Brainstem and Reticular Formation

What is included in the brainstem

Midbrain, pons, medulla

What cranial nerves are located in the midbrain?

CN III + IV

What cranial nerves are located in the pons?

CN V - VIII

What cranial nerves are located in the medulla?

CN IX-XII

Where are CN I and II located?

Cerebrum (remain in the skull)

Brainstem main fnction

Great connector of the cerebrum, cerebellum and spinal cord

Two sections of the brainstem

Basilar and tegmentum

Longitudinal section of the midbrain

Tectum

Where does the basilar section of the brainstem sit?

Anterior/ventral

Where does the tegmentum section of the brainstem sit?

Posterior/dorsal

General function of the basilar section of the brainstem

Contains the motor system (Cortico___)

General function of the tegmentum of the brain stem

Sensory information, CN functions and neural activity (including eye movement)

Where does the tectum sit?

Located in the midbrain and posterior to the tegmentum

General function of the tectum of the midbrain

Regulation of eye reflexes and refelxive head movements

Two main strucutres of the external medulla

Pyramids and olives

Function of superior olives

Hearing

Function of inferior olives

Motor learning

What cranial nerves attach laterally to the olives?

9-11

What cranial nerve emerges between the pyramid and olives?

CN 12

Function of the medulla

Vital functions (cardiovascular, respirtory, visceral, swallowing)

Strucutres in the lower medulla

Corticospinal tract, CN structures, medial longitudinal fasiculus (medulla ends at the foramen magnum at the spinomedullary junction)

What cranial nerves synapse at the medial longituinal fasiculus and function?

CN 3, 4, 6 // for synchronized eye movements and balance head/neck

Strucutres in the upper medulla

4th ventricle, postural tracts (vestibulo / cerebellar), inferior cerebellar peduncles, solidary nucleus

What does the inferior cerebellar peduncles connect

Upper medulla and cerebellum

Function of the solidary nucleus

Links the vagus nerve to ANS (for PNS regulation)

Main function of the pons

Processes motor information from the cerebrum to the cerebellum

Structures in the pons

Corticopontine and corticobrainstem synapse, Parapontine reticular formation

Function of the PPRF (parapontine reticular formation)

Saccades and conjugate eye motions

Difference between MGN and PPRF in eye movement

MGN: allows eyes to stabilize during head movements

PPRF: allows eyes to move together in synchrony

What does the midbrain connect and through what strucutres?

Diencephalon and pons (through cerebral peduncles)

Where is the cerebral aqueduct found?

Midbrain (anterior to colliculi)

Strucutres in the basilar midbrain

Cerebral peduncles

Structure of the tegmentum midbrain

Superior cerebellar peduncle, red nucleus, PPN, periaqueductal grey, CN III and IV

Function of red nuclues

Distal UE extnesion

Function of PPN

Regulares muscle tone

Function of PAG (periaqueductal grey)

Pain suppression, ANS response to pain and emotionS

Structures of the tectum

Pretectal area, superior and inferior colliculi

Function of pretectal area

Pupillary, consensual, accomodation eye reflexes

Function of superior colliuli

Reflexive eye and head movement

Function of inferior colliculi

Relay auditory information

How is the cerebellum connected to the brainstem

Penuncles (superior: midbrain, middle: pons, inferior: medulla)

Functions of cerebellum

Coordination, motor planning, cognition (shifting attention)

Reticular formation function

Inegrate sensory/cortical info, motor activity, ANS, conciousness, pain

What aa supplies the brainstem

Vertebral aa

Main brainstem pathways

Two vertebral aa to one basilar aa to two posterior cerebral aa

Smaller branches of brainstem or cerebellum

PICA, AICA(posterior and anterior cerebellar aa), SCA (superior cerebellar aa), PCA (posterior cerebral aa)

What does the PICA supply?

Medulla and cerebellum

What does the AICA supply?

Pons and cerebellum

What does the SCA supply?

Pons and cerebellum

What does the PCA supply?

Midbrain and thalamus

What is mainly effected with Lateral medullary BS vasular issue? and sx?

PICA (inferior cerebellar peduncle), cerebellar issues (ataxia, nystagmus, nausea, vertigo, horners), decreased taste, hoarseess, dysphagia, facial numbeness (motor spared)

What is mainly effected with Lateral inferior pons BS vasular issue? and sx?

AICA (middle cerebellar peduncle), cerebellar issues (ataxia, nystagmus, nausea, vertigo, horners), hearing loss

Brainstem lesion general sx

Ipsilateral CN loss and contralalteral limbs, possible vital function/conciousness

Cotricobrainstem lesion sx

Motor impacts on Cranial nerves in the brainstem (except for eye motion - 3,4,6)

Facial (CN VII) injury v corticobrainstem stroke

CNVII: falccid paralysis in all muscle of ipsilateral face

CVA: paralysis of contralateral lower face, but sparing of the upper face (due to redundant innervation)

What cranial nerves do not have dual innervation?

CN VII and XII

Tumors of the BS or cerebellum causes

Increased intracranial pressure (HA, nausea, vomit, acute CN disorder, hydrocephalus or ataxia)

Midbrain dysfucntion sx

CN III and IV, ptosis, pupil dilation (loss of parasympathetic constriction), ataxia, decerbrate posture, decreased conciousnessDe

What is decerbrate posture

Exaggerated extensor tone

Pons dysnfucntion sx

CN 5-8 (abducens palsy, fascial weakness/numbness, equilibrium), pupils constricutes (loss of sympathetic dilation), apneustic, semi-comatose, decerbrate posture

Apneustic

Irregular respirations

Medulla dysfunction sx

CN 9-12 (ipsilateral), vertigo, nystagmus, ataxia, N/V, cough, gagging, vANS dysnfunction, pupils non reactive, possible coma

4 D’s of brainstem dysfucntion

Dyphagia, dysarthria, dysmetria, diplopia

What is the reticular formation?

Diffuse network of nerve pathways in the BS

Function of upper RF (and strucutres)

Mediates overall level of conciousness/sleep/arousal (midbrain and upper pons)

Function of Lower RF

ANS and reflexes (lower pons and medulla)

Where is the RF located

Tegmentum

3 Columns of RF

Lateral (parvocelluar), paramedian (magnocellular), median

Function of lateral RF (parvocellular)

Recieves afferent (sensory) information from CN and spinal nn

Function of paramedian RF (Magnocellular)

Sends efferent information (motor) to CN and anterior horn of SCFunc

Function of median RF

Series of raphe nuclei, sertonergic projections

NT associated to major location of RF:

VTA (ventral tegmental area)

PPN (pedunculopontine nucleus)

Raphe nuclei

Locus coeruleus and medial reticular area

VTA: dopamine

PPN: ACh

RN: seratonin

LC and MRA: Norepi

Function of dopamine and location in RF

VTA - pleasure and reward

Function of ACh and location in RF

PPN - arousal and motor pattern

Function of Seratonin and location in RF

RN - arousal, ANS and pain inhibition

Function of Norepi and location in RF

LC - ANS, attention, sleep/wake cycles, mood

System that controlled wakefulness, altertness and transition from sleep/wake

Ascending reticular activating system (lesion can cause coma, stupor, obtunded states)

What strucutre is mainly responsible for sleep induction

Raphe nucleus (seratonin release)

What strucutre causes analgesia and pain inhibition

Periaqueductal grey

What part of the brainstem has ANS control (resporation, breathing rate to CO2 concentration)

Medulla

Where does the solidary nucleus get information from to raise blood pressure

Barorecepotrs in carotid sinus and aortic arch

What center allows for sphincter control in RF

Pontine micturition center

Levels for PNS control of bladder

S2-S4

Repetitive movement from the RF

Conjugate eye movement (midbrain)

Chewing (pons)

Swllowing, coughing, sneeze (medulla)

What triggers vomiting or nausea when drugs or toxin enter the body

Chemotacic trigger zone (in the 4th ventricle) - blocked from BBB in CNS