WEEK SIX - AUTONOMIC NS ANATOMY/PHYSIOLOGY Flashcards
List differences between the autonomic (ANS) and somatic nervous system
ANS
effectors: smooth muscles, cardiac muscles, glands
control: involuntary
visceral organs and blood vessels [therefore regulate all body systems]
efferent pathways: two nerve fibers from CNS, synapse at ganglia
neurotransmitters: ACh and norenepinephrine
neuron has cell body in grey matter of dorsal horn
SNS
effectors: skeletal muscle
controls: voluntary
efferent pathways: one nerve from CNS directs to target cell
neurotransmitter - acetycholine [ACh]
neuron has cell body in grey matter of ventral horn
List & describe 2 structural differences between the 2 divisions of the ANS
- sympathetic nervous system [flight or fight]
shorter preganglionic, longer postganglionic neurons
origin of preganglionic fibre = lumbar and thoracic regions of spinal cord - parasympathetic nervous system [rest and digest]
longer preganglionic neuron, shorter postganglionic
origin of preganglionic fibre = craniosacral levels
Describe the general properties of visceral reflexes and give an example
- receptors
- afferent signals [sensory signals to CNS]
- integration centre [interneurons in CNS connect sensory –> motor neuron
- efferent neurons [motor signals –> effectors]
- effectors [glands, smooth/cardiac muscle]
example : high blood pressure
1. baroreceptor detects increase blood pressure
2. afferent neuron - glossopharyngeal nerve transmits signal –> medulla oblongata [integration centre]
3. efferent signal = vagus nerve transmits inhibitory signals to cardiac pacemaker
4. heart rate decreases = decrease in blood pressure
Describe 3 nerve fibre pathways of the sympathetic nervous system (SNS)
- pregang fibres enter ganglia, synapse onto postgang cell without travelling up/down sympathetic chain. postgang fibre exits spinal nerve at same level
- pregang fibre travels to higher/lower ganglia and synapses at different spinal level. postgang fibre exits through spinal nerve
- pregang fibres pass through sympathtic chain without synapsing, reaches collateral ganglia via splanchcic nerves where synapse occurs on postgang fibre near target organ
Describe the relationship between the adrenal glands and the SNS
paired glands sit on superior pole of each kidney
cortex [outer layer]
- secretes steroid hormones
medulla [inner core]
- secretes neurohormones into blood
- catecholamines 85% epinephrine 15% norepinephrine
Describe the nerve fibre pathways of the parasympathetic nervous system
origin = pons and medulla and sacral region of spinal cord
synapse in ganglia next to or within organs innervation [terminal ganglia]
travel within cranial nerves = form pelvic splanchnic nerves
sacral parasympathetic fibres inner LOWER half of intestine, rectum urinary and reproductive system
no parasympathic innervation of blood vessels, sweat glands and arrector pili muscle. [these structure only receive innervation by SNS - not dual innervation
State which cranial nerves carry parasympathetic nerve fibres & describe their actions
oculomotor nerve [CNIII]
- narrow pupil and focuses lens
facial nerve [CNVII]
- nasal and salivary glands
glossopharyngeal nerve [CNIX]
- parotid salivary gland
vagus nerve [CNX]
- major parasympathetic innervation to thoracic and abdominal viscera
- cardiac, pulmonary nad oesophageal plexus
Describe the enteric nervous system & explain its significance
nervous system of digestive gut
composed of 100 million neurons - found in walls of digestive tract
has own reflex arcs [persitalsis] - can operate without input of parasym/sym NS
regulates motility of viscera and secretion of digestive enzymes
State 5 actions of the sympathetic nervous system
increase heart rate
increase pulmonary airflow [bronchodilation]
redirect blood to vital areas eg muscles and lungs
inhibit digestive system
increase metabolism
State 5 actions of the parasympathetic nervous system
decrease HR
decrease in pulmonary airflow [bronchoconstriction]
penile erection
increased peristalsis and digestive enzyme activity
increased glandular secretion
Name the neurotransmitters used at the different ANS synapses
sympathetic
pre: ACh
post: mostly norepinephrine, some ACh
parasympathetic
pre + post = ACh
Name the receptors for these neurotransmitters & explain their autonomic effects
adrenergic - binds with epinephrine and norepinephrine
two main types - alpha [excitatory] and beta [inhibitory] receptors
cholinergic - binds with acetylcholine
two types - nicotinic receptors [excitatory]and muscarinic receptors [excitatory/inhibitory]
Explain how the ANS controls many target organs using dual innervation and give an example
most visceral organs receive both S and PS innervation but both divisions do not innervate equally
effects can be antagonistic = dual innervation
eg dual innervation of iris
sympathetic stimulation of radial muscles = pupils dilate
parasympathetic stimulation or circular muscles = pupils constrict
Explain how ANS control is exerted in the absence of dual innervation and give an example
some effectors receive only S input and NO PS input eg sweat glands, blood glands
regulated by frequency of AP
- baseline firing frequency, changes determine responses
- increase in frequency = vasoconstriction
- decrease in firing frequency = vasodilation
can allow for vasoconstriction of blood vessells to minimise bleeding from injury [vasomotor tone - partial constriction of blood vessel]
can allow prioritisation of blood flow to heart and muscles in emergency
Describe how the ANS is influenced by the central nervous system
ANS = regulated by several levels of CNS
cerebral cortex = emotional and sensory experiences
hypothalamus = major visceral motor cortex centre, nuclei for hunger, thirst, thermoregulation, sex drive
midbrain, pons, oblongata
nuclei for cardiac and vasomotor control
spinal cord reflexes
defecation and micturition reflexes
