session 2 the nervous system: overall structure ps111 brain & behaviour module 1: psychobiology

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