Mr P bio 6 nerves Flashcards
what are the two structures of the nervous system?
central nervous system (CNS) and peripheral nervous system
what is the CNS composed of?
brain and spinal cord
what is the peripheral nervous system composed of?
all the neurones that connect the CNS to the rest of the body
what are the two types of neurones within the peripheral nervous system?
sensory neurones
motor neurones
what do sensory neurones do?
carry nerve impulses from receptors towards the CNS
what do motor neurones do?
carry impulses away from the CNS to effector
what is the peripheral nervous system split into?
somatic- controls conscious activity
autonomic-controls unconscious activity
what is the autonomic nervous system split into?
sympathetic- ‘fight or flight’ system
parasympathetic- ‘rest and digest’ calms the body down
what are the 3 main types of neurones?
-sensory
-motor
-relay
what are neurones?
specialised cells which are adapted to their function- to carry electrical impulses from one part of the body to another
what does a sensory neurone do?
transmits impulses from receptors to the CNS
what does a motor neurone do?
transmits electrical impulses from the CNS to effectors
what does the relay neurone do?
transmits electrical impulses between sensory and motor neurones
what is the soma within a neurone?
nucleus and cytoplasm, produces proteins and neurotransmitters
what are the dendrites on a neurone?
carry impulses away from soma
what is the axon of a neurone?
carries impulses away from the soma
what do the schwann cells on a neurone do?
produce myelin
what is the myelin sheath?
myelin insulate the axon, increasing speed of transmission of impulse
what are the nodes of ranvier?
gaps between schwann cells where myelin sheath is absent
what is the axon terminal
connect neurone to effector
what is the spinal cord?
column of nervous tissue that runs along the back and lies inside the vertebral column for protection
what is a reflex?
a rapid, short lives, localised and involuntary response to a stimulus, to prevent further injury
what is the importance of a reflex arc?
protect the body from harm, they do not have to be learnt, fast
what is a nerve impulse?
a temporary reversal of the electrical potential differences across the axon membrane
what is the resting membrane potential?
in a neurones resting state, outside the membrane is + charged compared to inside so membrane is polarised. at rest, voltage around -70mV
how is the resting potential created and maintained?
by the sodium-potassium pumps and potassium ion channels
what do sodium-potassium pumps do?
use active transport to move 3 sodium ions out of the neurone for every 2 potassium ions moved in. ATP needed
are the potassium ion channels open or closed during rest? and how do they move K+ in/out?
potassium ion channels are open allowing facilitated diffusion of K+ out of the neurone down their conc grad making the axon permeable to K+
are sodium ion channels open or closed during resting potential?
closed- axon membrane not permeable to Na+
what causes an action potential to take place?
when a stimulus of sufficient size is detected by a receptor and its energy causes a temporary reversal of the charges either side of the axon membrane
what does the - charge inside neurone become during the action potential?
+40mV
what has occurred to the axon during an action potential?
depolarisation
describe an action potential
- stimulus causes Na+ channels to open
- Na+ ions rapidly diffuse into cell down an electrochemical gradient via diffusion
3.inside becomes more + in relation to the outside-> AP
what is hyperpolarisation?
more K+ outside the axon than in so inside becomes too negative
what happens during repolarisation after hyperpolarisation?
-potassium gates close
-sodium potassium pump restores the resting potential
what is the all or nothin principle?
in order for an action potential to occur, threshold must be reached where enough Na+ channels open in order for enough Na+ to diffuse in and make the membrane depolarised enough to cause an action potential or else there will be no AP
what is the refractory period? advantage?
time where no new action potential can occur because NA+ channels are closed and unable to open
A- keeps action potential travelling unidirectionally down an axon
what is a myelin sheath?
lipid which acts as an insulator and prevents Na+ and K+ through the axon membrane
what does a myelin sheath allow?
allows saltatory conduction to occur where depolarisation will only occur at the Nodes of Ranvier and action potentials will jump from node to node. if unmyelinated then AP will pass slower along axon
what effect does temp have on the action potential?
when hotter: Ions have more kinetic energy so facilitated diffusion of Na+ and K+ happens faster so faster depolarisation so faster AP
what effect does axon diameter have on the rate if transmission?
thicker the axon, the faster the rate of transmission as greater diameter= more ion channels over one area of the axon= less resistance to the flow of Na+ into the axon so faster depolarisation
what is a synapse?
the junction between two neurones
what is a synaptic knob?
the swollen end of the terminal branched of another neurone
describe the process of synaptic transmission
- incoming AP causes depolarisation in synaptic knob causing voltage gated calcium ion channels to open and calcium ions to diffuse in
- influx of calcium ions causes synaptic vesicles to fuse with presynaptic membrane causing neurotransmitters to be released into the cleft
- neurotransmitter (acetylcholine) released into synaptic cleft and diffuses across the synapse and binds to complimentary receptors on the post-synaptic membrane 4.this causes (ligand gated) sodium ion channels to open allowing sodium ions to diffuse in and cause depolarisation
- depolarisation inside the postsynaptic neurone must be above threshold value for a new AP to be sent along axon
what happens after synaptic transmission?
- a hydrolytic enzyme called acetylcholinesterase hydrolyses acetylcholine into acetyl and choline
- sodium ion channes close
- the acetyl and choline diffuse back across the cleft into the presynaptic neurone and are reuptaken
- allows the neurotransmitter to be recycled
why is acetylcholine broken down?
if the neurotransmitter is not broken down this could allow it to continuously generate new APs so breaking down acetylcholine prevents this
why can nerve impulses inly travel in one direction?
-vesicles containing neurotransmitters are only released from the presynaptic membrane
-receptors are only present on the postsynaptic membrane
what is summation?
where the effect of neurotransmitters released from many neurones is (or one thats stimulated more frequently in small amount of time) is added together
what is spatial summation?
2 or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone
what is temporal summation?
2 or more APs arrive in quick succession from the same presynaptic neurone
what do inhibitory neurotransmitters do?
prevent APs being generated in post-synaptic neurones. they stimulate K+ channels to open so K+ diffuses out of the cell body
what is the importance of inhibition?
-allows specific pathways to be stimulated whilst preventing random impulses all over the body
-allows you to learn specific skills and control movements. pathways become refined by inhibitory circuits
what is a neuromuscular junction?
between a motor neurone and a muscle cell and very similar to a cholinergic synapse
what are the similarities between a neuromuscular junction and a synapse?
-uses acetylcholine
-uses acetylcholinesterase
-NET moves by diffusion
-binding of NET causes influx of Na+
differences between NMJ and synapses?
-NMJ post synaptic membrane has more receptors
-lots of folds/ clefts which store acetylcholinesterase
-when AP reaches muscle, always triggers a response
-NMJ are always excitatory
-NMJ always use ACh
-synapse junction between 2 neurones and NMJ junction between motor neurone and muscle cell
how can drugs (agonists) affect synaptic transmission?
can be same shape as neurotransmitters so mimic their action at receptors meaning more receptors activated
how can drugs (antagonists) affect synaptic transmission?
some can block receptors so they cant be activated by neurotransmitters, so fewer activated
how do drugs (enzyme inhibitors) effect synaptic transmission?
some inhibit the enzyme that breaks don neurotransmitters resulting in more neurotransmitters in the cleft to bind to receptors and theyre there for longer
how can drugs (more neurotransmitters) affect synaptic transmission?
some stimulate the release of more neurotransmitters from the presynaptic membrane so more receptors stimulated
how can drugs (less neurotransmitters) affect synaptic transmission?
some inhibit the release of neurotransmitters from the presynpatic membrane so fewer receptors stimulated
