The neurone and synapse

Practical Box 21.1 Five-part short neurological examination

Looking at the patient General demeanour Speech Gait Arm swinging Examining the head Fundi Pupils Eye movements Facial movements Tongue Examining the upper limbs Posture of outstretched arms Wasting, fasciculation Power, tone Coordination Reflexes Examining the lower limbs Power (hip flexion, ankle dorsiflexion) Tone Reflexes Plantar responses Assessing sensation Ask the patient

The neurone is the functional unit of the nervous system. Its cell body and axon terminate in a synapse. The specificity, size and type of each group of neurones vary. A single α-motor neurone within an anterior horn of the thoracic spinal cord has an axonal length over 1 metre and innervates between several hundred and 2000 muscle fibres in one leg – a motor unit. By contrast, some spinal or intracerebral internuncial neurones have axons under 100μm long, terminating solely on one neuronal cell body.

Neurotransmitters

Synaptic transmission is mediated by neurotransmitters released by action potentials passing down an axon. Neurotransmitters then react with postsynaptic receptors and are removed by transporter proteins. The neurotransmitter-receptor reaction increases ionic permeability and propagates a further action potential. This combination of axonal electrical activity and synaptic chemical release is the basis of all neurological function.

Neurotransmitters include acetylcholine, norepinephrine (noradrenaline), epinephrine (adrenaline), 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA), opioid peptides, prostaglandins, histamine, dopamine, glutamate, nitric oxide, neuromelanin and vasoactive intestinal peptide (VIP). Of these, glutamate is the principal excitatory neurotransmitter.

The role of neurotransmitters and transporters in pathogenesis continues to be evaluated, but it is thought that a wide variety of acute and chronic neurological disease is mediated by a final common pathway of neuronal injury involving excessive stimulation of glutamate receptors.

1 Comment »

1. [...] is increasingly being used with or without Arguireline (the brand name for acetyl=hexapeptide 3) …Health Nova: Your Ultimate Medical Portal Functional …… facial movements, functional unit of the nervous system, gamma aminobutyric acid, hip flexion, [...]

   Pingback by gamma amino butyric acid — March 24, 2010 @ 7:56 pm

RSS feed for comments on this post. TrackBack URL

Leave a comment

Name (required)

Mail (will not be published) (required)

Website