Central Nervous System

biological organ
Cephalization become more apparent in higher order species
Increase

hints of its abilities
It is about two handfuls of delicate

Brain
stem

Cerebellum

Cerebral
hemisphere

pounds)
Average adult female’s brain weighs about 1450 g
Brain size

thickens along the dorsal midline axis of the embryo to

by neural folds

of the neural folds fuse, forming the neural tube
The tube

fourth week of pregnancy and differentiates rapidly into the CNS
The

laterally and locate between the surface ectoderm and the neural

formed, its anterior end begins to expand more rapidly than

off the three primary brain vesicles
Prosencephalon
(forebrain)
Mesencephalon
(midbrain)
Rhombencephalon
(hindbrain)
The remainder of the neural

of the secondary brain vesicles are evident
The forebrain has divided

rapidly to produce the major structures of the adult brain
The

stem
Pons
Cerebellum

stem
Medulla oblongata
All the midbrain and hindbrain structures, with the exception

enlarge in four areas to form the fluid filled ventricles
Telencephalon
Lateral

is also occurring in the relative position of its parts

that the cerebral hemispheres are forced to take a horseshoe

over and almost completely envelop the diencephalon and midbrain
The cerebral

their surfaces to crease and fold
Folding results in convolutions which

from tension on the young axons as they become arranged

are:
Cerebral hemi- spheres
Diencephalon
Thalamus
Hypothalamus
Epithalamus
Brain stem
Midbrain
Pons
Medulla
Cerebellum

CNS can be seen in the spinal cord
A central cavity

basic design except that it also contains additional regions of

gray matter changes with descent through the brain stem
The cortex

the expansion of the neural tube
They are continuous with each

cerebrospinal fluid and lined by ependymal cells

chambers that reflect the pattern of cerebral growth
One lateral

separated only by a thin median membrane called the septum

(foramen of Moro)

fourth ventricle via the canal-like cerebral aqueduct that runs through

the pons and posterior to the medulla, is continuous with

Pons

fourth ventricle
Paired lateral apertures
Median aperture
Apertures connect the ventricles to the

Pons

Subarachnoid space is filled with
cerebrospinal fluid to surround the brain

the brain
These two structures account for about 83% of the

is marked by elevated ridges of tissues called gyri separated

people
The median longitudinal fissure separates the hemispheres
The transverse fissure separates

lobes
Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe
Insula (located within the lateral sulcus)

Insula

Lateral sulcus of the hemisphere
Insula

sulcus
Parieto- occipital sulcus
Lateral sulcus
Transverse fissure

showing the Parieto- occipital sulcus

fossa
The anterior parts of the temporal lobes fill the middle

nervous system
It enables us to perceive, communicate, remember, understand, appreciate,

cells bodies, dendrites, and unmyelinated axons (plus support cells and

brain mass
The cortex contains billions of neurons arranged in six

cortex, white matter, and basal nuclei within the cerebral hemispheres

reveals that there are both specialized and diffuse areas of

functional areas
Motor areas / control voluntary motor function
Sensory areas /

the two hemispheres are not entirely equal in function, instead

part of the frontal lobes
Motor areas include the primary motor

precentral gyrus of the frontal lobe of each hemisphere
Large neurons

form the massive voluntary motor tracts called the pyramidal, or

Dendrites

Table 11.1

of the pyramidal cells located within the primary motor cortex

cortex of each hemisphere
Most of the neurons in these gyri

right side of body
The image is useful to conceptualize areas

motor cortex paralyzes the muscles controlled by this area
If the

patterned nature (typing or piano)
The premotor cortex coordinates the movement

motor cortex
Also influences motor actively more directly by supplying about

voluntary actions that depend on sensory feedback

of the motor skills in that region
Muscle strength and the

in only one hemisphere (usually left)
A special motor speech area

similar area in the opposite hemisphere become active as we

the eyes
Engaged when we look quickly at something, as in

the parietal, temporal and occipital lobes

postcentral gyrus of the parietal lobe
Neurons in this gyrus receive

root of spinal cord
Synapse with 2nd order neurons in medial

information and identify the precise area of the body being

right hemisphere receiving inputs from the left side of the

particular body region is related to how many sensory receptors

conscious ability to feel and localize touch, pressure, and vibrations

somata- sensory cortex and has many connections with it (Broadmann

of what is being felt relative to its size, texture

(coins, keys) without having to look at them
Someone with damage

the posterior and medial portions of the occipital lobe

on the medial aspect of the occipital lobe buried within

primary visual cortex receives visual information that originates on the

represented on the left visual cortex, the left half on

a series of cortical areas that process visual input
The processing

encompasses much of the occipital lobe (18, 19)
Communicating with the

light of past visual experiences so that we might recognize

far forward from the occipital lobe into the temporal and

of the entire temporal lobe and is responsible for recognizing

cortex to the postcentral gyrus and perceives spatial relationships among

important for spatial perception
The superior part of the lobe calculates

to the visual association areas results in an ability to

superior margin of the temporal lobe, primarily inside the lateral

ear transmit impulses to primary auditory cortex
Impulses related to loudness,

the primary auditory area Broadmann 22
This area evaluates and classifies

association areas lies in the center of Wernicke’s area
This functional

to comprehend speech

awareness of tase stimuli
Broadmann 43
It lies on the roof of

the sense of balance; specifically the position of the head

of the cerebrum in a small region called the piriform

cavity transmit impulses that are ultimately relayed to the olfactory

called the rhinencephalon (nose brain) which includes all parts of

and some nearby structures are all components of the rhinencephalon

involved in emotions, the limbic system, which explains why smells

involved in higher-order processing of smells
Consciously identifying and recalling specific

sensory and motor areas
The name reflects the fact that some

will probably be replaced by higher- order processing areas
Higher-order processing

frontal lobe anterior to the motor area
The most complicated cortical

intentionally remembering and recalling information
The prefrontal cortex is necessary for

planning, complex problem solving, mental flexibility, social skills, appreciating humor,

mood and has close links to the emotional (limbic) part

of specific parts of the prefrontal cortex
Completion of multi-step problem

the dorsolateral prefrontal cortex just anterior to the frontal eye

ventrally, below Broca’s area

by directing our attention to the relevant information in the

found to be active in solving the most complex problems

of neuroscience that says the farther rostrally one goes in

process emotions involved in “mentalization”, the ability to understand and

is debated
Once thought to be an area of integration of

left cerebral hemisphere is involved in various functions related to

(speech production); Wernicke’s area (speech comprehension); prefrontal cortex (conceptual analysis);

involved in the mechanics of language, act in the creative

are not well understood
Some parts function in language and some

every task and it appears the hemispheres share memories and

hemisphere has greater control over language abilities, mathematical abilities, and

are right-handed
In the remaining 10% the roles of the hemispheres

almost instantaneous communication with one another via connecting fiber tracts

matter deep to the gray matter of the cortex provides

bundled into large tracts
These fibers and the tracts they form

hemispheres
Projection tracts connect higher & lower areas of CNS
Projection
Fibers
Commissure
Fibers

enabling them to function as a whole
The Corpus callosum is

connect adjacent gyri or cortical areas
Long fibers are bundled into

the CNS
Impulses from receptors and to effectors move within these

the basal nuclei beyond which the radiate through the cerebral

Thalamus

into the white matter of the cerebral hemisphere

a groups of subcortical nuclei called the basal nuclei
The main

called the lentiform nucleus

diencephalon

called the corpus striatum because the fibers of the internal

nuclei (located in the floor of the diencephalon) and the

caudate nucleus, functionally it belongs to the limbic system

neural calculators that cooperate with the cerebral cortex in controlling

cortex as well as from other subcortical nuclei
Via relays through

by the primary motor cortex
The basal nuclei has no direct

are relatively slow and sustained or patterned
The nuclei also regulated

surrounded by the cerebral hemispheres

the third ventricle
Hypothalamus
Thalamus
Epithalamus

shown with the hemispheres removed

and forms the superolateral walls of the third ventricle

held together by a mid- line commissure called the intermediate

Thalamus

Third
Ventricle

Intermediate
mass

location
Each of these nuclei has a functional specialization
Each projects fibers

relayed through the thalamus
Every part of the brain that communicates

body converge on the thalamus and synapse with at least

and relayed via the internal capsule to the appropriate area

the cerebral cortex funnel through thalamic nuclei
Ventral posterior lateral nucleus
General

group
Regulation of emotion and visceral function
Ventral lateral nuclei
Direct motor activity

integration of sensory information and projection to specific association cortices

activities, cortical arousal, learning, and memory
It is truly the gateway

brain stem
Hypothalamus

chiasma to the posterior margin of the mammillary bodies

Mammillary
bodies
Optic
chiasma

from the hypothalamus that serve as relay stations in the

infundibulum
A stalk of the hypothalamic tissue connects the pituitary gland

small size, the hypothalamus is the main visceral control center

the activity of autonomic centers in the brain stem and

association areas, lower brain stem centers, and it lies at

system to initiate most physical expressions of emotion
Physical manifestations of

receives input from the thermoreceptors located in other parts of

temperature of the blood flowing through the hypothalamus

the hypothalamus initiates mechanisms to maintain relatively constant body temperature

glucose, amino acids, hormones, and salts in the blood, the

neurons called osmoreceptors are activated
These receptors excite hypothalamic nuclei that

helps regulate the complex phenomenon of sleep
It is responsible for

nucleus (our biological clock) sets the timing of the sleep-wake

of the endocrine system
By producing releasing hormones, it controls the

inputs from the major memory-processing structures of the cerebrum, the

the roof of the third ventricle
Epithalamus

and a small, unpaired knob called the pineal body
This gland,

epithalamus
The pineal gland secretes the hormone melatonin which signals

Pinal
Body

also part of the epithalamus
Choroid
Plexus

the brain is the brain stem
From superior to inferior, the

Midbrain

Pons

Medulla
oblongata

constitute 2.5% of total brain mass
The brain stem has several

as the spinal cord, with outer white matter surrounding an

the pons inferiorly

it into a tectum (dorsal surface) and paired cerebral peduncles
From

toward the spinal cord
The ventral part of each peduncle contains

connect midbrain to the cerebellum

that has two somewhat related functions

sympathetic reaction
The gray matter is a link between the amygdala

rate
Skyrocketing blood pressure
Wild fleeing or defensive freezing
The flexing of

response to visceral pain (as when nauseous) during which it

mattercontains cell bodies of motor neurons that contribute to two

largest of these nuclei are the corpora quadrigemia which raise

Corpora
quadrigemia

visual reflex centers that
coordinate head and eye movements when following

Superior
colliculus

from the hearing receptors of the ear to the sensory

Inferior
Colliculus

are two pigmented nuclei, the substantia nigra and the red

to the cerebral peduncle
It is the largest nuclear mass in

pigment, a precursor of dopamine a neurotransmitter released by these

and the cerebral aqueduct
It reddish hue is due to its

motor pathways that effect limb flexion
The red nuclei is the

between the midbrain and the medulla oblongata
Pons

fourth ventricle
It is chiefly composed of conduction tracts
The deep projection

Pons

superior-inferior pathway between the higher brain centers and the spinal

Pons

the motor cortex and the cerebellum
These fibers are orientated dorsally

Middle
Cerebellar
peduncles

nerve
Facial nerves

formation
The pneumotaxic center is a respiratory center
Functioning with medullary respiratory

of the brain stem
Medulla
oblongata

the level of the foramen magnum
The central canal of the

form longitudinal ridges on the ventral surface called the pyramids
These

Pyramids

the fibers cross over to the opposite side before continuing

Decussation
Of pyramids

hemisphere chiefly controls the voluntary movements of muscles on the

Decussation
Of pyramids

connect the medulla to the cerebellum dorsally
The olives are oval

state of stretch of our muscles and joints to the

the groove between the pyramid and olive on each side

the Glossopharyngeal, Vagus, and portions of the Accessary nerves

cochlear nuclei which receive information on auditory inputs

associated with ascending sensory tracts
The most dominant of these are

which general somatic sensory information ascends from the spinal cord

autonomic reflex center involved in maintaining body homeostasis
The cardiovascular center
The

and rate of heart contraction to meet bodily needs

by acting on smooth muscle in the walls of the

rate and depth of breathing and maintains respiratory rhythm

attributed to the hypothalamus
The overlap is easily explained
The hypothalamus exerts

cerebrum
It accounts for about 11% of total brain mass

medulla under the occipital lobe of the cerebral hemispheres
Cerebellum

transverse fissure
It rests in the posterior cranial fossa of the

brain stem nuclei
Sensory receptors
The cerebellum provides precise timing and appropriate

connected medially by the wormlike vermis
Vermis

surface exhibits fine, parallel, pleatlike gyri known as folia
Vermis

lobe
Flocculonodular lobe* (Cannot be seen in a surface view)
Anterior
Posterior

matter
Internal white matter
Small, deeply situated paired masses of gray matter

cortex
Stellate
Basket
Granule
Purkinje
Purkinje
Granule
Basket &
Stellate

are the only cortical neurons that send their axons through

to coordinate body movements
The lobes have completely overlapping sensory and

of the body and influence the motor activities of the

with the distal parts of the limbs and skilled movements

the association areas of the cerebral cortex and appear to

apparatus of the inner ears, are concerned with maintaining balance

the cerebellum to the brain stem

ipsilateral; from and to the same side of the body

midbrain. Fibers in these peduncles originate in the deep cerebellar

the cerebellar neurons, which enables the cerebellum to be advised

medulla

the cerebellum from (1) muscle proprioceptors throughout the body and

cerebral cortex indicates its intents to initiate voluntary muscle contractions
Through

information from the proprioceptors throughout the body
Tension in muscles,

calculates the best way to coordinate the force, direction, and

its “blueprint” for coordination to the cerebral motor cortex which

the body’s performance and sends out messages to initiate the

and clumsy, unsure movements, and sometimes even impaired thoughts about

work together but span relatively large distances with the brain
They

located on the medial aspect of each cerebral hemisphere and

the brain stem and includes
Septal nuclei, Cingulate gyrus, hippocampal formation,

memories reflects the fact that these structures are linked to

brain
Two parts seem especially important in emotions
The amygdala
The

fear and then stimulating the appropriate sympathetic response to fear

facial expression in others and to detect the precise direction

thoughts and to express our emotions through gestures

as unpleasant and resolves mental conflict during frustrating tasks

retrieving memories
The structures involved, both of which are in the

memories of facts and events
It first receives information to be

based entirely on their emotional impact, especially if related to

of the brain
Most output from the limbic system is relayed

experience visceral illnesses such as high blood pressure and heartburn
The

to be happening
We are consciously aware of the emotional aspect

system explains why emotions sometimes override logic
It also explains why

of the medulla oblongata, pons, and midbrain

clustered neurons in what is otherwise white matter

columns along the length of the brain stem
Raphe
Medial nuclear (large

their far-flung axonal connections
Individual reticular neurons project to the thalamus,

impulses to the cerebrum (through relays in the thalamus) thereby

sensory tracts enhancing arousal of the cerebrum
The RAS functions in

repetitive, familiar, or weak signals
It is estimated that 99% of

inhibited by sleep centers in the hypothalamus and other neural

if its motor nuclei project to motor neurons in the

is protected by
Bony enclosure / skull
Menbranes / meninges
Watery cushion

external to the central nervous system organs

vessels and enclose venous sinuses
Contain cerebrospinal fluid
Form partitions within the

external to the central nervous system organs

strongest of the meninges
Where it surrounds the brain it is

the inner surface of the skull
The deeper meningeal layer forms

in certain areas where they enclose the dural sinuses
The dural

inward to form flat septa that anchor the brain to

attaches to the crista galli of the ethmoid bone

runs along the vermis of the cerebellum

between the cerebral hemispheres and the cerebellum

over the surface of the cerebrum
It is separated from the

and contains the largest blood vessels serving the brain
Since the

and into the dural sinuses overlying the superior aspect of

that is richly invested with tiny blood vessels
It is the

and spinal cord
It forms a liquid cushion that gives bouyancy

plasma, from which it arises
It contains less protein and more

plexuses form CSF
The plexuses are clusters of thin walled capillaries

and tissue fluid filter continuously from the bloodstream

and have ion pumps that allow them to modify this

150 ml is replaced every 3-4 hours
900 ml is produced

in the walls of the fourth ventricle
The motion of the

surface of the brain and cord and then returns to

a stable environment for the brain
The brain is very dependent

the extra- cellular space and neurons by
Continuous endothelium of the

tight junctions
They are the least permeable capillaries in the body
The

Basal lamina (cut)

barrier
Nutrients, such as glucose, essential amino acids, and some electrolytes,

and carbon dioxide, and other fat-soluble molecules that diffuse easily

ischemic attacks
Degenerative Brain Diseases
Alzheimer’s Disease / Ach deficits
Parkinson’s Disease /