Nervous System Flashcards
What are the two different types/divisions of the nervous system?
• Central nervous system (CNS)
• Peripheral nervous system (PNS)
What makes up the CNS?
• Brain
• Spinal cord
What does the somatic nervous system control?
Conscious activities (e.g. running)
What does the autonomic nervous system control?
Unconscious actions (e.g. digestion)
What does the sympathetic nervous system control?
‘Fight or flight’ actions (releases the neurotransmitter ‘noradrenaline’)
What does the parasympathetic nervous system do?
Calms the body down - rest and digest (releases the neurotransmitter ‘acetylcholine’)
What is a nerve?
A bundle of many nerve fibres enclosed within a protective sheath.
What are nerve fibres?
The long axons of neurones together with any associated tissues.
How does the sympathetic nervous system prepare the body to ‘fight-or-flight’?
• Causes the release of adrenaline from the adrenal glands
• Adrenaline causes the heart rate to increase - allowing for a rapid increase in blood supply to respiring muscles, allowing the muscles to have more oxygen and glucose for respiration
• Enables high-intensity activities like running away from a predator to be an immediate response
Outline the pathway of a nervous system reaction
• Stimulus
• Receptor (in sense organ)
• Sensory neuron
• CNS
• Relay neuron
• Effector (muscle or gland)
• Response
What are the three types of neurons?
• Sensory neurons
• Relay neurons
• Motor neurons
Which type of neuron has the cell body in the middle/sticking upwards?
Sensory neurons
What are the branches at the start of a neuron called?
Dendrites
What are the insulating cells around an axon called?
Schwann cells
What do Schwann cells make up?
Myelin sheath
What does the myelin sheath do?
Insulates the axon to increase speed of action potential
What is the section between the dendrite and a cell body called?
Dendron
What are the unmyelinated areas of a motor neuron called?
Node of Ranvier
What are the branches at the end of a neuron called?
Axon terminals
Describe and explain the adaptations of neurons
• Highly branched endings (from dendrites), allows electrical impulses to pass from one to the other
• Myelin sheath, insulates most neurons, ensuring impulses travel rapidly along the axon
What is the receptor that you need to know?
Pacinian corpuscles
What are pacinian corpuscles?
• Mechanoreceptors that detect pressure and touch in the skin
• Composed of a sensory neuron which is wrapped in layers of lamellae
How do pacinian corpuscles transmit action potential?
• When it’s stimulated, the lamellae deform and press on the sensory nerve ending
• This causes sodium ion channels to open and sodium ions diffuse into the cell, creating a generator potential
• If the generator potential reaches the threshold, it triggers an action potential along the sensory neuron
What is the word that means to change energy from one form to another (e.g. from light energy to electrical energy)?
Transduction - sensory neurons are transducers
Where are myelinated neurons found?
• Most neurons in the CNS and PNS are myelinated (require fast conduction)
Where are unmyelinated neurons found?
• Mostly in the brain as grey matter
What happens in the cell during an action potential?
• Stimulus - stimulus excites the cell membrane, opening sodium ion channels (making the inside less negative as sodium diffuses in)
• Depolarised - if reaches voltage of -55mV, more sodium ion channels open
• Repolarised - when a voltage of 30mV is reached, sodium ion channels close and potassium ion channels open (potassium diffuses out)
• Hyperpolarised - potassium ions are slow to close so there’s an overshoot (less than -70mV voltage), allowing for a time delay between action potentials
• Resting potential - ion channels are result, sodium-potassium pump returns the membrane to its resting potential
What is the refractory period?
The time between when resting potential is reached after depolarisation and when it returns to resting potential after hyperpolarisation
How does the wave of depolarisation move along the neurone?
• When an action potential happens, some of the sodium ions that enter the neurone diffuse sideways
• This causes sodium ion channels in the next region of the neurone to open and sodium ions to diffuse into that part
What are the purposes of synapses?
• Allows neurones to communicate
• Ensure transmission between neurones is unidirectional
• Allows convergence
• Allows divergence
• Filters out low level stimuli
• Prevents fatigue/over-stimulation
Describe the stages of how neurones transmit action potentials between neurones.
• Action potential arrives at synaptic knob of presynaptic neurone, stimulating calcium ion channels to open, causing calcium ions to diffuse into synaptic knob
• Influx of calcium ions into synaptic knob causes synaptic vesicles to move to the presynaptic membrane (and fuse with it, causing exocytosis of neurotransmitters)
• Neurotransmitter diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane, causing sodium ion channels in postsynaptic neurone to open, causing depolarisation of postsynaptic neurone if generator threshold reached (neurotransmitter then removed from synaptic cleft)
What is the name of the type of synapse you need to know?
Cholinergic synapse
What is the name of the neurotransmitter you need to know, and which enzyme is it broken down by?
• Acetylcholine
• Acetylcholinesterase
What is the name of many neurones connecting to one neurone?
Synaptic convergence
What is the name of one neurone connecting to many neurones?
Synaptic divergence
What is spatial summation?
Multiple impulses arrive at the same time from different synaptic knobs, releasing large amounts of neurotransmitter into the same synaptic cleft
What is temporal summation?
When two or more nerve impulses arrive in quick succession from the same presynaptic neurone into the same synaptic cleft (the effect of the impulses are added together to generate an action potential)
