Nerves Flashcards
Action Potential
- A reversal of the resting potential
- About +40mv potential difference
- Which sweeps along the axon
- A stimuli causes some sodium channels to open and depolarise
Transducers
Changes one form of energy into another form
Mechanical to electrical
Receptors
- Transforms forms of energy/stimuli into nerve impulses
- Act as a transducer
Saltatory Conduction
Where the action potential ‘jumps’ from one node of Ranvier to the next
Speed of conduction of nerve impulses
- Wider the axon = increased speed
- Myelination = increased speed
- insulates
- bigger jumps between nodes of ranvier so cover a longer distance
- due to ions cant pass through sheath
How do action potentials carry info?
- All action potentials are the same size
- nature of stimuli = position/type of receptor
- stronger stimuli = more action potentials
- stronger stimuli = stimulates more neurones
Refractory period
- the time it takes to recover from an action potential
- hyperpolarisation
- stopping generating another action potential
Local circuit
- the depolarised region and the resting region on either side of the action potential cause a temporary circuit
Hyperpolarisation
- before returning to resting potential the membrane becomes more negative than the resting potential during the refractory period
Repolarisation
- Na+ channels close when too +ve
- k+ channels open and ions leave the cell down their electrochemical gradient
- Change returns to near resting potential
Depolarisation
- A stimuli causes some sodium channels in the plasma membrane to open
- Na+ ions enter the cell
- potential difference about +40mv
Electrochemical gradient
- The charge and concentration on one side of the membrane is different to that on the other side
- ie depolarisation in action potential
Voltage gated channels
- whether they are open or shut depends on the potential difference across the membrane
Resting potential
- the potential difference normally -70mv whilst not transmitting an action potential
- actively pumps 3na+ ions out while 2k+ ions in
- can be leaky = more k+ out
Perineurium
- protective covering of a nerve
Structure of a nerve
- Lots of neurones bundled together with a protective perineurium
- some only sensory neurones, some only motor neurones, some a mix
Reflex arc (stages)
Impulse-> sensory neurone-> dorsal root ganglion-> spinal cord-> (intermediate neurone) -> motor neurone -> axon-> effector (ie muscle contraction)
Reflex arc
- A pathway from which impulses are carried from a receptor to an effector
- without conscious thought
- helps when in danger
Effector
- part of the body that responds to a stimulus ie muscles/glands
Nodes of Ranvier
- Spaces between Schwann cells about every 1-3mm
Myelin/ myelin sheath
- a spiral layer of schwann cells that surround the axon
- increases the speed of conduction of nerve impulses
Axon
Conducts impulses away from the cell
Dendrites
- short cytoplasmic processes that transmit action potentials from one neurone to another
Neurones
- A nerve cell
- specialised for the rapid transmission of electrical impulses called action potentials
Organphosphorous insecticides
- inhibits acetylcholinesterase = continuous action potentials
- in flea sprays& sheep dip for ticks
- linked to illness in farmers
Botulinum toxin on the synapse
- botox
- can be in contaminated canned food
- prevents the release of acetylcholine from the pre synpatic membrane
- can be fatal
- medically stop muscle contractions/spasms ie eyelids
- smooths wrinkles
Nicotine on synapses
- fits into acetylcholine receptors on postsynaptic membrane = action potential
- not broken down quickly
- large dose can be fatal
Function of synapse
- transmit signals 1 way
- specific pathways
- some inhibitory synapses
- some join lots of neurones
- new synapses form linking& remembering factors
Recharging synapses
- if acetylcholine constantly bonded to the membrane
- Na+ channels constantly open
- constant action potential
- no new action potentials
- acetylcholinesterase = acetate + choline
- choline taken back to presynaptic knob+ acetyl coA &Atp =acetylcholine
Neuromuscular junction
- is the synapse between the end of the motor neurone & a muscle
- passes along muscles & causes fibres to contract
Postsynaptic membrane
The membrane after the synapse
Presynaptic membrane
Membrane before synapse
Transmitter substance
- A chemical that is released by a presynaptic neurone
- diffuses across the synaptic cleft
- binds to receptors on postsynaptic membrane
Crossing a synapse
- action potential arrives
- calcium ion channels open ca2+ flood into cytoplasm
- vesicle fuses with presynaptic membrabe leaves by exocytosis
- acetylcholine diffuses across synapse& binds to receptors
- na+ channels open depolarises membrane = action potential
Synaptic cleft
- the small gap between 2 neurones or a neurone and effector
Synapses
- the area in which a nerve impulses can be passed
- neurone- neurone
- neurone- effector
