AUTONOMIC NERVOUS SYSTEM

NERVOUS SYSTEM DIAGRAM

Nervous System

• Central Nervous System

• Peripheral Nervous System

  • Somatic Nervous System

  • Autonomic Nervous System

PARASYMPATHETIC SYSTEM

• rest and digest

• deaccelerate

• motor neurons in brain stem and sacral area of spinal cord

• ganglia close to innervated organ

• long post-synaptic ganglion axons

• short pre-synaptic ganglion axons

SYMPATHETIC SYSTEM

• fight or flight

• accelerate

• motor neurons in lumbar and thoracic area of spinal cord

• ganglia close to spinal cord

• long pre-synaptic ganglion axons

• short post-synaptic ganglion axons

SYMPATHTIC SYSTEM CHARACTERISTICS

• pupil dilation

• increase heart rate and contraction

• blood vessel constriction

• increase sweat secretion

• airway dilation

• decrease motility

• decreased bladder and GI activity

• adrenaline and noradrenaline secretion

PARASYMPATHETIC SYSTEM CHARACTERISTICS

• constriction of pupils

• decrease heart rate and contraction

• airway constriction

• increase motility

• blood vessel dilation

• bladder emptying

• insulin and glucagon increase

AUTONOMIC GANGLIA

Are a cluster of nerve cell bodies that bridge the central motor neurons and the effector organs.

CNS → Autonomic ganglia via pre-ganglionic fibres

Autonomic ganglia → Effector organs via post-ganglionic fibres

AUTONOMIC GANGLIA PATHWAY

1. Stimulus

2. Receptor in viscera (internal organ)

3. Visceral sensory neuron

4. Integration center

5. Motor neuron (pre or post-ganglionic neuron)

6. Visceral effector

7. Response

AXON TERMINALS

Axon terminals or ‘boutons’ are found at the terminal ends of axons where synapses occur with other neurons/cells.

SYMPATHETIC VARISCOCITIES

Variscocities = ‘string of beads’ where post-ganglionic axons terminate on the effector organ.

Two types of smooth visceral muscles:

• Single-unit smooth muscle cells

• Muli-unit smooth muscle cells

SINGLE UNIT SMOOTH MUSCLE CELLS

• Line walls of GI tract

• gap junctions

• enable electrical signals to be propagated to adjacent cells

  • results in synchronised depolarisation and contraction as a single unit

MULTI-UNIT SMOOTH MUSCLE CELLS

• in your eye

• each cell must be individually innervated

GANGLION CELL INNERVATION

1. Boutons release ACh which activates nicotonic ganglionic receptors

2. These are ion channels that result in post-synaptic potential

3. The potential activates the ganglia

4. Ganglia sends signals via post-synaptic fibres to effector organ

5. Smooth muscle cells activated by varicosities

CHOLINERGIC SIGNALS

1. Choline pumped into post-ganglionic nerve endings

2. Choline converted to ACh

3. ACh stored in vesicles

4. When nerve terminal stimulated by AP, calcium enters terminal

5. Calcium causes vesicle to move towards pre-synaptic membrane

6. Fusion, neurotransmitters released into synaptic cleft

7. Neurotransmitters act on ACh receptors = response

8. ACh also prohibits further release

MUSCARINIC CHOLINERGIC RECEPTORS

• G-protein coupled receptors

• M1 - CNS

• M2 - Cardiac muscle

• M3 - GI tract smooth muscle

• Stimulated by ACh

• Stimulates/inhibits function of target cell

NICOTONIC CHOLINERGIC RECEPTORS

• Ligand gated ion channels

• N1 - Skeletal muscle

  • cholinergic signalling in neuromuscular junction

• N1 - Neuronal

  • cholinergic signalling in the CNS

• Stimulated by ACh or nicotine

• Causes rapid depolarisation of cell

ADRENERGIC RECEPTORS

1. Tyrosine enters post-ganglionic terminal

2. Tyrosine converted to dopamine

3. Dopamine converted to noradrenaline

4. Noradrenaline stored in vesicles

5. When activated by AP, calcium enters terminal

6. Calcium causes vesicle to synpase on pre-synpatic membrane

7. Transmitters released into synaptic cleft

8. Transmitter acts on alpha and beta receptors

9. Negative feedback prohibits further release

ALPHA RECEPTORS

• A1 - GI tract

  • vasoconstriction

• A2 - CNS

  • Auto-inhibition

• Greater affinity for noradrenaline

• G-protein coupled receptors

BETA RECEPTORS

• B1 - Cardiac muscle cells

  • increased cardiac muscle contractility

• B2 - Muscle blood vessels

  • vasodilation and bronchodilation

• greater affinity for adrenaline

• G-protein coupled receptors

PRE-GANGLIONIC FIBRES (PARASYMPATHETIC + SYMPATHETIC)

• release ACh

• acts on nicotonic receptors located on post-ganglionic neurons at ganglion

POST-GANGLIONIC FIBRES (PARASYMPATHETIC)

• Parasympathetic varicosities release ACh onto muscarinic receptors on post-synaptic target organs

• M2 receptors are activated by ACh release during parasympathetic activation.

POST-GANGLIONIC FIBRES (SYMPATHETIC)

• Acts primarily by releasing adrenaline/noradrenaline to act on adrenergic receptors

• ATP can be co-released to activate post-synaptic voltage gated calcium channels (faster smooth muscle contraction)

• Can act through cholinergic pathways on certain organs and dopaminergic pathways in renal system

• Has a neuroendocrine component.