The Autonomic Nervous System Flashcards
What is the function of the ANS?
Ensures survival despite lack of conscious, cortical input
Largely outside of voluntary control
Receives sensory information about the state of the body and makes required changes to maintain steady state
Which nerves go from periphery to CNS?
Afferent
Which nerves go from CNS to periphery?
Efferent?
What are the effectors of the somatic nervous system?
Skeletal muscles
What are the effectors of the ANS?
Smooth muscle (e.g. GI tract lining), Cardiac muscle, Glands
What feeds into the CNS for the ANS?
Visceral nerves - brings signals about things being monitored in the body
What are the two efferent ANS pathways?
Sympathetic - Fight or flight
Parasympathetic -
When is the sympathetic pathway activated?
Exercise, excitement, emergency, embarrassment
Where is the parasympathetic pathway activated?
Coordinated, whole body response
or
Discrete and organ specific
When is the parasympathetic pathway activated?
Digestion, defecation, diuresis
Where is the parasympathetic pathway activated?
Discrete and organ specific
What happens to the body during sympathetic stimulation?
Eye - Pupils dilate
Heart - increase HR
Lungs - dilation of bronchioles
Liver - synthesise and release more glucose for energy substrate
What are the discrete functions of sympathetic stimulation?
- Reproductive system
- Preventing urination - allows relaxation of bladder smooth muscle
What happens to the body during parasympathetic stimulation?
Eyes - pupil constriction
Heart - decrease HR
GI tract - allows secretion
Bladder - allows urination - contraction of bladder wall and relaxation of urinary sphincter
Reproductive - vasodilation for more blood flow
How do the sympathetic and parasympathetic systems work together?
- Generally innervate the same tissues but have opposing effects
- Antagonistic to one another but work synergistically to make change
- Allows rapid and precise control
What is the general organisation of the ANS?
(Both sympathetic and parasympathetic)
- Preganglionic neuron in brain or spinal cord synapses with post ganglionic neuron in peripheral ganglion - synapses with target cell
What is the structure of Preganglionic neurones?
- Pre ganglionic fibre in CNS
- Synapse with postganglionic neurone within a ganglion
Explain neurotransmission in preganglionic neurones
- Are always cholinergic fibres - release ACh as primary NT
- ACh activates nicotinic ACh receptors on post synaptic cell
What is the structure of sympathetic neurones?
- Short, cholinergic preganglionic neurones from thoracic and lumbar spinal cord
- Long, adrenergic postganglionic neurones
Which receptors are expressed at sympathetic target tissue synapses?
Target tissue expresses alpha and beta adrenergic receptors (GPCR)
What NT is release from postganglionic sympathetic neurones?
Norepinephrine
- Crosses synaptic cleft and activates alpha and beta adrenergic GPCRs
What is an exception to the anatomical organisation?
Adrenal medulla
- Chromaffin cells (function similar to postganglionic neurones) release adrenaline into blood vessels
- Target tissues express alpha and beta adrenergic receptors
- Allows coordinated, widespread sympathetic activity
What is the structure of parasympathetic neurones?
- Long, cholinergic preganglionic neurones from brainstem and sacral spinal cord
- Short, cholinergic postganglionic neurons
Which receptors are expressed at parasympathetic target tissue synapses?
Muscarinic ACh receptors (GPCR)
What NT is released from parasympathetic postganglionic neurones?
Acetylcholine
What is the vagus nerve?
Cranial nerve from the brain
Carries 80% of total parasympathetic outflow
Carries visceral afferents
What are the central components of the ANS?
Spinal cord
- Mediates autonomic reflexes
- Receives sensory afferent and brainstem input
Brainstem nuclei
- Mediates autonomic reflexes
How does the hypothalamus integrate and coordinate?
- Feeds into the autonomic nuclei
- Modulates reflex activity
- Modulates output from ANS
Used for:
- Feeding, thermoregulation, circadian rhythms, water balance, sexual drive, reproduction
What is the importance of the forebrain?
Regulates ANS output
- Has minimal conscious cortical control but cortical processes regulate autonomic output
e.g. anxiety - GI disturbance
- fear - fight or flight
How are visceral afferents important?
Sensory input from visceral afferent neurones takes priority over cortical functions
e.g. bladder distension (only hold up to certain point)
