15: Nervous coordination and muscles Flashcards
Differences between the hormonal and nervous system
hormonal:
- communication by chemicals called hormones
- transmission is my blood
- transmission is slow
- hormones travel to all parts of body but only target cells respond
- response is widespread
- response is slow, long lasting
- effect may be permanent and irreversible
nervous system
- communication by nerve impulses
- transmission is by neurons
- transmissions rapid
- nerve impulses travel to specific parts of the body
- response is localised, rapid and short lived
- effects temporary and reversible
how to tell apart 3 neurons
sensory = long dendrites short axon
motor = long axon, short dendrites
relay = numerous short processes
whats a mammalian motor neurone made up of
- cell body (production of proteins and nts)
- dendrons (subidivide into dendrites. carry nerve impulses towards cell body
- axon (single long fibre carries nerve impulses away from cell body)
- schwann cells (surround axon, protecting and electrical insulation. carry out phagocytosis
- myelin sheath
- nodes of ranvier
Resting potential
- when a neurone is not conducting an impulse, there is a difference between the electrical change inside and outside of the neurone - the resting potential
- there are more positive ions, na and , OUTSIDE of neurone. inside is more negative at -70mV
- movement of ions is by phospohlipid bilayer, channel proteins, sodium-potassium pump
Establishing a resting potential
- maintained by sodium potassium pump
- moves 2K+ ions in and 3Na+ ions out
- this creates an electrochemical gradient causing K+ ions to diffuse out and Na+ ions to diffusein
- the membrane is more permebale to K+ ion, so more are moved out resulting in the -70mV
Action potential
- at resting potential, some K+ volttage gated channels are open but all sodium are closed
- energy of stimulus causes some sodium voltage-gated channels in axon membrane to open so sodium ions diffuse into axon along electrochemical gradient
- this causes more sodium channels to open
- once action potential of +40mV has been established, sodium gates close and potassium open
- the electrical gradient preventing potassium ionsout is now reversed so more k channels open so diffuse out of axon and cause repolarisation
- outward diffusion causes temporary overshoot of the electrical gradient as inside of axon is more negative
- potassium ions now close and -65mV reestablished and repolarised
All or nothing principle
- threshold value which triggers action potential
- if depolarisation doesnt exceed -65mV, an action potenital and impulse are not produced
factors affecting the speed at which an action potential travels
- myelin sheath (action potential jumps from node to node, so dont need to generate as many action potentials, so quicker)
- diameter of axon (wider diameter increases the speed of conductance, less leakage of ions)
- temperature (ions diffuse faster, enzymes work faster so more atp for active transport in sodiumpotassium pump)
function of synapse (unidirectional)
- action potential arrives at synaptic knob. depolarisation of this opens Ca2+ channels, which diffuse into knob
- vesicles containing NT move to presynaptic membrane and release into synaptic cleft
- NT diffuses down conc grad to post synaptic membrane, NT binds to complementary receptor
- this causes Na+ ion channels on post synaptic membrane to open and diffuse in, if theres enough of the NT than enough Na+ diffuses in to depolarise the post-synaptic neuron
why is action potential across synapse unidirectional
- vesicles containing NTs only on pre-synaptic knob
-NT diffuse down conc grad - receptors only on post membrane
Summation
- rapid build up of nts in the synapse to help generate an action potential by two methods
- temporal summation (single presynaptic neurone releases nts many times over a short period of time)
- spatial summation (multiple presynaptic neurons release enough nts to exceed threshold value)
Cholinergic synapse
neurotransmitter is ACETYLCHOLINE
- nts dont permanently bind as otherwise sodium channels would be constantly open
- so enzyme acetylcholinesterase hydrolyses acetylcholine into choline and acetate
- recycle
- atp released by mitochondria used to recombine
Inhibitory synapse
- cause chloride ions to move into the postsynaptic neuron and potassium ions to move out
- this makes the membrane potential decrease to -80mV. hyperpolarisation. so action potentials unlikely
Similarities and differences between neuromuscular junction and cholinergic synapse
- both unidirectional
neuromuscular junction:
- only excitatory
- connects motor neurone to muscles
- end point for the action potential
- acetylcholine binds to receptors on muscle fibre membrane
cholinergic synapse:
- excitatory or inhibitory
- connect two neurons, which could be sensory, motor or relay
- a new action potential is generated in the next neurone
- acetylcholine binds to receptors on post-synaptic membrane neurone.
Muscles
- example of effector
- act as an antagonistic pair against an incompressible skeleton to create movement
- this can be automatic reflex or conscious thought
