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Session 2
The Nervous System:Overall Structure
PS111
Brain & Behaviour
Module 1: Psychobiology
What’s a Nervous System Good For?
To interact with the environment:– register (‘sense’) the environment– interpret (‘make sense of’) those signals– generate an appropriate response
What about plants??
e.g., phototropism:
What’s a Nervous System Good For?
To interact with the environment:– register (‘sense’) the environment– interpret (‘make sense of’) those signals– generate an appropriate response
What about plants??appropriate
response!e.g., phototropism:
… without a nervous system.
What’s a Nervous System Good For?
To interact with the environment:– register (‘sense’) the environment– interpret (‘make sense of’) those signals– generate a response
What about plants? Animals, on the other hand...
flexibly!
VARIOUSappropriate responses!
What’s a Nervous System Good For?
To interact FLEXIBLY with the environment:– register (‘sense’) the environment;– interpret (‘make sense of’) those signals;– generate a response.
OrganismInput Response
Organism
Input
Response
Response
Response
Input
What’s a Nervous System Good For?
Organism Response
Response
Response
complex behaviour
complex NS
Input
Input
History of the Nervous System
Only multicellular animals without NS: Sponges
`
Only multicellular animals without NS: Sponges All other animals have a NS:
– a network of electro-chemically active cells (‘neurons’)– specialised to communicate with each other
Neuron1
Neuron2
Neuron3
Direction of Signal Transfer
History of the Nervous SystemInterlude…
– a network of electro-chemically active cells – specialised to communicate with each other
Neuron1
Direction of Signal Transfer
Only multicellular animals without NS: Sponges All other animals have a NS:
History of the Nervous SystemInterlude…
Axon terminals
Cell Body
Dendrites
Direction of Signal Transfer
Axon
– a network of electro-chemically active cells – specialised to communicate with each other
Only multicellular animals without NS: Sponges All other animals have a NS:
History of the Nervous SystemInterlude…
Neuron: Lecture 4
– a network of electro-chemically active cells – specialised to communicate with each other
Direction of Signal Transfer
Only multicellular animals without NS: Sponges All other animals have a NS:
History of the Nervous SystemInterlude…
Simplest form of nervous system: Uncentralised NS
Hydra Sea star
History of the Nervous System
Flatworm Leech Insect
NS of vertebrates similar, but more complex:
– Central and peripheral NS more clearly separated
– NS hierarchically organised
Even structurally simple animals have a centralised NS:
History of the Nervous System
Central Nervous System
Brain
SpinalCord
Somatic NS
Input from sense organs
Output: skeletal muscles (volun-
tary control)
Peripheral Nervous System
Everything else:
Central & Peripheral Nervous System
Parasympa-thetic part
‘rest & main-tenance’
Sympathetic part
‘fight or flight’
Autonomic NS
No external input
Output: muscles & glands (involuntary
control)
ANS: Year 2
Communication in the Nervous System
Function: Control and co-ordinate behaviour– NS enables an organism to react quickly & with high
precision to things happening in the environment
Simplest form: – detection, interpretation & motor command
performed by only 2 neurons (no brain being involved at all…)
3 basic processes:– Sensory signals must be detected– The signals must be interpreted– Motor signals must be sent to the muscles or glands
– Activity of muscles/glands must be registered & fed back into the nervous system!
Organism ResponseInput
Simple forms of behaviour (reflexes) already generated here!
Things to do without a brain Sensory signals from the body (except the head)
enter CNS via the spinal cord
Things to do without a brain Sensory signals from the body (except the head)
enter CNS via the spinal cord
greymatter
whitematter
sensoryneuron
Brain
SpinalCord
Things to do without a brain
greymatter
whitematter
motorneuron
sensoryneuron
Sensory signals from the body (except the head) enter CNS via the spinal cord
Motor signals to the body leave the CNS via the spinal cord
Things to do without a brain
– Specific receptors (muscle spindles) inside each muscle fibre
The monosynaptic reflex arc: The knee-jerk-reflex
– … activate sensory neuron when muscle is stretched
– axons enter spinal cord via dorsal root
– connect directly with motor neuron,
– axons exit spinal cord via ventral root,
– activate same muscle from which signals originated:
– causing it to contract
Things to do without a brain The monosynaptic reflex arc: The knee-jerk-reflex
– Specific receptors (muscle spindles) inside each muscle fibre
– … activate sensory neuron when muscle is stretched
– axons enter spinal cord via dorsal root
– connect directly with motor neuron,
– axons exit spinal cord via ventral root,
– activate same muscle from which signals originated:
– causing it to contract
Things to do without a brain The monosynaptic reflex arc: The knee-jerk-reflex
– Specific receptors (muscle spindles) inside each muscle fibre
– … activate sensory neuron when muscle is stretched
– axons enter spinal cord via dorsal root
– connect directly with motor neuron,
– axons exit spinal cord via ventral root,
– activate same muscle from which signals originated:
– causing it to contract
Things to do without a brain The monosynaptic reflex arc: The knee-jerk-reflex
– Specific receptors (muscle spindles) inside each muscle fibre
– … activate sensory neuron when muscle is stretched
– axons enter spinal cord via dorsal root
– connect directly with motor neuron,
– axons exit spinal cord via ventral root,
– activate same muscle from which signals originated:
– causing it to contract
Things to do without a brain The monosynaptic reflex arc: The knee-jerk-reflex
– Specific receptors (muscle spindles) inside each muscle fibre
– … activate sensory neuron when muscle is stretched
– axons enter spinal cord via dorsal root
– connect directly with motor neuron,
– axons exit spinal cord via ventral root,
– activate same muscle from which signals originated:
– causing it to contract
– Specific receptors (muscle spindles) inside each muscle fibre
– … activate sensory neuron when muscle is stretched
– axons enter spinal cord via dorsal root
– connect directly with motor neuron,
– axons exit spinal cord via ventral root,
– activate same muscle from which signals originated:
– causing it to contract
Things to do without a brain The monosynaptic reflex arc: The knee-jerk-reflex
??Wrong
Question!
Things to do without a brain The monosynaptic reflex arc: The knee-jerk-reflex
we DON’T need a knee-jerk reflex as such
– we DO need
monosynaptic reflex arcs:
All through your body, monosynaptic reflexes ‘resist’ or ‘dampen’
quick stretching of skeletal muscles,
providing smooth, stable movement.
Note: even a monosynaptic reflex can haveadditional synaptic connections!
Polysynaptic reflex arc: – Sensory & motor neu-
rons connected via one or more inter-neurons
– Receptor & effector at different places
e.g., withdrawal reflex:
More complex processing in the spinal cord:
Things to do without a brain
– More flexible arrange-ment
– can show simple forms of learning*
More complex processing in the spinal cord:
Things to do without a brain
Polysynaptic reflex arc: – Sensory & motor neu-
rons connected via one or more inter-neurons
– Receptor & effector at different places
Note: learning without a
brain!!
* as studied in aplysia
which of course does not have a spine…
Spinal cord neurons can even generate complex movement patterns (e.g., walking)– but can not voluntarily initiate movements patterns only elicited in response to appropriate
stimulation
Even more complex processing in the spinal cord:
Things to do without a brain
Things to do without a brain
Things to do without a brain
Even more complex processing in the spinal cord:
Spinal cord neurons can even generate complex movement patterns (e.g., walking)– but can not voluntarily initiate movements patterns only elicited in response to appropriate
stimulation
How do we knowthat this is done in the spinal cord alone
(and not in the brain?)
Things to do without a brain
Even more complex processing in the spinal cord:
Spinal cord neurons can even generate complex movement patterns (e.g., walking)– but can not voluntarily initiate movements– patterns only elicited in response to appropriate
stimulation
Things to do without a brain
Even more complex processing in the spinal cord:
Things to do without a brain
Even more complex processing in the spinal cord:
Côté, M.-P., Ménard, A., & Gossard, J.-P. (2003). Spinal Cats on the Treadmill: Changes in Load Pathways. The Journal of Neuroscience, 23, 2789-2796.
Spinal cord neurons can even generate complex movement patterns (e.g., walking)– but can not voluntarily initiate movements– patterns only elicited in response to appropriate
stimulation.
Things to do without a brain
Even more complex processing in the spinal cord:
“learning without a brain”
– With sufficient training, the legs of these cats can learn to support weight again!
– Recall:
Spinal cord neurons can even generate complex movement patterns (e.g., walking)– but can not voluntarily initiate movements– patterns only elicited in response to appropriate
stimulation
Every type of behavioural control that is more complicated than this NEEDS A BRAIN...
Every type of behavioural control that is more complicated than this
Things to do without a brain
Even more complex processing in the spinal cord:
Question Time
Question Time
1. What is the difference between the nervous system (NS) of insects and vertebrates?
a) Vertebrates have a NS, insects don't have a NS
b) Insect NS is uncentralised, vertebrate NS is centralised
c) Vertebrates have a both a central and a peripheral NS, insects only have a peripheral NS
d) Vertebrates have a hierarchically organised NS, insect NS is non-hierarchic
e) There is no fundamental difference between insect and vertebrate NS
Question Time
2. The peripheral nervous system consists of
a) Brain and spinal cord
b) Somatic and autonomic division
c) Sympathetic and parasympathetic division
d) Dorsal and ventral roots
e) Mono- and polysynaptic reflex arcs
Question Time
1
23
4
3. The figure below shows a section of the spinal cord. Which of the numbers indicates the cell body of a motor neuron?
a) 1
b) 2
c) 3
d) 4
e) None of these
Question Time
4. The figure below shows…
a) A monosynaptic reflex arc of a vertebrate
b) A monosynaptic reflex arc of an invertebrate
c) A polysynaptic reflex arc of a vertebrate
d) A polysynaptic reflex arc of an invertebrate
e) None of the above
Question Time
5. Why does a newborn’s stepping reflex disappear as the child grows older?
a) Because as the legs grow heavier, they can no longer be moved by small signals
b) Because as the leg muscles become stronger, they can resist the reflex
c) Because as the nervous system matures, the interneurons that mediate the reflex disappear
d) Because as the nervous system matures, voluntary signals from the brain begin to override the reflex
e) None of these – the reflex does not disappear
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