07 - Neurophysiology and behaviour

Synaptic transmission

Synaptic transmission is the process by which neurons communicate, using chemical messengers (neurotransmitters) to transmit signals across a small gap, the synaptic cleft, from a presynaptic neuron to a postsynaptic neuron.

Synaptic transmission - chemical

• Signal uses neurotransmitters

• Small gap = synaptic cleft

• Slower than electrical synapses

• Unidirectional (pre → post)

• Highly modifiable (learning, drugs, etc.)

Synaptic transmission - electrical

• Direct connection via gap junctions

• Ions flow directly between cells

• Very fast

• Bidirectional (can go both ways)

• No neurotransmitters involved

• Less flexible (no modulation)

Events in chemical synaptic transmission

1. Action potential arrives

   • Reaches presynaptic terminal

2. Voltage-gated Ca²⁺ channels open

   • Ca²⁺ enters neuron

3. Neurotransmitter release

   • Vesicles fuse with membrane

   • Neurotransmitter released into synaptic cleft (exocytosis)

4. Neurotransmitter binds receptors

   • On postsynaptic membrane

5. Ion channels open

   • Causes:

     • Depolarization (EPSP) or

     • Hyperpolarization (IPSP)

6. Neurotransmitter removed by:

   • Reuptake

   • Enzymatic breakdown

   • Diffusion

Examples of neural control of simple behaviours

The reflex arc

Central pattern generator

Synaptic plasticity

The reflex arc

stereotyped behaviour (you cna predict whats going to happen ) to a distinct stimulus (withdrawal reflex (putting your hands on oven and putting it away away), knee jerk in humans, tail flick in crayfish, startle response is cockroaches)

Central pattern generator

controls rhythmic behaviours (breathing, walking, flying, suckling)

Synaptic plasticity

changes in synaptic strength over time (learning and memory)

The reflex arc

Types of Central Pattern Generators

Cellular oscillator

Network oscillator

Cellular oscillator

• more simpler

• Generates temporally patterned activity by itself

• 2 types

  • Oscillating and generating impuleses

    • Driven by one cell that creates a regular rhythm (A).

    • This cell depolarizes fully, generating action potentials at consistent intervals.

    • Example: Typical sinoatrial (SA) node cells in the heart.

  • oscilliation without impulses

    • Also driven by one cell, but it never depolarizes fully to generate an action potential (B).

    • The membrane oscillates but remains subthreshold, producing no impulses on its own.

    • Can influence other cells that do generate impulses when coupled electrically.

Network oscillator

• A network of neurons that interact

• much more stable, find them throughout

• half centre model of an oscillatory network

• closed-loop model of an oscillatory network (most common)

• half centre model of an oscillatory network

>two neurons received excitatory Signal at the same time from another neuron

>one of them is abit quicker to respond to this

>one fires AP + inhibits other neuron

>after Ap is Fired → inhibition is released

> other Neurons then fires

> as soon as exitory stimmas stops where network stops = unstable

• closed-loop model of an oscillatory network (most common)

> closed loop cuz once you have exitation pattern can continue

> 1 quicker to respond + iinhibit 3 → can't inhib 2 → 2 fires → inhibs 1 → 3 not ihibited

> 3 fires

>loopContinue

An example of a CPG (crustacean digestion)

Central pattern generators in the spinal cord (salamander )

main idea: can get complicated, we don't just have where multiple are interacting with each other

oscillator symbol

what is this diagram abt

Several central pattern generators can interact (e.g. breathing in humans)