ANS - Adrenal Gland and Enteric Nervous System

What is the adrenal medulla?

• Inner part of the adrenal glands which are located on top of each kidney

What hormones does the adrenal medulla secrete?

Chromaffin cells produce…

• Noradrenaline (20%)

• Adrenaline (80%)

Why do adrenaline/noradrenaline hormones have a longer effect than neural stimulation?

• They are not degraded as quickly since they must be metabolized by the liver

• Also circulate throughout the body for a longer period of time while neurotransmitters are rapidly broken down or reabsorbed

Adrenaline generally has the same effects as _______ but greater effects at the __ Receptors, causing…

noradrenaline, B

• Increased effect on heart rate

• Smaller effect on vasculature in muscle

• Has 5-10x the affect on metabolism (can double metabolic rate), compared to NA

What is tone? Do the PNS and SNS express it?

constant low-level activity or the baseline state of the system

• Yes, both divisions of the ANS are continually active

Does the adrenal gland show tone?

• Yes, there is continous low-level secretions of hormones like adrenaline / NA

• It is important because this maintains a baseline level of readiness, preparing the body for quick responses and stressors

Why does the ANS have low frequency stimulation and why does skeletal muscle have high frequency stimulation?

ANS

• AP sent at 1-20 a second, signals are sent at a slower rate which results in prolonged effects on target organs, does not require rapid changes, instead low, steady influence

Skeletal

• 50 - 500 AP per second, indicates motor neurons fire repeatedly and rapidly to produce strong, quick contractions in the skeletal muscle, allowing precise movements and bursts of activity

Why might the nervous system engage in co-transmission, what is it and how might it increase efficiency?

• Single neuron releases multiple NTs simultaneously

• Such as non-peptides, peptides and ATP

• Results in longer and larger responses than if we did not have ATP or the other NTs

• Enables enhanced signaling

What are some autonomic reflexes?

1.) Cardiovascular (several reflexes)

2.) Baroreceptor reflex

• Pressure, monitored by receptors in major arteries, sends signals to brainstem which changes sympathetic impulses to the heart and blood vessels, affecting HR or dilation of vessels

• Helps maintain BP

3.) Bladder reflex - stretch - impulses to sacral cord contraction of bladder and relaxation of sphincter

4.) Sexual Reflex - physiological and physical stimulation

• Activation of parasympathetic NS - erection

• Stimulation of the glans penis - activation of sympathetic NS - ejaculation

What is the enteric nervous system?

• System of neurons contained within the gut, beginning at the oesophagus and ending at the anus

• Controls the gastrointestinal function but also influences movement and secretion

• Contains 100 million neurons (The same as the spinal cord)

What is the structure of the ENS? (outside —> inside)

What role does each structure have?

Longitudinal Muscle

• Runs along length of intestine, aids in peristalsis, contraction shortens it

Myenteric Plexus

• Located between longitudinal and circular muscle layers

  • Controls tonic contraction of gut wall

  • Intensity of the rhythmical contractions

  • Rate of rhythmical contractions via the pacemaker cell

  • Speed of peristaltic waves

  • Alters the sphincters

Circular Muscle

• Encircles the intestine, contraction narrows the lumen, helping mix and propel contents

Submucosal Plexus

• Has more local functions to regulate:

  • Absorption and secretion

Epithelium + Brush border layer

• Forming outside of the lumen of GI tract

Throughout: Sensory Neurons

• Take information from all throughout the GI tract, sending signals to myenteric and submucosal plexuses

• Takes info to prevertebral ganglia, spinal cord and brain stem

How does the ENS interact with sympathetic and parasympathetic nervous systems?

Sympathetic

• Generally functions to inhibit GI activity

• Cell bodies of post-ganglionic cells terminate on GI smooth muscle and enteric NS

Parasympathetic

• Stimulates GI function

• Post-ganglionic fibers incorporated into myenteric and submucosal

What is notable about the NTs in the ENS?

• Lots of NTs but the specific functions of all are not known

What are three types of Enteric reflexes?

1.) Within the Enteric

• GI secretions and paristalsis

2.) GI / Prevertebral / GI

• Gastrocholic Reflex - Signal from stomach causes evacuation of the colon

• Enterogastric - Signal from the colon and small intestine to exhibit stomach motility and secretion

3.) GI / Spinal Cord - Brain Stem / GI

• Control of gastric motor and secretory activity via signals generates in the stomach and duodenum

• Pain reflexes - inhibit entire tract

• Defecation reflexes