PHA 538 Lab 9: Brain and Cranial Nerves

Lab Overview and Objectives: PHA 538 Lab 9

  • Pre-Lab Preparation Requirements

    • Read the lab study guide in its entirety.

    • Watch the supplemental videos listed on the Supplemental Videos Document posted in Moodle.

  • In-Lab Procedures

    • Collaborate with the lab group to review materials for each of the 6 lab stations.

    • Utilize an anatomy atlas to locate specific anatomical structures in models, cadavers, and specimens.

    • Consult the instructor or TA with questions before departing the lab.

  • Post-Lab Activities

    • Read the corresponding textbook sections.

    • Rewatch the supplemental videos on Moodle.

    • Attend office hours or open labs with specific prepared questions.

  • Core Learning Objectives

    • Identify and understand functions of major brain structures on models, specimens, and cadavers.

    • Identify and describe the three meninges of the brain, associated structures, and their functions.

    • Identify anatomical structures associated with the formation, circulation, and drainage of Cerebrospinal Fluid (CSF).

    • Identify the 12 cranial nerves by name and number, including their origin, course through the skull, and function.

    • Apply anatomical knowledge to understand the affected anatomy in specific medical conditions.

External Cerebrum: Hemispheres, Lobes, and Sulci

  • Cerebral Hemispheres

    • Right and Left Hemispheres: The cerebrum is divided into these two halves, separated by the longitudinal fissure. Each hemisphere contains five distinct regions known as lobes.

  • Cerebral Lobes

    • Frontal Lobe (1): The most anterior lobe, located immediately deep to the frontal bone. It is responsible for planning and initiating muscle contractions and regulating higher-order cognitive behaviors (reasoning, problem-solving, task planning).

    • Parietal Lobe (2): Located deep to the parietal bone and superior to the lateral sulcus. It integrates sensory information including pain, temperature, pressure, and touch.

    • Temporal Lobe (2): Located deep to the temporal bone in the middle cranial fossa. It assists with language understanding, memory, processing auditory information, and some visual perception.

    • Occipital Lobe (1): Located deep to the occipital bone. It houses the major visual processing center of the brain.

    • Insula (2): A deep cerebral lobe forming the floor of the lateral sulcus. It is involved in cortical processes including awareness of visceral sensations, pain, temperature, olfaction, hearing, taste, emotion, and behavior.

  • Primary Sulci and Gyri

    • Longitudinal Fissure: A deep sagittal groove that separates the two cerebral hemispheres.

    • Central Sulcus: A deep coronal groove that separates the frontal lobe from the parietal lobes.

    • Lateral Sulcus: A deep horizontal groove separating the temporal lobe from the frontal and parietal lobes.

    • Calcarine Sulcus: A deep groove on the internal surface of the occipital lobe; it separates gyri associated with vision.

    • Cingulate Gyrus: A raised ridge on the medial surface of the cerebrum, superior to the corpus callosum. It regulates autonomic and endocrine responses to emotions, predicts behavior outcomes, and assists with visuospatial orientation.

    • Precentral Gyrus: A raised ridge anterior to the central sulcus. It contains cell bodies of interneurons for processing motor information.

    • Postcentral Gyrus: A raised ridge posterior to the central sulcus. It contains cell bodies of neurons for processing somatosensory information.

Functional Areas of the Cerebral Cortex

  • General Cortex Structure

    • Cerebral Cortex: The outer layer of the cerebrum composed of gray matter. It contains cell bodies and mostly unmyelinated axons responsible for higher nervous system functions.

  • Functional Motor Areas

    • Primary Motor Cortex: Located in the precentral gyrus. Long axons project to the spinal cord to control precise skeletal muscle movements on the contralateral side of the body.

    • Premotor Cortex: Located in the frontal lobe anterior to the primary motor cortex. It helps plan complex tasks by sequencing basic motor movements.

    • Broca’s Area: Located in the frontal lobe inferior to the premotor cortex in the dominant hemisphere. It controls skeletal muscles for speech planning and production.

  • Functional Sensory Areas

    • Primary Somatosensory Cortex: Located in the postcentral gyrus. Receives general sensory info from skin and proprioceptors in muscles/joints/tendons for spatial discrimination.

    • Primary Visual Cortex: Located in the occipital lobe near the calcarine sulcus. Receives visual information from the retina of the contralateral eye.

    • Primary Auditory Cortex: Located in the temporal lobe inferior to the lateral sulcus. Receives and processes auditory information.

    • Primary Olfactory Cortex: Located on the inferior medial surface of the temporal lobe. Processes olfactory stimuli from the nasal cavity.

    • Primary Gustatory Cortex: Located in the insular lobe. Processes taste stimuli from the tongue, larynx, pharynx, and epiglottis.

  • Multimodal Association Areas

    • Prefrontal Cortex: Located on the most anterior surface of the frontal lobe. Responsible for cognition, planning, reasoning, judgment, and personality.

Internal Structures of the Brain

  • Septum Pellucidum: A thin connective tissue membrane located between the lateral ventricles, inferior to the corpus callosum.

  • Corpus Callosum: A major white matter commissural tract connecting the two hemispheres, allowing for rapid communication between them.

  • Basal Nuclei: Collections of gray matter deep in the cerebrum that regulate skeletal motor functions, cognition, and emotion.

  • Amygdala: A gray matter structure anterior to the inferior horn of the lateral ventricle in the temporal lobe. It regulates fear and anxiety-related responses.

  • Hippocampus: Gray matter structure deep in the temporal lobe, inferior to the amygdala. Regulates learning, memory, behavior, and spatial navigation.

  • Fornix: A white matter tract on the inferior border of the septum pellucidum. It connects the hippocampus to subcortical regions to aid long-term memory formation.

Diencephalon, Brainstem, and Cerebellum

  • The Diencephalon

    • Epithalamus: Superior and posterior to the thalamus; connects limbic system structures to the rest of the brain.

      • Pineal Gland: Secretes melatonin to regulate wake-sleep cycles and influences other endocrine glands (pituitary, thyroid, adrenal).

    • Thalamus: "Egg-shaped" nuclei collection; relays sensory and motor information between the cortex, spinal cord, and brainstem.

      • Lateral Geniculate Nucleus: Main relay for the visual pathway at the end of the optic tract; houses cell bodies of the optic radiation.

      • Medial Geniculate Nucleus: Main relay for the auditory pathway between the inferior colliculus and the primary auditory cortex.

    • Hypothalamus: Located inferior/anterior to the thalamus. Control center for endocrine and autonomic systems. Monitors hunger, body weight, thirst, temperature, heart rate, and pituitary activity.

    • Subthalamus: Located ventral to the thalamus. Regulates motor movements in conjunction with basal nuclei.

  • The Brainstem

    • Midbrain: Superior region containing descending tracts for motor impulses.

      • Superior Colliculus: Gray matter on the midbrain roof; processes visual info and initiates reflexive eye/head movements.

      • Inferior Colliculus: Gray matter on the midbrain roof; processes sound location, pitch, rhythm, and body orientation.

    • Pons: Middle region; connects cerebellum to brainstem and spinal cord to higher centers. Houses cranial nerve nuclei.

    • Medulla Oblongata: Inferior region connecting to the spinal cord. Houses cardiac, respiratory, and abdominothoracic centers. Controls heart rate, BP, respiratory rhythm (rate/depth), swallowing, coughing, sneezing, and vomiting.

  • The Cerebellum

    • General Structure: Posteroinferior region; fine-tunes movements via proprioceptive info.

    • Arbor Vitae: "Tree-like" white matter tracts providing afferent and efferent pathways.

    • Vermis: Connects cerebellar hemispheres; coordinates movement of head, trunk, and proximal superior limbs.

    • Cerebellar Tonsils: Small rounded lobes on the inferomedial surface; regulate limb movements.

      • Clinical Significance: Increased intracranial pressure can cause tonsils/medulla to herniate through the foramen magnum, potentially causing cardiorespiratory arrest.

Meninges and Cerebrospinal Fluid (CSF) System

  • Meninges (Three Protection Layers)

    • Dura Mater: Outermost tough layer. In the brain, it has two layers (periosteal and meningeal); protects the brain.

      • Falx Cerebri: Dural fold in the sagittal plane separating cerebral hemispheres.

      • Falx Cerebelli: Dural fold in the sagittal plane separating cerebellar hemispheres.

      • Tentorium Cerebelli: Horizontal dural fold between the cerebellum and occipital lobe; suspends the occipital lobe.

    • Arachnoid Mater: Thin, weblike middle layer; protects blood vessels.

    • Pia Mater: Thin, transparent innermost layer adhering directly to nervous tissue and following sulci.

  • Meningeal Spaces

    • Epidural Space: Potential space between skull and dura. Clinical Note: Epidural hematomas occur here.

    • Subdural Space: Potential space between dura and arachnoid containing serous fluid. Clinical Note: Subdural hematomas occur here.

    • Subarachnoid Space: Deep to arachnoid; contains blood vessels and CSF.

  • Cerebrospinal Fluid (CSF)

    • Definition: Clear fluid derived from blood.

    • Production: Produced by choroid plexuses (blood capillaries lined by ependymal cells) within brain ventricles.

    • Functions: Provides protection (cushioning), nourishment, and waste removal.

  • Ventricular System

    • Lateral Ventricles: C-shaped cavities in hemispheres; start CSF circulation.

    • Interventricular Foramina: Openings between lateral ventricles and the third ventricle.

    • Third Ventricle: Located in the diencephalon between thalami; produces and receives CSF.

    • Cerebral Aqueduct: Tubular channel in the midbrain connecting 3rd and 4th ventricles.

    • Fourth Ventricle: Diamond-shaped cavity between brainstem and cerebellum.

    • Median and Lateral Apertures: Drain CSF from the 4th ventricle into the subarachnoid space.

    • Central Canal: Takes CSF from the 4th ventricle into the spinal cord.

    • Arachnoid Granulations: Pockets of arachnoid membrane for CSF reabsorption into venous circulation (dural venous sinuses).

Cranial Nerves: Part 1 (I - VI)

Nerve

Origin

Foramina

Target

Type

Function

Injury Result

Clinical Test

I. Olfactory

Olfactory epithelium

Cribriform foramina

Primary olfactory cortex

Sensory

Smelling

Anosmia (loss of smell)

Identify non-irritating odors one nostril at a time

II. Optic

Retina

Optic canal

Primary visual cortex

Sensory

Vision

Blindness; Anopsia (post-chiasma injury)

Ophthalmoscope exam of disc/vessels

III. Oculomotor

Pontomesencephalic junction

Superior orbital fissure

Eye muscles, iris, lens

Motor

Eye movement, pupil constriction, lens accommodation

External strabismus, ptosis, double vision

Pupillary reflex; H-test for tracking

IV. Trochlear

Dorsal midbrain

Superior orbital fissure

Superior oblique m.

Motor

Abducts, depresses, rotates eye medially

Double vision; difficulty rotating eye in/down

Tracking in/down during H-test

V. Trigeminal

Pons

V1: Sup. Orbital Fissure; V2: F. Rotundum; V3: F. Ovale

Face skin/mucosa, muscles of mastication

Mixed

Face sensation; chewing muscles

Trigeminal neuralgia; loss of face sensation

V1: Cornea touch; V2: Touch/pain; V3: Clench teeth/move jaw

VI. Abducens

Pontomedullary junction

Superior orbital fissure

Lateral rectus m.

Motor

Eye abduction (lateral movement)

Eye cannot move laterally

H-test: Look for difficulty moving eye outward

Cranial Nerves: Part 2 (VII - XII)

Nerve

Origin

Foramina

Target

Type

Function

Injury Result

Clinical Test

VII. Facial

Pontomedullary junction

Internal acoustic meatus; Stylomastoid foramen

Face muscles, Tongue (ant. 2/3), glands

Mixed

Facial expression; Taste (ant. 2/3); Tears/saliva

Bell’s palsy; taste loss; dripping tears

Check face symmetry/smile; Taste test (sweet/sour); Ammonia for tears

VIII. Vestibulocochlear

Inner ear

Internal acoustic meatus

Pontomedullary junction

Sensory

Equilibrium and hearing

Central deafness; dizziness; nausea

Tuning fork (air and bone conduction)

IX. Glossopharyngeal

Medulla oblongata

Jugular foramen

Pharynx, parotid gland, Tongue (post. 1/3)

Mixed

Pharynx muscles; Saliva (parotid); Taste (post. 1/3)

Impaired swallowing/taste

Gag reflex; check uvula; Swallow/cough; Taste post. 1/3

X. Vagus

Medulla oblongata

Jugular foramen

Thoracic/abdominal organs, Pharynx/Larynx

Mixed

Heart rate; digestion; breathing; Pharynx/Larynx; Taste (epiglottis)

Hoarseness/voice loss; digestive/swallowing issues

Gag reflex; monitor HR during deep breathing

XI. Spinal Accessory

Cervical spinal cord rootlets

F. Magnum; Jugular foramen

SCM and Trapezius

Motor

Innervates SCM and Trapezius

Head turns toward injured side (SCM paralysis)

Shrug shoulders/rotate head against resistance

XII. Hypoglossal

Medulla oblongata

Hypoglossal canal

Tongue muscles

Motor

Tongue movement for chewing, swallowing, speech

Speech/swallowing difficulty; cannot protrude tongue if bilateral

Protrude and retract tongue

Applied Anatomy and Medical Conditions

  • Hydrocephalus

    • Description: Excessive accumulation of CSF inside or outside the brain.

    • Cause: blockage within the CSF pathway.

  • Agenesis of the Corpus Callosum

    • Description: A congenital condition.

    • Phenomenon: The corpus callosum is either partially or completely absent.

  • Meningitis

    • Description: Inflammation of the meninges.

    • Cause: Typically due to bacterial or viral infections.

  • Cerebellar Tonsils Herniation

    • Description: Condition where cerebellar tonsils herniate through the foramen magnum.

    • Pathophysiology: Blocks CSF pathway, potentially leading to hydrocephalus in the brain or syringomyelia in the spinal cord.

    • Contributing Factors: Small posterior cranial fossa or premature closure of skull sutures.

    • Critical Risk: Can damage the cardiorespiratory center in the medulla oblongata, leading to arrest and death.