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HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
The
notes
in
this
document
cover
IB
topics
11.2
and
option
E.1,
E.2,
E.4
and
E.5.
Organization
of
the
Nervous
System
The
nervous
system
is
divided
into
the
peripheral
nervous
system
(PNS)
and
central
nervous
system
(CNS).
The
PNS
consists
of


sensory
neurons
running
from
stimulus
receptors
that
inform
the
CNS
of
the
stimuli
motor
neurons
running
from
the
CNS
to
the
effectors
(muscles
and
glands)
that
respond
to
the
stimuli
The
CNS
consists
of


the
spinal
cord
the
brain
The
Peripheral
Nervous
System
Sensory Neurons
Sensory Neurons
Internal
Environment
Autonomic
NS
CNS
SensorySomatic
NS
External
Environment
Motor Neurons
Motor Neurons
The
PNS
is
subdivided
into

the
sensory‐somatic
nervous
system
which
connects
the
external
environment
and
the
CNS
there
are
12
pairs
of
cranial
nerves,
which
connect
directly
to
the
brain
(e.g.
the
optic
nerve),
and
they
may
be
sensory,
motor,
or
mixed
nerves
 there
are
31
pairs
of
spinal
nerves,
all
of
which
are
mixed
 all
our
conscious
awareness
of
the
external
environment
and
all
our
motor
activity
to
cope
with
it
operate
through
the
sensory‐somatic
division
of
the
PNS
 actions
of
the
sensory‐somatic
nervous
system
are
largely
voluntary
–
skeletal
muscle
is
controlled
by
this
system


the
autonomic
nervous
system
(ANS)
which
connects
the
internal
environment
and
the
CNS
consists
of
sensory
neurons
and
motor
neurons
that
run
between
the
CNS
and
various
internal
organs
 it
is
responsible
for
monitoring
conditions
in
the
internal
environment
and
bringing
about
appropriate
changes
in
them
 actions
of
the
autonomic
nervous
system
are
largely
involuntary
‐
cardiac
muscle
(heart),
blood
vessels,
digestive
system,
smooth
muscle,
and
glands
are
controlled
by
this
system
 uses
two
groups
of
motor
neurons
to
stimulate
the
effectors

A.
De
Jong/TFSS
2007
1
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
preganglionic
neurons
arise
in
the
CNS
and
run
to
a
ganglion
in
the
body
■ postganglionic
neurons
run
to
the
effector
organ
(synapse
occurs
in
the
ganglion
 further
subdivided
into
the
sympathetic
and
parasympathetic
nervous
systems,
which
are
largely
antagonistic
to
each
other:
■
Image
from
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/autonomic.gif
The
Sympathetic
Nervous
System
The
neurotransmitter
of
the
preganglionic
neurons
is
acetylcholine
(Ach).
It
stimulates
action
potentials
in
the
postganglionic
neurons.
The
neurotransmitter
of
the
postganglionic
neurons
is
noradrenaline.
The
action
of
noradrenaline
on
a
particular
gland
or
muscle
may
be
excitatory
or
inhibitory.
Stimulation
of
the
sympathetic
branch
of
the
ANS
prepares
the
body
for
emergencies:
“fight
or
flight”.
The
Parasympathetic
Nervous
System
The
main
nerves
of
the
parasympathetic
nervous
system
are
the
vagus
nerves,
which
originate
in
the
medulla
oblongata.
Acetylcholine
is
the
neuro‐transmitter
at
all
pre‐
and
many
postganglionic
neurons.
Some
postganglionic
neurons
release
nitric
oxide
as
their
neurotransmitter.
The
parasympathetic
nervous
system
returns
the
body
to
normal
after
they
have
been
altered
by
sympathetic
stimulation:
“rest
and
digest”.
A.
De
Jong/TFSS
2007
2
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Although
the
ANS
is
considered
to
be
involuntary,
this
is
not
entirely
true.
A
certain
amount
of
conscious
control
can
be
exerted
over
it
as
has
long
been
demonstrated
by
practitioners
of
yoga
and
Zen
Buddhism.
During
their
periods
of
meditation,
these
people
are
able
to
alter
a
number
of
autonomic
functions
including
heart
rate
and
the
rate
of
oxygen
consumption.
These
changes
are
not
simply
a
reflection
of
decreased
physical
activity
because
they
are
lower
than
levels
found
during
sleep
or
hypnosis.
Another
example
of
conscious
control
of
the
ANS
is
the
control
of
emptying
of
the
bladder
and
bowels.
The
Central
Nervous
System
The
spinal
cord
conducts
sensory
information
from
the
PNS
to
the
brain,
and
conducts
motor
information
from
the
brain
to
the
effectors,
including
skeletal,
smooth
and
cardiac
muscle,
and
glands.
It
also
serves
as
a
minor
reflex
centre.
The
brain
receives
sensory
input
from
the
spinal
cord
and
its
own
nerves.
It
devotes
most
of
its
computational
power
to
processing
its
various
sensory
inputs
and
initiating
appropriate
and
coordinated
motor
outputs.
Both
the
spinal
cord
and
brain
consist
of
white
matter
(bundles
of
axons
coated
with
myelin
sheaths)
and
grey
matter
(cell
bodies
&
dendrites,
covered
in
synapses).
They
are
also
covered
with
connective
tissue
called
the
meninges.
An
extracellular
fluid
that
differs
in
its
composition
from
the
ECF
in
the
rest
of
the
body
surrounds
the
cells
of
the
CNS.
Cerebrospinal
fluid
(CSF)
contains
less
protein
than
ECF,
and
is
found
within
the
cerebrospinal
canal
of
the
spinal
cord
and
within
the
four
ventricles
of
the
brain.
The
Spinal
Cord
Image
from
http://neuro.wehealny.org/images/14_01.jpg
There
are
31
pairs
of
spinal
nerves.
These
are
all
classed
as
mixed
nerves
because
they
contain
both
sensory
and
motor
axons.


sensory
axons
pass
into
the
dorsal
root
ganglion
where
their
cell
bodies
are
located
and
then
on
into
the
spinal
cord
itself
motor
axons
pass
into
pass
into
the
ventral
roots
before
uniting
with
the
sensory
axons
to
form
the
mixed
nerves
A.
De
Jong/TFSS
2007
3
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
The
primary
functions
of
the
spinal
cord:

it
connects
a
large
part
of
the
PNS
to
the
brain

it
is
a
minor
coordinating
centre
responsible
for
some
simple
reflexes
such
as
the
withdrawal
reflex
The
Brain

Medulla
Oblongata
controls
involuntary
and
visceral
activities

Cerebellum
controls
body
balance,
muscular
coordination
and
equilibrium.

Hypothalamus
maintains
the
internal
environment

regulates
body
temperature,
thirst,
hunger,
metabolism,
pleasure,
pain,
etc.

Thalamus
sorts
incoming
and
outgoing
impulses
and
sends
to
the
appropriate
centre

Cerebral
Cortex
centre
of
all
voluntary
muscle
control
and
mental
activity




analysis
coding
info.
storage
recognition




memory
understanding
intelligence
sense
integration
Image
from
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/brain_3.gif
The
pituitary
gland,
located
at
the
base
of
the
brain,
is
approximately
the
size
of
a
pea,
and
is
composed
of
two
lobes.

anterior
lobe:
stimulated
by
the
hypothalamus
of
the
brain
to
secrete
several
hormones




thyroid
stimulating
hormone
(TSH)
follicle‐stimulating
hormone
(FSH)
luteinizing
hormone
(LH)



prolactin
growth
hormone
adrenocorticotropic
hormone
(ACTH)
posterior
lobe:
releases
two
hormones,
synthesized
by
the
hypothalamus,
into
the
bloodstream


antidiuretic
hormone
(ADH)
oxytocin
A.
De
Jong/TFSS
2007
4
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
How
do
we
know
what
the
brain
does?

Investigating
brain‐damaged
patients
o For
example,
the
experiences
of
soldiers
surviving
bullet‐wounds
to
the
rear
of
the
skull
led
to
the
discovery
of
the
role
of
the
visual
cortex
on
the
rear
of
the
cerebral
hemispheres.
o Patients
who
are
not
immediately
killed
by
a
stroke
often
experience
paralysis
or
loss
of
a
specific
body
function
–
post‐mortem
analysis
identifies
the
particular
part
of
the
brain
affected
by
the
stroke.

Animal
experiments
o We
have
learned
a
lot
about
brain
function
by
studying
mammals
and
other
vertebrates,
removing
parts
of
a
healthy
brain
or
severing
connections
between
neurons.
o In
one
investigation
using
cats,
severing
the
fibres
that
cross
over
in
the
centre
of
the
brain
below
the
two
halves
of
the
cerebral
hemispheres
gave
clues
to
the
interaction
of
left
and
right
halves
of
the
brain.

fMRI
o Functional
magnetic
resonance
imaging
is
an
advanced
form
of
MRI
that
detects
the
parts
of
the
brain
that
are
active
when
the
body
performs
specific
tasks.
There
is
always
a
demand
for
oxygen
and
glucose
(food
energy)
in
the
brain,
but
there
are
local
increases
in
demand
when
a
particular
area
of
the
brain
is
in
use.
fMRI
detects
increases
in
red
blood
cell
oxygenation
at
the
site
of
neural
activity.
A.
De
Jong/TFSS
2007
5
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Neurons
All
neurons
are
specialized
cells
that
carry
an
electrochemical
impulse
called
an
action
potential.
Sensory
neurons
run
from
the
stimulus
receptors
(e.g.
for
touch,
vision,
sound,
odour
and
taste)
to
the
CNS.
Interneurons,
found
only
in
the
CNS,
and
are
stimulated
by
sensory
neurons,
other
interneurons,
or
both.
The
brain
is
estimated
to
contain
100
billion
interneurons
averaging
1000
synapses
each.
Motor
neurons
such
as
the
one
pictured
can
have
an
axon
that
is
up
to
one
metre
in
length.
They
transmit
impulses
from
the
brain
to
the
effectors
–
muscles
and
glands.
Image
from
http://www.gonzaga.k12.nf.ca/academics/science/sci_page/biology/neuron1.gif
Nerve
Impulse
Transmission
Neurons
send
messages
electrochemically,
which
means
that
chemicals
cause
an
electric
signal.
Ions
have
either
a
positive
(+)
or
negative
(‐)
charge.
Important
ions
for
nerve
impulse
transmission
are:


sodium
(Na+)
potassium
(K+)


calcium
(Ca++)
chloride
(Cl‐)
Some
definitions:

Membrane
potential:
the
electrical
potential
difference
(voltage)
across
a
cell's
membrane.

Action
potential:
a
wave
of
electrical
discharge
that
travels
along
the
membrane
of
a
cell.
Action
potentials
are
used
by
the
nervous
system
to
transmit
information
between
neurons,
and
between
neurons
and
effectors.

Resting
potential:
the
membrane
potential
that
would
be
maintained
if
there
were
no
action
potentials,
synaptic
potentials
or
other
active
changes
in
the
membrane
potential.
For
most
cells,
this
is
a
negative
number.
The
resting
potential
of
a
neuron
is
usually
‐
70
mV.
At
rest,
K+
can
easily
cross
through
the
membrane,
while
Cl‐
and
Na+
have
more
trouble
crossing.
The
negatively‐charged
protein
molecules
(A‐)
cannot
cross
the
membrane.
In
addition,
the
sodium‐potassium
ion
pump
is
actively
pumping
three
Na+
out
for
every
two
K+
it
puts
in.
Image
from
http://faculty.washington.edu/chudler/gif/ioncon.gif
A.
De
Jong/TFSS
2007
6
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
An
action
potential
occurs
when
a
neuron
sends
an
impulse
down
an
axon,
away
from
the
cell
body.
It
is
an
explosion
of
electrical
activity
that
is
created
by
a
depolarizing
current.
(This
means
that
a
stimulus
has
caused
the
resting
potential
to
move
toward
0
mV.)
When
the
depolarization
reaches
about
‐55
mV,
a
neuron
will
fire
an
action
potential.
This
value
is
called
the
threshold.
If
this
value
is
not
reached,
the
action
potential
will
not
fire.
*
The
action
potential
for
any
given
neuron
is
always
the
same.
There
is
no
“big”
or
“small”
action
potential
for
a
neuron.
Action
potentials
are
caused
by
an
exchange
of
ions
across
the
membrane
of
a
neuron:

A
stimulus
causes
sodium
channels
to
open,
allowing
sodium
ions
to
enter
the
cell.

This
causes
depolarization,
because
the
sodium
ions
are
positively
charged.

The
potassium
channels
open
after
depolarization
begins,
which
causes
potassium
to
leave
the
cell,
reversing
the
depolarization.

Around
this
time,
sodium
channels
begin
to
close,
which
causes
a
repolarisation,
as
the
action
potential
goes
back
toward
‐70
mV.

The
action
potential
actually
goes
past
‐70
mV
(a
hyperpolarisation)
because
the
potassium
channels
stay
open
a
bit
too
long.

Gradually,
the
ion
concentrations
go
back
to
resting
levels
and
the
cell
returns
to
‐70
mV.
Image
from
http://faculty.washington.edu/chudler/ap3.gif
Synapses
Nerve
impulses
are
transmitted
along
an
individual
neuron
by
means
of
an
action
potential.
Since
these
signals
must
be
transmitted
not
only
along
a
single
neuron,
but
from
one
neuron
to
another,
or
from
a
neuron
to
an
effector,
there
must
be
a
means
of
passing
the
signal
from
one
neuron
to
another.
A
junction
between
two
neurons
is
called
a
synapse.
For
information
to
pass
between
neurons,
it
must
cross
the
synapse.
Invertebrates,
and
some
fish
have
electrical
synapses,
in
which
the
action
potential
in
the
pre‐synaptic
neuron
can
trigger
an
action
potential
in
the
post‐synaptic
neuron
because
there
is
a
physical
connection
between
the
two
neurons.
Electrical
synapses
are
faster
than
chemical
synapses.
Most
nerves
are
connected
by
chemical
synapses,
which
consist
of:
 a
pre‐synaptic
ending
that
contains
neurotransmitters,
mitochondria
and
other
cell
organelles
 a
neurotransmitter
is
a
substance
(such
as
norepinephrine
or
acetylcholine)
that
transmits
nerve
impulses
across
a
synapse

a
post‐synaptic
ending
that
contains
receptor
sites
for
neurotransmitters
A.
De
Jong/TFSS
2007
7
of
21
HL
Biology

Notes
for
Nerves,
Muscles
&
Movement
a
synaptic
cleft
or
space
between
the
pre‐synaptic
and
post‐synaptic
endings
For
communication
between
neurons
to
occur,
an
electrical
impulse
must
travel
down
an
axon
to
the
synaptic
terminal.
Action
of
Neurotransmitters:
1. At
the
pre‐synaptic
terminal,
an
electrical
impulse
(action
potential)
causes
a
change
in
membrane
permeability
to
Ca++,
which
allows
Ca++
to
flow
into
the
synaptic
knob.
Image
from
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Synapse.gif
2. Presence
of
Ca++
will
trigger
the
migration
of
vesicles
containing
neurotransmitters
toward
the
pre‐synaptic
membrane.
3. The
vesicle
membrane
will
fuse
with
the
pre‐synaptic
membrane,
releasing
neurotransmitters
into
the
synaptic
cleft.
(an
example
of
exocytosis)
4. Neurotransmitter
molecules
diffuse
across
the
synaptic
cleft
where
they
can
bind
with
receptor
sites
on
the
post‐synaptic
ending
to
influence
the
electrical
response
in
the
post‐synaptic
neuron.

When
a
neurotransmitter
binds
to
a
post‐synaptic
receptor,
it
changes
the
post‐synaptic
cell's
excitability,
making
it
either
more
or
less
likely
to
fire
an
action
potential.

If
the
number
of
excitatory
post‐synaptic
events
is
large
enough,
they
will
add
to
cause
an
action
potential
in
the
post‐synaptic
cell
and
a
continuation
of
the
“message”.
Many
psychoactive
drugs
and
neurotoxins
can
change
the
properties
of
neurotransmitter
release,
neurotransmitter
reuptake
and
the
availability
of
receptor
binding
sites.
Neurotransmitters
and
Synapses
Synapses
of
the
PNS
are
classified
according
to
the
neurotransmitter
used.
Each
synapse
uses
only
one
neuro‐transmitter.



Most
synapses
in
the
parasympathetic
nervous
system
are
cholinergic
synapses,
and
use
acetylcholine.
Neuromuscular
junctions
are
also
cholinergic.
Most
synapses
in
the
sympathetic
nervous
system
are
adrenergic
synapses,
and
use
noradrenaline.
Synapses
of
the
brain
use
a
much
wider
range
of
neurotransmitters,
including
dopamine
and
enkephalins.
A.
De
Jong/TFSS
2007
8
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Neurotransmitters
bind
to
receptors
on
the
postsynaptic
membrane,
causing
temporary
changes
in
its
permeability.

Some
neurotransmitters
cause
Na+
or
other
positive
ions
to
enter
the
post‐synaptic
neuron,
helping
to
depolarize
it
and
cause
an
action
potential.


Other
neurotransmitters
cause
Cl‐
to
move
into
the
post‐synaptic
neuron
–
this
causes
hyperpolarisation.
Hyperpolarisation
makes
it
more
difficult
to
create
an
action
potential
(further
from
threshold).


These
are
called
excitatory
synapses.
These
are
called
inhibitory
synapses.
Most
post‐synaptic
neurons
have
synapses
with
more
than
one
pre‐synaptic
neuron
–
these
may
be
a
mix
of
excitatory
and
inhibitory
synapses,
and
whether
an
action
potential
is
initiated
in
the
post‐synaptic
neuron
is
determined
by
the
sum
of
all
neurotransmitter
messages.
Parkinson's
Disease
is
caused
by
the
death
of
neurons
in
a
part
of
the
brain
called
the
substantia
nigra.
These
neurons
release
the
neurotransmitter
dopamine
at
inhibitory
synapses
with
neurons
that
help
to
control
muscle
contractions.
Without
dopamine,
muscle
contractions
cannot
be
properly
controlled
–
this
causes
the
symptoms
of
Parkinson's:



early
symptoms
include
feeling
tired
and
shaky,
and
a
loss
of
concentration
eventually,
the
body
becomes
stiff
because
antagonistic
muscles
cannot
relax
uncontrollable
shaking
affects
the
hands
and
other
body
parts
and
movements
become
very
slow
Pain
receptors
are
found
in
the
skin
and
other
organs.
They
consist
of
free
nerve
endings,
which
perceive
mechanical,
chemical
or
thermal
stimuli.
Pain
signals
are
sent
from
these
nerve
endings
to
the
spinal
cord
via
nerve
fibres,
which
carry
them
up
to
the
thalamus
or
brain
stem.
From
here,
pain
signals
may
be
passed
on
to
sensory
areas
of
the
cerebral
cortex,
giving
conscious
recognition
of
pain.
Since
there
are
both
fast
and
slow
nerve
endings,
a
painful
stimulus
causes
an
initial
sharp
pain
sensation,
followed
by
a
slow,
burning
pain.
The
sensation
of
pain
is
necessary
to
tell
the
body
when
it
is
being
damaged
–
this
allows
the
pain
withdrawal
reflex
or
other
reactions
to
occur.
Sometimes
pain
interferes
with
the
ability
to
concentrate.
In
these
situations,
pain
control
systems
in
the
brain
and
spinal
cord
can
be
used
to
reduce
or
prevent
feelings
of
pain.
This
involves
two
natural
painkillers:

enkephalins
released
by
the
brain
block
calcium
channels
in
the
membrane
of
the
pre‐synaptic
neurons,
blocking
synaptic
transmission
so
that
pain
signals
do
not
reach
the
brain

endorphins
produced
by
the
pituitary
gland
are
carried
to
the
brain
and
other
organs
by
the
blood,
and
bind
to
receptors
in
the
membranes
of
neurons
that
send
pain
signals
to
the
brain
–
endorphins
are
secreted
during
stressful
times,
after
injuries,
and
sometimes
during
physical
exercise
such
as
running
Psychoactive
Drugs
Psychoactive
drugs
affect
the
brain
and
personality.
They
either
increase
or
decrease
synaptic
transmission:

they
can
bind
to
the
receptor
site
on
post‐synaptic
membranes,
mimicking
the
neurotransmitter
or
blocking
the
binding
of
the
neurotransmitter
A.
De
Jong/TFSS
2007
9
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement

they
can
also
reduce
the
effect
of
the
enzyme
which
normally
breaks
down
the
neurotransmitter,
which
causes
an
increase
in
the
effect
of
the
neurotransmitter

nicotine
mimics
acetylcholine,
while
curare
blocks
acetylcholine

Excitatory
Psychoactive
Drugs
increase
the
activity
of
the
nervous
system,
and
may
have
different
effects
on
behaviour:
Nicotine
stimulates
synaptic
transmission
at
cholinergic
synapses
in
many
parts
of
the
brain,
and
causes
release
of
adrenaline
from
the
adrenal
gland.
This
results
in
increased
blood
pressure
and
cardiac
frequency.
It
affects
mood,
acting
like
a
stimulant
and
causing
euphoria.
 Cocaine
blocks
the
reabsorption
of
dopamine
and
noradrenaline
at
synapses
in
the
brain,
causing
increased
energy,
alertness
and
talkativeness.
It
gives
an
intense
feeling
of
euphoria.
Physical
effects
include
increased
cardiac
frequency
and
body
temperature,
and
dilation
of
the
pupils.
 Amphetamines
stimulate
transmission
at
adrenergic
synapses
and
have
similar
effects
to
cocaine.
Users
experience
increased
alertness
and
reduced
appetite.
“Ecstasy”
is
a
derivative
of
amphetamines.
It
causes
feelings
of
empathy,
openness
and
caring,
lowering
aggression
and
increasing
sexual
behaviour.
 Caffeine
increases
heart
rate
and
urine
production.
It
causes
some
mood
elevation
and
increases
alertness.


Inhibitory
Psychoactive
Drugs
decrease
the
activity
of
the
nervous
system.
Benzodiazepines
such
as
Valium®
relax
muscles,
decrease
circulation,
respiration
and
blood
pressure.
They
reduce
anxiety
and
elevate
mood.
In
high
doses
they
cause
drowsiness,
slurred
speech
and
loss
of
muscle
control.
Doctors
prescribe
them
for
use
as
tranquillizers.
 Cannabis
contains
many
chemicals,
including
THC,
which
binds
to
cannabinoid
receptors
in
the
rain,
blocking
synaptic
transmission.
Its
users
claim
it
increases
the
intensity
of
sensory
perception,
gives
a
feeling
of
emotional
well‐being
and
allows
clear
thinking
about
complex
ideas.
There
is
strong
evidence,
though,
that
the
ability
to
concentrate,
control
muscle
contractions
and
judge
times
and
distances
is
diminished.
 Alcohol
acts
as
an
inhibitor
in
at
least
two
ways
(enhances
GABA,
an
inhibitory
neurotransmitter,
and
by
decreasing
the
activity
of
glutamate,
an
excitatory
neurotransmitter.)
In
small
quantities,
alcohol
reduces
inhibitions,
making
people
more
confident
and
talkative.
It
also
reduces
reaction
times
and
fine
muscle
coordination.
In
larger
quantities
it
causes
memory
loss,
slurred
speech,
loss
of
balance
and
poor
muscle
coordination,
and
may
cause
violent
behaviour.

Addiction
is
a
state
of
taking
a
mood‐altering
drug
habitually
and
being
unable
to
give
it
up
without
experiencing
unpleasant
side
effects.
It
has
many
causes:

THC
interferes
with
dopamine
metabolism
–
this
produces
a
state
of
dependence,
with
more
&
more
of
the
drug
being
required
to
produce
its
effect.

Genetic
predisposition
may
be
a
factor
with
some
people
–
insufficient
levels
of
the
enzymes
required
to
break
down
the
drug,
for
example,
or
a
personality
type
that
is
inclined
towards
unnecessary
risk‐taking.

Social
factors:
poor
diet,
high
unemployment
&
limited
access
to
education
&
training
that
could
lead
to
rewarding
employment,
combined
with
little
opportunity
for
self‐fulfilment
can
generate
a
sense
of
hopelessness
that
could
lead
to
seeing
drugs
as
an
escape
mechanism.
A.
De
Jong/TFSS
2007
10
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Perception
of
Stimuli
Sensory
receptors
act
as
energy
transducers.
This
means
that
they
convert
a
non‐electrical
signal
(e.g.
light
or
sound)
to
an
electrical
one.
This
results
in
an
action
potential
in
a
sensory
neuron
because
gated
ion
channels
(for
Na+)
are
opened.
Types
of
Sensory
Receptors

chemoreceptors
have
membrane
proteins
which
bind
a
particular
substance
 binding
results
in
depolarization
of
the
membrane
 action
potential
brings
message
to
the
brain
 e.g.
scent,
taste,
pH
of
blood

mechanoreceptors
are
sensitive
to
movement
 in
humans,
semi‐circular
canals
in
the
inner
ear
associated
with
a
system
of
hair
cells
 a
change
in
speed
or
direction
(of
the
body)
moves
fluid
in
the
canals,
which
bends
the
hairs
 this
causes
action
potentials
to
the
brain

thermoreceptors
are
sensitive
to
temperature
 cold
receptors
in
the
skin
send
an
action
potential
when
the
temperature
drops
 warm
receptors
(deeper
in
the
skin
than
cold
receptors)
send
an
action
potential
when
temperature
increases
 the
temperature
centre
in
the
hypothalamus
also
contains
thermoreceptors,
which
monitor
the
temperature
of
the
blood
(body)

photoreceptors
are
sensitive
to
light
 rods
and
cones
in
the
eye
contain
photopigments
which
break
down
when
exposed
to
light
 this
causes
an
action
potential
to
the
brain
■ rods
contain
rhodopsin
and
are
sensitive
to
light
intensity
■ cones
contain
iodopsins
(red,
green
or
blue)
and
are
responsible
for
colour
vision
Reflexes
are
a
fast
response
to
a
stimulus.
Spinal
Reflexes
involve
the
spinal
cord
and
not
the
brain.
They
are
part
of
innate
behaviour,
and
involve
only
two
or
three
nerve
cells.

Knee
Jerk
Reflex
 the
knee
is
tapped;
this
stretches
the
tendon
 stretch
receptor
in
the
muscle
sends
an
action
potential
to
the
spinal
cord
 the
action
potential
is
passed
to
a
motor
neuron,
which
makes
the
muscle
contract
 the
lower
leg
moves

Pain
Withdrawal
Reflex
 you
prick
your
finger
(or
stub
your
toe)
 a
pain
receptor
neuron
sends
and
action
potential
to
the
spinal
cord
 an
association
neuron
passes
the
action
potential
to
a
motor
neuron
 this
causes
the
biceps
to
contract,
moving
your
finger
away
from
the
source
of
the
pain
Cranial
Reflexes
involve
the
nerves
of
the
brain:
 Pupil
Reflex
 when
bright
light
is
perceived,
the
iris
will
immediately
contract
 this
will
reduce
the
amount
of
light
upon
the
retina
so
that
it
is
not
damaged
 the
brain
stem
is
responsible
for
this
reflex
‐
absence
of
the
pupil
reflex
can
indicate
damage
to
the
brain
stem
(brain
death)
A.
De
Jong/TFSS
2007
11
of
21
HL
Biology

Notes
for
Nerves,
Muscles
&
Movement
Blink
Reflex
 when
an
object
comes
close
to
the
eye,
you
will
blink
or
close
your
eye
 this
helps
prevent
damage
to
the
eye
 you
can
learn
to
control
your
blink
reflex,
for
example,
learning
to
put
in
contact
lenses
Reflex
Arc
Image
from
http://www.biotopics.co.uk/humans/refarc.gif
Structure
of
the
Eye
fovea
Image
from
http://www.ai.rug.nl/~lambert/projects/BCI/literature/misc/oog‐retina.gif
A.
De
Jong/TFSS
2007
12
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Structure
of
the
Retina
Image
from
http://www.rhsmpsychology.com/images/retina.jpg
Processing
Visual
Stimuli
The
retina
contains
rods,
cones,
and
nerve
cells
responsible
for
vision.
Rods
are
responsible
for
detecting
light
intensity,
while
cones
are
responsible
for
colour
vision.
The
fovea
is
a
“yellow
spot”
on
the
retina
which
is
entirely
composed
of
cones
–
this
is
the
site
of
most
accurate
vision.
The
fovea
is
found
just
above
the
blind
spot,
where
the
optic
nerve
connects
at
the
back
of
the
eye.
White
light
hitting
the
fovea
triggers
action
potentials
in
all
cones
and
is
perceived
as
white
by
the
brain.
 Blue
light
hitting
the
fovea
triggers
action
potentials
in
blue
cones,
and
is
perceived
as
blue
by
the
brain.
 There
is
a
certain
amount
of
overlap
in
the
absorption
of
colour,
particularly
between
green
and
red
–
this
means
that
red
or
green
light
could
trigger
action
potentials
in
both
red
and
green
cones.
Light
entering
the
eye
is
refracted
by
the
cornea
and
lens.
It
passes
through
the
vitreous
humour
(clear)
to
reach
the
retina.


light
must
also
pass
through
ganglia
and
bipolar
neurons
to
reach
the
rods
and
cones


cones
are
mostly
located
in
the
fovea
rods
are
found
throughout
the
retina
(except
the
fovea)
Cones
are
linked
individually
to
bipolar
neurons.
This
makes
them
less
sensitive
to
light
but
increases
their
accuracy.
A.
De
Jong/TFSS
2007
13
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Several
rods
are
connected
to
a
single
bipolar
neuron.
This
makes
them
more
sensitive
to
light
but
reduces
their
accuracy.
When
light
has
caused
an
action
potential
in
the
rods
or
cones,
it
is
passed
on
to
the
bipolar
neurons.


action
potentials
from
other
cells
may
inhibit
or
further
excite
a
bipolar
cell
action
potentials
are
passed
from
bipolar
cells
to
ganglia
and
on
to
the
optic
nerve
The
optic
nerve
is
composed
of
many
nerve
fibres,
which
are
connected
to
different
parts
of
the
retina.


some
fibres
connect
in
the
optic
chiasma,
while
others
do
not
as
a
result
a
complete
picture
is
transmitted
to
the
brain
Image
from
http://media‐2.web.britannica.com/eb‐media/48/63348‐004‐3D434AC1.gif
Contralateral
processing
is
due
to
the
optic
chiasma,
where
the
right
brain
processes
information
from
the
left
visual
field,
and
vice
versa,
as
illustrated
above.
Edge
enhancement
occurs
within
the
retina,
and
is
best
demonstrated
by
the
Hermann
grid
illusion
(at
right):
•
dark,
grey
blobs
appear
at
the
‘crossroads’
where
the
white
lines
intersect
–
unless
you
are
directly
looking
at
that
spot
•
this
has
to
do
with
the
receptive
fields
of
the
retina,
which
are
smaller
when
looking
directly
at
the
intersection
points
(see
left)
Images
from
http://www.michaelbach.de/ot/lum_herGrid/index.html
A.
De
Jong/TFSS
2007
14
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Colour
Blindness
is
a
result
of
a
deficiency
in
one
or
more
types
of
cones.
The
most
common
type
is
a
red‐
green
deficiency,
in
which
it
is
difficult
to
distinguish
between
certain
shades
of
red
and
green.
Those
with
red‐green
colour‐blindness
would
be
unable
to
see
the
number
“15”
in
the
image
below:
Image
from
http://www.biologie.uni‐hamburg.de/b‐online/library/falk/vision/colorblind.jpg
Controlling
How
Light
Enters
the
Eye
Light
enters
the
eye
through
the
pupil,
and
opening
in
the
centre
in
the
iris
(the
coloured
part
of
the
eye).
Pupil
Size
changes
in
response
to
brightness
of
light.


In
bright
light,
the
circular
muscles
of
the
iris
contract,
and
the
pupil
becomes
smaller.
This
reduces
the
amount
of
light
entering
the
eye
to
prevent
retina
damage.
In
dim
light,
these
muscles
relax,
opening
the
pupil.
This
increases
the
amount
of
light
that
enters
the
eye.
Image
from
http://www.schools.net.au/edu/lesson_ideas/optics/images/eye_contract.gif
Lens
Thickness
changes
in
order
to
focus
light
on
the
retina.


Light
reflected
off
a
distant
object
has
parallel
rays.
Refraction
through
the
lens
focuses
it
on
the
retina.
Light
reflected
off
a
near
object
has
divergent
rays.
Light
has
to
be
refracted
more
in
order
to
focus
properly
on
the
retina,
so
the
lens
thickens.
A.
De
Jong/TFSS
2007
15
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Brain
Death
and
the
Pupil
Reflex
Brain
death
is
defined
as
the
irreversible
cessation
of
all
brain
functions.
Modern
medical
technology
can
keep
a
patient
alive
(heart
beating,
lungs
‘breathing’)
long
after
the
brain
stops
directing
these
functions
–
because
of
this,
and
the
possibility
of
using
brain‐dead
patients’
organs
for
transplant
surgery,
it
is
necessary
to
have
indicators
of
brain
death.
The
agreed
criteria
for
brain
death
(absence
of
all
brain
function)
are:
absence
of
pupil
reflex
absence
of
blink
reflex
eyes
do
not
rotate
in
their
sockets
when
the
head
is
moved
eyes
do
not
move
when
iced
water
is
placed
in
the
outer
ear
canal
no
cough
(or
gagging)
when
a
suction
tube
is
placed
deep
into
the
trachea
breathing
does
not
commence
when
the
patient
is
taken
off
the
ventilator
Structure
of
the
Human
Ear






Image
from
http://www.perceptualentropy.com/wiki/images/7/7c/HumanEar.jpg
The
malleus
(hammer),
incus
(anvil)
and
stapes
(stirrups)
are
the
ossicles
(bones)
of
the
inner
ear.
A.
De
Jong/TFSS
2007
16
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Perception
of
Sound
The
ear
consists
of
three
basic
parts
‐
the
outer
ear,
the
middle
ear,
and
the
inner
ear.
Each
part
of
the
ear
serves
a
specific
purpose
in
the
task
of
detecting
and
interpreting
sound:

The
outer
ear
(pinna
and
ear
canal)
serves
to
collect
and
channel
sound
to
the
middle
ear.
o Sound
entering
the
ear
canal
is
a
pressure
wave,
with
alternating
high
and
low
pressure
regions:
o When
the
sound
reaches
the
eardrum
(tympanic
membrane),
the
energy
causes
it
to
vibrate.

The
middle
ear
serves
to
transform
the
energy
of
a
sound
wave
into
the
internal
vibrations
of
the
bone
structure
of
the
middle
ear
and
ultimately
transform
these
vibrations
into
a
compressional
wave
in
the
inner
ear.
o The
middle
ear
is
an
air‐filled
cavity.
o Vibration
of
the
tympanic
membrane
causes
the
interconnected
ossicles
to
vibrate,
transmitting
the
sound
wave
to
the
fluid
of
the
inner
ear.
o The
middle
ear
is
connected
to
the
mouth
by
the
Eustachian
tube,
which
allows
for
equalization
of
pressure
within
the
middle
ear.

The
inner
ear
serves
to
transform
the
energy
of
a
compressional
wave
within
the
inner
ear
fluid
into
nerve
impulses
that
can
be
transmitted
to
the
brain.
o The
inner
ear
consists
of
the
cochlea,
semicircular
canals
and
the
auditory
nerve.
o The
semicircular
canals
have
no
role
in
hearing
–
they
act
as
accelerometers
that
assist
with
balance.
o The
cochlea
is
fluid‐filled
and
lined
with
hair‐like
cells.
When
the
ossicles
vibrate,
they
transmit
the
energy
of
the
vibration
to
the
cochlea
via
the
oval
window.
o Because
each
of
the
hair‐like
nerve
cells
differs
in
length
and
sensitivity
to
the
fluid’s
motion,
each
responds
to
a
different
frequency.
When
stimulated
by
its
natural
frequency,
the
nerve
cell
will
vibrate,
triggering
an
action
potential
in
the
auditory
nerve.
A.
De
Jong/TFSS
2007
17
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Muscles
Humans
have
three
types
of
muscle
tissue:

skeletal
muscle
is
attached
to
bones
via
tendons
called
striated
muscle
because
of
its
striped
appearance
under
the
microscope
 can
contract
quickly
and
powerfully
but
tires
easily
 under
voluntary
control


smooth
muscle
is
not
striated
it
is
controlled
automatically
by
the
nervous
system
■ therefore
it
is
involuntary
muscle
 found
in
the
digestive
tract
and
blood
vessels
 takes
longer
to
contract,
but
does
not
tire
as
easily
as
skeletal
muscle


cardiac
muscle
is
found
in
the
heart

it
is
myogenic
(beats
of
its
own
accord)
and
is
under
influence
of
the
nervous
system
Images
from
http://biodidac.bio.uottawa.ca
The
Muscle
Fibre
Skeletal
muscle
is
made
up
of
thousands
of
cylindrical
muscle
fibres
often
running
all
the
way
from
origin
to
insertion.
The
fibres
are
bound
together
by
connective
tissue
through
which
run
blood
vessels
and
nerves.
Each
muscle
fibre
contains:
an
array
of
myofibrils
that
are
stacked
lengthwise
and
run
the
entire
length
of
the
fibre.
mitochondria
an
extensive
smooth
endoplasmic
reticulum
(SER)
many
nuclei.
The
multiple
nuclei
arise
from
the
fact
that
each
muscle
fibre
develops
from
the
fusion
of
many
cells
(called
myoblasts).




Because
a
muscle
fibre
is
not
a
single
cell,
its
parts
are
often
given
special
names
such
as
sarcolemma
(plasma
membrane),
sarcoplasmic
reticulum
(endoplasmic
reticulum),
sarcosome
(mitochondrion)
and
sarcoplasm
(cytoplasm);
although
this
tends
to
obscure
the
essential
similarity
in
structure
and
function
of
these
structures
and
those
found
in
other
cells.


nuclei
and
mitochondria
are
located
just
beneath
the
plasma
membrane
the
endoplasmic
reticulum
extends
between
the
myofibrils.
A.
De
Jong/TFSS
2007
18
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Seen
from
the
side
under
the
microscope,
skeletal
muscle
fibres
show
a
pattern
of
cross
banding,
which
gives
rise
to
the
other
name:
striated
muscle.
The
striated
appearance
of
the
muscle
fibre
is
created
by
a
pattern
of
alternating
dark
A
bands
and
light
I
bands.
o The
A
bands
are
bisected
by
the
H
zone
o The
I
bands
are
bisected
by
the
Z
line.
Each
myofibril
is
made
up
of
arrays
of
parallel
filaments.



The
thick
filaments
have
a
diameter
of
about
15
nm.
They
are
composed
of
the
protein
myosin.
The
thin
filaments
have
a
diameter
of
about
5
nm.
They
are
composed
chiefly
of
the
protein
actin
along
with
smaller
amounts
of
two
other
proteins:
troponin
and
tropomyosin.
Image
from
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/sarcomere.gif
The
anatomy
of
a
sarcomere
 The
thick
filaments
produce
the
dark
A
band.
 The
thin
filaments
extend
in
each
direction
from
the
Z
line.
Where
they
do
not
overlap
the
thick
filaments,
they
create
the
light
I
band.
 The
H
zone
is
that
portion
of
the
A
band
where
the
thick
and
thin
filaments
do
not
overlap.
The
entire
array
of
thick
and
thin
filaments
between
the
Z
lines
is
called
a
sarcomere.
Shortening
of
the
sarcomeres
in
a
myofibril
produces
the
shortening
of
the
myofibril
and,
in
turn,
of
the
muscle
fibre
of
which
it
is
a
part.
Image
from
http://www.mrothery.co.uk/images/
Imag109.gif
A.
De
Jong/TFSS
2007
19
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Neuromuscular
Junctions
A
synapse
between
a
motor
neuron
and
a
muscle
is
called
a
neuromuscular
junction:
Image
from
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/synapse.gif
Muscle
Contraction
&
Sliding
Filament
Theory
During
muscle
contraction
the
myofilaments
myosin
and
actin
slide
toward
each
other
and
overlap.
This
shortens
the
sarcomeres
and
the
entire
muscle.
Muscle
cells
are
“shocked”
by
nerve
impulses
from
motor
neurons.
The
point
of
attachment
of
the
nerve
to
the
muscle
is
called
the
neuromuscular
junction.
A
motor
neuron
and
its
muscle
cells
are
referred
to
as
a
motor
unit.
The
nerve
impulse
is
carried
from
the
motor
neuron
across
the
gap
to
the
sarcolemma
(membrane)
of
the
muscle
cell
by
a
neurotransmitter
called
acetylcholine
(ACh).
After
the
impulse
has
passed,
an
enzyme
called
cholinesterase
deactivates
acetylcholine,
readying
the
muscle
for
the
next
nerve
impulse.
Stimulation
of
the
muscle
cells
causes
Ca++
to
be
released
into
the
cell.
The
Ca++
binds
to
the
actin
filaments
causing
them
to
expose
active
sites
to
the
myosin
cross‐bridges.
The
cross
bridges
bind
to
the
active
sites,
forming
a
new
molecular
structure,
which
causes
the
cross‐bridge
to
bend
toward
the
centre,
pulling
the
actin
filament
with
it.
Energy
from
ATP
is
used
to
break
the
bond,
straighten
the
cross
bridge,
and
allow
the
cross
bridge
to
form
a
new
bond
with
another
active
site
further
down
the
actin
filament.
This
cycle
continues
until
the
muscle
contraction
is
complete.
Then,
ATP
is
used
to
cause
active
transport,
moving
the
calcium
ions
out
of
the
muscle
fibre,
resulting
in
relaxation
of
the
muscle.
The
Nervous
System
&
Movement
Nerves
stimulate
muscle
contraction.
Each
different
muscle
used
in
locomotion
must
contract
at
the
correct
time,
so
the
movement
is
coordinated.
Since
muscles
are
connected
to
bones
(by
tendons),
contraction
causes
the
bones
to
move.
The
movement
is
usually
reversed
by
another
muscle
on
the
opposite
side
of
the
bone
–
an
antagonistic
pair.
Joints
are
places
where
bones
meet,
and
are
classified
by
the
range
of
motion
at
the
joint
and
type
of
connection:
o fibrous:
no
movement
(e.g.
sutures
between
bones
of
the
cranium)
o cartilaginous:
bones
connected
by
cartilage;
limited
range
of
motion
(e.g.
between
vertebrae)
o synovial:
fluid‐filled
cavities
between
the
bones
allow
greater
range
of
motion
 elbow:
a
hinge
joint
allows
for
extension
&
retraction
 hip:
a
ball
and
socket
joint
with
a
wide
range
of
motion
A.
De
Jong/TFSS
2007
20
of
21
HL
Biology
Notes
for
Nerves,
Muscles
&
Movement
Antagonistic
Pair:
Images
from
www.saburchill.com/chapters/chap0009.html
The
elbow
is
a
typical
hinge
joint
involving
bones,
cartilage,
ligaments,
tendons
and
muscles:
Image
from
http://www.botany.uwc.ac.za/sci_ed/grade10/manphys/images/man/hinge.gif






bones
support
the
body
and
allow
for
locomotion
muscles
move
the
bones
nerves
stimulate
muscle
contraction
synovial
fluid
protects
the
bones
and
lubricates
the
joint
and
is
contained
within
bursa
ligaments
connect
bones
to
bones
tendons
connect
muscles
to
bones
A.
De
Jong/TFSS
2007
21
of
21