Autonomic Nervous System Flashcards
Somatic effectors
Reflexes, actions, behaviours
Autonomic effectors
Reflexes, coordination and optimisation (tuning body to suit behaviours)
What does the autonomic nervous system control?
The ANS controls/organises physiology: blood flow, metabolism, internal organs and water balance. It manages the body to meet needs efficiently.
What are the two main patterns of physiological regulation?
Maintenance: conservation and rebuilding Action: periods of peak performance.
What parts of the CNS to preganglionic PSNS fibres leave?
The craniosacral.
What part of the CNS do preganglionic SNS fibres leave?
Thoracolumbar: T1 to L2
Actions of the sympathetic nervous system
Raises heart rate, blood pressure Relaxes and opens airways Mobilises energy stores Increases blood flow to muscles Stimulates sweating Shunts blood to heart, lungs and brain Suppresses digestion Relaxes bladder and rectum (no voiding) Also mediates sexual orgasm
Chain ganglia
A component of the sympathetic nervous system. They are highly interconnected and run the length of the spinal cord. They send postganglionic fibres in every spinal nerve, innervating sweat glands, hair erectors and blood vessels. They also innervate the heart, lungs, salivary glands and pupils via special nerves.
Collateral ganglia
There are three midline collateral ganglia, which innervate GI and urinary tracts, and genitals.
Parasympahetic nervous system
Relaxation and refuelling (rest and digest)
Lowers blood pressure (via heart rate)
Closes off airways, slows respiration
Constriction of pupils; focus on near objects
Boosts the digestive system by increasing:
- GI smooth muscle activity
- GI blood flow
- Digestive enzyme secretion
- GI hormone secretion (nutrient absorption/use)
Contracts bladder and rectum for voiding
Sexual arousal (blood flow, glandular activity)
Autonoic short reflex
Does nto involve the CNS
Autonomic long reflex
Via teh spinal cord or the brainstem
Nicotinic receptors
Autonomic receptor for acteylcholine
Ionotropic (ion channel), excitatory effect
Used by both SNS and PSNS at teh first synapse
Also used by alpha neurons
Muscarinic receptors
Autonomic acetylcholine receptors
Metabotropic (activates internal signalling)
Used by PSNS at postganglionic synapse
Also some SNS efferents to sweat glands
Noradrenal & adrenalin
Used by SNS only: postganglionic synapses, adrenal gland releases adrenaline into the blood, and tissues choose how to respond via receptors.
All receptors are metabotropic (internal signalling): alpha (vasoconstriction, GI shutdown, etc.) and beta (vasodilation, increase cardiac output, etc.)
How do all pre-ganglionics in both the PSNS and SNS activate ganglion neurons?
Using ACh onto nicotinic receptors.
What are the neurotransmitters used by post-gangionic fibres when influencing target tissues?
PSNS: ACh
SNS: A/NA
Heterotropic interactions
One neurotransmitter affects teh release of another.
E.g. heart, myenteric plexus of the GI
Homotropic interactions
Transmitter binds to presynaptic receptors on its own terminals. Self-inhibitory feedback.
SAM axis
Sympathetic-adreno-medullary: adrenaline secretion by the adrenal medulla
HPA axis
Hypothalamix-pituitary-adrenal: secretion of glucocorticoids (particularly cortisol) by teh adrenal cortex.
Cortisol
- Normally secreted at low levels.
- Essential for normal physiology.
- Elevates on waking
- Allows body to cope with stress - adrenalectomy can make stress fatal
- Glucocorticoid - affectes glucose traffic
- Gluconeogenesis in teh liver
- Catabolic rendering down of proteins and lipids
- Liberation of energy sources
- Facilitates A/NA/DA actions (e.g. vessels)
Chronic cortisol elevation
- Caused by chronic stress
- Chronic effects are often opposite to its acute effects
- Suppresses immue function - cuts down inflammation by suppressing synthesis of arachidonic acid (source of prostaglandins)
- Susceptibility to illness
- Slowed wound healing
- Hippocampal neurogenesis is impaired - memory formation disrupted
- Sleep is disrupted - less REM, more slow-wave sleep, mroe waking (may lead to insomnia)
- Strong elevation or depression of mood may occur; sexual drive reduced
- The HPA axis can become sensitised to stresses - magnifying future responses
