histology #08

8/14/2019 histology #08

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8/14/2019 histology #08


Nervous tissue

Addition to the last sheet:

‐We can call the dorsal root ganglion: spinal ganglion, sensory ganglion because it attached to the dorsal root of the spinal nerve which is sensory root.

‐The sensation of muscle & joint is more important than sensation of skin.

‐Sympathetic chain a sequence of neuron found on the both side of vertebral column in the thoracic and abdomen and it contains ganglions.

‐Somatic nerve: is a motor nerve that supply skeletal muscle.

PAGE 3B:

‐There is 3 relationship between preganglionic & postganglionic:

1‐ the preganglionic neuron come from lateral horn and pass through ventral root and inter the sympathetic ganglion in the sympathetic chain and form synapse with postganglionic neuron,

this relation applied to only 14 spinal segments(T1 ‐L2).

2‐ the preganglion inter the sympathetic chain but doesn’t form synapse but it ascends to form synapse in 3 ganglion found in the cervical region, this relation applied to the upper thoracic

region.

3‐ the preganglion inter the sympathetic chain and get out of it without forming any synapse and inter the collateral ganglion (prevertebral ganglion) and form synapse with postganglion

that go to stomach, intestine, liver and pancreas.( these nerves are called splanchnic nerves), this relation applied to the lower thoracic nerve.

‐T1‐T12 & L1‐L2 have only pre & post ganglionic neuron, the rest have only postganglionic neuron.

PAGE 4A:

‐The anatomical name of sympathetic is thoraco ‐lumber out flow, the name come from the 14 spinal segments (only have lateral horn).

‐The only sourse of sympathetic are the 14 spinal segments (T1‐L2), the head & neak from upper thoracic, and leg from lower thoracic.

‐The anatomical name for parasympathetic is cranio ‐sacral out flow.

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‐Pay attention that certain cranial nerve (3,7,9,10) have parasympathetic not all.

‐The cervical, lower lumber (L3‐L5), sacral and coccygeal spinal segments don’t have lateral horn , so from where they get preganglion?

From the picture we see that preganglionic neuron come from upper thoracic(T1,T2) inter the sympathetic chain and don’t form synapse but it ascend upward inside the sympathetic chain and inter 3 ganglion in each it give branch that form synapse with cells inside the ganglion and

give postganglion.

‐If we interrupt the sympathetic chain at the root of the neck the upper half of the neck & head

will not have sympathetic, so there will be no sweating on the head, and the sympathetic dilate

the pupil of the eye to see things that are far away from you these are called Horner syndrome.

PAGE 4B:

‐Each neuron has got single dendrite or multiple dendrites & single axon.

‐Nissle body can be used as away to differentiate between dendrites & axon because it present at the beginning of dendrites but absent at axon hillock.

‐SER: site for uptake & release of (Ca++ ) & it may form vesicles but not it’s contents.

PAGE 5:

‐We say that we have well developed RER so, it must have a well developed golgi apparatus.

‐Neuron never go mitosis after bearth(post metosis).

PAGE 6:

‐Axon coud be myelinated or nonmyelinated but dendrites never be myelinated.

‐Microtubule transport protein, vesicle and mitochondria.

PAGE7:

‐Ganglion blockers: stopes the synapse and stop the transition of the impulse from pre to postganglion, it was used to treat hypertension by blocks the sympathetic that make blood vessels contract.

‐Any movement in the body doesn’t begin from the zero, it need muscle tone (partially contraction).

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‐The muscle tone of Gasrtrocnemius & soleus play an important role in conveying the blood in

the blood vessel against the gravity.

Component of any reflex : 1‐ receptor(convert any stimulus into A.P).

2‐ sensory (afferent) nerve fiber. 3‐ center (motor neuron of spinal cord). 4‐ efferent nerve fiber. 5‐ Effector organ.

‐If you measured the distance between the origin and the insertion of a muscle you will find it longer than the length of the muscle and this is mean that the muscle is stretched this simple stretch upon the muscle make it to move stretch ‐reflex the result from this stretch

reflex is partial contraction (muscle tone).

‐In the stomach there are muscle tone in the smooth muscle this mean that the muscle can form A.P. by it’s self.

‐Stretch reflex is more important and faster than withdrawal reflex .

‐Motor unit : is the motor neuron and the muscle fiber that innervated with it.

‐Small motor unit for fine movement and large motor unit for less accurate movement.

‐Motor neuron in ventral horn : 1)they are multiple polar.

2)they are golgi type one (the length of some axon reach 1‐1.5 m).

3)lower motor neuron

4) final common path : upper motor neuron is found in the brain and they are give orders

and lowe motor neuron perform that order, that’s why it’s called final common path.

‐Poliomyelitis : it’s a viral infection, the virus attack the cell body of motor neuron, and that’s lead to muscle paralysis and the atomy come from un use of the muscle.

‐The neuron receive thousands (some receive 18000 synapse) of axon at its dendrites and cell body.

‐If

the

axon

form

synapse

with

dendrite

it’s

called

axodendritic

synapse.

‐If the axon form synapse with cell body it’s called axosomatic synapse.

‐If the axon form synapse with another axon it’s called axoaxonic synapse.

Peripheral nerve has 3 sheath:

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1) epineurom: it’s the outer sheath and formed from dence irregular connective tissue.

2) perineurom: it’s dence C.T. that cover single or few bundles.

3) endoneurium: it’s a thin layer surround a single nerve fiber.

If we take a cross section to nerve fiber we will notice the following:

‐the axon will appear as a dark point and there is an empty space around it, this place was occupied by myelin, and this space is surrounded by a thin ring which represent the cytoplasm

of Schwann cell and its nucleus(peripheral dark point) and the dark point outside the ring represent the nucleus of fibroblast cell of endoneurium.

‐The greatest the diameter of the axon, the thicker myelin sheath, the faster the conduction.

‐If the neuron is myelinated or not it’s surrounded by schawann cell(in peripheral nerve) or

oligodendrocyte (in the CNS).

‐Osmium tetroxide is a pigment that stains myelin

Note: Osmium tetroxide is used to stain both proteins and lipids.

‐Motor fibers are faster in conduction than sensory.

‐The most difficult part of CNS to be stained is the axon.

‐Purkinji cells is stained by silver salt.

PAGE 13

‐Salutatory conduction is 50 times faster than continuous conduction.

‐The length between 2 subsequence nodes is 1‐2 mm

‐Schwann cell = neurolemmal sheath

‐The lack of myelin in unmylenated nerve fiber happens because the Schwann cells cannot rotate around the axon.

‐CNS become myelinated lately, while peripheral myelination begins in the 4 th month of fetal life

‐Mesaxon assemble the mesentery of small intestine.

PAGE 25 B

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Receptors of Ach is either:

• Nicotinic: they act as receptors and ionic channels at the same time. If we use

nicotin instead of Ach it will do the same function. These receptors are found in the preganglionic in autonomic NS.

• Mascerinic (M1, M2, M5): they react with mascarine which is produced by some type of mushrooms, it’s found in the heart, smooth muscle, glands.

Receptors of NE: either Alpha or Beta.

‐Ach released from all presynaptic neurons whether it’s symp. or parasymp.

‐ Adernal gland (called suprarenal glands in human) are found above the kidneys, but in animals

it’s located near the kidney.

‐It’s formed from cortex and medulla which was a sympathetic ganglion and then was modified.

‐Adrenal medulla: supporting organ of sympathetic nervous system, and there is a huge

similarity between Adrenal medulla and symp NSin there affect on the heart and walls of blood vessels but although each has different properties.

‐Adrenal medulla secrets 80% epinephrine and 20% NE

PAGE 24 A

‐ Exitability: the ability of an excitable tissue (muscle or nerve) to respond to stimulus to form action poteintial.

PAGE 24 B

‐The neuron can’t be replaced but the the peripheral nerve (axon) could be regenerated

‐Axon (around it) Schwann cells (neurolemmal sheath) endoneurium

‐If a peripheral nerve like sciatic nerve has been injured or cut do we expect the nerve to recover?

‐We say that the percentage of recovering is less than 20% (why?) because maybe a motor axon enter a tunnel of sensory axon and vice versa so we say that the result is disappointed.

‐The percent of nerve recovering in the CNS is 0%

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‐Nerve growth factor is a substance that is secreted from salivary glands and enter the blood

stream and don’t reach the brain but reach the peripheral nervous system.

‐The most important factor that appose the regeneration of axon in CNS is glia scar.

ELECTRICAL ACTIVITY OF NERVOUS SYSTEM

‐The most important thing to form an action potential or gradient potential is the presence of resting membrane potential.

‐All the cells of our body either it’s excitable or non ‐excitable has RMP.

‐Graded potential can be depolarizing or hyperpolarizing but AP is always depolarizing

‐Action potential is formed in the cell membrane of axon where we find a lot of voltage gated –channels (activated by change in membrane potential i.e. change in voltage) but graded formed

in cell membrane of dendrites or cell body where they wrap few gated ionic channel or they aren’t found at all. But we found chemical gated ionic channel (united with receptors before it’s activated)

Figure 4-2 PAGE 28

‐Stimuli have different effects on the membrane potential (‐70 to ‐60) but notice that if we decrease the potential to ‐50 or ‐40 we exceed threshold but we will not fire an action potential

because there is no voltage ionic channel.

‐Most of action potential in our body starts as graded potential ‐Depolarization opens some voltage gated Na+ channels and lead to influx of Na+ and further

depolarization lead to further opening of Na + voltage gated ionic channel until we open all Na+ channels in the site of excitation and this process results in increasing of Na+ permeability from

500 – 5000 times.

‐The molecular base of AP is opening and closing of voltage gated ionic channels and we focus here on K+ and Na+ ionic channels.

PAGE 20

The curves:

A: upstroke = rising phase = depolarization: it begins slowly until it reaches threshold the it will rise rapidly

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The peak (reversal polarizing): ‐30 mv, and here we ask why we don’t reach +61 which is Na+ eq

potential ???

1. K+ outflux which apposes Na+ influx

2. Na+

‐K+

pump. B: downstroke = falling phase = repolarization

C: after downstroke we reach RMP (‐70mv) but the K+ is still open for few mseconds and Na+

channel is still closed so we reach undershoot phase (hyperpolarization) then K+ channel is closed and we return to ‐70 (RMP)

‐The AP is spread by waves of depolarization

‐The length between 2 subsequent nodes in myelinated nerve fibers is 1‐2 mm, and that’s so

important so that we won’t lose electrical flow though myelin is strong insulator but some leakage occur.

Refractory period

‐The function of refractory period: to guarantee the propagation of AP is unidirectional away from cell body and to determine the frequency of AP.

‐The relative refractory period contain hyperpolarization phase in which the membrane potential reaches ‐80 ‐‐85 mv so we need a very strong stimulus (stronger than normal) to

oppose the influx of K+

and open Na+

channel. ‐During the refractory period we can’t fire a normal AP, but that doesn’t mean that we can’t fire action potential at all during that period.

PAGE 16

‐Electrical synapse (gap junction) is rarely found in nervous system but we can find in smooth and cardiac muscle, but not all of them. It allows the ion to move in both directions.

‐in Presynaptic element wecan call the axon terminal (synaptic knop, synaptic button)

‐The neurotransmitter (e.g. Ach) may return to the presynaptic element (reuptake)as a whole or may be degrade choline and acetate by Ach esterase and both may reuptake to the cell to

form newly Ach of it may be diffused.

PAGE 22

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‐We said in page 29 that the end plate potential (EPP) is an example of graded potential but

here we said that an AP is happening in motor end plate, we explain this that the graded

potential here is large and through the local current it can form an action potential. But in neuron ‐neuron synapse the graded potential is small so we do summation to form an AP.

Corrections for sheet 7

• The gray matter is formed of 2:

1.ventral horn

2. dorsal horn (not lateral)

• Gray commissure which has central canal.

And finally I want to dedicate this sheet to all my colleagues in the faculity of medicine and I want to thank Abduallah taqash and Hamza Jassar that helped me in writing this sheet.

m7md bader

histology #08

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