neurobiology Flashcards
proprioception
part of sensory input
where organs compared to each other
integrating system
make decisions from sensory and stored record of previous experience
purpose of dendrites
increase SA to recieve input from as many places where contact other neurones as possible
anterograde transport
from soma down axon to terminals
rapid or slow
retrograde transport
from terminals to soma
like worn out mitochondria/SER
rapid
axonal transport
anterograde or retrograde
requires hydrolysis of ATP
motors walk along microtubules
myelin sheath in diff areas of nervous system
oligodendrocytes form myelin sheath in central NS, 1 cell can cover many axons and neurones
Schwann cells in peripheral NS, 1 per axon
glia cells
non-neuronal cells in NS
microglial
respond to damage and clean cellular debris, launch immune system
astrocytes
star shaped, foot processes on blood vessels, restrict what can enter brain because molecules have to go through astrocytes
connected to neurones as well
release gliotransmitters
provide metabolic fuel for neurones
ganglia
collections of nerve cells
neuropil
dense regions of nerve fibers devoid of cell bodies
encephalisation
ganglia fuse to brain and spinal cord
autonomic NS
somatic NS
fight or flight - para/sympathetic
skeletal muscles under voluntary control
spinal cord arrangment
grey matter - where cell bodies of axons are
axons enter from periphery into white matter
diff segments (cervical, thoracic, lumbar, sacral)
related to diff parts of body
can see where injuries to spinal cord affect
meninges
surrounds CNS and protects
brain suspended in jacket of cerebrospinal fluid - fluid filled cavities
3 layers cover brain - Dura mater, Arachnoid mater, Pia mater
CSF
cerebral spinal fluid made by choroid plexuses in ventricles (fluid filled cavities)
removes waste
supplies CNS with nutrients
buffers blood pressure changes
changes in CSF can mean disorder
should be clear
blood - subarachnoid haemorrhage
yellow - old blood or jaundice
brainstem structure
medulla - respiration, cardiovascular function
pons - links with cerebellum, modifies medulla output
cerebellum - balance, fine movement, posture
midbrain - visual, audio, motor control, sensation
hypothalamus
autonomic ontrol appetite reproductive behaviour homeostasis endocrine control
thalamus
integrates sensory info
ionic movement for resting membrane potential
impermeable to Na so lots outside
more K inside
equilibrium between conc and electrical gradient
changing sodium conc
will not affect resting potential
but reducing sodium around axon decreased size of (action) potential
why is the membrane potential in reality less negative than Ek?
cell membrane not completely impermeable to Na, and some K leakage
sodium-potassium pump
3 sodium pumped outside
2 potassium in
both against conc. gradients so use ATP
how long does AP last?
depends on temp but usually 1ms
driving force of Na moving in cell when channels open
down conc gradient because less Na in cell
down electrical gradient because negative in cell and Na is positive
subthreshold
don’t reach threshold of action potential (about +50)
conductance
flow of ions
why is potassium ion flow slower than sodium, during AP?
starts slower because activation of voltage-gated channels slower for potassium
repolarisation
potassium channels open after a delay, K moves out of cell down conc gradient and down electrical gradient
Na channels close
refractory period
can’t activate again for period of time
absolute - AP can’t initiate again, channels inactivated
relative - can AP but need bigger stimulus
axon hillock
initial segment
full of channels
decides whether to fire AP
speed of AP conduction depends on
axon diameter
bigger diameter means faster conduction
difference in speed between myelinated and non?
100 fold
electrical synapses
touching - connexons pair up between cells delay
can be 2 way
little plasticity
main inhibitory and excitatory chemical neurotransmitter?
regulation of food uptake?
GABA
glutamate
orexin
axodendritic synapses
axosomatic
axoaxonic
synapse on dendritic spine or shaft itself
on soma - very powerful
close to axon hilic
filling vesicle with neurotransmitter
ATP pumps H ions into vesicle
pushes against conc and electrical gradient
get NT in from exchange of H ions
H out provides energy to pump NT in
peptide vs non-peptide NTs
non peptide made locally where needed in synapse
peptide made in cell body and travel to synaptic cleft via anterograde transport in vesicle
synaptotagmin
snare protein
senses calcium influx so tension and fusion of vesicle to membrane
features of Ca dependent transmitter release
requires binding of multiple (3-5)
quick
blocked Ca entry means can’t release transmitter
vesicle recycling
endocytosis
clathrin surrounds membrane that needs to be retrieved
4 postsynaptic effects
in speed order - fast to slow
ionotropic - channel-linked receptors, cellular effects
metabotropic - G-protein coupled receptors
kinase-linked receptors
nuclear receptors -receptors linked to gene transcription
synthesis of ACh
acetyl-CoA and choline turn into acetylcholine by choline acetyltransferase (CHAT)
nicotinic receptor
muscarinic receptor
selectively activated by nicotine - ionotropic, fast
selectively activated by muscarine - metabotropic, slow
how many pairs of spinal nerves in humans that come out of spinal cord?
31
where are motor neurones and sensory neurone situated?
motor in ventral roots (towards gut) dorsal roots (back)
fascicle
bundles on axons
2 types of motor neurones
lower - comes out spinal cord to go to muscle, cell body in ventral horn
upper - synapses onto lower, fire so activate lower, in spinal cord only
cortocospinal pathway
motor pathway
starts in motor cortex (divided into gyri and sulcus, out and in bumps)
gyri jsut before central sulcus is the motor cortex
post-central gyrus is where sensory info comes in
axons from cortex to pyramids in medulla to spinal cord to lower motor neurones then to muscles
somatotopic map
diff parts of motor cortex correspond to diff parts of body
why can’t you get summation of contractions in heart?
AP in heart is same length as contraction
good because need to keep flow of blood correct
increasing force of contraction
recruitment
temporal summation
why do muscles fatigue?
depletion of glycogen accumulation of extracellular K accumulation of lactate accumulation of ADP + Pi central fatigue - psychological
diff types of muscle fibres show diff resistance to fatigue
type 1 doesn’t because low force + slow
type 2 does a lot
what detects how much muscle contracted?
Golgi organ in tendon
muscle spindles
in middle of muscle, intrafusal
sensory fibres go to spinal cord
contract muscle - spindle goes floppy so can’t detect anything, gamma motor neurones cause contraction so can continue to detect
Golgi tendon reflex
reduce contraction to stop damage
cutaneous sensory receptors (touch)
Meissners corpuscles - upper dermis, vibration
Pacinian corpuscles - deep in dermis, deep pressure
Merkels discs - base of epidermis, sustained pressure
Ruffinis corpuscles - deep in dermis, sustained pressure
tonic vs phasic
slowly adapting
rapidly adapting
2 point discrimination
2 nerves in same receptive field - feel like same place because 1 signal to brain
not in receptive field - don’t feel it
functions of autonomic NS
contraction of smooth muscle
exocrine/endocrine secretion
control of heartbeat
steps in intermediary metabolism
noradrenaline receptors
alpha and beta adrenoceptors - metabotropic (G protein coupled)
varicosities
swellings
synapses in ANS after postganglionic neurone
sympathetic:
superior cervical ganglion
coeliac ganglion
superior mesenteric ganglion
inferior mesenteric ganglion
eye, lacrimal glands, salivary glands
heart, larynx, trachea, bronchi, lung
oesophagus, stomach, small intestine, liver, bilary system, large intestine, adrenal gland
large intestine
large intestine, kidney, bladder, reproductive organs
paravertebreal chain (sympathetic chain)
spinal cord autonomic fibres within peripheral nerve preganglionic neurone in lateral horn axon out into sympathetic chain synapse in sympathetic ganglion to postganglionic neurone and back into spinal nerve to heart/blood vessels/other plexuses and ganglia/other swelling and synapse there
autonomic reflexes are controlled by what?
hypothalamus
presbyopia
loss of near vision as lens becomes less elastic
ciliary muscle relaxed for far vision and contracted for near vision (fatter so bend light more)
Horner syndrome
damage on 1 side of ANS going to face
loss of sweat on 1 side of face, eyelid falls, large pupil
isometric muscle contraction
length doesn’t change but increase force and tension
e.g. forearm muscle when holding object
isotonic muscle contraction
tension doesn’t change but length changes, anchored at top but not at bottom
sphincter
circular muscle maintains constriction of natural body passage
e.g. relax when urinate so mostly always contracted
which smooth muscles always contracted and which partially?
sphincters always fully
blood vessels/airways partially
micturition
peeing
smooth muscle multi-unit vs single unit
separate and act independently, like in iris/piloerector (hair stands up)
cells coupled, all active together, controlled by 1 varicosity
force produced by muscle contraction depends on…
recruitment - no. active muscle fibres
temporal summation - frequency of stimulation
rate at which muscle shortens
cross sectional area of muscle
initial resting length of muscle
tetanus
muscle fully contracted
initial resting length of sarcomere - muscle tension effect
optimal length generates most force - stretch receptors pull to optimal
not enough overlap between actin and myosin - can’t produce any force
too overlapped - already contracted so can’t overlap any more and generate force
triad junction
at junction of A and I bands
sources of ATP for muscle contraction
glycogen to glucose from aerobic R
anaerobic R
phosphocreatine - ADP + creatin phosphate –> ATP + creatine
rigor mortis after death
stiff muscles because no ATP to break corss-bridges
tropomyosin
bound to troponin
TnC binds to calcium
then conformational change allows myosin bind to actin
DHPR
RYR
di-hydra pyridine receptors
di-hydra pyridine blocked calcium receptors
ryanodine receptor - stores of calcium (SR)
how is contraction of skeletal muscles terminated?
by calcium removal
taken up into SR by SERCA-type pump (sarcoplasmic and endoplasmic reticulum calcium ATPase) requires ATP
