lecture 3 Flashcards
why do more complex organisms need a NS
Cells on the inside of the body are not in direct contact with the outside world
- also live in different environments
- have become specialised
in order for the organisms to function cell activities must be
coordinated
what systems are used to coordinate cella activity
endocrine and NS
ES
specialised to secrete chemicals - hormones into the blood stream - relatively slow and general
NS
specialised to transit electrical impulses between two or more cells
fast and precise
neural impulses provide
constant/ rapid communication
Neurons are specialised to
generate and transmit electrical impulses which are rapid , over great distances and precise
neurons virtually have no
possibility to store energy
so glucose and oxygen must constantly be supplied
life span of neutron s
neurons do not divide
they develop from neural stem cells - neurogenesis
glia cells
provide protected environment for euros to survive
types of glia cells
astrocytes
microglia
oligodendroglia
astrocytes
star shaped
physical and nutritional support for neurons
transport nutrients from blood vessels to neurones
plays role in neural signals transmitting
microglia
very small
mobile for defensive function
produce chemicals that aid repair of damaged neurons
digest dead neurons - phagocytosis
oligodendroglia
large flat branches
wrapped around axons
consist of fatty substance - myelin
insulating the axon
electrical activity - resin potential
when a neuron is not sending a signal - its at rest
inside of the Huron is negative to the outside
protein channels in cell membranes allows
specific ions to enter/ leave the cell
sodium potassium pump
maintains resting potential
3 sodiums fo OUT
2 potassium IN
If channels were passive
ions would freely flow - membrane would depolarise so there is no concentration differences = no electrical activity
sodium ions go
against the concentration gradient
depolarisation
positive ions In (negative ions out)
inside is less negative than usual
hyperpolarisation
negative ions IN(positive ions out)
inside MORE negative than usual
signal transmission - electrical
in the dendrites and soma
passive process
transmission in the axon is
active
ions move locally through the cell membrane
generated at axon hillock
sodium channels open or close in response
to electrical changes at the membrane
inflow of sodium ions
membrane depolarises - less negative
sodium channels open
sodium ions enter
membrane depolarises further- more positive on the inside
if membrane potential at axon hillock remains below threshold
resting potential returns
if membrane depolarises further
more sodium channels open - more depolarisation
when threshold is reached
all sodium channels open
generated action potential
when threshold is reached , potassium channels
open - potassium ions rush OUT of cell - membrane reprises
why does the action potential not travel backward
because during hyperpolarisation (more negative ) membrane is more difficult to depolarise
each burst of depolarisation acts as a
trigger - influx of positive ions
opens sodium channels
properties of AP
no decay
all or nothing principle
discontinuous - minimal time between subsequent AP
fast
saltatory conduction
sensory and motor neurons are myelinated
insulation - prevent ion inflow and outflow
rapid
nodes of ranvier
gaps that interrupt insulation every 1-2mm
