Unit 6- Nervous Co-ordination Flashcards
describe the general structure of a motor neuron
cell body contains organelles and high proportion of RER
dendrons branch into dendrites which carry impulses towards cell body
axon ling unbranched fibre carrier nerve impulses away from cell body
describe the additional features of a myelinated motor neurone
- Schwann cells which wrap around the axon many time
- Myelin sheath made of membranes of Schwann cells
- Nodes of Ranvier which are short gaps between Schwann cells where there isn’t any myelin sheath
name 3 processes Schwann cells are involved in
electrical insulation
phagocytosis
nerve recognition
how does an action potential pass along an unmyelinated neuron
- stimulus leads to influx of Na+ ions and the first section of the membrane depolarises
- Local electrical currents cause sodium voltage gated channels to open further along the membrane
- Sequential wave depolarisation occurs
explain why the myelinated axons conduct impulses faster than unmyelinated axons
Saltatory conduction which is the idea that the impulse jumps between one node of Ranvier to another and depolarisation cannot occur where the myelin sheath acts as an electrical conductos so the impulse doesnt travel along the whole axon length
what is resting potential and the number
the potential difference across neuron membrane when not stimulated
-70mV
how is resting potential established
- membrane is more permeable to K+ rather than Na+
- sodium potassium pump actively transports 3Na+ out of the cell and 2K+ into the cell and this leads to a electrochemical gradient where the inside of the cell is more negative than the extracellular environment
name the stages in generating an action potential
- Depolarisation
- Repolarisaion
- Hyperpolarisation
- Returning to resting potential
what happens during depolarisation
- stimulus causes the facilitated diffusion of Na+ ions into the cell down the concentration gradient
- potential difference across the membrane becomes more positive
- the membrane reaches the threshold potential of -50mV and the voltage gated channels for Na+ open
- significant influx of Na+ ions reverses the potential different to +40mV
what happens during repolarisation
- Voltage gated Na+ channels close and Voltage gated K+ channels open
- facilitated diffusion of K+ ions out of cell down their electrochemical gradient
- potential difference across the membrane becomes more negative
what happens during hyperpolarisation
- the K+ ions diffuse out and the pd becomes more negative then the resting potential causing overshoot
- there is a refractory period where no stimulus is large enough to raise membrane potential to threshold
- Voltage gates K+ channels close and the sodium potassium pump re-establishes resting potential
explain the importance of the refractory period
no action potential can be generated in hyperpolarised sections of the membrane
- ensures unidirectional impulse
- ensures discrete impulses
- limits freq of impulse transmission
what is the all or nothing principle
any stimulus that causes the membrane to reach threshold value will generate an action potential
all action potentials have the same magnitude
name the factors that affect the speed of conductance
- myelin sheath
- axon diameter
- temperature
how does axon diameter affect the speed of conductance
greater the diameter the faster
- less resistance to flow of ions
- less leakage of ions
how does temperature affect speed of conductance
higher the temp the faster
- the rate of diffusion is faster
- faster rate of respiration so more ATP available to re-establish resting potential
suggest an appropriate stat test to determine whether a factor has a significant effect on the speed of conductance
student T-test
suggest appropriate units for the max freq of impulse conduction
Hz
how can an organism detect the strength of a stimulus
larger the stimulus raises the membrane to threshold potential and the more quickly hyperpolarisation happens and therefore greater frequency of impulses
what is the function of a synapse
new impulses can be initiated in several different neurons for multiple simultaneous responses
describe the structure of a synapse
presynaptic neuron ends in a synaptic knob which contains lots of mitoch, ER and vesicles
synaptic cleft which is the gap between neurons
postynaptic neuron has complementary receptors
outline what happens in the presynaptic neuron when an action potential is transmitted from one neuron to another
- wave of depolarisation travels down the presynaptic neuron causing Ca2+ voltage gated channels to open
- vesicles move towards and fuse with presynaptic membrane
- exocytosis of neurotransmitter into the synaptic cleft
how do neurotransmitters cross the synaptic cleft
simple diff
outline what happens in the postsynaptic neuron when an action potential is transmitted from one neuron to another
- neurotransmitter binds to specific receptor on postsynaptic membrane
- ligand gated Na+ channels open
- influx of Na+ ions raises the threshold potential and an action potential is created
explain why synaptic transmission is unidirectional
- only presyn neuron has vesicles with neurotransmitter
- only postsyn neuron has complementary receptors
define summation and name the 2 types
neurotransmitters are accumulated to generate an action potential
- temporal
- spatial
what is the difference between temporal and spatial summation
temporal- one pre neuron release neurotransmitter several times in quick succession
spatial- multiple presyn neurons release neurotransmitter
what are cholinergic synapses
use acetylcholine as a primary neurotransmitter
located:
-preganglionic neurons
-parasympathetic postganglionic neurons
- motor end plate
what happens to acetycholine from the synaptic cleft
- hydrolysis into acetyl and choline by enzyme acetylcholinesterase ( AChE)
- acetyl and choline diffuse back into pre neu
- ATP is used to reform acetylcholine for storage in vesicles
explain the importance of AChE
prevents overstimulation of skeletal muscles
enables acetyl and choline to be recycled
what happens in an inhibitory synapse
- neurotransmitter binds to and opens Cl- channels on postsynaptic membrane and triggers the K+ channels to open
- Cl- moves in and K+ moves out via facilitated diffusion
- pd becomes more negative: hyperpolarisation
describe the structure of a neuromuscular junction
synaptic cleft between a presynaptic neuron and a skeletal muscle cell
contrast a cholinergic synapse and a neuromuscular junction
-cholinergic is found in motor, sensory abd relay and NMJ only motor
- cholinergic are excitatory and inhibitory, NMJ always excitatory
- cholingeric AChE is in the synaptic cleft, NMJ post membrane
how might drugs increase synaptic transmission
inhibit AChE
mimoc shaoe of neurotransmitter
how might drugs decrease synaptic transmission
- inhibit release of neurotransmitter
- decrease permeability of postsynaptic membrane to ions
- hyperpolarise postsynaptic membrane
