Week 5 - Autonomic Nervous System

Question 1

Compare and contrast the two branches of Autonomic nervous system:

Answer 1

1. Sympathetic division
   a) Mobilises body systems during activity
   b) Flight or fight
   c) Promotes adjustments during exercise or when threatened
   i) Increased heart rate
   ii) Blood flow is shunted to skeletal muscles and heart
   iii) Bronchioles dilate
   iv) Liver releases glucose to make ATP
2. Parasympathetic division
   a) Conserves energy when not active
   b) Promotes maintenance activities and conserves body energy ‘rest and digest’
   i) Reduces blood pressure, heart rate, and respiration rate
   ii) Gastrointestinal tract activity is high

Question 2

Where are the preganglionic and post ganglionic neurons of sympathetic and parasympathetic nervous systems located?

Answer 2

1. Pre-ganglionic neurons
   a) Myelin
   b) Located within CNS
2. Post-ganglionic neurons
   a) No myelin
   b) Located at target
3. In sympathetic:
   a) Short preganglionic axon are in thoracolumbar section of spinal cord
   b) Long postganglionic axon in the sympathetic trunk
   c) Ganglia located close to spinal cord
4. In parasympathetic:
   a) Long preganglionic axon in craniosacral region
   b) Short post-ganglionic axon
   c) Ganglia located in/close to target organ

Question 3

What is sympathetic tone?

Answer 3

1. Sympathetic division controls blood pressure, even at rest
   a) Sympathetic tone keeps blood vessels in continual state of partial constriction
2. Sympathetic fibres fire more rapidly to constrict blood vessels and cause blood pressure to rise
3. Sympathetic fibres fire less rapidly to prompt vessels to dilate to decrease blood pressure

Question 4

What is parasympathetic tone?

Answer 4

1. Parasympathetic division normally dominates the heart and smooth muscle of digestive and urinary tract:
   a) Slows the heart via vagus nerve
   b) Dictates normal activity levels of the digestive and urinary tracts
2. Can be overridden by sympathetic division in times of stress

Question 5

Describe neurotransmitters involved in activation of sympathetic and parasympathetic nervous systems and their related receptors:

Answer 5

1. Parasympathetic:
   a) Acetylcholine - preganglionic fibres release and it acts on nicotinic receptors
   b) Acetylcholine - postganglionic fibres at nerve terminal and it acts on muscarinic receptors
2. Sympathetic:
   a) Acetylcholine - preganglionic fibres release and it acts on nicotinic receptors
   b) Noradrenaline - postganglionic fibres at nerve terminal and it acts on adrenergic receptors

Question 6

What is the difference between muscarinic and nicotinic receptors?

Answer 6

1. Muscarinic - activated molecules inside the cell to cause function
   b) Phosphorylation = signal transduction
   a) Transmembrane receptors
2. Nicotinic - ion channels that allow ions in/out of the cell
   a) Cause action potentials
3. Adrenergic
   a) Four types; alpha1 and beta1 (excitation), and alpha2 and beta2 (inhibition)

Question 7

Identify the role of brain structures involved in sympathetic and parasympathetic nervous systems:

Answer 7

1. Hypothalamus:
   a) Function:
   i) Control over basic survival strategies; reproduction, growth, metabolism, hunger, thirst, temperature control, sleep-wakefulness
   b) Effect via;
   i) Neural control - ANS
   ii) Hormone secretion - endocrine system (either direct effect or effect via a second hormone)
2. Anterior pituitary:
   a) Function:
   i) Release important hormones

Question 8

How does hypothalamus control critical systems?

Answer 8

1. Cardiovascular regulation - neural control
2. Regulation of body temperature - neural control
3. Gastrointestinal and feeding regulation - neural control
4. Regulation of body water:
   a) Control of thirst - neural control
   b) Control of excretion of water into urine - hormonal control (antidiuretic hormone)
5. Regulation of uterine contractility and milk production - hormonal control (oxytocin)
6. Control of the anterior pituitary

Question 9

How does control of hypothalamus work?

Answer 9

1. Hypothalamus releases hormone which can activate anterior pituitary
2. Anterior pituitary releases hormone which travels through blood stream to target organ
3. Target organ will secrete releasing or inhibiting hormone to hypothalamus
   a) Hormone will also cause target metabolic process on target organ

Question 10

What hormones does the anterior pituitary release?

Answer 10

1. Thyroid stimulating hormone
   a) Acts on thyroid gland
   b) Causes excretion of thyroid hormones (metabolic rate)
2. Growth hormone
   a) Acts on skeletal muscle and bone
   b) Causes growth promoting factors from liver and kidneys to grow skeletal muscle and bone
3. Adrenocorticotropic hormone
   a) Acts on adrenal cortex
   b) Causes excretion of glucocorticoids and mineralocorticoids
4. Follicle stimulating hormone and luteinising hormone
   a) Acts on gonads
   b) Causes ovum maturation and sperm differentiation; as well as secretion of oestrogen, progesterone, and testosterone

Question 11

Define what is the enteric nervous system:

Answer 11

1. A subsection of the ANS which is important in controlling the function of the digestive organs

Question 12

Explain the organisation, function, and significance of the enteric nervous system:

Answer 12

1. Organisation:
   a) Intrinsic neuronal network stretching from the upper part of the oesophagus to the rectum
   b) Organised into two interconnecting networks (layers); Submucosal (Meissner’s) plexus and Myenteric (Auerbach’s) plexus
   c) Composed of excitatory and inhibitory neurons that;
   i) Innervate smooth muscle cells
   ii) Innervate secretory and hormone releasing cells
   iii) Regulate/modify the secretory and absorptive functions of the epithelium
   d) The efferent nerves are controlled by inputs originating from intrinsic chemo and mechanoreceptors, as well as the ANS
2. Function:
   a) Control of digestive organs
3. Significance:
   a) Accommodates about 200-600 million neuros; spinal cord has about 197-222 million neurons meaning gastrointestinal tract has its own ‘spinal cord’ and holds a huge amount of automaticity

Question 13

Describe the interrelationship between the ENS and the sympathetic and parasympathetic divisions of the autonomic nervous system:

Answer 13

1. Sympathetic activity
   a) Mainly inhibitory
   i) Decreased motility (via NANC (non-adrenergic, non-cholinergic) neurotransmitters)
   ii) Decreased secretory function
   b) Some exceptions to inhibition;
   i) Saliva secretion is stimulated by sympathetic activity
   ii) Gastric HCI secretion is stimulated by sympathetic activity
   iii) Sphincters are stimulated by sympathetic activity (via alpha1 receptors)
2. Parasympathetic activity:
   a) Mainly stimulatory
   i) Increased motility
   ii) Increased secretory function
   b) An exception to stimulation;
   i) Sphincters are inhibited by parasympathetic activity

Question 14

List the most important neurotransmitters of the ENS and explain their functions:

Answer 14

1. Acetylcholine - stimulatory effect on GIT function

2. Noradrenalin (and to small degree adrenalin) mostly inhibits GIT activity

Question 15

Describe the organisation and function of local, short, long, and cephalic gastrointestinal relfexes:

Answer 15

1. Organisation:
   a) Local - each element of reflex arc is within the wall of the GI tract
   b) Short - reflex arc leaves wall of GI tract but does not reach CNS
   i) Reflex centre is located in nearby sympathetic region
   c) Long - reflex arc leaves wall of GIT and reaches CNS
   i) Reflex centre is located in spinal cord or brainstem
   d) Cephalic - begins with activation of receptors that on the head (oral cavity, eyes, ears, nose)
2. Function:
   a) Cephalic - activation of receptors evokes change of function in GI tract
   i) Increased salivation
   ii) Increased gastric juice production
   iii) Increased pancreatic juice production
   iv) Increased motility