neurones communications mod 5 (laake booklet) Flashcards
where are chemoreceptors found and their function?
- in carotid arteries
- detect increase or decrease in blood ph
where are the baroreceptors found and their function?
- in blood vessels
- detect increase or decrease in pressure
what are receptor cells?
specialised cells which respond to a specific stimulus by initiating action potential
sensory receptor in nose?
olfactory cells
sensory receptor in retina
rods and cones
what receptor detects change in muscle length?
proprioreceptors
why would the response not continue to increase if a stimulus is constant?
receptor only detects changes in environments
what is sensory adaptation?
sensory receptors in the brain reduce their sensitivity to a continuous, unchanging stimuli.
what is habituation?
animal may learn to ignore a stimulus which is used to elicit stronger response -> due to repeat exposure
whats in the PNS (peripheral nervous system)
sensory and motor neurones
CNS
brain + spinal cord
what is the somatic nervous system? (THINK ‘S’)
voluntary/involuntary movement from skeletal muscles via motor neurone
what is the sympathetic nervous system
flight/fight response w/ noradrenaline
parasympathetic nervous system (+enzyme present)
relaxing responses e.g. REST AND DIGEST w/ enzyme * ACETYLCHOLINE + VAGOUS NERVE
what is neurone resting potential
-65mv
what is neurone threshold potential
-55mv
what is a change in electrical potential of membrane generated in response to stimulus called?
receptor potential
what is the magnitude of action potential?
+40mv
what happens when vibration is applied to a pacinian corpuscle…
lamellae are compressed and deformation causes NA+ channels to open
depolarisation is…
the entry of sodium ions (NA+)
what is a monosynaptic reflex
one synapse in the reflex arc e.g. sensory -> motor
what fraction of peripheral neurones are myelinated?
1/3
what is the myelin sheath made up of
schwaan cells
how is the myelin sheath kept alive?
schwaan cell nucleus and cytoplasm
function of myeline sheath
prevents ion movement across neurone membrane so it only occurs at nodes of ranvier so impulse jumps from node to node = rapid conduction
conduction of impulse in myelinated neurones
saltatory
conduction of impulse in non-myelinated neurones
continuous wave
function of non-myelinated neurones
coordinate actions where speed less important e.g. digestion
function of myelinated neurones
carry action potential over long distances quickly
as the diameter of axon decreases
rate of transmission decreases as there is more resistance to flow of ions = slower
speed of myelinated neuronal transmission
120 m/s
how does myelination affect speed of conduction
Na+ and K+ cannot diffuse through myelin sheath (insulator) so rapidly jumps between nodes increasing speed
how does temp affect speed of conduction
increase kinetic energy = ions diffuse quicker along axon
what is the concentration distribution of ions at rest?
Na+ higher on outside and K+ higher on inside (note: inorganic ions too big to pass out membrane)
how does neurone actively transmit Na+ and K+ without an action potential
sodium potassium pump
describe positive feedback relative to communication
if threshold potential reached, voltage gated Na+ ions channels open. Many Na+ diffuse in = depolarisation -> action potential
what is hyper-polarisation?
eventually voltage goes below the original -65mv
how does neurone restore the original resting potential after hyperpolarisation?
neurone redistributes ions by active pumping = 3 sodium ions out and 2 potassium ions in = voltage becomes less negative
at rest which ion is the membrane more permeable to?
potassium - as most sodium ion channels are closed but some of potassium ion channels are open
why is the inside of the axon always negative in relative to the outside
potassium ions lead out rapidly and cannot be replaced by sodium - This combined with presence of negative anions which are too large to leave neurone.
how to investigate ionic basis of nerve impulse (STATE key terminology first)
- axoplasm
-ions
-radioactive isotopes
-rest
-electrodes
-electrical charge
-voltage
how to investigate ionic basis of nerve impulse
- extract axoplasm and analyse chemically
- replace ions with radioactive isotopes
- trace movement at rest during transmission of impulse
- insert tiny electrodes into axoplasm of axon to measure electrical charge
what is an action potential caused by?
changed in permeability of the plasma membrane to Na+ and K+.
describe what the resting potential is
- membrane is polarised
- there is a stimulus caused by either a receptor/synapse
describe what depolarisation is
- sodium channels open and sodium diffused in (faciliated) potential difference becomes less negative = generator potential
- if threshold is reached positive feedback occurs = voltage gated Na+ channels open, many Na+ diffuse in = depolarisation
what is a monosynaptic reflex?
one synapse in reflex arc e.g. sensory -> motor
give an example of an autonomic response
pupil reflex -> reflex involving smooth muscle
what are responses to change in environment that doesn’t involve brain processing
reflex
what fraction of neurone is myelinated?
1/3
what type of cell is schwaan cell?
glial cell
how is the myelin sheath kept alive?
schwann cell nucleus and cytoplasm squeezed to periphery as the sheath forms
how long is a schwaan cell
1mm
function of the myelin sheath
-prevents ion movement across the N-membrane
-so movement can only occur at nodes of ranvier
-impulse jumps from node to node
- saltatory conduction
- = making conduction more rapid
describe the structure of non myelinated neurones
enveloped by schwaan cell, no extra layers or wrapping or phospholipid bilayer = no myelin sheath is formed
how does structure of non myelinated neurones affect the transmission?
ion movement is not prevented so action potential travel across neurone in a continuous conductive wave rather than jumping from node to node = slower transmission
function of myelinated neurones
carry action potentials over long distances quickly
function of non myelinated neurones
coordinates reactions where speed is less important e.g. digestion
what 3 factors is speed of conduction affected by?
- axon diameter
- myelination
- temperature
how does diameter affect the speed of conduction
greater diameter = faster speed bc if narrow there is a greater resistance to flow of ions (current) so slower
why does myelination increase speed of conduction
- Na+ and K+ cannot diffuse through the myelin sheaths
- so ionic movements can only occur at nodes
- therefore local currents elongated from one node to next
- axon potential jumps from node to node = saltatory conduction (faster)
differences between sensory and motor neurone
- SN cell body outside CNS, MN body within
- SN has dendron, MN doesnt
- SN long dendrites, short axon, MN opp.
- SN transmit msgs to CNS, motor recieves signals from CNS to initiate muscle/gland to contract/secrete
similarities between sensory and motor neurone
- both contain cell body, with a nucleus, and carry action potentials via neurotransmitters, contain pumps, has axon which carries impulses etc…
how is relay neurone different?
- only in CNS
- no schwaan cell
- very short neurone
how does facilitated diffusion oppose the pumping of ions during resting potential?
membrane is more permeable to K+ than Na+ as most of sodium channels are closed but some of the potassium channels are open = K+ diffuse down conc grad
why is inside of axon always more negative than outside
K+ leak rapidly and cannot be replaced by sodium readily & presence of anions in which are too large to leave ion make it more negative.
