Unit 4: Nervous SystemLab 3: Cranial/Spinal Nerves &

Lab 4, Part 1: Introduction to the Eye

Jessica Radke-Snead, RD, MSBio 241 Anatomy & Physiology

Reminders

• Today’s Lab– Cranial and spinal nerves– Introduction to Lab 4

• Wednesday– Human eye/vision– Histology of the retina– Human ear and physiological aspects of hearing– Histology of the cochlea– Visual acuity tests (observe on your own)– Hearing tests (observe on your own)

I Olfactory Nerve

Type: Sensory

Function: Smell (olfaction)

Olfactory receptors (olfactory epithelium) extend through olfactory foramina (cribiform plate, ethmoid bone) and collectively form the right and left olfactory nerves and olfactory bulbs. Axons of the olfactory tracts end in the primary olfactory area (temporal lobe).

II Optic NerveType: Sensory

Function: Vision1. Eye, rods and cones

initiate visual signals2. Signals relayed via optic

nerve, which merge to form the optic chiasm (optic foramina) and optic tracts (posterior)

3. Axons from optic tracts project to the primary visual area (occipital lobe)

III Oculomotor, IV Trochlear and VI Abducens Nerves

Type: Motor axons that exit the brain stem.

Sensory axons (extrinsic eyeball muscles) initially travel through each of these nerves and enter the midbrain (V Trigeminal nerve).

Function: Pass through Sup Orb Fissure to control the muscles that move the eyeballs.

Sensory: proprioception (non-visual perception)

III Oculomotor“eye-mover”

• Type: Motor and Sensory• Extends from midbrain (junction with pons)• Somatic motor axons innervate:– Extrinsic eyeball muscles (SR, MR, IR & IOb)

Eyeball movement– Levator palebrae superioris raising the upper lid

• Autonomic motor axons innervate intrinsic eyeball muscles (Ciliary) adjust the shape of the lens and iris to adjust the size of the pupil

IV Trochlear Nerve“pulley”

• Type: Motor and Sensory• Posterior side of midbrain, wraps around the

pons• Somatic motor axons innervate extrinsic

muscle (SOb) movement of the eyeball– Trochlea: cartilage that supports the “pulley”

action of the SOb, thus nerve is called “trochlear”

VI Abducens Nerves“Away to lead”

• Type: Motor and Sensory• Originates in the pons• Somatic motor axons innervate extrinsic

muscle (LR) lateral rotation of eyeball– “ABDuction” or lateral movement of eye =

ABDucens nerve

V Trigeminal Nerve“triple branches”

Type: Motor and Sensory

Function: Sensory axons • Touch, pain and temp pons• Proprioceptors in the jawMotor axons supply jaw muscles for mastication

3 Branches:1. Ophthalmic (exits through Sup Orb

Fissure)

2. Maxillary (exits through foramen rotundum)

3. Mandibular (exits through foramen ovale)

• Ophthalmic nerve– Sensory axons from the upper eyelid, eyeball, lacrimal

glands, nasal cavity, nose, forehead and anterior scalp• Maxillary nerve – Sensory axons from the nose, palate, upper mouth

and lower eyelid• Mandibular nerve– Sensory axons from the anterior tongue (not taste),

cheek, skin over the jaw and side of the head and lower mouth

V Trigeminal Nerve“triple branches”

VII Facial Nerve

Type: Motor and SensorySensory axons: • Touch, pain and temperature

from ear canal• Proprioception from face and

scalp muscles

Motor neurons (pons) innervate facial, scalp and neck muscles for facial expression

Autonomic motor neurons innervate lacrimal and salivary glands

VIII Vestibulocochlear Nerve“small, spiral/snail like”

Type: Sensory• 2 Branches– Vestibular: impulses for equilibrium from the

semicircular canals, saccule and utricle of the inner ear to the pons and cerebellum

– Cochlear: impulses for hearing from the spiral organ of the inner ear to the primary auditory area (temporal lobe)

VIII Vestibulocochlear Nerve“small, spiral/snail like”

IX Glossopharyngeal Nerve“tongue, throat”

Type: Motor and SensorySensory axons – Arise from taste buds (posterior tongue) and external ear

to convey touch, pain and temperature– Proprioceptors in swallowing muscles– Neck region: info from baroreceptors (carotid sinus) that

monitor BP and chemoreceptors (carotid bodies) that monitor blood gas

Motor axons– Arise in medulla oblongata, pass through the jugular

foramen to innervate muscle in pharynx for swallowing– Autonomic axons stimulate the parotid gland (saliva)

IX Glossopharyngeal Nerve“tongue, throat”

X Va

gus

Ner

ve“v

agra

nt, w

ande

rer”

X Vagus Nerve“vagrant, wanderer”

Type: Motor and SensorySensory axons arise from:– External ear: touch, pain and temperature– Taste buds (throat)– Proprioceptors in muscles of the neck and throat– Carotid sinus: monitor BP– Carotid body and aortic bodies: monitor blood gas levels– Organs (thoracic, abdominal cavities): hunger, fullness

and discomfort

Sensory axons pass through jugular foramen Medulla oblongata

X Vagus Nerve“vagrant, wanderer”

Type: Motor and Sensory

Motor neurons: muscles of the pharynx and larynx for speech and swallowing

Autonomic motor neurons: lungs, heart and smooth muscle and glands of the respiratory passageways and GI tract

XI Accessory Nerve“assisting”

Type: Motor and Sensory

Motor axons– Arise in the anterior gray horn of the spinal cord (cervical

portion)– Exit the spinal cord laterally– Enter the foramen magnum– Exit through the jugular foramen (along with IX and X) why it’s considered a cranial vs spinal nerve

Convey impulses to the SCL and trapezius muscles coordinate head movements

XI Accessory Nerve“assisting”

Type: Motor and Sensory

Sensory axons arise from – Proprioceptors in the SCL and trapezius muscles– Eventually join nerves at the cervical plexus

Enter the spinal cord Medulla oblongata

XI Accessory Nerve“assisting”

XII Hypoglossal Nerve

Type: Motor and Sensory

Motor neurons originate in the medulla oblongata hypoglossal canal tongue muscles for speech and swallowing

Sensory axons originate from proprioceptors in the tongue muscles extend toward the brain (hypoglossal nerve) then leave hypoglossal nerve to join the cervical spinal nerves medulla oblongata

XII Hypoglossal Nerve

Spin

al C

ord

and

Spin

al N

erve

s • Posterior root + Anterior root = spinal nerve at the vertebral foramen– Posterior root contains sensory axons– Anterior root contains motor axons

Spinal Nerves• Spinal cord ends near the L2 vertebrae• Roots of the lumbar, sacral and coccygeal nerves

descend at an angle vertebral foramina (caudal equina)

• 31 pairs of spinal nerves– Identified by the region and level of vertebral column

from which they emerge– 8 pairs cervical– 12 pairs thoracic– 5 pairs lumbar– 5 pairs sacral– 1 pair coccygeal

Anatomy of Spinal Nerves• Upon passing through its

intervertebral foramen, a spinal nerve divides into branches (rami)– Posterior ramus: serves the

muscles and skin of the posterior trunk

– Anterior ramus• Muscles and structures of the

upper and lower limbs • Skin of the lateral and anterior

trunk

– Meningeal branch: vertebrae, spinal cord and meninges

– Rami communicantes: components of the ANS

Rami communicantes

Plexuses

• Network of axons formed on both sides of the body by joining with various numbers of axons

• Names often describe the general regions they serve or the course they take

• Primary plexuses– Cervical– Brachial– Lumbar– Sacral

Thoracic nerves T2-T12 follow each rib laterally and do not form plexuses

Cervical Plexus

Cervical Plexus

• Formed via C1-C4, part of C5, nerves• Supplies:– Skin and muscles on the head, and neck– Superior part of the shoulders and chest

• Important nerve arising from this plexsus– Phrenic (spinal nerves C3-C5)• Motor nerve: Diaphragm

Brachial Plexus• Formed by C5-C8 and T1 spinal nerves• Provides majority of the nerve supply to the shoulders and limbs• Complex structure: Roots Trunks Divisions Cords Branches

Brachial Plexus• From the cords, important nerves are:– Axillary (C5-C6)

• Motor nerve: Deltoid and Teres minor• Sensory nerve: Lateral arm to the deltoid tuberosity

– Radial (C5-T1)• Motor nerve: Triceps, Supinator, Brahcioradialis• Sensory nerve: Posterior arm and forearm, medial side of posterior

hand

– Median (C5-T1)• Motor nerve: Pronator teres and Flexor carpi radialis• Sensory nerve: Palmar aspect of 2nd-4th fingers

– Ulnar (C8-T1)• Motor nerve: Flexor carpi ulnaris• Sensory nerve: Medial portion of 4th and entire 5th finger

Lum

bar P

lexu

s• Formed by L1-L4 spinal nerves• Supplies the

– Anterior and lateral abdominal wall– External genitals– Part of lower limbs

Lumbar Plexus• Important nerves arising from

this plexus are:– Femoral (L2-L4)• Motor nerve: Iliacus, Pectineus,

Quadriceps femoris and Sartorius• Sensory nerve: Skin of the lateral

anterior thigh and dorsum of the foot

– Genitofemoral (L1-L2)• Motor nerve: Cremaster muscle• Sensory nerve: Skin of the medial

and anterior thigh, scrotum (male) or labia major (female)

Sacral Plexus

Sacral Plexus• Formed by L4-S4 spinal nerves• Supplies the buttocks, perineum and lower limbs• Important nerves that arise are– Pudendal

• Motor nerve: Ischiocavernosus, Bulbospongiosus, Levator ani and External anal sphincter

• Sensory nerve: Skin of the penis and scrotum, clitoris, labia major and minora, vagina

– Sciatic (posterior)• Branches into tibial and fibular nerves• Motor nerve: Semimembranosus, Semitendinosus, Biceps

femoris, Adductor magnus• Sensory: Lateral posterior leg, lateral aspect and plantar

surface of the foot

Introduction to the Human Eye

• Surface anatomy• Extrinsic and intrinsic eye muscles• Layers forming the posterior wall of the eye• Internal anatomy of the eye– Posterior/vitreous cavity– Anterior cavity

Review on your own• Extrinsic eye muscles– Medial rectus, Superior rectus, Lateral rectus, Inferior

rectus, Superior oblique, Inferior oblique and Levator palpebrae superioris

• Intrinsic eye muscles– Via Oculomotor nerve (cranial)– Circular iris muscle: (parasympathetic; bright light) pupil

constriction– Radial iris muscle: (sympathetic; dim light, action) pupil

dilation– Ciliary muscle: smooth muscle that changes the

tightness of zonular fibers to change shape of the lens

Surf

ace

anat

omy

of th

e Ey

eTarsal plate

Surface Anatomy of the Eye: Eyelids

• Eyelid/Palpebrae– Tarsal plate: elongated dense CT that forms the shape of

each palpebrae– Levator palpebrae superioris: raises the upper lid– Oribicularis oculi: closes the eyelid

• Superior and inferior palpebral sulci: upper and lower lid creases

• Conjunctiva: protective mucous membrane– Palpebral: lines each eyelid– Bulbar: from eyelids into the anterior surface of the

eyeball and covers the sclera

Structures of the Eyeball

• Fibrous tunic (avascular outer layer)– Cornea: admits and refracts light– Sclera: provides shape and protection

• Vascular tunic (middle layer)– Iris: regulates amount of light that enters the eyeball– Ciliary body: secretes aqueous humor and alters

shape of lens for near/far vision– Choroid: provides blood supply and absorbs

scattered light (melanin)

• Retina (inner layer)– Receives light receptor potentials and nerve impulses– Provides output to the brain via axons (ganglion cells) optic

nerve• Macula lutea: highly pigmented spot near the center of

the retina• Fovea centralis: small pit that contains cones (color

vision); area of highest visual acuity (sharpness)– Move head and eyes to place images on this point– No rods—periphery of retina; more light sensitive—why you

can see a dim star better if you look just to the side of it

Structures of the Eyeball

Internal anatomy of the Eye

• Lens: refracts light and focuses images on the retina to facilitate vision

• Posterior/vitreous cavity (lens to wall of retina)– Vitreous body helps maintain the shape of the eyeball

and supports retinal attachment to the eyeball• Anterior cavity (cornea to lens)– Aqueous humor helps maintain shape of eyeball and

supplies oxygen and nutrients to lens and cornea

Objectives

• Today’s Lab 3– Cranial and spinal nerves– Surface anatomy of the eye– Intrinsic muscles of the eye– 3 layers of the eye– Internal anatomy of the eye– Lacrimal apparatus (if time permits)

• Wednesday– Human eye/vision– Histology of the retina– Human ear and physiological aspects of hearing– Histology of the cochlea– Visual acuity tests (observe on your own)– Hearing tests (observe on your own)