Week 3- Neurotransmission and Activity

What is the nervous system

Central hub for collating information from cells and tissues organizing it and prioritising the animals response including behavioural and physioloigcal actions

What is the nervous system composed of

Neurons- the basic unit of the nervous system

What is the central nervous system

Includes brain and spinal cord and majority of neurons that innervate effectors

Central is then sent to the peripheral

What is the peripheral nervous system

Primarily outside of the brain and spinal cord includes nerves and ganglia

What are neurons

Specialised nerve cells that are:

1. Fundamental unit of nervous system

2. Responsible for receiving and processing sensory information then transmitting to other cells

3. Communicate info via electrical and chemical signal that are rapid and provide directed info to the parts of the body that need it

Whats the difference between afferent and efferent neurons

Afferent neurons: Carry sensory signals to integrative centers of CNS

Efferent neurons: Relay control signals from CNS to target cells

What is the structure of a neurone like

Synapse: specialized areas of contact between neighbouring neurons’ axon and dendrite

Dendrite: Interface with other nerve cells/organs/tissues, short transmitting signals from other neurons to cell body, branch extensively creating tree like structure

Axon: Signal carrying extension that conducts action potentials away from cell to target, dictate speed of transmission by axon diameter, one per neuron , in PNS a bundle is called a nerve

Cell body: Responsible for metabolic maintenance of cell and site of signal generation, in PNS a bundle is called a ganglion, in CNS it is called nucleus

What gives neurons polarity

Information transmits unidirectionally

Dendrites- Cell Body- Axon- Synapse

What is an action potential

Primary nervous system signal, stimulated by brief change in membrane voltage

Stimulated by brief change in membrane voltage

All or none events

Dictated by opening and closing of Na+ and K+ channels

What are the four stages of an action potential

Resting membrane potential, Stimulus, Depolarisation, Repolarisation

What is resting membrane potential

• -70mV

• Dictated by ion leakage/pumping across cell membrane, unchanging without stimulus

What is depolarisation

Na+ channel opens

Moves membrane potential to zero

If threshold potential reached (-55mV), action potential initiated

What is repolarisation

Increasing membrane potential triggers opening of K+ channels , that repolarize the cell to resting membrane potential

What are gilal cells

Works in several supporting roles to neurons and is an area of active research. For example gilal cells ensure that neurons metabolic needs are met and provide structural support for neuronal tissue

What are the three types of neurons

Sensory, interneuron, motor

What are sensory neurons

Transmit information collected from internal/external stimuli

What are interneurons

Connect other neurons in the nervous system

What are motor neurons

Carry signals to effector organs

What is a synapse

Location for signalling between neurons

What is an electrical and chemical synapse

Electrical: direct connection of electrical current between two cells allow ions to pass directly from one cell to the next

Chemical: chemical signal is released from one cell and affects another

What are neurotransmitters

Bodys chemical messengers

• Small fast acting molecules used to convey signals within nervous system

• Carry signals across synapses in neighbouring neurons

• Critical machinery for animal behaviour

What is the structure of a chemical synapse

Synaptic cleft: Small gap between neurons

Neurotransmitter stored in synaptic vesicles

Vesicle binds to pre synaptic membrane- released by exocytosis

How does a chemical synapse work

Diffuses across synaptic cleft

Binds to receptor on postsynaptic neuron

Binding leads to channel opening in post synaptic neuron and changes in membrane potential

What s neurotransmitter release dependent on

Number of action potentials

Frequency of action potentials

What are neurotransmitters and what do they do

Neurons specialised to synthesise and release one more specific neurotransmitter

When neurons contain and release multiple neurotransmitters these are termed cotransmitter

Action of one transmitter is dependent on the action of another

What is the criteria to categorise a molecule as a neurotransmitter

• Present in pre-synaptic neuron

• Released upon stimulation of pre-synaptic neuron

• Addition of neurotransmitter to synapse

• Must have a mechanism for removal from the synapse

What can neurotransmitters impact

Diverse impacts on animal behaviour

What is space use in terms of behavioural traits

Concept that describes the places that an animal regularly visits as a results of their daily activities e.g. forage, socialise

What is exploration in terms of behavioural traits

An individual’s behavioural response to a new situation as influenced by prior experience/age/motivation

What is inspection in terms of behavioural traits

Time or thoroughness of investigation of a novel object, as a measure of propensity to take risks

• Invertebrates you would not expect can show distinctive and quantifable behaviours

• Anenomes propensity to take risks assessed by exposinf individuals to smooth versus rough beads, with time to reject the bead assessed as inspection

• Individuals took longer to reject the rough bead than the smooth one

How to test activity

Emergence test

Open field test- round tanks to see how they react round it is- more willing they are to come/cross so called safe area in middle

Novel object test

Maze test- some sort of something (food resource) in one of arms- can give as many arms how long it takes to explore

Refuge test- different refuges how long to explore less safe areas

How to brain regions link to behaviour

• Offactory lobes process chemosensory stimuli

• Optic lobes receive visual stimuli

• Cerebellum coordinates motor activity

• Different types of neurons can be aggregated in different brain areas, dictating that brain region’s role in behaviour

Explain serotonin synthesis

Tryptophan (from diet) is converted into 5-HTP and then serotonin (5-HT).
During inflammation, more tryptophan is diverted into the kynurenine pathway, reducing the amount available for serotonin production.

Explain serotonin signalling

Serotonin is stored in vesicles, released into the synapse, binds to 5-HT receptors, then is either taken back up by the serotonin transporter (SERT) or broken down by monoamine oxidase (MAO) into 5-HIAA, which indicates serotonergic activity.

What is dopamine

• Synthesises from tyrosine (amino acid) that can only be acquired through diet

• Key component of reward-seeking behaviour across animal phyla

What is norepinephrine

• Synthesised through series of enzymatic steps from tyrosine to dopamine to norepinephrine

• Mediates range of stress related responses that prepare animal for extreme physical exertion

What is acetylcholine

• Synthesised from compounds choline and acetyl co-enzyme A

• Associated with signalling at at neuromuscular junctions where motor neurons in spinal cord synapse with muscles in the body

What is gamma-aminobutyric acid (GABA)

• Synthesised from glutamate

• Strong inhibitory neurotransmitter in vertebrates thought to reduce anxiety, stress and fear resulting in a decrease aggression and increase in cooperative social behaviour

What are agonist neurotransmitters

Substances that bind to a synaptic receptor and increase the effect of a neurotransmitter

What are antagonist neurotransmitter

Substances that bind to synaptic receptor but decrease action by a neurotransmitter

How can you measure neurotransmitter activity

High Performance Liquid Chromatography (HPLC) with electrochemical detection

Is neurotransmission a permanent trait

No, it exhibits plasticity in which the nervous system changes and adapts to maximise the efficiency of signalling through time

Occurs through a range of mechanisms including: Synaptic plasticity, neurogenesis, neural plasticity

Define synaptic plasticity

Defined as activity- dependent modification of the strength or efficacy of synaptic transmission at pre exisiting synapses following an excitatory signal

Describe the stages of synaptic plasticity

1. More neurotransmitter released from pre-synaptic neuron

2. More receptors on post-synaptic neuron

What is neurogenesis

Proliferation and survival of new neurons

What is the history of neurogenesis research

• originallly thought to only occur in developmemt

• Recent researcvh suggests in adulthood too

What is the rate of neurogenesis impacted by

1. Physical Activity

2. Environmental conditions

3. Hormone and neurotransmitter activity

What is neural plasticity

The ability of the CNS to maximise efficiency of signalling by reorganizing sturcure functions and or connections

What can neural plasticity occur through

1. Activation of parallel pathways to mantain function within a damaged area

2. Activation of silent synapses

3. Synaptic plasticity

4. Synaptogenesis

5. Neurogenesis