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14.2 MS
Pathophysiology/Physiology
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Jessica Jardine
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Cards (46)
What would an issue with the ventral pathway for vision lead to?
Object recognition difficulties
What do ganglion cells act as?
Output cells
-> their
axons
form the
optic nerve
What is a receptor potential?
Electrical signals
generated in response to a
stimulus
by a
sensory receptor
-> when
activated
, produces
receptor potential
that causes a change in
cell membrane potential
What do amacrine & horizontal cells do?
Enhance
contrast
&
adjust
to different
levels
of
light
What is location coding?
Encoded by the
spinal pattern
of
neural activity
-> allows
brain
to
determine
the
location
of
stimulus
What do bipolar cells do?
Acts as a
'middle man'
-> passes
info
from the
PR
cell to the
ganglion
cell
What is type coding?
Different types
of
sensory stimuli
are detected by
different types
of
sensory receptor cells
What is intensity coding?
Frequency
&
amplitude
of
neural activity
->
higher intensity
stimuli = more
frequent
&
stronger neural responses
What would an issue with the dorsal pathway for vision lead to?
Spatial awareness deficits
What is duration coding?
Length
of
time
that
neural activity persists
What is the tectospinal tract for?
Mediating movements
in
response
to
visual stimuli
What protein is found in cones?
Opsin
What protein is found in rods?
Rhodopsin
Where are rods & cones found?
In
photoreceptor
cells
What is the cornea?
Clear
,
transparent
,
avascular
structure
Provides
78
% of
focusing power
of the
eye
What are the 5 layers of the cornea?
Epithelium
Bowman's layer
Stroma
Descemet's membrane
Endothelium
What are the endothelial cells of the cornea responsible for?
Maintaining
clarity
of
cornea
by
continuously pumping fluid out
of the
tissue
What is the sclera?
Opaque white
structure
Covers
4
/5 of the globe,
continuous
with
cornea
Extraocular muscles
are attached to
sclera
Optic nerve
perforates sclera
posteriorly
What is the conjunctiva?
Richly vascularized
&
innervated
mucous membrane
Covers
anterior surface
of
sclera
What is the anterior chamber?
Space
between
cornea
&
lens
Filled with aqueous humour → produced by
ciliary body
, provides
nutrients
&
O2
to
avascular cornea
Any factor that impedes
aqueous humour
→
raises intra-ocular pressure
What is the uveal tract?
Iris
Ciliary body
Choroid
What is the iris?
Coloured
part of eye
Under
transparent cornea
Muscles
of
iris
regulate
size
of
pupil
What is the ciliary body?
Muscles
control the
accommodation
of the
lens
Secretory epithelium
produces
aqueous humour
What is the choroid?
Highly vascular
Inner
aspect of
sclera
What is the lens?
Responsible for
22
% of
refractive power
of
eye
Changes
shape
of
lens
→ alters
refractive power
→ allows to
focus
on
nearby
objects
By
40s
, ability to
change shape
of lens declines
What is the vitreous humour?
Clear gel-like substance in the
eye
Fills
cavity
between
retina
&
lens
What is the retina?
The retina is the
light-sensitive
layer of tissue at the
back
of the
eye
that contains
photoreceptor
cells
Macula
->
centre
(where
cones
are most
concentrated
)
What is the blood supply to the eye?
Ophthalmic
artery
Central retinal
artery -> supplies
inner retitnal layers
What is the venous drainage of the eye?
Central retinal
&
ophthalmic veins
What is the lympathic drainage of the eye?
Pre-auricular
&
submental
nodes
What provides sensory innervation to the eye?
Trigeminal
What provides motor innervation to the eye?
Oculomotor
nerve
Trochlear
nerve
Abducens
nerve
Pupuil dilation
Sympathetic
NS
-> stimulates
contraction
of
radial
muscles (
dilator pupillae
) Begins in
hypothalamus
&
descends
through
midbrain
->
synapses
in
spinal
cord
(
C8-T2
) ->
preganglionic
sympathetic
neuron
exits
spinal
cord
(through
ventral
roots
) -> projects to
superior
cervical
ganglion
&
synapses
->
long
ciliary
nerve
projects to
dilator
pupillae
(
radial
muscle) -> pupil
dilation
Pupil constriction
Parasympathetic
NS
-> stimulates
contraction
of
circular
muscles (
sphincter
pupillae
)
Light
enters
eye
-> stimulates
retina
-> signals travel via
optic
nerve
&
synapse
with the
pre-tectal
nucleus
-> synapses with
Edinger-Westphal
(
oculomotor
)
nucleus
-> gives rise to
bilateral
oculomotor
outputs
to
ciliary
ganglion
->
short
ciliary
nerve
innervates the
sphincter
pupillae
(
circular
muscle) ->
pupil
constriction
Accommodation reflex - what is it? what does it involve?
Visual
response
to focusing on
nearby
objects
Involves;
contraction
of
medial
recti
muscles ->
convergence
constriction
of
pupils
(
parasympathetic NS
)
contractions
of
ciliary
body
->
broadens lens
&
increases
refractive
power
What is the role of the optic nerve?
Carries afferent fibres from
retina
to
visual
cortices
of the
brain
-> transmits
visual
image
Surrounded by
cranial
meninges
Where does the optic nerve leave the skull?
Optic canal
What is the function of oculomotor nerve?
Movement of most
extraocular
muscles (except
LR
&
SO
) +
levator palpebrae superiosis
Parasympathetic
division
responsible for
pupillary
constriction
-> pupillary
reflex
Where does the oculomotor nerve exit the skull?
Superior orbital fissure
What is the function of the trochlear nerve?
Innervates superior
oblique
-> assists in
depressing
& abducting eye
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