C2.2 Neural signaling

Nerve

many individual neurons grouped together into a single structure

Central nervous system

spinal cord and brain

Sensory neurons

carry information to the CNS

Motor neurons

carry repsonse information to the muscles

Peripheral nerves

motor and sensory neurons

Peripheral nerves system

nerves

axon

contains synaptic terminal buttons which realease the neurotrasmitter

dendrite

receive action potentail

cell body

contains cytoplasm and nucleus

How is resting potential generated

sodium potassium pump

• 3 sodium ions pumped outside of the cell

• 2 calcium ions pumped into the cell

Generating an action potential

1. Depolarization: A stimuli triggers a threshodl to be reached (around -55 mV) which causes the opening of voltage gated sodium channles causing an inlufx of Na+ ions in the inside of the neuron, causing charge to become positive in comaprison with the outside

2. Repolarization: the membrane immiedtaley tries to restore the resting potential so volateg gated potassium channles open causing an influx of K+ ions outisde restoring the resting potential

Speed of nerve impluse depends on:

• myelination - shwann cells create myelin sheets called nodes of ranvier allowing the action potential to jump from one to the other

• diameter of the axon - wider diameter indicates less leakege of iosn

Resting potential (how much )

-70 mV

Synapse

junction between two neurons or neruon and a muscle cell

Synapse process

1. action potential arrives at terminal buttons causing depolarization of presynaptic membrane and uptake of Ca2+ ions into terminal buttons

2. Ca2+ ions act as a signaling chemical activating vesicles with neurotrasmitter to fuse with the presynaptic membrane

3. Neurotransmitter released into the synaptic cleft

4. Neurotransimtter binds with a protein receptor on postsynaptic membrane

5. Binding reuslts in opening of Na+ channels causing depolarization and hence generation of an action potential

6. Na+ channels close

7. Neurotrasmitter binded to receptors is released to synaptic cleft to be degraded by enzymes or reassembled at terminal buttons

Acetylcholine enzyme

acetylcholine when its the neurotramsiterr its broken down by acetylcholinestarase to ensure action potential occurs only onced

Device that shows a graph of electrical signal

osciloscope

Saltatory conduction

When action potential jumps from one node of Ranvier to another

Exogenous chemicals

produced outside the body

Endogenous chemicals

chemicals produced inside the body

Neocotinoid insecticides

• chemical binds to receptor on postsynaptic membrane where acetylcholine binds prohibiting the action potential from being propagated

• The chemicals are not relased and broken down leading to blockage and hence paralysis and then death of the insect

Cocaine

• affect the neurotransimtter domaine

• cocaine prevents removal of domaine from synaptic celft by atatching to the domaine transporter which normlayy removes domaine and blcoking the removal process leaidng to accumulation of domaine

Excitatory neurotrasmitter

generate action potentail by increasing permability of postsynaptic membrane to positive ions

Inhibitory neurotrasmitter

causes hyperpolarization (inisde of neuron more negative then normallly) making it harder to generate action potential

GABA

• inhibitory neurotransimitter

• Binds to receptors which relase negative chloride ions into the postsynapantic membrane or for positive potassium ions to move out of the postsynaptic membrane

Summation of inhibtiory and exciatory effects

Postsyanptic neuron can receive many the sum matters

Nociceptors

sense pain

Example of reaction to pain

Hot Chili Peppers

• Contain chemcial called capsaicin which can bind to nocicpetor causing an opening of ion channel letting Ca2+ ions if threshold is recahed the action poetntail is sent to the brain and its interpretd as pain or heat

Emergent property

• looking at all systems together

• example: consciousness