Ch 14 The Brain & Cranial Nerves Flashcards
Where do the major parts of the adult brain are directly derived from?
The embyonic brain vesicles
The 5 seconfary brain vesicles:
(from superior to inferior)
1. telecephalon»_space; cerebrum
2. diencephalon»_space; Thylamus/ hypothalamus/ epithalamus
3. mesencephalon»_space; midbrain
4. metenscephalon»_space; pons & cerebellum
5. myelencephalon»_space; medulla oblongata
the ** spinal cord** is located below the myelencephalon
What are the parts of the brain that is already existed at birth?
1) cerebral hemisphere
2) diencephalon
3) cerebellum
4) brain stem:
- midbrain
- pons
- medulla
- oblongata
- spinal cord
At birth, the neonatal brain looks very much like that of an adult and almost all the neurons the brain will ever have are already present
we have:
100 billion neurons
100 trillion connections
supported by 10 trillion neuroglia cells
what are the 4 general structures of an adult brain?
1) cerebrum
- responsible for higher functions; contains a convoluated surface called the Cortex , is divided into left & right **hemispheres **
2) diencephalon
- consists of the thalamus, hypothalamus, limbic system and pituitary gland
3) cerebellum
- coordinate body movement & helps maintain balance and postural control
- involved in planning and coordinating movement on the fly
- also divided into hemispheres (10% brain volme but 50% of brains’ neurons)
4) brain stem
- consists of the midbrain, the pons, and the medulla oblongata, which are involved in autonomic functions
What is the cerebrum?
- convoluted urface f the cerebrum conssists of gyri and sulci (deeper sulci called fissures)
= incerase the area of the brain and form anatomical landmarks - is divided into lobes, which are named according to the bone which protects them
» has layers - the outer = gray matter (nerual cell bodies)
- the inner = white matter (myelinated axons)
(nuclei are clusters of gray matter that lie in deeper regions of the brain)
Where is the longitudinal fissure located?
Between frontal lobes (left & right hemispheres)
- precentral gyrus (primary motor cortex) is loctaed before the central sulcus, in left hemisphere
Where is the central sulcus?
Between the fronal lobes and parietal lobes
- postcentral gyrus (somatosensory cortex) is located in left hemisphere after cetnral sulcus
What are the ventricles of the brain?
During empryonic development, large hollow chambers are foremd int he cerebrum. These cavities are called the Lateral ventricles (one in each hemisphere)
- Lateral ventricles are connected via the interventricular foramen to the third ventricle in the diencephalon
the ventricles are filled w/ CSF and are lined w/ ependymal cells that circulates & absorb CSF via Cilia & microvilli
Explain the location of the third & fourth ventricles
- Lateral ventricles are connected via the interventricular foramen to the third ventricle in the diencephalon
-
Fourth ventricle is located posterior to the brainstem and is connected to the third ventricle by the cerebral aqueduct
(the fourth ventricle is contrinuous w/ the central canal of the spinal cord & contains Apertures that connect w/ the subarachnoid space) 12p
What are the ventricles lined with?
Ependymal cells filled with cerebrospinal fluid (CSF)
- ependymal cells: produces, circulates & absorve CSF via cilia & microvili
The three ways protecting the brain
1) the bony cranium
2) the meninges (= dense irregular CT)
3) cerebral spinal fuid (CSF)
What are the menings?
: the connective tissue converings of the brain & spinal cord = **the menings **
consists 3 layers
1) the dura mater(very thick - right below the skull bones)
- periosteal
- meningeal
2) the arachnoid mater
3) pia mater
2 types of protections & support of the brain
- physical/ mechanical protection:
a) cranium bones
b) cranial meninges
- the cranial dura mater
» an eternal periosteal layer
» an internal meningeal layer
(the spinal dura mater has only one)
- arachnoid mater
- the pia mater
c) CSF
= all continous with those of spinal cord
- biochemical protection:
a) blood brain barrier
= several mechanisms that isolate CNS from general circulation
(e.g. astrocytes)
b) cerebrospinal fluid (CSF)
What is dura-mater?
two layers (both fibrous)
1. outer: fused to periosteum
2. inner: meningeal layer
= between layers: tissue fluids & blood vessels including several large venous sinueses called dural sinuses
- veins of the brain open into these sinuses, which deliver venous blood to** internal jugular veins **of the neck
3 layers of the branial meninges:
**the dura mater/ arachnoid mater/ Pia mater **
**the dura mater: **
- dura mater (endosteal layer)
- dural sinus (collects blood)
- dura mater (meningeal layer)
arachnoid mater:
- arachnoid membrane
- subarachnoid space
- arachnoid trabeculae
pia mater
- is bound to surface of brain by astrocytes
what are those between inner & outer dura mater layers?
tissue fluids & blood vessels including several large venous sinuses
- the veins of the brain open into these sinuses, which deliver venous blood to internal jugular veins of the neck = all connected to your cardiovascular circuit
What is arachnoid mater?
: layer of epithelium w/ web like extensions to pia mater
- subarachnoid space = filled w/ CSF
- pia mater: covers entire surface following folds
anchored by:
- processes (branches) from astroctyes
What are the dural folds?
= sheets of dura mater that dip into deep folds of brain and return to surface
* located within dural folds: dural sinuses (collecting veins - lined with endothelial cells)
Three major dural folds:
1) falx cerebri: in the longitudinal fissure betwen two hemispheres of cererbums
2) tentorium cerebelli: between cerebrum and cerebellum
3) falx cerebelli: between two hemispheres of cerebellum
= seat belt - holds the brain in position
What does the dural sinuses contain?
- venous blood (deoxygenated blood)
- old CSF
What are the protective function of meninges?
1) dural folds: “seat belt” - hold the brain in position
2) cerebrospinal fluid: cushions, supports (floats the brain)
What are the locations and funtions of cerebrospinal fluid?
location:
- 4 ventricles
- subarchnoid space of cranium & spinal cord
- central canal of the spinal cord
functions:
- cushioning
- supporting (floating brain weighs only 50 g when supported by CSF)
- transporting nutrients, chemical messengers & waste
What is the cerebrospinal fluid produced by?
produced by choroid plexuses
= capillaries surrounded by specialized ependymall cells
located “in each of the ventricles”
So what is CSF?
- formed from blood plasma, giving it is a similar composition (sugar, oxygen and nutrients)
- is produced in the choroid plexuses in the ventricles
= capillary fluid is allowe dto filter out of the blood stream, but only certain molecules are permitte past the ependymal cells - contains gluces, O2, CO2, vitatmins, and other ions
(but low K+ cz of its size) - it reenters the blood steram through the arachnoid villi
what is the blood-brain barrier?
- the capillaries supplying the brain are very selective in what they allow to eneter the brain and CSF
- proteins, amino acids, waste products, most drugs and K+ are not permitted access
- the barrier is ineffective against fast-soluble molecules (i.e. alcohol, nicotine, anesthetics)
How does the CSF circulate?
The total volume of CSF at any time = 150mL
the total volume produced/ day = 500 mL
pressure remains constant, because the rate of fluid reabsorption equals the rate of fluid production = 20 mL/hr
- enters subarachnoid space through 2 lateral apertures and a median aperture = flows around brain, spinal cord, and cauda equina and into central canla and ventricles
What is menigitis?
inflammation of the meninges = a serious life threatening conditions
- bacterial/ viral menigitis can spread to the brain or spinal cord
( if the brain become inflamed = encephalitis)
- can be diagnosed by examining a sample of cerebral spinal fluid taken from the subarachnoid space in the spinal column
[drainage of CSF through archnoid granulations]
How does the drainage of CSF happening through arachnoid granulation?
1) extension of arachnoid mater
- project into the superior sagittal sinus (a dural sinus)
2) CSF moves into the superior sagittal sinus, that colelcts CSF and returns it to the jugular veins for frainage to the heart
What is hydrocephalus?
= a condition where CSF accumulates
- in adult, this leads to an increase in intracranial pressure & compression of the brain
- can occur as a result of congenital abnormalities, head injury and meningitis
- in neonates (infants), the bones of the skull have not yet fused as immovable sutures and spaecs bewteen bone still exist. (these space = fontanelles)
- hydrocephalus in the neonates is a serious condition if left untreated; however, the skull can expand to compensate forthe additional volume and temporarily prevent a rise in ICP
(ealry signs invlude bulging at the fontanels- recording head size in the neonate is common practice)
1) internal hydrocephalus: blockage within ventricles
2) external hydrocephalus: blockage at subarachnoid granualtions
explain the unusal architecture of the vasular endothelium aournd brain capillaries.
The vascular endothelium around brain capillaries differs from most other organs of the body in that it forms tight junctions with the end-feet of neraby astrocytes
As a result of this unusal architecture, a blood brain barrier (BBB) is formed:
- astrocytes
- pericytes (contractille)
- tight junctions (between endothelial cells)
What is the funtion of blood brain barrier
funtions: to isolate tissue of CNS from general circulation = tight control over CSF
( basically CSF is filltered blood plasma)
Capillaries in CNS is interlocked by tight junctions
The movement of substances between brain capillaries and interstitial fluid:
- lipid soluble substances: O2, Co2 can diffuse across membrane
-
water, alcohol and ions: Ca++, Na+, K+, Mg++, Cl-, H+
: move through protein channles (most drugs are water soluble & can’t cross BBB) -
larger substacnes: glucose moved by protein channels
= 2,3 both reguire channles & somtimes ATP (slower rate of transport
-
covering surface of capillaries in CNS: astrocytes that control permeability of the endothelium
(compared to blood, CSF is 7.33 has low protein, few WBCs no RBCs & different ion concentrations (through the same overall osmolarity)
The names of the lobes in cerebrum
the lobes of the cerebrum correspond to theboens of the braincase whicih bear the same names
1) frontal lobe
2) parietal lobes
3) temporal lobes
4) occipital lobe
What are the lists of cortex
neurons of common function are localized together in areas of the cortex
1) primary motor cortex (in precentral gyrus)
2) primary somatosensory cortex (in postcentral cortex)
- sensory; behind the central sulcus
3) custatory cortex
4) pretrontal cortex (conscious intellect)
5) guastatory cortex = taste