Introduction to the Organization of the Brain- contains about 98% of neural tissue. 4 major regions: cerebrum, cerebellum, diencephalon, brain stem.
▪Cerebrum- majority of brain, divided into two hemispheres
▫Covered in neural cortex (gray matter)
▫Gyri
▫Sulci
▫Fissures
▫Conducts higher mental functions; intellect, memory, complex movements
▪Cerebellum- posterior and inferior to cerebrum, also has two hemispheres
▫Also covered in a cortex, the cerebellar cortex
▫Adjusts ongoing movements on the basis of comparison.
▪Diencephalon- deep inside the brain, composed of many parts; thalamus, hypothalamus, pituitary gland. (discussed in greater detail later)
▫Structural and functional link between the cerebrum and the brain stem.
▪Brain Stem- important for relaying information headed to and from the cerebrum and cerebellum. Composed of many parts; midbrain, pons, medulla oblongata. (discussed in greater detail later)
▪Embryology of the Brain
▫CNS begins as a hollow tube known as the neural tube, contains a fluid filled cavity called the neurocoel
▫Enlargements of the neurocoel create 3 prominent vesicles; primary brain vesicles.
-Prosencephalon, mesencephalon, rhombencephalon
▫Secondary brain vesicles form later in development (6 weeks)
-Telencephalon and diencephalon develops from the prosencephalon
-Mesencephalon, remains throughout development
-Metencephalon and myelencephalon develops from the rhombencephalon.
▫At birth, the secondary brain vesicles have developed into these brain regions:
-Cerebrum from the telencephalon
-Diencephalon remains
-Mesencephalon remains
-Cerebellum and pons from the metencephalon
-Medulla oblongata from the myelencephalon

▪Ventricles of the Brain
▫During development, ventricles, open chambers, are formed from the neurocoel inside the cerebral hemispheres, diencephalon, metencephalon, and the medulla oblongata.
▫Lateral ventricles
▫Third ventricle
▫Fourth ventricle
-cerebral aquaduct connects the third ventricle with the fourth ventricle.
▫Ventricles are filled with CSF.
Protection and Support of the Brain
▪Cranial Meninges- protective tissue layers surrounding the brain, continuous with the spinal meninges.
▫Dura mater
-Periosteal layer
-Meningeal layer
-These two layers are separated by a slender gap that contains tissue fluid and blood vessels.
▫Arachnoid mater
-Trabeculae cross the subarachnoid space and connect to the pia mater.
-Does not follow the brains folds
▫Pia mater
-Anchored by processes of astrocytes
-Follows every fold, goes with blood vessels as they penetrate the brain to deeper structures.
▫Dural Folds and Sinuses
-falx cerebri
-tentorium cerebelli
-falx cerebelli
▪Cerebrospinal Fluid (CSF)- completely surrounds and bathes the exposed surfaces of the CNS.
▫Functions of the CSF

▫Formation of CSF
-produced by the choroid plexus found in the roof of third ventricle and side of fourth ventricle.
-secreted by specialized ependymal cells into the ventricles.
-composition is different than that of blood plasma.
-CSF does not contain any soluble proteins, and concentrations of individual ions, amino acids, and waste products are different.
▫Circulation of CSF
-circulates from the choroid plexus through the ventricles and the central canal of the spinal cord
-CSF reaches the subarachnoid space through two lateral apertures and one median aperture found in the fourth ventricle.
-CSF is absorbed into the venous circulation at the arachnoid granulations.
-500 ml/day is produced, total volume at any moment is 150 ml. Means CSF is replaced roughly every 8 hours.
▪Blood Supply to the Brain
▫Brain has high demands for blood, needs nutrients and oxygen.
▫Blood is brought to the brain via the internal carotid arteries and the vertebral arteries.
▫Blood is drained from the brain via the internal jugular veins.
▫Blood Brain Barrier- isolates the neural tissue of the CNS from the general circulation.
-endothelial cells that line the capillaries of the CNS are extensively interconnected by tight junctions.
-prevents diffusion of material between adjacent cells, material must pass through the lipid bilayer of the cell membranes
▫BBB is incomplete in 4 noteworthy locations:

Medulla Oblongata- most inferior part of brain, continuous with the spinal cord
▪Central canal opens into the fourth ventricle.
▪All communications between the brain and spinal cord involves tracts that ascend or descend through the medulla oblongata.
▪A center for the coordination of relatively complex autonomic reflexes and the control of visceral function.
▪Three groups of nuclei (gray matter):
1.
Autonomic nuclei controlling visceral activities
2.
Sensory and motor nuclei of cranial nerves (VIII, IX, X, XI, XII)
3. Relay Stations along sensory and motor pathways.
Pons- links the cerebellum with the midbrain, diencephalon, cerebrum, and spinal cord.
▪Contains four groups of components:
1.
Sensory and motor nuclei of cranial nerves (V, VI, VII, VIII)
2.
Nuclei involved with the control of respiration
3.
Nuclei and tracts that process and relay information heading to or from the cerebellum
4.
Ascending, descending, and transverse tracts (white matter)
Cerebellum- automatic processing center with
▪Two primary functions:

1. Adjusting the postural muscles of the body
2. Programming and fine-tuning movements controlled at the conscious and
▪Folia subconscious levels.
▪Has anterior and posterior lobes separated by the primary fissure.
▪The vermis
▪Purkinje cells are large, highly branched neurons that receive input from up to 200,000 synapses.
▪Arbor vitae
▪Superior, Middle, and Inferior cerebellar peduncles link the cerebellum with the: midbrain, diencephalon, and cerebrum; pons; medulla oblongata and spinal cord, respectively.
Midbrain- “mesencephalon”
▪Tectum
▪Corpora quadrigemina
▫Superior colliculus
▫Inferior colliculus
▪Red Nucleus
▪Substantia Nigra
▪Cerebral Peduncles
▪Reticular Activating System (RAS)
Diencephalon- plays a vital role in integrating conscious and unconscious sensory information and motor commands. Contains the epithalamus, thalamus, and hypothalamus.
▪Epithalamus

▪Thalamus
▫Left and right thalamus are separated by the third ventricle
▫5 Thalamic nuclei; anterior, medial, ventral, posterior, and lateral.
▪Hypothalamus- contains important control and integrative centers.
▫Mamillary bodies
▫Infundibulum
▫Tuberal Area
▫Hypothalamic centers can be stimulated by:
1. sensory information from the cerebrum, brain stem, or spinal cord.
2. changes in composition of the CSF or interstitial fluid
3. chemical stimuli in the circulating blood. (hormones, ion changes, etc.)
▫Hypothalamus has many functions:

The Limbic System- a functional grouping including nuclei and tracts along the border between the cerebrum and diencephalon.
▪Has three main functions
1) establishing emotional states
2) linking the conscious, intellectual function of the cerebral cortex with the unconscious and autonomic functions of the brainstem
3) facilitating memory storage and retrieval.
▪Amygdaloid body- plays a role in the regulation of heart rate, in the control of the “fight or flight” response, and in linking emotions with specific memories.
▪Limbic Lobe- consists of gyri and underlying structures adjacent to the diencephalon. There are three gyri in the limbic lobe.
▫Cingulate gyrus, dentate gyrus, parahippocampal gyrus.
▪Hippocampus- located within the gyri of the limbic lobe. Important in learning, especially in the storage and retrieval of new long-term memories.
▪Fornix- tracts of white matter that connects the hippocampus with the hypothalamus.
The Cerebrum- the largest region of the brain.
▪The cerebral hemispheres are separated into lobes by distinct sulci and fissures.
▫Longitudinal fissure
▫Central sulcus
▫Lateral sulcus
▫Parieto-occipital sulcus
▫Insula
▪Three important points to remember about cerebral hemispheres.
1. Each cerebral hemisphere receives sensory information from and sends motor commands to, the opposite side of the body.
2. The two hemispheres have different functions, even though they look almost identical
3. The assignment of a specific function to a specific region of the cerebral cortex is imprecise.

▪White Matter of the Cerebrum- The axons of white matter can be classified as association fibers, commissural fibers, and projection fibers.
▫Association fibers
-arcuate fibers
-longitudinal fasiculi
▫Commissural fibers
▫Projection fibers
▪Basal Nuclei- masses of gray matter that lie within each hemisphere deep to the floor of the lateral ventricle. Major nuclei are caudate and lentiform; which consists of the globus pallidus, and putamen.
▫Basal nuclei are involved with the subconscious control of skeletal muscle tone and the coordination of learned movement patterns.
▪Motor and Sensory Areas of the Cortex
▫Primary Motor Cortex
-pyramidal cells- neurons in the primary motor cortex.
▫Primary Sensory Cortex
▫Visual Cortex
▫Auditory Cortex
▫Olfactory Cortex
▫Gustatory Cortex
▪Association Areas- regions of the cortex that interpret incoming data or coordinate a motor response.
▫Somatic Sensory Association Area
▫Visual Association Area

▫Auditory Association Area
▫Somatic Motor Association Area (premotor cortex)
▪Integrative Centers- receive information from many association areas and direct extremely complex motor activities. Also perform complicated analytical functions.
▫Located in the lobes and cortical areas of both cerebral hemispheres.
▫Integrative centers concerned with speech, writing, math computation, and understanding spatial relationships are restricted to either the left or the right hemisphere.
-General interpretive area- receives information from all the sensory association areas.
-Present in only one hemisphere (usually the left).
-essential in personality by integrating sensory information and coordinating access to complex visual and auditory memories.
-Speech center- lies along the edge of the premotor cortex in the same hemisphere as the general interpretive area.
-regulates the patterns of breathing and vocalization needed for normal speech.
-coordinates the activities of the respiratory muscles, laryngeal and pharyngeal muscles, and the muscles of the tongue, cheeks, lips, and jaws.
-Prefrontal Cortex- coordinates information relayed from the association areas of the entire cortex .
-Performs abstract intellectual functions; predicting the consequences of events or actions.
-Has extensive connections with other cortical areas and other portions of the brain.
▪Hemispheric Lateralization- each hemisphere is responsible for specific functions that are not ordinarily performed by the opposite hemisphere.
▫In most people the left hemisphere contains the general interpretive and speech centers and is responsible for language-based skills.
▫In most people the right hemisphere analyzes sensory information and relates the body to the sensory environment.
▪Brain Activity: The Electroencephalogram- a printed report of the electrical activity of the brain.

▫Alpha waves
▫Beta waves
▫Theta waves
▫Delta waves
Cranial Nerves- pgs 492 to 502
▪From Summary Table 14-4, focus on:
-Number and Name
-Primary Function
-Innervation