Transcript The Nervous System: Overall Organisation

PS111
Brain & Behaviour
Module 1: Psychobiology
Session 2
The Nervous System:
Overall Structure
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??
e.g.,
phototropism:
What’s a Nervous System Good For?
flexibly!

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...
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.
Input
Organism
Response
Response
Input
Organism
Response
Input
Response
What’s a Nervous System Good For?
complex behaviour
Response
Input
complex
NS
Organism
Input
Response
Response
History of the Nervous System

Only multicellular animals without NS: Sponges
History of the Nervous System


Interlude…
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
Direction of Signal Transfer
Neuron
1
Neuron
2
Neuron
3
History of the Nervous System


Interlude…
Only multicellular animals without NS: Sponges
All other animals have a NS:
– a network of electro-chemically active cells
– specialised to communicate with each other
Direction of Signal Transfer
Neuron
1
History of the Nervous System


Interlude…
Only multicellular animals without NS: Sponges
All other animals have a NS:
– a network of electro-chemically active cells
– specialised to communicate with each other
Direction of Signal Transfer
Cell Body
Axon
Dendrites
Axon
terminals
History of the Nervous System


Interlude…
Only multicellular animals without NS: Sponges
All other animals have a NS:
– a network of electro-chemically active cells
– specialised to communicate with each other
Direction of Signal Transfer
Neuron: Lecture 4
History of the Nervous System

Simplest form of nervous system: Uncentralised NS
Hydra
Sea star
History of the Nervous System

Even structurally simple animals have a centralised NS:
Flatworm

Leech
Insect
NS of vertebrates similar, but more complex:
– Central and peripheral NS more clearly separated
– NS hierarchically organised
Central & Peripheral Nervous System
Brain
Everything else:
Peripheral Nervous System
Central
Nervous
System
Spinal
Cord
Somatic NS
Autonomic NS
Input from sense
organs
No external input
Output: skeletal
muscles (voluntary control)
Output: muscles &
glands (involuntary
control)
Sympathetic
part
‘fight or flight’
Parasympathetic part
‘rest & maintenance’
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

3 basic processes:
– Sensory signals must be detected
– The signals must be interpreted
– Motor signals must be sent to the muscles or glands
Input
Organism
Response
– Activity of muscles/glands must be registered & fed back
into the nervous system!

Simplest form:
– detection, interpretation & motor command
performed by only 2 neurons
(no brain being involved at all…)
Things to do without a brain

Sensory signals from the body (except the
head) enter CNS via the spinal cord

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
Spinal
Cord
Brain
white
matter
grey
matter
sensory
neuron
Things to do without a brain

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
white
matter
grey
matter
sensory
neuron
motor
neuron
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
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
All through your body,
monosynaptic reflexes ‘resist’ or ‘dampen’
quick stretching of skeletal muscles,
providing smooth, stable movement.
Note: even a monosynaptic reflex can have
additional synaptic connections!
Things to do without a brain
More complex processing in the spinal cord:

Polysynaptic reflex
arc:
– Sensory & motor neurons connected via
one or more
– Receptor & effector at
different places
e.g., withdrawal reflex:
Things to do without a brain
More complex processing in the spinal cord:

Polysynaptic reflex
arc:
– Sensory & motor neurons connected via
one or more
– Receptor & effector at
different places
– More flexible arrangement
– can show simple
forms of learning*
* as studied in aplysia
which of course does not have a spine…
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
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 know
that 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:
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:

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.
– With sufficient
training, the legs
of these cats can
learn to support
weight again!
– Recall:
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.
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

Every type of behavioural control that is more complicated
than this NEEDS A BRAIN...
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
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
1
2
4
3
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