Visual Pathway
Function: is to provide sight, for the recognition and location of objects, control eye movement and
provide info in limb and postural control.
How light enters: Right visual field always goes to the left side of both eyes. Left Visual field always
goes to the right side of both eyes. All the information about the left visual hemifield is directed to the
right side of the brain. All the information about the right visual hemifield is directed to the left side
of the brain. Nasal fibers are closest to the nose, while temporal fibers are closest to the temple.
Partial decussation- only nasal fibers decussate (at optic chiasm).
Where it goes:
1. Lateral geniculate body (dorsal thalamus)and have axons that project to the primary visual cortex.
“Geniculocalcarine fibers”-geniculate body to calcarine sulcus (Brodmann’s area 17) visual cortex.
Optic radiation- take place in the retrolenticular limb of the internal capsule (posterior limb). LGN-is
the gateway to the visual cortex and which leads to conscious visual perception.
2.Hypothalamus- Circadian rhythm (sleep and wakefulness and daily dark-light cycle).
3.Mid-brain Pretectum- control size of the pupil and certain types of eye movement.
Superior colliculus-orienting the eyes in response to new stimuli in the visual periphery.
Nuerotransmitters: Cholesystokinin (+)
Pupillary Pathway
Function: Parasympathetic control of the pupillary sphincter and cilliary muscle. (pupillary light
reflex)
How light enters: Same way as in the visual pathway
Where it goes:
1. Lateral geniculate body
2. Both Edinger-westphal nucleus: synapses in pretectal nucleus  posterior commisure  EdingerWestphal preganglionic nucleus
Pupillary light reflex: “A complete lesion of the optic nerve will result in blindness and loss of the
pupillary light reflex (direct response) in the eye on the injured side and loss of the pupillary light
reflex (consensual response) in the opposite eye when shining a light in the blind eye.”Consensual
response- constriction of the opposite pupil.“Shining a light in the normal eye will result in a
pupillary light reflex (direct) in that eye and a consensual response in the blind eye.”
Neurotransmitter: Acetylcholine
Auditory Pathway
Function:
 auditory processing/turning eyes and head toward sound
 look back at Professor Burnell’s PowerPoint for how sound becomes an electrical signal
Components and their function:
 Spiral ganglion= group of nerve cells that sense hearing by sending signals from the cochlea
 Cochlear nuclei= preserve or even enhance the timing information that is provided by each fiber of
the cochlear nerve
 Ventral nuclei
o Superior Olive= collection of nuclei that measure the time difference of arrival of sounds
between the ears, and measure the difference in sound intensity between the ears
o Lateral lemniscus= collection of axons as they travel up to the colliculi
o Inferior Colliculus= relays auditory info to superior colliculus, medial gen. nucleus, and
cerebellum
o Reticular Formation= activating effect of sounds on the entire CNS; alertness/attention
 Dorsal Nuclei
o Decussate in pons and goes up lateral lemniscus to inferior colliculus, then to medial
geniculate body, and finally to the auditory cortext
o Also goes to reticular formation
Neurotransmitters:
 Aspartate (+), glutamate (+)
Simplified Pathway: Also be sure to go to blackboard and print out the auditory simplified drawing
and trace the path yourselves!
Vestibular Pathways
Pathway
Start
Finish
Neurotransmitter
s
Function
Medial Longitudinal
Fasciculus (MLF)
Vestibular
Nuclei
Trochlear,
Oculomotor,
Abducens CN’s
GABA (-)
Eye and Head
movements
Vestibulospinal
Vestibular
Nuclei
SC
“
Posture
Vestibulocolic
Vestibular
Nuclei
Accessory Nerve
“
Head Position
Vestibular
Nuclei
Thalamus ->
“
Conscious
awareness of head
position and
movement and
input to
Corticospinal tracts
Vestibulocerebellar
Vestibular
Nuclei
Cerebellum
“
Controls magnitude
of muscle
responses to
vestibular
information (gain
of vestibulo-ocular
reflex) MOTOR
Vestibular Afferents
1. Ampulla
Inner Ear
2. Pass through
Inferior
Cerebellar
Peduncle ->
“
1.Sends BALANCE
info
2.Sends
Coordination
information to
receive MOTOR
input
Vestibulothalamocortical
2. Cerebellum
(SCM and
Trapezius)
Vestibular
Cortex
1. & 2.
Vestibular
Nuclei
Just a few notes about the Vestibular System (From green packets):
 Function: “Equilibrium” – maintaining balance (keeping CG over BOS)
 Uses 1. Sensory , 2. Proprioceptive , 3. Vestibular … information to do this
 This system requires nerve impulses from the vestibular apparatus to motor
neurons through pathways in …
o SC, BS, Cerebellum and Cortex (Vestibular)
 REMEMBER! They all use the same Neurotransmitter: GABA