Download File

The Central Nervous System
(CNS)
Physiology -II
PHL 226
1
The Human Nervous System
 It is the most important system in the body.
Major divisions of the Nervous System :
1- The central nervous system (CNS), consisting of
the brain and spinal cord.
2- The peripheral nervous system (PNS), consisting
of a network of cranial and spinal nerves which
connect the organs to the CNS.
2
The peripheral nervous system
(PNS)
Cranial Nerves
 There are 12 pairs of nerves that
originate from the brain itself.
 These nerves are responsible for
specific activities and are named
and numbered as follows:
3
Cranial Nerves
Major Functions
I
Olfactory Nerve
Smell
II
Optic Nerve
Vision
III
Oculomotor Nerve
Eye movements and opening of the eyelid
IV
Trochlear Nerve
Eye movement
V
Trigeminal Nerve
Facial sensation and jaw movement
VI
Abducens Nerve
eye movement
VII
Facial Nerve
Eyelid closing, facial expression and taste sensation
Vestibulocochlear Nerve
Hearing and sense of balance
Glossopharyngeal Nerve
Taste sensation and swallowing
Vagus Nerve
Control most viscera & glands
Spinal Accessory Nerve
Control neck and shoulder muscles
Hypoglossal Nerve
Controls tongue movements
VIII
IX
X
XI
XII
4
Spinal Nerves
 There are 31 pairs of nerves that originate
from the spinal cord.
 These nerves are responsible for specific
activities and are distributed as follows:
• 8 Cervical
• 12 Thoracic
• 5
Lumbar
• 5
Sacral
• 1
Coccygeal
5
The cranial and Spinal Nerves may be:
1- Sensory nerves (Afferent ):
 Transmits impulses from peripheral
organs to the CNS.
2- Motor nerves (Efferent ):
 Transmits impulses from the CNS to
the peripheral organs to cause an
action.
6
The Central Nervous System
The CNS consists of 2 main components:
1- The brain is responsible for integrating most sensory information and
coordinating body functions.
 Complex functions such as thinking, emotions, movement, speech, consciousness
and body temperature are controlled by different parts of the brain.
2- The spinal cord acts as a channel for signals between the brain and the rest of the
body.
7
The brain and spinal cord share some features:
1- Living nervous tissue has the consistency of jelly and requires special protection
against physical damage SO the entire CNS is encased in bone.
 The brain is protected within the cranium, while the spinal cord runs within a canal
through the vertebrae.
NOTE:
The bony covering around the brain is called the cranium, which combines with the facial
bones to create the skull.
2- Within its bony case, the entire CNS is bathed in a cerebrospinal fluid (CSF).
 CSF is a colorless fluid produced by special structures in the brain.
3- The special chemical environment of nervous tissue is maintained by the relatively
impermeable membranes of capillaries known as the blood-brain barrier (BBB).
4- There are two general types of tissue in the CNS:
o Gray matter consists of nerve cell bodies, dendrites, and axons.
o White matter consists mostly of axons, causing it to look white due to the
myelin sheathing of the axons.
8
Cells of the Nervous System
The nervous system is made up of 2 types of cells:
1- Neurons (nerve cells)
2- Neuroglia (glial cells)
9
a- Neuron (Nerve cell):
 Neuron represents the basic unit of the
nervous system.
 It is the "conducting“ cell that transmits
impulses from one part of the body to
another part.
Neuron is composed of 3 parts:
1- The cell body: Contains a nucleus
2- The dendrites:
 The dendrites are hair-like structures
surrounding the cell body.
 They conduct the nerve impulse toward the
cell body.
10
3- The axon (Nerve fiber):
 The axons are differ in length from a mm
to a meter.
 It carry the nerve impulse from the cell
body to another neuron or tissue.
 There is usually only one axon per
neuron.
11
b- The neuroglia (glial cells):
 The neuroglia are non-conductive cells.
 They covers some axons forming a
layer called myelin sheath.
 Myelin is composed largely of lipid
tissue SO it give white colour to the
myelinated axons.
 Myelin sheath support and protect the
neurons and provide insulations.
 Clinically, these cells are important
because they are a common source of
tumors of the nervous system.
12
Synapse
 Neurons communicate with one
another through connections called
synapses.
 Synapse is the junction between
two neurons or more.
13
Neurons, Nerves & Tracts
 Neurons are nerve cells in either CNS or
PNS
 Nerves are bundles of axons within the
PNS
 Tracts are bundles of axons within the CNS
NOTE:
There are no cell bodies in nerves or in tracts
14
Ganglia & Nuclei
 Ganglia are collections of cell
bodies within the PNS
 Nuclei are collections of cell bodies
within the CNS
15
The Brain
 The brain is the most complex part of the
human body. It is the seat of intelligence,
imagination and memory.
 It represent the control centre of the body.
 It controls everything in the body: from basic
body functions such as breathing, heart beat
and blood pressure to body movement, speech
and senses.
16
The Brain Facts:
 The entire brain weighs 1.3 Kg
 There are no pain receptors in the brain
 The brain is the fattest organ in the body
 The brain is made up of 75% of water
 The brain is composed of up to one
trillion nerve cells.
 At any given moment; the brain has 14
billion neurons firing at speeds of 450
miles per hour.
17
Brain Matter:
• The CNS has two types of tissue: gray matter and white matter.
1- Gray (Grey) matter:
 It locates on the outer surface of the brain.
 Grey matter is the major component of the CNS, consisting of the cell bodies of
neurons, dendrites and both unmyelinated and myelinated axons, and capillaries.
 It is grey because most nerves in this area lack the insulation (glial cells).
 In the living brain, gray matter actually has a pinkish-grey color due to the
presence of blood capillaries and neuronal cell bodies.
18
2- White matter:
 It locates on the inside part of the brain.
 White matter consists mostly of myelinated axons (axons covered with glial cells).
 In the living brain, white matter actually has a pinkish-white color due to the
presence of blood capillaries and myelin (glial cells).
NOTES:
 Grey matter contains cell bodies of neurons, in contrast to white matter, which
does not and mostly contains myelinated axons.
 The color difference arises mainly from the whiteness of myelin.
19
Major parts of the brain:
The brain consists of 4 major parts:
I- The cerebrum.
II- The cerebellum.
III- The diencephalon:
 Thalamus
 Hypothalamus
IV- The brain stem:
 Midbrain
 Pons
 Medulla oblongata
20
I- The cerebrum
 Cerebrum is the largest part of the brain. It
forms the major portion of the brain –
represent about 83% of brain’s mass.
 The cerebrum separates by a groove called
the great longitudinal fissure into 2
hemispheres (left and right), each of
which is divided into four lobes.
 The outer surface of the cerebrum is called
the cerebral cortex or gray matter.
Functions:
 The cerebrum is responsible for conscious
sensation and voluntary movement, as
well as advanced functions such as
thinking, learning and emotion.
21
Cerebral hemispheres
 The 2 hemispheres are joined at the bottom
of the great longitudinal fissure by a thick
band of nerve fibers called the corpus
callosum which allows communication
between the two sides of the brain.
 Each hemisphere acts contralaterally i.e.
controls the opposite side of the body SO
the right hemisphere controls the left side of
the body and the left hemisphere controls
the right side of the body.
22
Cerebral cortex
 The cerebral cortex is the outer surface of the
cerebral hemispheres (2–5 mm thick). It is
often referred to as gray matter.
 The cerebral cortex contains billions of
neurons that make connections called
synapses.
 It is very deeply wrinkled ‫متجعد‬.
 The grooves that make these wrinkles are
called sulci and the ridges between the grooves
are called gyri.
 The gyri increase the surface area of the brain
SO increase the amount of gray matter and
therefore increase the quantity of information
that can be processed.
23
Major Lobes of the Cerebral Cortex
 The cerebrum or the cerebral cortex
is further divided into 4 sections
called lobes.
 These include the frontal, parietal,
temporal and occipital lobes.
 Each lobe performs specific
functions.
24
1- Frontal lobes :
 The frontal lobes are locate at the anterior
part of the brain behind the eyes.
 They control voluntary movement, memory,
intelligence, concentration, emotions,
speech, behaviour, and intellectual
functions such as problem solving, decision
making and planning.
 There are 2 specific areas in the frontal
lobes: (Motor cortex & Broca's area)
A- Motor Cortex
 It locates in the back of the frontal lobes.
 It sends signals (motor neurons) to tell the
body (like fingers) to move.
 The top of the motor cortex controls the
bottom of the body and the bottom of the
cortex controls the top of the body.
25
B- Broca's Area (the motor speech area):
 It locates in the left frontal lobe.
 In some left handed people, Broca's area is on the
right side.
 Broca’s area is involved in translating thoughts
into speech.
 Impulses from this area control the muscles of
the mouth and larynx that enable a person to
speak.
NOTE:
 Damage of Broca's area (called Broca's
Aphasia) lead to inability to talk.
26
2- Parietal lobes :
 The parietal lobes are locate at the back of the
frontal lobes directly under the skull bone.
 The parietal lobes control the sensory information
such as touch, pressure, pain, taste and temperature.
NOTE:
 Damage to the parietal lobes can result in:
o Inability to process sensory information, such as
temperature and touch.
o Difficulty with basic skills, such as reading, writing,
and mathematics.
27
There is a specific area in the parietal lobes:
Sensory Cortex
 It locates in the front of the parietal lobe
(directly behind the motor cortex of the
frontal lobe).
 Sensory cortex is responsible for feeling
touch sensations (both pleasurable and
pain).
 Touch sensations send signals through
sensory neurons to the thalamus then to the
sensory cortex SO we can feel it.
 The bottom of the cortex is responsible for
the top of the body and the top of the cortex
is responsible for the bottom of the body.
28
3- Occipital lobes:
 The occipital lobes locate at the back of the
brain
 It controls vision and colour recognition.
 There is a specific area in the occipital
lobes:
The primary visual cortex :
 It helps to interpret the information sent to
the brain by the eyes (recognition of size,
color, light, motion, dimensions, etc.).
NOTE:
 Damage to the occipital lobes can result in
inability to identify colours.
29
4- Temporal lobes:
 The temporal lobes are locate on both sides
of the head just above the ears.
 The temporal lobes control hearing, memory
and emotions.
 The left temporal lobe also controls speech.
 There are specific 3 areas in the temporal
lobes :
A- Wernicke's Area:
 Locates in the left temporal lobe.
 It is responsible for interpreting BOTH
written and spoken speech.
NOTES:
 A person with damaged Wernicke's Area
would be unable to understand what he is
reading or hearing.
 Language comprehension locates on the left
temporal lobe.
30
B- Primary Auditory Cortex :
 It is responsible for hearing.
C- Primary Olfactory Cortex:
 It is responsible for the sense of smell.
NOTES:
 Damage to the primary auditory cortex
may lead to some hearing problems.
 Damage to the primary olfactory cortex
may lead to some problems in the sense
of smell.
31
II- The cerebellum
 Cerebellum means: Small brain.
 It locates at the lower back of the brain beneath the
occipital lobes.
 Cerebellum is the second largest part in the brain.
It represent 11% of the total brain mass.
 It divided into 2 parts or hemispheres and has grey
and white matter, much like the cerebrum.
Functions:
The cerebellum is responsible for:
 Maintaining balance.
 Coordinating movements (All motor activities in
the body depends on the cerebellum).
NOTE:
 Abnormalities in either side of the cerebellum
produce symptoms on the same side of the body.
32
III- The diencephalon
 The diencephalon locates above the
midbrain.
 It consists of 2 major parts:
a- The Thalamus
b- The Hypothalamus
33
a- The thalamus



The thalamus is a large mass of grey matter
locates under the cerebral cortex and above the
brainstem.
The thalamus connects areas of the cerebral
cortex that are involved in sensory perception
and movement with other parts of the brain and
spinal cord that also have a role in sensation and
movement.
The thalamus is responsible for pain sensation,
attention, sleep and wakefulness.
NOTE:
 The thalamus is responsible for pain sensation.
 It receives sensory impulses (pain/pressure) and
send them to the cerebral cortex where the
impulses are interpreted.
34
b- The hypothalamus



The hypothalamus locates below the thalamus just
above the brain stem.
The hypothalamus is a structure that communicates
with the pituitary gland in order to manage hormone
secretions .
The hypothalamus is critical for homeostasis (the
maintenance of the body's internal environment) as
well as controlling functions such as body
temperature, eating, drinking, sexual behavior,
sleep and emotions.
Functions:
 Controls the normal body temperature.
 Regulates the hormonal release from pituitary
gland.
 Informs the body when it is hungry, full, or thirsty.
 Regulate sleep and wakefulness.
35
Pituitary Gland:
• The pituitary gland is a small structure that is
attached to the base of the brain.
• This gland controls the secretion of several
hormones which regulate growth and
function of various organs (kidneys, breasts,
and uterus), and the function of other glands
(thyroid gland, gonads, and the adrenal
glands).
36
IV- The brain stem
 The brain stem is the smallest part of the brain.
 It is a bundle of nerve tissue locates at the base of
the brain.
 It connects the cerebrum to the spinal cord and
sends messages between different parts of the
body and the brain.
 It is the source for ten of the twelve cranial nerves
(III – XII).
 It consists of 3 major parts:
o The midbrain.
o The pons.
o The medulla oblongata.
37
a- The midbrain
The midbrain contains:
a- Auditory and Visual reflex centers.
b- 2 cranial nerves (III & IV).
 III (Oculomotor Nerve) and IV (Trochlear
Nerve): They are responsible for eyeball
movement.
Functions:
 It controls the response to hearing and sight
in addition to eyeball movement.
38
b- The pons
The Pons contain:
a- Inspiratory center which prolongs inspiration.
b- 4 cranial nerves (V – VIII).
 V (Trigeminal Nerve): It has 3 branches:
a. Ophthalmic Nerve- To upper eyelid.
b. Maxillary Nerve – To upper teeth.
c. Mandibular Nerve – To lower teeth, muscles
of mastication which are responsible for
chewing.
 VI (Abducens Nerve) – Controls eyeball
movement.
39
 VII (Facial Nerve) – Control facial expressions, taste (anterior 2/3 of the
tongue), tears , saliva.
 VIII (Vestibulocochlear Nerve): It has 2 branches:
a. Vestibular: controls equilibrium (balance).
b. Cochlear: controls hearing.
Functions:
• Control breathing.
• Coordinates eyeball movement, facial sensation, hearing, and balance.
40
c- The medulla oblongata
 Medulla is the most inferior part of the brain. It appears
as a swelling at the upper end of the spinal cord.
 It connects the brain into the spinal cord.
The Medulla contains:
a- 3 vital centers:
 Vagal center: Control heartbeat.
 Respiratory center: Control rate of breathing.
 Vasomotor center: Control diameter of the blood
vessels.
b- Other centers:
 Vomiting center.
 Coughing center.
41
c- 4 cranial nerves (IX - XII)
 IX (Glossopharyneal Nerve): Responsible for taste (posterior 1/3 of the
tongue) and swallowing.
 X (Vagus Nerve): Responsible for parasympathetic activity.
 XI (Accessory Nerve): Responsible for rotation of the head and shoulder.
 XII (Hypoglossal Nerve): Controls tongue movements (speaking, swallowing).
Function:
 The medulla oblongata controls autonomic functions such as breathing, heart
rate, digestion, blood pressure, swallowing and sneezing, vomiting and
coughing.
42
Protection of the Brain
The brain is protected by:
 Bone “Cranium”.
 Meninges.
 Cerebrospinal fluid.
43
Meninges
 The brain and spinal cord are covered by a
tissue known as the meninges, which is made
up of 3 layers: dura mater, arachnoid layer,
and pia mater.
1- The dura mater “tough mother” is the
outermost layer and is made of strong
connective tissue.
2- The arachnoid membrane is the middle
layer, a web-like structure filled with fluid
(CSF).
3- The pia mater “delicate mother” is the
innermost layer (delicate layer).
44
Functions :
 Protect the CNS.
 Protect the cerebral blood vessels.
 Contain CSF.
45
The Cerebrospinal Fluid (CSF)
 CSF is a clear colourless fluid that surrounds the
brain and spinal cord.
 It is similar in composition to blood plasma
“contains electrolytes, proteins, and glucose”.
 In the adults, the total volume of CSF is about
150 mL.
 This fluid is formed by the choroids plexuses
which is housed inside spaces within the brain
called ventricles.
Functions:
 The CSF helps to cushion (protect) the brain and
spinal cord against different types of trauma
(shock absorber).
 Nourishes the brain (carry nutrients from the
blood to the brain).
 Removes waste products from the brain.
46
NOTES:
1- Brain ventricles are a system of 4 cavities, which
are connected by a series of tubes and holes and direct
the flow of CSF within the brain.
These ventricles include:
o lateral ventricles (right and left),
o The third ventricle in the center of the brain.
o The fourth ventricle.
 CSF exits the ventricular system through several
holes in the wall of the fourth ventricle after which
it circulates around the brain and spinal cord where
is it finally reabsorbed..
47
2- Pineal Gland: The pineal gland is an
outgrowth from the back portion of the third
ventricle, and has some role in sexual
maturation, although the exact function of the
pineal gland in humans is unclear.
48
Blood-Brain Barrier (BBB)
 Is a selective permeable membrane that
separate between the blood and the CSF.
 It acts as a filter:
 It prevent the passage of most drugs, ions
and microorganisms “viruses” from the
blood into the CSF and thus into the brain.
 Lipid-soluble substances “alcohol, caffeine,
nicotine”, and glucose, oxygen, water, most
anaesthetics can pass rapidly from the blood
into brain cells.
49