Skull, Brain and Cranial Nerves

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Skull, Brain and Cranial Nerves
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www.uberreview.com
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Skull

• Part of Axial Skeleton
• Cranial bones cranium
• Enclose and protect brain
• Attachment for head neck muscles
• Facial bones framework of face
• Form cavities for sense organs
• Opening for air food passage
• Hold teeth
• Anchor face muscles

pg 800
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Cranial and Facial Bones

• Cranial - 8
• Frontal
• Occipital
• Sphenoid
• Ethmoid
• Parietal (2)
• Temporal (2)

• Facial 14
• Mandible
• Maxilla (2)
• Zygomatic (2)
• Nasal (2)
• Lacrimal (2)
• Palatine (2)
• Vomer
• Inf. Nasal Conchae(2)

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Bones of Skull

• Flat bones thin, flattened, some curve
• Sutures immovable joints joining bones
• Calvaria Skullcap Vault
• Superior, Lateral, Posterior part of skull
• Floor Base
• Inferior part of skull
• 85 openings in skull
• Spinal cord, blood vessels, nerves
• Foramina, meatus, canal, fissure, notch

pg 818
pg 825
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Cranial Fossae

• Created by bony ridges
• Supports, encircles brain
• 3 Fossae
• Anterior
• Middle
• Posterior
• All the bones visible from this view are the
  cranial bones!!

pg 825
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Other Cavities of Skull
pg 904
pg 813

• Orbits
• Nasal Cavity

Middle Ear Inner Ear
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Skull through Life

• Ossifies late in 2nd month of development
• Frontal Mandible start as 2 halves-then fuse
• Growth of Skull
• ½ adult size by age 9 months
• ¾ adult size by 2 years
• 100 adult size by 8-9 years
• Face enlarges between ages 6-13 years

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Fetal Skull

• Skull bones separated by unossified membranes
  Fontanels
• Allow compression of skull during delivery
• Allows rapid growth of brain
• Mostly replaced w/bone after 1st year

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The Brain

• 4 Parts
• Cerebrum
• Diencephalon
• Brain Stem
• Midbrain
• Pons
• Medulla
• Cerebellum
• Gray matter surrounded by White matter w/outer
  cortex of gray matter
• some texts consider this part of brain stem

Pg 836
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Meninges 3 membranes around brain and spinal cord

• Made of Connective tissue
• Functions
• Cover, Protect CNS
• Enclose, protect blood vessels supplying CNS
• Contain CSF
• 3 Layers
• Dura Mater (external)
• Arachnoid Mater (middle)
• Pia Mater (internal)

pg 833
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Meninges (continued)

• Dura mater
• Strongest, 2 Layers, Fibrous Connective Tissue
• Periosteal layer (Periosteum) External/superficia
  l layer
• Meningeal layer Internal/deep layer
• Layers fused except around dural sinuses (venous
  blood filled? internal jugular vein)

pg 818
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Extensions of Dura Mater

• Partitions limit movement of brain
• Falx Cerebri vertical, between cerebral
  hemispheres
• Falx Cerebelli -vertical, between cerebellar
  hemispheres
• Tentorium Cerebelli horizontal, between
  cerebrum and cerebellum

pg 831
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Meninges

• Arachnoid Mater
• Middle layer
• Subarachnoid Space-between arachnoid mater and
  pia mater (contains most of CSF, blood vessels)
• Arachnoid Villi (Granulations)- projections of
  arachnoid mater through dura into superior
  sagittal sinus, act as valves to help CSF pass
  into dural sinuses

pg 833
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Meninges (continued)

• Pia Mater
• Innermost layer
• Delicate, highly vascular
• Clings directly to brain tissue, dips into
  convolutions

pg 833
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Ventricles

• Expansions of brains central cavity
• Lined with Ependymal Cells
• Filled with CSF (cerebrospinal fluid)
• Ventricles continuous w/each other central
  canal of spinal cord

Pg 836
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Ventricles (continued)

• Lateral Ventricles (12)
• Cerebral Hemisphere
• Separated by Septum Pellucidum
• Third Ventricle
• Diencephalon
• Interventricular Foramen connects to lateral
  ventricle
• Fourth Ventricle
• Hindbrain
• Cerebral Aqueduct connects 3rd and 4th
  ventricles
• Connects to central canal of spinal cord
  medulla
• 3 openings connect 4th to subarachnoid space
• 2 lateral apertures
• 1 median aperture

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Cerebrospinal Fluid

• Liquid cushion for brain and spinal cord
• Nourishes brain
• Removes waste
• Conducts chemical signals between parts of CNS
  (e.g. hormones)
• Forms as a filtrate of blood in choroid plexuses

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Choroid Plexuses

• Choroid Plexuses groups of capillaries
  surrounded by ependymal cells
• Made of sodium, chloride ions, proteins, glucose,
  O2

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Flow of CSF

• Formed in Choroid plexuses
• Through Ventricles
• Into Subarachnoid space central canal from 4th
  ventricle
• Through Arachnoid Villi into Superior Sagittal
  Sinus
• Into Internal Jugular Vein

faculty.washington.edu
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Organization of the Brain

• Composed of gray and white matter
• Different organization than in the spinal cord
• Centrally located gray matter surrounded by white
  matter
• Cortex external sheets of gray matter in
  cerebrum cerebellum (some parts of brain)
• Nuclei deep masses of gray matter surrounded by
  white matter
• (some parts of brain)

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Cerebrum

• Executive Suite of nervous system
• Self-awareness, initiate control voluntary
  movements, communicate, remember, understanding,
  language
• Most superior region
• Covers diencephalon top of brain stem like
  mushroom cap
• Cerebral cortex

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Cerebral Hemispheres

• Fissures and Grooves
• Fissures deepest
• Transverse cerebral fissure
• Separates cerebral hemispheres from cerebellum
• Longitudinal fissure
• Separates R and L cerebral hemispheres
• Sulci
• Grooves on surface
• Gyri
• Ridges of brain tissue among the sulci

pg 836
pg 833
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Cerebral Hemispheres

• Each hemisphere divided into 5 lobes
• Frontal
• Parietal
• Occipital
• Temporal
• Insula
• Created by deep sulci
• Functional areas motor, sensory
• Associative areas integrate

pg 836
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Cerebral Hemispheres

• The 2 hemispheres control opposite sides of body
• Corpus callosum
• The largest commissure between the hemispheres
• Hemispheres specialized for different cognitive
  functions
• Left Cerebral hemisphere
• Language, mathematics and logic
• Right Cerebral hemisphere
• Visual-spatial, interpreting facial expressions,
  intuition, emotion, artistic/musical skills

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Diencephalon

• Surrounded by cerebral hemispheres
• Made of 3 Paired Structures
• Thalamus gateway
• Communicates sensory info of cerebral cortex
• Hypothalamus
• Regulates many body activities
• Emotion, sleep, memory, etc.
• Pituitary Gland
• Growth Hormone
• Thyroid Stimulating Hormone
• Epithalamus
• Pineal Gland
• Melatonin

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Brainstem

• Midbrain, Pons, Medulla Oblongata
• Passage of all signals between spinal cord and
  brain
• Regulates basic physiological functions
• Innervation of head and neck

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Brainstem

• Midbrain
• Visual and Auditory reflex centers
• Attachment for CN III, IV
• Pons
• Attachment for CN V, VI, VII, VIII
• Medulla oblongata
• Regulates several basic physiological functions
• Attachment of CN IX, X, XI, XII

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Cerebellum

• Smooths coordinates body movements directed by
  other parts of brain
• 2 Cerebellar Hemispheres
• Cerebellar cortex surrounds Arbor vitae
• Functions
• Information on equilibrium
• Movement of neck, trunk, limbs
• Information from cerebral cortex on voluntary
  movement

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Blood Brain Barrier

• Protects brain from blood-borne toxins (e.g.
  urea, food toxins, bacteria)
• Endothelium of brain capillaries are loaded with
  tight junction to decrease permeability
• Not complete protection, some things still have
  to get through (e.g. fat-soluble molecules can
  pass through)

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Blood Supply to Brain

• Arteries
• External carotid arteries and branches
• Tissues of head face, skin, muscles
• Middle meningeal a. brain
• Boxers!
• Internal carotid arteries and branches
• Opthalmic a. Eye Orbits
• Ant Middle Cerebral arts Cerebrum
• Branches form Cerebral Arterial Circle
  Anastomosis
• Vertebral arteries
• Posterior brain
• Vertebrae Cervical Spinal Cord
• Branches form Cerebral Arterial Circle
  Anastomosis

pg 832
pg 838
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Blood Supply to the Brain

• Veins
• Dural sinuses
• Superior Inferior Sagittal, transverse,
  sigmoid, straight, etc
• Internal jugular
• Receives from dural sinuses
• External jugular
• Drains scalp and face (superficial)
• Vertebral
• Drains cervical vertebrae, cervical spinal cord,
  small neck muscles

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pg 842
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Cranial Nerves

• 12 Pairs I-XII
• Numbered Anterior to Posterior
• Attach to inferior surface of brain
• Exit brain through foramina in skull
• I II attach to Forebrain (cerebrum
  diencephalon)
• III-XII attach to Brainstem (midbrain, pons,
  medulla)
• Only X goes beyond the head-neck

pg 851
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Foramina serving Cranial Nerves

• You must know what foramina each CN leaves the
  skull through
• (refer to lab manual)

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How to Remember CN I-XII
Oh! Oh! Oh! To Touch And Feel Very Good
Velvet! Ah Heaven!
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I Olfactory (oh) II Optic (oh) III Oculomotor
(oh) IV Trochlear (to) V Trigeminal
(1-3) (touch) VI Abducens (and) VII Facial (fee
l) VIII Vestibulocochlear (very) IX Glossopharyng
eal (good) X Vagus (velvet) XI Accessory (ah) X
II Hypoglossal (heaven)
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Motor vs. Sensory Nerves

• Sensory Afferent
• Send nervous impulse from sensory receptors to
  brain to bring in information
• e.g. pressure, temperature, pain
• Motor Efferent
• Send nervous impulses from brain to body to
  accomplish an action
• e.g. movement of a muscle, activation of a gland

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Sensory Nerves

• Sensory Afferent
• Visceral Sensory (sensory innervation of viscera)
• stretch, pain, temp., chemical changes,
  irritation in viscera
• Special taste
• Somatic Sensory (sensory innervation of outer
  part body)
• touch, pain, pressure, vibration, temp. in skin,
  body wall, limbs
• Special hearing, equilibrium, vision, smell

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Motor Nerves

• Motor Nerves
• Visceral Motor (motor innervation muscle in
  viscera glands)
• innervation smooth cardiac muscle, glands
• Somatic Motor (motor innervation of skeletal
  muscle)
• innervation of skeletal muscles (except
  pharyngeal arch m.)

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Mnemonic for CN Function

• Some (CN I)
• Say (CN II)
• Marry (CN III)
• Money (CN IV)
• But (CN V)
• My (CN VI)
• Brother (CN VII)
• Says (CN VIII)
• Big (CN IX)
• Brains (CN X)
• Matter (CN XI)
• Most! (CN XII)
• S Sensory function M Motor
  function
• B BOTH (Sensory and Motor function)

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Cranial Nerve Function
I Olfactory--------Sensory--smell II Optic------
-------Sensory--vision III Oculomotor----Motor----
extrinsic eye muscles IV Trochlear-------Motor----
extrinsic eye muscles V Trigeminal V1
Opthalmic-----Sensory-cornea, nasal mucosa, face
skin V2 Maxillary------Sensory-skin of
face, oral cavity, teeth V3
Mandibular---Motor-muscles of mastication ---Se
nsory-face skin, teeth, tongue (general)
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Cranial Nerves (continued)
VI Abducens--------------Motor-----eye abduction
muscles VII Facial-------------------Sensory---par
t of tongue (taste) -------------------
Motor------muscles of facial expression VIII
Vestibulocochlear---Sensory----hearing,
equilibrium IX Glossopharyngeal----Motor------styl
opharyngeus muscle ----Sensory----tongue
(gen taste), pharynx X Vagus------------------Mo
tor-------pharynx, larynx
-------------------Sensory----pharynx, larynx,
abd. organs XI Accessory-------------Motor------tr
apezius, sternocleidomastoid XII Hypoglossal------
----Motor-------tongue muscles
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CN I Olfactory Nerve

• Attaches to cerebrum
• Many nerve endings from olfactory bulbs
• Pass through olfactory foramina in cribriform
  plate of ethmoid bone to receptors in roof of
  nasal cavity
• Sensory for smell

Fig 8.48
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CN II Optic Nerve

• Attaches to Diencephalon
• Enters orbit through optic canal
• Sensory for vision

Fig 8.83
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CN III Oculomotor Nerve

• Attaches to Midbrain
• Enters orbit through superior orbital fissure
• Motor to 3 of 4 extrinsic muscles of eye
• Superior, inferior and medial rectus muscles
  inferior oblique muscle
• Parasympathetic to muscles controlling pupil
  lens of eye

Fig 8.83
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CN IV Trochlear Nerve

• Attaches to Midbrain
• Enters orbit through superior orbital fissure
• Motor to superior oblique muscle of eye

Fig 8.83
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CN V1 Ophthalmic Nerve

• First branch of Trigeminal nerve (CN V)
• Attaches to Pons
• Enters orbit through superior orbital fissure,
  then exits orbit through supraorbital
  foramen/notch
• Sensory-cornea, nasal mucosa, face skin

Fig 8.83
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CN V2 Maxillary Nerve

• Second branch of Trigeminal nerve (CN V)
• Attaches to the pons
• Passes through the foramen rotundum, inferior
  orbital fissure and out the infraorbital foramen
• Sensory-skin of face, oral cavity, teeth

Fig 8.138
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CN V3 Mandibular Nerve

• Third branch of Trigeminal nerve (CN V)
• Attaches to Pons
• Exits cranial cavity through foramen ovale, into
  the mandibular foramen and out the mental foramen
• Motor-muscles of mastication
• Sensory-face skin, teeth, anterior 2/3 tongue
  (general)
  

Fig 8.139
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Distribution of sensory innervation to skin of
face from CN V
CN V Trigeminal V1 Opthalmic V2
Maxillary V3 Mandibular
pg 867
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CN VI Abducens Nerve

• Attaches to Pons
• Enters orbit through superior orbital fissure
• Motor to lateral rectus muscle of eye

Fig 8.83
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CN VII Facial Nerve

• Attaches to Pons
• Exits cranial cavity through internal acoustic
  meatus, then exits skull through stylomastoid
  foramen
• Sensory to anterior 2/3 tongue for taste
• Motor to muscles of facial expression
• Parasympathetic to Mandibular Sublingual
  glands, Lacrimal gland

Fig 8.60
52
CN VIII Vestibulocochlear Nerve

• Attaches to Pons
• Enters inner ear through internal acoustic meatus
• Sensory to organs of hearing and equilibrium

Fig 8.119
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CN IX Glossopharyngeal nerve

• Attaches to medulla oblongata
• Exits cranial cavity through jugular foramen
• Motor to stylopharyngeus muscle
• Sensory to posterior 1/3 tongue (general
  taste), pharynx
• Parasympathetic to parotid gland

Figs 8.162, 8.247
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CN X Vagus Nerve

• Attaches to Medulla oblongata
• Exits cranial cavity through jugular foramen
• Nicknamed the wanderer
• Motor to pharynx, larynx
• Sensory to pharynx, larynx, abdominal organs
• Parasympathetic to thoracic and abdominal organs

Figs 8.164
55
CN XI Accessory Nerve

• Attaches to Medulla oblongata
• Exits cranial cavity through jugular foramen
• Joined by a spinal segment passing through
  foramen magnum
• Motor to trapezius sternocleidomastoid muscles

Fig 8.165
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CN XII Hypoglossal Nerve

• Attaches to Medulla oblongata
• Exits cranial cavity through hypoglossal canal
• Motor to tongue muscles

Fig 8.166
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Summary of Functional Groups

• Purely Sensory I, II, VIII
• Primarily Motor III, IV, VI, XI, XII
• Mixed V, VII, IX, X
• Parasympathetic Fibers III, VII, IX,
  X (Division of Autonomic NS Visceral Motor)

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Parasympathetic Fibers

• CN III Oculomotor
• Contracts Iris (controls pupil)
• Contracts Ciliary Muscle (controls lens)
• CN VII Facial
• Innervates Salivary glands (mandibular
  sublingual)
• Innervates Lacrimal gland
• CN IX Glossopharyngeal
• Innervates Parotid Salivary gland
• CN X Vagus
• Innervates thoracic abdominal viscera

pg 48