Neuro Lecture 6: Brainstem and Cranial Nerves I, II, III, IV, VI, VIII

Which cranial nerves are specialized sensory nerves (3)?

I, II, VIII

Which cranial nerves control extraocular muscles (and intrinsic eye muscles)(3)?

III, (oculomotor)

IV (trochlear)

VI (abducens)

What is the general function of the olfactory nerve (CN I)?

Sense of smell

In the olfactory nerve, which receptors are first order?

Receptors’ axons then synapse onto neurons in where?

Second order neurons’ axons then synapse onto which cortex and structure (2)?

Chemoreceptors

Olfactory bulb

Ipsilateral primary olfactory cortex and amygdala

Third order neurons of the olfactory nerve (CN I) project onto which 3 structures? *not as important to know

1. Hippocampus and limbic lobe

2. Hypothalamus

3. Thalamus then oribtofrontalcortex

What are 2 clinical syndromes associated with the olfactory nerve?

2 deficits?

Anosmia (no sense of smell) or hyponosmia (decrease sense of smell)

• Peripheral deficit: affecting peripheral receptors in nose

• Central deficit: Tumors or strokes at or near ventral part of forebrain

What is the generalized function of the optic nerve (CN II)?

Initial, sensory stages of vision

This cranial nerve has specialized photoreceptors in the retina of the eye

Optic nerve (CN II)

Axons of what cells form the optic nerve?

Ganglion cells

Optic nerve crosses where and continues as the optic tract within the brain

Optic chiasm

Most axons from the optic tract will synapse onto second order neurons where (1 main structure with 2 substructures)?

LGN (lateral geniculate nucleus) of thalamus

• Superior colliculus and suprachiasmatic nucleus

LGN axons project to the primary visual cortex via what?

Optic radiation

The primary visual cortex from which lobe will project to multiple visual association areas?

Occipital lobe

Optic chiasm takes info from the right visual field to where?

Left

At the optic chiasm, axons from the _________ cross, while ________ axons continue ipsilaterally (straight back)

Nasal retina cross; temporal axons continue ipsilaterally

The area of the world seen by the eye as it is focused on one region

*Helps with depth perception

Visual field

The temporal retina conveys information from what receptive field?

*Distinction between receptive field and retina

Nasal receptive field

If the optic chiasm is damaged, which fibers are affected?

Nasal

These paths are initiated at photoreceptor level are kept separate throughout visual system

Controlling color, form, ‘what is it’

Movement, location, ‘where is it’

Parallel paths

Superior fibers of optic radiation/geniculocalcarine tract see what visual fields?

Inferior fibers see what?

Middle fibers see what?

1. See contralateral inferior visual fields

   1. Ex. Right superior axons carrying info about left inferior field

2. See contralateral superior visual fields

3. See central vision

*Everything reversed

The visual field of each eye is divided into what 4 quadrants?

1. Temporal upper (nasal lower retina carries info)

2. Temporal lower'

3. Nasal upper

4. Nasal lower

Scenario

If you have blindness in your right eye, can you still see some of the right visual field from your left eye?

Yes

Scenario

If there is optic chiasm damage where the bilateral temporal field is cut, there becomes damage to what?

*Tunnel vision

Nasal retina (lose temporal field)

Sceanrio

If there is homonymous hemianopsia (cannot see one of half of visual field) with right optic tract damage, which visual field is affected

Left

Scenario - Optic radiation, temporal region > upper quadrant anopsia

The inferior fibers of the right LGM are damaged, which visual field has a deficit?

Left superior visual field lost