Exam 1 Flashcards
(42 cards)
How heavy is the brain?
The size of brains varies considerably around a mean of 1.6 kg (3.5 lbs) in men.
Describe the primary functions of the brain.
The brain is the “supercomputer” of the body. It is the primary integration center (processes sensory input and motor output) and is responsible for higher order functions such as memory, planning, personality, emotions, and language.
What percentage of neurons are found in the brain?
97% in brain
2% in spinal cord; 1% in PNS
Describe the primary regions of the brain.
Cerebrum
- Makes up 83% of the brain
- Composed of 2 large lateral hemispheres
Cerebellum
-Contains half of the neurons in the brain
Brain Stem, composed of:
- Diencephalon (thalamus and hypothalamus)
- Midbrain
- Pons
- Medulla oblongata
What is the central cavity?
The central cavity consists of 4 spaces known as ventricles that contain CSF. It is continuous with the central canal of the spinal cord. Grey matter completely surrounds the central cavity in the brain stem but doesn’t completely surround the ventricles.
What type of matter makes up the cerebral and cerebellar cortex (cortex=bark or rind)?
Grey matter makes up the cerebral cortex and cerebellar cortex.
What makes up white matter? What makes up grey matter?
White matter is made up of myelinated axons; grey matter is made up of neuron cell bodies and dendrites.
What are nuclei?
Nuclei are collections of neuron cell bodies surrounded by white matter. Examples include basal nuclei of cerebrum and nuclei of brain stem.
What are the three layers of the cranial meninges from superficial to deep?
Dura Mater
-Periosteal layer: pressed against cranial bones; only layer not continuous with spinal meninges
-Meningeal layer: forms falx cerebri, tentorium cerebelli and falx cerebelli
Arachnoid Mater
Pia Mater
Note: No epidural space exists in the cranium.
Meningitis: Who is at risk? What is the cause? What are the s/sx? How is meningitis diagnosed?
Meningitis primarily affects young children ages 3 months-2 years.
Can be bacterial (Streptococcus, Escherichia, Listeria and Neisseria), viral or fungal. Often enters through nose or throat.
Infx can spread from arachnoid and pia mater to nervous tissue.
S/Sx: Drowsiness, intense headache, stiff neck, vomiting, rash (in some), photophobia, phonophobia, and high fever.
Lumbar puncture used to collect CSF for diagnosis.
Describe the location of the 4 ventricles of the central cavity and the connections between them.
One large lateral ventricle is located in each cerebral hemisphere. These two lateral ventricles are separated medially by the septum pellucidum. They connect to the third ventricle via the interventricular foramina.
The third ventricle is located deep inside the diencephalon. It connects to the fourth ventricle via the the cerebral aquaduct, which runs through the midbrain.
The fourth ventricle is located between the posterior pons and anterior cerebellum and is continuous with the central canal.
What is a choroid plexus? Where is it located? What is its function?
A choroid plexus is a cluster of pia mater (containing capillaries) and ependymal cells. One choroid plexus is found in each ventricle. The choroid plexus produces CSF. (CSF is also produced by ependymal cells that line the central cavity and central canal.)
How much CSF is present in the body (central cavity, central canal and arachnoid space)? How much CSF is produced daily?
500mL of CSF is produced daily; however, only 100-160mL is present in the body at any given time. The CSF is drained at the same rate it is produced.
Where is the CSF produced? Where is it drained?
CSF is produced in the choroid plexuses of the ventricles and from the ependymal cells that line the central cavity and central canal.
The CSF is drained through the arachnoid villi into the superior sagittal sinus (a space formed between the two layers of the cranial dura mater).
Compare the composition of CSF to that of blood plasma.
CSF is very similar in composition to blood plasma; however, it is slightly altered by the ependymal cells to contain more sodium and less potassium and protein. The higher sodium levels facilitate the conductivity of nervous tissue.
What are the functions of CSF?
1) Floats the brain, reducing the weight of the brain from 3 lbs to 50g
2) Absorbs shock when the skulls is hit
3) Transport of gases, wastes, and nutrients
4) Maintains appropriate environment for action potentials
What two factors contribute to the circulation of CSF?
1) Cranial blood pressure pulses cause CSF pressure pulses that cause CSF to circulate.
2) Cilia of ependymal cells also cause CSF to circulate.
How does CSF move from the central cavity to the subarachnoid space?
The CSF flows from the central cavity to the subarachnoid space via two lateral apertures and one median aperture in the walls of the fourth ventricle.
Describe the condition hydrocephalus.
Hydrocephalus occurs when a tube of the central canal is blocked by a tumor, inflammation, injury, hemorrhage, or developmental malformation. Because of the blockage, CSF cannot drain and pressure inside the central cavity increases, leading to compression of brain tissue which can kill neurons. Because of the malleability of the infant skull, an infant’s entire head can enlarge.
Hydrocephalus is treated by inserting a tube into the central cavity and draining CSF into a vein in the neck, abdomen or subarachnoid space.
Which vessels deliver blood to the brain?
The internal carotid arteries deliver blood to the brain.
Which vessels return blood to venous circulation, removing it from the head?
The blood returns to venous circulation and leaves the head via the internal jugular veins.
What percentages of the body’s total blood, oxygen and glucose are used by the brain?
15% of the body’s blood supply is used by the brain
20% of the body’s O2 and glucose is used by the brain
How long can neurons survive during oxygen deprivation? Why?
Neuronal death begins within 4 minutes from the onset of oxygen deprivation. This is because it takes 4 minutes for venous reserve (O2 not offloaded from hgb during normal circumstances) to be depleted.
Describe the positive feedback loop that occurs when neuronal death begins to occur.
When a neuron dies, its lysosomes’ contents are released the extracellular space, including glutamate which causes neighboring cells to die and release glutamate from their lysosomes, and the process goes on and on.
