Physiology 2042 Body Systems
Autonomic Nervous System
Terminology
Ganglion (Ganglia): A mass of nerve cell bodies
Synapse: A minute gap between two nerve cells across which impulses pass by diffusion of transmitter Afferent: Carry messages towards the CNS
Efferent: Carry messages away from the CNS Peripheral Nervous System
Somatic Nervous System
- 1 motor neuron from spinal cord to target tissue Autonomic Nervous System
- 2 neurons at a pre-ganglion and post ganglion - Ganglion separates the two neurons
- Activity of an organ results from sympathetic speeding up and parasympathetic slowing down Parasympathetic Division
- Long pre-ganglionic neurons - Short post-ganglionic neurons
- Arises from the brain and spinal cord Sympathetic Division
- Short pre-ganglionic neurons - Long post-ganglionic neurons - Arises from the spinal cord
- Adrenal gland directly innervated by sympathetic pre-ganglionic neurons
Neurotransmitters Somatic Nervous System
- ACh released between the pre- and post-ganglionic neurons
- Noradrenaline released between the post ganglionic neuron and effector cell
Peripheral Nervous System
- ACh released between the pre-and post-ganglionic neurons
- ACh is also released between the post ganglionic neurons and effector cell
Neurotransmitter Receptors Ionotropic Receptors
Form an ionic channel pore through binding of the neurotransmitter to receptor results in the opening of the ion channel
Nicotinic Receptors
- ACh binds and causes a change in skeletal muscle Metabotropic
Indirectly linked with ion channels (G-protein coupled receptors, tyrosine kinases, guanylyl cyclase) by binding of the
neurotransmitter to receptor activates G-protein Muscarinic Receptors
- ACh binds to receptor and activates a G-protein
How Ionotropic Receptors Activated?
Neurotransmitter within ganglia:
Acetylcholine: Acts on nicotinic receptors on post-ganglion neurons Nicotinic Receptors: Activated by binding of the neurotransmitter
How are Metabotropic Receptors Activated?
Neurotransmitter within Ganglia
ACh acts on muscarinic receptors on post ganglion neurons Neuron-to-Effector Transmission
- Parasympathetic NS: ACh on Muscarinic Receptors
- Sympathetic NS: Usually Noradrenaline on alpha ans beta receptors Muscarinic Receptors
Activated by binding of the neurotransmitters ACh
Adrenal Gland
- Neuroendocrine Organ
- Cells in the adrenal medulla secrete hormones into the blood stream when activated by sympathetic pre-ganglionic neurons
- Adrenal cortex is a true endocrine gland
- Adrenal medulla is a modified sympathetic ganglion Functions of the Adrenal Glands
- Adrenal medulla is composed of chromaffin cells
- Consists of cells that secrete adrenaline (epinephrine) and noradrenaline (norepinephrine) - This is in response to stimulation by sympathetic pre-ganglionic neurons
- Cells in the adrenal medulla are modified postganglionic neurons
Adrenaline
- Acts on Alpha and Beta adrenoceptors on target tissues - Particularly Beta1 Adrenoceptors on heart to increase rate and
force of contraction Fight or Flight
Heart
- B1 Adrenoceptors
- Decrease conduction time through AV node - Increase discharge rate of SA node
- Increase contractility of cardiac muscle - Force and Rate of Contraction Increases
- cAMP is produced from ATP and causes Ca2+ from SR, and causes contraction
Coronary Arteries - B2 adrenoceptors - Vasodilation
- Increased blood flow to the heart muscle
- cAMP and Ca2+ causes relaxation when Adrenaline and Noradrenaline acts on B2 receptors
