The Brain
 Develops from the embryonic neural tube
 The anterior end expands and constrictions appear forming the primary brain vesicles namely:
 Prosencephalon (fore brain)
 Mesencephalon (midbrain)
 Rhombencephalon (hindbrain)
 The primary brain vesicles differentiate into secondary brain vesicles
 Procencephalon
 Telencephalon (cerebrum)
 Diencephalon (thalamus, hypothalamus and Epithalamus)
 Mesencephalon
 Brain stem: midbrain
 Rhombencephalon
 Metencephalon
 Brain stem: Pons and cerebellum
 Myelencephalon
 Brain stem: medulla oblongata
Regional Organization
 Cerebral Hemispheres
 Has three basic regions; Outer gray matter, internal white matter and the basal nuclei
 Conscious thoughts, intellect, memory, sensations and complex movements originate
from here regional organization
 Marked by elevated tissue folds called gyri (increase surface area of the cortex)
 Gyri are separated by shallow grooves called sulci
 Deeper grooves, called fissures separate larger brain regions
 Longitudinal fissure
 Separates the two cerebral hemispheres
 Transverse fissure
 Separates the cerebral hemispheres from the cerebellum
 Some sulci divide each hemisphere into lobes,

Frontal, parietal, temporal, occipital, and insula
 Regional Organization
 Central Sulcus
 Lies in the frontal plane
 Separates the frontal lobe from the parietal lobe
 It is bordered anteriorly by the precentral gyrus (primary motor area) and posteriorly by
the postcentral gyrus (primary somatosensory area)
 The parieto-occipital sulcus
 Located on the medial surface of each hemisphere
 Separates the occipital lobe from the parietal lobe
 The lateral sulcus
 Outlines the temporal lobe and separates it from the parietal and frontal lobes
 Regional Organization
 The Insula
 Lies deep to the temporal lobe and forms part of its floor
 Covered by portions of the frontal, parietal and temporal lobes
Generalizations about brain regions
 The cortex contains 3 kinds of functional areas: motor, sensory and association
 Each hemisphere is chiefly concerned with motor and sensory functions from the
opposite side of the body
 Two hemispheres are not entirely equal in function (Lateralization) specialization of
cortical functions exist
 No functional area of the cortex acts alone
Regional Organization
Motor areas
 Primary (somatic) motor cortex
 Conscious control of precise or skilled voluntary movements of the skeletal
muscles
 Premotor cortex
 Lies anterior to the precentral gyrus
 Controls learned motor skills of a repetitious or patterned nature such as typing
or playing a musical instrument
 Broca’s area
 Lies anterior of the premotor area on one hemisphere (usually left) only
 Controls muscles involved in speech production
 Frontal eye field
 Located partially in and anterior to the premotor cortex and superior to the
broca’s area
 Controls voluntary movement of the eyes
Sensory areas
 Primary somatosensory area
 Receives information from general somatic receptors in the skin and
proprioceptors in skeletal muscles
 Spatial discrimination, the ability to identify the regions being stimulated occurs
here
 Somatosensory association cortex
 Lies posterior to the somatosensory cortex
 Integrates temperature, pressure etc, relayed from the primary somatosensory
cortex to produce an understanding of any object being felt
 Visual area
 Lies on the extreme posterior tip of the occipital lobe
 Receives visual information from the retina of the eye
 The visual association area communicates with the visual area to interpret visual
stimuli (color, form, movement)
 Regional Organization
 Auditory areas
 Located in the temporal lobe
 Converts impulses from the ear and relate them to pitch, rhythm and loudness
 The auditory association area permits the perception of sound stimulus which
we hear as music, scream, noise etc
 Olfactory cortex
 Medial aspect of temporal lobes
 Enables us to be aware of changes in odors
 Regional Organization
 Gustatory cortex
 Located in the insula
 Involved in the reception of taste
 Visceral Sensory Area
 Posterior to gustatory cortex
 Conscious perception of visceral sensations, e.g., upset stomach or full bladder
 Vestibular cortex
 Posterior part of the insula and adjacent parietal cortex
 Responsible for conscious awareness of balance (position of the head in space)
Multimodal Association Areas
 Receive inputs from multiple sensory areas
 Send outputs to multiple areas, including the premotor cortex
 Allow us to give meaning to information received, store it as memory, compare it to
previous experience, and decide on action to take
 Three parts of multimodal association area
 Anterior association area (prefrontal cortex)
 Posterior association area
 Limbic association area
 Anterior association area (Prefrontal cortex)
 Most complicated cortical region
 Involved with intellect, cognition, recall, and personality
 Contains working memory needed for judgment, reasoning, persistence, and conscience
 Development depends on feedback from social environment
 Posterior Association Area
 Large region in temporal, parietal, and occipital lobes
 Plays a role in recognizing patterns and faces and localizing us in space
 Involved in understanding written and spoken language (Wernicke’s area)
 Limbic Association Area
 Part of the limbic system
 Provides emotional impact that helps establish memories
Cerebral white matter
 Lies deep to the cortical gray matter
 Responsible for communication between the cerebral areas, cortex and lower CNS
centers
 Consists mostly of myelinated fibers bundled into large tracts
 Fibers are classified according to the direction in which they run
 Commisures (Commisural fibers)
 Connect corresponding gray areas of the two hemispheres enabling them to function as
a whole
 The largest commisure is the corpus callosum
 Anterior and posterior commisures are less important
 Regional Organization
 Association fibers
 Connect different parts of the same hemisphere
 Short fibers connect adjacent gyri
 Long fibers are bundled in tracts that connect different lobes
 Projection fibers
 Fibers that enter and leave the to lower brain or cord centers
Basal Nuclei (ganglia)
 Subcortical nuclei
 Consists of the corpus striatum
 Caudate nucleus
 Lentiform nucleus (putamen + globus pallidus)
 Functionally associated with the subthalamic nuclei (diencephalon) and the substantia
nigra (midbrain
 Functions of Basal Nuclei
 Though somewhat elusive, the following are thought to be functions of basal nuclei
 Influence muscular control
 Help regulate attention and cognition
 Regulate intensity of slow or stereotyped movements
 Inhibit antagonistic and unnecessary movements

Diencephalon
 Forms the central core of the forebrain
 Thalamus
 Egg-shaped and forms the superolateral walls of the third ventricle and contains several
nuclei
 Its bilateral masses of gray matter are held together by the intermediate mass
 Principal relay station for directing sensory information from the spinal cord, medulla
and cerebellum to the cortex
 Relays and processes taste, visual, auditory and somatosnsory information
 Hypothalamus
 Lies below the thalamus, caps the brain stem and forms the inferolateral wall of the
third ventricle
 It contains many functionally important nuclei and is the main visceral control center of
the body
 Processes and relays olfactory information, integrates the ANS, produce hormones (ADH
and Oxytocin), control over heart rate, digestive tract activity, rage and aggression, body
temperature regulation, water balance and thirst, hunger and satiety centers and sleep
pattern
 Epithalamus
 The most dorsal portion of the diencephalon
 Forms the roof of the third ventricle
 The pineal gland lies on the exterior of its posterior border
 The pineal gland secretes melatonin that plays a role in the regulation of the sleepwake cycle
Brain stem
 Made up of the midbrain, pons and medulla
 Has a deep gray matter surrounded by white matter with nuclei of gray matter
embedded in the white matter
 Produce rigidly programmed automatic behavior necessary for survival
 Provides a pathway for fibers running between higher and lower neural centers
 Is associated with 10 of the 12 cranial nerves
 Regional Organization
 Midbrain
 Located between the diencephalon and the pons
 The ventral surface has cerebral peduncles that consists of fiber tracts descending
toward the spinal cord
 The superior peduncles contain tracts that link the midbrain to the cerebellum
 The cerebral aqueduct runs through the midbrain connecting the third and forth
ventricle
 On the dorsal surface are superior and inferior colliculi (corpora quadrigemina) that
coordinate head and neck movements in response to visual and auditory stimuli
respectively
 Regional Organization
 Pons
 Brainstem swellings that lie between the mid brain and the medulla oblongata
 Dorsally it forms part of the anterior wall of the fourth ventricle
 Longitudinal fibers connects the medulla with higher brain center
 Transverse fibers connect the cerebral hemispheres within the midbrain
 Respiratory centers of the reticular formation that help to maintain the normal rhythm
of breathing are located here
 Medulla oblongata
 Cone shaped and lies between the pons and the spinal cord
 The foramen magnum is the anatomical landmark used to differentiate brain structures
from spinal cord structures
 The ventral aspect has two longitudinal ridges called pyramids formed by large
pyramidal fibers descending from the motor cortex
 These fibers decussate (pyramidal decussation) before they enter the spinal cord
 On the dorsal surface are the nucleus cuneatus and gracilis that serve as relay nuclei for
tracts that carry sensory information from the spinal cord and relay them to the
thalamus
 These fibers decussate in the medulla
 Has a cardiovascular center(cardiac and vasomotor center), respiratory center (rate and
depth of breathing) and other centers that regulates vomiting, sneezing, hiccups,
swallowing etc
Cerebellum
 Located dorsal to the pons and medulla and lies under the occipital lobe of the cerebral
hemisphere from which it is separated by the transverse fissure
 Consists of two hemispheres that are connected in the midline by the vermis
 It functions primarily by fine-tuning movement and adjusting body posture to maintain
balance