Neurons and Synapses

Neurons and Synapses Nervous System Outline the divisions of the nervous system Central Nervous System Peripheral Nervous System Brain and spinal cord Composed of peripheral nerves Sensory (Afferent) Division Motor (Efferent) Division Sends signals to the CNS from receptors Sends signals from the CNS to effectors Somatic Nervous System Autonomic Nervous System Controls voluntary movements Controls involuntary movements Sympathetic Division Parasympathetic Division ‘Fight or flight’ responses ‘Rest and digest’ responses State the role of sensory, motor and relay neurons (interneurons) Sends signals from receptors to the central nervous system Sensory: …………………………………………………………………………………………………………………………………………. Sends signals from the central nervous system to effectors Motor: ……………………………………………………………………………………………………………………………………………. Sends signals within the central nervous system Relay: …………………………………………………………………………………………………………………………………………….. Label the diagram of a typical motor neuron Dendrite 1. ………………………………………… Soma (cell body) 2. ………………………………………… Axon 3. ………………………………………… Axon terminal 4. ………………………………………… Myelin sheath / Schwann cell 5. ………………………………………… Draw direction of nerve impulse Define the following terms Resting potential The charge difference across a membrane when the neuron is not firing (-70 mV) ………………………………………………………………………………………………………………………………………………….......... Maintained by the sodium-potassium pump ………………………………………………………………………………………………………………………………………………….......... Action Potential The charge difference across a membrane when the neuron is firing (+30 mV) ………………………………………………………………………………………………………………………………………………….......... Involves depolarisation and repolarisation ………………………………………………………………………………………………………………………………………………….......... Depolarisation A sudden change in membrane potential – usually from a (relatively) negative to positive internal charge ………………………………………………………………………………………………………………………………………………….......... Depolarisation involves Na+ channels opening ………………………………………………………………………………………………………………………………………………….......... Repolarisation The restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge) ………………………………………………………………………………………………………………………………………………….......... Repolarisation involves K+ channels opening ………………………………………………………………………………………………………………………………………………….......... Explain, with the aid of the diagram, how a nerve impulse passes along a non-myelinated neuron 1. The sodium-potassium pump maintains a resting potential ……………………………………………………………………………………… It expels 3 sodium per 2 potassium admitted (active transport) ……………………………………………………………………………………… This results in a negative membrane potential (roughly -70 mV) ……………………………………………………………………………………… 2. Sodium channels open in response to signal at receptor/dendrite ……………………………………………………………………………………… There is a passive influx of sodium ions to cause depolarisation ……………………………………………………………………………………… 3. Potassium channels open in response to depolarisation ……………………………………………………………………………………… There is a passive efflux of potassium ions (repolarisation) ……………………………………………………………………………………… 4. The is a length of time needed before the neuron re-fires ……………………………………………………………………………………… During this refractory period, the resting potential is ……………………………………………………………………………………… re-established by the sodium-potassium (Na+/K+) pump ……………………………………………………………………………………… State what a threshold potential represents The minimum level of depolarisation required for an action potential to occur (i.e. the ‘all-or-none’ rule) ………………………………………………………………………………………………………………………………………………….......... Explain how the myelin sheath enables salutatory conduction This myelin sheath functions to improve transmission speed (via saltatory conduction) ………………………………………………………………………………………………………………………………………………….......... The action potential ‘hops’ between the gaps in the myelin sheath (called nodes of Ranvier) ………………………………………………………………………………………………………………………………………………….......... This increases transmission speed by ~ ×100 ………………………………………………………………………………………………………………………………………………….......... Synaptic Transfer Label the diagram and explain the process of synaptic transmission Action potential (pre-synaptic neuron) 1. ………………………………………………………………………... Calcium channels 2. ………………………………………………………………………... Vesicles (containing neurotransmitters) 3. ………………………………………………………………………... Receptor (on post-synaptic neuron) 4. ………………………………………………………………………... Neurotransmitter 5. ………………………………………………………………………... Action potential (post-synaptic neuron) 6. ………………………………………………………………………... Synapse 7. ………………………………………………………………………... Describe how synaptic transfer enables complex decision making in the CNS Excitatory neurotransmitters will depolarise a post-synaptic neuron (more likely to fire), whereas inhibitory ………………………………………………………………………………………………………………………………………………….......... neurotransmitters will hyperpolarise a post-synaptic neuron (less likely to fire) ………………………………………………………………………………………………………………………………………………….......... The sum of excitatory and inhibitory signals determines whether the threshold for an action potential is reached ………………………………………………………………………………………………………………………………………………….......... Hence, the composition of neurotransmitters released determines the differential pathways of nerve signals ………………………………………………………………………………………………………………………………………………….......... Describe the secretion and reabsorption of acetylcholine Acetylcholine is a neurotransmitter that serves excitatory and inhibitory functions - it is used to stimulate ………………………………………………………………………………………………………………………………………………….......... muscular contractions and it also promotes parasympathetic responses ………………………………………………………………………………………………………………………………………………….......... Acetylcholine is broken down in synapses by acetylcholinesterase (AChE) to prevent overstimulation of receptors ………………………………………………………………………………………………………………………………………………….......... Identify how neonicotinoid pesticides affect acetylcholine transmission Neonicotinoid pesticides bind irreversibly to acetylcholine receptors in insects ………………………………………………………………………………………………………………………………………………….......... AChE cannot break down the neonicotinoids - this causes fatal overstimulation of receptors …………………………………………………………………………………………………………………………………………………..........