BIO 3200: chapter 10

Nervous systems are remarkable for two characteristics, what are they?

emergent properties and plasticity

Emergent properties

properties that cannot be predicted to exist based only on knowledge of the systems individual components

Plasticity

the ability to change circuit connections

How does plasticity contribute to emergent properties?

by using sensory input and past experience to modify synapses

How do many neurons that make up neural networks develop emergent properties not found in single neurons?

affective properties and cognitive behaviors

Affective properties are related to

feeling and emotion

Cognitive behaviors are related to

thinking

What differs one species from another?

the number and organization of neurons

What is the cerebrum?

the brain's main center for thinking, sensing, and voluntary behavior.

the largest region in the forebrain

What is the cerebellum?

a region of the hindbrain devoted to coordinating movement and balance

Neural plate

a flattened region where cells that will become the nervous system lie in

What happens during day 20 of an embryo developing?

the neural plate cells migrate towards the midline and the neural crest migrate with the neural plate cells

What happens by day 23 in embryonic development?

neural tube formation is almost complete

1) two openings of neural tube form (anterior and posteror)

2) the neural crest becomes peripheral nervous system PNS

3) the neural tube comes the CNS

The Neural tube

embryonic cells develop into the CNS

The cells lining the neural tube either differentiate into what two things?

(1) ependyma or (2) remains neural stem cells

What happens by week 4 of embryonic development?

the anterior portion of the neural tube begins to specialize into three divisions:

1) forebrain, 2) midbrain, and 3) hindbrain (becomes the spinal cord)

What happens by week 6 of embryonic development?

• The CNS has formed seven major divisions or regions of the brain

—(1) cerebrum, (2) diencephalon, (3) midbrain, (4)(5) cerebellum and pons, and (6) medulla oblongata, (7) is the spinal cord

• the central cavity (lumen) of the neural tube turn into hollow ventricles

• — two lateral ventricles and two descending ventricles

• central cavity of hte neural tube also becomes the central canal of the spinal cord

What two regions develop from the forebrain?

the cerebrum and diencephalon

What are the divisions of the hindbrain?

cerebellum, pons, and medulla oblongata

What happens by week 11 of embryonic development?

• the cerebrum becomes noticably enlarged

• at birth, the cerebrum is the largest and the most obvious structure

What surrounds the diencephalon, midbrain, and pons?

the fully developed cerebrum

The tissues of the CNS are divided into

gray matter and white matter

Gray matter consists of

unmyleinated nerve cell bodies, dendrites, and axon terminals

White matter consists of

myelinated axons and contains very few neuronal cell bodies

Why is white matter pale?

due to the myelin sheaths that surround the axons

Tracts are

bundles of axons that connect different regions of the CNS

What is equivalent to PNS nerves in the CNS?

tracts

Where does the spinal cord run through?

a canal in the vertebral column

How do nerves of the PNS leave the spinal cord?

by passing through notches between the stacked vertebrae

Meninges

three layers of membrane that lie between the spinal cord and vertebrae, or brain and skull

function: help stabilize the neural tissue and protect it from bruising against the bones of the skeleton

What are the three membranes of meninges?

(1) dura mater, (2) arachnoid membrane, and (3) the pia mater

Of the three membranes in meninges, which is the thickest?

the dura mater bc its associated with veins that drain blood from the brain through vessels or sinuses

the middle layer, arachnoid membrane, is loosely tied to the inner membrane, which leaves what between the two layers?

subarachnoid space

The inner membrane, pia mater, is

a thin membrane that adheres to the surface of the brain and spinal cord

it contains arteries that supply blood to the brain

What is the final protective component of the CNS?

extracellular fluid, which helps cushion the delicate neural tissue

The cranium has an internal volume of 1.4L, how much do cells occupy of that volume?

1 L

The remaining volume (0.4L) of the cranium is divided into what two distinct extracellular compartments?

blood (100-150mL), and the cerebrospinal fluid+Interstitial fluid (250-300mL0

What two fluids form the extracellular environment for neurons?

the cerebrospinal fluid and intersitial fluid

Where is intersitial fluid found in the brain?

inside the pia mater

Where is cerebrospinal fluid found in the cranium?

in ventricles and in the space between the piamater and arachnoid membrane (subarachnoid space)

The CNS equivalent to ganglions is a

nucleus

How is cerebrospinal fluid secreted?

the choroid plexus- a specialized region on the walls of ventricles

What does the choroid plexus cells do?

selectively pump sodium and other solutes from plasma into ventricles

The choroid plexus transports ions and nutrients from

the blood → cerebrospinal fluid

How is cerebrospinal fluid reabsorbed into the blood?

at finger-like projections of the arachnoid membrane called villi

The aqueduct of Slyvius (cerebral aqueduct) is the

narrow passageway between the third and fourth ventricles

What happens to the CSF flow if the aqueduct becomes blocked by infection or tumor (aqueductal stenosis)?

it will cause the CSF to accumulate in the first, second, and third ventricles

blockage near the frontal lobe will cause fluid build up in all ventricles

if the fourth ventricle is swollen, yk the blockage is near the frontal lobe

On a 3D imaging study of the brain, how would u distinguish aqueductal stenosis from a blockage of CSF flow in the subarachnoid space near the frontal lobe?

look for enlargement of the fourth ventricle to help localize the site of blockage

How often can CSF be replinished a day?

3 times a day

What are the two purposes of Cerebrospinal fluid?

(1) physical protection and (2) chemical protection

What is the concentration of K⁺ in cerebrospinal fluid compared to its plasma?

low compared to plasma

What is the concentration of H⁺ in cerebrospinal fluid compared to its plasma?

high compared to its plasma

What is the concentration of Na⁺ in cerebrospinal fluid compared to its plasma?

usually the same concentration

Clincally, what is an indicator of the chemical environment in the brain?

cerebrospinal fluid retreived through a spinal tap or a lumbar puncture

How is a spinal tap or lumbar puncture done?

by withdrawing fluid from the subarachnoid space between vertebrae at the lower end of the spinal cord

Why is the CSF’s pH lower than the bloods pH?

bc of the high H⁺ concentration in the CSF, causing pH to decrease

subdural hemotoma

blood collects in the space between the membranes, pushing on the soft brain tissue under the skull

caused by a rupture in a blood vessel running between the meninges

Is CSF more like plasma or more like interstitial fluid?

its more like intersitial fluid bc they both contain little protein and no blood cells

The blood-brain barrier

the final layer of protection for the brain between interstitial fluid and blood

Why is the blood-brain barrier necessary?

to isolate the body’s main control center from potentially harmful substances in the blood and blood-borne pathogens like bacteria

What creates the blood-brain barrier?

400 miles of brain capiliaries

What makes the blood-brain barrier behave like a barrier?

the highly selective permeability of brain capillaries shelters the brain from toxins, fluctuations in hormones ions and neuroactive substances, like neurotransmitters in the blood

Why are brain capillaries less permeable than other capillaries?

brain capillaries have endothelial cells that form tight junctions with one another, which prevents solute movement between cells.

What induces tight junction formation in blood capillaries?

paracrine signals from astrocytes that surround the capillary and from adjacent contractile cells called pericytes

Pericytes regulate blood flow through

blood capillaries

The selective permeability of the blood-brain barrier can be attributed to

its transport properties; any water-soluble molecule that it not transported on these carriers cannot cross the blood-brain barrier

• the capillary endothelium: uses selected membrane carriers and channels to move nutrients and other useful materials from the blood into the brain interstitial fluid

• other transporters: move wasters fromm interstitial fluid into plasma

Parkisons

a neurological disorder where brain levels of the neurotransmitter dopamine are too low bc dopaminergic neurons are damaged or dead

Since parkisons is related to damaged dopamine receptors, why cant a dopamine injection or pill fix it?

its ineffective bc dopamine cannot cross the blood-brain barrier

Why is L-dopa administered to treat the deficiency in dopamine for parkisons?

its a precursor that binds on an amino acid transporter to cross the blood-brain barrier, once they reach the interstitial fluid, they metabolize into dopamine and treat the deficiency

What type of molecule can diffuse through the cell membrane of the blood-brain barrier?

small lipid-soluble molecules

Why did older antihistamines make you sleepy?

they were lipid-soluble amines that readily crossed the blood-brain barrier and acted on brain centers controlling alertness

Why dont newer antihistamine drugs have the same sedative effect as older antihistamine drugs?

they are much less lipid-soluble, so they cannot cross the blood-brain barrier as much

What are two areas other of the brain that lack a functional blood-brain barrier, and their capillaries have leaky endothelium like most of the body?

(1) hypothalamic-hypophyseal portal system and (2) vomiting center of medulla oblongata

What initiates the vomiting reflex in the medulla oblongata?

neurons that detect the blood has possibly toxic foreign substances, like drugs

Paravascular route of CSF (glymphatics)

moving CSF along the outside of blood vessels, aided by water movement across astrocytes

The buildup of brain proteins in diseases like alzheimers may be the result of poor _______ _______.

glymphatic function

What is a unique property to the CNS?

its specialized metabolism

How much blood pumped by the heart goes to the brain and distributed through extensive cerebral vascular system?

15%

to supply the oxygen and glucose to make ATP for active transport

How much O² does the brain take at any moment?

1/5 of the bloods oxygen supply

TRUE OR FALSE: oxygen can pass freely across the blood-brain barrier

TRUE

What is the only energy source for neurons?

glucose, making blood glucose homeostasis critical

How does glucose pass the blood-brain barrier?

plasma → barrier → CSF by membrane transporters

What happens if glucose homeostasis fails?

hypoglycemia that leads to confusion, unconsciousness, and evenually death

What organelle doe oxidative phosphorylation take place?

the mitochondria

What is the major pathway for information flowing back and forth between the brain and the skin, joints, and muscles of the body?

the spinal cord

Dorsal root

specialized to cary incoming sensory information

Dorsal root ganglia

swellings found on the dorsal roots prior to entering the cord, contain cell bodies of sensory neurons

Ventral root

carries outgoing information from the CNS to muscles and glands

Where do sensory fibers from the dorsal roots synapse with interneurons?

posterior horns (dorsal) of gray matter

What two distinct nuclei are the posterior horn cell bodies organized in?

(1) somatic information and (2) visceral information

The anterior horns

in gray matter that contain cell bodies of motor neurons that carry efferent signals to muscles and glands

How are the anterior horns nuclei organized?

(1) somatic motor and (2) autonomic nuclei

How do efferent fibers leave the spinal cord?

via the ventral root

White matter is use to

carry our communication systems

White matter can be divided into a number of

columns that are composed of tracts of axons that transfer information up and down the cord

Ascending tracts

take sensory information to the brain and occupy the dorsal and external lateral portions of the spinal cord

Descending tracts

carry mostly efferent (motor) signals from the brain to the cord, and they occupy the ventral and interior lateral portions of the white matter

Propriospinal tracts

remain within the spinal cord

What is the integrating center for simple spinal reflexes?

the spinal cord itself

Spinal reflexes

sensory information entering the spinal cord is acted on without input from the brain, but sensory information about the stimulus may be sent to the brain