C2.2 Neural signalling

C2.2.1 Neurons

Brain + spinal cord = Central Nervous System: receive sensory information from receptors, then interpret and process that sensory info. If response is needed, part of brain/spinal cord initiates the response.

Cells carrying info = neurons. Sensory: to CNS, Motor: to Muscles.

Together: peripheral nerves.

Neuron = individual cell carrying electrical impulse from 1→ 2, quickly.

Nerve = many neurons working tg

C2.2.1 Neuron structure

Dendrite (many short fibres) + cell body (nucleus) + axon(long fibre)
At end of axon = synaptic terminal buttons: release neurotransmitters → carry impulse to next neuron/muscle. Impulse carry from dendrite → axon → term.

Around axon = myelin sheath (Schwann cells), nodes of Ranvier (“holes”)

Impulse = action potential. electric (movement of + charged ions)

C2.2.2 Resting potential

Plasma memb restricts ion movement; so conc grad in vs out.

Neurons have membr pot of -70 mV, waiting for impulse transmission.

-70 bc. more Na out than K in so more + out then in

C2.2.3 Action potential

Electric signal = moving ion/electron

Nerve = + ions moving.

Nerve impulse is brief reversal of normal polarization (rest potential -70mV) of neuron membrane bc of facilitated Na⁺ K⁺ ion diffusion

1. Depolarization: Na⁺ channels open: Na⁺ into neuron; inside: +40mV

2. Repolarization: Right after: close Na⁺, open K⁺ , back to -70mV

3. Rebuilding gradients: after; Na⁺/K⁺-pump re-establish conc. grad

Propegation of nerve impulse: 1 action potential → another → another

C2.2.4 Variation in velocity of nerve impulses

Schwann cells = insulators → no “movement” of ions
Impulse goes from 1 node of ranvier to the next.

Myelin sheath prevent charge from leaking → faster and less E required

So: thicker + myelinated axons have faster moving impulse.

C2.2.5 Synapses

Synapse = junction between 2 cells in nervous system; signal only passed on 1 direction.

Transmitting neuron: pre-synaptic membrane: terminal (vesicles w neurtransm)
20-40 nm gap - synaptic cleft
Receiving neuron: post-synaptic membrane : dendrites

Chemical substance (neurotransm) transfers signal.

Response = carry signal to muscle or gland cell

C2.2.6 Neurotransmission

Sequence of event transferring impulse prom pre→post.

1. Action potential arrives at terminal button → depolarized of presyn/mem → take up calcium ions

2. Ca²⁺ = signalling chemical → pathway moving vesicles containing neurotrans through cell → vesicle ecocytosis (fuse w presyn membr)

3. Neurotransmitters released into synaptic cleft

4. Neurotrans bind w protein receptor on postsyn neuron mem

5. → ion channel opening: Na⁺ diffuse through channel into cell

6. Initiate action potential to move down post-synapt (depolarized)

7. Any bound neurotransmitters are released back into cleft → broken down by enzymes

8. Ion channel in postsynaptic membr close to Na⁺ ions

9. Fragments of neurotransm diffuse back across clefs and reessembled (endocytosis) in presynaptic neuron

C2.2.4 Correlation coefficients

Correlation: 2 variables vary tg - interdependent

+ correlation: increase/decrease tg: /

- correlation: one increases while other decreases

correlation coefficient: R: how strong associated:close to ±1=strong correlation

coefficient of determination: R² : same thing, just more spread

C2.2.7 Excitatory postsynaptic potential

Acetylcholine: neuromuscular junction neurotransmitter.

Acetylcholinesterase: enzyme that breaks down neurotrans in synaptic cleft into fragments that are retaken up by presyn-membrane. Broken down so the action potential only happens once.

C2.2.8 Depol & Repol during action potential

Action potential is generated when stimulus causes increase in + charged Na⁺ ions into axon of neuron → depolarization of membr of neuron → action pot move through neuron in wave of depol/repol

Depolarization: voltage gate Na⁺channel open: 3Na⁺ into cell: -70mV→+40mV
Repolarization: Na close, K⁺ open: 2K⁺ out of cell: +40→-70mV
Hyperpolarization: too much K⁺ out of cell, -90 mV
Reestablish resting potential: Na⁺ out, K⁺ into cell. PUMP not channel:use ATP

In order for action potential to occur: threshold potential = reached: -50mV

C2.2.9 Propagation of action potential

Nerve impulse = action pot traveling from 1 end of axon to next.

Local current = movement of Na⁺ ions by diffusion between 1 depolarized part

Na⁺ : move from high conc to lower → local current to make potential less → depolarized area to polarized/repolarizde area

C2.2.10 Oscilloscope: show rest vs action pot

Electronic insturment displaying changes in voltage, see graph for c2.2.8.

C2.2.11 Saltatory conduction

action potentials only occur at nodes of Ranvier (gaps between schwan cells). → speeds up prop of nerve impulse. C

C2.2.12 Exogenous chemicals

Produced outside the body.can have effect on transmission of action.pot in syn

Eg. neonicotinoids + concaine

Neonicotinoid insecticides: similar to nic, receptor of neurot perm blocked; used for death of insects

Cocaine: increases neurotrans action (dopamin) → make happy; addictive
Brain becomes less sensitive to natural reinforces of dopamine.

C2.2.13 Excitatory vs inhibitory neurotransmitters

Excitatory: eg. acetylcholine: generate action pot by increase permeability of postsynaptic mem to + ions. Na⁺ diffuses into cell. Neuron depolarized → impulse carried forward: -70 → -50 or more

Inhibitory: hyperpolarization of neuron → inhibit action potential → inside of neuron more negative than normal (Cl^- in or K⁺ out)→ inhibit impulse -70→-80

C2.2.14 Summation

Single neuron can form synapses w many other neurons. The more → the greater action potential so greater chance that it occurs cuz threshold overtook.

If both inhibatory and excitatory neurotransmitters → sum of them

C2.2.15 Perception of pain

Neuroreceptors notice change in T, pain(nocireceptor), EM, light, pressure, chemo etc…

Nocireceptors: notice pain: (actual or potential tissue damage). Eg. if you eat chili; they contain capsaicin → trigger opening of ion channel → allow calcium ions into neuron → interprets impulse as pain or heat.

C2.2.16 Consciousness

Conscious = aware. Not actively thinking persé.

Emergent property: different systems work tg.