Chapter 3 - Cells, Genes & Behavior Flashcards
Neurons
functional units in NS that enable us to receive info, process & act on it
- nerve cells
- 80 billion
Glial Cells
Neuroglia or Glia
non-neuronal cells that provide multiple support functions
- 100 billion
Nervous System is made up of? (2)
Neurons & Glia
Neurons communicate via?
Electrochemical signals
Nucleus
- (2) definitions
1) structure within cell body containing chromosomes
* house genetic material
2) cluster of similar cells that form functional grouping
* functionally related & densely packed
Properties of Neurons (3)
- continously changing (plasticity)
- making new & losing old connections
- behavior produced by groups of neurons
- most have longevity
- not continuously replaced
Most Neurons have longevity
- (2) exceptions
2 regions:
- Hippocampus
- Olfactory bulb
Neurons: Basic Structure
- (3) main parts
1) Dendrites
2) Soma (cell body)
3) Axon
1) Dendrites
- define
- (3) characteristics
- part(s)
branching extensions of neuronal membrane
- Unmyelinated (few exceptions - somatosensory)
- # per neuron varies
- gathers input (afferent part of neuron)
→ Dendritic Spines
Dendrites are usually unmyelinated
- Exception?
Somatosensory Neurons
1) Dendrites → Dendritic Spines
- function
- location of?
membranous protrusions from dendrite that typically recieve input from single synapse of axon (usual point of contact)
- increase SA
- where most synapses are found
2) Soma (Cell Body)
- contains?
- functions? (2)
- (2) additional points
contains nucleus → genetic material (DNA)
- cellular functions (i.e. protein synthesis)
- processes input → integrates (excitatory & inhibitory)
→to determine whether or not to fire - can have synapses
- connects to axon via axon hillock
Axon Hillock
specialized part of soma that connects to axon
- last site** in soma where **membrane potentials propogated** from **synaptic inputs** are **summated** before being **transmitted** to **axon
3) Axon
→ define
→ (3)
→ components (3)
long, slender projection of neuron that carries msgs to other neurons
- 1 per neuron
- usually myelinated
- occurs with maturation
- sends output (carries info to other cells)
→ Axon Collaterals
→ Nodes of Ranvier
→ Terminal Boutons (Axon Terminals)
Axon → Axon Collaterals
branches of axon
3) Axon → Nodes of Ranvier
gaps between myelin sheaths (uninsulated)
- regenerates AP sent down axon
3) Axon → myelin sheath
- forms when?
- functions (2)
Myelination occurs with maturation
- protects
-
speeds up communication
- allows saltatory (jumping) propogation of AP
Nerve
bundle of axons in PNS
Tract
bundle of axons in CNS
3) Axon
→ Terminal Boutons (Axon Terminals)
distal terminal branches of axon that convey info to other cells
- site where electrical message converted to chemical & sent to next cell
Synapse (Synaptic Cleft)
‘almost connection’ usually between terminal bouton of presynaptic neuron & dendritic spines of postsynaptic neuron
- site of information-transfer
→ permits passing of electrical/chemical signal to another neuron
Types of Neurons (3)
different types of neurons are specialized for different types of functions
1) Sensory
2) Interneuron
3) Motor
Types of Neurons (3)
1) Sensory
- axon
- cell body (soma)
recieves input from sensory receptors & sends to CNS
→ PNS
- axon projects from periphery (dendrites in PNS) to CNS via dorsal root
- cell body in dorsal root ganglion OR sensory cranial nerve ganglia
Sensory Neurons → Somatosensory Neurons
- dendrites
- axon
- soma
brings sensory info from body into spinal cord
- few myelinated dendrites (in PNS) connect directly to axon, which projects into CNS
- soma off to side in dorsal root ganglia (PNS)
Types of Neurons (3)
2) Interneuron
integrates info from sensory neurons & conveys to motor neurons
link sensory & motor neural activity in CNS
Types of Neurons (3)
3) Motor
- cell body
- axon
sends output from CNS to effector organs
→ PNS (lower motor neurons)
- soma & dendrites in CNS (spinal cord & brainstem)
- axon projects into PNS forming spinal/cranial nerves → innervate effector organs
Motor Neurons → Upper vs. Lower
Upper → entirely in CNS & carry motor info to lower MN
Lower → project from spinal cord & innervate effector organs
Specialization of Neurons is reflected in their ___?
Structure, which reflects function
Specialization of Neurons is Reflected in Structure
- (3)
1) # of dendrites
2) Size of Soma
3) length of axon
Types of Neurons → Sensory Neurons
- structure
- function
-
bring info to CNS
- ex) somatosensory
-
few dendrites
- innervate small region to allow greater distinction of touch on different parts of body
Unipolar or Bipolar
Types of Neurons → Interneurons
- function
- structure
- examples (2)
link sensory & motor activity within CNS
axons branch into numerous collaterals
Examples:
- Pyramidal → throughout cortex
- Purkinje → in cerebellum
Interneurons → Pyramidal Cell
pyramid-shaped body
long axon
2 sets of dendrites projecting from apex & sides
Interneurons → Purkinje cells
extremely branched & fan-shaped dendrites
Types of Neurons → Motor Neurons
- function
- structure
send signals from CNS to muscle
axons project from spinal cord/brain forming spinal/cranial nerves
Glia
- provide support to neurons through? (5)
Insulation
Nutrients
Structural Support
Aid in Neuron Repair
Waste Removal
Glia
- Unlike neuron’s characteristic of longevity…
Glia are continuously being replaced
Types of Glia (4)
1) Ependymal Cells
2) Astroglia/Astrocytes
3) Microglia
4) Oligodendroglia & Schwann Cells
Types of Glia (4)
1) Ependymal Cells
- location
- function
found on ventricle walls (within choroid plexus)
produce & secrete CSF
Types of Glia
1) Ependymal Cells
* Hydrocephalus
blockage of CSF (leads to hydrocephalus) → accumulation causing ↑ intracranial pressure
-
obstruction in
- interventricular foramen, cerebral aqueduct or 4th ventricle → non-communicating
- subarachnoid space due to prior bleeding or meningitis → communicating
treatment → 1 end of shunt (tube) inserted into blocked ventricle & other into vein, allowing CSF to drain into blood stream
Types of Glia
2) Astroglia/Astrocytes
- functions (5)
star-shaped cells
-
structural support for CNS
- holds onto BV & neurons
- nutrient & waste bridge between BV & neurons
- part of blood-brain barrier
- feet hold endothelial cells closely
- allow certain substances across
- feet hold endothelial cells closely
- stimulate BV dilation → enhance brain activity
- Form scar to seal damage
Types of Glia
2) Astrocytes/Astroglia
- Scar formation to seal damage
- pros/cons
In acute damage phase → beneficial - seals off damaged area
- prevents cascade events from affecting other neurons (further microbial infections/spread of cellular damage)
In long-term → harmful
- scar tissue prevents regrowth & new connections
Blood-Brain Barrier (BBB)
- definition
- formed by?
- function
highly selective permeable membrane seperating blood from brain’s ECF in CNS
- formed by endothelial cells connected by tight junctions
- encircled by astrocyte feet
- provide biochemical support
- encircled by astrocyte feet
- protect brain from substances in blood
Types of Glia
3) Microglia
originate in blood
-
monitor health of brain tissue → immune system role
- provide growth factors to repair damaged neurons
- phagocytosis - engulf foreign tissue & dead cells
→ drawn to damaged area
Types of Glia → 3) Microglia
- PHAGOCYTOSIS
p[rocess of engulfing foreign tissue & dead cells
Types of Glia
4) Oligodendroglia & Schwann Cells
support & insulate axons
form myelin sheath (glial coating surrounding & insulating axon)
Myelin Sheath
glial coating surrounding & insulating axon
- keeps info localized & distinct
Types of Glia → Oligodendroglia
- function
- axonal regeneration?
provide myelin sheath in CNS
- Branches form segments of myelin on adjacent axons
-
axons do NOT regenerate in CNS
- prevents by creating hostile, non-permissive growth environment
Types of Glia → Schwann Cells
provide myelin sheath in PNS
- facilitate regeneration of axons in PNS
Multiple Sclerosis
NS disorder resulting from loss of/damage to myelin in CNS
- cognitive & motor effects
- since myelin can’t be regenerated in CNS*
Neuron Repair in PNS →via Schwann Cells
- (4)
14 - 35 days
i) peripheral axon cut → dies
ii) Schwann cells shrink & then divide, forming glial cells along axon’s former path (secrete chemical signal)
iii) Neuron sprouts axons (proximal segment - attached to cell body) → 1 finds Schwann-cell path & becomes new axon
* distal segment degenerates
iv) Schwann cells envelop new axon to form myelin
Regeneration in CNS
- Why don’t cells regenerate in CNS? (2)
Glial environment in CNS prevents regrowth
Astrocyte scars form (chemical & physical) barrier blocking regrowth
Oligodendroglia do NOT form path & release chemical that repels regrowing axons
Attempts at Regenerating Neurons (3)
- Placement of Tubes across Injured Area
- Insertion of Immature Glial Cells
- Use of Chemicals to Stimulate Axon Growth
Attempts to Regenerate Neurons
1) Placement of Tubes across Injured Area
to provide path for axons
Parts of Cell Body (10)
1) Nucleus
2) Nuclear Membrane
3) Endoplasmic Reticulum (ER)
4) Mitochondria
5) ICF
6) Microtubules
7) Cell membrane
8) Lysosomes
9) Microfilaments
10) Golgi Bodies
Soma
1) Nucleus
contains genetic material (xsomes & genes)
Soma
2) Nuclear Membrane
double-layered membrane surrounding nucleus
protective barrier
Soma
3) Endoplasmic Reticulum (ER)
folded extension of nuclear membrane
- involved in protein & lipid synthesis
→ Smooth
→ Rough
Soma → Endoplasmic Reticulum
Smooth ER
lacks ribosomes
functions in lipid & carbohydrate metabolism & drug detoxification
Soma → Endoplasmic Reticulum
Rough ER
studded with ribosomes
site of protein synthesis
Soma
4) Mitochondria
double-membraned organelle that provides cellular energy (ATP)
- gathers, stores & releases energy
Soma
6) Microtubules
component of cytoskeleton
structural support & pathway for synaptic vesicles
Soma
7) Cell membrane
protective barrier surrounding entire neuron that seperates intracellular & extracellular components
Soma
8) Lysosomes
organelle enclosing degradative enzymes
- clean up waste within cell
Soma
9) Microfilaments
component of cytoskeleton
- actin filaments (thinnest)
- provide structural support
- cell motility
Soma
10) Golgi Bodies
membranous organelle
- packages proteins in vesicles (to protect from degradation) for transport to destination
Cell membrane → Structure
phospholipid bilayer that seperates ICF & ECF → critical for neural functioning & protection
- embedded proteins control passage of substances
- Interior: hydrophobic non-polar lipid tails
- Exterior: hydrophillic polar phosphate heads
Cell membrane regulates?
- movement of substances in/out of cell
- [ions] & [water]
Storage of Genetic Materal
- location?
nucleus
Genes
segment of DNA that encode synthesis of particular proteins
- contained within chromosomes
Chromosomes
- # in human somatic cell
double-helix structurse that hold entire DNA sequence
- 23 pairs (46 total)
Deoxyribonucleic Acid (DNA)
- made up of?
sequence of nucleotides bases
- Adenine (A)
- Thymine (T)
- Guanine (G)
- Cytosine (C)
Gene Transcription
- location
- process
occurs in nucleus
-
gene segment of DNA uncoils
- 1 strand serves as template → attracts free-floating nucleotides
- thymine replaced by uracil
- complementary mRNA strand formed
- leaves nucleus
Translation
- process
mRNA carries genetic code out of nucleus to ER
- comes into contact with ribosomes, which move along mRNA strand
-
tRNA drop off AAs encoded by consecutive sequence of 3 nucleotide bases, forming polypeptide chain
- forms protein
Translation
- codon
sequence of 3 bases that encodes for particular AA
Protein vs. Polypeptide
protein = folded-up polypeptide chain
Proteins → Packaging & Shipping
- functions (4)
proteins
→ have various functions
- cell structures, enzymes, hormones, neurotransmitters
→ packaged in golgi bodies & shipped to destination along microtubules
Protein Destinations (3)
1) Incorporated into membrane
2) Remain within cell as enzyme
3) Excreted via exocytosis
Proteins Embedded in Cell Membrane
- ability?
- occurs when?
ability to change shape
- occurs in response to changes in:
- chemicals
- voltage
- touch/stretch (stimuli)
Types of Proteins in Cell Membrane (3)
1) Channel
2) Gated Channel
3) Pump
Types of Proteins in Cell Membrane
1) Channel
opening in protein embedded in cell membrane that allows passage of certain ions
Types of Proteins in Cell Membrane
2) Gated Channel
protein embedded in membrane that allows passage of substances through on certain occasions
- gates open/close in response to trigger
Types of Proteins in Cell Membrane
3) Pump
protein embedded in membrane that actively transports substances across
Genes do not _____ cause behavior
Genes do not directly cause behavior
Genes code for proteins, but other factors influence protein production (4)
1) Gene pairs → 1 expressed, other may not be
2) Enzymes change mRNA in nucleus
3) Enzymes break-down proteins to make more
4) Proteins merge to create different proteins
Behavioral Variation
- flow chart
Genetic Variation
→ Different proteins
→ Different cell function
→ Behavioral variation
Abnormal Behavior
- flow chart
Abnormal genes
→ defective proteins
→ impaired cell function
→ abnormal behavior
Autosomes
NON-sex-determining xsome
pairs 1-22
Sex Chromosomes
pair 23 of human somatic cells
Alleles
alternate forms of a gene
→ gene pair contains 2 alleles
- pairs of xsomes → pairs of genes
Homozygous
having 2 identical alleles for a trait
- code for same protein
Heterozygous
having 2 different alleles for a trait
wild-type allele
most common nucleotide sequence in a population
- encodes most common phenotype
Mutation
alteration of allele that yields a different version
less frequently occuring sequence of nucleotides
Heterozygous Alleles → Dominant Allele
member of gene pair that is routinely expressed as a trait
Heterozygous Alleles → Recessive Allele
member of gene pair that is routinely unexpressed
Phenotype
physical & behavioral traits expressed by organism
- depends upon genotype
Genotype
genetic makeup of organism (genes), which influences phenotype (determines specific characteristics)
- can refer to 2 alleles of particular gene
Codominance
traits of both alleles are expressed completely
Examples of Codominance (2)
AB blood
Calico cats (only female)
- X chromosome has color gene
Allele Disorders (2)
1) Tay-Sachs Disease
2) Huntington’s Chorea
Tay-Sachs Disease
- caused by?
- results in?
caused by recessive allele on xsome 15
- causes defective HexA enzyme that fails to break down lipids in brain
- lipids accumulate in neurons
- results in retardation, physical changes (atypical growth) & death by ~ age 5
Tay-Sachs Disease
→ Normal Carrier x Normal
- possible outcomes & probability for offspring?
Normal carrier → 50%
Normal → 50%
Tay-Sachs Disease
→ Normal Carrier x Normal Carrier
- possible outcomes & probability for offspring?
Tay-Sachs → 25%
Normal → 25%
Normal Carrier → 50%
Huntingtons Chorea
- caused by?
- results in? when?
caused by dominant allele
- due to ↑ in # of CAG repeats on xsome 4
- > 40
- presents middle age (earlier if ↑ repeats)
- results in motor & cognitive disturbances
Huntington’s Chorea
→ Normal Carrier x Normal
- possible outcomes & probability for offspring?
Huntingtons → 50%
Normal → 50%
Huntington’s Chorea
→ Carrier x Carrier (will have if live long enough)
possible outcomes & probability for offspring?
Huntingtons → 75%
Normal → 25%
Relationship between Genotype & Phenotype
1 Genotype can produce many phenotypes
Phenotype is affected by? (2)
Gene Expression
Environment
Phenotypic Plasticity
capacity of one genotype to be expressed as more than one phenotype when exposed to different environments
- even cloned animals have different phenotypes despite identical genotype
Down Syndrome
chromosomal abnormality resulting in mental retardation & other abnormalities
caused by extra #21 xsome
Epigenetics
differences in gene expression related to environment & experience
Epigenetics
- How can environmental factors affect protein production? (3)
1) Histone Modification
2) DNA Modification
3) mRNA Modification
1) Histone Modification
genes may be:
- exposed via acetylation
- prevented from being exposed via methylation
… of tails of histones
which affects transcription
2) DNA Modification
DNA transcription into mRNA enabled/blocked
- methyl (CH3) groups bind to CG base pairs to block transcription
3) mRNA Modification
mRNA translation may be enabled/blocked
- binding of ncRNA to mRNA prevents translation