Chapter 3: The Nervous System's Functional Units Flashcards
where did the theory of the neuron emerge from?
controversy between Golgi and Ramon y Cajal
how did Golgi stain tissue?
immerse thin slice of brain tissue in solution w/ silver nitrate
what did Golgi’s staining suggest?
the nervous system is an interconnected network of fibres
Golgi thought information flowed around a ___, and so produced ___
nerve net (like water running thru pipes), behaviour
Ramon y Cajal used Golgi’s stain to study
chick embryos’ brain tissue
what did Cajal conclude about the nervous system?
- made up of discrete cells that begin life as a rather simple structure, becomes more complex w/ age
- when mature, each cell has a main body w/ many extensions projecting from it
who’s neuron theory is now accepted?
Cajal’s
the ___ neurons an animal has, the ___ complex its behaviour
more, more
we can implant tiny microscopes called ___ or ___ into the brain to view the structure and activity of its ___
endoscopes, microendoscopes, neurons
research has confirmed ___ nerve net, a covering called a ___ that forms around neurons as they mature
Golgi’s, perineuronal net
soma
cell body
what collects information from other cells?
dendrites
what would carry messages to other neurons?
axon
a neuron only has one ___, but may have many ___
axon, dendrites
dendrites ___ info, the soma ___ info, the axon ___ info
collect, integrates, passes
a. axon from another neuron
b. dendrites
c. soma (cell body)
d. nucleus
e. axon
f. axon collateral
g. teleodendria
h. terminal button (end foot)
i. dendrites from another neuron
the human nervous system contains ___ neurons and ___ glial cells
86 billion, 87 billion
neurons regulate body processes such as
breathing, heartbeat, body temperature
functional groups of neurons called ___ connect wide areas of the ___
neural networks, brain & spinal cord
in what ways are neurons “active”?
- making/losing branches
- making/losing connections w/ each other
the dynamic activity of the neuron underlies both the constancies and changes in our ___
behaviour
a neuron’s ___ is increased immensely by its extensions into dendrites and axon
surface area
a neuron may have up to ___ dendrites
20
juncture of soma + axon
axon hillock
branch of an axon
axon collaterals
axon collaterals may divide into multiple smaller branches called
telodendria
at the end of each telodendrion is a knob called a
terminal button (end foot)
the terminal button does not ___ a dendritic spine, this near-connection is called a
touch, synapse
a synapse includes
- surface of end foot
- surface of neighbouring dendritic spine
- space between
the general shape of a neuron suggests it works in a similar way to a
river
conduct information from sensory receptors in/on the body into the spinal cord + brain
sensory neurons
associate sensory + motor activity in CNS
interneurons
carry info from brain + spinal cord out to the body’s muscles
motor neurons
sensory neurons
- bipolar neuron (retina)
- somatosensory neuron (skin/muscle)
a) dendrite
b) axon
interneurons
- stellate cell (thalamus)
- pyramidal cell (cortex)
- purkinje cell (cerebellum)
- motor neuron (spinal cord)
a) dendrites
b) axon
structurally the simplest of the 3 types of neurons
sensory neurons
a ___ has a single short dendrite one one side of its soma, and a single short axon on the other
bipolar neuron
bipolar neurons transmit ___ info from the ___ to the neurons that carry info into the brain’s ___
afferent/incoming sensory, retina’s light receptors, visual centres
brings sensory information from the body into the spinal cord
somatosensory neuron
the ___ dendrite connects directly to its axon, so the cell body sits to the side of this long pathway
somatosensory
association cells
interneurons
a small interneuron w/ many dendrites extending around the cell body
stellate (star-shaped) cell
what is one of the main reason brain sizes vary between species?
there are many more interneurons in larger brains than smaller, giving a correlation between interneuron # and behavioural complexity
- long axon
- pyramid-shaped cell body
- two sets of dendrites
pyramidal cell
distinctive interneuron w/ extremely branched dendrites that form a fan shape
purkinje cell
- extensive dendritic networks
- large cell bodies
- long axons that connect to muscle
motor neurons
all efferent/outgoing neural info must pass thru ___ to reach muscles
motor neurons
3 functions/features of neuronal networks
input, association, output
___ carry info to distant parts of the nervous system, while ___ are engaged in local processing
long extensions, short extensions
somatosensory neurons can send information over more than ___
2 metres
pyramidal neurons must reach from the cortex to the lower spinal cord, which can be as long as ___
1 metre
each neuron receives up to ___ of excitatory + inhibitory signals every second
thousands
how does a neuron pick which input to use?
it sums them all up, follows whichever input exceeds the other
AI is based on the principles of
nervous system function
Barbara Webb constructed a
cricket robot
___ parts are constructed to mimic parts of a human body
anthropomimetic robots
glial cells help neurons by
- binding them together
- providing support, nutrients, protection
5 types of glial cells
- ependymal cell
- astrocyte
- microglial cell
- oligodendroglial cell
- schwann cell
small ovoid, secretes CSF
ependymal cell
- star-shaped
contributes to - neuronal nutrition, support + repair
- forming blood-brain barrier
- healing scarring after injury
astrocyte
small, derived from blood, defensive function to remove dead tissue
microglial cell
forms myelin around CNS axons in brain + spinal cord
oligodendroglial cell
wraps around peripheral nerves to form myelin
schwann cell
errors in ___ replication are a main source of ___
glial cell, brain tumors/abnormal growths
an uncontrolled growth of new tissue that is independent of surrounding structures
tumor
incidence of brain tumors in the US is ___ according to CBTR
20 per 100,000
in adults, brain tumors grow from ___, but in infants they may grow from ___
glia/supporting cells, developing neurons
___ are not likely to recur after removal
benign tumors
___ are likely to progress + invade other tissue, and apt to recur after removal
malignant tumors
3 major types of brain tumors
- gliomas (from glial cells)
- meningiomas (attached to meninges)
- metastatic tumors (cells transfer regions)
- found on the walls of ventricles
- produce/secrete CSF
ependymal cells
functions of CSF
- shock absorber for brain
- carries away waste products
- assist constant brain temperature
- source of nutrients for parts of brain
hydrocephalus is the buildup of fluid pressure in the brain and, in infant, swelling of the head, due to the ___; can cause severe intellectual impairment
flow of CSF being blocked
- provide structural support to CNS
- extensions attach to blood vessels + brain’s lining, forming a scaffolding that holds neurons in place
- provide pathways for nutrients to move between blood vessels + neurons
- secrete chemical that keep neurons healthy + help them heal if injured
- contribute to blood-brain barrier
astrocytes
protective partition between blood vessels + the brain formed by tight junctions between the cells that compose blood vessels in the brain, prohibits entry of certain substances like toxins into the brain
blood-brain barrier
a. astrocyte
b. blood vessel
c. blood vessel cells
d. astrocyte end feet
e. tight junctions
f. myelinated axon
g. neuron
why are brain infections difficult to treat?
many useful drugs cannot pass thru the blood-brain barrier
how do astrocytes enhance brain activity?
pass along signals from neurons to blood vessels to increase blood flow + fuel supply in response to a behaviour
how do astrocytes contribute to the healing of damaged brain tissue?
form a scar to seal off the damaged area
- originate in the blood as an offshoot of immune system
- migrate thru nervous system
- make up 20% of all glial cells
microglia
how do microglia play an important role in monitoring/maintaining the health of brain tissue?
- identify + attack foreign tissue
- invade damaged areas to provide growth factors that aid in repair
___ engulf any foreign tissue + dead brain cells, an immune process called ___
microglia, phagocytosis
a characteristic of Alzheimer disease, a degenerative brain disorder commonly associated w/ aging, is:
the deposit of distinctive bodies called plaques in regions of damage
microglia may play a harmful role in Alzheimers by
consuming inflamed tissue rather than protecting it
___ interact w/ astrocytes in brain healing
microglia
which 2 glial cells insulate neuronal axons?
- oligodendroglia
- schwann cells
myelinated neurons send information ___ than neurons without myelin
much faster
neurons that send messages over long distances quickly, like __, are ___ to increase their messaging speed
sensory and motor neurons, heavily myelinated
oligodendroglia myelinate axons in the brain + spinal cord by
sending out large, flat branches that enclose + separate adjacent axons
schwann cells myelinate axons in the PNS by
wrapping itself repeatedly around a part of an axon, forming a structure somewhat like beads on a string
in addition to myelination, schwann cells and oligodendroglia contribute to a neuron’s nutrition + functioning by
- absorbing chemicals the neuron releases
- releasing chemicals the neuron absorbs
multiple sclerosis (MS) is associated w/ damage to the ___ that leaves a _, rather than myelin, on neurons in nervous system pathways, resulting in ___ , producing ___
oligodendroglia, scar, information flow impairment, impaired movement + cognitive function
loss of both movement + sensation
paralysis
___ participate in repairing damage to the peripheral nervous system
microglia + schwann cells
neuron repair
- when peripheral axon is cut, the axon dies
- schwann cells shrink, then divide, forming glial cells along the axon’s former path
- neuron sends out axon sprouts, one of which finds the schwann cell path + becomes a new axon
- schwann cells envelop the new axon, forming new myelin
when the CNS is damaged, does regrowth and repair occur?
no
why may regrowth/repair in CNS not occur?
as neural circuits mature, they become finely tuned to mediate individualized behaviour + develop chemical strategies that prevent the proliferation of new cells or regrowth of existing cells
a cell’s ___ determine its characteristics + functions
proteins
a cell’s ___ separates the cell from its surroundings + allows it to regulate what enters/leaves its domain
cell membrane
nerve cell
a. dendrite
b. dendritic spine
c. nucleus
d. nuclear membrane
e. mitochondrion
f. endoplasmic reticulum
g. intracellular fluid
h. tubule
I. cell membrane
j. axon
k. golgi body
l. lysosomes
m. microfilaments
very few substance can enter/leave a cell spontaneously because
the cell membrane is virtually impermeable
proteins embedded in the cell membrane facilitate:
transport of substances in/out of the cell
what happens inside the nucleus?
genetic blueprints for proteins are stored, copied, and sent to the ER
structure that gathers, stores, and releases energy
mitochondrion
folded layers of membrane where proteins are assembled
endoplasmic reticulum
tiny tube that transports molecules + helps give the cell its shape
tubule
membranous structure that packages protein molecules for transport
golgi body
sacs containing enzymes that break down wastes
lysosomes
threadlike fibres making up much of the cell’s “skeleton”
microfilaments
more ___ are found in old cells vs. new ones
lysosomes
the cell membrane regulates the differing concentrations of ___ on its inner/outer sides
salts + other chemicals
what allows cell membranes to regulate water + salt concentrations?
phospholipids
phospholipid heads are ___, and the lipid tails are ___
polar + hydrophilic, hydrophobic
what can traverse a phospholipid bilayer?
small molecules such as
- oxygen
- CO2
- sugar glucose
segments of DNA that encode the synthesis of particular proteins
genes
genes are contained within ___, which are ___
chromosomes, double-helix structures that hold an organism’s DNA library
what happens when chromosomes change shape to occupy the best location in the nucleus?
they expose different genes to the surrounding fluid, allowing the gene to begin the process of making a protein
a human somatic/body cell has __ of chromosomes, or ___ in all
23 pairs, 46
each chromosome is a double-stranded molecule of
deoxyribonucleic acid (DNA)
4 nucleotide bases
(A) adenine
(T) thymine
(G) guanine
(C) cytosine
_ always pairs with T, _ always pairs with C
A; G
how are the 2 strand of the DNA helix bound together?
by the attraction between the 2 bases in each pair
sequences of ___ within the chromosomes spell out the genetic code
hundreds of nucleotide bases
the sequence of base pairs spell out the order in which ___ should be assembled to construct a certain ___
amino acids (the constituent molecules of protein); protein
2 steps of transcription
- DNA uncoils to expose a gene, a sequence of nucleotide bases that encodes a protein
- 1 strand of the gene serves as a template for transcribing a molecule of mRNA
what is different about RNA vs. DNA?
RNA has the base uracil (U) instead of thymine (T)
the transcribed strand of RNA is called ___ because ___
messenger RNA (mRNA); it carries the protein code (message) out of the nucleus to the ER
a distinguishing feature of the ER is that it may be studded with ___, which are ___
ribosomes; protein structures that act as catalysts to facilitate the building of proteins
when mRNA reaches the ER, it passes thru a ___, where its ___
ribosome; genetic code is read
2 steps of translation
- the mRNA leaves the nucleus + comes into contact w/ ribosomes in the ER
- as a ribosome moves along the mRNA, it translates the bases -> amino acid chain = protein
what does transfer RNA (tRNA) do?
assists in translating nucelotide bases into amino acids
___ encodes one particular amino acid
each group of 3 consecutive nucleotide bases along an mRNA
what 3 bases encode the amino acid tryptophan (Trp)?
UGG
what 3 bases encode the amino acid phenylalanine (Phe)?
UUU
the sequence of ___ determines the sequence of the resulting amino acid chain
codons on the mRNA strand
a. template strand
b. DNA
c. mRNA
d. codon
e. polypeptide chain
f. amino acids
humans utilize __ different amino acids
20
amino acid chemical structure
a central carbon (C), bound to:
- a hydrogen atom (H)
- an amino group (NH3+)
- a carboxyl group (COO-)
- a side chain (R)
each amino group is bound to the carboxyl group (COO-) by a ___, which gives the amino acid chain the alt name of ___
peptide bond; polypeptide chain
summary of info flow driven by the genetic code
gene transcribed into mRNA -> ribosomes translate it into a chain of amino acids (polypeptide chain) = forms a protein
folded-up polypeptide chain that serves a particular function in the body
protein
primary structure
amino acid chain
secondary structure
pleated sheet or helix
tertiary structure
protein
quaternary structure
complex protein
a. primary
b. secondary
c. tertiary
d. quaternary
any one neuron contains up to ___ genes, and they can produce as many as ___ different protein molecules
20,000; 20,000
the # of proteins that can ultimately be made by a neuron is far ___ than the # of its genes
larger
a protein’s ___ and ___ are central to its function
shape; its ability to change shape/combine w/ other proteins
2 steps of protein export
- proteins formed in ER enter Golgi bodies, then wrapped in a membrane + given a shipping address
- each protein package is attached to a motor molecule + moves along a microtubule to its destination
3 membrane proteins
- channels
- gates
- pumps
a protein’s ability to change shape is analogous to
a lock in a door - needs the right key
small molecules can bind to a protein’s ___ and cause the protein to change shape
receptors
changes in shape allow the proteins to ___
serve a new function
how does a protein channel work?
an opening lets specific ions thru based on size
how does a protein gate work?
it changes shape to allow the passage of substances when the gates are open, and prevents passage when they are closed
how does a protein pump work?
the pump transporter changes shape to carry substances across the membrane
whose research led to the concept of the gene?
Gregor Mendel
what is the objective of epigenetics?
to study how the environment influences gene expression
chromosome pairs are numbered from 1-23, according to ___, with chromosome 1 being the ___
size; largest
chromosome pairs 1-22 are called ___ because ___
autosomes; they contain the genes that contribute most to our physical appearance + behaviour
the 23rd pair of chromosomes are called the ___ which ___
sex chromosomes; contribute to our physical/behavioural sexual characteristics
the Y chromosome contains the ___, which triggers ___
SRY (sex-determining region) gene; testes development
two copies of a gene
alleles
two identical nucleotide sequences in a pair of alleles
homozygous
two different nucleotide sequences in a pair of alleles
heterozygous
the nucleotide sequence most common in a population is called the ___, while a less frequently occurring sequence is called a ___
wild-type allele; mutation
if both alleles are homozygous, they encode ___
the same protein
if both alleles are heterozygous, they encode ___
somewhat different proteins
3 possible outcomes from the heterozygous condition when their proteins express a physical/behavioural trait
- only the allele from mother may be expressed
- only the allele from father may be expressed
- both alleles may be expressed simultaneously
an member of a gene pair that is routinely expressed
dominant allele
an unexpressed allele
recessive allele
in complete dominance, ___ is expressed in the phenotype
only the allele’s own trait
in incomplete dominance, ___ expressed
the allele’s own trait is partially
in codominance, ___ expressed
both the allele’s own train + that of the other allele is completely
a mutation may be as small as
a change in 1 single nucleotide base = single nucleotide polymorphism (SNP)
more than ___ mutations of the breast cancer gene (BRCA1) have been found
1000
is a mutation always bad?
a mutation can be beneficial, disruptive, or both
what is the most common genetic blood disease, affecting 80,000 US citizens
sickle-cell anemia
what causes sickle-cell anemia?
a SNP on chromosome 11 where T is substituted for an A base in the HBB (hemoglobin) gene
why does it make sense that neurons can get mutations?
most neurons are with us/are metabolically active for life!
at 1 year of age, a neuron may have up to ___ mutations, but by 80 it may have as many as ___ mutations
300-900; 2000
despite our genome being inherited from our parents, it actually ___ as we develop and age
gets modified a lot
Gregor Mendel introduced dominant + recessive alleles thru the use of
pea plants
what is Tay-Sachs disease?
inherited birth defect, appears 4-6 months after birth, results in intellectual disability, physical changes, and death by age 5
what causes Tay-Sachs disease?
dysfunction in the HEXA gene on chromosome 15 = lipids accumulate in brain cells = cell damage
to have Tay Sach’s disease, ___ must carry the mutation
both parents
hereditary disease characterized by chorea (ceaseless involuntary jerky movements) and progressive dementia, ending in death
Huntington disease
how does Huntington disease work?
buildup of an abnormal version of the huntingtin protein kills brain cells, esp in basal ganglia + cortex
to get Huntington disease, __ must carry the allele
only one parent
the HTT (huntingtin) gene is found on chromosome _, where part of the gene contains repeats of the base sequence ___
4; CAG
aberrations in a part of a chromosome/an entire chromosome
copy number variation
copy number variations are related to disorders such as
- autism
- schizophrenia
- learning disabilities
chromosomal abnormality resulting in intellectual impairment + other abnormalities, usually caused by an extra chromosome 21
Down syndrome
how does one get Down syndrome?
one parent (usually mom) passes on 2 copies of chromosome 21 - this combined with 1 from dad = trisomy
3 techniques of genetic engineering
- selective breeding
- cloning
- transgenics
how has selective breeding influenced the dog brain?
- made it smaller than a wolf’s
- larger # of cortical neurons
how do scientists clone animals like Dolly the sheep?
- cell nucleus w/ DNA is placed in an egg cell that had its nucleus removed
- egg stimulated to start dividing
- implant new embryo in uterus of a female
transgenic technology allows scientists to
introduce genes into an embryo OR remove genes from it
___ is used when 1+ genes from one species is added to the genome of another species, passed along, and expressed in subsequent generations, creating ___
knock-in technology; transgenic animals
___ is used to inactivate a gene so that a line of lab animals fail to express it
knockout technology
our phenotypic plasticity is due to
- the genome’s capacity to express a large # of phenotypes
- epigenetics/the influence of environment + experience on phenotypic expression
incidence of similar behavioural traits
concordance
the concordance rate between identical twins for an array of diseases such as ___, is between ___
schizophrenia, Alzheimer’s, MS, Chron’s, asthma, diabetes, prostate cancer; 30-60%
epigenetic mechanisms create ___ without ___
phenotypic variation; altering the base pair nucleotide sequence of the genes
chromosomes are wrapped around supporting molecules of a protein called
histone
for any gene to be transcribed into mRNA, its DNA must be ___, then the gene must be ___, then the mRNA must be ___
unspooled from the histone, instructed to transcribe mRNA, translated into an amino acid chain that forms the protein
3 epigenetic mechanisms
- histone modification
- gene (DNA) methylation
- mRNA modification
histone modification
a methyl group/other molecules bind to the tail of histones, either blocking them from opening or allowing them to open for transcription
gene (DNA) methylation
methyl groups bind to CG base pairs to block transcription
mRNA modification
ncRNA (noncoding) binds to mRNA, preventing translation
a. histone modification
b. gene (DNA) methylation
c. mRNA modification
who found that individuals’ nutritional experiences can affect their offspring’s health?
Lars Olov Bygren
what was interesting about Bygren’s findings?
the descendants of individuals who have plenty of food had higher rates of cardiovascular disease, diabetes, and a life expectancy of 7 years shorter vs. the famine group
what scan is used for MS?
MRI
in the 1950’s, what microscope was used for synapse discovery?
electron microscope
easiest tumor to remove
meningiomas
Huntington vs. Parkinson disease
Huntington: more jerky movement + cognitive/psychological symptoms
Parkinson: rigidity/slowed movements
