brain anatomy

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Central Nervous System (CNS)

� CNS – composed of the brain and spinal cord

� Cephalization

� Elaboration of the anterior portion of the CNS

� Increase in number of neurons in the head

� Highest level is reached in the human brain


I take

exception to

that!


The Brain

� Surface anatomy includes cerebral hemispheres,

cerebellum, and brain stem


Embryonic Development

� During the first 26 days of development:

� Ectoderm thickens forming the neural plate

� The neural plate invaginates, forming the neural folds

� Superior edges fuse forming neural tube which detaches

from the ectoderm and sinks deeper

� Neural tube differentiates into the CNS

� Brain forms from neural tube (rostrally) as well as spinal

cord (posterior/dorsally)

� Neural crest cells give rise to some neurons destined to

reside in ganglia


Embryonic Development

Figure 12.1


Brain Development: Primary Brain Vesicles

� The anterior end of the neural tube expands and

constricts to form the three primary brain vesicles

� Prosencephalon – the forebrain

� Mesencephalon – the midbrain

� Rhombencephalon – hindbrain

� Remainder of neural tube becomes the spinal cord


Neural Tube and Primary Brain Vesicles

Figure 12.2a, b


Secondary Brain Vesicles

� In week 5 of embryonic development, secondary

brain vesicles form

� Telencephalon and diencephalon arise from the

forebrain

� Mesencephalon remains undivided

� Metencephalon and myelencephalon arise from the

hindbrain


Secondary Brain Vesicles

Figure 12.2c


Adult Brain Structures

� Fates of the secondary brain vesicles:

� Telencephalon – cerebrum: cortex, white matter,

and basal nuclei

� Diencephalon – thalamus, hypothalamus, and

epithalamus

� Mesencephalon – brain stem: midbrain

� Metencephalon – brain stem: pons

� Myelencephalon – brain stem: medulla oblongata


Adult Neural Canal Regions

Figure 12.2c, d



� Adult structures derived from the neural canal

� Telencephalon – lateral ventricles

� Diencephalon – third ventricle

� Mesencephalon – cerebral aqueduct

� Metencephalon and myelencephalon – fourth

ventricle



Figure 12.2c, e


Space Restriction and Brain Development

Figure 12.3


Space Restriction and Brain Development

� Flexures: midbrain and cervical, which bend the

forebrain toward the brain stem

� Cerebral hemispheres: grow posteriorly and

laterally and envelop the diencephalon and

midbrain

� Continued growth causes the surface to crease

and fold producing convolutions thus increasing

the surface area


Basic Pattern of the Central Nervous System

� Spinal Cord

� Central cavity surrounded by a gray matter core

� External to which is white matter composed of myelinated fiber tracts

� Brain

� Similar to spinal cord but with additional areas of gray matter

� Cerebellum has gray matter in nuclei

� Cerebrum has nuclei and additional gray matter in the cortex


Basic Pattern of the Central Nervous System

Figure 12.4


Ventricles of the Brain

� Continuous with one another and with the central canal of the spinal cord

� Filled with cerebrospinal fluid and lined with ependymal cells

� C-shaped reflects the pattern of cerebral growth

� Septum pallucidum separates lateral ventricles via the interventricular foreamen

� Third ventricle connected to the fourth ventricle via the cerebral aquaduct

� Fourth ventricle is continuous with the central canal of the spinal cord

� Fourth ventricle is also continuous with the fluid filled space surrounding the brain (subarachnoid) via lateral and medial apertures.


Ventricles of the Brain

Figure 12.5


Cerebral Hemispheres

� Form the superior part of the brain and make up 83% of its mass

� Contain ridges (gyri) and shallow grooves (sulci)

� Contain deep sulci called fissures

� Are separated by the longitudinal fissure

� Transverse fissure separates the cerebral hemispheres from the cerebellum

� Have three basic regions: cortex, white matter, and basal nuclei


Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere

� Prominent sulci divide the hemispheres into five

lobes:

� Frontal, parietal, temporal, occipital, and insula

� These are named for the cranial bones under which

they lie

� Central sulcus – separates the frontal and parietal

lobes.

� Bordered by the precentral gyrus (anteriorly)

and the postcentral gyrus (posteriorly)


Brain Lobes

Figure 12.6a–b


Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere

� Parieto-occipital sulcus – separates the parietal and

occipital lobes

� Lateral sulcus – outlines the temporal lobe and

separates the parietal and temporal lobes

� Insula: buried within the lateral sulcus and forms

part of the floor of the cerebral hemispheres


Cerebral Cortex: Our “conscious mind”

� The cortex – superficial gray matter; accounts for

40% of the mass of the brain.

� Gray matter: neuron cell bodies, dendrites,

associated glia, blood vessels

� It enables sensation, communication, memory,

understanding, and voluntary movements

� Each hemisphere acts contralaterally (controls the

opposite side of the body)

� Cerebral cortex has been extensively mapped


Functional Areas of the Cerebral Cortex

� The three types of functional areas are:

� Motor areas – control voluntary movement

� Sensory areas – conscious awareness of sensation

� Association areas – integrate diverse information

� All neurons here are interneurons not sensory & motor

neurons

� Each hemisphere is chiefly concerned with the sensory and

motor functions of the opposite side of the body

� Each side has specialization and is not necessarily bilateral



Figure 12.8a



Figure 12.8b


Cerebral Cortex: Motor Areas (Voluntary Movement)

� Lie in the posterior part of the frontal lobes:

� Primary (somatic) motor cortex

� Premotor cortex

� Broca’s area

� Frontal eye field


Primary Motor Cortex (Brodmman’s Area #4)

� Located in the precentral gyrus of the

frontal lobe of each hemisphere

� Pyramidal cells:

� allow conscious control of

precise, skilled, voluntary

movements.

� Their long axons project into the

spinal cord forming the massive

pyramidal tracts (corticospinal

tracts)


Primary Motor Cortex (Brodmman’s Area #4)

� The entire body is represented spatially in the

primary motor cortex of each hemisphere (this

type of mapping is called somatotopy)


Premotor Cortex (Brodmman’s Area #6)

� Located anterior to the precentral gyrus in the frontal lobe

� Controls learned, repetitious, or patterned motor skills

� Coordinates movement by sending impulses to the primary

motor cortex

� Involved in the planning of movements

� Controls voluntary movements that depend on sensory feedback


Broca’s Area: Brodmann Area #44 & 45

� Broca’s area

� Located anterior to the inferior region of the premotor area

� Present in one hemisphere (usually the left)

� A motor speech area that directs muscles of the tongue

� Is active as one is planning to speak


Frontal Eye Field: Brodmann’s Area #8

� Frontal eye field

� Located anterior to the premotor cortex and

superior to Broca’s area

� Controls voluntary eye movement


Sensory Areas

� Primary somatosensory cortex

� Somatosensory association cortex

� Visual and auditory areas

� Olfactory, gustatory, and vestibular cortices


Sensory Areas

Figure 12.8a


Primary Somatosensory Cortex: Brodmann’s Area #1-3

� Located in the postcentral gyrus of parietal lobe

� Receives info. from sensory receptors in the skin and

proprioceptors in the skeletal muscles, joints, tendons

� Neurons identify the body region being stimulated (spatial

discrimination)


Primary Somatosensory Cortex: Brodmann’s Area #1-3

� Body is represented

spatially: contralaterally

and upside down

� The amount of sensory

cortex devoted to a given

body region is related to

the degree of sensitivity

in that region, and not the

body size (e.g. face, lips,

fingertips)


Somatosensory Association Cortex: Brodmann’s Areas 5 &7

� Located posterior to the primary somatosensory cortex

� Integrates sensory information relayed from the primary

somatosensory cortex to produce an understanding of the object

being felt

� Determines size, texture, and relationship of parts


Visual Areas: Brodmann’s Areas 17-19

� Primary visual (striate) cortex

� Seen on the extreme posterior tip of the occipital lobe

� Most of it is buried in the calcarine sulcus

� Receives visual information from the retinas

� Visual association area

� Surrounds the primary visual cortex

� Interprets visual stimuli (e.g., color, form, and movement)


Auditory Areas: Brodmann’s Areas 41-43

� Primary auditory cortex

� Located at the superior margin of the temporal lobe

� Receives information related to pitch, rhythm, and volume

� Auditory association area

� Located posterior to the primary auditory cortex

� Stores memories of sounds and permits perception of sounds

� Wernicke’s area


Olfactory Cortex: Brodmann’s Areas: 28 & 34

� Located in the medial aspect of the temporal lobe dominated by

the uncus

� Afferent fibers from smell receptors in the superior nasal

cavities send impulses along olfactory tracts and relay them to

the olfactory cortex

� The O.C. is part of the primitive rhinencephalon


…and the other corteces

� Gustatory cortex (located in the insula)

� Deep to the temporal lobe

� Taste

� Visceral sensory area (also in the insula)

� Located just posterior to the gustatory cortex

� Perception of visceral sensations

� Vestibular (equilibrium) cortex

� Located in the posterior part of the insula

� Balance


Multimodal Association Areas

� Information flows from sensory neurons to

� Primary sensory cortex to

� Sensory association cortex to

� Multimodal association cortex

� Gives meaning to the information

� Stores it in memory

� Decision making area

� Relay decisions to premotor cortex and then the motor

cortex


Prefrontal Cortex (Anterior Association Area)

� Located in the anterior portion of the frontal lobe

� Most complicated cortical region

� Involved with intellect, cognition, recall, and

personality

� Necessary for judgment, reasoning, persistence,

and conscience

� Matures slowly, dependent on positive/negative

feedback


Posterior Association Area

� Region encompassing parts of: temporal, parietal,

and occipital lobes

� Involved in recognizing patterns, surroundings,

bringing different sensory inputs into a whole

� Brings conscious attention to an area in space or to

an area of one’s own body

� Problems here can result in a smelly, half naked

lady!


Language Areas

� Located in a large area surrounding the left (or language-dominant) lateral sulcus

� Major parts and functions:

� Wernicke’s area –sounding out unfamiliar words

� Broca’s area – speech preparation and production

� Lateral prefrontal cortex – language comprehension and word analysis

� Lateral and ventral temporal lobe – coordinate auditory and visual aspects of language


Lateralization of Cortical Function

� Lateralization – each hemisphere has abilities not shared

with its partner

� Cerebral dominance – designates the hemisphere dominant

for a given task

� Left hemisphere – controls language, math, and logic

� E.g. Dad buys half a cow for conversation sake

� Right hemisphere – controls visual-spatial skills, emotion,

and artistic skills

� Most “righties” are left cerebral dominant, while most

“south paws” are right cerebral dominant.


Cerebral White Matter

� Located deep to the cortical grey matter

� It is responsible for communication between the

cerebral cortex and lower CNS center, and within

areas of the cerebrum

� Consists of deep myelinated fibers and their large

tracts


Cerebral White Matter

� Tracts are classified according to the direction in which they run

� Types include:

� Commissures – connect corresponding gray areas of the two hemispheres.

� E.g. corpus collosum

� Fibers run horizontally

� Association fibers – connect different parts of the same hemisphere

� E.g. connect adjacent gyri

� Long fibers can connect different cortical lobes

� Fibers run horizonatally

� Projection fibers – enter the hemispheres from lower brain or cord centers

� Tie the cortex to the rest of the nervous system and to the body’s receptors and effectors

� E.g. corona radiata: fan like projection of fibers from the brain stem to the cortex

� Fibers run vertically


Fiber Tracts in White Matter

Figure 12.10a


Basal Nuclei

� Masses of gray matter found deep within the

cortical white matter

� The corpus striatum (striped appearance) is

composed of three parts

� Caudate nucleus

� Lentiform nucleus – composed of the putamen and

the globus pallidus

� Fibers of internal capsule running between and

through caudate and lentiform nuclei


Basal Nuclei

Figure 12.11a


Basal Nuclei

Figure 12.11b


Functions of Basal Nuclei

� Nuclei of the corpus striatum receive input from

the entire cerebral cortex

� The basal nuclei project signals to the premotor

and prefrontal cortices (logic and reasoning of a

movement and how to best execute it)

� And influences muscle movements

(subsequently directed by the primary motor

cortex)

� Precise function of basal nuclei is still elusive


Diencephalon

� Central core of the forebrain

� Surrounded by the cerebral hemispheres

� Consists of three paired structures – thalamus,

hypothalamus, and epithalamus

� Encloses the third ventricle


Diencephalon

Figure 12.12


Thalamus

� Paired, egg-shaped masses that form the

superolateral walls of the third ventricle

� Connected at the midline by the intermediate mass

� Contains four groups of nuclei – anterior, ventral,

dorsal, and posterior

� Nuclei project and receive fibers from the cerebral

cortex

� Thalamus, thyroid, thymus


Thalamus

Figure 12.13a


Thalamic Function

� Afferent fibers from all senses and all parts of the body

converge and synapse in the thalamus

� Impulses of similar function are sorted out, edited, and

relayed as a group (e.g. “The Hot Bowl of Soup”)

� All inputs ascending to the cerebral cortex pass through the

thalamus

� Mediates sensation, motor activities, cortical arousal,

learning, and memory

� Thalamus is the “gateway” to the cerebral cortex


Hypothalamus

� The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis).

� Located below the thalamus, it caps the brainstem and forms the inferolateral walls of the third ventricle

� Extends from the optic chiasma to the posterior margin of the mammillary bodies

� Main visceral control center of the body

� Vital for homeostasis


Hypothalamus Associated Structures

� Mammillary bodies

� Small, paired nuclei bulging anteriorly from

the hypothalamus

� Involved with recognition memory

� Relay station for olfactory pathways

� Infundibulum – stalk of the hypothalamus; connects

to the pituitary gland


Hypothalamic Nuclei

Figure 12.13b


Hypothalamic Function

� Autonomic control center: controls autonomic nervous system.

� Regulates cardiac and smooth muscle

� Regulates gland secretion

� Influences blood pressure, heartbeat rate, digestive tract motility, eye pupil size

� Emotional response center

� Center for pleasure, fear, rage

� Body temperature regulation

� Sweating, shivering

� Regulation of food intake

� Regulates the feeling of hunger and satiation

� Regulation of water balance and thirst

� Regulates release of antidiuretic hormone causing kidneys to retain water

� Regulates sleep wake cycle


Endocrine Functions of the Hypothalamus

� Releasing hormones control secretion of hormones

by the anterior pituitary gland

� E.g. The supraoptic and paraventricular nuclei

produce ADH and oxytocin


Epithalamus

� Most dorsal portion of the diencephalon; forms

roof of the third ventricle

� Pineal gland – extends from the posterior border

and secretes melatonin

� Melatonin – a hormone involved with sleep

regulation, sleep-wake cycles, and mood


Epithalamus

Figure 12.12


Brain Stem

� Consists of three regions – midbrain (mesencephalon), pons, and medulla oblongata

� Similar to spinal cord but contains embedded nuclei

� Controls automatic behaviors necessary for survival

� Provides the pathway for tracts between higher and lower brain centers

� Associated with 10 of the 12 pairs of cranial nerves


Human Brain: Ventral Aspect

Figure 12.14


Brain Stem

Figure 12.15a


Brain Stem

Figure 12.15b


Brain Stem

Figure 12.15c


Midbrain (Mesencephalon)

� Located between the diencephalon and the pons

� Midbrain structures include:

� Cerebral peduncles – two bulging structures that

contain pyramidal motor tracts descending toward

the spinal cord

� Cerebral aqueduct – hollow tube that connects the

third and fourth ventricles

� Various nuclei


Midbrain Nuclei

� Corpora quadrigemina – four domelike protrusions

of the dorsal midbrain (superior and inferior

colliculi)

� Superior colliculi: visual reflex centers

� Inferior colliculi: auditory relay (startle reflex)


Midbrain Nuclei

� 2 pigmented nuclei:

� Substantia nigra – pigmented from melanin

� Precursor of dopamine released here. Disorders here, e.g.

Parkinson’s disease

� Red nucleus – largest nucleus of the reticular formation

� Controls some movements of the shoulder & upper arm

� Red coloration due to high degree of vascularization


Pons

� Bulging brainstem region between the midbrain and the medulla

oblongata

� Forms part of the anterior wall of the fourth ventricle

� Formed of tracts coursing in 2 directions

� Deep projections: connect higher brain centers and

spinal cord

� Superficial projections relay between the motor cortex

of the cerebrum and the cerebellum


Medulla Oblongata

� Most inferior part of the brain stem

� Along with the pons, forms the ventral wall of the

fourth ventricle

� Contains a choroid plexus of the fourth ventricle

� Pyramids – two longitudinal ridges formed by

corticospinal tracts

� Decussation of the pyramids – crossover points of

the corticospinal tracts


Medulla Oblongata

Figure 12.16c


Medulla Nuclei

� Inferior olivary nuclei – gray matter that relays

sensory information on the state of stretch of

muscles and joints to the cerebellum

� Cochlear nuclei: auditory relays

� Vestibular nuclear complex – synapses that

mediate and maintain equilibrium

� Nucleus gracilis and caneatus: where somatic

sensory information ascends from the spinal cord

to the somatosensory cortex


Medulla Nuclei

� Involved in autonomic reflex center involved in

homeostasis

� Cardiovascular control center – adjusts force

and rate of heart contraction

� Respiratory centers – control rate and depth of

breathing

� Additional centers – regulate vomiting,

hiccuping, swallowing, coughing, and sneezing


The Cerebellum

� Located dorsal to the pons and medulla

� Protrudes under the occipital lobes of the cerebrum

� Makes up 11% of the brain’s mass

� Provides precise timing and appropriate patterns of

skeletal muscle contraction subconsciously

� E.g. coordination


The Cerebellum

Figure 12.17b


Anatomy of the Cerebellum

� Two bilaterally symmetrical hemispheres connected medially by the vermis

� Contains folia – transversely oriented gyri

� Fissures subdivide each hemisphere into three lobes – anterior, posterior, and flocculonodular

� Neural arrangement – gray matter cortex, internal white matter, scattered nuclei

� Arbor vitae – distinctive treelike pattern of the cerebellar white matter


Cerebellar Peduncles

� Three paired fiber tracts that connect the cerebellum to the brain stem

� All fibers in the cerebellum are ipsilateral

� Superior peduncles connect the cerebellum to the midbrain

� Middle peduncles connect the pons to the cerebellum

� Inferior peduncles connect the medulla to the cerebellum


Cerebellar Processing

� Cerebellum receives impulses of the intent to

initiate voluntary muscle contraction

� Proprioceptors and visual signals “inform” the

cerebellum of the body’s condition

� Cerebellar cortex calculates the best way to

perform a movement

� A “blueprint” of coordinated movement is sent to

the cerebral pre-motor cortex

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