Brainstem & Cranial Nerves

Maryann Martone, Ph. D.

NEU 256

October 13, 2005

Review: Levels of the Spinal Cord

Ventricles in brainstem

• Mesencephalon cerebral aqueduct

• Metencephalon 4th ventricle

• Mylencephalon 4th ventricle

vermis

Occipital LobeThalamus

Corpus callosum

Hypothalamus

Fornix

Anterior commissure

Optic nerve

4th ventricle

Posterior commissure

pyramid

Mammillary body

Quadrigeminal cistern

internal capsulebasal ganglia

optic nerveoptic tract

hypothalamusmammillary body

cerebral peduncle

interpeduncular fossa

flocculusinferior olivary

nuclear complex

cerebellum

cerebellar tonsil

pyramid

pyramidal decussation

pons

optic chiasm

Anterior view of brainstem

optic tract

optic nerve

hypothalamus

optic chiasm

middle cerebellar peduncle

trigeminal nerve

vestibulocochlear nerve

flocculus

cuneate tubercle

inferior olivary nuclear complex

anterior median fissure pyramid

pons

cerebral peduncle

Lateral view of brainstem

Middle cerebellar peduncle

Superior colliculus

Inferior colliculusCerebral peduncle

Superior cerebellar peduncle

Inferior cerebellar peduncle

Medulla

4th ventricle

Posterior view of brainstem

Components of the brainstem

• Sensory ascending pathways (dorsal)• Motor descending pathways (ventral)• Cerebellar pathways• Cranial nerve sensory and motor tracts• CPGs: rhythmic chewing, respiration,

cardiovascular regulation & gain adjustments for reflexes

• Modulatory systems: locus coeruleus, raphe & substantia nigra

Ascending sensory pathways

Fine discriminitive touch, conscious proprioception• Fasciculus gracilis: Terminates in the nucleus gracilis (medulla)• Fasciculus cuneatus: Terminates (medulla) in the cuneate and accessory cuneate nuclei

Sensations of pain and temperature• Lateral Spinothalamic Tract

– origin dorsal horn cells of the gray matter– Fibers cross contralaterally through the anterior commissure and ascend to the VPL

nucleus

Transmits sensations of touch• Ventral Spinothalamic Tract

– origin cells of the posterior horn– Fibers cross to the opposite side in the anterior commissure

Descending motor pathwaysVoluntary movement • Lateral Corticospinal Tract

– Originates in large pyramidal cells (precentral gyrus) – cross to the opposite side of the cord at the pyramidal decussation & terminate in the dorsal

horn cells• Ventral Corticospinal Tract

– Originates in the pyramidal cells (motor area of the cortex)

Impulses related to equilibrium and antigravity reflexes• Vestibulospinal Tract

– Fibers originate in the vestibular nuclei of the medulla and terminate at level of the sacral spinal nerves

Connects vestibular complex and head and eye movement coordination center in medulla• Medial Longitudinal Fasciculus

– Contains both ascending and descending fibers

Motor Hierarchy•Lateral group (extremities; fine motor control)

•Corticospinal tract

•Rubrospinal tract

•Medial group (axial musculature; rhythmic and postural movements)

•Vestibulospinal tract

•Tectospinal tract

•Reticulospinal tract

•“Final common path”: motor pool

Reticular Formation

• “Core” of brainstem (midbrain, pons and medulla) composed of loosely organized neurons, outside of the major nuclear groups of the brainstem.

• Medial-to-lateral: raphe nuclei, gigantocellular region, small cell region

• Participate in widespread connections

• Rostral continuation of interneuronal network found in spinal cord

Cerebellar pathways

Conduct impulses from the leg and trunk muscles for unconscious proprioception

• Dorsal & Ventral Spinocerebellar Tracts– Enter cerebellum via inferior cerebellar peduncle

Brainstem Internal Anatomy

Components of the brainstem

• Sensory ascending pathways (dorsal):– Relay nuclei, tracts

• Motor descending pathways (ventral)– Tracts, motor nuclei brainstem

• Cerebellar pathways– Tracts, cerebellar afferent and efferent nuclei

• Cranial nerve sensory and motor tracts– Cranial nerve nuclei, nerve entry and exit points

• CPGs: rhythmic chewing, respiration, cardiovascular regulation & gain adjustments for reflexes

• Modulatory systems: locus coeruleus, raphe & substantia nigra– Chemically coded nuclei

Tracing through the brainstem: Dorsal Column/Medial Lemniscal

System

Corticospinal Tract

Caudal Medulla

Caudal Medulla

“Closed” medulla

Medulla

Rostral Medulla

Rostral Medulla

Medulla-Pons Junction

Mesencephalon

The Cranial Nerves

• The head and neck are not innervated by spinal nerves

• Sensory information is received and motor information is sent via 12 cranial nerves

• Considered part of the PNS they convey messages to and from the body's muscles and glands.

Each cranial nerve….

• Can be referred to by a name or number!

• Has a general function• Has at least a motor, sensory or

parasympathetic component• Some have more than one component• Has associated brainstem nuclei• Innervates a structure(s)

I

I

IIIII

IVVVI

VIIIVII

IXX

XI XII

Cranial nerves can be identified on the ventral surface of the brain

I Olfactory On Some

II Optic Old Say

III Occulomotor Olympus Marry*

IV Trochlear Towering Money

V Trigeminal Tops But

VI Abducens A My

VII Facial Frenchman Brother*

VIII Auditory/Vestibulocochlear And Says

IX Glossopharyngeal German Big*

X Vagus Viewed Business*

XI Spinal/Accessory Some Makes

XII Hypoglossal Hops Money

Some tricks to learning cranial nerve numbers, names & components…

S = SensoryM = MotorB = Both/Mixed Sensory & Motor* = Parasympathetic

Arrangement of brainstem

cranial nerve nuclei in columns

• Midbrain

• Pons

• Medulla

Insert picture with different levels differentiated

General Rules of Thumb

•Most motor nuclei are associated with a single cranial nerve

•Afferent nuclei often receive fibers from several cranial nerves

•All associated with a single function however, e.g., nucleus of solitary tract

Functions of Cranial Nerves

www.neurophys.com/EMG/Cranial_Nerves/

Cranial Nerve I: OlfactoryComponent: Sensory

Function: Smell

Tract: Olfactory cells of nasal mucosa Olfactory Bulbs pyriform cortex

Cranial Nerve II: Optic

Component(s): Sensory

Function: Vision

Tract: retinal ganglion cells optic chiasm thalamus primary visual cortex in occipital lobe

Cranial Nerve III: OculomotorComponent #1: Motor

Function(s): Movement of eyeball & lens accomodation

Structure(s) Innervated:

4 eyeball muscles & 1 eyelid muscle

Component #2: Parasympathetic

Nucleus location: midbrain

Function: pupil constriction

Structure(s) Innervated:

ciliary muscle and pupillary constrictor muscles

Cranial Nerve III: Oculomotor

Cranial Nerve IV: Trochlear

Component: Motor

Function: moves eyeball

Nucleus location: midbrain

Structure(s) Innervated:

superior oblique muscles

Cranial Nerve V: Trigeminal

Component #1: Sensory(impulses of touch, pain, heat and cold)

Locations of nuclei: pons & medulla

Function: (1) sensations; (2) general sensory from tongue; (3) proprioception

Structure(s) Innervated:

(1) face, scalp, teeth, lips, eyeballs, nose & throat lining; (2) anterior 2/3 of tonque; (3) muscles of mastication

Cranial Nerve V: Trigeminal

Component #2: Motor

Function: chewing

Nucleus location: trigeminal motor nucleus in pons

Structure(s) Innervated:

muscles of mastication

Cranial Nerve V: Trigeminal

Cranial Nerve VI: Abducens

Component: Motor

Function: Eyeball movement

Nucleus: abducens nucleus in pons

Structure(s) Innervated:

lateral rectus muscle of eye

Cranial Nerve VII: Facial

Component #2: Motor

Nucleus location: facial motor nucleus in pons

Function: facial expressions

Structure(s) Innervated:

muscles of the face

Component #1: Sensory

Nucleus location: medulla

Function: (1) taste & (2) proprioception

Structure(s) Innervated:

(1) anterior 2/3 of tongue & (2) face and scalp

Cranial Nerve VII: Facial

Component #3: Parasympathetic

Nucleus location: Superior salivatory nucleus in medulla

Function: salivation and lacrimation (drooling and tears)

Structure(s) Innervated:

salivary and lacrimal glands via submandibular and pterygopalatine gamglia

Cranial Nerve VIII: Vestibulocochlear (aka acoustic or auditory nerve)

Component: Sensory

Functions: (1) Balance

(2) Hearing

Nucleus: In pons and medulla

Structure(s) Innervated:

• vestibular apparatus of internal ear• cochlear of internal ear auditory cortex in the temporal lobes

Cranial Nerve VIII: Vestibulocochlear (aka acoustic or auditory nerve)

Cranial Nerve IX: Glossopharyngeal

Component #1: Sensory

Nucleus location: medulla

Function: (1) taste; (2) proprioception for swallowing & (3) blood pressure receptors

Structure(s) Innervated:

(1) posterior two thirds of tongue; (2) throat muscles & (3) carotid sinuses

Cranial Nerve IX: Glossopharyngeal

Component #2: Motor

Nucleus location: medulla

Function: (1) swallowing and gag reflexes & (2) tear production

Structure(s) Innervated:

(1) throat muscles and (2) lacrimal glands

Cranial Nerve IX: Glossopharyngeal

Component #3: Parasympathetic

Function: saliva production

Structure(s) Innervated:

parotid glands

Cranial Nerve X: Vagus

Component #1: Sensory

Nucleus location: medulla

Function: (1) chemoreceptors; (2) pain receptors; (3) sensations; (4) taste

Structure(s) Innervated:

(1) blood oxygen concentration, carotid bodies; (2) respiratory & digestive tracts; (3) external ear, larynx & pharynx (4) tongue

Cranial Nerve X: Vagus

Component #2: Motor

Nucleus location: medulla

Function(s): (1) heart rate & stroke volume; (2) peristalsis; (3) air flow; (4) speech & swallowing

Structure(s) Innervated:

(1) pacemaker & ventricular muscles; (2) smooth muscles of the digestive tract (3) smooth muscles in bronchial tubes (4) muscles of larynx a & pharynx

Cranial Nerve X: Vagus

Component #3: Parasympathetic

Structure(s) Innervated:

smooth muscles and glands of the same areas innervated by motor component, as well as thoracic and abdominal areas

Cranial Nerve XI: Spinal Accessory

Component: Motor

Function: head rotation (& shoulder shrugging!)

Nucleus location: accessory nucleus in medulla

Structure(s) Innervated:

trapezius & sternocleidomastoid muscles

Cranial Nerve XII: Hypoglossal

Component: Motor

Function: Speech and swallowing

Nucleus location: In medulla

Structure(s) Innervated:

Throat and tongue muscles

Cranial Nerve XII: Hypoglossal