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Neuro lab #9
Wednesday, 3/5/2011
Heeeeeey everyone….I want just to pay your attention to
study neuro sheets beside the Dr's slides in order to help u 
‫بسم هللا الرحمن الرحيم‬
Midbrain
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It is the most superior part of brainstem.
0.8 inch in length.
Connects the pons & cerebellum with the forebrain.
Features of midbrain : the most important feature is Cerebral Aquiduct
(connection between 3rd & 4th ventricles)
 External features of midbrain :
 Posterior view :
Consist of 4 round eminences 2 superior 2 superior colliculi (center
of eye reflexes)
2 inferior  2 inferior colliculi
(below it on both sides ,it pass 4th cranial nerve
"trochlear nerve" ,which is responsible for eye muscles & it emerges from
posterior then pass anterior ) & it is responsible for hearing.
Note : trochlear nerve ,the only nerve that emerges from posterior aspect
from brainstem ,but all other cranial nerves in (medulla & pons &
midbrain) emerge anterolateral aspect of brainstem.
 Anterior view : consist of
* 2 crus cerebri right & left
* interpeduncular fossa : fossa between 2 crus cerebri
There it will emerge 3rd CN (occulomotor) medial to both crus
cerebri ,which is motor nerve controls eye muscles.
Floor of this fossa  contain post perforated substance which
has perforations due to presence of vessels.
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Note : brainstem contain nuclei of (3-12) CN distributed in
midbrain,pons & medulla except optic & olfactory nerve that
emerge from higher levels not from brainstem.
 Cross-section view :
2 cerebral peduncle right & left
Each one divided ant crus cerebri "basis"
post tegmentumpost to it tectum (Which is
part of tegmentum & area of colliculi)
Substantia nigra separates crus cerebri from tegmentum .
Cerebral aquiduct separate tegmentum from tectum .
(ant to cerebral aquiduct tegmentum
Post to it tectum)
* Lower midbrain : we can see :
 2 inferior colliculi
 Cerebral aquiduct
 Substantia nigra
 Crus cerebri
Cerebral aquiduct aroun it there is grey matter ,anterior to it on both
sides there is trochlear nucleus .
Substantia nigra large motor nucleus in all the levels of midbrain
responsible for controlling the muscles tone & decrease in its
neurotransmitter "dopamine" will cause Parkinson disease)
 melanin-containing cells ,that’s the cause of its name &
its colour is black.
Note: trochlear nucleus ant to cerebral aquiduct
post to MLF
In this section we can see also mesencephalic nucleus of trigeminal.
We have took till now 4 types of trigeminal nucleus:
Sensory , spinal, motor & mesencephalic nuclei.
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Note : trochlear nerve  the only nerve emerges from post aspect ,so
trochlear nucleus will give fibers backward around cerebral aquiduct & then
cross to opposite side posteriorly to emerge from post aspect of midbrain "the
decussation will be post to cerebral aquiduct "
Medial lemniscus tracts & lateral lamniscus & trigeminal lemniscus run post
to substantia nigra .
Crus cerebri "ant to substantia nigra" contain a lot of fibers .
1. middle 2/3 of crus cerebri  corticospinal tract (we don't call it
pyramidal tracts in this level ,cause pyramids just formed in medulla)
corticobulbar tract ( from cortex to nuclei
of CN)
2. ant of crus cerebri  fronto-pontine fibers
3. lateral of crus cerebri  tempro-pontine fibers
* Upper midbrain :
Contain the same features that found in lower midbrain with some addition
of features :
 cerebral aquiduct
 substantia nigra
 superior colliculus
 crus cerebri
 red nucleus
 nucleus of occulomotor nerve  ant to cerebral aquiduct .
red nucleus  post to substantia nigra / ant to cerebra aquiduct
 large nucleus in upper midbrain in tegmentum
fresh specimen its colour red due to high vascularity &
Iron-containing pigments
 ralay from cotex & cerebellum to spinal cord ,thalamus,
reticular Formation & substantia nigra.
it has too much afferent & efferent fibers.
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Nucleus of occulomotor nerve  consist of 2 parts : parasympathetic &
motor .
1. Major motor nucleus
2. Edinger Westfal nucleus  post to major motor nucleus.
Cranial Nerves (CN)
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12 in number.
Parts of PNS (peripheral nervous system)
All exit the cranial cavity through foramina & fissures .
All originate from brain except Accessory Nerve.
Pure sensory or pure motor or mixed.
Special sensory component are associated with hearing , vision ,smelling
, balancing & tasting.
 Special motor component include those that innervate muscles derived
from pharyngeal arches ,ex : facial & masticatory muscles.
Note: General sensation "we mean" exteroceptive
(touch,pressure,tempreture,pain).
proprioceptive
(position sensation in muscles,tendons & joints)
interoceptive (related to viscera)
General motor "we mean"  to muscles & glands.
1. Sensory CN (pure sensory) contain only afferent fibers.
 I (olfactory nerve)
 П ( optic nerve)
 VШ (vistibulocochlear)
but these sensation component differ from one nerve to another.
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2. Motor CN (pure motor)  contain only efferent fibers.
 Ш ( occulomotor nerve)
 IV (trochlear nerve)
 VI (abducent nerve)
 XI (accessory nerve)
 XII (hypoglossal nerve)
 but these motor component differ from one nerve to another (that
means that some of them contain general & some of them contain special
motor component) .
3. Mixed CN  contain both afferent & efferent fibers.
 V ( trigeminal nerve)
 VII (facial nerve)
 IX (glossopharyngeal nerve)
 X (vagus nerve)
Functional component
 General somatic afferent fibers (GSA)
Transmit exteroceptive & proproceptive impulses from head & face to
somatic sensory nuclei. ex : (V , VII , X )CN .
 Special somatic afferent fibers (SSA)
Transmit sensory impulses from special sense organs of vision, equilibrium &
hearing to the brain. Ex : (VIII , II) CN.
 General visceral afferent fibers (GVA)
Transmit interoceptive impulses from the viscera to the visceral sensory
nuclei. Ex : (IX ,X )CN .
 Special visceral afferent fibers (SVA)
Transmit sensory impulses from special sense organs of smell & taste to the
brain .ex : I CN .
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 General somatic efferent fibers (GSE)
Innervate skeletal muscles of the eye & tongue (head & neck).
 Special visceral efferent fibers (SVE)
Transmit motor impulses from the brain to skeletal muscles derived from
pharyngeal arches of embryo ,include muscle of mastication & facial
expression.
 General visceral efferent fibers (GVE)
Transmit motor impulses from general visceral motor nuclei & relayed in
parasympathetic ganglion.the postganglionic fibers supply cardiac & smooth
muscles & glands.
Olfactory Nerve
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Oldest sensory modality.
1st CN .
Pure sensory.
Detects odor & influence social/sexual behaviors.
Located in the upper part of nasal cavity (roof).
Olfactory epithelium contains 3 types of cells :
1. basal cells.
2. supporting cells.
3. olfactory receptor cells (bipolar cells)these cells give 2 processes
peripheral (as dendrites) inside the mucosa to detect odor
substances & it has olfactory hairs .
central (as axons) to enter olfactory bulb.
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** The pathway in order to smell any odor substances :
A. as we said that bipolar cells give peripheral process inside the olfactory
mucosa ,in order to detect odor substances that entered the nose.
B. Detecting these odors ,it will stimulate the bipolar cells itself, transmitting
these sensory information(impulses) to central processes (axons).
C. These axons will pass through cribriform plate of ethmoid bone to enter
olfactory bulb.
D. In the olfactory bulb these axons will make the 1st synapse with mitral cells
"which is the largest nerve cells in olfactory bulb".
E. Mitral cells' axon will continue transmitting impulses through(inside)
olfactory tract until it reach certain distance to be divided into :
 Medial striaeit makes decussation & pass to the other side to enter
olfactory bulb (at the opposite side).
 Lateral striaecarry impulses to the primary olfactory center in the
cortex.(primary cotex) prepiriform cortex
 periamygdaloid nucleus
F. After reaching primary cortex ,these impulses will continue to secondary
cortex "uncus" for appreciation of smell sensation ,detecting the source of
sensation ,memory & emotional responses.
Note : olfactory bulb its ovoid structure possesses several types of
nerve cells, but the largest one is Mitral cells. ( the most important cell
here to know).
Olfactory tract  its narrow band of white matter runs from
posterior end of olfactory bulb , its projection of mitral cells' axon & it
pass posteriorly to divid into 2 striae.(medial & lateral).
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Injuries
Anosmia (loss of smell)
1. Bilateral anosmia :
 Complete loss of smell at both sides.
 Its causes : allergies(ex: during spring season) , cold & flu, ...etc.
 2 cerebral hemispheres damage.
there is no smell at all.
2. Unilateral anosmia :
 Loss of smell at one side (partial loss).
 Its causes : tumor, injuries.
 Injury of one of cerebral hemispheres.
 if there is injury at one side of (cerebral hemisphere, olfactory bulb,
olfactory nerve, olfactory tract) ,there is NO COMPLETE loss of smell
,because of the medial striae that will transfer sensation between 2
tracts(decussation)& because of lateral striae when it reaches primary
olfactory center in the cortex it will give information to both right & left at the
same time.
…...GOOD LUCK EVERYONE …
Dedicated to all people who had dedicated me in their sheets … ;))…
Done by :
Fayzah Omar Khalifeh 
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