neurones and related cells

three main functional classes of neurone

sensory neurone, interneuron and motor neurone

this can also be sensory input (eye), integration (brain) and then motor output

a typical neurone

a neurone like this has the potential to sum incoming inputs, a form of integration or processing

a typical neurone: axonal transport

showcases how sensory inputs can be processed to therefore carry out an action

resting membrane potential

the resting membrane potential is maintained by potassium and sodium leak channels

a typical chemical synapse

a typical chemical synapse between neurones:

1. presynaptic neurones release chemical transmitters like ACh

2. these diffuse across the synaptic cleft

3. these activate post synaptic receptors on the dendrites of the post synaptic cell

4. this leads to local transient changes in membrane potential

chemically gated ion channels can detect neurotransmitters and affect resting membrane potential, as well as this, they can also attach to the receptor

neurones triggering an action potential

regenerative wave of electrical excitation can travel at different speeds from 1-2 m/s to150 m/s

voltage gated ion channels

these voltage gated ion channels detect passive changes in the membrane potential, an action potential is triggered at the axon hillock by the opening changes in the membrane potential. (examples can be sodium, calcium and potassium).

action potentials can travel long distances and the information flow is on the left side

the action potential

there are different stages of the action potential, some of these are the resting state, depolarisation etc

schwann cells

this is conduction velocity with Schwann cells and salutatory nerve conduction. the conduction velocity would depend on axon diameter and the myelination.

there is also the node of ranvier and it is good to know that the sodium channels are not evenly distributed

the presynaptic terminal (bouton)

this is another word for the chemical synapse

how does the synaptic response subside

the removal of neurotransmitters occurs in three ways

1. diffusion- this is released in the synaptic cleft and then diffuses away

2. enzymatic degradation- this is then broken down by enzymes

3. uptake by cells- this is returned to neuron (reuptake), transported to neighbouring cells

graded potential and summation

how can the membrane depolarise to threshold?

transmitters, receptors and integration

input of signals from other neurones and integration may or may not trigger the action potential. there would be a nerve conduction and this would depolarise the terminal boutons. there is also calcium dependent/ transmitters release and a calcium influx

graded potential

• local event is passive

• affects over short distance

• variable amplitude

• repolarisation is a simple decay over time and can summate

action potential

• regenerative wave is active

• affects over long distance possible

• all or nothing event - set amplitude

• repolarisation is dependent on the ion channels that can summate

electrical synapse

these are not chemical but can direct an electrical connection. the connections can bridge between cells and the functional syncytium

glial cells

there are four main neuroglia support CNS neurones, these are astrocytes, microglial cells, ependymal cells and oligodendrocytes

the two major neuroglia seen in the PNS are the Schwann cells and the satellite cells

glial cells general role

• surround and support neurones

• electrical insulation

• supply nutrients

• maintain chemical environment

• destroy / remove dead cells and pathogen

PNS glia

potential key terms

astrocytes (CNS), oligodendrocytes (CNS), ependymal cells (CNS) and microglia cells

nerve anatomy

nerve ageing: some generalities

• central - neuronal atrophy, loss of myelination, noisy processing and dopamine loss

• peripheral - declined axon transport, axonal atrophy, myelin loss and impaired regeneration