Protected by Cranium

Surrounded by meninges and bathed in CSF.

Ventricles are CSF-filled chambers in the brain.

Lateral ventricle found within each cerebral hemisphere.

Choroid plexus forms CSF --> CSF circulates thru ventricles and central canal of spinal cord. It reaches subarachnoid space via apertures and then flows thru the subarachnoid space of brain and spinal cord. Arachnoid villi absorb CSF and return it to the venous system.

Clinical Condition: Hydrocephalus ("water on the brain") if reabsorption of CSF is blocked in infancy. Expansion of ventricles causes thinning of cortex. Image.

Blood supply: Brain receives about the same amount blood at all times-- 20% of blood flow at rest; percentage falls during exercise but total flow increases so, little difference between rest and exercise in terms of flow.

High metabolism -- uses glucose for energy and doesn't store energy, so constant supply of glucose is necessary. High oxygen demand -- if interrupted, neuron death can occur rapidly.

Clinical Condition: Strokes (or cerebrovascular accident -- CVA)

*       Interruption of blood supply to the brain, typically involves a large artery.

*       Occurs most often in 50-to-70 age range.

*       Stroke can be produced by:

  1. Thrombosis--narrowing of blood vessel, with eventual complete blockage (thrombus) that cuts off blood supply to the rest of the artery and the surrounding brain tissue. -- Accounts for over 50% of CVA's

  2. Embolism--an occlusion by material such as blood clot, fat body or bacterial clump that travels from a remote site, finally lodging as the vessel narrows. --Less than 20% of CVA's

  3. Hemorrhage--rupture of vessel wall releasing blood into surrounding tissue. Not only is blood supply cut off, but escaping blood acts as a foreign space-occupying body. -Less than 20% of CVA's, but most likely fatal.

Treatment: if stroke is due to an embolism, a "clotbuster" , e.g., TPA, may be used.

Aneurysm: thin wall of cerebral blood vessel expands and may rupture.

Blood-Brain Barrier:

Two aspects of barrier function: 1: physical (capillary/astrocytes) 2:physiological (transport mechanisms)

Large molecules generally cannot pass from blood to the brain.

Capillaries are not very permeable. Lipid soluble materials get in easily (e.g., alcohol). Endothelial transport is very selective.

Regions of the Brain

Forebrain, Midbrain and Hindbrain -- found in early embryo.

These are further subdivided:


*       Telencephalon: cerebral hemispheres

*       Diencephalon: thalamus and hypothalamus


*       Mesencephalon: colliculi (visual and auditory reflexes)


*       Metencephalon: pons and cerebellum

*       Myelencephalon: medulla oblongata


Left and right hemispheres separated by longitudinal fissure.

Fissures: deep gap between hemispheres and some lobes.

Corpus callosum -- tract that connects left and right sides.

"Split Brain" experiments of Sperry.

Segregation of some functions. Gender differences.

Convolutions: consist of gyrus/gyri (fold/folds) and sulcus/sulci (groove/grooves). Function: increases surface area, complexity.

Example: Central Sulcus: Separates Frontal from Parietal Lobes. See pre- and post-central gyri below.

Lobes of Cerebrum:

Frontal Lobe:

"higher" thought, motor functions (voluntary).

Broca's area (speech-motor). Left side typically.

Wernicke's area at junction of occipital, temporal and parietal is involved in recognition of spoken and written words.

Connection between Wernike's area and Broca's area:

Sensory (visual & auditory information related to language) is relayed to the Wernicke's Area. If a word

is to be spoken, then the message will be sent to Broca's area.

Precentral gyrus -- motor representation of body.

Pre-motor Cortex: "fills in details" related to motor control. Sends input to primary motor cortex.

Phineus Gage: Famous case history which demonstrated that part of our "social brain" was localized to

the frontal lobe.

In mid 1800's there was a raging debate over whether specific functions resided in specific areas of the brain. Phrenology, a popular pseudoscience of that era centered around the belief that functions and personality traits could be discerned by examining bumps on the skull. Phrenologists had it partly right -- there is a localization of function to specific brain regions, but not skull regions!

Parietal Lobe: Sensory. Evaluation of general senses and taste.

Postcentral gyrus -- sensory representation of body.

Temporal Lobe:

Interpretative (Wernike's) area. Auditory cortex. Vestibular senses: motion, equilibrium & balance

Memory--short and long term memory integrated. Interface with limbic system.

Temporal lobe epilepsy can produce auditory hallucinations, feelings of deja vu, loss of sense of time.

Occipital Lobe: Visual perception primarily. Each part of retina (visual space) is represented by specific parts of primary visual cortex (area 17). Further processing (interpreting images) is done in areas 18 and 19 of occipital lobe.

Receives input from retinas via the lateral geniculate nucleus, or LGN, of the thalamus.

Limbic Lobe & limbic system:

Deep, medial portion of cerebral cortex (temporal lobe).

Insula: a "lobe" deep to temporal lobe. Part of olfactory cortex; connects with amygdala.

Limbic system as a whole involves other areas of brain, particularly relating to memory and autonomic nervous system.

Regulation and display of "emotions." A factor in autism?

Hippocampus -- case history of H.M. (lesion resulted in "anterograde amnesia" -- he couldn't remember new things). Because of his case, researchers mistakenly believed that the hippocampus was the key place where conversion of short-term to long-term memory occurred -- as always, it's more complicated than that!. The hippocampus and medial temporal lobe areas associated with converting short term into long term memory. Hippocampus does have a role in attention.

Amygdala: interfaces with sensory areas of other parts of brain; involved in memory. Recognition and display of fear.

White matter of cerebrum: large tracts. 3 classes

  1. Association: connect areas within a cortical hemisphere.

  2. Commissures: connect left and right hemispheres.

  3. Projections: connect cortex with other area of brain


Thalamus: primary relay center for sensory and motor pathways.

Thalamic Radiations: tracts going from thalamus to cortex

Hypothalamus: Integrates autonomic nervous system -cardiovascular control, body temperature, water/electrolyte regulation, hunger, sleep/wake cycles, sexual responses, control of pituitary gland. Maintains homeostasis.

Remember the "4 F's": feeding, fighting, fleeing, fooling around

Area related to sexual orientation? (Work of Simon LeVay)

Epithalamus: major structure is pineal gland (discussed in endocrine system). Produces melatonin at night.

Mesencephalon (Midbrain):

Cerebral peduncles

"Corpora quadrigemina." 2 pair of colliculi ("little hills")

Superior colliculi: visual reflexes

Inferior colliculi: auditory reflexes

Substantia nigra: motor activities. Affected in Parkinson's disease.


Pons: relay station between medulla oblongata and midbrain. Origin of cranial nerves 5-8. Dorsal pons contains part of reticular formation (see below).

Cerebellum: lobed structure. Coordinate skeletal muscle contractions, muscle tone, balance, and timing. Integrates information from proprioceptors which monitor muscle and ligament tension, joint angles.

Cerebellum surface structure: note distinctive folia (rather than gyri) of cerebellum.

Vermis ("worm" - between left and right cerebellar hemispheres)

White mater: arbor vitae or "tree of life"


Medulla oblongata: at foramen magnum, becomes spinal cord. Similar to spinal cord except for "pyramids"--motor and sensory control tracts that run down spinal cord. Site of crossover (decussation) of left and right sides of body.

Origin of cranial nerves 8-12 (yes #8 is shared by Mesen- and Myelen-)

Control centers for respiration, heart beat and vasomotor control.

Brainstem = medulla, pons and midbrain.

Brainstem core contains reticular formation. Contains sensory (ascending) and motor (descending) pathways. Has centers for regulation of body functions. Lesion can result in coma.

Reticular activating system = the projections of the reticular formation. An "arousal" system. Sensory projections influence and regulate level of arousal and awareness -- sleep/wake cycles, motivation, levels of sensory perception, and emotions.

Human Brain: mid-sagittal section

Clinical Considerations:

Alzheimer's Disease: neurodegeneration with progressive accumulation of amyloid protein; "plaques" or "neurofibrillary tangles" form. Loss of memory. Genetic link.

Epilepsy: Spontaneous discharges (seizures) in different regions of brain.

Types of Seizures: Petit mal, Grand mal and Psychomotor. Severity and form of seizure dependent upon how much, and which part, of brain is affected.

Cerebral Palsy: Quite variable since different regions of the brain can be affected. Motor disorder primarily, but mental retardation also occurs frequently. Can be bilateral or unilateral. Generally from prenatal or early postnatal cause -- trauma, low oxygen, strokes, meningitis. Rarely genetic.

Cranial Nerves: 12 pairs

1) Olfactory: Relays sensory (olfactory) information from olfactory mucosa to olfactory bulb.

Olfactory Nerve/Tract

2) Optic: Axons of cells from retina. Sensory (visual) information. Nerves cross at optic chiasma.

3) Oculomotor: Motor axons to most of the extrinsic muscles of eye and intrinsic muscles of iris--cause dilation of pupil. Some sensory info.

4) Trochlear: to superior oblique muscle. Trochlea means pulley or spool. Note sharp angle of superior oblique as it passes thru the trochlea of orbit.

5) Trigeminal: 3 branches--ophthalmic, maxillary and mandibular.

  1. Ophthalmic: sensory from cornea and skin around eyes & forehead.

  2. Maxillary: sensory from upper teeth, palate, upper lip.

  3. Mandibular: sensory and motor to muscles of mastication. Sensory from teeth of mandible. Lingual branch to tongue. Important in dentistry.

Tic douloureux: (Trigeminal Neuralgia) Disorder of maxillary and mandibular branches of Trigeminal. Very Painful. Can be treated with medication or surgery.

6) Abducens: sensory and motor to lateral rectus.

7) Facial: sensory and motor--facial expression and taste (front of tongue-sweet and salt), salivary glands of mouth. Five major branches.

Bell's palsy: dysfunction of facial nerve. Inflammation or stroke results in loss of function, for example facial paralysis. Recent studies have linked many cases to the "cold sore virus" a.k.a. herpes simplex virus type 1 (HSV-1).

8) Vestibulocochlear (also called acuoutic or auditory nerve -- older terminology). Sensory primarily -- originates from semicircular canals (balance--vestibular sense) and from cochlea (hearing). Damage causes loss of hearing and/or problems with balance (vertigo).

9) Glossopharyngeal: motor to muscles for swallowing. Sensory from taste buds at back of tongue (bitter and sour).

10) Vagus: motor and sensory to viscera--heart, lungs, intestine etc. Carries some taste info. Major nerve of parasympathetic nervous system.

11) Accessory: sensory and motor to trapezius and sternocleidomastoid.

12) Hypoglossal: sensory and motor to muscles of tongue (intrinsic. & extrinsic)