New Brainstem And Cranial Nerves

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

Corpus callosum

Posterior commissure

Fornix Occipital Lobe

Thalamus Anterior commissure

Quadrigeminal cistern

Hypothalamus

vermis Optic nerve 4th ventricle Mammillary body

pyramid

Anterior view of brainstem basal ganglia

internal capsule optic chiasm

optic nerve hypothalamus

optic tract mammillary body

cerebral peduncle interpeduncular fossa

pons flocculus

inferior olivary nuclear complex cerebellum pyramid

cerebellar tonsil pyramidal decussation

Lateral view of brainstem optic tract

cerebral peduncle

trigeminal nerve

optic nerve middle cerebellar peduncle optic chiasm vestibulocochlear nerve flocculus

hypothalamus

cuneate tubercle pons

inferior olivary nuclear complex

anterior median fissure

pyramid

Posterior view of brainstem

Superior colliculus Cerebral peduncle Superior cerebellar peduncle Middle cerebellar peduncle

Inferior colliculus

4th ventricle

Inferior cerebellar peduncle

Medulla

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 pathways Voluntary 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

“Closed” medulla

Caudal 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)

Cranial nerves can be identified on the ventral surface of the brain I I II III

VII

IV V VI

X XI

XII

VIII IX

Some tricks to learning cranial nerve numbers, names & components… I II III IV V VI VII VIII IX X XI XII

Olfactory

On

Some

Optic Occulomotor Trochlear Trigeminal Abducens Facial Auditory/Vestibulocochlear Glossopharyngeal Vagus Spinal/Accessory Hypoglossal

Old Olympus Towering Tops A Frenchman And German Viewed Some Hops

Say Marry* Money But My Brother* Says Big* Business* Makes Money S = Sensory M = Motor B = 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: Olfactory Component:

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: Oculomotor Component #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 #1:

Sensory

Nucleus location:

medulla

Function:

(1) taste & (2) proprioception

Structure(s) Innervated:

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

Component #2:

Motor

Nucleus location:

facial motor nucleus in pons

Function:

facial expressions

Structure(s) Innervated:

muscles of the face

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 trapezius & sternocleidomastoid muscles

Structure(s) Innervated:

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