Human Nervous
System
1-Central nervous system (CNS)
Includes the brain and spinal cord
Lies in the midline of the body.
2-The peripheral nervous system (PNS)
Contains cranial nerves and spinal nerves that
Gather information from sensors and conduct decisions to
effectors. It also contains ganglia.
Lies outside the CNS
1
Homeostasis
Human
nervous
system
CNS
Spinal Cord
Endocrine
system
PNS
Brain
Spinal nerves
Ganglia
Cranial Nerves
The nervous system is divided into: CNS (brain + spinal
cord), and PNS consisting of nerves (collection of axons) &
ganglia.
2
Spinal Nerves
3
Central nervous system (CNS) Enables us
to:
1-subconsciously regulate human internal environment
2- experience emotions
3-voluntary control movement
4- perceive (be consciously aware of) your body and
your surroundings
5- high cognitive processes such as thoughts and
memory. The term cognition refers to act or process
of knowing , awareness, and judgment.
4
The CNS contains nuclei + tracts.
CNS is composed Histologicaly of :
1-Gray Matter: Consists of 100 billion neuron’s
cell bodies (nuclei ) and dendrites that are present in
brain cerebral cortex and any other nuclei
2-White Matter: Consists of axons (tracts) of
the 100 billion neuron (Myelin sheath is white)
In the spinal cord similar histological composition but
with opposite order.
The white matter is at the surface, whereas, the gray
matter lies inside.
5
Sulci, Gyri, and Fissure
• A sulcus (Latin: "furrow", pl. sulci) is a depression or sallow fissure
in the surface of the brain.
• It surrounds the gyri (convolution), creating the characteristic
appearance of the brain in humans and other large mammals.
• Large furrows (sulci) that divide the brain into lobes are often called
fissures.
6
7
The CNS is protected by:
• 1-Hair; Scalp
• 2- Cranium: The brain is protected by
the skull, and the spinal cord is
protected by the vertebral column.
• 3- Meninges
• 4-CSF
• 5-Blood brain barrier: neuronal tissue
is biochemically isolated from general
circulation by Blood brain barrier.
• Blood brain barrier=
astrocytes+PM+tight junctions.
8
BBB
• The mammalian brain restricts the entrance of ions and solutes
circulating in the bloodstream by the blood-brain barrier (BBB).
• BBB strictly limits exchange between blood and the brain
protecting from chemical fluctuations in the blood and minimizing
the possibility that blood borne substances might reach the
nervous tissue.
• BBB consists of tight junctions around the capillaries that do not
exist in normal circulation. Endothelial cells restrict the diffusion
of microscopic objects (e.g., bacteria) and large
or hydrophilic molecules (glucose /a.a/ ions) into the
cerebrospinal fluid (CSF), while allowing the diffusion of
small hydrophobic molecules (O2, CO2, steroid hormones,
alcohol).
• Cells of the barrier actively transport metabolic products such as
glucose across the barrier with carrier proteins.
• On the negative side the BBB limits the use of the drugs
9
Brain
major parts
1.Forebrain
2.Cerebellum
3.Brainstem
Identify:
•Brainstem
and its levels, medulla (open and
closed portions), pons, and midbrain.
•Fourth ventricle.
•Tegmentum of pons and midbrain.
•Base of pons.
•Tectum of the midbrain, with the inferior and
superior colliculi..
•Diencephalon, including the thalamus and
hypothalamus.
•Frontal,
parietal, and occipital lobes.
•Parieto-occipital sulcus.
•Calcarine sulcus, separating the cuneus gyrus
(above) from the lingual gyrus (below).
•Cingulate gyrus.
•Corpus callosum and anterior commisure.
•Fornix.
•Lateral Ventricle and the interventricular
foramen.
• Cerebral aqueduct.
10
•Cerebellum.
Brain major parts
I.
Forebrain
1-Telencephalone= (cerebrum)
A-Cerebral cortex
B-Basal nuclei
2-Diencephalon
A- Thalamus.
B.Hypothalamus
C. Part of pituitary gland
D. Epithalamus
II. Cerebellum
III. Brainstem
A- Medulla oblongata
B- Pons
C-Midbrain
11
The brain stem
1. Controls many life sustaining processes such as
respiration , circulation and digestion. These are called
vegetative functions , meaning functions performed
unconsciously or involuntary.
2. Origin of many cranial nerves.
3. Regulate muscle reflexes involved with equilibrium and
posture.
4. Reception and integration of all synaptic input from
spinal cord.
5. Arousal and activation of cerebral cortex.
6. Role in sleep and awake cycle.
12
The medulla oblongata
• Embryology: The
medulla oblongata
forms from the lower
(caudal) half of the
embryonic
rhombencephalon
(Hindbrain).
13

Myelencephalon: (medulla oblingata)
Medulla oblongata (3 cm) is located between pons
and spinal cord
– Medulla oblongata white matter contains
ascending (sensory)& descending (motor) tracts,
that communicate between spinal cord & various
brain parts.
– Tracts decussate at an area called pyramid.
– Pyramid: Large corticospinal tracts that cause
elevation (thus called pyramid). Corticospinal
tracts control voluntary movement of limbs and
trunk.
– ‫الجزء من الجسم الذي يتصل به اليدان والرجالن من تحت الرقبه‬
14
Many
• Section of the
medulla
oblongata at
the level of the
decussating of
the pyramids.
of these tracts 90
% cross to the
contralateral side (brain
left side receives sensory
information from body’s
right side & vice versa).
15

Myelencephalon: (Medulla oblongata)
Medulla oblongata also contains the following nuclei
which constitute the following centers:
1-cardiac control center: controls autonomic
innervations of heart: heart rate and force
2- respiratory center: controls respiration rhythm
3- vasomotor centers: controls autonomic
innervations of blood vessels: vasoconstriction,
vasodilatation, diameter of blood vessels.
4- reflex centers for a-vomiting, b-coughing, csneezing, d- hiccupping, and e- swallowing.
16

Myelencephalon: (Medulla oblongata
cont.)
5-Nuclei associated with sensation: masses of
gray matter known as the nucleus gracilis and
the nucleus cuneatus. They sense touch,
pressure, vibration, conscious proprioception.
Proprioception: is the sense of the relative position of
neighboring parts of the body and strength of effort being
employed in movement
17
Posterior
Fasciculus-Medial Lemniscal Pathway
The
fasciculus cuneatus (tract
is a bundle of nerves in the spinal
cord).
Axons
in the fasciculus gracilis
and fasciculus cuneatus are fibers
whose cell bodies lie in the dorsal
root ganglia.
Fibers
in fasciculus gracilis end
in nucleus gracilis, while fibers in
fasciculus cuneatus end in
nucleus cuneatus.
The
axons band in white matter
called medial lemniscus.
18
19
20

Myelencephalon:
(Medulla oblongata
cont.)
6- The inferior olivary nucleus, which relays to
the cerebellum.
A- adjust muscle activity
B-learn new motor skills.
7- Gustatory nucleus: nuclei associated with
gustation (taste)
8- The cochlear and vestibular nuclei
21
Myelencephalon: (Medulla oblongata cont.)
– 9- Nuclei which constitute the origin of 5 cranial
nerves
– VIII or vestibulocochlear;
– IX, glossopharyngeal; 9
– X, vagus;10
– XI, accessory; 11
– XII, hypoglossal 12.
Injury of MO can be fatal.
‫اما الجرح الغير قاتل فممكن أن يؤدي الى فقد االحساس‬
‫كما ان الجرعه العاليه من الكحول ممكن ان توقف مركز‬
‫التنفس وتسبب الموت‬
22
Pons.
• Named after the Latin word for "bridge"
• (Metencephalon produces cerebellum + Pons).
• Pons is located between midbrain and Medulla oblongata.
• A-It consists of ascending (sensory) and descending (motor)
fiber tracts that pass from medulla oblongata through Pons to
midbrain and nuclei.
23
B- pons harbors nuclei for 4 Cranial
Nerve pairs:
• IV or Trochlear,4
• V or trigeminal, 5
VI or abducens,6
VII or facial, 7
24
Pons
• 1- Crainal nerve nucleus (facial VII):These lower motor
neurons innervate the muscles of facial expression and the
stapedius.
• 2-It contains apneustic & pneumotaxic respiratory centers.
Helps regulate breathing
• 3-pontine nucleus of the trigeminal nerve sensory nucleus (V).
The trigeminal nerve (the fifth cranial nerve, also called the
fifth nerve, or simply CN5) is responsible for sensation in the
face. The fifth nerve is primarily a sensory nerve, but it also
has certain motor functions (biting, chewing, and swallowing).
25
Trigeminal nerve (yellow)
Signals
from
cerebral cortex
related to
voluntary
movement are
relayed through
several pontine
nuclei to
cerebellum
26
4-
The trochlear nerve is a
somatic efferent nerve controls the
superior oblique muscle of the eye
5-The abducens nerve or
abducent nerve (the sixth cranial
nerve) is a somatic efferent nerve
that controls the movement of the
lateral rectus muscle of the eye, in
humans.
Inferior
view of the human brain,
with the cranial nerves labeled. 27
Located
Midbrain
between Diencephalon and pons (brain stem).
28
Midbrain (Product of mesencephalon)
• It contains the
following nuclei
• A-the corpora
quadrigemina nuclei:
are 4 rounded
elevations on the
dorsal surface of mid
brain.
29
Midbrain
(mesencephalon)
corpora
quadrigemina
nuclei
superior colliculi
visual reflexes)
inferior colliculi
auditory information
• A-The corpora quadrigemina nuclei
• 2 upper: the superior colliculi are involved in visual reflexes:
1. receive visual information then deliver it to thalamus (Lateral
geniculate nuclei)
2. control reflex movement of the eye, head, neck, in response to
visual stimulus.
• 2 inferior colliculi are relay centers for auditory information:
• 1- receive auditory information then deliver it to thalamus (Medial
geniculate nuclei)
• 2- control reflex movement of the head neck trunk in response to
voice stimulus.
30
Midbrain (mesencephalon)
cont.
• B-red nucleus: gray matter connected to the
cerebrum and cerebellum by fibers and is
involved in motor coordination
Controls
muscles tone and limb position.
31
Midbrain (mesencephalon)
cont.
C-Substantia nigra:
neurons that
release dopamine,
they are connected
to the basal nuclei
by fiber tract called
nigrostriatal
32
Cerebellum
• The cerebellum consists of
two deeply-convoluted
hemispheres.
•
Although it represents
only 10% of the weight of
the brain, it contains as
many neurons as all the rest
of the brain combined.
(hundred billion nerve cell)
• Outer gray matter and
inner white matter
33
Cerebellum
• It is connected to Telencephalone (cerebrum) by fibers
going though red nucleus (midbrain) to thalamus to
motor area’s in cerebral cortex.
• It is connected by fibers to Pons, medulla oblongata, and
spinal cord.
• It receives information (sensory input) from
proprioceptors (receptors that sense the position) present
in muscles, tendons, and joints, then it sends motor
impulses out the brain stem to the skeletal muscles.
• Thus it works together with basal nuclei and motor area’s
in cerebral cortex to coordinate movement.
34
Cerebellum functions
it is needed to coordinate skeletal muscle movements.
1-It is needed to coordinate movements of different joints during the
move.
2-It is needed for Proper timing and force needed for limb position.
3-To evaluate how well movements initiated by motor areas in
cerebrum are actually being carried out correctly, the cerebellum
detects discrepancies. It then sends feedback signals to motor areas
in cerebral cortex, via its connection to the thalamus. The feedback
signals help correct errors smooth movement and coordinate
complex sequence of skeletal muscle contractions.
4-All skilled muscular activity from speaking to dancing.
35
– Ataxia: People with damaged cerebellum are able to
perceive the world as before and to contract their muscles,
but their motions are jerky and uncoordinated.
– Unable to touch their nose with their finger or to put the
food in their mouth, find keys by touching their pocket.
– Change in speech pattern
– ‫الكحول يثبط المخيخ وبالتالي يظهر الناس اغراض االتاكسيا‬
36
DIENCEPHALON :is the second
part of Forebrain
Extends
from brain stem to Cerebrum
37
Diencephalon
together with
cerebrum constitute
forebrain.
Diencephalon is
almost completely
surrounded by
cerebral
hemispheres.
The third ventricle is
located within the
diencephalon.
38
Forebrain ( Prosencephalon) first part is
.
DIENCEPHALON
• Diencephalon
consists of:
• 1. Thalamus.
‫تعني الحجرة الداخلية‬
• 2.Hypothalamus
• 3. pituitary
gland
• 4. Epithalamus
39
The thalamus
The thalamus composes 4/5
diencephalon (80%).
The thalamus is hanging on top
of the brainstem, near the
center of the brain, with nerve
fibers projecting out to the
cerebral cortex in all
directions.
It forms most of the walls of
3rd ventricle.
40
The thalamus
1. The thalamus acts primarily as a relay center through which all
sensory information (except for olfaction- smell) passes on the
way to the primary sensory areas of the cerebral cortex.
2.
Maintenance of consciousness
3. Signals from the cerebellum and basal nuclei pass through
thalamus on the way to the primary motor areas of the
cerebral cortex.
41
Thalamus
42
• The basal ganglia and cerebellum are large collections of nuclei
that modify movement on a minute-to-minute basis. Motor
cortex sends information to both, and both structures send
information right back to cortex via the thalamus. (Remember,
to get to cortex you must go through thalamus).
• The output of the cerebellum is excitatory, while the basal
ganglia are inhibitory. The balance between these two systems
allows for smooth, coordinated movement, and a disturbance in
either system will show up as movement disorders.
43
44
Thalamus contains the following nuclei
1. E.g Lateral geniculate nuclei relay visual
information coming (from each optic nerve) before
it goes to occipital region.
2. Medial geniculate nuclei relay auditory information
before it goes to temporal region.
3. Intralaminar nuclei : alertness and arousal (being
reactive to stimuli) from sleep in response to any
strong stimulus. (Activation of cerebral cortex from
brain stem and RAS.
4. Ventrobasal complex : sensory relay area
45

Diencephalon
• 2-Epithalamus This part
represents dorsal portion
of Diencephalon. It
contains:
• A- Choroid plexus that
secretes over 3rd ventricle
(forms CSF)
• B- Pineal gland that
secretes melatonin
(controls biological clocks).
46
3-Hypothalamus
• Hypothalamus is diencephalon’s most inferior portion. Located
below the thalamus, it forms the floor and part of the lateral walls
of the 3rd ventricle. It has 6 major functions:
1- Regulation of emotional and behavioral pattern
• It contains neural centers that controls _working together with
limbic system- thirst, hunger, body temperature, sleep, wakefulness,
sexuality, emotions (pleasure, pain, fear, anger and satiety ‫)الشبع‬
2-Production and Regulation of Hormones
Regulation of pituitary gland (pituitary gland is beneath it).
3-Regulation of ANS (act with medulla oblongata). Therefore
Hypothalamus controls visceral activities such as
A. Regulation of heart rate.
B. Movement of GI tract.
C. Contraction of urinary bladder.
D. Regulation of body temperature.
47
4-Regulation of circadian rhythm: Sleep and
wakefulness
5- Regulation of eating and drinking
• E.g Stimulation of lateral hypothalamus makes us eat
while stimulation of medial hypothalamus makes us stop
eating.
6-Regulation of body temperature
• E.g : cooling Anterior lobe causes shivering (somatic
motor response) while heating it results in
vasodilatation, salivation, sweat glands secretion
(regulated by sympathetic nerve).
• Damage to the hypothalamus is quickly fatal as the
normal homeostasis of body temperature, blood
chemistry, etc. goes out of control.
48
The second part of Forebrain (prosencephalon) is (cerebrum also
called Telencephalon)
Cerebrum : is the largest part of the brain.
• It comprises 80% of brain weight (1.5 kilos).
• The cerebrum consists of two large cerebral hemispheres due
to Longitudinal fissure.
• Right hemisphere
• Lift hemisphere
• hemispheres include cerebral cortex, white matter, basal
nuclei.
49
• The 2 cerebral
hemispheres cover the
diencephalon,
midbrain, & a portion of
hindbrain. Adult brain
contains 100 billion
neurons, weighs 1.5 kg.
• The two hemispheres
are connected by a
large fiber tract called
the corpus callosum
Although
the brain is only
about 2% of the total body
weight in humans, it receives
15-20% of the body's blood
supply.
50
• The cerebral cortex directs the brain's higher cognitive
and emotional functions.
• The cerebral cortex is a thin but highly convoluted outer
layer of gray matter that covers the cerebral
hemispheres.
• It is followed by white matter (axons), and another gray
matter (basal nuclei) located deep within cerebral white
matter.
– White matter is composed of descending tracts and
ascending tracts
51
Central
Sulcus
Longitudinal
Fissure
Sylvian/Lateral
Fissure
Transverse
http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg
Fissure
http://www.dalbsoutss.eq.edu.au/Sheepbrains_Me/human_brain.gif
52
Cerebrum white matter has three types of tracts:
• 1- Association tracts : axons that conduct nerve
impulses between gyri in the same hemisphere.
• 2- Commissural tracts: such as corpus callosum
axons that conduct nerve impulses from gyri in the
one hemisphere to corresponding gyri on the other
hemisphere.
• 3-Projection tracts: axons that conduct nerve
impulses from cerebrum to lower parts of CNS
(thalamus, brainstem, and spinal cord).
53
54
(Telencephalone): Basal nuclei
Basal Nuclei/basal ganglia:
• These are 3 masses of gray matter located
deep within cerebral white matter within each
cerebral hemisphere.
•
55
Basal nuclei functions:
1-controls voluntary muscle movements.
• Inhibiting muscle tone (It helps to maintain posture)
through out the body .
• Selecting and maintaining purposeful muscle activity
while suppressing useless or unwanted patterns of
movement.
2- Non motor functions: Influence cortical functions
including limbic, cognitive and linguistic
Basal nuclei receive input from cerebral cortex.
Basal nuclei sends output to the primary motor areas of
the cerebral cortex via neural connection with the
thalamus.
56
Basal nuclei inhibits the thalamus to eliminate useless
or unwanted movement.
Parkinson: a degenerative disorder of the central
nervous system. It results from the death of
dopamine-generating cells in midbrain; causing
deficiency of dopamine (NT) in basal nuclei.
Because basal nuclei lack enough dopamine to exert
its normal role three motor disturbances result
1-increase in muscle tone,
2- involuntary unwanted movement (tremor).
3- slowness of movement and difficulty with walking.
57
Parts of Cerebrum: Cerebral Cortex
• Cerebral Cortex covers the cerebral hemispheres
• The Cerebral cortex is a thin but highly convoluted outer
layer of gray matter.
58
Cerebral Cortex
1-Higher-order mental functions:
– conscious and unconscious processing of
information are involved in higher-order mental
functions such as:
self-consciousness, learning, memory, thinking,
decision making, and reasoning.
2-Sensory perception
3-Voluntary control of movement
4-Personality trait
5-language.
59
17-59
• Cerebral cortex is divided into 5 Parts (lobes) by sulci which
are depressed grooves (deep folds) and gyri which are
convoluted elevated grooves.
• These lobes are frontal, parietal, temporal, and occipital,
which are visible from the surface, and a deep insula covered
by portions of the frontal, parietal, and temporal lobes.
60
• Central sulcus: also called Central groove or Central fissure.
It separates Frontal lobe from parietal lobe .
• Lateral sulcus or fissure separates Frontal and parietal lobes from
temporal lobe
• All precentral gyrus are motor (in Frontal lobe)
• All post central gyrus are sensory (in parietal lobe)
61
• Frontal lobes: three main functions: 1-elaboration of thoughts
controls personality, thinking, intellectual behavior (mental capacity),
emotions, judgment, planning, problem solving, intelligence,
concentration, and self awareness. 2-speaking and writing (Broca’s
area), 3-Voluntary control of movement.
• Parietal lobes: receiving and processing sensory input (cutaneous &
muscular sensation); interpretation of textures and shapes and
understanding speech and formulating words to express thoughts
and emotions.
• Occipital lobes are responsible for vision and the coordination of eye
movements.
• Temporal lobes Contain auditory centers ; that receive sensory fibers
from cochlea.
– Interpretation and association of auditory and visual information.
• Insula: 1-memory encoding, 2-integration of sensory information
(principally pain) ) with visceral responses 3-coordinate
cardiovascular response to stress (Sympathetic and Parasympathetic
systems).
62

Functional organization of Cerebral cortex
• Sensory, motor and integrative signals are
processed in certain regions of cerebral
cortex.
• Sensory areas: receive sensory information
and are involved in perception: which is
conscious awareness of sensation.
• Motor areas: execute voluntary movement
63
Sensory areas are two types:
• 1- Primary sensory areas: receive sensory info.
that has been relayed from peripheral sensory
receptors through lower regions of the brain.
• 2- Sensory association areas: receive sensory
information from primary sensory areas and
other regions of the brain. They monitor,
interpret and integrate the information to
generate meaningful pattern of recognition
and awareness.
64
• e.g visual association area: monitor activity of
visual cortex, you see c, a, r by stimulation of
receptors in your eye which lead to stimulation
of neurons in visual cortex.
• The visual association area interpret them as
car otherwise they are meaningless.
• A person with damaged primary visual area
would be blind, but a person with damaged
visual association area might see normally yet
be unable to recognize ordinary objects such as
a lamp just by looking at it.
65
Primary
Somatosensory
Cortex/ Postcentral
Gyrus
Somatosensory
Association Cortex
Primary
Gustatory
Cortex
Modified
from:
http://www.bioon.com/book/biology/whole/i
mage/1/1-8.tif.jpg
66
Important sensory areas
• 1-Primary somatosensory area: A region in cerebral cortex in the
postcentral gyrus of the parietal lobe of the cerebrum that receive
sensory information from thalamic nerve projections. Primary
somatosensory area can localize the point of the body where somatic
sensation originate.
• Sensation from the surface of the body such as touch, pressure,
vibration, itch, tickle, temperature, cold, heat, pain, and
proprioception: awareness of body position (joints and muscle
position).
• Afferent neurons relay information to somatosensory cortex.
• Each region within the somatosensory cortex receives the
somesthetic and proprioceptive input from a specific area of the
body. This distribution is called sensory homunculus.
• The body is represented upside down on the somatosensory cortex
67
and different parts of the body are not equally represented.

68
• The exaggerated size of the face , tongue,
hands, and genitalia indicates the high
degree of sensory perception associated
with these body parts.
• Simple awareness of touch, pressure,..ext
is detected by the thalamus, but
somatosensory cortex goes beyond pure
recognition to full sensory perception.
• The somatosensory cortex, in turn,
projects this sensory input for further
elaboration and analysis to other areas
called Somatosensory association areas.
• These can perform simultaneous
appreciation of texture, firmness,
temperature, shape, position and location
of the object you are holding
69
Important sensory areas cont.
2- primary visual area: Receives visual information that
originates on the retina
3- primary auditory area
4-primary gustatory area
5- primary olfactory area
70
Motor areas
• Motor areas: Motor output flows from anterior
part of each hemisphere.
• Primary motor area: A region in cerebral cortex
in the precentral gyrus of the frontal lobe of the
cerebrum that control voluntary contraction of
specific skeletal muscles or groups of muscles.
• Motor homunculus represents the distribution of motor output
from the primary motor cortex to different parts of the body.
• The fingers , tongue, are exaggerated, indicating the fine degree
of motor control over these body parts, compared to trunk and
lower extremities which are not capable of such complex
movement.
71
72
Motor areas cont.
73
Other brain regions beside the primary motor
cortex are important in motor control
• Lower brain regions and spinal cord control
skeletal muscle activity, such as maintaining
posture.
• Some play a role in maintaining and coordinating
voluntary activity that the primary motor cortex
has set in motion.
• Although primary motor cortex can activate
motor neurons to bring about voluntary muscle
contraction, the primary motor cortex does not
initiate the voluntary muscle contraction alone.
74
•
•
1.
2.
3.
•
The primary motor cortex is activated by widespread
pattern of neuronal discharge, the readiness potential ,
which occurs about 750 msec before electrical activity is
detected in the primary motor cortex .
These higher motor areas which all command the primary
motor cortex include:
Posterior Parietal Cortex
Secondary/supplementary motor areas
Premotor cortex
Cerebellum sends to motor areas of the cortex input
thereby exerts a role in planning, initiating, and timing
certain kinds of movements.
75
76
77
•
Secondary/supplementary motor areas: plays preparatory
role in programming complex sequence of movements.
•
Premotor cortex is important in orienting the body and
arms towards specific target. To command the primary
motor cortex to bring about the appropriate skeletal
muscle contraction, the Premotor cortex must be informed
of the body position in relation to the target. The Premotor
cortex is guided by sensory input processed by Posterior
Parietal Cortex.
•
No single region is responsible for voluntary movement.
78
Initiating and executing purposeful voluntary movement actually
include complex neuronal interplay involving output from the motor
regions guided by integrated sensory information: Picking up an
apple
• Your memory tells you the fruit is in the bowl.
• Your memory tells you that the bowl is on the table, on
kitchen.
• Sensory systems, coupled with your knowledge based on past
experience enables you to distinguish the apple from other
fruits in the bowl.
• On receiving this integrated information, motor system issues
commands as needed, based on continual updating provided
by sensory input about the position of your body relative to
the goal.
• Then there is the issue of motivation and behavior.
• Why are you reaching the apple in the first place? Is it
because you are hungry ( detected by the neural system in the
hypothalamus)?or because you saw someone eating? Why
79
did you choose the apple not banana?

Language
• Broca’s speech area : Motor area of the brain that is located in the
frontal lobe. It translates thoughts into speech.
• Broca’s speech area is involved in articulation ‫ نطق‬of speech
• Neuronal circuits between Broca’s speech area, and primary motor
area activate muscles of larynx, pharynx, mouth and breathing.
• People who suffer stroke in Broca’s speech area can still have clear
thoughts but are unable to form words. (non fluent aphasia).
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Wernicke’s area : posterior language area:
• interpret the meanings of speech by recognizing spoken words and
written language.
• Contributes to verbal communication by adding emotional content
such as anger or joy to spoken words.
• Further more it is responsible for formulating coherent pattern of
speech that are transferred via bundle of fibers to Broca’s area, which
in turn controls articulation of speech.
• Wernicke’s area receives input from visual cortex in occipital lobe,
pathway important in reading comprehension, and in describing
objects as seen, as well as auditory cortex in temporal lobe , a
pathway essential for understanding spoken words. Wernicke’s area
also receives input from Somatosensory cortex, pathway important
to read Braille.
• People who suffer stroke in Wernicke’s area can still speak , but
cannot arrange words in coherent fashion. (fluent aphasia) words
salad.
81

Language: Speech areas
in left hemisphere
• Q1 What will happen if there is damage in Broca’s area?
• A1 Broca’s aphasia: People are reluctant to speak and
their speech is slow, their comprehension is intact, they
understand the sentence but are unable to speak it out.
• Q2 What will happen if there is damage in Wernicke’s
area?
• A2 Wernicke’s aphasia: rapid and fluent speech but
meaningless. People cannot understand spoken /written
language. Comprehension is damaged, they do not
understand their own words.
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Broca’s
speech
area : located in
the frontal lobe.
Wernicke’s
area
Located at the
left cortex at the
junction of
parietaltemporaloccipital lobes.
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Important association areas
The motor and sensory areas account for only
about half of the total cerebral cortex. The
remaining areas called association areas are
involved in higher functions.
There are three association areas
1- the prefrontal association cortex
2- The parietal-temporal-occipital association
cortex
3- The limbic association cortex
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Prefrontal cortex: association area
• Front portion of the frontal lobe just anterior to
premotor cortex.
• Role in:
1-Creativity: Performs cognitive functions
– All aspects of thinking and perceiving
– Remembering and recalling information
2- Planning for voluntary activity
3- decision making (that is weighing consequences of
future actions and choosing between different options
for various social or physical situations.
– 4- Personality trait:
– 5-Also related to mood: Has close links to the limbic
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part of the forebrain.

The
yellow
represents
The
prefrontal
cortex
(PFC)
Which is
the anterior
part of the
frontal
lobes of the
brain
15-86
The parietal-temporal-occipital association
cortex
• Lie at the interface of the three lobes.
• It pools and integrate somatic, auditory and
visual sensations projected from these three
lobes for complex perceptual processing.
• It is involved in language pathway connecting
Wernick’es area to auditory and visual
cortices.
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Important Association Areas cont.
1. Somatosensory association area: determine
shape and texture of an object by feeling it. Store
memory about it.
2. Visual association area: relates present and past
visual experience.
3. Facial recognition area: recognize people by face.
4. Auditory association area: recognize sound as speech or
music :Lies in the center of Wernicke’s area
5. Visceral Association Area: Insula conscious perception of
sensations from the internal organs. (i.e full bladder)
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Motor
Frontal
lobe
cortex
(control of
skeletal muscles)
Prefrontal
cortex
(decision making,
planning)
Somatosensory
cortex
(sense of touch)
Parietal
lobe
Sensory
association
cortex (integration of
sensory information)
Visual
association
cortex (combining
images and object
recognition)
Broca’s
area
(forming speech)
Temporal
Auditory
lobe
Occipital
lobe
cortex (hearing)
Visual
Wernicke’s
area
(comprehending language)
cortex
Cerebellum (processing visual
stimuli and pattern
recognition)
89
15-90
Cerebral lateralization
Motor and sensory fibers originating from the left
hemispheres controls the right side of the body.
Motor and sensory fibers originating from the right hemispheres
controls the left side of the body.
Cerebral
lateralization is the specialization of function in each hemisphere.
Each hemisphere tends to be specialized for certain tasks.
Higher-order centers in both hemispheres tend to have different but
complementary functions.
 Due to decussation (Crossing Over) of spinal tracts (fibers) the left
hemisphere of the forebrain deals with the right side of the body and vice
versa.
 Each hemispheres receives information from both sides of the body
because hemispheres communicate via called corpus callosum (Large
tract composed of 200 million fibers) and vice versa.
91

Cerebral dominance: most language and analytical
abilities reside in the left hemisphere.

Right hemisphere is specialized with different
tasks so right and left hemispheres are
complementary to each other not one dominant
and the other subordinates.

Cerebral lateralization term is better used than
Cerebral dominance.
Cerebral lateralization : 90% of population are
right handed so the control is exerted by left
hemisphere, that leaves only 10% left handed.

92
Functional Brain Systems
• Networks of neurons functioning together
– The limbic system – spread widely in the forebrain
– The reticular formation – spans the brain stem
15-93
The limbic system
Parts in the brain involved in emotions and motivations are:
A-Hypothalamus (in Diencephalon)
B-limbic system
The limbic system: is a group of tract and nuclei along the
boarder between cerebrum and Diencephalon.
Is made up of:




A-Hippocampus
B- Amygdala
C- Septal nuclei
D-Cingulate gyrus
Fornix
and other
tracts link the
limbic system
together
94
• The system functions in
• 1- Establishing emotional state: limbic system appears to be a
center of emotions (e.g., fear).
• 2-Memory storage and retrieval
95
• 3-Olfaction

Functional Brain Systems – The
Reticular Formation
• Network of nuclei and fibers scattered within brain stem
(midbrain, Medulla oblongata, and pons), thalamus and
hypothalamus that functions as reticular activating system
(RAS).
15-96
Reticular formation
• RAS controls arousal of the cerebral cortex in response to
incoming sensory information.
• RAS is involved with consciousness, sleep and awake.
• They are activated in non specific manner by any modality
sensory information.
• Nerves from RAS project to cerebral cortex resulting in
nonspecific arousal to sensory information.
• General anesthetics produce unconsciousness by depressing
RAS
97
Reticular
formation
Widespread
connections
Ideal for
arousal of the
brain as a
whole
98
Spinal Cord

Extends from skull (foramen magnum) to the
first lumbar vertebra. ‫لو دخلت االبرة لمستوى اعلى‬
‫يحدث شلل للمريض‬
99



The spinal cord is
composed of:
1-Outer white matter
(myelinated axons give
white matter its color. It
consists of ascending
(sensory)& descending
(motor) tracts.
2- Inner gray matter (Cell
bodies and short
unmyelinated fibers give
the gray matter its color).
100

The fiber tracts are named to indicate whether they are
ascending or descending.
ascending (sensory): if the prefix spino comes first then it
indicates sensory fiber, this prefix will be followed by the
name of the brain region where the spinal cord fiber first
synapes.
E.G spinothalamic fiber synapses in thalumus.



descending (motor) tracts: the word spinal comes second
after the name of the brain region that gives rise to the fiber
first.
E.G lateral corticospinal tract begins in cerebral cortex and
descends the spinal cord
101
102


The spinal cord has two main functions
1-Center for many reflex actions
2-Means of communication between the brain
and spinal nerves: the ascending tracts
transmitting sensory information (from
receptors in the skin (cutneous receptors),
skeletal muscles, joints (proprioceptors) &
various visceral receptors).
and the descending tracts transmitting motor
information (to skeletal muscles, smooth
muscle, cardiac muscle, & glands).
103
• Descending tracts originating from brain
consists of two major groups:
• 1- Pyramidal tracts: refers to both the
corticospinal and corticobulbar tracts.
• 2-Extrapyramidal tracts.
104
• 1- Corticospinal Pyramidal tracts: descends directly without
any synaptic interruption from cerebral cortex to spinal cord
thus called corticospinal tracts.
• Cell bodies of these pyramidal tracts are located in
precentral gyrus (motor cortex)
• 80-90% of pyramidal tracts decussate at pyramids of
medulla and descend as lateral corticospinal tracts.
• 10-20% descend as anterior corticospinal tracts decussate at
spinal cord.
• The corticospinal tract is concerned specifically with
discrete voluntary skilled movements, such as precise
movement of the fingers and toes.
105
• 2-Extrapyramidal tracts: originate from any
area below cerebral cortex: ie brain stem
regions.
• Reticulospinal tracts: from RAS
• Vestibulospinal tracts: function in maintaining
balance.
106