Lecture 2 Flashcards
The nervous system I : Overall structure
How does an organism flexibly behave
1 - register ( sense environment )
2 - transform ( interpret - make sense of those signals )
3 - Generate appropriate response
Behaviour
an organisms internally coordinated response as a result of changes in its internal or external environment
Behaviour in simple organisms eg
plants ( although phototropism - growing plant follows path of sun )
Behaviour in complex organisms eg.
animals
- Involves constant monitoring
why does an animal need an NS?
to integrate the complex signals and select appropriate response from many options
what happens in complex system
if a change is strong enough, it causes the signal to be transmitted down the chain of cells ( neural pathway )
–> this is a chain that feedsback on its self ( cycles of signal generation ) –> which will eventually reach some output system eg. Motor neurone leading to some behaviour
cascade of cascades
communication of signals from one cell to the next as the cell changes its internal chemistry and as a result another cell changes its internal chemisty
ADHD example
have to think about every little movement so not much left attention for other things
register
sense info from environment
eg. magnetic fields - birds sense it and plan flight direction but humans cannot do that
transformation
internal change ( coordinated response )
process change
eg. prick by needle, there is a mechanical change but if your under anaesthesia, you won’t recognise this change
res
Response
brains respond
no conscious thought
automatic
difference between plant and animal ?
Animal can register more than just light, but also sound
animals can respond to complex stimuli eg. chainsaw and we can’t always predict their behaviour
Only multicellular animal without NS
sponge
Nervous system
network of electro-chemically active cells ( neurones) that are specialised to communicate with eachother
direction of signal transfer
1 - strong enough chemical change
2 - signal
3 - change to active from inactive
etc.
simplest form of NS
uncentralised
( hydra - sea star eg. ) - no nerve centre
every part is as important
evenly set our network of neurones condensed to ring an radial arms
cell body – axon – cell body – axon
hydra - what does nerve centre control
activity of groups of other neurones
actions of distant body parts
structurally centralised NS examples
flatworm
leech
insect
( with separate CNS ) - protobrain, nerve cord , PNS
nerve cords scattered around body
CNS - brain, nerve cord
PNS - all other neurones spread out
NS of vertebrates ( animal with spine just like us ) structure
CNS + PNS more clearly separated
NS vertebrates function
more hierarchy organised
brain - specialised to direct communication between neurones control actions of distant body parts
PNS more under control of CNS
CNS
brain + spinal cord
encased in bones
brain - skull
spinal cord - vertebrates
PNS - input from sense organs
somatic NS
somatic NS
picks up info from environment ( 5 senses )
and produces output in muscles
voluntary control
whats in input and output of somatic NS
input - senses
output - skeletal muscles
voluntary
PNS - no external output
autonomic NS
autonomic NS parts
1 - sympathetic part ( fight or flight ) - eg, exam - get sweaty hands
2 - parasympathetic part ( rest and maintenance ) eg. lying down
autonomic NS
doesn’t have any external input
not directly connected to senses
only receives input from CNS
output of Autonomic NS
muscles + glands
involuntary control ( eg movement of gut )
Can we ‘behave’ without brain ?
we can detect, transform, motor command by 2 neurones in spinal cord ( so no brain )
what are the links between PNS and CNS
sensory signals from body ( x head ) –> CNS
via spinal cord
Motor signals leave CNS via spinal cord
white matter
myelinated axons of neurones
grey matter
highly condensed neurones cell bodies
cortex + sub-cortical nuclei
NS function
control + coordinate behaviour
so we can react
quickly
flexibly
high precision
in response to environment
monosynaptic reflex arc example
knee jerk reflex
one connection
monosynaptic reflex arc
specific receptors ( muscle spindles ) in muscle fibre
activate sensory neurone when stretched
axons go to spinal cord via dorsal root
dorsal root directly connects to motor neurone , which send their axons out via ventral root
same muscle activated from which signal originated
muscle contracts
why do we need monosynaptic refelxes
to ‘resist’ and ‘dampen’ quick stretching of skeletal muscles, enabling smooth, stable movement
can monosynaptic reflex arcs have more than one synaptic connection ?
yes. BUT
only 1 connection between sensory and motor neurone
the other connection may be where the sensory or motor neurone receives the input from
polysynaptic reflex arc
sensory and motor connected by 1+ interneurones
receptor end of sensory enurone + effector end - diff places
( withdrawal reflex )
more flexible arrangement can sometimes show simple forms of learning - eg. aplysia
synapse
signalling link between neurone and another cell / neurone
synapse structure
specialised sender part of neurone is close to specialised recipient part of target cell
2 neurones have many synapses
many contact points - but all for same signal
function of synapse - monosynaptic
one synapse linking sensory and motor neurone
function synapse - polysynaptic
many synapses between sensory and motor
bi-synaptic - 2
try-synaptic - 3
polysynaptic - many
central pattern generators
spinal cord neurones can generate complex movement patterns - in response to appropriate stimulation
cannot voluntarily initiate movements eg ‘ I want to walk’
example of central pattern generators
cat with spinal cord resection walking on treadmill
cat spinal cord explanation
cat accident - spinal cord cut
initial signal arriving from hind legs cannot be sent to brain so that signal has no effect as motor neurone isn’t aware of the signal
on treadmill..
provide support + keep body upright
set in motion ( moving stimulus below feet )
cat feet move in coordinated stepping pattern
- must happen locally in spinal cord as connection with brain is severed
