines perception
• diencephalon
• stores memory
• brain stem
• reasoning
• cerebellum
• makes decisions
• coordinates muscular
movements
• regulates visceral activities
• determines personality
11-16
Brain Development
Three Major Vesicles
1. Forebrain
2. Midbrain
3. Hindbrain
Forebrain (prosencephalon)
• anterior portion (telencephalon)
• cerebrum
• basal ganglia
• posterior portion (diencephalon)
• thalamus
• hypothalamus
• posterior pituitary
• pineal gland
11-17
Brain Development
Midbrain (mesencephalon)
• midbrain
Hindbrain (rhombencephalon)
• anterior portion (metencephalon)
• cerebellum
• pons
• posterior portion (myelencephalon)
• medulla oblongata
11-18
Structure of Cerebrum
• corpus callosum
• connects hemispheres
• convolutions
• bumps or gyri
• sulci
• grooves
• longitudinal fissure
• separates hemispheres
• transverse fissure
• separates cerebrum from
cerebellum
11-19
Lobes of Cerebrum
• Frontal
• Parietal
• Temporal
• Occipital
• Insula
11-20
Functions of Cerebrum
• interpretation
• initiating voluntary movements
• storing memory
• retrieving memory
• reasoning
• center for intelligence and personality
11-21
Functional Regions of
Cerebral Cortex
Cerebral Cortex – thin layer of gray matter that
constitutes the outermost portion of cerebrum; contains
75% of all neurons in nervous system
11-22
Motor Areas
• Primary Motor Areas
• frontal lobes
• control voluntary muscles
• Broca’s Area
• anterior to primary motor
cortex
• usually in one hemisphere
• controls muscles needed for
speech
• Frontal Eye Field
• above Broca’s area
• controls voluntary
movements of eyes and
eyelids
11-23
Motor Areas
11-24
Sensory Areas
• Cutaneous Sensory
Area
• parietal lobe
• interprets sensations
on skin
• Visual Area
• occipital lobe
• interprets vision
• Auditory Area
• temporal lobe
• interprets hearing
11-25
Sensory Areas
11-26
Association Areas
• regions of cortex that are not primary motor or primary
sensory areas
• widespread throughout the cerebral cortex
• analyze and interpret sensory experiences
• provide memory, reasoning, verbalization, judgment, emotions
11-27
Association Areas
Frontal Lobe Association Areas
• concentrating
• planning
• problem solving
• judging
Temporal Lobe Association Areas
• remember visual scenes
• remember music
• remember complex patterns
Parietal Lobe Association Areas
• understanding speech
• using words to express
thought
Occipital Lobe Association Areas
• combine visual images with
other sensory experiences
11-28
Memory
Short Term
• working memory
• closed circuit
• circuit is stimulated over
and over
• when impulse flow
stops, memory disappears
Long Term
• changes structure
and function of
neurons
• enhanced synaptic
transmission
11-30
Basal Nuclei
• masses of gray matter
• deep within cerebral
hemispheres
• caudate nucleus, putamen,
globus pallidus
• produce dopamine
• control certain muscular
activities
11-31
Diencephalon
• between cerebral hemispheres and brainstem
• surrounds third ventricle
• thalamus
• hypothalamus
• optic tracts
• optic chiasm
• infundibulum
• posterior pituitary
• mammillary bodies
• pineal gland
11-32
Diencephalon
Thalamus
• gateway for sensory impulses heading to cerebral cortex
• receives all sensory impulses (except smell)
• channels impulses to appropriate part of cerebral cortex
for interpretation
Hypothalamus
• maintains homeostasis by regulating visceral activities
• links nervous and endocrine systems
11-33
Limbic System
Consists of
• portions of frontal lobe
• portions of temporal lobe
• hypothalamus
• thalamus
• basal nuclei
• other deep nuclei
Functions
• controls emotions
• produces feelings
• interpret sensory impulses
11-34
Brain Stem
Three Parts
1. Midbrain
2. Pons
3. Medulla Oblongata
11-35
Midbrain
• between diencephalon and
pons
• contains bundles of fibers
that join lower parts of
brainstem and spinal cord
with higher part of brain
• cerebral aqueduct
• cerebral peduncles –
bundles of nerve fibers
• corpora quadrigemina –
centers for visual and
auditory reflexes
11-36
Pons
• rounded bulge on underside of
brainstem
• between medulla oblongata
and midbrain
• helps regulate rate and depth
of breathing
• relays nerve impulses to and
from medulla oblongata and
cerebellum
11-37
Medulla Oblongata
• enlarged continuation of
spinal cord
• conducts ascending and
descending impulses between
brain and spinal cord
• contains cardiac, vasomotor,
and respiratory control
centers
• contains various nonvital
reflex control centers
(coughing, sneezing,
vomiting)
11-38
Reticular Formation
• complex network of
nerve fibers scattered
throughout the brain stem
• extends into the
diencephalon
• connects to centers of
hypothalamus, basal
nuclei, cerebellum, and
cerebrum
• filters incoming sensory
information
• arouses cerebral cortex
into state of wakefulness
11-39
Cerebellum
• inferior to occipital lobes
• posterior to pons and medulla
oblongata
• two hemispheres
• vermis connects hemispheres
• cerebellar cortex – gray matter
• arbor vitae – white matter
• cerebellar peduncles – nerve fiber
tracts
• dentate nucleus – largest nucleus in
cerebellum
• integrates sensory information
concerning position of body parts
• coordinates skeletal muscle activity
• maintains posture
11-41
Peripheral Nervous System
• Cranial nerves arising from the brain
• Somatic fibers connecting to the skin and skeletal muscles
• Autonomic fibers connecting to viscera
• Spinal nerves arising from the spinal cord
• Somatic fibers connecting to the skin and skeletal muscles
• Autonomic fibers connecting to viscera
11-42
Structure of a Peripheral Nerve
11-43
Nerve Fiber Classification
• Sensory Nerves – conduct impulses into CNS
• Motor Nerves – conduct impulses to muscles or glands
• Mixed Nerves – contain both sensory nerve fibers and
motor nerve fibers; most nerves
General somatic efferent fibers
• carry motor impulses from
CNS to skeletal muscles
General somatic afferent fibers
• carry sensory impulses to
CNS from skin and skeletal
muscles
General visceral efferent fibers
• carry motor impulses away from
CNS to smooth muscles and
glands
General visceral afferent fibers
• carry sensory impulses to CNS
from blood vessels and internal
organs
11-44
Nerve Fiber Classification
Special somatic efferent fibers
• carry motor impulses from brain to muscles
used in chewing, swallowing, speaking, and
forming facial expressions
Special visceral afferent fibers
• carry sensory impulses to brain from olfactory and
taste receptors
Special somatic afferent fibers
• carry sensory impulses to brain from receptors of
sight, hearing, and equilibrium
11-45
Cranial Nerves
11-46
Cranial Nerves I and II
Olfactory (I)
• sensory
• fibers
transmit
impulses
associated
with smell
Optic (II)
• sensory
• fibers
transmit
impulses
associated
with vision
11-47
Cranial Nerves III and IV
Oculomotor (III)
• primarily motor
• motor impulses
to muscles that
• raise eyelids
• move the eyes
• focus lens
•adjust light
entering eye
Trochlear (IV)
• primarily motor
• motor impulses
to muscles that
move the eyes
11-48
Cranial Nerve V
Trigeminal (V)
• mixed
• opthalmic division
• sensory from surface of eyes,
tear glands, scalp, forehead, and
upper eyelids
• maxillary division
• sensory from upper teeth,
upper gum, upper lip, palate,
and skin of face
• mandibular division
• sensory from scalp, skin of jaw,
lower teeth, lower gum, and
lower lip
• motor to muscles of mastication
and muscles in floor of mouth
11-49
Cranial Nerves VI and VII
Abducens (VI)
• primarily motor
• motor impulses to
muscles that move
the eyes
Facial (VII)
• mixed
• sensory from taste
receptors
• motor to muscles of
facial expression,
tear glands, and
salivary glands
11-50
Cranial Nerves VIII and IX
Vestibulocochlear (VIII)
• sensory
• sensory from
equilibrium
receptors of ear
• sensory from
hearing receptors
Glossopharyngeal (IX)
• mixed
• sensory from
pharynx, tonsils,
tongue, and carotid
arteries
• motor to salivary
glands and muscles
of pharynx
11-51
Cranial Nerve X
Vagus (X)
• mixed
• somatic motor to
muscles of speech
and swallowing
• autonomic motor to
viscera of thorax and
abdomen
• sensory from
pharynx, larynx,
esophagus, and
viscera of thorax and
abdomen
11-52
Cranial Nerves XI and XII
Accessory (XI)
• primarily motor
• motor to muscles of
soft palate, pharynx,
larynx, neck, and
back
Hypoglossal (XII)
• primarily motor
• motor to muscles of
the tongue
11-53
Spinal Nerves
• mixed nerves
• 31 pairs
• 8 cervical (C1 to C8)
• 12 thoracic (T1 to T12)
• 5 lumbar (L1 to L5)
• 5 sacral (S1 to S5)
• 1 coccygeal (Co)
11-54
Spinal Nerves
Dorsal root
• axons of sensory
neurons in the
dorsal root
ganglion
Dorsal root ganglion
• cell bodies of
sensory neurons
Ventral root
• axons of motor
neurons whose
cell bodies are in
spinal cord
Spinal nerve
• union of ventral root
and dorsal root
11-55
Dermatome
• an area of skin that the sensory nerve fibers of a particular
spinal nerve innervate
11-56
Cervical Plexus
Nerve plexus – complex networks formed by anterior branches
of spinal nerves; fibers of various spinal nerves are sorted and
recombined
Cervical Plexus
• C1-C4
• lies deep in the neck
• supply muscles and
skin of the neck
• contribute to phrenic
nerve
11-57
Brachial Plexus
• C5-T1
• lies deep within shoulders
• musculocutaneous nerves
• supply muscles of anterior arms
and skin of forearms
• ulnar nerves
• supply muscles of forearms and
hands
• supply skin of hands
• radial nerves
• supply posterior muscles of
arms and skin of forearms and
hands
• axillary nerves
• supply muscles and skin of
superior, lateral, and posterior
arms
11-58
Lumbosacral Plexus
• T12 – S5
• extend from lumbar
region into pelvic cavity
• obturator nerves
• supply adductors of
thighs
• femoral nerves
• supply muscles and skin
of thighs and legs
• sciatic nerves
• supply muscles and skin
of thighs, legs, and feet
11-59
Autonomic Nervous System
• functions without conscious effort
• controls visceral activities
• regulates smooth muscle, cardiac muscle, and glands
• efferent fibers typically lead to ganglia outside CNS
Two Divisions
• sympathetic – prepares body for fight or flight
situations
• parasympathetic – prepares body for resting
and digesting activities
11-60
Autonomic Nerve Fibers
• all are motor (efferent)
• preganglionic fibers
• axons of preganglionic
neurons
• neuron cell bodies in
CNS
• postganglionic fibers
• axons of postganglionic
neurons
• neuron cell bodies in
ganglia
11-61
Sympathetic Division
• thoracolumbar divison –
location of preganglionic
neurons
• preganglionic fibers leave
spinal nerves through white
rami and enter
paravertebral ganglia
• paraverterbral ganglia
and fibers that connect
them make up the
sympathetic trunk
11-62
Sympathetic Division
• postganglionic fibers
extend from sympathetic
ganglia to visceral organs
• postganglionic fibers
usually pass through gray
rami and return to a spinal
nerve before proceeding to
an effector
• preganglionic fibers to
adrenal medulla do not
synapse with postganglionic
neurons
11-63
Sympathetic Division
11-64
Parasympathetic Division
• craniosacral division –
location of preganglionic
neurons
• preganglionic fibers of the
head in III, VII, and IX
• ganglia are near or
within various organs
• preganglionic fibers of
thorax and abdomen in X
• short postganlionic
fibers
11-65
Parasympathetic Division
11-66
Autonomic Neurotransmitters
Cholinergic Fibers
• release acetylcholine
• preganglionic
sympathetic fibers
• preganglionic
parasympathetic
fibers
• postganglionic
parasympathetic
fibers
Adrenergic Fibers
• release
norepinephrine
• postganglionic
sympathetic
fibers
11-67
Actions of Autonomic
Neurotransmitters
• depend on receptor
Cholinergic receptors
• bind to acetlycholine
• muscarinic
• excitatory
• nicotinic
• excitatory
Adrenergic Receptors
• bind to
norepinephrine
• alpha
• different responses
on various effectors
• beta
• different responses
on various effectors
11-68
Actions of Autonomic
Insert figure 11.39
Neurotransmitters
11-69
Control of Autonomic
Activity
• Controlled largely by CNS
• Medulla oblongata regulates cardiac, vasomotor and
respiratory activities
• Hypothalamus regulates visceral functions
• Limbic system and cerebral cortex control emotional
responses
11-70
PowerPoint Lecture Outlines
to accompany
Hole’s Human
Anatomy and Physiology
Eleventh Edition
Shier w Butler w Lewis
Chapter
12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Senses
Sensory Receptors
• specialized cells or multicellular structures that collect
information from the environment
• stimulate neurons to send impulses along sensory fibers to
the brain
Sensation
• a feeling that occurs when brain becomes aware of sensory
impulse
Perception
• a person’s view of the stimulus; the way the brain
interprets the information
SENSORY RECEPTION
• Sensory receptors convert stimulus energy to
action potentials
– Sensory receptors
•
Are specialized cells or neurons that detect
stimuli
– Sensory transduction converts stimulus energy
into receptor potentials
•
Which trigger action potentials that are
transmitted to the brain
Sugar
molecule
Taste
pore
Tongue
Taste
bud
1
Sugar
molecule
(stimulus)
Membrane
of sensory
receptor cell
2
Sensory
receptor
cells
Signal
transduction
pathway
Ion
channels
Sensory
receptor
cell
3


Ion
Sensory neuron
Receptor
potential
4
Neurotransmitter
Sensory neuron
mV
Action potential
No sugar
Figure 29.2A
5 Action potentials
Sugar present
– Action potential frequency
•
Reflects stimulus strength
Sugar
receptor
“Sugar” interneuron
“Salt” interneuron
Salt
receptor
Brain
Sensory
neurons
Taste
bud
No sugar
Figure 29.2B
Taste
bud
No salt
Increasing sweetness
Increasing saltiness
• Mechanoreceptors
– Mechanoreceptors
•
Respond to mechanical energy such as touch,
pressure, and sound
“Hairs” of
receptor cell
Neurotransmitter
at synapse
More
neurotransmitter
Less
neurotransmitter
Sensory
neuron
Action
potentials
Action
potentials
1 Receptor cell at rest
Figure 29.3B
2 Fluid moving in one direction
3 Fluid moving in other direction
– Repeated stimulus
•
May lead to adaptation, a decrease in
sensitivity
• Specialized sensory receptors detect five
categories of stimuli
– A section of human skin
•
Reveals many types of sensory receptors
Light
Heat touch
Pain
Cold Hair
Light
touch
Epidermis
Dermis
Figure 29.3A
Hair
Nerve Connective
movement
tissue
Strong
pressure
Receptor Types
Chemoreceptors
• respond to changes in chemical concentrations
Pain receptors (Nociceptors)
• respond to tissue damage
Thermoreceptors
• respond to changes in temperature
Mechanoreceptors
• respond to mechanical forces
Photoreceptors
• respond to light
Sensory Impulses
• stimulation of receptor causes local change in its receptor potential
• a graded electrical current is generated that reflects intensity of stimulation
• if receptor is part of a neuron, the membrane potential may generate an
action potential
• if receptor is not part of a neuron, the receptor potential must be
transferred to a neuron to trigger an action potential
• peripheral nerves transmit impulses to CNS where they are analyzed and
interpreted in the brain
Sensations
Projection
process in which the brain projects the sensation
back to the apparent source
it allows a person to pinpoint the region of
stimulation
Sensory Adaptation
• ability to ignore unimportant stimuli
• involves a decreased response to a particular stimulus
from the receptors (peripheral adaptations) or along
the CNS pathways leading to the cerebral cortex
(central adaptation)
• sensory impulses become less frequent and may cease
• stronger stimulus is required to trigger impulses
Touch and Pressure Senses
Free nerve endings
• common in epithelial
tissues
• simplest receptors
• sense itching
Meissner’s corpuscles
• abundant in hairless portions
of skin; lips
• detect fine touch; distinguish
between two points on the skin
Pacinian corpuscles
• common in deeper subcutaneous
tissues, tendons, and ligaments
• detect heavy pressure and
vibrations
Temperature Senses
Warm receptors
• sensitive to temperatures above 25oC (77o F)
• unresponsive to temperature above 45oC (113oF)
Cold receptors
• sensitive to temperature between 10oC (50oF) and 20oC
(68oF)
Pain receptors
• respond to temperatures below 10oC
• respond to temperatures above 45oC
Sense of Pain
• free nerve endings
• widely distributed
• nervous tissue of brain lacks pain receptors
• stimulated by tissue damage, chemical, mechanical forces,
or extremes in temperature
• adapt very little, if at all
Visceral Pain
• pain receptors are the only receptors in viscera whose
stimulation produces sensations
• pain receptors respond differently to stimulation
• not well localized
• may feel as if coming from some other part of the body
• known as referred pain
Referred Pain
• may occur due to sensory impulses from two regions
following a common nerve pathway to brain
Pain Nerve Pathways
Acute pain fibers
• A-delta fibers
•thin, myelinated
• conduct impulses
rapidly
• associated with
sharp pain
• well localized
Chronic pain fibers
• C fibers
•thin, unmyelinated
• conduct impulses more
slowly
• associated with dull,
aching pain
• difficult to pinpoint
Regulation of Pain Impulses
Thalamus
• allows person to be aware
of pain
Cerebral Cortex
• judges intensity of pain
• locates source of pain
• produces emotional and
motor responses to pain
Pain Inhibiting Substances
• enkephalins
• serotonin
• endorphins
Proprioceptors
• mechanoreceptors
• send information to spinal cord and CNS about body
position and length and tension of muscles
• Main kinds of proprioreceptors
• Pacinian corpuscles – in joints
• muscle spindles – in skeletal muscles*
• Golgi tendon organs – in tendons*
*stretch receptors
Stretch Receptors
Sense of Smell
Olfactory Receptors
• chemoreceptors
• respond to chemicals dissolved in liquids
Olfactory Organs
• contain olfactory receptors and supporting epithelial
cells
• cover parts of nasal cavity, superior nasal conchae,
and a portion of the nasal septum
Olfactory Receptors
Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses
travel through
• olfactory nerves
olfactory bulbs
olfactory
tracts
limbic system (for emotions) and
olfactory cortex/temporal lobe (for interpretation)
Olfactory Stimulation
• olfactory organs located high in the nasal cavity
above the usual pathway of inhaled air
• olfactory receptors undergo sensory adaptation
rapidly
• sense of smell drops by 50% within a second after
stimulation
Sense of Taste
Taste Buds
• organs of taste
• located on papillae of tongue, roof of mouth, linings of
cheeks and walls of pharynx
Taste Receptors
• chemoreceptors
• taste cells – modified epithelial cells that function
as receptors
• taste hairs –microvilli that protrude from taste
cells; sensitive parts of taste cells
Taste Receptors
Taste Nerve Pathways
Sensory impulses from taste receptors travel along
• cranial nerves to
• medulla oblongata to
• thalamus to
• gustatory cortex / parietal lobes (for interpretation)
Hearing
Ear – organ of hearing
Three Sections
• External
• Middle
• Inner
External Ear
• auricle
• collects sounds waves
• external auditory meatus
• lined with ceruminous glands
• carries sound to tympanic
membrane
• terminates with tympanic
membrane
• tympanic membrane
• vibrates in response to sound
waves
Middle Ear
• tympanic cavity
• air-filled space in temporal
bone
• auditory ossicles
• vibrate in response to tympanic
membrane
• malleus, incus, and stapes
• oval window
• opening in wall of tympanic
cavity
• stapes vibrates against it to
move fluids in inner ear
Auditory Tube
• eustachian tube
• connects middle ear to
throat
• helps maintain equal
pressure on both sides
of tympanic membrane
• usually closed by
valve-like flaps in throat
Inner Ear
• complex system of labyrinths
• osseous labyrinth
• bony canal in temporal
bone
• filled with perilymph
• membranous labyrinth
• tube within osseous
labyrinth
• filled with endolymph
Inner Ear
Three Parts of Labyrinths
• cochlea
• functions in hearing
• semicircular canals
• functions in
equilibrium
• vestibule
• functions in
equilibrium
Cochlea
Scala vestibuli
• upper compartment
• leads from oval window to
apex of spiral
• part of bony labyrinth
Scala tympani
• lower compartment
• extends from apex of the
cochlea to round window
• part of bony labyrinth
Cochlea
Cochlear duct
• portion of membranous
labyrinth in cochlea
Vestibular membrane
• separates cochlear duct
from scala vestibuli
Basilar membrane
• separates cochlear duct
from scala tympani
Organ of Corti
• group of hearing receptor cells
(hair cells)
• on upper surface of basilar
membrane
• different frequencies of vibration
move different parts of basilar
membrane
• particular sound frequencies cause
hairs of receptor cells to bend
• nerve impulse generated
Auditory Nerve Pathways
Summary of the Generation of
Sensory Impulses from the Ear
Equilibrium
Static Equilibrium
• vestibule
• sense position of
head when body is
not moving
Dynamic Equilibrium
• semicircular canals
• sense rotation and
movement of head and
body
Vestibule
• Utricle
• communicates with
saccule and
membranous portion of
semicircular canals
• Saccule
• communicates with
cochlear duct
• Macula
• hair cells of utricle and
saccule
Macula
• responds to
changes in head
position
• bending of hairs
results in generation
of nerve impulse
Semicircular Canals
• three canals at right angles
• ampulla
• swelling of membranous
labyrinth that communicates
with the vestibule
• crista ampullaris
• sensory organ of ampulla
• hair cells and supporting
cells
• rapid turns of head or body
stimulate hair cells
Crista Ampullaris
Sight
Visual Accessory Organs
• eyelids
• lacrimal apparatus
• extrinsic eye muscles
Eyelid
• palpebra
• composed of four layers
• skin
• muscle
• connective tissue
• conjunctiva
• orbicularis oculi - closes
• levator palperbrae superioris –
opens
• tarsal glands – secrete oil onto
eyelashes
• conjunctiva – mucous
membrane; lines eyelid and
covers portion of eyeball
Lacrimal Apparatus
• lacrimal gland
• lateral to eye
• secretes tears
• canaliculi
• collect tears
• lacrimal sac
• collects from canaliculi
• nasolacrimal duct
• collects from lacrimal
sac
• empties tears into nasal
cavity
Extrinsic Eye Muscles
Superior rectus
• rotates eye up and
medially
Inferior rectus
• rotates eye down
and medially
Medial rectus
• rotates eye
medially
Extrinsic Eye Muscles
Lateral rectus
• rotates eye
laterally
Superior oblique
• rotates eye down and
laterally
Inferior oblique
• rotates eye up and
laterally
Structure of the Eye
• hollow
• spherical
• wall has 3 layers
• outer fibrous tunic
• middle vascular tunic
• inner nervous tunic
Outer Tunic
Cornea
• anterior portion
• transparent
• light transmission
• light refraction
Sclera
• posterior portion
• opaque
• protection
Middle Tunic
Iris
• anterior portion
• pigmented
• controls light intensity
Ciliary body
• anterior portion
• pigmented
• holds lens
• moves lens for focusing
Choroid coat
• provides blood supply
• pigments absorb extra light
Anterior Portion of Eye
• filled with aqueous humor
Lens
• transparent
• biconvex
• lies behind iris
• largely composed of
lens fibers
• elastic
• held in place by
suspensory ligaments
of ciliary body
Ciliary Body
• forms internal ring around front of eye
• ciliary processes – radiating folds
• ciliary muscles – contract and relax to move lens
Accommodation
• changing of lens shape to view objects
• To focus, a lens changes position or shape
– Focusing
•
Involves changing the shape of the lens
Choroid
Ciliary muscle contracted
Ligaments slacken
Retina
Light from a near object
(diverging rays)
Near vision (accommodation)
Ciliary muscle relaxed
Ligaments pull on lens
Light from a distant object
(parallel rays)
Figure 29.6
Distance vision
Lens
Iris
• composed of connective
tissue and smooth muscle
• pupil is hole in iris
• dim light stimulates
radial muscles and pupil
dilates
• bright light stimulates
circular muscles and
pupil constricts
Aqueous Humor
• fluid in anterior cavity of eye
• secreted by epithelium on inner surface of the ciliary body
• provides nutrients
• maintains shape of anterior portion of eye
• leaves cavity through canal of Schlemm
Inner Tunic
• retina
• contains visual receptors
• continuous with optic nerve
• ends just behind margin of the ciliary body
• composed of several layers
• macula lutea – yellowish spot in retina
• fovea centralis – center of macula lutea; produces
sharpest vision
• optic disc – blind spot; contains no visual receptors
• vitreous humor – thick gel that holds retina flat against
choroid coat
Posterior Cavity
• contains vitreous humor – thick gel that holds retina
flat against choroid coat
Major Groups of Retinal Neurons
• receptor cells, bipolar cells, and ganglion cells - provide
pathway for impulses triggered by photoreceptors to reach the
optic nerve
• horizontal cells and amacrine cells – modify impulses
Layers of the Eye
Visual Receptors
Rods
• long, thin projections
• contain light sensitive
pigment called rhodopsin
• hundred times more
sensitive to light than cones
• provide vision in dim light
• produce colorless vision
• produce outlines of objects
Cones
• short, blunt projections
• contain light sensitive
pigments called
erythrolabe, chlorolabe,
and cyanolabe
• provide vision in bright
light
• produce sharp images
• produce color vision
Visual Pigments
Rhodopsin
• light-sensitive pigment in rods
• decomposes in presence of
light
• triggers a complex series of
reactions that initiate nerve
impulses
• impulses travel along optic
nerve
Pigments on Cones
• each set contains different lightsensitive pigment
• each set is sensitive to different
wavelengths
• color perceived depends on
which sets of cones are stimulated
• erythrolabe – responds to red
• chlorolabe – responds to green
• cyanolabe – responds to blue
Visual Nerve Pathway