Neuroscience Anat (CN II, III, IV, VI) Flashcards
VISION, state the
- sensory organ
- sensory receptors
- pathway
VISION, state the
- sensory organ = eye (retina)
- sensory receptors = rods and cones in retina
- pathwa: CN II (optic N) –> lateral geniculate nucleus (thalamus) –> primary visual cortex
VISION
State the structures in
1. outer
2. intermediate
3. innermost
VISION
1. outer (FIBROUS) - sclera and cornea
2. intermediate (VASCULAR AND PIGMENTED) - choroid, ciliary body, lens (suspensory ligaments), iris with dilator pupillae and sphincter pupillae
3. innermost (NERVOUS) - retina (outgrowth of brain into orbit)
State the 3 radially disposed sets and 2 tangential sets of structures in retina (nervous layer) and include their function.
RADIALLY DISPOSED SETS:
1. photoreceptors - receive and transduce light energy to action potential
2. bipolar cells - transmit information to ganglion cells
3. ganglion cells - project to thalamus and brainstem
TANGENTIAL SETS - integrate and modulate information
1. horizontal cell
2. amacrine cells
State the 8 layers of the retina from superficial to deep.
- pigment layer
- photoreceptor
- outer nuclear
- outer plexiform
- inner nuclear
- inner plexiform
- ganglion cell
- nerve fiber
State the funtions of photoreceptors and name the types of photoreceptors found.
State the difference between the types of photoreceptors.
PHOTORECEPTORS
- function = transduce light energy into chemical energy (action potential)
- types = rods and cones
RODS - CONES
sensitive to dim light - sensitive to bright light
colour sense - no colour sense and accurate detail
absent in fovea - most numerous in fovea
FOVEA
- located behind ____ and ____
- only contains ____, ____ are located more ____
- located within ____ (most ____ part of eye)
OPTIC DISC
- does not contain ____ or ____
- ____ ____ if light falls onto optic disc
- also where ____ N exits
FOVEA
- located behind PUPIL and LENS
- only contains CONES, RODS are located more PERIPHERALLY
- located within MACULA (most SENSITIVE part of eye)
OPTIC DISC
- does not contain RODS or CONES
- BLIND SPOT if light falls onto optic disc
- also where OPTIC N exits
IMPORTANT:
The visual image is ____ and ____ by the lens
____ of visual field is binocular
____ of visual field is monocular
The visual image is INVERTED and REVERSED by the lens
2/3 of visual field is binocular
1/6 (ON EACH SIDE) of visual field is monocular
Left hemisfield - supplied by ____ ____ and ____ ____
Right hemisfield - supplied by ____ ____ and ____ ____
Left hemisfield - supplied by LEFT NASAL HEMI-RETINA and RIGHT TEMPORAL HEMI-RETINA
Right hemisfield - supplied by RIGHT NASAL HEMI-RETINA and LEFT TEMPORAL HEMI-RETINA
State the pathway for the basic visual pathway from stimulus to effector
- light
- retina (receptor)
- optic nerve
- optic chiasma (partial decussation)
- optic tract
- lateral geniculate nucleus (thalamus)
- optic radiation
- primary visual cortex in occipital lobe
OPTIC RADIATION
- Connects the ____ ____ ____ to the ____ ____ ____
- Also known as ____ ____
- Is the collection of axons from relay neurons in ____ of thalamus carrying ____ information in the ____ ____
- ____ ____ is located within the optic radiation - has fibres representing the ____ retinal quadrants or ____ visual fields (____ fibres of optic radiation represent the ____ retinal quadrants/____ visual field)
OPTIC RADIATION
- Connects the LATERAL GENICULATE NUCLLEUS to the PRIMARY VISUAL CORTEX
- Also known as GENICULO-CALCARINE TRACT
- Is the collection of axons from relay neurons in LGN of thalamus carrying VISUAL information in the VISUAL CORTEX
- MEYER’S LOOP is located within the optic radiation - has fibres representing the INFERIOR retinal quadrants or SUPERIOR visual fields (UPPER fibres of optic radiation represent the SUPERIOR retinal quadrants/LOWER visual field)
State the 2 types of collateral fibres given off by optic tract
- SUPERIOR COLLICULUS (tectospinal tract) - EOM for visual reflexes
- PRETECTAL NUCLEUS - photopupillary and accommodation
Locate (1) Primary visual cortex (VC1) and (2) Visual associaton area (VC2)
Located on both banks of the CINGULATE GYRUS
State the function and pathway of
(1) VENTRAL VISUAL PATHWAY
(2) DORSAL VISUAL PATHWAY
(1) VENTRAL VISUAL PATHWAY - WHAT
- function = processing of form and colour information
- pathway = continues into cortex on under side of temporal lobe
(2) DORSAL VISUAL PATHWAY - WHERE, HOW
- function = processing of motion and spatial relationships
- pathway = continues into posterior parietal lobe
State the 4 common visual field defects
- monocular blindness - one-eyed blindness
- bitemporal hemianopia - lateral half of both eyes blind
- binasal hemianopia - medial half of both eyes blind
- homonymous hemianopia - letft/right half of both eyes blind
State the cause of each of the 4 common visual field defect.
(1) MONOCULAR BLINDNESS
- one-sided blindness
- cause = lesion in left/right optic N
(2) BITEMPORAL HEMIANOPIA
- lateral half of both eyes blind
- cause = lesion in optic chiasma of the nasal hemiretina
(3) BINASAL HEMIANOPIA
- medial half of both eyes blind
- cause = lesion in optic chiasma of the temporal hemiretina
(4) HOMONYMOUS HEMIANOPIA
- left/ right side of both eyes blind
- cause = lesion in left/right optic tract
State the 2 rarer (advanced) visual field defects
- quadrantopia (optic radiation) - blindness in the same quadrant of both eyes
- homonymous hemianopia with macular sparing - blindness in the same half of both eyes with macular sparing
State the cause of each of the 2 rarer (advanced) visual field defect.
(1) QUADRANTOPIA
- blindness in the same quadrant of both eyes
- MEYER’S LOOP LESION
- left superior quadrantopia = lesion in lower fibres of right optic radiation that transmit information to the left upper visual quadrant
- left inferior quadrantopia = lesion in upper fibres of right optic radiation that transmit information to the left lower visual quadrant
- right superior quadrantopia = lesion in lower fibres of left optic radiation that transmit information to the right upper visual quadrant
- right inferior quadrantopia = lesion in upper fibres of left optic radiation that transmit information to the right lower visual quadrant
(2) HOMONYMOUS HEMIANOPIA WITH MACULAR SPARING
- blindness in the same half on both eyes
- vascular lesion affecting left or right visual cortex –> affects right or left (opposite) visual cortexes
- as the fovea and macula are supplied by MCA and PCA (2 arteries involved), one down, other compensate = macular sparing
Recap:
State the
(1) intrinsic muscles of eye
(2) extrinsic muscles of eye
State any autonomic supply relevant.
State the pathways involved for autonomic supply.
(1) INTRINSIC MUSCLES OF EYE
- ciliary muscles (parasympathetic - sympathetic)
- sphincter pupillae (parasympathetic)
- dilator pupillae (sympathetic)
(2) EXTRINSIC MUSCLES OF EYE
- LR - CN6
- SO - CN4
- SR, IR, MR, IO - CN 3
PARASYMPATHETIC PATHWAY:
CN III - Edinger-Westphal Nc –> ciliary G –> muscle
SYMPATHETIC PATHWAY:
Superior cervical ganglion
What axis is parallel to reti muscles?
axis of ORBIT
Relate the
(1) 3 axis of movement
(2) 3 reference points
(3) 3 types of movement
(1) axis - (2) reference point - (3) movements
VERTICAL - PUPIL - elevation & depression
ANTERO-POSTERIOR - 12 O CLOCK - extorsion & intorsion
SIDE-TO-SIDE - PUPIL - abduction & adduction
State the function of each extraocular muscle (EOM).
- medial rectus - adduction
- lateral rectus - abduction
- inferior oblique - elevation, abduction, extorsion
- superior oblique - depression, abduction, intorsion
- superior rectus - elevation, adduction, introsion
- inferior rectus - depression, adduction, extorsion
State the course of the CN III, IV, VI
(1) motor nuclei
(2) intracranial course
(3) extracranial course
(1) MOTOR NUCLEI
- exits from brainstem in PCF
(2) INTRACRANIAL COURSE
- crosses over to MCF (cavernous sinus)
(3) EXTRACRANIAL COURSE
- enters orbit by superior orbital fissure
CN VI - ABDUCENS N
(1) State the course of the nerve from orign to the EOM
(2) State effects of a lesion to CN VI
CN VI - ABDUCENS N
(1) COURSE
- Exits at pontomedullary junction
- Courses in PCF and enters into MCF via cavernous sinus
- Enters orbit by passing through the superior orbital fissure
- Innervates LR (lateral rectus)
(2) LESION TO CN VI
- no ptosis - LPS unaffected
- affected eye will be adducted due to unopposed adduction from paralysis of LR which is involved in abduction
- diplopia occurs on lateral gaze to side of affected eye
CN IV - TROCHLEAR N
(1) State the course of the nerve from orign to the EOM
(2) State effects of a lesion to CN IV
CN IV - TROCHLEAR N
(1) COURSE
- Exits at midbrain level (inferior colliculis)
- Crosses midline before leaving PCF
- Wraps around the lateral aspect of the cerebral peduncle before entering MCF via cavernous sinus
- Enters orbit by superior orbital fissure
- Innervates SO (superior oblique)
(2) LESION TO CN IV
- no ptosis - LPS unaffected
- affected eye will be elevated due to paralysis of SO which acts to depress, abduct and intort eye
- elevation of affected eye is increased when head is tilted towards the affected side
- diplopia
CN III - OCULOMOTOR N
(1) State the course of the nerve from orign to the EOM
(2) State effects of a lesion to CN III
CN III - OCULOMOTOR N
(1) COURSE
- Exits at midbrain level (superior colliculis)
- Travels ventrally leaving brainstem between the cerebral peduncles to MCF
- Enters cavernous sinuses
- Exits cranial cavity by superior orbital fissure to orbit
- Innervates IO, SR, IR, MR and LPS
(2) LESION TO CN III
- ptosis - LPS paralysed
- pupil dilated - sphincter pupillae paralysed unable to constrict pupil of affected eye
- affected eye laterally deviated because of unopposed action of LR (lateral rectus) which is not innervated by CN III
- diplopia present in all directions of gaze except lateral gaze of involved side
EYE MOVEMENTS:
(1) Vergence = direct the 2 ____ at the same object
(2) Saccades = ____, darting ____ movement from one eye position to another
(3) Smooth pursuit = ____ ____ movement which allow tracking of a moving object
(4) Optokinetic reflex = combination of ____ and ____ to allow tracking of sequential moving targets
(5) Vestibulo-Ocular Reflex (VOR) = ____ smooth pursuit, coordinated by ____ ____ and does not require ____ input
EYE MOVEMENTS:
(1) Vergence = direct the 2 FOVEA at the same object
(2) Saccades = QUICK, darting CONJUGATE movement from one eye position to another
(3) Smooth pursuit = SLOWER CONJUGATE movement which allow tracking of a moving object
(4) Optokinetic reflex = combination of SACCADES and SMOOTH PURSUIT to allow tracking of sequential moving targets
(5) Vestibulo-Ocular Reflex (VOR) = REFLEXIVE smooth pursuit, coordinated by REFLEX ARC and does not require CORTICAL input
Explain everything you know about the vestibulo-ocular reflex (VOR).
VESTIBULO-OCULAR REFLEX (VOR)
- function = stabilise image in retina during rotations of the head
- rotation of head detected –> triggers inhibitory signal to EOM on one side + excitatory signal to muscles on other side –> compensatory movement of the eyes
- pathway = rotational acceleration/deceleration of head –> receptors in semicircular canals –> vestibular nuclei –> ocular motor nuclei –> extraocular muscles
State the 4 structures involved in central control of eye movement
- frontal eye field (FEF)
- paramedian pontine reticular formation (PPRF)
- superior colliculus
- medial longitudinal fasciculus (MLF)
State the 3 visual reflexes.
- light - pupillary light reflex
- near objects - accommodation/convergence
- pain/emotional state - pupillary dilation
Explain the pathway behind pupillary light reflex and consensual light reflex
Explain the pathway for accommodation (near and far objects)
NEAR OBJECTS - require more focus power
- ciliary muscles contract –> suspensory ligaments relax –> lens thickening (parasympathetic)
FAR OBJECTS - require less focus power
- ciliary muscles relax –> suspensory ligaments contract –> lens thinning (sympathetic)
Explain the pathway for pupillary dilation (in response to pain and emotion)
