ANA 303 Meninges, Synapses & Blood Supply To The Brain Flashcards
The cranial meninges are composed of 3 membranous connective tissue layers namely:
Dura mater (dura): tough, thick external fibrous layer
Arachnoid mater (arachnoid): thin intermediate layer
Pia mater (pia): delicate internal vasculated layer
Dura mater is also called the__________
pachymeninx
The dura mater is adherent to the internal table of the_________
calvaria
Layers of the dura mater
external periosteal layer
an internal meningeal layer
what is the epidural space?
The internal meningeal layer is intimately fused with the external periosteal layer, but separation can occur pathologically creating an actual (blood or fluid filled) space
The____________forms dural infoldings which divide the cranial cavity into compartments, forming partial partitions (dural septa) between certain parts of the brain
internal meningeal layer
list the dural infoldings of the internal meningeal layer
Cerebral falx (falx cerebri)
Cerebellar tentorium ( tentorium cerebelli)
Cerebellar falx ( falx cerebelli)
Sellar diaphragm (diaphragma sellae)
Describe the falx cerebri (shape, size and location)
is a sickle shape structure
the largest dural infolding
lies in the longitudinal cerebral fissure and separates the right and left cerebral hemispheres
Attachments of falx cerebri
Anteriorly: median plane from the frontal crest of the frontal bone and crista galli of the ethmoid bone
posteriorly: to the internal occipital protuberance
Boundaries of the cerebri falx
The superior sagittal sinus runs in its upper fixed margin
the inferior sagittal sinus runs in its lower concave free margin
It ends by becoming continuous with the cerebellar tentorium
and the straight sinus runs along its attachment to the tentorium cerebelli
Discuss the size and shape of the Cerebellar tentorium
the 2nd largest dural infolding
is a wide crescentic septum
Cerebellar tentorium separates the__________ from the cerebellum
occipital lobes of the cerebral hemispheres
Cerebellar tentorium it covers the____________ and supports the occipital lobe
upper surface of the cerebellum
The cerebellar tentorium divides__________
the cranial cavity into supratentorial and infratentorial compartments
The supratentorial compartment is divided into right and left halves by the__________
cerebral falx
Describe the Cerebellar falx and its role
is a vertical dural infolding that lies inferior to the cerebellar tentorium in the posterior part of the posterior cranial fossa
It is attached to the internal occipital crest
partially separates the cerebellar hemispheres
Describe the Sellar Diaphragm and its role
the smallest dural infolding
is a circular sheet of dura that is suspended between the clinoid processes
forms a partial roof over the hypophysial fossa in the sphenoid
The sellar diaphragm covers the pituitary gland in this fossa and has an aperture for passage of the infundibulum and hypophysial veins
The arterial supply to the dura mater travels in the_________ of the dura
outer periosteal layer
The arterial supply to the dura mater consists of:
- anterior meningeal arteries in the anterior cranial fossa
- middle and
- accessory meningeal arteries in the middle cranial fossa
- posterior meningeal artery and other meningeal branches in the posterior cranial fossa
All are small arteries except for the__________
middle meningeal artery which is much larger
Which artery supplies the greatest part of the dura?
middle meningeal artery
The anterior meningeal arteries are branches of the___________
ethmoidal arteries
The middle meningeal artery is a branch of the __________
maxillary artery
The middle meningeal artery enters the middle cranial fossa through the_____________
divides into;
foramen spinosum
anterior branch
posterior branch
Describe the Venous drainage of the dura, particularly the m.m.a and where it drains
The veins of the dura accompany the meningeal arteries
The middle meningeal veins accompany the middle meningeal artery, leave the cranial cavity through the foramen spinosum and drain into the pterygoid venous plexus
Describe the innervation of the dura in the anterior cranial fossa
meningeal branches from the ethmoidal nerves (branches of the ophthalmic nerve [V1]) supply______________
the floor and the anterior part of the falx cerebri
Additionally a meningeal branch of the ophthalmic nerve [V1] supply____________
the tentorium cerebelli and the posterior part of the falx cerebri
Describe the innervation of the middle cranial fossa
the middle cranial fossa is supplied
medially by meningeal branches from the maxillary nerve [V2]
laterally by meningeal branches from the mandibular nerve [V3]
Describe the innervation of the posterior cranial fossa
The posterior cranial fossa is supplied by
meningeal branches from the 1st , 2nd , and sometimes, 3rd cervical nerves
The arachnoid mater and pia mater are together refer to as_____________
leptomeninges
Clinical significance of the pterion
The pterion is an important area because it overlies the middle meningeal artery
Fracture to the pterion can rupture the anterior branch of this artery resulting in hematoma which exerts pressure on the underlying cerebral cortex
An untreated meningeal artery can cause hemorrhage which can lead to death in a few hours
The pia and arachnoid mater develop from a single layer of mesenchyme surrounding the embryonic brain, becoming the________________
parietal part (arachnoid mater) and visceral part (pia mater) of the leptomeninx
Describe the arachnoid mater
is a thin, avascular membrane
It is not adherent to the inner surface of the dura mater
From its inner surface thin processes called____________arise and cross the subarachnoid space
trabeculae
In between the arachnoid and the pia, is a real space called the___________
What does the space contain?
subarachnoid space
This real space contains CSF, trabecular cells, arteries, and veins
Describe the subarachnoid space
The subarachnoid space surrounds the brain and spinal cord and in certain locations it enlarges into expanded areas called subarachnoid cisterns
The arachnoid and pia enter the grooves of the brain T/F
FALSE
Unlike the pia, the arachnoid does not enter the grooves or fissures of the brain
Describe the pia mater
is an even thinner membrane
that is highly vascularized by a network of fine blood vessels
The pia is difficult to see, but it gives the surface of the brain a shiny appearance
The pia adheres to the surface of the brain and follows all its contours
Define a synapse
A synapse is described as a special zone of contact at which one neuron communicates with another
It is a specialized junction where axon terminals contact another neuron or cell type
Describe electrical transmission
In electrical transmission between nerve cells, the current generated by an impulse in one neuron spreads to another neuron through a pathway of low electrical resistance via gap junctions
In an electrical synapse, ion channels
connect the cytoplasm of the presynaptic and postsynaptic cells
Several neurons may take part in forming complex synapses encapsulated by neuroglial cells to form__________
synaptic glomeruli
The importance of electrical synapses
In the adult mammalian CNS, electrical synapses are present where the activity of neighboring neurons needs to be highly synchronized.
For example, hormone-secreting neurons in the mammalian hypothalamus are connected with electrical synapses so that they fire almost simultaneously and secrete a burst of hormones into the circulation.
Two types of synaptic transmission
electrical and chemical
Directionality of electrical synapses
Most electrical synapses
in the mammalian nervous system are believed to be the non-rectifying or bidirectional type of synapse.
What is a gap junction?
The area where the two neurons are
apposed to each other, at an electrical synapse
The channels that connect neurons at the gap junction are called
gap junction channels
The extracellular space between
presynaptic and postsynaptic neurons at an electrical synapse is___________
Compare it to the usual extracellular space
3 to 3.5 nm, which is much smaller than the usual extracellular space (about 20–50 nm) between neurons.
connexons
connex
Describe chemical synapse and its directionality
There is no continuity between the cytoplasm of the presynaptic terminal and the postsynaptic neuron at chemical synapses. Instead, the cells are separated by synaptic clefts, which are fluid-filled gaps (about 20–50 nm). The presynaptic and postsynaptic membranes adhere to each other due to the presence of a matrix of extracellular fibrous protein in the synaptic cleft.
unidirectional
What is a neurotransmitter?
Neurotransmitters are substances which neurons use to communicate with one another and with their target tissues in the process of synaptic transmission (neurotransmission).
Neurotransmitters are synthetized in and released from nerve endings into the synaptic cleft. From there, neurotransmitters bind to receptor proteins in the cellular membrane of the target tissue. The target tissue gets excited, inhibited, or functionally modified in some other way.
What is the active zone?
Active zones are the specialized release sites in the presynaptic terminal. The vesicles containing the neurotransmitter
are aggregated near the active zones.
Types of synapses
axodendritic
axosomatic
axoaxonic
dendrodendritic
symmetrical
asymmetrical
Axodendritic synapse
A synapse in which the postsynaptic membrane is on a dendrite of another neuron. This type of synapse can occur at the spine or shaft of the dendrite. About 30% of the synapses in the CNS are estimated to be axodendritic type.
Axosomatic synapse:
A synapse in which the postsynaptic membrane is on the cell body (soma) of another neuron. About 6% of the synapses in the CNS are estimated to be axosomatic type.
Axoaxonic synapse
A synapse in which the postsynaptic membrane is on the axon of another neuron
This type of synapse is rare.
Dendrodendritic synapse
A synapse in which dendrites of specialized neurons form synapses with each other.
Symmetrical synapse
A synapse in which the postsynaptic and presynaptic membranes are similar in thickness.
This type of synapse is usually inhibitory
Asymmetrical synapse
A synapse in which the postsynaptic membrane of a synapse is thicker than the presynaptic membrane. This type of synapse is usually
excitatory
The brain is supplied by
two internal carotid
two vertebral arteries
The four arteries lie within the_____________and their branches anastomose on the inferior surface of the brain to form the_________________
subarachnoid space
Circle of Willis
Internal carotid arteries arise in the neck from which artery?
the common carotid artery
Terminal branches of the ICA
Anterior cerebral arteries
Middle cerebral arteries
The anterior cerebral arteries are joined together by the__________
anterior communicating artery
The internal carotid arteries are joined by the posterior communicating arteries to the________________
posterior cerebral arteries
the cortical branches of each cerebral artery supply
branches to deeper parts of the brain, the supply a surface and a pole of the cerebrum
The cortical branches of the:
Anterior cerebral artery supply
most of the medial and superior surfaces of the brain and the frontal pole
The cortical branches of the:
Middle cerebral artery supply
the lateral surface of the brain and the temporal pole
The cortical branches of the:
Posterior cerebral artery supply
the inferior surface of the brain and the occipital pole
Describe the vertebral arteries
Where is arises from, what it forms etc.
•They arise from the first part of subclavian arteries
•They unite at the lower border of the pons to form the basilar artery
•The basilar artery ends by dividing into two posterior cerebral arteries
•Other branches such as the anterior inferior cerebellar arteries, several small pontine arteries, and the superior cerebellar arteries arise from the basilar artery
What does the basilar artery supply?
The basilar artery supply the brainstem, cerebellum and cerebrum
What’s the main blood vessel that forms the posterior circulation of the brain?
Basilar artery
