Biology chapter 13 neurones

motor, relay and sensory

what are the three types of neurones?

neurones transmit impulses from a relay neuron or sensory neurone to an effector such as a muscle or gland

label parts of motor neurone

what do they do?

transmit impulses from sensory receptor cell to a relay neurone, motor neurone or brain

what do sensory neurones do

transmit impulses between neurones

what do relay neurones do and look like

nucleus and teh cytoplasm has lots of endoplasmic reticulum and mitochondria to make neurotransmitters

what does the cell body contain?

short extensions from the cell body that split into dendrites. transmit impulses towards cell body

what do dendrons do?

singular elongated nerve fibres that transmit away from cell body

what do axons do?

• Schwann cells produce layers of membranes by growing around the axon many times

• acts as an insulating layer

• allows faster conduction as the action potential jumps between the nodes of Ranvier

• called saltatory conduction

what is a myelin sheath and how does it affect trasmission of impulses?

convert stimulus they detect into a nervous impulse.

they are transducers

information passed through nervous system and to CNS.

what do sensory receptors do?

specific sensory receptors that detect mechanical pressure. deep within your skin.

• end of the sensory neurone is found within layers of connective tissue.

• membrane has Na+ ion channels

what is a pacinian corpuscle?

how do they look (draw)?

structure

• in the resting state, the stretch-mediated sodium ion channels in the membrane are closed.

• This is the resting potential. Higher Na+ conc outside the cell.

• when pressure applied, membrane changes shape

• membrane stretches and stretch-mediated Na+ ion channels open

• influx of positive ions, the membrane becomes depolarised.

• the generator potential creates an action potential

how does pacinian corpuscle converts pressure into a nervous impulse?

• -70mV, the outside is more positive than the inside

• 3 Na+ ions actively transported out

• 2 K+ ions actively transported into the neurone

• done by sodium potassium pump

• so more sodium ions outside than inside so sodium ions diffuse back and potassium ions diffuse out

• but most of the gated sodium channels are closed while potassium channels are open so more positive outside than inside as K+ diffuses out

what is happening at resting potential in a neurone?

• action potential, occurs when protein channels change shape due to a voltage

• at the resting potential the potassium ion channels open and sodium VGC are closed.

• energy of the stimulus triggers sodium VGC to open and sodium diffuses in. Inside is now more positive.

• threshold potential reaches at -50mv which triggers more sodium VGC to open.

• when potential difference reaches +40mV the sodium VGC close and the potassium VGC open.

• potassium diffuses out, and inside is more negative.

• First, lots of potassium diffuse out, but then it becomes hyperpolarised. potassium VGC close.

• The sodium-potassium pump causes sodium ions to move out and potassium to move in, returning to the resting potential

what happens to generate an action potential?

• When the first region of the membrane is depolarised, this acts as a stimulus for the next region to become depolarised

• Once Na+ are inside, they are attracted by the negative charge further along, so they diffuse along.

• This causes the sodium VGC further along to open and Na+ moves in.

• behind the depolarization, the Na+ VGC close and K+ ones open so K+ ions diffuse out.

• returns to a polarised state.

propogation of an action potential

• a certain level of stimulus, the threshold value, will always trigger a response

• no matter how large the stimulus is, the same size AP is generated

• if the threshold is not reached, AP not generated

• if stimulus is larger, the frequency of AP increases

what is the all or nothing principle?

• axon diameter (the bigger it is, the faster the impulse as less resistance to flow of ions)

• temperature (higher temp means faster diffusion)

what two factors other than myelination affect transmision speed?

label parts of the synapse

• excitatory - result in depolarisation (acetylcholine)

• inhibitory - hyperpolarisation of membrane (prevents action potential being generated)

what are the types of neurotransmitters?

• action potential reaches pre synaptic knob

• depolarisation of membrane and causes calcium ion voltage gated channels to open

• Calcium diffuses in

• Synaptic vesicles with neurotransmitters fuse and exit by exocytosis and travel across the synaptic cleft

• bind to receptor molecules on the postsynaptic membrane

• causes sodium ion channels to open

• Sodium ions diffuse into the postsynaptic neurone

• triggers AP

• Then, acetylcholine is broken down by acetylcholinesterase so that the response doesn’t happen again

how are impulses transmitted across the synapse

sometimes the amount of neurotransmitter is not enough to reach threshold potential so the neurotransmitter needs to be built up.

• spatial summation - lots of neurones connect to one post synaptic neurone. each one releases enough to trigger AP

• temporal summation - single neurone release neurotransmitter several times over a short period to build up. (think: temporal means over time)

what is summation?

what are the two types?

• ensure impulses are unidirectional

• allow one neurone to transmit to many synapses

• or multiple neurones can feed into one neurone

role of synapses