The Mammalian Nervous System Flashcards
What 2 divisions is the nervous system made up of
Central nervous system
Peripheral nervous system
What is the CNS and PNS made up of
CNS - brain and spinal cord
PNS - pairs of nerves which originate from either the brain or spinal cord
What are the 2 divisions of the PNS
Voluntary nervous system - impulses under voluntary or conscious control
Autonomic nervous system - carries impulses to smooth muscle, glands and cardiac muscles (involuntary)
What are the 2 divisions of the autonomic nervous system
Sympathetic (speeds up)
Parasympathetic (slows down)
Difference in function of the sympathetic and parasympathetic
Sympathetic - produces noradrenaline, involved in fight or flight, activated when stressed or active
Parasympathetic - slower + more inhibitory, produces acetylcholine, maintains normal functioning of the body
Structure of sensory neurone
Cell body in the middle, myelinated
Structure of relay neurone
Cell body in middle, non myelinated
Structure of motor neurone
Cell body at beginning, myelinated
Myelination formation and purpose
Wrapped in a specialised cell called a Schwann cell
This cell forms a fatty layer around the neurone known as myelins sheath
Myelin sheath protects nerve from damage and speeds up impulse (saltatory conduction)
Is resting potential
When the inside of an axon is negatively charged compared to the outside (polarised) at around -70mV
What is an action potential
A wave of depolarisation (inside of axon turns positive) which occurs when a neurone sends information from its cell body down its axon
What are the stages of an action potential
Depolarisation
Depolarisation
Hyperpolarisation
How is resting potential maintained
Na - K pump that pumps 3Na+ out and 2K+ in using active transport (most Na+ channels are closed and most K+ channels are open)
What is the charge of an action potential
+40mV
Steps of an action potential
Na+ channels open reacting to stimuli
Na+ diffuse rapidly into the axon
Positive feedback happens so more Na+ move in
Axon is +40mV (threshold)
Na+ gates close
Na-K pump pumps excess sodium ions out
K+ channels open
Too many move out resulting in hyperpolarisation
Gates K+ channels close
Inside of to axon returns to resting potential (-70mV)
What is the refractory period
The recovery time of an axon
What is the purpose of a refractory period
Ensures that action potential were propagated in one direction only
Produces discrete impulses (action potentials are separated from each other)
Limits the number of action potential
What is a synapse
The gap between two neurones
What are the events at a synapse
Action potential arrives at the presynaptic nob
Calcium channels open and Ca+ moves in
Triggers vesicles to fuse to ore synaptic membrane
Neurotransmitter is released into the synaptic cleft
NT diffuses across cleft
NT binds to specific protein receptors on the Na+ channel on the post synaptic membrane
Causes Na+ channels to open and Na+ diffuses in
Excitatory response is set up in the post synaptic nob
What is an inhibitory post synaptic potential (IPSP)
A synaptic potential that makes a post synaptic neurone less likely to generate a potential
Different ion channels open allowing negative ions to diffuse in
Post synaptic nob is more negative that normal rest in potential making an action potential less likely to occur
Breakdown of neurotransmitters
NTs are broken down by hydrologic enzymes
They then move back across the cleft and back into the synaptic nob (recycled)
What is acetylcholine
A NT that binds to receptors and is broke down by acetylcholinesterase
Hydrolyses acetylcholine into acetate and choline
Acetylcholine and choline diffuse back across cleft to be recycled
What are the 2 main types of synapse
Adrenergic - sympathetic, noradrenaline
Cholinergic - parasympathetic, acetylcholine
Nicotine on the synapse
Mimics effects of acetylcholine
Triggers an action potential in postsynaptic membrane but receptors remain unresponsive for a while
Triggers release of dopamine (pleasure)
Has stimulating effects but too much can be lethal
Lidocaine on the synapse
Used as a local anaesthetic by dentists
Blocks voltage gated Na+ channels preventing action potential,s
Can be used to prevent heart arrhythmias as it prevents early or extra action potentials
Cobra venom in the synapse
Binds reversible to acetylcholine receptors so prevents trans,issue. Of impulses across the synapse
Muscles aren’t stimulated to contract so the person becomes paralysed
What is transduction
Converts light into nerve impulses (takes place in the retina)
Rod cells
Spread evenly across the retina (except fovea)
More numerous than cone cells
Provides image in black and white as they can’t distinguish between wavelengths
Detect light at a very low intensity
Certain threshold must be met for a generator potential to occur
Have low visual acuity
Generator potential rod cells
Generated in bipolar cell which they are connected to as rod cells are 3:1 (retinal convergence)
This makes threshold more likely to be reached during summation
Rod cells - low light
Rhodopsin pigment must be broken down to create a generator potential
Low light intensity has enough energy to break this down
Cone cells
Tightly packed at the fovea
3 different types of cone cells responding to different wavelengths of light
1:1 with bipolar neurone
Only respond to high light intensity as summation can’t occur
Brain can distinguish between seperate sources of light
Cone cells - high light
Contain iodopsin which requires a higher intensity of light to be broken down
Contain different types of iodopsin which respond to different wavelengths of light
What is the fovea
Part of the retina that light is focused upon
Receives the greatest intensity of light so cone cells are found here
How does rhodopsin work
Formed from opsin and retinal
Retinal exists as cis retinal and trans retinal
In dark all retinal is cis form
When a photon hits rhodopsin it converts from cis to trans
Thus puts strain on opsin and retinal Retinal exists, bond g breaking up the molecule
This is known as bleaching
What is bleaching
Red cells are usually permeable to Na+ ions
When rhodopsin is bleached it causes Na channels to close making it less permeable
The Na pump continues to work
This makes the rod cells more negative than normal
This is generator potential
Calculation for cardiac output
Cardiac output = stroke volume x heart rate
Which part of the brain controls heart rate
Medulla oblongata
Chemoreceptor and baroreceptor
Chemoreceptor (carotid artery) - detects a change in chemicals (CO2 + pH)
Baroreceptor (aorta and carotid artery)- detects a change in pressure (blood pressure)
High CO2 / low pH
Chemoreceptor detects change and sends impulse to medulla along sympathetic
Noradrenaline binds to receptors on SAN increasing heart rate
Low CO2 / high pH
Chemoreceptor detects change and sends impulse to medulla along parasympathetic
Acetylcholine binds to receptors in SAN and heart rate decreases to norm
Low blood pressure
Detected by baroreceptor which sends impulse along sensory neurone (sympathetic) to medulla
Secretes noradrenaline which binds to receptors in SAN increasing heart rate
High blood pressure
Detected by baroreceptors which send impulses to medulla along parasympathetic
Secretes acetylcholine which binds to receptors on SAN decreasing heart rate to norm
