Neurones or nerve cells

part of module one of

unit F214

Communication, homeostasis and energy

Independent work for Monday 16th Nov1) a) Draw and fully label a sensory neurone and a

motor neurone to show their structure.b) State the function of sensory and motor neurones.

2) Describe and explain at least 4 ways in which neurones are adapted for their function.

3) Write a definition for each of these terms:- a) relay neurone b) CNS c) polarised membrane d) resting potential

4) a) Name at least 4 types of sensory receptors in humans, their position and the stimulus detected;

b) Explain why receptors can be called transducers?

5) State at least 5 facts about synapses.

Revision plan for F212 resits – evidence of revision needed by Lloyd, Georgina, Emily

1) By Monday 23rd NovBiological molecules – carbohydrates,

proteins, lipids, water, enzymes, DNA, RNA

2) By Monday 30th NovDiet, food, antibodies, vaccination, smoking,

cardiovascular disease

3) By Monday 7th December Biodiversity, conservation, classification,

natural selection and evolution

Resting potential

• negative inside neurone plasma membrane and positive outside

• -65 / -70 mV difference• produced by active transport using sodium

– potassium pumps in the plasma membrane

• 3 Na+ out of cell and 2 K+ in• K+ diffuses back; Na+ does not

• Resting potential• http://www.youtube.com/watch?v=iA-Gdkje6pg&feature=related

How do neurones carry information?

resting potential refractory period

action potential all or nothing law

depolarisation local circuits

repolarisation saltatory conduction

Action potential and transmission

http://www.youtube.com/watch?v=SCasruJT-DU&feature=related

Why do nervous impulses travel at different speeds? Can you describe and explain this

data?type of neurone diameter / um myelinated or

unmyelinated?speed of impulses in m/s

cat axon 1 unmyelinated 3

squid axon 1000 unmyelinated 30

frog axon 10 unmyelinated 20

cat axon 10 myelinated 50

Aims of today’s lesson

• Remind about SMART targets for Biology

• Review resting potential and action potentials – notes and questions

• Learn about function of myelin sheath

• Learn about synapses – gaps between 2 neurones or a neurone and muscle cell

Resting potentials and action potentials

Resting potential

• negative inside neurone plasma membrane and positive outside

• -65 / -70 mV difference• produced by active transport using sodium

– potassium pumps in the plasma membrane

• 3 Na+ out of cell and 2 K+ in• K+ diffuses back; Na+ does not

• Resting potential• http://www.youtube.com/watch?v=iA-Gdkje6pg&feature=related

How do neurones carry information?

resting potential refractory period

action potential all or nothing law

depolarisation local circuits

repolarisation saltatory conduction

Action potential and transmission

http://www.youtube.com/watch?v=SCasruJT-DU&feature=related

synapses

Synaptic cleft = gap between 2 neurones

Synapse = synaptic cleft + parts of neurones near cleft

Neuromuscular junction = where axon meets muscle

Aims of today’s lesson

• Complete individual research on synapses

• Check exam questions 3 and 4 set yesterday

• Answer exam questions 5, 6 and 7 - to be checked in tomorrow’s lesson

• Start on exam questions 8, 9, 10 and 11 – to be checked on Monday 23rd Nov

• All work on nerves to be learned by Tuesday 24th November – you will answer an exam question in the lesson

• Complete progress reviews

• http://www.wisc-online.com/objects/index_tj.asp?objID=AP1201

Aims of today’s lesson• Check individual research on synapses and add notes

on the function of synapseshttp://www.wisc-online.com/objects/index_tj.asp?objID=AP1201

• Check exam questions 5, 6 and 7 set yesterday

• Reminder - exam questions 8, 9, 10 and 11 – to be checked on Monday 23rd Nov

• Reminder - all work on nerves to be learned by Tuesday 24th November – you will answer an exam question in the lesson

• Reminder – 5 lessons next week (i.e. including Friday)

• Overview of co-ordination by nerves

A cholinergic synapseHow does it function? And what is the role of each organelle?

Drugs and synapses• Nicotine mimics acetylcholine and binds to

receptors so more impulses occur• Amphetamines and cocaine mimic

neurotransmitter (noradrenaline) in the synaptic cleft so more impulses occur

• Heroin and morphine mimic the neurotransmitter endorphin (an inhibitor) so fewer impulses and pain not felt

• Nerve gas and strychnine poison prevent acetyl cholinesterase enzyme working so impulses continually generated

• Curare (a poison from plants) binds to receptors on postsynaptic membrane of muscles and causes paralysis as no impulses occur

Why have synapses?• Action potential transmitted from one neurone to the next

Action potentials only travel in one direction

• Filters out weak stimuli – not enough neurotransmitter released so no action potential

• Acclimatisation – repeated stimulation no longer produces response – vesicles of neurotransmitter not reformed

• Co-ordination convergence = several neurones onedivergence = one neurone manysummation – temporal or spatial – results in enough neurotransmitter being released

• Memory – creating synaptic pathways

Receptors as transducers

Transmission down the axon

Local currentsare themovement ofions by diffusionalong the neurone.

Action potential and transmission

• http://www.youtube.com/watch?v=SCasruJT-DU&feature=related

• Resting potential

• http://www.youtube.com/watch?v=iA-Gdkje6pg&feature=related

• Neuron Structure

• http://www.youtube.com/watch?v=XgIaAs_ONG4&feature=related

Reflex actions and the reflex arc• Answer SAQ 6.10 about reflex actions.

• State 5 characteristics of all reflex actions.

• What is a reflex arc? How many neurones are involved and what are their names?

Complete the drawing by adding a sensory neurone, an intermediate neurone and a motor neurone (excitatory).

Label the diagram fully and show the direction of the nervous impulse / action potential.

Brain warm up – nerve cells

• Name 3 types of neurone.• What is an axon?• Why could impulses travel at different speeds?• What is a node of Ranvier?• Where are the cell bodies of neurones?• State 3 characteristics of reflex actions.• What are the grey matter and the white matter?• What is a synapse?

In mammals, changes in the internal and external environment are detected by receptors ( June 2004)

a) State the general name given to changes in the environment that can be detected by receptors. (1)

b) Explain why it is important for mammals to be able to detect changes in their internal environment.

(3)

c) Receptors are often described as biological transducers, structures which convert energy from one form into another. Explain how receptors in mammals convert energy into action potentials. Use named examples of receptors in your answers. (8)

Jan 2002, number 6 - answera) E synaptic cleft F postsynaptic membrane

G synaptic knob / bulb H vesicle / neurotransmitter

b) depolarisation of presynaptic membrane by action potential (reject impulse);calcium channels open so calcium ions diffuse in;vesicles fuse with presynaptic membrane;acetylcholine / neurotransmitter released into synaptic cleft;ACh diffuses across cleft;binds to receptors on postsynaptic membrane;sodium channels open and sodium ions diffuse in;membrane depolarised;if over threshold, action potential produced;role of hydrolysis enzyme;role of mitochondria e.g. active transport or synthesising ACh;

c) myelin sheath = electrical resistance/insulation;depolarisation only at nodes;action potential jumps from node to node / saltatory conduction;fast conduction;

d) action potential has fixed size;produced at full size if stimulus / depolarisation is greater than threshold or not at all;