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12

Darweesh Badran

Lecture Notes

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The ervous tissueYou have to know that the sheet is NOT enough, Refer to the slides please !

We previously talked about the epithelium, C.T, muscles, cartilage, bone, and blood

(out of sudden o.O) .

In this lec. We are going to discuss the basics of nervous tissue because the details

will be taken later in the neuroscience in sec. semester of the third year (inshallah 3ala

5air) .

We will start talking about the origin of the nervous tissue which is from the

embryology.

When we talked about the epi. Tissue , we said that it starts from the embryo , the

embryo was a bilaminar structure (epiblast and haypoblast) , but then under theinduction of notochords some cells moved and sandwiched themselves in between

the two layers so by this the embryo became a trilaminar structure (ectoderm ,

endoderm and mesoderm) . We also said that the C.T and the muscles grow from the

mesoderm but the epi. grow from endoderm ,ectoderm ,mesoderm .

So this ectoderm (that formed from the cells of the epiblast ) is basically formed from

the induction of the notochord that present in the middle of the back head .

It starts sending messengers that start to elevate the overlaying epiblast ,

consequently the most lateral (extreme ) part we call it the surface ectoderm , and the

middle piece starts to elevate gradually , the place that the elevation starts into we callit the neural plate , which represents the future central nervous system , as it raise

upward, the two points that separate the surface ectoderm from the "so called " neural

ectoderm they start approaching each other , at some point these two points (the

junction between the surface and the neural ectoderm) will fuse with each other .

Now the surface ectoderm is separated from the neural ectoderm and the neural crest

is between them.

The most extreme parts became the surface ectoderm.*

* The junction with the neural crest became the neural tube.

the surface ectoderm will form the epidermis keratinized stratified squamous epi.)

plus the epidermal derivatives like sebaceous gland (holocrine gland) , sweat gland ,

hair follicles ,nail .

Surface ectodermepidermisepidermal derivatives

The area that saperate the neural ectoderm and the and the surface ectoderm ( the ones

that we later named them epidermis and the neural tube ) its name become the

neural crest .

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Some cells starts to de-attach from the neural crest and they migrate else where.

Anatomically ,histlogically embroyologically and functionally any structure migrate

from one place to another ,its migration might be interrupted anywhere by any reason

, in this case we'll have either : 1- congenital malformation

e.g : testis that originally formed at the back of the abdomen region , sometimes itdoesnt take its place in the scrotum .

2. Or it might cause the ectopic tissue .

Ectopic tissue : is which the structure starts to exert its function in the wrong place

.(the tissue exist in an inappropriate place ).

e.g : when someone is having a thyroid disease , we find that the thyroid is normal but

there is another tissue like the thyroid tissue is working outside its proper place, in a

place it doesnt supposed to be there .

**e.g about cells originate from the neural crest 1) sympathetic ganglia of a nerve

.

*2) Melanocytes (the source of our skin color )

when the fetal is 10 weeks , those melanocytes go out from the neural crest to

reach the epidermis when the fetal is 11 week. ((notice here that the journey

from the neural crest to the epidermis takes 1 week)) ..those melanocyts get

interrupted and they start secreting the melanin elsewhere and thats what people call

A birthmark () .A lot of changes occur >> somites appear and give 1) sclerotomesmigrates to the

posterior medial of the body so they can make the vertebral colomn around the neural

tube .

2)dermatomytomes(derm:skin, mytomes: muscle)they form the future muscular

system and its covering skin , so the muscles will grow and the skin will accompany

this growing , in some point the muscle will stop growing and the skin will continue ,

so they (skin) will pull their nerves with them , so the innervations of muscles are

always fixed, and we count on it to instimate the origin of the muscle .

For e.g : brachial plexus (c5,c6,c7,c8,T1)(ironman age :P )

The nerves of the hand stretch them as it grow .

The sternocleidomastoid and trapezius Muscles are innervated by the accessory nerveone from the posterior part and one from the anterior , which mean that they are very

close in their innervations but functionally they are separated

*adductor magnus it has two innervationsobturator and sciatic nerves , they fused

together but they kept their function like it is .

e.g : there is a sensory part of T10 in the umbilical region so if we stick this place with

a needle and he didnt feel it , so there is a problem the rectus abdomin us take the

motor part of T10 and other nerves so both of these parts are close together but

different in function .

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**all the activeties in the body thats related to the fear , fight ,fright, it's symapathatic

, But eating ,sex,..etc . are parasymapathatic .

** the spinal cord forms from 31 pairs of spinal nerves exist in the cervical , thoracic ,

lumber and sacrococcygeal

** the brain is subdivided into partsforebrain

midbrainhindbrain

I will put the extra info. About each part but u have to memorize the devisions from

the diagram .

**Forebrain:-

1.Telecephalon :-

*Cerebral cortex : it include the whole brain

*All of the divisions of the forebrain relate to the sensing things , memory andemotions, and they are a part of the limbic system .

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2. Diencephalon: - two divisions.

**Midbrain:-

It controls lots of vital functions in human body .

**hindbrain:-

1. Metencephalpon: a)pons: it has nuclei of certain cranial nerves..

b)cerebellum: it is responsible for the balance of the body .

2.mylincephalon: Medulla : its the structure that continue growing downwards and

form the spinal cord .

Properties of the nerves: (refer to slide 4)

Excitable: they have the ability to respond to the environment, they work as

receptor to hot ,cold and pain.

Conductivity : they are able to conduct impulse from one place to the other .

Secretion: in epithilum we call a certin secrotery cells DNES (diffuse neuro

endocrine system )

e.g : the adrenaline ,norepinephren ,serotonin and GABA ..etc. all of these

are secreted by a nerve !

We can divide nerves in functionally way: ((refer to slide 5))

1.Sensory(afferent) 2.motor(efferent) 3. Interneuron(its the link between the

previous two and they r always in CNS).

*the sensory takes the stimuli from outside leading these sensations to the CNS

, the motor do the exact opposite so it should be a link between them which is

the interneuron.

The most important thing is the neuron and its structure .

*There are numerous no. of neurons in the human body, so we will divide

them according to the structure. If we do this it will be divided into 3categories .

1. Multipolar

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2. bipolar

3. unipolar

*Each neuron should have a cell body, axon and dendrites.

*The dendrites are the base of classification.

Refer to slides no. (10, 11, 12, and 13)

**if the dendrites are branching from all over the cell bodyits Multipolar

**if there is a single dendrite arrise from the body then after this single one the

branching of dendrites beginits bipolar

**if a short stem arises from the cell body and from this short stem the dendrites

dividedits pseudounipolar

MOST of neuronsMultipolar

Places with special senses(retina ,olfactory epi ,inner ear)bipolarSpinal gangliaunipolar

Before moving for the next lec. We need to be reminded of certain things.

*For example: let's take the sciatic nerve its divided into two parts , the motor

(anterior) and the sensory (posterior) , then the nerve we see is a mixed one contains a

sensory and a motor part , the sensory takes a stimuli from a certain place, the

impulses from the motor will come to the same place .

*The sensory go to the dorsal root of ganglia which is purely sensory . In other words

if we hit the anterior of any area then we are hitting the motor root, if we hit the

posterior one then we are hitting the sensory root. But actually if we hit a nerve

peripherally we are hitting both of the sensory and the motor parts. We can't

differentiate which is which except on the spinal cord.

Please refer to the slides the dr mentioned the SAME information written there

Epi >> epithelium