Chapter 14 - Brain Flashcards
Rostral
toward the nose/forehead
Caudal
toward the “tail” / spinal cord
Neural tube
becomes your brain & SC
Notochord
- stays in your body central axis
- helps cue up development of left and right sides of body
- extends from head to tail of the embryo
- eventually becomes the nucleus pulposa in the pads of tissue between the vertebrae
Major portions of brain
Cerebrum, Cerebellum, and Brainstem
Corpus callosum
thick myelinated nerve bundle at bottom of longitudinal fissure that connects hemispheres
Falx cerebri
separates R & L cerebral hemispheres
Tentorium cerebelli
seperates cerebrum from cerebellum
Falx cerebelli
separates R & L halves of cerebellum
Gray Matter
- not shiny, dull, corresponds to unmyelinated parts of neurons, mainly cell bodies of neurons where synapses occur between axon terminals of one neuron with the dendrites and somas of other neurons
White matter
-myelinated axons
- coordinates with myelinated axons, shiny, glossy
- tracts, bundles of axons traveling together
Meninges
- protect the brain
-sandwiched between the brain and skull - provide structural framework for the CNS arteries and veins
Flow of CSF
S: secretes choroid plexus into lateral ventricles
F: flows through inter ventricular foramina into third ventricle
A: Choroid plexus adds more CSF into third ventricle
D: Flows down cerebral aqueduct to fourth ventricle
A: Choroid plexus adds more CSF in fourth ventricle
T: Flows out two lateral apertures and one median aperture
B: fills subarachnoid space and bathes external surfaces of brain and spinal cord
R: reabsorbes into venous blood of dural venous sinuses
CSF
Clear, colorless liquid that fills
– the ventricles & canals of CNS
– subarachnoid space (meninges, external surface of brain)
* Brain produces and absorbs 500 mL/day.
– 100 to 160 mL normally present at one time
Functions of CSF
Buoyancy, Protection, Chemical stability
Buoyancy
- Brains weigh approx 1.5 kg (3 lb).
- If it rested on floor of cranium, the pressure would kill the nervous tissue.
Protection
- Protects the brain from striking the cranium when the head is jolted.
- Shaken child syndrome and concussions do occur from severe jolting.
Chemical Stability
- Flow of CSF rinses away metabolic wastes.
- Homeostatically regulates: electrolytes, pH, osmolarity, etc.
Blood supply
Brain is only 2% of adult body weight, but receives 15% of the blood.
– 750 mL/min.
* Neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical!!!
– A 10-sec interruption of blood flow may cause loss of consciousness.
– A 1 to 2 min interruption can cause significant impairment of neural function.
– Going 4 min without blood causes irreversible brain damage.
What are the benefits and obstacles of having a BBB?
- Benefit - protects us from pathogens and hydrophilic toxins.
- Obstacle for delivering medications such as antibiotics and cancer drugs.
- Also, trauma and inflammation can damage BBB and allow pathogens to enter brain tissue
Astrocyte foot processes
secrete paracrines that promote tight junction formation
Tight Junction
prevents solute movement between endothelial cells
BBB-
Blood Brain Barrier
- Key components: Astrocytes, Endothelial cells and Tight junctions
BCB - Blood CSF Barrier
Protects brain at the choroid plexus.
○ Forms tight junctions between the ependymal cells.
○ Tight junctions are absent from ependymal cells elsewhere.
■ Important to allow exchange between brain tissue & CSF. What does get in the brain easily?….
● Highly permeable to: water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics.
● Slightly permeable to: Na+, K+, Cl-, and the waste products urea and creatinine.
CVOS - Circumventricular Organs
Are places in the third and fourth ventricles where the barrier is
absent.
* Blood has direct access to the brain.
* Enables the brain to “sample blood” in order to monitor and respond to fluctuations in blood glucose, pH, osmolarity, and other variables. Ex. at the hypothalamus
* CVOs afford a route for invasion by the human immunodeficiency virus (HIV).
Functions of Medulla Oblongata
Sensory:
Hearing Equilibrium Taste
Touch Pressure Temperature Pain
Motor:
Chewing
Salivation Swallowing
Speech
Head movement Neck movement Shoulder movement
More Motor… Keeping you alive:
Gagging
Vomiting
Respiration
Coughing
Sneezing
Sweating
Cardiovascular control
Gastrointestinal control
Hippocampus
Deep in temporal lobe
* Consolidation (where short-term
memory
becomes long-term memory)
* Damaged hippocampus → anterograde amnesia (no new long-term memories will be made)
Optic sensory (II)
eye
Olfactory (I)
nose
Oculomotor (III)
all eye muscles
Trochlear (IV)
superior oblique
Abducent motor (VI)
external rectus muscle
Trigeminal (V)
face, teeth, sinuses
muscles of mastication
Intermediate
Submaxillary and sublingual gland, anterir part of tongue and soft palate
Glossopharyngeal (IX)
posterior part of tonge, tonsil, pharynx
Vestibulocochlear (VIII)
inner ear
Vagus (X)
heart, lungs, bronchi, trachea, larynx, pharynx, gastrointestinal tract, external ear
Accessory (XI)
sternocleidomastoid and trapezius muscles
Hypoglossal (XII)
muscles of the tongue
Facial motor (VII)
muscles of the face
Cranial dura mater
Has two layers
– Outer periosteal = periosteum of cranial bones.
– Inner meningeal continues into vertebral canal and forms dural sheath around spinal cord.
– Layers separated by dural sinuses (#5 in fig) which collect blood & CSF circulating through brain.
2. Dura mater is pressed closely against cranial bones.
* No epidural space (like spinal cord).
Cranial Arachnoid mater
Similar to arachnoid mater in SC.
2. Transparent membrane with “fibers”.
3. Subarachnoid space separates it from pia mater below.
4. Subdural space separates it from dura mater above in some places.
5. Arachnoid villi/granulations discussed later with CSF flow (CSF enters dural sinuses/venous blood).
Cranial Pia Mater
Similar to Pia mater in the SC.
Very thin mb that follows contours of brain, dipping into sulci.
Not usually visible without a microscope.
