Lecture 8-Cranial Nerves & Ascending pathways

Question 1

Five Main Cranial Nerves

Answer 1

1) Optic Nerve (CN II)
2) Vagus Nerve CN X
3) Abducent Nerve (CN VI)
4) Trochelar Nerve (CN IV)
5) Ocolomotor Nerve (CN III)
6) Facial Nerve (CN VII),

Question 2

Almost all cranial nerves emerge _____​

Answer 2

ventrally

Question 3

What does the optic nerve carry?

Answer 3

The optic nerve carries afferent signals from the eyes.

Question 4

What happens to signals from the nasal/medial half of each eye at the optic chiasm?

Answer 4

All signals from the nasal/medial half of each eye decussate (cross over) at the optic chiasm.

Question 5

What happens to signals from the temporal half of each eye at the optic chiasm?

Answer 5

Signals from the temporal half of each eye do not decussate (they remain on the same side).

Question 6

Where do the signals from the optic nerve synapse in the brain?

Answer 6

The signals from the optic nerve synapse in several areas, including the lateral geniculate nucleus (LGN), superior colliculus, pretectum, and hypothalamus.

Question 7

What type of signals does the Oculomotor Nerve (CN III) carry?

Answer 7

The Oculomotor Nerve (CN III) carries efferent signals to the eyes (signals that travel from the CNS, typically originating in the brain, to the muscles of the eyes.

Question 8

Which eye muscles receive signals from the Oculomotor Nerve (CN III) to control eye movements? What do these signals allow for?

Answer 8

1. Superior rectus muscle
2. Medial rectus muscle
3. Inferior rectus muscle
4. Inferior oblique muscle
   Allow your eye to move in different directions

Question 9

What is the role of the Oculomotor Nerve in relation to the levator palpebrae superioris muscle?

Answer 9

The Oculomotor Nerve innervates the levator palpebrae superioris muscle, which helps lift the upper eyelid.

Question 10

Which muscles receive parasympathetic innervation from the Oculomotor Nerve, and what functions do they serve?

Answer 10

The Oculomotor Nerve provides parasympathetic innervation to the ciliary muscle (which changes the shape of the lens) and the sphincter pupillae muscle (which controls pupil dilation).

Question 11

Clinical Considerations of lesions to oculomotor nerve

Answer 11

1) Pupil does not dilate/constrict
2) Lens does not accommodate
3) “Down and out” deviation of eye
4) Eyelid droop

Question 12

What is unique about the Trochlear Nerve compared to other cranial nerves?

Answer 12

The Trochlear Nerve (CN IV) is the thinnest, emerges from the dorsal surface of the brainstem and originates completely from the contralateral nucleus, which sets it apart from most other cranial nerves.

Question 13

Which muscle does the Trochlear Nerve innervate and what type of movement does it control?

Answer 13

The Trochlear Nerve innervates the superior oblique muscle, which is responsible for rotational movements of the eye (vertical).

Question 14

What happens to the eyes when there is damage to the Trochlear Nerve?

Answer 14

Can lead to the eyes looking up and out, resulting in a condition called diplopia, where a person sees double.

Question 15

How does the diplopia worsen when the head is tilted, and how is it typically compensated for?

Answer 15

Diplopia worsens when the head is tilted towards the side of damage. To compensate, individuals often lean their head to the other side to reduce double vision.

Question 16

What is the primary function of the Abducens Nerve (CN VI)?

Answer 16

The Abducens Nerve coordinates horizontal movements of the two eyes to ensure they point in the same direction.

Question 17

How does the Abducens Nerve achieve the coordination of eye movements?

Answer 17

It achieves this by causing the simultaneous contraction of the lateral rectus muscle of one eye and the medial rectus muscle of the other eye.

Question 18

Where do most of the projections from the Abducens Nerve go, and how do they contribute to eye movements?

Answer 18

About 70% of the projections go directly from motorneurons to the ipsilateral lateral rectus muscle, while approximately 30% are sent to interneurons in the oculomotor nucleus. These interneurons then project to the contralateral medial rectus muscle. This coordinated action helps the eyes turn together.

Question 19

Vagus Nerve (CN X) Functions

Answer 19

Controls the parasympathetic nervous system, regulate body’s stress response, carries sensory information from internal organs

Question 20

Vagus Nerve Distribution

Answer 20

Extensive distribution in the body, cranial nerve that has the most innervating structures in the head but also the neck, thorax, and
abdomen

Question 21

Facial nerve function

Answer 21

Controls facial expressions, taste sensation, and salivary gland functions.

Question 22

Ascending Pathways

Answer 22

Neural circuits in the central nervous system (CNS) that transmit sensory information from the periphery (e.g., skin, muscles, organs) to higher centers in the brain

Question 23

What type of sensations does the Dorsal Column-Medial Lemniscus Pathway (DCML) transmit?

Answer 23

The DCML pathway transmits sensations related to fine touch, proprioception, and vibration.

Question 24

What is the primary function of the Anterolateral Pathway (Spinothalamic Tract)?

Answer 24

The Anterolateral Pathway conveys information about pain and temperature sensations.

Question 25

What is the role of the Spinocerebellar Pathways?

Answer 25

Carry proprioceptive information to the cerebellum, contributing to muscle movement coordination and balance.

Question 26

DCLM Pathway

Answer 26

1)First-order neurons carrying sensory input from mechanoreceptors synapse in specific nuclei, namely the nucleus gracilis for the lower body and the nucleus cuneatus for the upper body, located in the medulla oblongonta

2)Second-order neurons from the cuneate tubercle and gracilis tubercle project their axons as the fasciculus cuneatus and fasciculus gracilis, respectively, carrying sensory information. These axons cross the midline in the brainstem (pons) and form the medial lemniscus. They then ascend to the thalamus, primarily targeting the ventral posterior lateral nucleus (VPL).

Third-order neurons in the ventral posterior lateral nucleus (VPL) relay precise sensory information to the somatosensory cortex for conscious perception. The cortex processes and interprets this information, allowing us to perceive fine touch and proprioceptive sensations from the body.