module 5 - neuronal communication Flashcards
why do cells need to be co-ordinated?
cells in complex organisms perform specific functions which all need to be co-ordinated to operate efficiently (only heart functions independently)
when does cell co-ordination occur?
when there’s a change in external or internal environment
what is cell signalling?
cell will release a chemical that effects its target cell cor-ordinating a response
how can cell signalling occur?
transfer signals locally - neurones at synapses
transfer signals over long distances - using hormones
homeostasis and neuronal communication?
different organisms have different functions and they all need o be co-ordinated to MAINTAIN CONSTANT INTERNAL ENVIRONMENT = homeostasis
neurone structure - cell body
contains nucleus
surrounded by cytoplasm
large amounts of ER and mitochondria
involved in production of neurotransmitters
neurone structure - dendrons
short extensions from the cell body
divide into smaller branches = dendrites
transport electrical impulses INTO cell body
neurone structure - axon
cellular elongated nerve fibre
transmits impulses AWAY from cell body
cylindrical shape
narrow hollow tubes of cytoplasm
surrounded my plasma membrane
neurone type - sensory
transmit impulses from sensory receptor to relay, motor, or to CNS
have 1 dendron - carries impulses into cell body
have 1 axon - carries impulses away from cell body
neurone type - relay
transmits impulses between neurones
e.g sensory to motor
many short axons and dendrons
neurone type - motor
transmits impulse from relay or sensory to effector (muscle or gland)
1 long axon many short dendrites
common pathway of an impulse?
receptor - sensory - relay - motor - effector cell
what are transducers?
convert stimulus to nerve impulse e.g photoreceptor, thermoreceptor, mechanoreceptor
what are sensory receptors?
they’re specific to a single type of stimulus
act as transducers - convert stimulus to nerve impulse
what is the role of sensory receptor?
converts stimulus into electrical impulse
information passed from nervous system to CNS then to effector cell to express desired response
pacinian corpuscle
detect change in pressure (mechanoreceptor)
features of pacinian corpuscle and their role
blood capillary
neurone ending
capsule
layers of connective tissue
neurone
specialised Na+ ion channels called stretch-mediated sodium channels
= channels change shape
= permeability to Na+ changes depending on pressure
= responsible for transportation of Na+ across membrane
how does Pacinian Corpuscle convert mechanical pressure into nerve impulse?
1- at resting state SMSC are too narrow to allow Na+ through
2- pressure applied causes corpuscle to change shape and so the membrane stretches
3- this in turn allows Na+ to diffuse into neurone
4- Na+ influx changes potential of membrane - it becomes depolarised = creates generator potential
5- this generator potential creates an action potential that passes to the sensory neurone
what is resting potential?
the period when no neurone is being transmitted across the membrane
outside os membrane becomes more positively charged then inside the axon
what mv is resting potential?
-70mV as membrane is said to be polarised
what is resting potential a result of?
result of changing movement of Na+ and K+ across membrane
how is action potential reached?
occurs when protein channels change shape the axon membrane due to change in voltage across the membrane
what is the result of action potential being reached?
channels opening and closing (voltage gated ion channels) due to change in protein channel shape
steps that happen during an action potential:
1- at resting potential (no neurone is being transmitted) some of the K+ channels for open (mainly those that are not voltage-gated) and all Na+ channels are closed
2- energy of stimulus triggers Na+ voltage-gated channels to open causing membrane to be more permeable to Na+ (diffuse down electrochemical gradient)
inside of neurone = less negative
3- change in charge causes more Na+ channels to open - POSITIVE FEEDBACK
4- potential difference reaches +40mV so Na+ voltage-gated channels close and k+ open (membrane now more permeable to K+) = HYPERPOLARISATION
5- K+ diffuse out of axon down electrochemical gradient (inside axon more negative)
6- K+ close and Na+open
Propagation of action potential:
1- at resting potential the conc of Na+ is higher outside of the membrane then the inside and the conc of K+ higher on the inside than the outside of the membrane IT IS POLARISED
2- a stimulus will cause a sudden influx of Na+ creating an action potential causing the membrane to DEPOLARISE
3- localised electrical circuit is established by increasing Na+ causing Na+ voltage-gated channels to open further down the axon, K+ channels begin to open as Na+ close. K+ leave axon down the electrochemical gradient
4- action potential is propagated further down the axon causing the membrane behind the action potential to return to its original charge as its REPOLARISED
5- axon membrane returns to its resting potential ready for new stimulus
what are the key components of a synapse?
synaptic cleft
presynaptic neurone
postsynaptic neurone
synaptic knob
synaptic vesicles
neurotransmitter receptors
role of synaptic cleft:
gap which separates the axon of one neurone from the dendrite of another
role of the presynaptic neurone:
it is the neurone that passes the impulse along
role of the postsynaptic neurone:
neurone that receives the neurotransmitter
role of the synaptic knob:
swollen end of the presynaptic neurone
contains many mitochondria and large amounts of endoplasmic reticulum to manufacture neurotransmitters
role of synaptic vesicles:
vesicles containing neurotransmitters
fuse with presynaptic membrane and release contents into the synaptic cleft
role of neurotransmitter receptors:
receptor molecules which a specific neurotransmitter will bind to in the postsynaptic membrane
what are the 2 types of neurotransmitters?
EXCITATORY = cause depolarisation of postsynaptic neurone
INHIBITORY = cause the hyper polarisation of the postsynaptic membrane
function of excitatory neurotransmitter:
cause the depolarisation of the postsynaptic membrane
allows threshold to be reached in the postsynaptic membrane then an action potential is triggered
e.g acetylcholine
function of inhibitory neurotransmitter:
cause the hyperpolarisation of the postsynaptic membrane
prevents the generation of an action potential
e.g GABA (gamma-aminobutyric acid)
what are the steps to transmission of an impulse across a synapse?
1- action potential is reaches in the presynaptic membrane
2- causes Ca2+ channels to open due to the depolarisation
3- Ca2+ diffuse into presynaptic knob
4- causes synaptic vesicles containing NTs to fuse with the presynaptic membrane = NTs are released into th synaptic cleft via exocytosis
5- NTs diffuse across cleft and bind with specific receptors on the postsynaptic membrane
6- causes Na+ channels to open
7- Na+ diffuse into postsynaptic neurone
8- triggers an action potential and the impulse is propogated along postsynaptic neurone
where are cholinergic synapses commonly located and what neurone is used?
acetylcholine and most common in CNS and at neuromuscular junctions
first step to cholinergic synapse transmission:
action potential at the end of the presynaptic membrane is reached causing Ca2+ channels to open and enter the synaptic knob
second step to cholinergic synapse transmission:
influx of Ca2+ cases synaptic vesicles to fuse with presynaptic membrane and release acetylcholine into the synaptic cleft
third step to cholinergic synapse transmission:
acetylcholine molecules fuse with receptor sites on Na+ channels in the postsynaptic membrane causing Na+ channels to open and diffuse in rapidly along electrochemical gradient
forth step to cholinergic synapse transmission:
influx of Na+ causes and new action potential to be generated in the postsynaptic neurone
fifth step to cholinergic synapse transmission:
acetylcholinesterase hydrolyses acetylcholine into ethnic acid (acetyl) and choline which diffuses back across synaptic cleft into presynaptic neurone (recycled)
the breakdown of acetylcholine Aldo prevents it from continuously generating a new action potential
sixth step to cholinergic synapse transmission:
ATP released by mitochondria is used to recombine ethnic acid and choline into acetylcholine
this is stored in the synaptic vesicles for future use
Na+ channels close due to absence of acetylcholine
what is the role of a synapse?
ensure impulses are unidirectional = neurotransmitter receptors are only on the postsynaptic membrane so impose can only travels from pre to post
allows impulses from one neurone to be transmitted to a number of neurones at multiple synapses = single stimulus creating multiple simultaneous responses
alternatively allows a number of neurones to feed into the same synapse with single postsynaptic neurone = stimulus from multiple receptors create a single response
what is it called when neurotransmitters must build up to reach threshold?
summation
what is summation?
each stimuli produces the same amount of neurotransmitters but sometimes this is not enough to reach the threshold and produce an action potential
therefore the NTs must build up to trigger an action potential = SUMMATION
what are the 2 types of summation?
spacial and temporal
spacial summation:
number of presynaptic neurones connect to one postsynaptic neurone
each releases neurotransmitter which builds up in synapse to trigger action potential in SINGLE POSTSYNAPTIC NEURONE
temporal summation:
a single presynaptic neurone releases neurotransmitter as a result of action potential several times over a short period until its built enough up to trigger an action potential
what is the structural organisation of the nervous system?
the central nervous system (CNS) = brain and spinal cord
the peripheral nervous system (PNS)= consists of all neurones that connect the CNS to the rest of the body = the sensory neurones that carry nerve impulses away from the CNS
what is the functional organisation of the nervous system?
the somatic nervous system
the automatic nervous system
role of somatic nervous system:
system under conscious control
used when you voluntarily decide to do something
e.g decide to move muscle in you’re arm
role of automatic nervous system:
system works continuously under subconscious control
used when body does something automatically
e.g heart to beat, to digest something
it carries nerve impulses to glands, smooth muscle, cardia muscle
which functional system is further divided?
automatic nervous system
how is the automatic nervous system further divided?
sympathetic nervous system = outcome will result in an increase in activity e.g increasing hear rate
parasympathetic nervous system = outcome will result in a decrease in activity e.g decrease in hear rate or breathing rate after exercise
components of the brain:
cerebrum - consoles voluntary actions
cerebellum - consoles unconscious function
medulla oblongata - consoles involuntary action
hypothalamus - regulatory centre
pituitary gland - stores and releases hormones
what happens to all the bands, lines and zones during muscle contraction?
light band becomes narrower
z lines move closer together (shortening the sarcomere)
h zone become shorter
dark band remains the same width as myosin filaments haven’t moved the actin just overlaps it more
what is the structure of myosin?
they have globular heads that are hinged allowing them to move forwards and backwards during muscle contraction
the heads are blinding sites for actin (muscle contracting) and ATP (muscle relaxing)
what is the structure of actin?
they have binding sites for myosin heads called actin-myosin binding sites
why are the actin-myosin binding sites usually blocked during muscle relaxation?
the binding sites are blocked by tropomyosin held in place by the protein troponin
it prevents the filaments from sliding past each other as the myosin heads are prevented from binding
what happens at the actin myosin binding sites during contraction?
actin-myosin cross-bridges form
myosin heads then flex (change angle) in unison pulling the actin filament across the myosin
using ATP myosin heads will detach (returning back to normal angle) allowing muscle to relax
where are neuromuscular junctions located?
where the motor neurone meets the skeletal muscle fibre
what is a motor unit in relation to neuromuscular junctions and what do they ensure?
they are muscle fibres supplied by a single motor neurone
there are may located along a muscle to ensure simultaneous contraction
what happens when action potential reaches a neuromuscular junction?
1- Ca2+ channels open and the ions are released into he synaptic knob
2- this causes synaptic vesicles to fuse to the presynaptic membrane
3- acetylcholine is released into the synaptic cleft and fuses with the receptors on the postsynaptic membrane (sarcolemma) causing Na+ channels to open
4- acetylcholine is broken down into ethanoic acid an choline by acetylcholinesterase where it returns to the presynaptic neurone ready for reuse
what happens at the sarcoplasm?
the depolarisation of sarcolemma travels deep into the muscles via t-tubles which are in contact with the sarcoplasmic reticulum (releases Ca2+ when action potential is reached flooding the sarcoplasm)
what role does sarcoplasmic reticulum have in the sliding filament theory?
SR releases ca2+ flooding the sarcoplasm
Ca2+ binds to the troponin casing it to change shape pulling the tropomyosin away from the actin-myosin binding site
this exposes the binding site allowing muslin heads to attach creating actin-myosin cross-bridges
now muscle contraction can occur
