Nervous systems Flashcards
What is a nerve impulse
Self propagating wave of electrical disturbance travelling along surface of axon membrane
What is resting potential
Potential difference across he axon when a neuron is at rest
What are the charges of inside and outside of an axon
Inside is negatively charged relative to outside
What is an axon
The long fibre in a neurone tat conducts impulses away from the cell body
What is the purpose of the myelin sheath
Made of schwaan cells that insulates the axon, shields the axon from surrounding tissue fluid and insulates it from other neurones
What is depolarisation
A rapid temporary reversal of the resting membrane potential
What is re polarisation
A return to the resting membrane potential
How is resting potential maintained?
Membrane more permeable to potassium ions and less to sodium ions
Sodium ions are actively transported out and potassium ions pumped in
How does MS lead to slower responses to stimuli?
Myelin sheath broken down
Impulse is unable to jump from node to node
More depolarisation over length of membrane
How does a lower temperature lead to slower nerve impulse conduction?
Ions have less kenetic energy and therefore they diffuse more slowly
What factors affect speed of nerve impulse conduction
Myelination
Diameter of axon
Temperature
What is the absolute refractory period?
After generation of an action potential
Voltage gated sodium channels are inactivated
They cannot respond to further stimulus
What is a synapse?
Junction between neurones
Where are neurotransmitters made and where are they stored?
Made in pre synaptic neurones
Stored in synaptic vesicles
What is summation?
Arrival of multiple action potentials leading to a build up of neurotransmitter
Why does depolarisation happen?
Sodium ion gates open
Why can another action potential not be generated once one has just been generated?
Membrane more impermeable to sodium ions
Sodium ion cannot enter axon
Membrane becomes more negative than resting potential
Explain why a neurotransmitter (e.g. acetylcholine) can only bind with one type of receptor protein in the postsynaptic membrane.
Unique shape of receptor protein / binding site Due to (tertiary) structure of protein molecule
What is the role of calcium ions (Ca2+) in synaptic transmission?
Cause vesicles to move to presynaptic membrane
How is an action potential generated?
Sodium ion channels open;
Allowing rapid influx of sodium ions
How does an increase in exercise cause an increase in heart rate?
Chemoreceptors detect rise in PH sends impulse to medulla. More impulses to SAN by sympathetic nervous system.
DDT binds to sodium channels, and consequently channels remain open, how does this kill?
Neurones remain depolarised
No action potentials generated
What does the SAN do?
Sends waves of excitation through the atria initiating the heart beat
What delays the contraction of the ventricles?
Non- conductive tissue prevents electrical impulse from reaching ventricles
Electrical impulse forced via AVN
Why is it important that there is a delay before the contraction of the ventricles?
Allows the atria to fully contract and empty
Why does the left ventricle have the highest blood pressure and why is this important?
It has the most cardiac muscle so it contracts at a higher force which is important as it pumps blood to the whole body
What is the role of the Purkyne tissue and the bundle of his?
Conduct the electrical impulse
What is the effect of adrenaline on heart muscle?
Beats faster
Beats stronger : myoctyes contract with greater force
How does adrenaline increase heart rate?
It binds to specific receptors on the membranes of cells in the SAN
What do baroreceptors detect?
Change in pressure
Response to high blood pressure in the heart
Detected by baroreceptors
Then via parasympathetic
Releases acetylcholine
How are the parasympathetic and sympathetic nervous systems antagonistic?
If one system contracts a muscle then the other relaxes
The sympathetic nervous system does what to an activity?
Speeds up activity
The parasympathetic nervous system does what to an activity?
Inhibits effectors and so slows down any activity
Changes to heart rate are controlled by which region of the brain?
Medulla oblongata
What do rods detect in the eye?
Light vs dark
What do cones detect in the eye?
Wavelength i.e colour
Describe a simple reflex arc
Stimulus-receptor-sensory neurone-motor neurone- effector- response
What are the types of photoreceptors in the eye?
Cones and rods
Why do rod cells provide low visual acuity?
More than one rod cell shares the same synapse with a biopolar cell. As a result multiple rods need to be stimulated to give a generator potential
Why do cone cells provide good visual acuity?
each cone cell has its own synapse via a bipolar neurone connecting to the optic nerve
The speed of an action potential depends on?
Presence or absence of a myelin sheath
Diameter of an axon
Temperature
What is the refractory period?
A period where the neuron cannot become excited as sodium ion channels enter a recovery stage
Why is the refractory period important
Prevents action potentials travelling in the wrong direction
What are some of the roles of synapses?
Prevent action potentials travelling in the wrong direction
Amplify the effects of low frequency action potentials
Inhibitory or excitory
What happens when an action potential reaches a synapse?
Presynaptic membrane depolarises
Ca2+ channels open
Calcium ions diffuse into presynaptic neurone
Roles of calcium ions in transmission across a synapse?
Causes the fusion of vesicles filled with neurotransmistter with presynaptic membrane
Role of neurotransmitter in transmission across a synapse
Released into synaptic cleft
Binds to receptors in the post synaptic membrane which stimulates the opening of Na+ channels allowing Na+ ions to enter neurone
What happens to acetylchloline after an action potential has been generated?
Acetylchloinesterase hydrolyses it and it diffuses back into presynaptic membrane where it can be reused and prevents continous generation of an action potential
Why is the response in heart beat less in diabetic rats?
Damage to autonomic nervous system Pressure receptors dont work as well Damage to medulla Change in number of impulses to medulla Damage to sympathetic system so doesnt speed up enough
