Week 6 Bioscience

Question 1

Dual innervation

Answer 1

• Most effector organs are innervated by both sympathetic and parasympathetic divisions
• ANS divisions can work independently or together
• Divisions generally have opposing effects
  
  • One division predominates in specific circumstances
• Divisions counterbalance to control organ function and maintain homeostasis

Question 2

Sympathetic function

Answer 2

Prepares the body for heightened activity, i.e. exercise, excitement, emergency, embarrassment
→ fight-or-flight

Question 3

Parasympathetic function

Answer 3

Stimulates abdominal visceral activity, conserves energy - rest and digest

Question 4

Somatic vs autonomic nervous systems

Answer 4

• Both are efferent divisions that distribute motor commands
• Differ in:
  1. Neural (efferent) pathways (i.e. from CNS to effector)
  2. Effectors (target organs)
  3. Organ response
  4. Neurotransmitters (NT)

Question 5

Parasympathetic division

Answer 5

• Also called the craniosacral division
• Preganglionic neurons arise from opposite ends of the CNS
• Brain stem - axons exit CNS via cranial nerves
• Sacral region of spinal cord (S2 – S4) - axons exit via spinal nerves (ventral root)
• Ganglia located close to, or within, the target organ
• Preganglionic axon = long
• Postganglionic axon = short

Question 6

Sympathetic division

Answer 6

Also called the thoracolumbar division
* All preganglionic fibres arise within spinal cord segments T1 - L2
* Cell bodies in motor nuclei of lateral gray horns
* Axons exit spinal cord via spinal nerves (ventral root)
* Ganglia located close to spinal cord
* Preganglionic axon = short
* Postganglionic axon = long

Question 7

Neurotransmitters

Answer 7

• Preganglionic neurons - release ACh
• Postganglionic neurons:
• Sympathetic - release NA
• Parasympathetic - release ACh

Question 8

Neurotransmitter receptors

Answer 8

• Peripheral motor neurons release either acetylcholine (ACh) or noradrenalin (NA)
• Receptors that bind acetylcholine are called cholinergic receptors (term is also used for neurons that release ACh or synapses where ACh is used)
• Receptors that bind noradrenalin (and adrenalin) are called adrenergic receptors (term is also used for neurons that release NA or synapses where NA is used)
• Receptors that bind acetylcholine are called cholinergic receptors – 2 subtypes: nicotinic and muscarinic
• Receptors that bind noradrenalin are called adrenergic receptors – 2 subtypes: a and b (also bind adrenalin)

Question 9

Cholinergic receptors bind Ach

Answer 9

• Two subtypes of cholinergic receptors (named after drugs – nicotine and muscarine)
  1. Nicotinic – always excitatory - increases target activity
  2. Muscarinic – excitatory or inhibitory - increases or decreases target activity respectively

Question 10

Adrenergic receptors bind NA and A

Answer 10

• Two major subtypes of adrenergic receptors
  1. Alpha (a; subtypes a1, a2)
  2. Beta (b; subtypes b1, b2, b3)

Question 11

Neurotransmitters

Answer 11

• NT (and electrical signals) are the language of the nervous system
• Some neurons make only 1 NT
• Most neurons make 2 or more NT
• Induce excitatory or inhibitory responses in postsynaptic membranes
• More than 50 NT identified (M&H Table 11.5)
• Many neuropsychological disorders (e.g. depression) traditionally thought to be caused by NT imbalances – this theory now questionable

Question 12

Biogenic amines

Answer 12

• Broadly distributed in the brain
• Emotional behaviour
• Regulate biological clock
• Imbalances associated with mental illness??? (no consistent evidence to support this!!)
• drugs that enhance NT release or block reuptake associated with relief of symptoms of anxiety and depression in some people

Question 13

Amino acids

Answer 13

GABA (g-aminobutyric acid)
* Main inhibitory NT in the brain
* Helps to regulate sleep/wakefulness
* Involved in motor control - helps to regulate skeletal muscle tone by dampening activity
* GABA blockers (i.e. no dampening) - convulsions
* Alcohol increases dampening effect → impaired motor coordination

Glutamate
* Involved in learning and memory
* Excessive release - excitotoxicity (kills surrounding neurons), e.g. CVA, Alzheimer’s disease

Question 14

Neuropeptides

Answer 14

Substance P
* Produced by damaged tissue
* Stimulates peripheral nociceptors
* Mediates pain transmission to the CNS

Endorphins
* Includes endorphins and enkephalins
* Inhibits perception of pain in the CNS
* Natural opiates – chemically similar to morphine (agonist) - analgaesia, sleepiness, wellbeing