Physiological Basis of Animal Behaviour - MyPlayer · Physiological Basis of Animal Behaviour ... sympathetic signals send a speed ... sedative and an anti-emetic prior to surgery

MOD002787 Biological Bases of Behaviour

Dr. Toby Carter (Bry 114, x 2777) [email protected]

Physiological Basis of Animal Behaviour


Neurophysiology Part 2

Nerve Junctions

The nerve Junction or synapse: the basic model

The basics on nerve junction mechanisms

Neurotransmitter vesicle

Neurotransmitter Molecule

Some Neurotransmitter components are recycled & repackaged they are transported actively (using ATP) from region B

Calcium channels open when the action potential has reached the nerve end (*)

*

Calcium ions Cause the vesicles to empty

Post synaptic membrane region B

Receptor for neurotransmitter

occupied receptor opens Na channels here

1

2

3

Na

Neurotransmitter dissociates & is dismantled by enzymes

A

4

5

A Pre-synaptic membrane

Calcium channel

Hormones & Neurotransmitters

-  Appear to have common evolutionary origin

-  As organisms grew more complex, two routes diverged

-  Neurotransmitter: rapid, specific, point-to-point communication

- Hormone: involves circulatory system, slow, diffuse, widespread communication

There are many neurotransmitters in the nervous system (over 100 identified). •  Acetylcholine is mainly in the peripheral system

Neurotransmitters

There are many neurotransmitters in the nervous system (over 100 identified). •  Acetylcholine is mainly in the peripheral system •  Noradrenalin (norepinephrine) mainly peripheral

Neurotransmitters




There are many neurotransmitters in the nervous system (over 100 identified). •  Acetylcholine is mainly in the peripheral system •  Noradrenalin (norepinephrine) mainly peripheral •  GABA (Gamma Amino, Butyric Acid) in brain •  Glutamate CNS & PNS

Neurotransmitters

There are many neurotransmitters in the nervous system (over 100 identified). •  Acetylcholine is mainly in the peripheral system •  Noradrenalin mainly peripheral •  GABA (Gamma Amino, Butyric Acid) in brain •  Glutamate CNS & PNS •  Serotonin (5-α hydroxytryptamine) CNS & PNS •  Dopamine mainly in cerebral cortex

Neurotransmitters

All neurotransmitters are in some way broken down after they have interacted with and then dissociated from their receptor. Some use only one enzyme to do this, others have a complex array of enzymes which have multiple dismantling stages. Example 1 – acetylcholine is broken down in one simple stage acetylcholinesterase cleaves the neurotransmitter leaving acetate & choline, acetate is excreted and choline is recycled.

Example 2 Noradrenalin is broken down by an enzyme series :

(MAO) monoamine oxidase (COMPT) catecholamine –o-methyl transferase

Regulating the release of neurotransmitter Example – Noradrenalin (NA) regulates its own release

Alpha-2 Receptor On pre- Synaptic membrane

When neurotransmitter Is released there is a build up in the cleft (C). If lots of NA has been produced, the chances of accumulation at (C) Increases - some NA float in to an α-2 receptor. NA release is then switched off

C

1

2 Alpha-2 activated- NA vesicles remain closed

NA vesicle = NA

More on synapses 1. Not all synapses are excitatory, some are inhibitory, the

different synapses can not interchange function, the excitatory and inhibitory junctions are anatomically distinct.




The Inhibitory Synapse

-  - - -  - - -

Ions with (-) charge chloride Cl- rush in through their channels

Post synaptic membrane polarised / made more negative inside therefore Inhibited (‘forced’ back to, or kept in in resting state)

** Remember that in an excitatory neuron the neurotransmitter opens Na gates carrying (+) charge thus depolarising next neuron

Neurotransmitter Receptor Neurotransmitter

Cl Channels

Neurotransmitter release

Occupied receptor opens Cl channels

2. There are slow and fast synapses. The slow synapse undergoes a multi-stage transfer of information to the next neuron whereas the fast synapses combine their complex role into one single stage.

FAST SYNAPSE - ionotropic

Fast synapse in action

SLOW SYNAPSE - metabotropic

Slow synapse in action Supp-HO

Synapses instruct and influence other synapses

Synapses instruct their neighbouring synapses: They can actually influence and MODIFY the behaviour of other synapses

HOW?

•  Certain synapses can modify the behaviour of their neighbours by altering the quantity of neurotransmitter released from their vesicles

•  This will in turn influence the quantity of neurotransmitter released from the next synapse (this could be a very weak or very strong excitatory signal or a very weak or very strong inhibitory signal).

•  Remember that the inhibitory or excitatory synapses are anatomically distinct and are placed in strategic places. This means a process can be geared up OR dampened down




When the nerve INCREASES the amount of neurotransmitter in the next nerve, this process is called PRE-SYNAPTIC FACILITATION When the nerve DECREASES the amount neurotransmitter in the next nerve, this process is called PRE-SYNAPTIC INHIBITION

Examples of pathways which have an inhibitory and excitatory nerve circuit •  One nerve tells one muscle in the limb to contract while another nerve is instructing another not to contract at the same time so the arm will bend

Excite & Inhibit

Example 2 •  The heart receives excitatory and inhibitory signals at the same time, sympathetic signals send a speed up message, the parasympathetic send a slow down message. Both messages have equal input Result = just the right speed When stressed the excitatory message from the sympathetic becomes greater and heart rate increases.

Impulses Are All or Nothing – But Synapse Potentials Are Graded

Synapse potentials •  Post synaptic potentials can be excitatory or inhibitory (EPSP’s or IPSP’s) They are Graded not all or nothing.

The vesicle release can be large or small. This depends the kind of information the synapse has received.

This means that a synapse will respond according to the input from another nerve. It appears that the synapse Is making a kind of ‘decision’ The input from the other nerve which the synapse has to respond to, is the number and rate or frequency at which the action potentials are coming in

The Anatomy of Post Synaptic Potential: is from post synaptic membrane to axon hillock,

beyond the hillock – all or nothing applies

Which ‘bit’ of the neuron conducts graded potentials



Physiological Basis of Animal Behaviour More on Post Synaptic Potentials

•  The post synaptic potential decrease as they spread from the site of the junction up to the axon hillock. •  This means that not all the PSP’s will have the same influence on the axon hillock. Synapse 1 will have less influence on the axon hillock than synapse 4 (see previous slide) Synapse 1 is further away.

Synapses can add up their input

A synapse can add up the in coming signals, this is how It is able to respond to increases or decreases in input frequency. This process is called SUMMATION •  Spatial summation : adds up the simultaneous Influences of synapses from different sites on the post Synaptic cell.

Synapses can add up their input

A synapse can add up the in coming signals, this is how It is able to respond to increases or decreases in input frequency. This process is called SUMMATION •  Spatial summation : adds up the simultaneous Influences of synapses from different sites on the post Synaptic cell. •  Temporal summation : adds up the post synaptic potentials generated at the same site but are coming in, in rapid sequence

Compare Action Potentials (AP’s) and Post Synaptic Potentials (PSP’s)

Three Important Differences Propagation: PSP’s arise and fade away rapidly, this is all that

is needed – they are short distance messages only, AP’s are long distance messages.

Amplitude: AP’s following the all or nothing law, PSP’s are

graded potentials. This is dependent on amount of neurotransmitter released.

Refractory period: AP’s display a refractory period, PSP’s do

not

The Spinal Tree in The Biped

Sympathetic nerves arise from:- T 1 -12 and L1 – L2

The autonomic Nervous System Anatomically distinct location of autonomic divisions




Parasympathetic nerves arise from: - CN 111 VII IX And X and S2 –S4

A closer look at those branches from the CNS

Autonomic

Muscurinic Receptors & Nicotinic Receptors Pre-ganglion on the sympathetic nerve – Nicotinic the Receptor is a specialised ion channel.

TM =Acetylcholine Post-ganglion on the sympathetic nerve – Adrenergic

TM= Noradrenalin

TM = Transmitter Molecule

Muscurinic Receptors & Nicotinic Receptors Pre-ganglion on the sympathetic nerve – Nicotinic the Receptor is a specialised ion channel.

TM =Acetylcholine Post-ganglion on the sympathetic nerve – Adrenergic

TM= Noradrenalin Pre-ganglion on the parasympathetic nerve – Nicotinic the receptor is a specialised ion channel.

TM=Acetylcholine Post-ganglion on the parasympathetic nerve- – Muscurinic (G-protein activated –slow synapse)

TM= Acetylcholine

TM = Transmitter Molecule

How drugs affect neurons Agonist: mimics or increases the effect of a neurotransmitter system Antagonist: blocks or decreases the effect of a neurotransmitter system -  Agonist

- drug stimulates receptor (mimics NT) - drug stimulates more release of NT - drug blocks reabsorption of NT at synapse - drug inactivates enzyme that breaks down NT

How drugs affect neurons Agonist: mimics or increases the effect of a neurotransmitter system Antagonist: blocks or decreases the effect of a neurotransmitter system -  Antagonist

- drug blocks receptor - drug inhibits release of NT - drug blocks NT transporter - drug stimulates autoreceptors (e.g. alpha2)



Physiological Basis of Animal Behaviour Synapse Mechanisms Affected by Drugs

Drugs acting on the synapse can: •  * Block the post synaptic receptors in PNS and CNS •  * Inhibit the release of neurotransmitter

•  Affect the destruction of the used neurotransmitter

*Several examples from the list above are used in treating psychological disorders in humans, symptoms of stress and behavioural management in domestic animals

Examples of Drugs

Blockade : Receptors sites on the post synaptic membrane are occupied by the drug. 1 In somatic PNS – anaesthetic muscle relaxant – Drug name Pancuronium 2 Noradrenalin receptors blocked in the same way in ANS to reduce heart excitability and the symptoms of stress- Beta blockers –a specific drug name - Propanalol 3 Central nervous system specific receptor blockade - dopamine receptor blockade - Neuroleptic drugs, subtype phenothiazines – examples Promazine and Acepromazine*

Alpha-2 Receptor On pre- Synaptic membrane

When neurotransmitter Is released there is a build up in the cleft (C). If lots of NA has been produced, the chances of accumulation at (C) Increases - some NA float in to an ά-2receptor. NA release is then switched off

C

1

2 Alpha-2 activated- NA vesicles remain closed

NA vesicle = NA

Drugs that interfere with release of noradrenalin by blocking the pre synaptic self regulating adreno- receptor (alpha2) – reduces blood pressure – Drug name – Clonidine see next slide for A2 receptor

•  Acepromazine (ACP) is often given as a sedative and an anti-emetic prior to surgery in veterinary practices •  When used for its correct purpose in the veterinary context, it is an effective and safe drug

•  ACP blocks dopamine receptors in the brain thus reducing awareness

•  ACP also blocks the muscurinic receptors (but to a lesser extent) thus there is some reduction of parasympathetic function

Acepromazine (ACP)

When should ACP not be used? - Illegal supply by 'non-vets' for use as a tranquilliser to make aggressive animals easier to handle during shows - The aim is to make the animal behave better and more predictably

- ACP is likely to increase unpredictability

ACP – behaviour modification

•  ACP will make the animal dopey or lethargic but not relaxed. •  The animals decision making processes are blunted •  They may react slowly at first, but impulsively and inappropriately •  Some dogs that have had ACP can become 'disinhibited' so they can actually become more aggressive.

Problems with ACP




Important considerations in long travel: •  ACP affects the animal's ability to regulate its body temperature. •  They need to be kept at a safe temperature and should be checked regularly to make sure they are getting neither too hot or too cold

ACP also used to reduce travel problems.

Summary -  Synapses -  Neurotransmitters -  Action potentials and post synaptic action

potentials -  Targets and effects of drugs

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Physiological Basis of Animal Behaviour - MyPlayer · Physiological Basis of Animal Behaviour ... sympathetic signals send a speed ... sedative and an anti-emetic prior to surgery