neuronal communication Flashcards
describe the structure of a neurone
cell body (contains nucleus and other organelles)
dendrons (carry impulse towards cell body)
axons (carry impulse away from cell body)
What are three types of neurones
sensory
motor
relay
What do motor neurones do
involved in transmitting electrical
impulses from the CNS to effectors
What do sensory neurones do
transmit impulses from receptors to CNS
What do relay neurones do
located in the CNS and transmit impulses from sensory to motor neurones
describe the nature of neurones
polarised
at resting state outside of neurone is positive and inside is negative
this allows them to carry action potentials
how is speed of transmission increased
myelin sheath ( insulates axons)
formed by Schwann cells
mechanism that speeds transmission is known as saltatory conduction
action potential jumps between gaps of myelin sheath known as nodes of Ranvier
Why are neurones polarised
imbalance between sodium and potassium ions
potential difference across membrane with value of -70mv (resting potential)
How is resting potential maintained
sodium-potassium pumps move sodium ions out of neurone
creates electrochemical gradient as conc of Na is higher outside
membrane not permeable to Na so cannot enter
potassium pumps transport potassium into neurone but potassium diffuses back out due to potassium ion channels
describe stimulation of a neurone
excitation by stimulus causes sodium ion channels to open
makes neurone permeable to sodium ions so sodium ions diffuse into neurone down electrochemical gradient
makes inside less negative
when threshold is reached -55mv, more sodium channels open
giving p.d of 30mv ( end of depolarisation)
Repolarisation is achieved as a result of sodium ion channels closing and potassium channels opening
potassium ions diffuse out of neurone and eventually restore resting potential
closing of K channels is delayed so p.d becomes greater than resting
restored with sodium potassium pumps
What are synapses
junctions between two neurones
Explain what happens at the synapse
upon arrival of action potential
presynaptic membrane depolarises
causing ca channels to open
calcium ions enter neurone
fusion of synaptic vesicles and presynaptic membrane
neurotransmitter is released into synaptic cleft and diffuses through it
neurotransmitter binds to receptor in postsynaptic membrane
cation channels open
sodium ions enter
another action potential occurs
What are receptors
cells specialised for detection of stimuli
feature of receptors
transducers-convert wone form of energy into another
What are pacnian corpuscles
pressure receptors found in skin
convert mechanical energy to electrical energy
