unit 6 Flashcards
imagine if ninja got a low taper fade
Stimulus
Detectable change in the
environment
detected by cells called
receptors
Simple reflex
arc
Stimulus (touching hot object)
-> receptor
-> sensory neurone
-> coordinator (CNS / relay
neurone
-> motor neurone
-> effector (muscle)
-> response (contraction)
Importance of
simple reflexes
Rapid - short pathway
only three neurones & few
synapses
autonomic
conscious thought not
involved - spinal cord
coordination
protect from harmful stimuli
e.g., burning
Nervous system
structure
Central nervous system = brain
and spinal cord
peripheral nervous system =
receptors, sensory and motor
neurones
Tropism
Response of plants to stimuli
via growth
can be positive (growing
towards stimulus) or negative
(growing away from stimulus)
controlled by specific growth
factors (IAA)
Indoleacetic
acid
Type of auxin (plant hormone)
controls cell elongation in shoots
inhibits growth of cells in roots
made in tips of roots / shoots
can diffuse to other cells
Specific
tropisms
Response to light
phototropism
response to gravity
gravitropism
response to water
hydrotropism
Phototropism
in shoots
Shoot tip produces IAA
diffuses to other cells
IAA accumulates on shaded
side of shoot
IAA stimulates cell elongation
so plant bends towards light
positive phototropism
Phototropism
in roots
Root tip produces IAA
IAA concentration increases on
lower (darker) side
IAA inhibits cell elongation
root cells grow on lighter side
root bends away from light
negative phototropism
Gravitropism
in shoots
Shoot tip produces IAA
IAA diffuses from upper side to
lower side of shoot in response
to gravity
IAA stimulates cell elongation
so plant grows upwards
negative gravitropism
Cone cells
Concentrated on the fovea
fewer at periphery of retina
3 types of cones containing
different iodopsin pigments
one cone connects to one
neurone
detect coloured light
Gravitropism
in roots
Root tip produces IAA
IAA accumulates on lower side
of root in response to gravity
IAA inhibits cell elongation
root bends down towards
gravity and anchors plant
positive gravitropism
Kinesis
When an organism changes its
speed of movement and rate of
change of direction in response to
a stimulus
if an organism moves to a region
of unfavourable stimuli it will
increase rate of turning to return
to origin
if surrounded by negative stimuli,
rate of turning decreases - move
in straight line
Taxis
Directional response by simple
mobile organisms
move towards favourable
stimuli (positive taxis) or away
from unfavourable stimuli
(negative taxis)
Receptors
Responds to specific stimuli
stimulation of receptor leads to
establishment of a generator
potential - causing a response
pacinian corpuscle
rods
cones
Pacinian
corpuscle
Receptor responds to pressure
changes
occur deep in skin mainly in
fingers and feet
sensory neurone wrapped with
layers of tissue
Pacinian
corpuscle
structure
OUTER CAPSULES, LAMELLAE, SENSORY NEURONE, SCHWANN CELL
How pacinian
corpuscle
detects pressure
When pressure is applied,
stretch-mediated sodium ion
channels are deformed
sodium ions diffuse into
sensory neurone
influx increases membrane
potential - establishment of
generator potential
Rod cells
Concentrated at periphery of
retina
contains rhodopsin pigment
connected in groups to one
bipolar cell (retinal
convergence)
do not detect colour
Rods and cones:
describe
differences in
sensitivity to light
Rods are more sensitive to light
cones are less sensitive to light
Rods and cones:
describe
differences in
visual acuity
Cones give higher visual acuity
rods have a lower visual acuity
Importance of short
delay between SAN
and AVN waves of
depolarisation
Ensures enough time for atria to
pump all blood into ventricles
ventricle becomes full
Visual acuity
Ability to distinguish between
separate sources of light
a higher visual acuity means
more detailed, focused vision
Rods and cones:
describe
differences in
colour vision
Rods allow monochromatic
vision (black and white)
cones allow colour vision
Why rods have
high sensitivity
to light
Rods are connected in groups to
one bipolar cell
retinal convergence
spatial summation
stimulation of each individualcell alone is sub-threshold but
because rods are connected in
groups more likely threshold
potential is reached
Why cones have
low sensitivity
to light
One cone joins to one neurone
no retinal convergence / spatial
summation
higher light intensity required
to reach threshold potential
Why rods have
low visual
acuity
Rods connected in groups to
one bipolar cell
retinal convergence
spatial summation
many neurones only generate 1
impulse / action potential ->
cannot distinguish between
separate sources of light
Why cones
have high
visual acuity
One cone joins to one neurone
2 adjacent cones are
stimulated, brain receives 2
impulses
can distinguish between
separate sources of light
Why rods have
monochromatic
vision
One type of rod cell
one pigment (rhodopsin)
Why cones give
colour vision
3 types of cone cells with
different optical pigments
which absorb different
wavelengths of light
red-sensitive, green-sensitive
and blue-sensitive cones
stimulation of different
proportions of cones gives
greater range of colour
perception
Myogenic
When a muscle (cardiac
muscle) can contract and relax
without receiving signals from
nerves
Sinoatrial
node
Located in right atrium and is
known as the pacemaker
releases wave of depolarisation
across the atria, causing
muscles to contract
Atrioventricular
node
Located near the border of the
right / left ventricle within atria
releases another wave of
depolarisation after a short
delay when it detects the first
wave from the SAN
Bundle of His
Runs through septum
can conduct and pass the wave
of depolarisation down the
septum and Purkyne fibres in
walls of ventricles
Purkyne fibres
In walls of ventricles
spread wave of depolarisation
from AVN across bottom of the
heart
the muscular walls of ventricles
contract from the bottom up
Role of nonconductive
tissue
Located between atria and
ventricles
prevents wave of depolarisation
travelling down to ventricles
causes slight delay in ventricles
contracting so that ventricles
fill before contraction
Role of the
medulla
oblongata
Controls heart rate via the
autonomic nervous system
uses sympathetic and
parasympathetic nervous
system to control SAN rhythm
Chemoreceptors
Located in carotid artery and
aorta
responds to pH / CO2 conc.
changes
Baroreceptors
Located in carotid artery and
aorta
responds to p
Response to high
blood pressure
Baroreceptor detects high blood
pressure
impulse sent to medulla
more impulses sent to SAN
along parasympathetic
neurones (releasing
noradrenaline)
heart rate slowed
Response to low
blood pressure
Baroreceptor detects low blood
pressure
impulse sent to medulla
more impulses sent to SAN
along sympathetic neurones
(releasing adrenaline)
heart rate increase
Response to
high blood pH
Chemoreceptor detects low CO2
conc / high pH
impulse sent to medulla
more impulses sent to SAN
along parasympathetic
neurones (releasing
noradrenaline)
heart rate slowed so less CO2
removed and pH lowers
Response to
low blood pH
Chemoreceptor detects low CO2
conc / high pH
impulse sent to medulla
more impulses sent to SAN
along sympathetic neurones
(releasing adrenaline)
heart rate increases to deliver
blood to heart to remove CO2
Structure of
myelinated
motor neurone
dendrite, nucleus, cell body, axon, mylein sheath, schwann cell, node of ranvier, axon terminal,
Resting
potential
The difference between
electrical charge inside and
outside the axon when a neuron
is not conducting an impulse
more positive ions (Na+/K+)
outside axon compared to
inside
inside the axon -70mV
Action potential:
stimulus
Voltage-gated Na+ channels
open - membrane more
permeable to Na+
Na+ diffuse (facilitated) into
neurone down conc. gradient
voltage across membrane
increases
How is resting
potential
established
Sodium potassium pump
actively transports 3 Na+ out of
the axon, 2 K+ into the axon
membrane more permeable to
K+ (more channels and always
open)
K+ diffuses out down conc.
gradient - facilitated diffusion
membrane less permeable to
Na+ (closed Na+ channels)
higher conc. Na+ outside
Action
potential
When the neurone’s voltage
increases beyond the -55mV
threshold
nervous impulse generated
generated due to membrane
becoming more permeable to
Na+
Action potential:
repolarisation
Na+ channels close, membrane
less permeable it Na+
K+ voltage-gated channels
open, membrane more
permeable to K+
K+ diffuse out neuron down
conc. gradient
voltage rapidly decreases
Action potential:
depolarisation
When a threshold potential is
reached, an action potential is
generated
more voltage-gated Na+
channels open
Na+ move by facilitated
diffusion down conc. gradient
into axon
potential inside becomes more
positive
Action potential:
hyperpolarisation
K+ channels slow to close ->
overshoot in voltage
too many K+ diffuse out of
neurone
potential difference decrease to
-80mV
sodium-potassium pump
returns neurone to resting
potential
All or nothing
principle
If depolarisation does not
exceed -55 mV threshold, action
potential is not produced
any stimulus that does trigger
depolarisation to -55mV will
always peak at the same
maximum voltage
Importance of all
or nothing
principle
Makes sure animals only
respond to large enough stimuli
rather than responding to every
small change in environment
(overwhelming)
Refractory
period
After an action potential has
been generated, the membrane
enters a period where it cannot
be stimulated
because Na+ channels are
recovering and cannot be
opened
Importance of
refractory period
Ensures discrete impulses
produced - action potentials
separate and cannot be
generated immediately
unidirectional - cannot generate
action potential in refractory
region
limits number of impulse
transmissions - prevent
overwhelming
Factors affecting
speed of
conductance
Myelination (increases speed)
axon diameter (increases
speed)
temperature (increases speed)
How
myelination
affects speed
With myelination -
depolarisation occurs at Nodes
of Ranvier only -> saltatory
conduction
impulse jumps from node-node
in non-myelinated neurones,
depolarisation occurs along full
length of axon - slower
How axon
diameter affects
speed
Increases speed of conductance
less leakage of ions
Saltatory
conduction
Gaps between myelin sheath
are nodes of Ranvier
action potential can “jump”
from node to node via saltatory
conduction - action potential
travels faster as depolarisation
across whole length of axon not
required
How
temperature
affects speed
Increases speed of conductance
increases rate of movement of
ions as more kinetic energy
(active transport/diffusion)
higher rate of respiration as
enzyme activity faster so ATP is
produced faster - active
transport faster
Synapse
Gaps between end of axon of
one neurone and dendrite of
another
impulses are transmitted as
neurotransmitters
Role of calcium
ions in synaptic
transmission
Depolarisation of the presynaptic knob opens voltage
gated Ca2+ channels and Ca2+
diffuses into synaptic knob.
stimulates vesicles containing
neurotransmitter to fuse with
membrane and release
neurotransmitter into the
synaptic cleft via exocytosis
Why are
synapses
unidirectional
Receptors only present on the
post-synaptic membrane
enzymes in synaptic cleft break
down excess-unbound
neurotransmitter -
concentration gradient
established from pre-post
synaptic neurone
neurotransmitter only released
from the pre-synaptic neurone
Cholinergic
synapse
The neurotransmitter is
acetylcholine
enzyme breaking down
acetylcholine = acetylcholineesterase
breaks down acetylcholine to
acetate and choline to be
recycled in the pre-synaptic
neurone
Summation
Rapid build-up of
neurotransmitters in the
synapse to help generate an
action potential by 2 methods:
spatial or temporal
required because some action
potentials do not result in
sufficient concentrations of
neurotransmitters released to
generate a new action potential
Spatial
summation
Many different neurones
collectively trigger a new action
potential by combining the
neurotransmitter they release
to exceed the threshold value
e.g., retinal convergence for
rod cells
Inhibitory
synapses
Causes chloride ions (Cl-) to
move into post-synaptic
neurone and K+ to move out
makes membrane hyperpolarise
(more negative) so less likely an
action potential will be
propagated
Temporal
summation
When one neurone releases
neurotransmitters repeatedly
over a short period of time to
exceed the threshold value
e.g., 1 cone cell signalling 1
image to the brain
Compare the NMJ
with a cholinergic
synapse
unidirectional - neurotransmitters receptors only on post synaptic membranes
NMJ - only excitatory, connects motor n - muscles, end point for action potentials, ach bind to receptors on muscle fibres
CHOLINERGIC - excitatory or inhibitory, connect two neurones, new action potential generated in next neurone, ach bin to receptors on post synaptic membrane
Neuromuscular
junction
Synapse that occurs between a
motor neurone and a muscle
similar to synaptic junction
Myofibril
Made up of fused cells that
share nuclei/cytoplasm
(sarcoplasm) and many
mitochondria
millions of muscle fibres make
myofibrils - bringing about
movement
Role of Ca2+ in
sliding filament
theory
Ca2+ enter from sarcoplasmic
reticulum and causes
tropomyosin to change shape
myosin heads attach to exposed
binding sites on actin forming
actin-myosin cross bridge
activates ATPase on myosin
ATP hydrolysed so energy for
myosin heads to be recocked
Role of
tropomyosin in
sliding filament
theory
Tropomyosin covers binding
site on actin filament
Ca2+ bind to tropomyosin on
actin so it changes shape
exposes binding site
allows myosin to bind to actin,
forming cross bridge
Role of ATP in
myofibril
contraction
Hydrolysis of ATP -> ADP + Pi
releases energy
movement of myosin heads
pulls actin - power stroke
ATP binds to myosin head
causing it to detach, breaking
cross bridge
myosin heads recocked
active transport of Ca2+ back to
sarcoplasmic reticulum
Phosphocreatine
A chemical which is stored in
muscles
when ATP concentration is low,
this can rapidly regenerate ATP
from ADP by providing a Pi
group.
for continued muscle
contraction
Role of myosin
in myofibril
contraction
Myosin heads (with ADP
attached) attach to binding
sites on actin.
form actin-myosin cross bridge
power stroke - myosin heads
move pulling actin
requires ATP to release energy
ATP binds to myosin head to
break cross bridge so myosin
heads can move further along
actin
Slow-twitch
muscle fibres
Specialised for slow, sustained
contractions (endurance)
lots of myoglobin
many mitochondria - high rate
aerobic respiration to release
ATP
many capillaries - supply high
concentrations of glucose/O2 &
prevent build-up of lactic acid
e.g. thighs / calf
Fast-twitch
muscle fibres
Specialised in producing rapid,
intense contractions of short
duration
glycogen -> hydrolysed to
glucose -> glycolysis
higher concentration of
enzymes involved in anaerobic
respiration - fast glycolysis
phosphocreatine store
e.g., eyelids/biceps
Homeostasis
Maintenance of constant
internal environment via
physiological control systems
control temperature, blood pH,
blood glucose concentration
and water potential within
limits
Negative
feedback
When there is a deviation from
normal values and restorative
systems are put in place to
return this back to the original
level
involves the nervous system
and hormones
Islets of
Langerhans
Region in the pancreas
containing cells involved in
detecting changes in blood
glucose levels
contains endocrine cells (alpha
cells and beta cells) which
release hormones to restore
blood glucose levels
Alpha cells
Located in the islets of
Langerhans
release glucagon
when detect blood glucose
concentration is too low
Beta cells
Located in the islets of
Langerhans
release insulin
when detect blood glucose
concentration is too high
Factors affecting
blood glucose
concentration
Eating food containing
carbohydrates -> glucose
absorbed from the intestine to
the blood
exercise -> increases rate of
respiration, using glucose
Action of
insulin
Binds to specific receptors on
membranes of liver cells
increases permeability of cell
membrane (GLUT-4 channels
fuse with membrane)
glucose can enter from blood by
facilitated diffusion
activation of enzymes in liver
for glycogenesis
rate of respiration increases
Action of
glucagon
Binds to specific receptors on
membranes of liver cells
activates enzymes for
glycogenolysis
activates enzymes for
gluconeogenesis
rate of respiration decreases
blood glucose concentration
increases
Role of
adrenaline
Secreted by adrenal glands
above the kidney when glucose
concentration is too low
(exercising)
activates secretion of glucagon
glycogenolysis and
gluconeogenesis
works via secondary messenger
model
Gluconeogenesis
Creating glucose from noncarbohydrate stores in liver e.g.
amino acids -> glucose
occurs when all glycogen has
been hydrolysed and body
requires more glucose
initiate by glucagon when blood
glucose concentrations are low
Glycogenesis
Process of glucose being
converted to glycogen when
blood glucose is higher than
normal
caused by insulin to lower blood
glucose concentration
Glycogenolysis
Hydrolysis of glycogen back into
glucose
occurs due to the action of
glucagon to increase blood
glucose concentration
What is a second
messenger model
Stimulation of a molecule
(usually an enzyme) which can
then stimulate more molecules
to bring about desired response
adrenaline and glucagon
demonstrate this because they
cause glycogenolysis to occur
inside the cell when binding to
receptors on the outside
Diabetes
A disease when blood glucose
concentration cannot be
controlled naturally
Second
messenger
model process
Adrenaline/glucagon bind to
specific complementary
receptors on the cell membrane
activate adenylate cyclase
converts ATP to cyclic AMP
(secondary messenger)
cAMP activates protein kinase A
(enzyme)
protein kinase A activates a
cascade to break down glycogen
to glucose (glycogenolysis)
Type 2
diabetes
Due to receptors in target cells
losing responsiveness to insulin
usually develops due to obesity
and poor diet
treated by controlling diet and
increasing exercise with insulin
injections
Type 1 diabetes
Due to body being unable to
produce insulin
starts in childhood
autoimmune disease where
beta cells attacked
treated using insulin injections
Osmoregulation
Process of controlling the water
potential of the blood
controlled by hormones e.g.,
antidiuretic hormone (affects
distal convoluted tubule and
collecting duct)
Nephron
he structure in the kidney
where blood is filtered, and
useful substances are
reabsorbed into the blood
Formation of
glomerular
filtrate
Diameter of efferent arteriole is
smaller than afferent arteriole
build-up of hydrostatic pressure
water/glucose / ions squeezed
out capillary into Bowman’s
capsule through pores in
capillary endothelium,
basement membrane and
podocytes
large proteins too large to pass
Reabsorption
of glucose by
PCT
Co-transport mechanism
walls made of microvilli
epithelial cells to provide large
surface area for diffusion of
glucose into cells from PCT
sodium actively transported out
cells into intercellular space to
create a concentration gradient
glucose can diffuse into the
blood again
Counter current
multiplier
mechanism
Describes how to maintain a
gradient of Na+ in medulla by
the loop of Henle.
Na+ actively transported out
ascending limb to medulla to
lower water potential
water moves out descending
limb + DCT + collecting duct by
osmosis due to this water
potential gradient
Reabsorbtion of
water by DCT /
collecting duct
Water moves out of DCT and
collecting duct by osmosis
down a water potential gradient
controlled by ADH which
changes the permeability of
membranes to water
Role of pituitary
gland in
osmoregulation
ADH moves to the pituitary
gland from the hypothalamus
releases ADH into capillaries
travels through blood -> kidney
Anti-diuretic
hormone
Produced by hypothalamus,
released by pituitary gland
affects permeability of walls of
collecting duct & DCT to water
more ADH means more
aquaporins fuse with walls so
more water is reabsorbed back
to blood- urine more
concentrated.
Role of
hypothalamus in
osmoregulation
Contains osmoreceptors which
detect changes in water
potential
produces ADH
when blood has low water
potential, osmoreceptors shrink
and stimulate more ADH to be
made so more released from the
pituitary gland
