NSCI 2101 Exam 1

developmental processes of the brain

1. fertilization of embryonic disk

2. gastrulation

3. neurulation

4. further development of the brain

timeline of embryo development

fertilization → zygote → morula → blastocyst

zygote

single cell with two nuclei (from mom and dad)

morula

clump of 16-32 cells that arise from zygote division

• zygote divided by mitosis

blastocyst

fluid accumulates in morula to create a hollow ball of cells

• consists of an outer layer of cells and inner layer of cells

• “hatches” to embed in uterus

• inner cell mass becomes embryo

• formation of embryonic disk and primitive streak

embryonic disk

2 layers of cells with a primitive streak

• forms from blastocyst

primitive streak

forms brain and spinal cord

• cells divide and move ventrally at this point

gastrulation

3 primary germ layers are formed (days 14-17) that form different body parts

• ectoderm, mesoderm, endoderm

• cell layers move ventrally, each layer replacing the one below it

ectoderm

dorsal layer that becomes the skin, PNS, and CNS

mesoderm

middle layer that becomes bones, blood, muscle

neurulation

underlying mesoderm induces neural ectoderm (days 15-21)

• ectoderm can become future neurons

• neural plate forms

neural plate

specialized area of ectoderm (elongated disk) that forms the spinal cord

• elongated disk folds to create the neural groove, that then forms the neural tube

neural tube

gives life to CNS. arises from neural groove

• fusion of neural tube starts in the middle of the ectoderm and zippers up

neural crest cells

2 populations of cells that detach from neural tube and non-neural ectoderm

• contributes to the PNS

spina bifida

defect in closure of posterior neural tube

anencephaly

defect in closure of anterior neural tube

vesicles

swellings (that hold CSF) on embryo from where different regions will develop

3 primary vesicles

forebrain (prosencephalon), midbrain (mesencephalon), hindbrain (rhombencephalon)

• eventually subdivide into 5 vesicles

5 secondary vesicles

[spinal cord]

1. myelencephalon

2. metencephalon

3. mesencephalon

4. diencephalon

5. telencephalon

where does optic nerve form?

from the optic vesicle on the diencephalon

pontine flexture

opens at 4th ventricle and initiates development of cerebellum

(example from class: bending paper towel roll)

development of the forebrain (3 steps)

1. telencephalon enlarges @ rostral end

2. expansion = C shape

3. telencephalon grows to cover cortex

CNS development in 5 steps

1. 3 vesicles and spinal cord

2. subdivides into 5 vesicles

3. 3 flextures develop

4. cerebellum develops on top 4th ventricle

5. forebrain develops in C shape (rostral→caudal)

from where does the PNS derive?

neural crest cells and neural placodes

neural crest cells

give rise to different types of cells. terminally differentiate at the end of migration

• sensory ganglia

• autonomic ganglia

• schwann cells

• melanocytes

• enteric nervous system

placcodes

thickenings of non-neural ectoderm in the head

neurogenic placcodes

purpose of meninges, ventricles, and CSF

• protect from physical damage (anchors brain/spinal cord and absorbs shock)

• delivers nutrients and clears waste

• protects against pathogenic factors

meninges

tissue between the skull and the brain. also surrounds spinal cord

3 layers of meninges

1. dura mater

2. arachniod mater

3. pia mater

dura mater

toughest and outermost meninx layer

arachnoid mater

contains connective tissue

• stringy matter between arachnoid and pia called subarachnoid space

pia mater

single cell layer membrane that follows the contours of the brain

what 3 components do the meninges contain?

1. blood vessels

2. nerve fibers (only dura has sensory nerves)

3. CSF (subarachnoid space filled with CSF)

dural folds

folds in the dura that divide the brain into smaller compartments

falx cerebri

dural fold that dips into the interhemispheric fissure

• part of the dura that is in the midsaggital “fold” of the brain

• prevents brain from moving from side to side too much

tentorium cerebelli

separates cerebrum and cerebellum

• horizontal dura

• stabilizes and prevents up and down movement

ventricles

interconnected cavities of the brain filled with CSF

• located in the middle of the brain

cerebral ventricles

derive from secondary neural vesicles (~40 days)

lateral ventricles

c-shaped ventricle that arose from the enlargement of the telencephalon

composition of CSF

similar to extracellular fluid: high sodium, low potassium

choroid plexus

network of blood vessels

arachnoid granulations

structures that drain CSF from the sub arachnoid space

• helps CSF exit the brain

how much CSF is produced a day?

~500 ml

how much CSF do the ventricles and subarachnoid space hold?

~150ml

hydrocephalus

excess buildup of CSF

• congenital or can develop later in life

• increases pressure in the brain

• uses shunt to drain from ventricles to abdomen

what do changes in CSF indicate?

disease. leakage can cause injury

what percent of blood flows to the brain?

20%

vascular indicators

use these to infer if there is illness

• vasculatory system impacts health of the brain

artery

high pressure blood vessel that carries blood away from the heart

vein

low pressure blood vessel that carries blood toward the heart

path of blood

heart → arteries → capillaries → venules → veins → heart

• vessels get smaller

anterior brain arteries

internal carotid arteries

posterior brain arteries

vertebral arteries

circle of willis

connection between arteries (anastemosis)

what region does the anterior cerebral artery supply?

midline of the cerebral cortex

what region does the middle cerebral artery supply?

lateral side of cerebral cortex

what region does the posterior cerebral artery supply?

posterior-inferior cerebral cortex

what region does the vertebral and basilar arteries supply?

brainstem and cerebellum

venuous drainage of the brain

• drains into venous sinuses

• dural venuos sinuses drain into internal jugular vein, then back to the heart

where do major arteries run?

subarachnoid space

venuos sinuses

where deoxygenated blood from the brain drains

• functions like veins

• these drain back into internal jugular vein, then back to heart

superior sagittal sinus

dural venuos sinus that ends at transverse sinus

• think midsagittal cross section

transverse sinus

dural venuos sinus that allows blood to drain from the back of the head

• (looked like two small holes on dissection)

jugular foramen

where jugular vein connects to venuos sinus

formen magnum

where spinal cord connects to brain

vasodilation

increased CO2

• hypoxia (increase of blood flow)

vasconstriction

decreased CO2

changes in blood oxygenation equals…

changes in brain activity

blood brain barrier

controls access to the brain by regulating chemicals

feautres of blood brain barrier

• tight junctions clock diffusion between capillary endothelium

• surrounded by astrocytes

• nutrients enter and toxins exit

drugs and the blood brain barrier

• lipid soluble drugs enter more easily (heroine)

• can slow the removal of some drugs from the brain

• drugs can be trapped in lipids int he brain and release much later

functions of blood brain barrier

needs to sense and react

• senses salt— thirst

• hormone release

• senses toxins

where does the brain release hormones?

blood brain barrier

where is most of the volume of a neuron?

axon

kinesins

motors that move cargo in anterograde direction

• AWAY from cell body

dyneins

motors that move cargo in retrograde direction

• TOWARD cell body

fast anterograde transport

when things are needed at the axon terminal

• vesicles and organelles

slow anterograde transport

movement of microtubules and neurofilaments

rabies

type of axonal transport disease

• introduced through skin and taken up via peripheral nerve terminals

• transports retrogradely into cell body of CNS

• hijack nervous system

glia

non-neuronal cells of the nervous system

CNS glia

• astrocytes

• oligodendrocytes

• ependymal cells

• microglia

PNS glia

• satellite cells

• schwaan cells

• macrophages

astrocytes

support neurons

• surround most neurons and blood vessels

• contribute to scaffolding of CNS

• mediate exchange between capillaries and neurons

oligodendrocytes

myelinate axons

• increase conduction velocity

ependymal cells

line ventricular system

microglia

housekeepers

• regulate brain development

• maintain neuronal networks

• activated by injury

2 types of neuronal communication

electrical (within a cell)

chemical (between other cells)

resting membrane potential

electrical potential difference across the cell’s plasma membrane

• responds to excitatory or inhibitory inputs

action potential

initiates release of neurotransmitters at synapeses - self propagate unchanged along length of axon

what is the neuron resting membrane potential?

-70mV

why is the resting membrane potential negative?

inside of cell is more negative than outside cell

neuron at rest

• K+ concentration HIGHER INSIDE CELL

• Na+ and Cl- concentration HIGHER non-volOUTSIDE CELL

non-voltage gated K+ channels

• more non-voltage gated K+ channels

• K+ equilibrium is more important to the cell

ration of Na+ to K+

pump moves 3 Na OUT for every 2 K IN

what does activation of neurotransmitter receptors induce?

changes in ion conductance in the dendrites and soma

inhibitory synaptic activity

• MORE NEG!!

• hyperpolarizes neuron

• membrane potential becomes MORE NEG!!

excitatory synaptic

• MORE POS!!!

• depolarizes the neuron

arousal threshold

cell is sufficently depolarized and AP is generated

• positive enough = AP

voltage gated Na+ channels

monitor neuron activity level

• channels open when cell reached threshold