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Neurones + Synapses - Coggle Diagram
Neurones + Synapses
Nervous System
based on system of neurones
that transmit electrical nerve impulses
through body
nerve
-
bundle of neurones grouped together protected with outer protective layer
can contain
sensory neurones only
motor neurones only
both types
Nervous Control
1. Receptors
sensitive to a particular
type of stimulus
eye, ear, nose etc
3. Effectors
produce response
muscles + glands
2. Coordinator
links receptor to effector +
coordinates response
involves central nervous system
(brain + spinal cord)
faster
+
more precise
than
hormone action
Excitatory
Synapses
Structure
impulses transmitted from 1 neurone to next
be chemicals =
NEUROTRANSMITTERS
diffuse across small gap =
SYNAPTIC CLEFT
Neurotransmitters
pass across synaptic cleft
cause depolarisation
allowing nerve impulse continue 1 neurone to next
PRE
-synaptic neurone
releases
NT
@ end of neurone
thickened into
SYNAPTIC BULB
which contain
large no. mitochondria
(
manufactures NT
)
large no. synaptic vesicles
(
stores NT
)
POST
-synaptic neurone
receives
NT
membrane contains
receptors
complementary to type of NT involved in particular synapse
Transmission @
Synapses
1.impulse arrives @ PRE
calcium ion channels
open
Ca 2+ diffuse into synaptic bulb
2.Ca2+ cause
synaptic vesicles
move towards PRE membrane
3.synaptic vesicle
FUSE
with PRE membrane
release NT
(acetylcholine)
by exocytosis
into
synaptic cleft
4.AcCh diffuses across
synaptic cleft
binds
to AcCh receptors
on POST membrane
5.binding causes
opening of Na+
ion channels
in POST membrane of
positive ions
diffuse
through POST membrane
membrane gradually
depolarised
(raised above -70mV)
enough +ve ions enter
excitatory post-synaptic potential generated (EPSP)
sufficient depolarisation
EPSP reaches threshold potential (-55mv)
AP produced
8.
enzyme acetylcholinesterase
breaks down
AcCh
removed
from receptors
produces
choline
ethanoic acid (acetyl)
released into CLEFT
choline + acetyl
diffuse
back across cleft
absorbed into
synaptic bulb
10.in
synaptic bulb
acetylcholine
re-synthesised
from choline + acetyl
stored
in
synaptic vesicle
ATP REQUIRED
(produced in mitochondria)
Function
disadvantages
makes
SLOWER
having to
diffuse
chemicals across
short gap
than conduction of impulse along myelinated neurones
advantages
nerve impulses can pass
from neurone to neurone
allow nervous communication
despite neurones not continuous
ensure
unidirectionally
nerve impulses only pass from
PRE to POST
NT only made in PRE
NT receptors only present in POST
prevent overstimulation
of effectors
too many impulses pass along same neurone short time...
exhaust supply of NT than built up
synapse fatigue
provide
integration
number of PRE forming
junction with 1 POST
provides
flexibility
if no synapses -
nervous activity produces
automatic
never-changing response
aided through
summation
D: junction between axon of 1 neurone
and dendrite (dendron/centron)
of adjacent neurone
Neurones
Sensory
Neurones
D: carry impulses from
receptors to CNS
Connector
Neurones
D: connect neurones
WITHIN
the CNS
Motor
Neurones
D: carry impulses from the
CNS to effectors
role
conduct nerve impulses
differ in
location
much longer than appear in diagram
1,000s of Schwann cells
structure
centron/cell body
contains
nucleus
mitochondria
Nissl's granules
(large group of ribosomes)
extended nerve fibre
bit of cytoplasm stretched out
axon
nerve fibre transmits impulse
AWAY
from cell body
(in MN entire cell nerve fibre is axon)
dendron
nerve fibre carries impulse
TOWARDS
cell body
synaptic bulb
where axons terminate
neurilemma
cell surface membrane
of neurone
MYELINATED
nerve fibres
D: dendrons + axons covered
with insulating myelin sheath
myelin sheath
rich in lipid myelin
made from Schwann cells repeatedly
wrapped round axon
function
speed up nervous conduction
protect nerve fibre
Schwann cells
arranged @ intervals along nerve
nodes of Ranvier
small gaps between Schwann cells
where axon/dendron is exposed
occurs in
some mammals
Summation
provides
complexity +
flexibility
infrequent AP reaching synapse may not cause AP in POST
series of impulses along SAME neurone
OR
number PRE operating in UNISON
enough to cause EPSP
Inhibitory Synapses
makes MORE DIFFICULT for
synaptic transmission to take place
NT released makes more difficult for EPSP to form in POST
inhibitory NT
leads to
influx of -ve ions
in POST membrane
inside more negative (than -70mV) than outside
creates
IPSP in POST
like
HYPERPOLARISATION
more negative than normal resting potential
function
reducing input of background
stimuli that clutters nervous activity
prevent some
reflex actions
Neurotransmitter
Substances
Acetylcholine
primary neurotransmitter
in central nervous system of vertebrates
Noradrenaline
used in involuntary control
eg regulation of gut movements
each synaptic bulb produces
1 type of NT
GABA (aminobutyric acid)
released @
inhibitory synapses
chief inhibitory NT in mammals
causes -ve ions flow out of POST
causing HYPERPOLARISATION
ROLES
helps reduce anxiety + panic attacks
dampening down nerve pathways in brain
