Brain Anatomy and Function

• The adult human brain ranges from 750 cc to 2100 cc.
• Almost 97% of the body’s neural tissue is in the brain.
• The adult human brain weighs about 1.4 kg (3 lb).

Six Regions of the Brain

• Cerebrum
• Cerebellum
• Diencephalon
• Mesencephalon
• Pons
• Medulla oblongata

Cerebrum

• The cerebrum is the largest part of the brain.
• The cerebrum controls higher mental functions.
• The cerebrum is divided into left and right cerebral hemispheres.
• The neural cortex is the cerebrum's surface layer of gray matter.

Neural Cortex (Cerebral Cortex)

• A folded surface increases surface area.
• Elevated ridges are gyri.
• Shallow depressions are sulci.
• Deep grooves are fissures.
• Its functions include conscious thought processes, intellectual functions, memory storage and processing, and conscious & subconscious regulation of skeletal muscle contractions

Cerebellum

• The cerebellum is the second largest part of the brain.
• The cerebellum coordinates repetitive body movement.
• The cerebellum has two hemispheres.
• The cerebellar cortex covers the cerebellum.

Diencephalon

• The diencephalon is located under the cerebrum and cerebellum.
• The diencephalon links the cerebrum with the brain stem.
• The left thalamus, right thalamus, and hypothalamus are the three divisions of the diencephalon.

Diencephalon: Thalamus

• The thalamus relays and processes sensory information.

Diencephalon: Hypothalamus

• The hypothalamus functions in hormone production, emotion, and autonomic function.

Diencephalon: Pituitary Gland

• The pituitary gland is a major endocrine gland connected to the hypothalamus via the infundibulum (stalk).
• It interfaces with the nervous and endocrine systems.

The Brain Stem

• The brain stem processes information between the spinal cord and cerebrum or cerebellum.
• The brainstem includes the midbrain, pons, and medulla oblongata.

Midbrain (mesencephalon)

• The midbrain processes sight, sound, and associated reflexes and maintains consciousness.

Pons

• The pons connects the cerebellum to the brain stem.
• The pons is involved in somatic and visceral motor control.

Medulla Oblongata

• The medulla oblongata connects the brain to the spinal cord.
• The medulla oblongata relays information and regulates autonomic functions like heart rate, blood pressure, and digestion.

The Brain

• The brain is a large, delicate mass of neural tissue.
• The brain contains internal passageways and chambers filled with cerebrospinal fluid.
• Each of the six major brain regions has specific functions.
• As the brain ascends from the medulla oblongata to the cerebrum, brain functions become more complex and variable.
• Conscious thought and intelligence are produced in the neural cortex of the cerebral hemispheres.

Brain Protection and Support

• Physical protection includes the bones of the cranium, cranial meninges, and cerebrospinal fluid.
• Biochemical Isolation includes the blood-brain barrier.

Cranial Meninges

• The cranial meninges have three layers: dura mater, arachnoid mater, and pia mater.
• They are continuous with spinal meninges.
• It protects the brain from cranial trauma.

Cranial Meninges: Dura Mater

• Inner fibrous layer (meningeal layer).
• Outer fibrous layer (endosteal layer) fused to periosteum.
• There are venous sinuses between the two layers.

Cranial Meninges: Arachnoid Mater

• It covers the brain.
• Makes contact with the epithelial layer of dura mater.
• There is a subarachnoid space between the arachnoid mater and pia mater.

Cranial Meninges: Pia Mater

• It is attached to the brain's surface by astrocytes.

Cerebrospinal Fluid (CSF)

• CSF is located in the subarachnoid space.
• Arachnoid villi are extensions of the subarachnoid space reponsible for arachnoid granulations, which are large clusters of villi.
• It absorbs CSF into venous circulation.

Functions of Cerebrospinal Fluid (CSF)

• CSF surrounds all exposed surfaces of CNS and interchanges with interstitial fluid of brain.
• It cushions delicate neural structures, supports the brain, and transports nutrients, chemical messengers, and waste products.

Cerebrospinal Fluid (CSF): Choroid Plexus

• Choroid plexus is specialized ependymal cells and capillaries responsible for secreting CSF into ventricles, removing waste products from CSF, and adjusting its composition.
• Choroid plexus produces about 500 mL of CSF/day.

Cerebrovascular Disease

• Cerebrovascular disease includes disorders that interfere with blood circulation to brain and stroke, also known as cerebrovascular accident (CVA), which shuts off blood to portion of brain, leading to neuron death.

Ischemic (STROKE)

• A part of the brain loses blood due to blockage in an artery
• This leads to a range of symptoms referred to as "FAST" including Face Drooping, Arm Weakness, Speech Difficulties, Time
• If within 24 hours it leads to a transient ischemic attack.
• Risk factors causing ischemic Stroke include, smoking, hypertension, diabeties and a high fat diet.

Hemorrhagic (STROKE)

• Part of the brain loses blood due to artery ruptures
• Leads to Hemiplegia (paralysis of one side of the body) and aphasia
• Risk factors that cause hemorrahage include : hypertensions or blood vessel abnormalties

Blood-Brain Barrier (BBB)

• The blood-brain barrier isolates CNS neural tissue from general circulation.
• It is formed by a network of tight junctions between endothelial cells of CNS capillaries.
• Lipid-soluble compounds (O2, CO2), steroids, and prostaglandins diffuse into interstitial fluid of brain and spinal cord.
• Astrocytes control the blood-brain barrier by releasing chemicals that control the permeability of the endothelium.

Blood-CSF Barrier

• Formed by special ependymal cells; surrounds capillaries of choroid plexus.
• It limits the movement of compounds transferred.
• Allows for the differing chemical compostion of blood and CSF.

Brain: Protection and Support

• Meninges stabilize the brain in the cranial cavity.
• Cerebrospinal fluid protects against sudden movement and CSF provides nutrients and removes wastes.
• The blood-brain barrier and blood-CSF barrier selectively isolate the brain from chemicals in the blood that might disrupt neural function.

Medulla Oblongata

• Allows the brain and spinal cord to communicate and coordinates complex autonomic reflexes.
• Nuclei in the medulla control visceral functions.
• Autonomic nuclei control visceral activities, sensory and motor nuclei of cranial nerves, and relay stations along sensory and motor pathways.

Medulla Oblongata: Three Groups Of Nuclei

• Autonomic nuclei
• Sensory and motor nuclei of cranial nerves
• Relay stations along sensory and motor pathways

Medulla Oblongata: Autonomic Nuclei

• Reflex Centers control peripheral systems.
• Cardiovascular centers: cardiac center and control blood flow through peripheral tissues.
• Respiratory rhythmicity centers: set pace for respiratory movements.

Medulla Oblongata: Relay Stations

• Nucleus gracilis and nucleus cuneatus pass somatic sensory information to thalamus.
• The solitary nucleus receives visceral sensory information.
• The olivary nuclei (olives) relay information about somatic motor commands.

Pons

• Function: sensory and motor nuclei of cranial nerves.
• Nuclei involved with respiration.
• Contains apneustic center and pneumotaxic center, which modify respiratory rhythmicity center activity. Includes nucei that process and relay information to and from cerebellumContains Ascending, descending, and transverse tracts.

Cerebellum

• The cerebellum adjusts postural muscles and fine-tunes conscious and subconscious movements.

Cerebellum: Structures

• Purkinje cells: large, branched cells in cerebellar cortex receive input from up to 200,000 synapses.
• Arbor vitae (“tree of life”): highly branched, internal white matter.
• Cerebellar nuclei embedded in arbor vitae which relay information to Purkinje cells.

The Peduncles

• Tracts link cerebellum with brain stem, cerebrum, and spinal cord.
• Superior cerebellar peduncles.
• Middle cerebellar peduncles.
• Inferior cerebellar peduncles.

Cerebellum Disorders

• Ataxia is damage from trauma or stroke, intoxication, and disturbs muscle coordination.

The Midbrain: Structures

• Tectum two pairs of sensory nuclei that include (corpora quadrigemina).
• Superior colliculus (visual)
• Inferior colliculus (auditory)
• Tegmentum (Red nucleus -many blood vessels) & substantia nigra (pigmented gray matter).
• Cerebral peduncles (Nerve fiber bundles on ventrolateral surfaces).
• Descending fibers to cerebellum & Motor command fibers.

The Diencephalon

• Integrates sensory information and motor commands and includes the thalamus, epithalamus, and hypothalamus.
• The pineal gland is found in posterior epithalamus and secretes the hormone melatonin.

Thalamus

• Filters ascending sensory information for primary sensory cortex and relays information between basal nuclei and cerebral cortex.

Hypothalamus: Eight Functions

• Provides subconscious control of skeletal muscle.
• Controls autonomic function.
• Coordinates activities of nervous and endocrine systems.
• Secretes hormones (Antidiuretic hormone, Oxytocin).
• Produces emotions and behavioral drives (hunger)(thirst).
• Coordinates voluntary and autonomic functions.
• Regulates body temperature.
• Controls circadian rhythms (day-night cycles).

Limbic System

• It is a functional grouping that establishes emotional states, links conscious functions of cerebral cortex with autonomic functions of brain stem, and facilitates memory storage and retrieval.

Cerebrum (Largest Part)

• The Cerebrum is the largest part of the brain.
• The Cerebrum controls all conscious thoughts and intellectual functions.
• The cerebrum processes somatic sensory and motor information.

Cerebrum: Gray and White Matter

• Gray matter is in cerebral cortex and basal nuclei.
• White matter is deep to basal cortex and around basal nuclei.

Cerebrum: Structures

• Structures include gyri of neural cortex (increase surface area/number of cortical neurons, Insula ("island" of cortex) lies medial to lateral sulcus, Longitudinal fissure separates cerebral hemispheres, and Lobes divisions of hemispheres.

Cerebrum: The Central Sulcus

• Central sulcus divides the anterior frontal lobe from the posterior parietal lobe.
• The lateral sulcus divides frontal lobe from temporal lobe.
• Partieto-occipital sulcus divides parietal lobe from occipital lobe.

Cerebrum: Three Functional Principles

• Each cerebral hemisphere receives sensory information from and sends motor commands to the opposite side of the body.
• The two hemispheres have different functions, that have some overlap.
• Correspondence between a specific function and a specific region of cerebral cortex is not precise.

Cerebrum: White Matter

• Association Fibers: Connections within one hemisphere
• Commisural Fibers: Bands of fibers connecting two hemisphere.
• Projection Fibers: Connects cerebrum with lower areas.

Cerebrum: Types Of Commissural Fibers

• Corpus Callosum
• Anterior Commissure

Cerebrum: Types Of Association Fibers

• Arcuate fibers (short fibers connecting on gyrus to another)
• Longitudinal fasciculi (longer bundles connecting frontal lobe to other lobes in same hemisphere)

Cerebrum: Sensory Association

• Visual cortex: Information from sight receptors.
• Auditory cortex: Information from sound receptors.
• Olfactory cortex: Information from odor receptors.
• Gustatory cortex: Information from taste receptors.

Cerebrum: Sensory and Motor Information

• Visual association area: Interprets activity in visual cortex.
• Auditory association area: Monitors auditory cortex.
• Somatic motor association area (premotor cortex): Coordinates motor responses (learned movements).

Cerebrum: Integrative Centers

• Centers are located in lobes and cortical areas of both cerebral hemispheres.
• It receives information from association areas and Direct complex motor or analytical activities.

Cerebrum: General Integrative Area

• The general interpretive area is also called Wernicke's area and is present in only one hemisphere.
• It receives information from all sensory association areas, coordinates access to complex visual and auditory memories.

Cerebrum: Speech Center

• Associated with general interpretive area and coordinates all vocalization functions.

Cerebrum: Prefrontal Cortex

• Integrates information from sensory association areas and performs abstract intellectual activities (predicting consequences of actions).

Cerebrum: Hemispheric Lateralization

• Functional differences between left and right hemispheres.
• Each cerebral hemisphere performs certain functions that are not ordinarily performed by the opposite hemisphere.

Cerebrum: Left Hemisphere. Dominate Hemisphere

• Reading Writing and math
• Decision making
• Speech and language

Cerebrum: Left Hemisphere. Right Hemisphere

• Right cerebral hemisphere relates to senses such as touch ,smell, sight, taste and feel.It is also responsible for recognition (faces, voice inflections).

Cerebrum: Electroencephalogram

• Brain activity is assessed by electroencephalogram (EEG).
• Electrodes are placed on the skull, and patterns of electrical activity (brain waves) are printed out.

Cerebrum: Brain Waves

• Alpha Waves- (Found in healthy awake adults)
• Beta Waves- (Concentrating or mentally stressed)
• Theta Waves- (children/frustrated adults_
• Delta Waves- (During sleep/ awake adults with brain damage)

Cerebrum: Syncronization And Seisure

• A pacemaker mechanism synchronizes electrical activity between hemispheres.
• Brain damage can cause desynchronization.
• A seizure is a temporary cerebral disorder and changes the electroencephalogram.
• Symptoms depend on regions affected include paralysis of one side of the body, stiff muscles, loss of control of bowel or bladder function, jerking motions, breathing difficulties, and loss of consciousness and awareness.

Explore brain anatomy, including the pituitary gland, hypothalamus, pons, and medulla oblongata. Understand the function of cranial meninges and cerebrospinal fluid. Learn about the mesencephalon and white matter fiber tracts.