topic 9 Flashcards
9.2
what makes up the CNS
what makes up the PNS
the brain and spinal cord
everything outside the CNS
What are neurons vs nerves
neurons are individual cells and each one has a nerve fibre that carries the nerve impulse. nerves are a bundle of fibres called axons or dendrons.
fibres that transmit the nerve impulse away from the cell body..
fibres that transmit the nerve impulse towards the cell body..
axons
dendrons
whats the structure of a myelin sheath
schwann cells wrap itself around the nerve fibres/axon many times to form a myelin sheath. They contain gaps called node of ranvier
give 2 reasons as to why a myelin sheath is important
- protects the nerves from damage
- speeds up transmission of impulses
the speed at which impulses can travel at depend on what 2 things?
- diameter of nerve fibre - thicker = faster
- whether it contains a myelin sheath or not
whats the difference between a nerve and nerve fibre
a nerve fibre is one single axon, a nerve is a bundle of fibres
Membrane permeability of an axon
The axon membrane is impermeable to sodium ions but are permeable to potassium ions
When is an axon classed as at rest.
How is the resting potential generated
When it’s not conducting a nerve impulse (resting potential)
Na+/K+ pump, Na+ move out and k+ move in, k+ diffuse out thru k+ channels, membrane is impermeable to sodium ions, Na+ channels closed outside becomes positive and inside becomes negative
Because the outside of the cell is positive it makes the inside slightly negative …
What’s the value of resting potential
The membrane is polarised
-70mV
What happens In the action potential - depolarisation (membrane becomes less neg)
- a neuron is stimulated the axon membrane increases its permeability to sodium ions
-sodium ion channels open up allowing Na+ to move into the axon if enough Na+ moved into axon then an action potential / threshold potential is achieved
-as a result the potential diff across the membrane is reversed. The cell = +inside , - outside
pd at this point is +40mV
What happens in repolarisation
At the end of depolarisation (the last stage)
the Na+ channels close
-increased permeability of membrane to potassium ions , K+ channels open
-inside of axon is neg again
What happens in hyper polarisation
-membrane becomes too negative below -70mv bc K+ channels r slow to close
Resting potential restored
sodium potassium pump restores og ion distribution returning membrane to its resting potential
what happens during the absolute refractory period
Relative refractory period
sodium ion channels r blocked thus another action potential cant be generated
Can re stimulate action potential but with a very big stimulus
what is salatory conduction
where the action potential jumps between gaps in the cells of the myelin sheath called the nodes of ranvier, bc the myelin sheath is impermeable
what happens when an impulse arrives at the synaptic knob
1
-Arrival of impulse at
Pre synaptic knob increases permeability of presynaptic membrane to calcium ions, CALCIUM ION channels open
-synaptic vesicles containing acetylcholine fuse with (pre synaptic ) membrane releasing contents into synaptic cleft
-mols diffuse across gap and attach to receptor sites at the post synaptic membrane, opening Na+ channels
once the neurotransmitter binds to receptor sites what can happen
stimulates opening of Na+ channels enabling Na+ into neuron, membrane depolarises triggering another action potential. this is EPSP excitry post synaptic potential
OR
stimulates opening of Cl- channels, enabling Cl- ions to enter neuron, causing hyperpolarisation of membrane, this makes triggering a new action potential difficult IPSP inhibitory post synaptic potential
what effect does nicotine have on the nervous system?
mimics the effect of acetylcholine and triggers the release of dopamine, at high doses nicotine binds to and blocks acetylcholine receptors
what effect does lidocaine have on the nervous system?
its used as an anaesthetic which prevents you feeling pain
lidocaine molecules block voltage gated sodium channels preventing the production of an action potential in sensory nerves and preventing you from feeling pain.
how does cobra venom have an effect on the nervous system?
toxic, binds to and blocks acetylcholine receptors , prevents transmission pf impulses across synapses, causing paralysis
What are cells specialised for the detection of stimuli called
Receptors
What are the two types of photoreceptors in the retina called
Cones - which r involved in colour vision
rod - which produce monochromatic vision
How do the two photoreceptors differ in their lvl of sensitivity
Cones can only work in bright conditions whereas rods are more sensitive and dim light is sufficient for them .
What’s the light sensitive pigment in rod cells called
Rhodopsin which absorbs light energy and splits into retinal and opsin
Why aren’t rods stimulated in the dark?
Sodium ions diffuse into the cell thru open sodium channels, not enough rhospsin converted, causing membrane to be depolarised causing release of glutamate (neurotransmitter)
What does glutamate do
Works as an inhibitory neurotransmitter,It serves to inhibit the neurons which connect rod cells to the optic nerve and so no info is transmitted to the brain
In the presence of light what happens KEEP
Rhodopsin splits into retinal and opsin (bleaching) .
Opsin binds to membrane of cells causing Na+ channels to close . membrane becomes hyperpolarised
-action potential forms and is transmitted to brain via optic nerve
-less glutamate released
What’s the functions of the cerebellum , cerebrum , medulla , hypothalamus
Cerebellum - controls balance and coordination of movement
Cerebrum - initiates movement
Medulla - breathing and heart rate
Hypothalamus- controls thermo and osmoregulation
What’s the peripheral nervous system divided into
Voluntary and autonomic nervous system
What’s the autonomic nervous system split into
Sympathetic- produces noradrenaline, fight or flight , ganglia close to cns
Parasympathetic - produces acetylcholine, rest & digest, ganglia far from cns
What are differences between a sensory and motor neuron
- Sensory neurons have a longer dendron and shorter axon
- The cell body is in the middle
