Brain and Cranial N lecture presentation

Skull, Brain and Cranial Nerves

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

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)

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

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!!

Other Cavities of Skul

Orbits
Nasal Cavity
Middle Ear
Inner Ear
Skull through Life

• Ossifies late in 2 nd 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

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 1 st year

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

Meninges: 3 membranes around brain and spinal cord

Meninges (continued)

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

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

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

Meninges (continued)

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

Ventricles

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

Ventricles (continued)

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

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

Choroid Plexuses

• Choroid Plexuses: groups of capillaries surrounded by ependymal cells
• Made of sodium, chloride ions, proteins, glucose, O 2

Flow of CSF

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

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)

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

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

Cerebral Hemispheres:

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

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

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

Brainstem

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

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
• 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

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)

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

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

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

Foramina serving Cranial Nerves

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

How to Remember CN I-XII

Oh! Oh! Oh! To Touch And Feel Very Good Velvet! Ah Heaven!
I Olfactory (oh)
II Optic (oh)
III Oculomotor (oh)
IV Trochlear (to)
V Trigeminal (1-3) (touch)
VI Abducens (and)
VII Facial (feel)
VIII Vestibulocochlear (very)
IX Glossopharyngeal (good)
X Vagus (velvet)
XI Accessory (ah)
XII Hypoglossal (heaven)

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

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

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.)

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)
• 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
• V 1 Opthalmic-----Sensory-cornea, nasal mucosa, face skin
• V 2 Maxillary------Sensory-skin of face, oral cavity, teeth
• V 3 Mandibular---Motor-muscles of mastication
• ---Sensory-face skin, teeth, tongue (general)

Cranial Nerves (continued)

• VI Abducens--------------Motor-----eye abduction muscles
• VII Facial-------------------Sensory---part of tongue (taste)
• -------------------Motor------muscles of facial expression
• VIII Vestibulocochlear---Sensory----hearing, equilibrium
• IX Glossopharyngeal----Motor------stylopharyngeus muscle
• ----Sensory----tongue (gen & taste), pharynx
• X Vagus------------------Motor-------pharynx, larynx
• -------------------Sensory----pharynx, larynx, abd. organs
• XI Accessory-------------Motor------trapezius, sternocleidomastoid
• XII Hypoglossal----------Motor-------tongue muscles

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

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

CN IV: Trochlear Nerve

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

CN V 1: 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

CN V 2 : 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

CN V 3: 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)

Distribution of sensory innervation to skin of face from CN V

CN VI: Abducens Nerve

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

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

CN VIII: Vestibulocochlear Nerve

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

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

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

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

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

CN XII: Hypoglossal Nerve

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

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)

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

    download lecture presentation  Brain and Cranial N