CRANIAL NERVES PART 4: BRAINSTEM

CN III emerges from the

ventral aspect of the midbrain near its caudal aspect close to midline

CN IV arises along the

dorsal aspect of the midbrain

1. only CN that arises on the dorsal aspect of the CNS

from the ventral view, CN IV emerges

caudal and lateral to CN III

CN V is a large nerve emerging along the

lateral aspect of the pons

CN VI emerges from the pons near its

caudal aspect close to midline

CN VII emerges from the pons near its

caudal aspect lateral to CN VI (closer to the cerebellum) and anteromedial to CN VIII

CN VIII emerges from the pons near its

caudal aspect posterolateral to CN VII (closer to the cerebellum)

CN IX emerges

laterally from the rostral / superior aspect of the medulla

CN X emerges

laterally from the medulla caudal to CN IX

may appear as several rootlets

CN XI emerges as

rootlets along the lateral aspect of the upper cervical SC traveling rostrally / superiorly to converge caudal to CN X

CN XII emerges as

rootlets from the medulla medial to CN IX and CN X (closer to midline)

recall that these 2 cranial nerves are not associated with the brainstem

CN I

CN II

CN I located in the

olfactory epithelium & courses through the foramina of the cribiform plate

the olfactory bulb (2nd order cell bodies) is located on the

ventral surface of the frontal lobe

CN II is located

inferior / ventral to the frontal lobe

forms when 2 optic nerves merge & some of their fibers cross over

optic chiasm

prefrontal cortex

personality center

higher order functioning

1. working memory

subdivided into several regions with distinct, but coordinated actions

the prefrontal cortex in the brain is one of the last places to

mature

1. occurs in early to mid 20s

2. maturation = myelination

the prefrontal cortex processes

moment-to-moment input, compares to past experiences, & then reacts to them

1. coordination of cognitive & emotional processes

2. relies both on current goals & future plans

3. behavioral flexibility

prefrontal cortex lateral areas are more focused on

higher-level cognition

dorsolateral prefrontal cortex (DLPFC) central hub for

higher-order cognitive processes

DLPFC executive functions

working memory

sustained attention

decision making

cognitive control & flexibility

DLPFC receives somatosensory & visuospatial information from the

parietal lobe and auditory & visual object-related inputs from the temporal lobe

DLPFC primarily sends information to

motor areas

DLPFC has coordination with

orbitofrontal & medial PFC for top-down control of emotional regulation

venterolateral prefrontal cortex (VLPFC)

great prefrontal integrator

VLPFC receives input extensively from the

temporal lobe & limbic system and sends information to motor areas including basal ganglia

VLPFC mediates between

widespread prefrontal cortical systems

VLPFC inhibits

interfering information

VLPFC selection / retrieval of relevant information during

working memory (threat processing)

VLPFC activated during

Go / No-Go tasks (impulsiveness)

VLPFC processes language information at the highest levels

on the language dominant side (Broca’s area)

VLPFC with the limbic system is for

empathy

prefrontal medial areas are more focused on

emotion and judgement

dorsomedial prefrontal cortex (DMPFC)

social cognition (thinking of other’s mental states / mind)

cognitive evaluation of options & self-control

1. inhibits impulsive perspectives to favor delayed rewards

detects goal-relevant information & stimuli

reciprocal connections with the amygdala, hippocampus, and other PFC areas

ventromedial prefrontal cortex

value based decision making

1. encodes subjective value of social & non-social stimuli in a goal-dependent manner

2. represents value of decisions to guide behavior in terms of the reward-value of potential future outcomes

3. empathy, facial emotional recognition, moral reasoning, processing of social norms

4. safety learning / fear extinction

reciprocal connections to the amygdala, hippocampus, hypothalamus, thalamus, brainstem autonomic nuclei, basal ganglia, and others

orbitofrontal / orbital frontal cortex

considered to be a component of both cortical & limbic system

1. evaluates the value of rewards or punishments of a stimulus and adjusts these values based on current internal states

2. decision-making especially ‘learning from mistakes’ (switching behavior when an action is no longer rewarded)

3. social and emotional regulation

receives input from all sensory modalities to build a comprehensive internal model of the world

sends information to other areas of the PFC & limbic system including basal ganglia and hypothalamus