Lec 9: Fundamentals of NS (neurons & neural transmission within a cell) Flashcards
cells are specialized to perform specific ___
functions
human NS is comprised of what 2 types of cells
neurons
glia
neurons are specialized for _____
- 2 roles
communication
1) information transmission (e.g. about detected event or requirement movement)
2) information processing (e.g. to interpret a pattern of visual info as being a human face)
what did Cajal do?
first to demonstrate that the individual cells comprising the NS remained separate
- showed they did not grow into each other as previously believed
neurons contain which 5 structures?
1) membrane (separate inside from outside)
2) nucleus (contain chromosomes)
3) mitochondria (perform metabolic activities, provide energy the cell requires)
4) ribosomes (synthesize new proteins)
5) endoplasmic reticulum (new protein packaging system)
movement of afferent vs efferent???
afferent= towards CNS, from receptor in PNS
efferent= from CNS to muscles/glands
are sensory neurons afferent/efferent?
afferent
- sensory rec in PNS –> CNS
are motor neurons afferent/efferent?
efferent
- CNS–> muscles/glands
a sensory neuron is _____ at one end to b highly ____ to a particular type of _____
specialized
highly sensitive
stimulation (e.g. touch, temperature, odour)
motor neuron has its ____in the spinal cord and receives ____ from other neurons and conducts impulses along its ___ to a muscle
soma in spinal cord
receives excitation
axon to muscle
name 5 components similar in all neurons
dendrites
soma/cell body
axon
myelin sheath
presynaptic terminals
what are dendrites?
branching fibres with a surface lines with synaptic receptors responsible for bringing in information from other neurons
some dendrites contain ____ ___
dendritic spines
- further branch out and inc the surface area of the dendrite
what is contained within the soma?
nucleus
mitochondria
ribosomes
other structures found in other cells
what is the function of the soma?
responsible for the metabolic work of the neuron
what is an axon?
thin fiber of a neuron responsible for transmitting nerve impulses away to other neurons, glands or muscles
some neurons are covered with an insulating material called ____ ____
myelin sheath
interruptions in the myelin sheath are called __________
nodes of Ranvier
what are presynaptic terminals?
end points of an axon responsible for releasing chemicals to communicate with other neurons
what is an afferent axon?
bringing info INTO a structure
what is an efferent axon?
carry info AWAY from a structure
what are interneurons???
aka..?
aka intrinsic neurons
- dendrites/axons are completely contained within a structure
- responsible for the gating activity of other cells
T/F the function is closely related to the shape of a neuron?
TRUE
- shape determines its connection with other neurons
which type of neurons branch extremely widely within a single plane?
cerebellum purkinje cells
name 5 types of glia
astrocytes microglia oligodendrocytes schwann cells radial glia
what is the function of astrocytes?
help synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon
what is the function of microglia?
remove waste material and other micro-organisms that could prove harmful to the neuron
at what stage in development are microglia important?
during period of apoptosis in early development (where there is synaptic pruning)
- aid in cells being degraded
what is the function of oligodendrocytes and Schwann cells?
build the myelin sheath that surrounds the axon of some neurons
what is the function of radial glia?
guide the migration of neurons and the growth of their axons and dendrites during embryonic development
describe active transport in the NS
protein mediated process by which useful chemicals are brought into the brain
which 4 materials are transported via active transport int he brain?
glucose
hormones
amino acids
vitamins
- brought INTO brain via active transport
glucose is a ____ sugar, it is the primary source of ____ for neurons
simple sugar
nutrition
name a chemical that is necessary for the use of glucose in the brain
thiamine
what is the blood-brain barrier?
mechanism that surrounds the brain and blocks most chemicals from entering
- block incoming viruses, bacteria, and harmful material from entering b/c neurons do not regenerate
** where does neurogenesis occur in the adult brain? (3)
olfactory bulb
dentate gyrus
hippocampus
what are terminal buttons of axons?
form junctions with other cells and release NT
name the 3 main functions of a neuron
1) reception
2) conduction
3) transmission
during an AP, what is the direction of neural impulse?
toward axon terminals
describe neuron communication
- impulse releases NT from vesicles
- NT enters synaptic gap
- NT binds to receptors on the receiving neuron
information must be transmitted in 2 ways
1) WITHIN each neuron
2) BETWEEN neurons
neuron membrane is composed of ____ & _____
lipid & protein
what is embedded in the membrane? why?
protein channels
permit certain ions to cross through the membrane at a controlled rate
ion channels are what type of proteins?
pore-forming membrane proteins
what is the function of ion channels?
establish a resting membrane potential and shape AP by gating the flow of ions across the cell membrane
why is ACh important?
neuromuscular junctions
- association with ACh receptor to open the channel (= influx of Na)
- blocked by Na ions
What are the 2 types of ion channels?
- ligand gated (NT)
- voltage-gated
how do voltage-gated ion channels work?
open and close in response to small voltage changes across the plasma membrane
what is the resting potential?
electrical charge across the membrane, it is ~70mV differentce between inside and outside
-70mV
the membrane is ____ permeable which means
selectively permeable
- allowing some chemicals to pass more freely than others
what are ions?
electrically-charged molecules
e.g. Na, K, Cl
why does a resting potential exist?
because ions are concentrated on different sides of the mmebrane
which ions are inside the cell?
Na and Cl
which ions are outside the cell
K and organic anions
electical voltages and concentration gradients across the membrane exert ____ on the ions
forces
explain the forces exerted on ions
- K and Cl: forces of voltage and concentration are balanced
- organic anions are too large to pass through membrane
- BOTH voltage & concentration forces lead to Na entering the cell
list 2 ways that the resting potential is maintained
- Na ions are actively transported to maintain resting potential
- Na/K pump exchanges 3Na for 2 K
how many molecules of Na and K are exchanged using a Na/K pump?
3Na
2K
what is the Na/K pump?
protein complex that continually pumps 3Na out of the cells, while drawing 2K ions into the cell
main purpose of the Na/K pump?
help maintain electrical gradient
** 4 steps of the Na-K exchange pump
1) 3Na and ATP bind to the carrier molecule
2) ATP breaks down to ADP+P, and release energy. Carrier molecule changes shape, Na are transported across the membrane
3) Na diffuse away from the carrier, 2K bind to carrier, P is released
4) carrier molecule resumes original shape, transporting K across membrane, K diffuse away from carrier. Carrier can again bind to Na and ATP
in basic terms, what is an AP
rapid depolarization of the membrane
stimulation of the neuron past the threshold of excitation triggers ____ or ____
nerve impulse
AP
where does AP start?
axon hillock
- passes quickly along axon
following AP, the membrane is quickly ____ to allow subsequent firing
repolarized
describe the 4 main events that occur during the course of an AP
1) AP begins with partial depolarization
2) excitation threshold is reached, sudden large depolarization
3) followed rapidly by repolarization
4) then brief hyperpolarizaiton
what is the excitation threshold?
tells us what the membrane potential is that is required to be changed to commit to the depolarization
what are voltage-activated channels?
membrane channels
permeability depends upon the voltage different across the membrane
explain what happens during rapid depolarization
- when partial depolarization reaches activation threshold, voltage-gated Na channels open
- Na rush into
- nerve pulse occurs
- mem potential changes from =70mV to +40mV
- net pos charge inside, net neg charge outside= depolarization
what is depolarization?
decreasing the polarization towards 0
explain what happens during repolarization
- Na channels close, become refractory
- depolarization triggers opening of voltage-gated K channels
- K rush out of cell, repolarizing, then hyper-polarizing
- net neg inside, net pos outside
explain how the resting potential is resumed
- K channels closed
- repolarization resets Na channel
- ions diffuse away from the area
- Na/K transporter maintains repolarization
- membrane is ready to “fire” again
what is the function fo local anesthetic drugs on gated-ion channels
block Na channels
prevent AP
e.g. Novocain
what is the All-or-None response?
- AP
- always the same size
- either it is not triggered at all (membrane refractory) OR triggered completely
what is a refractory period?
- sensitivity of area to further stimulation decreased for a time
2 different types of refractory periods
absolute
relative
what is an absolute refractory period?
- complete insensitivity exists to another stimulus
- from beginning of AP until near end of repolarization
what is a relative refractory period?
stronger-than-threshold stimulus can initiate another AP
what does ‘propagation of AP’ mean?
transmission of AP down the axon
passive conduction ensures….
adjacent membrane depolarizes, so AP travels DOWN axon
transmission by continuous AP is relatively ____ (fast/slow) and energy consuming because _____
slow
b/c of Na/K pump
what is the faster, more efficient mechanism for conduction of AP
saltatory conduction
saltatory conduction is facilitated through….
myelination (wrapping of myelin)
what is a myelin sheath?
fatty material made by glial cells (oligodendrocytes/Schwann cells)
function of myelin sheath?
- insulate the axon
- prevent passage of ions over the membrane
- allow for rapid movement of electrical impulses along axon
what is a Node of Ranvier?
gaps in myelin sheath where AP are transmitted
- at each Node, the AP is regenerated by a chain of positively charged ion pushed along by the previous segment
what is the speed of a neural impulse?
2-200+ mph
explain saltatory conduction
- myelinated regions of axon are electrically insulated
- electrical charge moves ALONG the axon (vs across the membrane)
during saltatory conduction, where does AP occur?
only at unmyelinated regions
–> Nodes of Ranvier
benefit of “jumping” of AP in saltatory conduction
jumping of AP from node to node
- provides rapid conduction of impulses
- conserves energy of the cell
(saltatory conduction)
AP at node triggers ____ to the next node, where the membrane ____
AP at node triggers flow of current to the next node
membrane regenerates the AP
what would happen if there were no myelin sheaths?
a lot of current leakage
T/F there are nerves in the CNS
FALSE
in the CNS the groups/bundles of nerve fibres are called what???
tracts
e.g. spinothalamic tract
what is the definition of a nerve?
a distinct peripheral extension of the CNS conducting electronic messages (AP) to and from the CNS
every spinal/cranial nerve is surrounded and protected by ____ tissue
connective tissue
what is the endonerium?
wraps each neuron
what is the perineurium?
covers nerve bundles (fascicles)
what is the epineurium?
covers fascicles
intensity of AP is expressed as what?
impulses/second
IPS: 0-1000
conduction velocity is expressed as?
0.2- 120m/s
an AP is a rapid ____ electrical change that is ___, not graded. it obeys the ____ law
rapid reversible
maximal
all or none
what are NTs?
chemical messengers that traverse the synaptic gaps between neurons when released by the sending neuron
- travel across synapse, bind to receptor sites on receiving neuron
- influence whether it will generate neural impulse
what is ACh?
what is it involved in?
acetylcholine
- 1st substances identified as NT
- link motor neurons and muscles (contract/relax)
- involved in memory, learning, sleep, dreaming
what are endophins?
- bound like NT
- released during pain and discomfort
main functions of ACH
enables muscle action, learning, memory
examples of ACh malfunctions
- alzheimers disease
ACh- producing neurons deteriorate
main functions of DA?
influence movement, learning, attention, emotion
examples of DA malfuctions
- excess DA= schizophrenia
- lack DA= tremors, dec mobility, Parkinsons
main functions of 5-HT?
affects mood, hunger, sleep, arousal
examples of 5-HT malfunctions
- linked to depression
main functions of NE?
control alertness and arousal
result of lack of NE
depress mood
what is a major inhibitory NT?
GABA
undersupply of GABA linked to?
seizures, tremors, insomnia
what is a major excitatory NT?
what is it involved in?
glutamate
memory
oversupply of glutamate results in??
- can overstimulate brain
- migraines, seizures
what are effects of drugs on the brain?
- alter amount of NT released at synapses
- mimic/facilitate action of NT
- block action of NT
what is an agonist?
mimic/facilitate actions of NT
what is an antagonist?
oppose/block actions of NT
