The Central Nervous System (CNS)(CNS)

Physiology -IIPhysiology -II PHL 226PHL 226

1

The Human Nervous System The Human Nervous System

It is the most important system in the body.

Major divisions of the Nervous SystemMajor 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 The peripheral nervous system (PNS)(PNS)

Cranial NervesCranial 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

4

Cranial NervesCranial Nerves Major FunctionsMajor Functions

I I Olfactory Nerve Smell

II II Optic Nerve Vision

III III Oculomotor Nerve Eye movements and opening of the eyelid

IV IV Trochlear Nerve Eye movement

V V Trigeminal Nerve Facial sensation and jaw movement

VI VI Abducens Nerve eye movement

VII VII Facial Nerve Eyelid closing, facial expression and taste sensation

VIII VIII Vestibulocochlear Nerve Hearing and sense of balance

IX IX Glossopharyngeal Nerve Taste sensation and swallowing

XX Vagus Nerve Control most viscera & glands

XI XI Spinal Accessory Nerve Control neck and shoulder muscles

XII XII Hypoglossal Nerve Controls tongue movements

Spinal NervesSpinal 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:The cranial and Spinal Nerves may be:

1- Sensory nerves (Afferent ): 1- Sensory nerves (Afferent ): Transmits impulses from peripheral

organs to the CNS.

 

2- Motor nerves (Efferent ): 2- Motor nerves (Efferent ): Transmits impulses from the CNS to

the peripheral organs to cause an action.

6

The Central Nervous System 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- LivingLiving nervous tissue has the consistency of jellyjelly 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 SystemCells 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-a- NeuronNeuron (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 neurogliab- The neuroglia (glial cells): The neurogliaThe 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

SynapseSynapse

Neurons communicate with one another through connections called synapses.

Synapse is the junction between two neurons or more.

13

Neurons, Nerves & TractsNeurons, Nerves & Tracts

Neurons Neurons are nerve cells in either CNS or PNS

NervesNerves are bundles of axons within the PNS

TractsTracts are bundles of axons within the CNS

NOTE:

There are no cell bodies in nerves or in tracts

14

Ganglia & NucleiGanglia & Nuclei

GangliaGanglia are collections of cell bodies within the PNS

Nuclei Nuclei are collections of cell bodies within the CNS

15

The BrainThe 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 KgThere 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 mattergray matter and white matterwhite 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:Major parts of the brain:

The brain consists of 4 major parts:

I- The cerebrum.I- The cerebrum.

II- The cerebellum. II- The cerebellum.

III- The diencephalon:III- The diencephalon: Thalamus Hypothalamus

IV- The brain stem:IV- The brain stem: Midbrain Pons Medulla oblongata

20

I- The cerebrumI- 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 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 hemispheresCerebral hemispheres

The 2 hemispheres are joined at the bottom of the great longitudinal fissure by a thick band of nerve fibers called the corpus corpus callosum callosum which allows communication between the two sides of the brain.

Each hemisphere acts contralaterally 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 cortexCerebral 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 synapsessynapses.

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 CortexMajor Lobes of the Cerebral Cortex

The cerebrum or the cerebral cortex is further divided into 4 sections called lobes.

These include the frontalfrontal, parietalparietal, temporaltemporal and occipitaloccipital lobes.

Each lobe performs specific functions.

24

1- Frontal lobes : 1- Frontal lobes : The frontal lobes are locate at the anterior

part of the brain behind the eyes. They control voluntary movementvoluntary 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 :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 informationsensory 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 CortexIt 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:3- Occipital lobes: The occipital lobes locate at the back of the

brain It controls visionvision 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: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 temporal

lobes 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 cerebellumII- 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: Functions:

The cerebellum is responsible for: Maintaining balance. Coordinating movements (All motormotor 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 III- The diencephalon

The diencephalon locates above the midbrain.

It consists of 2 major parts:

a- The Thalamusa- The Thalamus

b- The Hypothalamusb- The Hypothalamus

33

a- The thalamusa- The thalamus The thalamus is a large mass of grey matter grey matter

locates under the cerebral cortex and above the brainstem.

The thalamus connects areas of the cerebral cortex that are involved in sensorysensory perception and movementmovement 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 painpain sensation.It receives sensory impulses (pain/pressure) and send them to the cerebral cortex where the impulses are interpreted.

34

b- The hypothalamusb- 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: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 stemIV- 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 midbraina- The midbrain

The midbrain contains: The midbrain contains:

a- Auditory and Visual reflex centers.

b- 2 cranial nerves (III & IV). III (Oculomotor Nerve) and IV (Trochlear III (Oculomotor Nerve) and IV (Trochlear

Nerve): Nerve): They are responsible for eyeball movement.

Functions:Functions: It controls the response to hearing and sight

in addition to eyeball movement.

38

b- The ponsb- The pons

The Pons contain: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:Functions:

• Control breathing.

• Coordinates eyeball movement, facial sensation, hearing, and balance.

40

c- The medulla oblongatac- 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:The Medulla contains:

a- 3 vital centersa- 3 vital centers: Vagal center: Vagal center: Control heartbeat. Respiratory center: Respiratory center: Control rate of breathing. Vasomotor center: Vasomotor center: Control diameter of the blood

vessels.

b- Other centers:b- Other centers: Vomiting center. Coughing center.

41

c- 4 cranial nerves (IX - XII)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 activityparasympathetic activity. XI (Accessory Nerve): Responsible for rotation of the head and shoulder. XII (Hypoglossal Nerve): Controls tongue movements (speaking, swallowing).

Function: Function: The medulla oblongata controls autonomic functions autonomic functions such as breathing, heart

rate, digestion, blood pressure, swallowing and sneezing, vomiting and coughing.

42

Protection of the BrainProtection of the Brain

The brain is protected by: The brain is protected by:

Bone “Cranium”. Meninges. Cerebrospinal fluid.

43

MeningesMeninges

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” 1- The dura mater “tough mother” is the outermost layer and is made of strong connective tissue.

2- The arachnoid membrane2- The arachnoid membrane is the middle layer, a web-like structure filled with fluid (CSF).

3- The pia mater “delicate mother” 3- The pia mater “delicate mother” is the innermost layer (delicate layer).

44

FunctionsFunctions :

Protect the CNS. Protect the cerebral blood vessels. Contain CSF.

45

The Cerebrospinal Fluid (CSF)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: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:These ventricles include:olateral ventricles (right and left), oThe third ventricle in the center of the brain.oThe 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)Blood-Brain Barrier (BBB)

Is a selective permeable membrane that separate between the blood and the CSF.

It acts as a filter: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