grey matter Flashcards
what is the central nervous system made up of
brain
spinal cord
what is the largest part of the brain
cerebrum
what are the functions of the cerebrum
vision
hearing
speech
thinking
memory
what are the 2 halves of the cerebrum
cerebral hemispheres
joined by a band of nerve fibres called the corpus callosum
right hemisphere controls left side of body and vice versa
what is the thin outer layer of the cerebrum
cerebral cortex/ grey matter
consists of cell bodies of neurones
highly folded
increases sa
so more neurones
more neurone connections
more ability of brain to carry out complex behaviours
what is beneath the cerebral cortex/ grey matter
white matter
consists of myelinated axons of neurones
what are the functions of the hypothalamus
monitors blood as it flows to the brain
releases hormones/ stimulates pituitary gland to do so
regulates body temp by monitoring blood temp
osmoregulation
water balance of blood
release ADH if blood too conc
AGH increases water absorption in kidneys
regulates digestive activity
hormones that control appetite
secretion of digestive enzymes
endocrine functions
metabolism, puberty
what are the functions of the cerebellum
coordinates movement
including balance which involves coordination between eyes, muscles, semicircular canals in ears
what are the functions of the medulla oblongata aka medulla
contains coordination centres that control diff functions
cardiac centre- heart rate
respiratory centre- breathing rate
what are neurones
specialised cells of the nervous system which carry electrical impulses around the body
what is a nerve
a bundle of neurones
what features are in all neurones
axon
cell body
axon terminal
what is an axon terminal
has many nerve endings
allows neurones to connect and receive impulses from others
what is a myelin sheath
insulates axon in myelinated cells
made of Schwann cells
uninsulated gaps between Schwann cells called nodes of Ranvier
why do myelinated cells have faster impulse transmissions
electron impulses dont travel down whole axon
jump from one node to the next
in non myelinated cells, impulse travels slower cos moves down entire length of axon
function of sensory neurone
carry electrical impulses from receptors to CNS
function of relay neurone
found entirely within CNS
connect sensory and motor
function of motor neurone
carry impulses from CNS to effector muscles or glands
structure of motor neurone
large cell body at one end in spinal cord/ brain
many highly branched dendrites extending from it
structure of sensory neurone
cell body that branches off in middle of axon
dendrites attached to a receptor cell
what is a stimulus
a change in the environment
what does a receptor do
detect stimuli
what are effectors
muscles or glands
that bring about a response
what is the pathway that nerve impulses pass along the nervous system
stimulus
receptor
sensory neurone
CNS
motor neurone
effector
what is the pathway that nerve impulses pass along the nervous system along when there is bright light
light receptors in eyes
sensory neurone
CNS
motor neurone
circular muscles in iris contracts
what does contraction of circular muscles cause
pupils to constrict
limits amt of light entering eye
prevents damage to retina
what is the pathway that nerve impulses pass along the nervous system along when there is low light
light receptors in eyes
sensory neurone
CNS
motor neurone
radial muscles in iris contracts
what does contraction of radial muscles cause
pupil to dilate
maximises amt of light entering eye
improving vision
what is the resting membrane potential
-70mV
what causes the potential difference across neurone membranes
diff numbers of ions
when is a membrane polarised
when there is a difference in charge across a membrane
what factors contribute to establishing and maintaining resting potential
active transport of sodium and potassium ions
difference in membrane permeability to sodium and potassium ions
during resting potential, does the outside or inside of an axon have a more negative electrical potential
inside
explain the active transport of sodium and potassium ions
carrier proteins called sodium- potassium pumps
in neurone membrane
use ATP to actively transport Na+ out
and K+ in to axon
for every 3 Na+ out, 2K+ in
creates conc grad
is the neurone membrane more permeable to sodium or potassium ions?
potassium
what does the difference in membrane permeability result in
K+ can diffuse out at a faster rate
than Na+ can diffuse back in
so more pos ions on outside
generating a neg charge inside
what does the neurone membrane need to be to initiate a nerve impulse?
depolarised
when are voltage gated channels closed
when the membrane is at rest
how is an action potential generated
neurone stimulated
small number of Na+ channels open
Na+ move into axon down conc grad
making inside less neg, lower pd
if pd reaches -55mV (threshold potential) more Na+ channels open (voltage gated channels)
influx of Na+
when charge reversed from -77 to around 30, membrane depolarised and action potential generated
what happens about 1 millisecond after action potential generated
voltage gated Na+ channels close
voltage gated K+ channels open
allowing K+ to diffuse out of axon down conc grad
so inside axon is more neg charged
this is repolarisation
what is hyper polarisation
short period when membrane potential is more neg than resting potential (-0.77mV)
what is the refractory period
membrane is hyperpolarised
membrane unresponsive to stimulation
new action potentials cant be generated
how are action potentials transmitted/ propagated
depolarisation at site of 1st action potential causes
Na+ to diffuse along cyto
into next axon section
depolarising membrane at this part
causing voltage gated Na+ channels to open
triggers another action potential
repeats
why is an action potential not generated if stimulus is weak
few Na+ channels open
membrane not sufficiently depolarised to reach threshold potential
what increases as stimulation intensity increases
frequency of action potentials transmitted along neurone
why is speed of conduction faster in myelinated neurones
myelin sheath stops depolarisation as it stops Na+ and K+ diffusion
Na+ diffuse along axon
nodes of Ranvier membrane depolarises when Na+ arrive
action potential jumps from 1 node to the next (saltatory conduction)
why may impulse transmission need to be prevented
painkillers
anaesthetics
how do some drugs prevent impulse transmission
bind to Na+ channels
prevent the opening
prevent Na+ influx when stimulation
prevent depolarisation
action potential cant be generated
where are synapses found
junctions between cells in nervous system
what is the neurone before the synapse called
presynaptic neurone
what is the neurone after the synapse called
postsynaptic neurone
eg of neurotransmitters
ACh
what is the gap between neurones called
synaptic cleft
what is the synaptic knob
rounded end of presynaptic neurone
where are the vesicles containing neurotransmitters
in the synaptic knob
what is summation
effect of multiple impulses added together
what is synaptic convergence
several presynaptic neurones converge to meet a single postsynaptic neurone
what do synapses enable
unidirectionality of impulse transmission
divergence of nerve impulses
amplification of nerve impulses by summation
what is the process of synaptic transmission
action potential arrives, depolarising presynaptic membrane
voltage gated Ca+ channels open, Ca+ diffuse in to synaptic knob
presynaptic vesicles fuse w membrane
ACh released into synaptic cleft by exocytosis
ACh diffuses across it and binds to receptor proteins on postsynaptic neurone
Na+ channels open, Na+ diffuses thru postsynaptic cell
post synaptic membrane depolarised
ACh broken down
what does the human nervous system consist of
central nervous system: brain and spinal cord
peripheral nervous system: all nerves in body
where are hormones produced
endocrine glands
where are hormones carried
blood
does the nervous or endocrine system have faster transmission
nervous
does the nervous or endocrine system have longer length of effect
endocrine
what is the pathway of hormone action
stimulus
receptor
hormone
effector
examples of stimuli that plants can respond to
light
gravity
physical objects
herbivory
water
physical touch
what is a phototropism
growth response to light
what is a geotropism
growth response to gravity
what is a positive tropism
growth towards a stimulus
what is a negative tropism
growth away from a stimulus
roles of plant hormone gibberellins
stem elongation
flowering
seed germination
role of plant hormone cytokines
cell growth and division
role of plant hormone abscisic acid (ABA)
leaf loss
seed dormancy
role of plant hormone ethene
fruit ripening
flowering
where are growth factors aka plant hormones produced
growing plants of a plant
how is IAA transported cell to cell
diffusion/ active transport
long distances in phloem
what type of tropism does IAA in plant shoots bring about
phototropism
in plant shoots, what does an increase in concentration of IAA bring about
increase in rate of cell elongation
what happens when light shines on one side of a plant stem
IAA transported to the shaded side
IAA gradient established
faster rate of cell elongation on shaded side
shoot bends towards source of light
what type of tropism does IAA in plant roots bring about
geotropism
in plant roots, what does an increase in concentration of IAA bring about
decrease in rate of cell elongation
how does IAA work in roots
IAA transported to lower side of plant roots
inhibits cell elongation there
lower side grows at a slower rate
root bends downwards
what stimulus controls flowering in plants
night length
how can night length be detected by plants
determines quantities of diff forms of phytochrome pigment in leaf
what is Pr form of phytochrome
inactive form
absorbs light from red wavelength part of spectrum
660 nm
what is Pfr form of phytochrome
active form
absorbs light from far red wavelength part of spectrum
730 nm
what happens when Pr absorbs red light
converted to Pfr
what happens when Pfr absorbs far red light
converted to Pr
what happens to phytochrome in the absence of red light
unstable Pfr gradually converts back into Pr
what happens to phytochrome during the day
high levels of Pfr
sunlight contains more 660nm than 730
more Pr being converted to Pfr
what happens to phytochrome during the night
high levels of Pr
red light wavelengths not available in dark
Pfr converts gradually to Pr
what does light enter the eye thru
pupil
where is light focused
fovea
(region of retina)
what controls amount of light entering eye
iris muscles
how is the shape of the lens controlled
ciliary muscles attached to lens by suspensory ligaments
what focuses light
lens
where are rod cells found
around outer retina
where are cone cells found
fovea
what are rod cells sensitive to
light intensity
what are cone cells sensitive to
diff wavelengths of visible light
what type of images are generated from rod cells
back and white
what type of images are generated from cone cells
coloured
how are action potentials generated in photoreceptors transmitted to brain
via optic nerve
where does optic nerve leave back of eye
blind spot
has no photoreceptors
what is rhodopsin
a light sensitive pigment in rod cells
what happens when light hits rhodopsin
breaks apart into
retinal, opsin
what is the breaking apart of light sensitive pigments called
bleaching
what does bleaching cause
chemical change in photoreceptor
generation of nerve impulse
travels along a bipolar neurone
to optic nerve
what happens in rod cells in the dark
Na+ pumped out
diffuse back in
membrane depolarised
inhibitory neurotransmitter released
action potential in bipolar neurone inhibited
what happens in rod cells in the light
rhodopsin bleached
Na+ pumped out
Na+ channels closed
Na+ cant diffuse back in
membrane hyper polarised
no inhibitory neurotransmitter released
action potential generated in bipolar neurone
what type of images do CT scans produce
cross section
what does CT scan stand for
computerised tomography
how do CT scans work
x ray beams aimed at patient from all angles around body
digital x ray scanners pick up beams as they exit body
denser tissues absorb more radiation so show up lighter
do CT scans show brain structure and function
no
j structure
who are CT scans not recommended for and why
pregnant women
children
radiation risk
what does MRI stand for
magnetic resonance imaging
what do MRIs use
magnetic field
radio waves
does CT or MRI have higher resolution
MRI
do MRI scans show brain structure and function
no
j structure
are CT or MRI scans more expensive
MRI
who cant have MRIs and why
patients w medical devices such as pacemakers and insulin pumps
what must patients do during MRIs
remain still
what do functional MRIs use
magnetic field
radio waves
do functional MRI scans show brain structure and function
yes
how do functional MRIs show brain function
show location of oxygenated and deoxygenated blood
so which brain regions active
measures ratio of oxygenated to deoxygenated haemoglobin
what does PET scan stand for
position emission tomography
what do PET scans use
radioactive tracers
in PET scans, where do the radioactive tracers collect
areas w increased blood flow, metabolism, neurotransmitters
in PET scans, what does the amount of tracer present in the brain region indicate
if region is active/ inactive
do PET scans show brain structure and function
yes
what is the visual cortex
region of cerebral cortex where visual info is processed
what is the cerebral cortex
outer layer of cerebrum
what happens in the visual cortex after birth
synapses form
critical period
why do both eyes need to be visually stimulated after birth
so neurones in visual cortex can be organised correctly
what happens to synapses that pass on nerve impulses during the critical period
strengthened
become permanent part of structure of visual cortex
what happens to synapses that don’t receive nerve impulses during the critical period
lost/ cant be reformed
can cause blindness
what did Hubel and Wiesel study
the long term impact of depriving animals of vision in 1 eye
what animals did Hubel and Wiesel test on
kittens
monkeys
what did Hubel and Wiesel do to the animals straight after birth
and what happened due to that
stitch 1 eye closed
after 3 months, blind in that eye
what are ocular dominance columns
groups of neurones in visual cortex
respond to light input from 1 eye
right ocular dominance columns receive info from right eye and vice versa
what did Hubel and Wiesel discover when they studied neurone activity in the visual cortex
ocular dominance columns corresponding to the stitched eye were smaller than normal
and the other eyes were larger
so concluded that ocular dominance columns for blind eye redistributed to correspond to normal eye- switched dominance
what is habituation
if a stimulus is repeated many times w no neg outcome, animal learns to not respond to it
why is habituation important
process of detecting and responding to stimuli requires energy
important animals don’t waste energy responding to non threatening stimuli
what is the process of habituation
less Ca2+ move into presynaptic neurone on arrival of a nerve impulse
less neurotransmitter released, less binds to post synaptic membrane receptors
less Na+ channels open, less move into axon, axon still neg charged, threshold potential not reached
action potential less likely generated in post synaptic neurone
nerve impulse doesn’t reach effector
