BRAIN ORGANIZATION, PROTECTION, AND NOURISHMENT

Brain regions

1. Cerebral hemisphere – anterior most part; two hemispheres which are connected

2. Diencephalon – includes the thalamus, the hypothalamus, and the epithalamus

3. Brain stem – includes the midbrain, the pons, and the medulla oblongata

4. Cerebellum – posterior and inferior to cerebrum

Meninges

1. Meninges (meninx) – coverings of the brain

-a. Functions – protect brain, blood vessels; cerebrospinal fluid; form partitions

2. Dura mater – really tough outer covering; made up of two layers

-a. Periosteal layer – outer layer; periosteum of skull; not found covering spinal cord

-b. Meningeal layer – the inner layer; around the spinal cord

-c. Dural sinuses – layers of the dura mater come apart and collect venous blood

-d. Subdural space – narrow serous cavity between dura and arachnoid mater

3. Arachnoid mater – lose brain covering; does not dip into contortions; middle layer

-a. Subarachnoid space – cerebrospinal fluid; web like extensions secure to pia

-b. Arachnoid villi – protrude into dural sinuses to return fluid to venous blood

4. Pia matter – the inner, delicate, intimate (follows contortions); many tiny vessels

5. Dural septa – forms as the dura extends inward into fissures

-a. Falx cerebri – large fold; down the longitudinal fissure; anchored to crista galli

-b. Falx cerebelli – continuous with above, midline portion runs along vermis

-c. Tentorium cerebelli – in transverse fissure; between cerebrum and cerebellum

Cerebrospinal fluid (CSF)

1. Functions – several

-a. Buoyancy – lightens brain by 97%; doesn’t crush under its own weight

-b. Protects – absorbs shock to CNS from physical contact

-c. Nourishment – also may carry chemical signals

2. Choroid plexuses – roof of each ventricle; fairly permeable capillaries

3. Central canal – some cerebral spinal fluid enter it

4. Subarachnoid space – from fourth ventricle through lateral and medial apertures

Blood-brain barrier

1. Blood brain barrier – flux in hormones, nutrients, and electrolytes can’t occur

2. Capillaries – are continuous and have a fairly thick basal lamina

3. Tight junctions – between capillary endothelial cells

4. Selective barrier – allows some things in, other out

-a. Facilitated diffusion – glucose, essential amino acids, and some electrolytes

-b. Actively pump – out nonessential amino acids and potassium

-c. Exclude – proteins and metabolic waste such as urea

Ventricles of the brain

1. Lateral ventricles – C shaped; deep cerebral hemisphere

-a. Septum pellucidum – membrane separates anterior segment of lateral vesicles

2. Interventricular foramina – openings lateral ventricles to third ventricle

3. Third ventricle – narrow ventricle found in the diencephalon

4. Cerebral aqueduct – connects third and fourth ventricles; runs through midbrain

5. Fourth ventricle – dorsal to the pons superior to medulla

-a. Median aperture – posteriomedial; 4th ventricle to the subarachnoid space

-b. Lateral apertures – laterally paired; 4th ventricle to the subarachnoid space

6. Central canal – of the spinal cord; continuous with fourth ventricle of the brain

BRAIN: BRAIN STEM

Medulla oblongata

1. Medulla oblongata – inferior portion of brain; blends into spinal cord

2. Fourth ventricle – medulla forms most of its anterior wall

3. Pyramids – large ventral ridges; fibers of the corticospinal motor pathway

4. Decussation of the pyramids – before descending into the spinal cord, they cross

5. Olives – oval swellings lateral to the pyramids; caused by

6. Inferior olivary nuclei – relay messages stretch of muscles/joints to cerebellum

7. Inferior cerebellar peduncles – connection between the medulla and cerebellum

8. Nucleus cuneatus – relays sensory information

9. Nucleus gracilis– relays sensory information

10. Cranial nerve nuclei – from VIII to XII

11. Visceral motor nuclei – autonomic functions; hypothalamus relays instructions

-a. Cardiovascular center – force, rate of heart contraction; dilation of blood vessels

-b. Respiratory centers – two centers; control rate and depth of breathing

-c. Other centers – vomiting, hiccupping, swallowing, coughing, and sneezing

Pons

1. Pons – bulging portion of the midbrain; anteriosuperior border of fourth ventricle

2. Middle cerebellar peduncles – connects the pons to the cerebellum

3. Pontine nuclei – relay cerebellum to motor cortex; middle cerebellar peduncle

4. Respiratory centers – work with those in medulla

5. Deep projection fibers – deep, longitudinal; pyramidal corticospinal motor tracts

6. Cranial nerve nuclei – V to VII

Midbrain

1. Midbrain – between the diencephalon superiorly and the pons inferiorly

2. Cerebral peduncles – large ventral columns; pyramidal corticospinal motor tracts

3. Superior cerebellar peduncles – dorsal nerve tracts; midbrain to the cerebellum

4. Cerebral aqueduct – between cerebral peduncles & dorsal aspect; 3rd- 4th ventricle

5. Corpora quadrigemina – four large nuclei which bulge dorsally

-a. Superior colliculi – visual reflexes; coordinate head and eye movement

-b. Inferior colliculi – part of auditory relay from ear to sensory cortex; sound reflex

6. Substantia nigra – nuclei deep to cerebral peduncles; linked to the basal nuclei

-a. Dopamine – from melanin; dark color

-b. Parkinson’s disease – degeneration of substantia nigra

7. Red nucleus – deep to above; relay nuclei for some descending motor pathways

8. Cranial nerve nuclei – oculomotor nerve (III) and trochlear nerve (IV)

Reticular formation

1. Reticular formation – neurons, extend through white matter of the brain stem

2. Far flung connections – to thalamus; hypothalamus; spinal cord; cerebral cortex

3. Function – ideal for governing arousal of the brain as a whole

4. Reticular activating system (RAS) – continuous stimulates cortex when awake

BRAIN: CEREBELLUM

General

1. Location – posterior to pons and medulla; inferior to occipital lobe

2. Function – subconscious coordinated movement; like ridding a bike

Cerebellar anatomy

1. Cerebellar hemispheres – there are two; right and left

2. Vermis – worm like medial connection between cerebellar hemispheres

3. Primary fissure – separates two lobes

4. Lobes – each hemisphere has three

-a. Anterior lobe – anterior to the primary fissure

-b. Posterior lobe – posterior to the primary fissure

-c. Flocculonodular lobe – propeller shaped; deep to the vermis and posterior lobe

5. Arbor vitae – branching white matter going through each cerebellar hemisphere

6. Cortex – like the cerebrum it has a layer of gray matter

7. Nuclei – also found in cerebellum; gray matter found deep in white matter

8. Functions – coordination of body movements

-a. Medial portion – concerned with torso

-b. Intermediate portion – distal appendages; skilled movements

-c. Lateral portions – connects to motor association areas; maybe planning of motion

-d. Flocculonodular lobe – equilibrium input (inner ear); adjust posture, balance

Cerebellar peduncles

1. Superior cerebellar peduncles – from midbrain to cerebellum

-a. Function – communicate with the cerebral motor cortex via thalamic relays

2. Middle cerebellar peduncles – one way communication from the pons

-a. Function – information on voluntary motor activities initiated by motor cortex

3. Inferior cerebellar peduncles – connecting medulla and cerebellum

-a. Function – afferent tracts from muscle proprioceptors and vestibular nuclei

Cerebellar processing

1. Input – from several sources

-a. Motor association area – from collateral; voluntary contraction is to be initiated

-b. Proprioceptors – from muscles

-c. Other information – on equilibrium and vision

2. Integration – cerebellar cortex assesses; determines how to coordinate contraction

3. Output – several

-a. Cerebral motor cortex – dispatches plan to, which makes adjustments

-b. Brain stem nuclei – like red nuclei; which influence motor neurons of spinal cord

4. Cognitive function – awareness, judgment, and memory

BRAIN: DIENCEPHALON

Thalamus

1. Thalamus – 80% of diencephalon; superior and lateral walls of the third ventricle

2. Lateral masses – located on each side; consist of thalamic nuclei

3. Intermediate mass – commissure connects the lateral masses; spans 3rd ventricle

4. Thalamic nuclei – numerous; specific functions; connections

-a. Sensory input – from senses and all parts of the body converge on the thalamus

-b. Sorting – impulses dealing with similar function grouped, to appropriate cortex

-c. Cerebral cortex – both the primary sensory corticies and the association areas

-d. Hypothalamus – sends impulses about emotions, visceral functions to thalamus

-e. Motor control – impulses from basal nuclei, cerebellum to thalamus

Hypothalamus

1. Hypothalamus – under the thalamus, bordered by the optic chiasma anteriorly

2. Mammillary body – paired; bulge inferiorly from hypothalamus; olfactory rely

3. Infundibulum – stalk connection from anterior hypothalamus to pituitary gland

4. Hypothalamic nuclei – many areas of gray numerous functions

5. Functions – include

-a. Autonomic control – via brains stem/spinal cord center; BP, HR, breathing, GI

-b. Emotions – perceive pleasure, fear, rage; physical expression, ex. pounding heart

-c. Drives – such as sex drive

-d. Body temperature – monitors blood temperature directly; initiates response

-e. Food intake – respond changes in blood nutrient, hormone; hunger and satiety

-f. Water balance – causes the kidneys to retain more water; causes thirst

-g. Sleep-wake cycle – working with other brain regions; uses light - darkness cues

-h. Endocrine control – targets anterior pituitary; produces ADH and oxytocin

Epithalamus

1. Epithalamus – superioposterior boundary of the third ventricle

2. Pineal gland – projecting posteriorly from the epithalamus; produces melatonin

-a. Melatonin – may work with hypothalamus to regulate sleep wake cycle and mood

3. Choroid plexus – cerebrospinal fluid producing structure

CEREBRUM

General

1. Lobes – most named after the cranial bones which lies atop

-a. Frontal lobe – each underlie the frontal bone of the skull

-b. Parietal lobe – each underlie one of the parietal bones of the skull

-c. Temporal lobe – each underlie one of temporal bone of the skull

-d. Occipital lobe – each underlie the occipital bone of the skull

-e. Insula – covered by frontal, parietal, temporal lobes; buried in the lateral sulcus

2. Fissures – deeper groves which separate the larger areas of the brain

-a. Longitudinal fissure – median fissure between the two cerebral hemispheres

-b. Transverse fissure – between the cerebral hemispheres from the cerebellum

3. Sulci – shallower groves; some of the deeper ones between the lobes

-a. Central sulcus – between the frontal and parietal lobes

-b. Parieto-occipital sulcus – medial surface; between parietal and occipital lobes

-c. Lateral sulcus – temporal lobe inferiorly; parietal and frontal lobes superiorly

4. Gyri – elevated ridges between the sulci

-a. Precentral gyrus – ridge anterior to the central sulcus; on the frontal lobe

-b. Postcentral gyrus – ridge posterior to the central sulcus; on the parietal lobe

5. Gray matter – cell bodies, unmyelinated axons, dendrites, supporting cells

6. White matter – myelinated nerve fibers

Cerebral white matter

1. Commissures – connect the different hemispheres

-a. Corpus callosum – the largest which lies superior to the lateral ventricles

-b. Others – less important; anterior and posterior commissures

2. Association fibers – parts of single hemisphere; between gyri and lobes

3. Projection fibers – cerebral hemisphere to spinal cord and lower brain

-a. Internal capsule – band projection fibers; between thalamus and basal nuclei

-b. Corona radiata – above radiates out into cerebral white matter

Basal ganglia (nuclei)

1. Basal ganglia (nuclei) – deep in the white matter; subcortical collections of gray matter

-a. Caudate nucleus – comma shaped; arches over diencephalon

-b. Putamen – pod shaped

-c. Globus pallidus – somewhat globe shaped

-d. Amygdala (amygdaloid nucleus) – tail of the caudate; limbic system

2. Corpus striatum – common name for the caudate nucleus and putamen

4. Connections – include

-a. Input – from cortex, subcortical nuclei, each other

-b. Output – via thalamus project fibers to the premotor and prefrontal corticies

5. Functions – include

-a. Stereotypical movements – starting, stopping, monitoring intensity of

-b. Inhibition – unnecessary movement

-c. Maintenance – posture and muscle tone

-d. Cognition – possible role

Limbic system

1. Limbic system – components encircle upper brain stem; emotions, memory

2. Rhinencephalon – found on the medial aspect of the temporal lobe

-a. Hippocampus – C shaped; nuclei

-b. Others – septal nuclei, cingulated, parahippocampal, dentate gyri

3. Amygdala – basal nuclei at tail of caudal nuclei

4. Hypothalamus – as part of the limbic system

5. Thalamus – part of it

6. Fornix – it, along with other fiber tracks, link the parts of the limbic system

7. Functions – include

-a. Hypothalamus – link to autonomic; unconscious; blushing; psychosomatic

-b. Cerebral cortex – feelings linked to thinking; understand to feel anything about it

-c. Long term memory – hippocampus, amygdale; new info to long term memory

CEREBRAL CORTEX

Cerebral cortex: general

1. Cerebral cortex – surface gray matter; 2 to 4 mm; convolutions, 40% weight

2. Consciousness – perceive, talk, memory, understand, voluntary movement

3. Brodmann system – K. 1906; differences in structure and thickness; 52

4. Domains – motor and sensory areas localized; PET scans, metabolic activity

5. Higher mental functions – memory, language; overlapping domains; more diffuse

6. Opposite sides – motor, sensory areas of a hemisphere for opposite side

Cerebral cortex: motor areas

1. Primary motor (somatic) cortex – precentral gyrus; conscious movement

2. Premotor cortex – anterior to above; frontal lobe; learned motor skills like typing

3. Broca’s area – anterior inferior part of above; left side; speech muscles control

4. Frontal eye field – front of premotor; above to Broca’s; voluntary eye movements

Cerebral cortex: sensory areas

1. Primary somatosensory cortex – postcentral gyrus parietal lobe; information from

-a. General sensory receptors – in the skin

-b. Proprioceptors – in the muscle; identify the body region being stimulated

2. Somatosensory association area – posterior to above; analyses information from it

-a. Function – integrates sensory info (touch) with memory; pick coin out of pocket

3. Visual areas – include

-a. Primary visual cortex – posterior, medial occipital lobe; visual info from retina

-b. Visual association area – surrounds above most occipital lobe; comprehends sight

4. Auditory areas – include

-a. Primary auditory cortex – superior temporal lobe; hearing receptors signals

-b. Auditory association area – posterior above; perception sound as speech, music

5. Olfactory cortex – medial temporal lobe; olfactory tract sends impulses here

-a. Function – conscious awareness of different odors

-b. Rhinencephalon – olfactory cortex part of it; much now to do with emotions

-b. Primitive vertebrates – most medial temporal lobe is associated with olfaction

-c. Higher vertebrates – much of it associated with emotions (part of limbic system)

6. Gustatory cortex – parietal lobe deep to temporal lobe; perception of taste stimuli

7. Vestibular (equilibrium) cortex – posterior insula; conscious awareness of balance

Cerebral cortex: association areas

1. Association areas – already mentioned; auditory, visual, somatosensory

2. Prefrontal cortex – anterior frontal lobe; intellect, complex learning, personality

-a. Development – slowly in children; feed back from social environment

-b. Limbic system – emotions, connection to prefrontal; intuitive judgment, mood

3. Language areas – occur in both hemispheres

-a. Wernicke’s area – posterior temporal; usually left; sound out unfamiliar words

-b. Broca’s area – on same side as Wernicke’s; plan from it; causes speech

-c. Affective language area – opposite hemisphere; detect and express emotions

4. Visceral association area – insula; perception of visceral sensations

Cerebral cortex: lateralization function

1. Cerebral dominance – hemisphere dominate for language; in 90% is left side

2. Handedness – most left brain dominate are right handed

2. Left brain – greater control over language, math, and logic

3. Right brain – visual-spatial skills, intuition, art appreciation, and insight

4. Cooperation – most task require hemisphere communicate constantly

Brain wave pattern

1. Electroencephalogram (EEG) – reading of electrical activity of neurons

2. Brain waves – ↑ frequency, ↑mental activity; ↑amplitude ↓ frequency (sleep)

-a. Alpha waves – calm, relaxed state of wakefulness; low amplitude

-b. Beta waves – mentally alert, like now; more irregular than alpha waves

-c. Theta waves – normal children; not adults; higher amplitude lower frequency

-d. Delta waves – ↓frequency very ↑amplitude; deep sleep; awake adults damage

3. Abnormal electrical activity – include

-a. Epileptic seizures – abnormal discharge groups brain neurons

-b. Petit mal – facial muscle twitch; face goes blank few seconds; gone by age ten

-c, Temporal lobe epilepsy – loss of contact with reality; hallucinations, rampage

-d. Grand mal – loss consciousness; bones broken, convulsions; bit tongue; loss bladder

CRANIAL NERVES

Olfactory nerve (CN I)

1. Origin – afferent fibers olfactory epithelium of the nasal cavity

2. Course – through cribiform plate of ethmoid to olfactory bulb

3. Function – olfaction (the sense of smell); purely sensory

Optic nerve (CN II)

1. Origin – afferent fibers from the retina to form optic nerve

2. Course – optic foramen, sphenoid; partially, optic chiasma; thalamic nuclei

3. Function – vision; purely sensory

Oculomotor nerve (CN III)

1. Origin – from ventral mid brain near junction with pons

2. Course – through superior orbital fissure

3. Function – mixed but mostly motor

-a. Motor – four of the six extrinsic eye muscle; eye lid muscle; ANS iris and lens

-b. Sensory – proprioceptors; extrinsic eye muscles

Trochlear nerve (CN IV)

1. Origin – from dorsal mid brain it travels ventrally

2. Course – enters orbit via the superior orbital fissure

3. Function – mixed but mostly motor

-a. Motor – extrinsic eye muscle (superior oblique)

-b. Sensory – proprioceptors

Trigeminal nerve (CN V)

1. Origin – from the ventral pons

2. Course – trigeminal ganglion; ophthalmic, maxillary, mandibular divisions

3. Function – mixed

-a. Motor – muscles of mastication (chewing)

-b. Sensory – most of face; nasal, oral cavity; teeth (upper, lower), tongue (non taste)

Abducens nerve (CN VI)

1. Origin – inferior pons

2. Course – through superior orbital fissure

3. Function – mixed; mostly motor

-a. Motor – extrinsic eye muscle; abducts the eye

-b. Sensory – proprioceptors

Facial nerve (CN VII)

1. Origin – from pons just lateral to abducens

2. Course – through internal acoustic meatus, temporal bone; 5 major branches

3. Function – mixed

-a. Motor – facial expression; autonomic: lacrimal (tear), nasal, salivary glands

-b. Sensory – taste from anterior two thirds of tongue; proprioceptors

Glossopharyngeal nerve (CN IX)

1. Origin – from the medulla

2. Course – leave the skull via the jugular foramen

3. Function – mixed

-a. Motor – tongue, pharynx; swallowing, gag; autonomic, parotid salivary gland

-b. Sensory – taste, sensation back tongue, pharynx; carotid chemo- mechano- (BP)

Vagus nerve (CN X)

1. Origin – from medulla

2. Course – through the skull via jugular foramen

3. Function – mixed

-a. Motor – mostly parasympathetic to visceral organs; swallowing muscles

-b. Sensory – some taste; baroreceptors and chemoreceptors carotid body (PB)

Accessory nerve (CN XI)

1. Origin – cranial root, medulla; spinal root, spinal cord; fuse

2. Course – leave from the jugular foramen; cranial and spinal nerve diverge

3. Function – mixed; mostly motor

-a. Motor – cranial division, larynx, pharynx, palate; spinal, head and neck muscles

-b. Sensory – proprioceptors

Hypoglossal nerve (CN XII)

1. Origin – from a series of roots out of the medulla

2. Course – leaves via the hypoglossal canal

3. Function – mixed; mostly motor

-a. Motor – tongue; speech and swallowing

-b. Sensory – proprioceptors

General information

1. Cranial sensory ganglia – cell bodies for sensory fibers (not optic and olfactory)

2. Motor neuron cell bodies – most found in gray matter (nuclei) of brain stem

3. Proprioception – in all those nerves which have a motor function

4. Autonomic functions – oculomotor, facial, glossopharyngeal, vagus nerves (PS)

EMBRYONIC DEVELOPMENT

Embryonic development

1. Neural tube development – in embryo

-a. Neural plate – starts 3rd week; a dorsal thickening midline axis of the embryo

-b. Neural folds – the plate forms a grove and these flanks the grove

-c. Neural groove – deepens to it becomes

-d. Neural tube – the grove deepens and the superior edges of the neural folds fuse

-e. Neural crest – from neural folds become sensory and some autonomic neurons

2. Primary brain vesicles – as soon as neural tube developed expand, constrictions

-a. Proencephalon (forebrain) – superior; becomes telencephalon and diencephalon

-b. Mesencephalon (midbrain) – inferior to proencephalon

-c. Rhombencephalon (hindbrain) – becomes metencephalon and myelencephalon

3. Secondary brain vesicles – 5th week 5 brain regions; develop into adult structures

-a. Telencephalon – cerebral hemispheres; lateral ventricles, superior 3rd ventricle

-b. Diencephalon – diencephalon in adults; associated with the third ventricle

-c. Mesencephalon – developed structures called the midbrain; cerebral aqueduct

-d. Metencephalon – becomes pons, part of brain stem, cerebellum; 4th ventricle

-e. Myelencephalon – becomes medulla oblongata, part of brain stem; 4th ventricle

4. Spinal cord – does not develop swellings; associated with the central canal

5. Posterior rotation – confined in skull, cerebrum, diencephalon, rotate atop stem

HOMEOSTATIC IMBALANCES

Brain

1. Trauma – include

-a. Concussion – slight injury; dizzy, see stars

-b. Contusion – brain stem could result in coma damage reticular activating system

-c. Hemorrhage – subdural or subarachnoid; swelling; brain stem; breathing, heart

-d. Cerebral edema – also a problem with swelling; give anti-inflammatory drugs

2. Cerebrovascular accident – stroke; tissue dies; deprived of blood

3. Degenerative brain diseases – include

-a. Alzheimer’s disease – memory loss, dementia; microtubules; no neuron transport

-b. Parkinsons disease – dopamine; substantia nigra; basal nuclei overactive; tremor

-c. Huntington’s disease – hereditary; massive destruction basal nuclei, cortex

4. Meningitis – inflammation of meninges; may become encephalitis

5. Encephalitis – brain inflammation

6. Hydrocephalus – drainage obstructed; shunt in adults; brain damage