Neurones and Action Potentials - Nervous System
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?- Created by: Molly Webb
- Created on: 16-02-16 11:54
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- The Nervous System
- Made up of neurones
- Sensory neurones
- Transmit nerve impulses from receptors to CNS (brain and spinal cord)
- Convert energy of a stimulus into electrical energy
- They are transducers (convert one form of energy to another)
- Convert energy of a stimulus into electrical energy
- Transmit nerve impulses from receptors to CNS (brain and spinal cord)
- Motor neurones
- transmit nerve impulses from the CNS to effectors
- Cell body at the end of the cell
- Many short dendrites off the cell body that carry nerve impulses from CNS to cell body
- One long axon to carry nerve impulses from cell body to effector cells
- Many short dendrites off the cell body that carry nerve impulses from CNS to cell body
- Cell body at the end of the cell
- transmit nerve impulses from the CNS to effectors
- Relay neurones
- transmit nerve impulses between sensory neurones and motor neurones
- Receptor
- Resting state
- Inside is -70mv as the outside is more positive due to more positive ions outside
- The membrane is polarised
- Resting potential
- Created and maintained by sodium-potassium pumps, sodium ion channels and potassium ion channels
- Resting potential
- The membrane is polarised
- Inside is -70mv as the outside is more positive due to more positive ions outside
- Myelinated neurones
- Some neurones have a myelin sheath made of Schwann cells
- These cells are electrical insulators
- Tiny gaps where there is bare membrane are nodes of Ranvier
- Sodium ion channels are concentrated at the nodes
- Depolarisation only occurs at these nodes
- Neurones cytoplasm conducts electrical charge to polarise next node - so they jump from node to node
- This is called saltatory conduction
- It is very fast
- This is called saltatory conduction
- Neurones cytoplasm conducts electrical charge to polarise next node - so they jump from node to node
- Depolarisation only occurs at these nodes
- Sodium ion channels are concentrated at the nodes
- Some neurones have a myelin sheath made of Schwann cells
- Sensory neurones
- Action Potentials
- How an Action Potential moves along neurone
- Sodium ions diffuse along the neurone sideways
- This causes sodium ion channels in the next region of the neurone to open
- sodium ions diffuse into that part of the neurone
- Causing a wave of depolarisation to travel along neurone
- sodium ions diffuse into that part of the neurone
- This causes sodium ion channels in the next region of the neurone to open
- Sodium ions diffuse along the neurone sideways
- Made up of neurones
- Nervous system receptor in resting state
- Difference in charge between inside cell vs outside cell
- Generated by ion pumps and ion channels
- Voltage across membrane = potential difference
- Potential difference at rest = resting state
- Membrane becomes more permeable when stimulus is detected
- More ions move in and out altering potential difference and this change = generator potential
- Membrane becomes more permeable when stimulus is detected
- Potential difference at rest = resting state
- Voltage across membrane = potential difference
- Generated by ion pumps and ion channels
- Difference in charge between inside cell vs outside cell
- Bigger stimulus = more excited = bigger generator potential
- If generator potential is big enough it triggers an action potential but only if it reaches the threshold level
- Cell body is in the middle of the sensory neurone
- Cell body have dendrite - carrying nerve impulses towards the cell body from the receptor cells
- Also has axons to carry the nerve impulse away from the cell body and to the axon terminal
- Long dendrite in the sensory neurone
- Short axon
- Neurone cell membranes become depolarised when stimulated
- Stimulus reaches threshold value and causes voltage- gated sodium ion channels to open
- Sodium diffuses into the neurone down sodium ion electrochemical gradient
- Inside of the neurone is less negative
- At around +40mV the sodium ion channels close
- Voltage gated potassium ion channels open
- Membrane is more permeable to potassium and so they diffuse out of the neurone down the potassium ion concentration gradient
- Starts to return to resting potential
- Voltage-gated potassium ion channels are too slow to close
- Overshoot and the neurone becomes more negative the resting potential
- Sodium-potassium pump returns the membrane to resting potential by moving 3 Potassium and 2 Sodium ions at a time
- Overshoot and the neurone becomes more negative the resting potential
- Voltage-gated potassium ion channels are too slow to close
- Starts to return to resting potential
- Membrane is more permeable to potassium and so they diffuse out of the neurone down the potassium ion concentration gradient
- Voltage gated potassium ion channels open
- At around +40mV the sodium ion channels close
- Inside of the neurone is less negative
- Sodium diffuses into the neurone down sodium ion electrochemical gradient
- Stimulus reaches threshold value and causes voltage- gated sodium ion channels to open
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Refractory Period
- After an action potential, the neurone cannot be excited straight away as they are recovering
- It moves away from parts in the refractory period because it can't fire an action potential there
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