Week 6 Bioscience Flashcards
Dual innervation
- 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
Sympathetic function
Prepares the body for heightened activity, i.e. exercise, excitement, emergency, embarrassment
→ fight-or-flight
Parasympathetic function
Stimulates abdominal visceral activity, conserves energy - rest and digest
Somatic vs autonomic nervous systems
- 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)
Parasympathetic division
- 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
Sympathetic division
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
Neurotransmitters
- Preganglionic neurons - release ACh
- Postganglionic neurons:
- Sympathetic - release NA
- Parasympathetic - release ACh
Neurotransmitter receptors
- 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)
Cholinergic receptors bind Ach
- 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
Adrenergic receptors bind NA and A
- Two major subtypes of adrenergic receptors
1. Alpha (a; subtypes a1, a2)
2. Beta (b; subtypes b1, b2, b3)
Neurotransmitters
- 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
Biogenic amines
- 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
Amino acids
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
Neuropeptides
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
