Unit 3

Midbrain:

Dopaminergic Neurons → parts/their functions

Periaqueductal gray (PAG)

Red nucleus

Midbrain:

• eye movement control

• auditory reflexes

• reward/motivation system (dopamine)

Dopaminergic Neurons - dopamine producing, 2 parts: SNC, VTA

1. Substantia Nigra pars Compacta (SNc) -

• movement initiation and facilitation,

• primary source of dopamine in the Basal Ganglia

• main location in Parkinsons

2. Ventral Tegmental Area (VTA)

• project to cortex and limbic basal ganglia

• reward processing, reinforcement learning, motivation

Periaqueductal gray (PAG)

• involved in emotive vocalization behaviors

• main modulation

• defensive behaviors

Red Nucleus

• involved in motor control

• interactions with cerebellum

Pons

Locus Coeruleus (LC)

Pons:

• cranial nerve nuclei located here with cerebellar connections

• head/face sensations

• motor control of eyes, face, mouth

• hearing

• equilibrium

• autonomic functions

Locus Coeruleus (LC)

• norepinephrine neurons, key NT in autonomic system

• in attention, arousal, and stress response

Medulla Oblongata:

Nucleus tractus solitarius (NTS; aka nucleus solitarius)

Nucleus Ambiguus

Pyramidal Decussation

Medulla Oblongata:

• brainstem connects to spinal cord

• vital functions

• reflexive actions

• some CN exit brainstem

Nucleus tractus solitarius (NTS; aka nucleus solitarius)

• major sensory nucleus - taste, touch

• sensory component of swallowing control

• trigger swallowing response

Nucleus Ambiguus

• key nucleus of vagus nerve - innervate pharynx and larynx

• motor execution of swallow response

Pyramidal Decussation

• 90% upper motor neurons cross

Distributed Structures and Functions of Brainstem

• ascending (sensory) and descending (motor) pathways

• Cranial nerve nuclei

• central pattern generators (CPGs)

• reticular formation

central pattern generators (CPGs)

• made up of several nuclei

• neural circuit producing specific output without requiring continual sensory input

• complex reflex - engages muscles/neurons to produce rhythmic activity (swallowing, breathing, walking)

Reticular Formation

• interconnected collection of nuclei to maintain basic life functions

• diffuse network of nuclei distributed throughout the medulla and pons with extension into midbrain

• basal ganglia can modulate RF

• contains many CPGs

• arousal and autonomic regulation

• arousal → modulate activity of the cortex for sleep wake cycles, wakefulness and alertness, - involved in maintenance of focused attention

• autonomic → respiration, coughing, regulating BP, swallowing

Reticular Formation CPGs for …

1. respiration

(both are key nuclei modulating respiratory system)

* pontine respiratory modulation

* medullary respiratory center

2. swallowing

* dorsal group neurons → associated with processing sensory event in swallowing

• nucleus solitarius

* ventral group neurons → execute swallow response (trigger muscles)

• nucleus ambiguous

innervation patterns:

• contralateral innervation

• bilateral innervation

• spinal nerves

• cranial nerves

• effect of LMN (cranial nerve) damage

• effect of damage to the UMN innervating the cranial nerve

contralateral innervation

• one motor cortex (a UMN) innervates LMN on opposite side of body

bilateral innervation

• one motor cortex (a UMN) innervates LMN on same and opposite side of body

spinal nerves

• contralateral innervation

cranial nerves

• most are bilaterally innervated (besides 2)

• this can provide “backup plan” if one side is damages!!

effect of LMN (cranial nerve) damage

• impairment to contract muscle that the nerve innervates on the same side

effect of damage to the UMN innervating the cranial nerve

• other cortex could supply innervation

***UMN is not a cranial or spinal nerve. The UMN feeds or supplies input to a LMN (cranial or spinal nerve)

UMN feed/supply/innervates input to the cranial nerve/LMN

Name Cranial Nerves

"Oh, Oh, Oh, To Touch And Feel Very Good Velvet, Ah Heaven"

I - Olfactory

II - Optic

III - Oculomotor

IV - Trochlear

V - Trigeminal

VI - Abducens

VII - Facial

VIII - Vestibulocochlear

IX - Glossopharyngeal

X - Vagus

XI - Accessory

XII - Hypoglossal

I - Olfactory

Type: Sensory

Function: Chemical sensation (smell)

Cranial Nerve Functions (Sensory vs. Motor)

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II - Optic

Type: sensory

Function: visual input - some input will cross midline (optic chiasm) before processed by cortex

III - Oculomotor

Type: motor

Function: movement of eyes