5.1.3 Neuronal Communication Flashcards
sensory receptor
specialised cells which respond to a specific stimulus by initiating an action potential
a receptor is a transducer as it transforms stimulus energy into electrical responses
pacinian corpuscles in skin stimulus
changes in pressure on skin
stretch receptor in muscles stimulus
changes in muscle length
baroreceptors stimulus
movement
osmoreceptors stimulus
solute concentration of blood
sensory adaptation
neural or sensory receptors in the brain change/reduce their sensitivity to continuous, unchanging stimuli
pacinian corpuscle energy change
kinetic energy to electrical energy
baroreceptor energy change
kinetic energy to electrical energy
osmoreceptor energy change
chemical energy to electrical energy
habituation
Over time, organisms may become more sensitive due to exposure
OPPOSITE OF SENSITISATION
stretch receptor energy change
kinetic energy to electrical energy
a nerve
an enclosed cable-like bundle of nerve fibres/neurones/cells
central nervous system
brain, spinal cord, relay neurones
peripheral nervous system
cranial, spinal nerves, containing sensory/motor neurones
somatic nervous system
voluntary movements and involuntary reflexes - output to skeletal muscle via motor neurones
autonomic nervous system
involuntary - output to smooth muscle or glands or cardiac muscle or internal organs
parasympathetic nervous system
relaxing responses - rest and digest
neurotransmitter is acetylcholine and many axons in the vagus nerve
sympathetic nervous system
internal alarm
fight or flight responses
ganglion
swelling that contains lots of synapses/cell bodies
grey matter
synapses, unmyelinated relay neurones, numerous cell bodies
white matter
myelinated axons of neurones, relatively few cell bodies
threshold value
the minimum receptor potential needed to generate an action potential
all-or-nothing response
if the stimulus reaches a certain level, above the threshold, a response will be triggered. if it does not meet the threshold, no response occurs
receptor potential
the change in electrical potential caused by a stimulus
monosynaptic reflex
one synapse in a reflex arc
e.g sensory to motor
reflex arc
responses to changes in environment that do not involve any processing in brain to coordinate movement
same stimulus produces same response every time
allow the body to make involuntary adjustments to changes in external environment to help control internal environment
stimulus of an action potential
stimulus triggers stretch-mediated sodium ion channels to open.
sodium ions diffuse into axon, down an electrochemical gradient
potential becomes more positive as ions move in
if enough ions diffuse in to make potential ≥ -55 mV, depolarisation is triggered
depolarisation of an action potential
when threshold (-55mV) is met or exceeded, voltage-gated sodium ion channels open and sodium ions diffuse into the axon, down an electrochemical gradient
the inside of the axon becomes less negative as more positive ions diffuse in - reducing potential difference
this triggers more channels to open = more sodium ions diffuse in = more depolarisation
example of positive feedback
repolarisation of action potential
after potential difference reaches +40mV, voltage-gated sodium ion channels close = stops further sodium ions diffusing into axon
voltage-gated potassium ion channels open, causing potassium ions to diffuse out of axon, down electrochemical gradient
axon becomes less positive and potential difference returns to -65mV
example of negative feedback
hyperpolarisation of an action potential
potential difference undershoots slightly, making axon more negative than at rest
potassium ion channels close too slowly and too many ions diffuse out
redistribution of ions to return to an action potential
sodium ion/potassium ion pump restores the normal distribution of ions, restoring the resting potential
maintenance of a resting potential
sodium/potassium ion pump: uses ATP to actively transport 3 Na+ OUT of axon, 2 K+ IN. = larger concentration of positive ions outside axon than inside the axon. establishes an electrochemical gradient
differential membrane permeability: selective protein channels allow Na+ and K+ to move across the membrane by facilitated diffusion.
protein channels less permeable to Na+ than K ions = K+ ions can diffuse back down their concentration gradient, out of the axon, at a faster rate than Na+ ions
function of a motor neurone
carry impulses from CNS towards effector
short dendrites, long axons
if connected to muscle= motor end plate
function of a relay neurone
intermediate neurones
found entirely within the CNS
connect sensory and motor neurones
absolute refractory period
during depolarisation
no additional stimulus can produce an action potential - sodium ion conc. is high in axon, sodium ion channels already open
relative refractory period
during repolarisation and hyperpolarisation
only a more intense stimulus can produce an action potential
refractory period
after an axon transmits an impulse, it cannot transmit another impulse immediately because:
Na+/K+ distribution is to be restored
membrane must be repolarised
importance of the refractory period
action potential is only propagated forwards, towards the region which is not in refractory period = 1 direction only
separates action potentials - by the time the second AP is generated, the first has passed further down = sets an upper frequency limit
the significance of the frequency of impulse transmission
a neurone will either conduct an action potential or not = all or nothing law.
a more intense stimulus does not cause a larger impulse - causes sensory neurons to produce more generator potentials = more frequent action potentials in sensory neurone
more vesicles released at the synapse, higher frequency of action potentials in the postsynaptic neurone and higher frequency of impulses to the brain
roles of synapses
to connect two neurones to pass a signal from one to the other - cell signalling
ensure one-way transmission between neurones
divergence
summation - spatial summation & temporal summation
memory and learning
synaptic fatigue prevents overstimulation
allows weak background stimuli to be filtered out - sensory adaptation e.g. smell of house
divergence
one presynaptic neurone might affect many postsynaptic neurones so one AP can be transmitted to several parts of the brain/body
e.g. reflexes - one pathway causes response, one pathway informs brain
summation
a type of neural integration whereby all input from several postsynaptic potentials are added together
spatial summation
convergence
one postsynaptic neurone could receive potentials from many presynaptic neurones
postsynaptic neurone adds together all stimuli from all presynaptic neurones = producing a coordinated response
temporal summation
repeated stimulation of the same synaptic ending in rapid succession may occur until sufficient neurotransmitters are released to allow EPSPs to combine & reach threshold potential to produce AP
ensures only stimulation that’s strong enough is passed on
function of myelin sheath
prevents ion movement
saltatory conduction
increases speed of impulse/action potential
insulates axon
