Physiology: Autonomic Nervous system

Neurons - Sympathetic vs parasympathetic

Sympathetic:

• preganglionic nerves are typically short while postganglionic nerves are relatively long

Parasympathetic:

• preganglionic nerves are relatively long with short postganglionic nerves

Autonomic neurotransmitters - nerves

Preganglionic nerves: acetylcholine (cholinergic)

Postganglionic sympathetic: noradrenaline (adrenergic)

Postganglionic parasympathetic: acetylcholine (cholinergic)

Somatic Neurotransmitter

• Somatic neurons activate skeletal muscle

• Activated by a cholinergic pathways

Sympathetic activation: adrenal gland

• Exception: No postganglionic neuron

• Preganglionic nerve releases acetylcholine

• Stimulates chromaffin cell to release noradrenaline (20%) (norepinephrine) and adrenaline (80%) (epinephrine)

Sympathetic activation: sweat glands

• sweat glands in the skin use acetylcholine at the ganglion and at the receptor cell.

Sympathetic - Adrenergic receptors: Alpha 1

• Tissue: Vascular smooth muscle (most)

• Effect: Stimulation - contraction

• Affinity: Higher in noradrenaline than adrenaline

Sympathetic - Adrenergic receptor - Alpha 2

• Tissue: Endocrine - pancreas

• Effect: inhibitory - reduced insulin release

• Affinity: Higher noradrenaline than adrenaline

Sympathetic - Adrenergic receptor - Beta 1

• Tissue: Heart

• Effect: Stimulation - increased force and rate of

• Affinity: Equal noradrenaline and adrenaline

Sympathetic - Adrenergic receptor - Beta 2

• Tissue: Airway smooth muscle and some vascular

• Effect: Inhibitory - relaxation (vasodilation)

• Affinity: A lot higher in adrenaline than noradrenaline

Adrenaline

• EFFECTS ARE DOES DEPENDANT

• At low doses, adrenaline attach to high affinity b2: vasodilation

• At high doses, adrenaline will attach to the abundant a1 receptors: vasoconstriction

Acetylcholine

• Nicotinic receptors: located on the postgangioliv cell body of autonomic nerves and skeletal muscle in the somatic division

• Target cells expression muscarinic receptors

Endocrine vs Exocrine

Endocrine:

• No ducts

• Hormones

• Bloodstream

Exocrine

• ducts

• Sweat/mucus

• Internal or external body surface

Intercellular receptors vs extracellular receptors

extracellular receptor: Peptide/Protein hormones (lipophobic)

Intracellular receptor: Steroid hormones (pass through the membrane and lipophilic)

Posterior Pituitary

• Hormones produced by hypothalamus but stored in posterior pituitary. (Vasopressin or antidiuretic)

• Neuron cell bodies originate in the hypothalamus but terminate in a ‘capillary blood supply’

Posteriori Pituitary: Vasopressin and oxytocin

• These hormones conserves water in the kidney

• Oxytocin acts on the breast and uterus - lactation and uterine contraction during childbirth.

Anterior pituitary

• releases (mostly) tropic hormones

• No neural connection with the hypothalamus

• Synthesises its own hormones

• TSH, ACTH, Growth hormone, LH/FSH, Prolactin

Anterior pituitary Hormones: TSH, ACTH, GH and LH/FSH

• TSH: Targets thyroid gland, secondary hormone thyroid hormone, effect: Increased metabolic rate

• ACTH: Targets adrenal cortex, secondary hormone cortisol, effect: involved in stress response.

• GH: Targets skeletal muscle, live and adipose tissue, secondary hormone insulin growth factor 1, effect: growth and metabolism

• LH/FSH: Gonads, secondary hormone: sex hormone secretions, effect: Gamete production (ova/sperm)

Negative feedback

• Puts a break on the hormone release

• Moves a physiological change in the opposite direction

• Without negative feedback hormone levels rise above physiological needs leading to complications.

Positive feedback

• amplifies a physiological change, eg. change produces more change

• Less common than negative feedback

Cortisol

• increase in blood glucose

• Prevents the uptake of glucose by other tissues, and stimulates glconeogenesis

• Stress hormone

• ATCH - released by anterior pituitary, which stimulates the release of cortisol by the adrenals cortex