Nerves A2

Question	Answer
what is a neuron?	It is the structural unit of the nervous system.
what are axons?	long single extensions that carry action potentials form the cell body to other nerve cells /effectors
what are dendrites?	Short multiple extensions that receive action potentials to the cell body
why is myelinated transmission quicker?	The action potentials jump from one node of the Ranvier to another by saltatory conduction.
what do myelin sheaths do?	electrical insulation speeds up the rate of impulse
what are the characteristics of a motor neurone?	1. short dendrons 2. Long axon 3.Cell body in the CNS 4. action potentials go to the effector
what are the characteristics of a sensory neurone?	1. Single long dendron 2. short axon 3. cell body in the CNS 4. Action potential from receptors to CNS
what are reflexes?	sub conscious actions that are not learned but in born
What are the roles of sensory neurones in mammals in converting energy into nerve impulses?	1. Light sensitive cells in the retina detect light intensity and range of wavelengths 2. Olfactory cells in the nasal cavity detect the presence of volatile chemicals. 3. Tastebuds detect the presence of soluble chemicals. 4. Pressure receptors in the skin detect pressure on the skin. 5. Sound receptors in the cochlea detect vibrations in the air.
What do tansductors do?	convert the stimulus to a nerve impulse.
What is the function of a sensory neurone?	To transmit action potentials from the sensory receptor to the CNS
What is the structure of a sensory neurone?	Myelin sheath One long dendron One short axon Many dendrites Cell body positioned just outside of the CNS in the dorsal root ganglion Synapatic knob ending
What is the function of the motor neurone?	To transmit action potentials from the CNS to the effectors ( muscles)
What is the structure of the motor neurone?	Myelin sheath Cell body positioned in the CNS Many dendrites One short dendron One long axon Motor end plate
how is the resting potential established and maintained?	When at rest, the potential difference across the membrane is -60mV. Sodium-Potassium pumps actively transport 3Na+ ions out for every 2 K+ ions in, using ATP.
How is an action potential generated?	1. The membrane is at resting state; -60mV inside 2. Na+ ion channels open and some Na+ ions diffuse out. 3. The membrane depolarises- it become less negative with respect to the outside and reaches the threshold potential of -40mV. 4. Voltage-gated sodium ion channels open and many Na+ ions enter. As more Na+ ions enter, the more positively changed the cell becomes, compared to outside. 5. The potential difference across the membrane reaches +40mV. The inside is now positive compared to the outside. 6. The Na+ ion channels shut and the K+ ion channels open. 7. K+ ions diffuse out of the cell, bringing the potential difference back to negative compared with the outside-repolarisation. 8. The potential difference overshoots slightly, making the cell hyperpolarised. 9. The original potential difference is restored, so the cell returns to its resting state.
How is an action potential transmitted in a myelinated neurone?	The action potential ‘jumps’ between the the nodes of Ranvier by Saltatory conduction.
What is the all or nothing rule?	When the stimulus reaches the threshold and an action potential is produced.
What is the significance of the frequency of the impulse transmission?	The higher the frequency of the signals the more intense the stimulus.
What is the structure of a myelinated neurone?	One neurone is surrounded by one Schwann cell which is wrapped around the neurone
What is the function of the myelinated sheath?	To provide a fast response time Used in movement
What is the structure of a non myelinated sheath?	Many neurones are surrounded by one Schwann cell
What is the function of the non myelinated sheath?	Slow response time Used in breathing and digestion
What is the structure of the synaptic knob?	• Many mitochondria • A large amount of smooth ER • Vesicles containing acetylcholine • Voltage gated sodium ion channels in the membrane
What is the structure of the post synaptic knob?	• Specialised sodium ion channels that will only open when acetylcholine binds to them
What is the cholinergic synapse made up of?	The synaptic knob and the post synaptic knob
What is a neurotransmitter?	A chemical that diffuses across the cleft of the synapse to transmit a signal to the post-synaptic neurone.
What neurotransmitter is used in cholinerginic synapses?	Acetlycholine
What is the role of neurotransmitters in the transmission of action potentials?	They cause the generation of a new action potential in the postsynaptic neurone.
Where is the acetylcholine stored?	It is stored in vesicles in the synaptic knob..
What happens in the synapatic knob when an action potential arrives?	The voltage gated sodium ion channels open, so calcium ions diffuse out. This causes the vesicles to fuse with the synaptic membrane. Acetylcholine is released by exocytosis. It diffuses across the cleft and binds to receptor sites on the sodium ion channels on the postsynaptic membrane. Sodium ions diffuse across the synaptic membrane into the postsynaptic neurone, creating a generator potential
What happen if the generator potential is sufficient?	The potential across the membrane reaches the threshold potential, and a new action potential is created.
what are the roles of synapses in the nervous system?	1. Allow action potential to pass to the next neurone. 2. ensure transmission is in one direction only 3. Allows inhibition of information flow 4. Allows intergration of impulses 5.Filters out weak responses 6. Prevents over stimulation
What is summation?	Persistent, low-level stimuli that will generate several successive generator potentials in the presynaptic neurone;
What are the two types of summation?	Temperal summation Spatial summation
What is temperal summation?	High frequency simulation by one presynaptic neurone
What is spatial summation?	simultanous stimulation by several presynaptic neurones.

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	Created by megan.radcliffe16 about 10 years ago