Lab 19

Cranial Nerves &

Brain dissection

Today

• Intro to the brain

• The cranial nerves

• Human and sheep brain anatomy

• Get to work

• CLEAN UP

Practical 4

• Thurs 12/6• 50 points: about half brain models and half

book figures (with a few fresh brains too)• Know:

– List of brain parts on objectives (names and locations only; you will need to know functions on the exam though)

– The 12 cranial nerves: names, locations, & functions (shown in blue in this lecture)

Brief intro to the brainExternal structures • cerebral hemispheres• cerebrum• midbrain• cerebellum• pons• medulla• central sulcus• precentral gyrus• postcentral gyrus• lateral sulcus• longitudinal fissure• frontal lobe• parietal lobe• occipital lobe• temporal lobe

Internal structures: • corpus callosum• basal ganglia (nucleus)

– Caudate– Putamen

• internal capsule• thalamus• hypothalamus• hippocampus• amygdala• pineal gland• pituitary gland• reticular formation• fornix• substantia nigra• cingulate gyrus • optic chiasm• lateral ventricles• mammilary bodies• corpora quadrigemina

– inferior colliculus– superior colliculus

Figure 14–1

Major Regions and Landmarks

Regions of the Adult Brain

• Telencephalon (cerebrum) – cortex, white matter, and basal nuclei

• Diencephalon – thalamus, hypothalamus, and epithalamus

• Mesencephalon –midbrain (brain stem)• Metencephalon – pons (brain stem),

cerebellum• Myelencephalon – medulla oblongata

(brain stem)

Some terms

• nucleus: collection of neuron cell bodies in the CNS

• tract: collection of axons in the CNS

• ganglia: collection of neuron cell bodies in the PNS

• nerve: collection of axons in the PNS– Cranial nerves– Spinal nerves

Tour through the brain

• From caudal/inferior to rostral/superior

The Brain Stem

• Includes:– mesencephalon (midbrain)– pons– medulla oblongata– Note: some consider the diencephalon part of

the brain stem as well

Anatomy:Brain stem

Most cranial nerves are located in the brain stem

Posterior view

Medulla Oblongata

Cerebellum

Cerebellum – side view

Mesencephalon

Mesencephalon

Figure 14–5a

The Diencephalon

• Thalamus• Hypothalamus• Pineal gland• Pituitary gland

Telencephalon

• Cerebrum– Largest part of brain, includes huge wrinkly

cerebral hemispheres

• Basal nuclei

Figure 14–14b, c

The Basal Nuclei (Ganglia)

Lateral Ventricles

Figure 14–11a

The Limbic System

Figure 14–12b

The Cerebral Cortex

4 Lobes:frontalparietaltemporaloccipital

Cerebral Cortex landmarks

• Lateral sulcus

• Longitudinal fissure

• Central sulcus

• Precentral gyrus (primary motor)

• Postcentral gyrus (primary sensory)

• Association areas are for integrating information

Figure 14–15a

Motor and Sensory Areas of the Cortex

• Central sulcus separates motor and sensory areas

Cranial Nerves

Figure 14–18

Cranial Nerves• 12 pairs connected to brain

Cranial Nerves

Figure 13.5a

Cranial Nerves

• Twelve pairs of cranial nerves arise from the brain

• They have sensory, motor, or both sensory and motor functions (mixed)

• Each nerve is identified by a number (I through XII) and a name

• Four cranial nerves carry parasympathetic fibers that serve muscles and glands

3 main types of Cranial Nerves

Sensory nerves:– carry somatic (touch) or special sensory

information

Motor nerves: – axons of somatic motor neurons

Mixed nerves: – mixture of motor and sensory fibers

Cranial Nerves

• I – Olfactory• II – Optic• III – Occulomotor• IV – Trochlear• V – Trigeminal• VI – Abducens

• VII – Facial• VIII – Vestibulococlear• IX – Glossopharyngeal• X – Vagus• XI – Accessory• XII – Hypoglossal

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Summary of Function of Cranial Nerves

Figure 13.5b

You need to learn:

• Names

• Numbers

• Locations

• Main functions (in blue)

Lateral view

Anterior View

Figure 14–19

The Olfactory Nerves (I)

Olfactory Nerves (I)

• Don’t originate or enter brainstem• Primary function:

– special sensory (smell)

• Arises from the olfactory epithelium• Passes through the cribriform plate of the ethmoid

bone• Fibers run through the olfactory bulb and

terminate in the primary olfactory cortex• Functions solely by carrying afferent impulses for

the sense of smell

Figure 14–20

The Optic Nerves (II)

Optic Nerves (II)

• Enter diencephalon• Primary function:

– special sensory (vision)

• Arises from the retina of the eye• Optic nerves pass through the optic canals

and converge at the optic chiasm• They continue to the thalamus

(diencephalon) where they synapse

CNs III,IV,VI

• All motor only

• All innervate eye muscles

Figure 14–21

The Oculomotor Nerves (III)

Oculomotor Nerves (III)

• Primary function: – motor (many eyeball movements, pupil

constriction, controlling lens shape)

• Origin: – mesencephalon

• Destination: – somatic motor: 4 extrinsic eye muscles: – visceral motor: parasympathetic NS cell

bodies in the ciliary ganglion, got to intrinsic eye muscles

Figure 14–21

The Trochlear Nerves (IV)

Trochlear Nerves (IV)

• Smallest CN• Primary function:

– motor (eye movement: looking down)

• Origin: – mesencephalon

• Destination: – superior oblique muscle (that’s it!)

The Abducens Nerves (VI)

Figure 14–21

The Abducens Nerves (VI)

• Primary function: – motor (eye movement: looking to the side)

• Origin: – pons

• Destination:– lateral rectus muscle (just one eye muscle)

Figure 14–22

The Trigeminal Nerves (V)

Trigeminal Nerves (V)

• Largest CN – it’s huge!• Primary function:

– mixed (sensory and motor) to face All sensory from face; motor for chewing

• Three branches – ophthalmic branch (sensory)– maxillary branch (sensory)– mandibular branch (sensory and motor)

• Destinations– sensory: sensory nuclei in pons– motor: muscles of mastication

Figure 14–23

The Facial Nerves (VII)

Facial Nerves (VII)

• Primary function: – mixed (sensory and motor) to faceMotor to facial muscles; taste

• sensory: – taste receptors on anterior 2/3 of tongue

• motor: – Facial muscles, parasympathetic to lacrimal

and salivary glands

**Bell’s Palsy

Figure 14–24

The Vestibulocochlear Nerves (VIII)

Vestibulocochlear Nerves (VIII)

• Primary function: special sensory – vestibular branch:

• balance and equilibrium

– cochlear branch: • hearing

• Origin: receptors of inner ear

• Destination: nuclei in both pons and medulla

Figure 14–25

The Glossopharyngeal Nerves (IX)

Glossopharyngeal Nerves (IX)

• Primary function: – mixed (sensory and motor) to head and neck Mainly: swallowing, some salivary gland function

• Origins:– sensory:

• posterior 1/3 of tongue• part of pharynx and palate• carotid bodies (blood pressure/CO2 sensors)

– motor: • motor nuclei of medulla

Figure 14–26

The Vagus Nerves (X)

Vagus Nerves (X)

• Primary function: – mixed (sensory and motor) of thorax and

abdomen– Only CN that extends beyond head and neck– “Mr. parasympathetic” motor to para-NS– Runs outside of spinal cord to visceral organs– Originates in medulla

Figure 14–27

The Accessory Nerves (XI)

Accessory Nerves (XI)

• Primary function: – motor to muscles of neck and upper back

• Origin: – motor nuclei of spinal cord and medulla oblongata

• Two roots:– The spinal root passes upward into the cranium via

the foramen magnum– The accessory nerve leaves the cranium via the

jugular foramen• Destinations:

– voluntary muscles of palate, pharynx, and larynx– sternocleidomastoid and trapezius muscles

Figure 14–27

The Hypoglossal Nerves (XII)

Hypoglossal Nerves (XII)

• Primary function: – motor (tongue movements)

• Origin: – motor nuclei of medulla

• Destination: – muscles of tongue which aid in speech

Gross Anatomy of the human brain

Human brain

Midsagittal

Coronal

InferiorView

Sheep brain

Sheep brain inferior view

Midsagittal

Anterior View

Follow instructions in lab book

• look at the meninges• start by examining the external brain

– Ventral surface first, then dorsal

• then look internally without cutting (fig 19.12)• cut it midsagittally to see inside• Try a coronal cut to see what you can find

• Review Sheet due next Thursday

To find:• Meninges• Cranial nerves I – XII (?)• fissures and sulci on

surface, lobes• pineal gland• corpora quadrigemina

(part of midbrain)• midbrain• pons• medulla• cerebellum • mamillary body (just one)• optic chiasm

• corpus callosum (central)• fornix• lateral ventricles• choroid plexus (inside

ventricles)• hypothalmus• “pituitatry gland” (hangs

off hypothalamus• arbor vitae (inside

cerebellum)