Session 2 The Nervous System: Overall Structure PS111 Brain & Behaviour Module 1: Psychobiology

What’s a Nervous System Good For? l To interact with the environment: – register (‘sense’) the environment – interpret (‘make sense of’) those signals – generate an appropriate response l What about plants?? e.g., phototropism:

What’s a Nervous System Good For? l To interact with the environment: – register (‘sense’) the environment – interpret (‘make sense of’) those signals – generate an appropriate response l What about plants?? e.g., phototropism:

What’s a Nervous System Good For? l To interact with the environment: – register (‘sense’) the environment – interpret (‘make sense of’) those signals – generate a response l What about plants? Animals, on the other hand... flexibly!

What’s a Nervous System Good For? l To interact FLEXIBLY with the environment: – register (‘sense’) the environment; – interpret (‘make sense of’) those signals; – generate a response. Organism InputResponse Organism Input Response Input

What’s a Nervous System Good For? Organism Response complex behaviour complex NS Input

History of the Nervous System l Only multicellular animals without NS: Sponges

` l All other animals have a NS: –a network of electro-chemically active cells (‘neurons’) –specialised to communicate with each other Neuron 1 Neuron 2 Neuron 3 Direction of Signal Transfer History of the Nervous System Interlude…

–a network of electro-chemically active cells –specialised to communicate with each other Neuron 1 Direction of Signal Transfer l Only multicellular animals without NS: Sponges l All other animals have a NS: History of the Nervous System Interlude…

Axon terminals Cell Body Dendrites Direction of Signal Transfer Axon –a network of electro-chemically active cells –specialised to communicate with each other l Only multicellular animals without NS: Sponges l All other animals have a NS: History of the Nervous System Interlude…

Neuron: Lecture 4 –a network of electro-chemically active cells –specialised to communicate with each other Direction of Signal Transfer l Only multicellular animals without NS: Sponges l All other animals have a NS: History of the Nervous System Interlude…

l Simplest form of nervous system: Uncentralised NS HydraSea star History of the Nervous System

FlatwormLeech Insect l NS of vertebrates similar, but more complex: –Central and peripheral NS more clearly separated –NS hierarchically organised l Even structurally simple animals have a centralised NS: History of the Nervous System

Central Nervous System Brain Spinal Cord 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 l Function: Control and co-ordinate behaviour –NS enables an organism to react quickly & with high precision to things happening in the environment l Simplest form: –detection, interpretation & motor command performed by only 2 neurons (no brain being involved at all…) l 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 Response Input

l Simple forms of behaviour (reflexes) already generated here! Things to do without a brain l Sensory signals from the body (except the head) enter CNS via the spinal cord

Things to do without a brain l Sensory signals from the body (except the head) enter CNS via the spinal cord grey matter white matter sensory neuron Brain Spinal Cord

Things to do without a brain grey matter white matter motor neuron sensory neuron l Sensory signals from the body (except the head) enter CNS via the spinal cord l 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 l 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 l 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 l 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 l 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 l 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 l The monosynaptic reflex arc: The knee-jerk-reflex

Things to do without a brain l 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!

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 * as studied in aplysia which of course does not have a spine…

l 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

Even more complex processing in the spinal cord: l 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:

l 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, l 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: –With sufficient training, the legs of these cats can learn to support weight again! –Recall:

l 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 NEEDS A BRAIN... l Every type of behavioural control that is more complicated than this NEEDS A BRAIN... l 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

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 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