7 - The autonomic nervous system - general organisation, autonomic nerve centres, ganglia, transmitters and receptors

sections

what is ans

general organisation of ans

two major subdivisions of ans

the two major ganglia

talk about post and preganglionic neuron

ans ganglia

important points baout fibres

ans receptor

cholinergic receptor

adrenergic receptor

what is ans

• Is a part of the nervous system that controls most of the visceral functions in the body.

• Involved in control many activities including heart =GI motility, smooth muscle of urinary bladder

general organisation of ans

Activated mainly by centres in the:

1) spinal cord

2) brain stem

3) hypothalamus

two major subdivisions of ans

• Sympathetic- fight or flight

• Parasympathetic- rest and digest

the two major ganglia

• sympathetic ganglia

• parasympathetic ganglia

1. Dorsal Root Ganglia - contains cell bodies of sensory neurons. The axons of dorsal root ganglia = afferents

2. Sympathetic Ganglia- deliver info to the body about stress -fight or-flight response

3. Parasympathetic Ganglia are the autonomic ganglia of the parasympathetic nervous system.

talk about post and preganglionic neuron

• First neuron preganglionic neuron.

• Its cell body sits in the CNS and its axon usually extends to a ganglion somewhere else in the body where it synapses with the dendrites of the second neuron in the chain.

• Second neuron is referred to as the postganglionic neuron. The axons of preganglionic parasympathetic neurons are usually long.

ans nerve fiber secretions

• Cholinergic and adrenergic fibres and Neurotransmitters

• The ANS nerve fibres can either secrete acetylcholine (Ach) or norepinephrine.

• Cholinergic fibres: secrete acetylcholine

• Adrenergic fibres: secrete norepinephrine (NE)-98% or epinephrine -2%(E).

important points about fibres

1. All preganglionic fibres are cholinergic in both the sympathetic and parasympathetic nervous systems

2. Most of the postganglionic neurones of the SYMPATHETIC system are adrenergic

3. Almost all of the postganglionic neurones of the PARASYMPATHETIC system are also cholinergic.

ans receptor

The neurotransmitters must bind to specific receptors on the effector cells.

Transmitter → binds to receptor → causes conformational change in the structure of the protein molecule → this can now either excite or inhibit the cell

cholinergic receptor

Ach activates two types of receptors:

1. Nicotinic:

   • always excitatory

   • Are ligand gated ion channel in autonomic ganglia at synapses between all preganglionic and postganglionic neurones of both sympathetic and parasympathetic nervous system.

2. Muscarinic:

   • uses G proteins as their signalling mechanism

   • M1- M5

   • found on all effector cells that are stimulated by the postganglionic cholinergic neurons of either parasympathetic or sympathetic nervous system

adrenergic receptor

Two major classes:

1. Alpha:

   • alpha 1 and alpha 2, which are linked to different G proteins.

2. Beta:

   • Beta 1-excitatory

   • beta 2-inhibt

   • beta 3

   • they are all linked to different G proteins