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Question 1

what is the autonomic or involuntary nervous system?

Answer 1

part of the CNS that controls: internal organs, blood flow, smooth, muscles of the eye, viscera, etc

Question 2

what are the two subsystems of the ANS?

Answer 2

• sympathetic: fight or flight
• parasympathetic: rest and digest

Question 3

what two systems does the ANS work closely with? what is this important for?

Answer 3

works with endocrine and behavioural state systems to maintain homeostasis

Question 4

ANS can be divided into its ———- and ———– components

Answer 4

preganglionic and postganglionic

Question 5

preganglionic

Answer 5

• preganglionic neuron cell bodies are located in the CNS, either in the brainstem or spinal cord
• preganglionic axons project to postganglionic neurons located between the CNS and the target tissue

Question 6

postganglionic axons project to

Answer 6

the target tissue

Question 7

describe the neurotransmitters and receptors of the ANS

Answer 7

• both sympathetic and parasympathetic preganglionic neurons release acetylcholine (Ach) onto nicotinic receptors
• sympathetic postganglionic neurons secrete norepinephrine (NE) onto adrenergic receptors
• parasympathetic postganglionic neurons secrete Ach onto muscarinic receptors

Question 8

describe the structure of the sympathetic nervous system

Answer 8

• preganglionic neurons originate in the thoracolumbar spinal cord
• synapse in the sympathetic chain ganglia via short axons
• long postganglionic axons project from the sympathetic chain to effector organs

Question 9

describe the structure of the parasympathetic nervous system

Answer 9

• preganglionic neurons originate in the brainstem or sacral spinal cord
• travel via long axons to ganglia located near or within the effector organ
• short postganglionic axons project from these ganglia to the effector organs.

Question 10

describe sympathetic efferents

Answer 10

• preganglionic efferents from intermedia-lateral horn of thoracic cord synapse in the chain of ganglia parallel to the spinal cord, for which the transmitter is acetylcholine
• postganglionic efferents then project to the target tissue, for which the transmitter is noradrenaline (NA)

Question 11

what is an exception to the typical pathway of sympathetic efferents?

Answer 11

ACh is transmitter between postganglionic efferents and the target tissue at skin sweat glands

Question 12

describe sympathetic activities

Answer 12

• fight or flight response
• prepare for emergency, stress, and exercise
• increase HR and blood pressure
• mobilise energy stores
• pupillary dilation
• decrease gastrointestinal and urinary functions
• releases epinephrine

Question 13

why do sympathetic activities have such a diffuse effect?

Answer 13

due to their widespread and interconnected innervations

Question 14

what is the adrenal medulla?

Answer 14

a specialised neuroendocrine tissue acting with the sympathetic nervous system

Question 15

how is the adrenal medulla sometimes described?

Answer 15

as a modified sympathetic ganglion

Question 16

describe the action of the adrenal medulla

Answer 16

preganglionic sympathetic neuron stimulates chromaffin cells to release epinephrine

Question 17

describe parasympathetic efferents

Answer 17

• originate in several cranial motor nuclei (III, VII, IX and X-vagus), and intermediolateral part of sacral cord
• project to ganglia embedded in the target organ, eg S-A of the heart, enteric nervous system of gut
• Ach is the transmitter

Question 18

what is an exception to the typical pathway of parasympathetic efferents?

Answer 18

NO (penile erection)

Question 19

describe parasympathetic activities

Answer 19

• quiet, relaxed states
• active in ‘rest and digest’
• increase gastrointestinal activities
• decrease heart rate and blood pressure

Question 20

what is dual innervations?

Answer 20

most organs are innervated by both the sympathetic and parasympathetic nervous systems
- tonic activity at rest
- both branches active but parasympathetic nervous system dominates
- the two systems are complementary rather than antagonistic

Question 21

describe the functional effects of dual innervations

Answer 21

• sympathetic: cardiac output increased, skin vasoconstriction, sweating, piloerection, blood diverted from gut and skin to muscle
• parasympathetic: digestion promoted, cardiac output reduced, slow breathing, urination

Question 22

what are the targets of autonomic neurons?

Answer 22

smooth muscle, cardiac muscle, glands

Question 23

define the neuroeffector junction

Answer 23

the synapse between the postganglionic autonomic neurons with its target cells

Question 24

describe the neuroeffector junction

Answer 24

• no discrete axon terminals
• contains varicosities (axon swelling that contains vesicles filled with NT)

Question 25

describe the release of NE at neuroeffector junctions

Answer 25

1. action potential arrives at the varicosity 2. depolarisation opens voltage-gated Ca2+ channels 3. Ca2+ entry triggers exocytosis of synaptic vesicles 4. NE binds to adrenergic receptor on target 5. receptor activation ceases when NE diffuses away from the synapse 6. NE is removed from the synapse 7. NE can be taken back into synaptic vesicles for re-release 8. NE is metabolised by monoamine oxidase (MAO)

Question 26

what is meant by the idea that autonomic reflexes can be modulated?

Answer 26

- ANS is linked to the sensory system to produce functional reflexes - this is ab example of negative feedback loops - overall goal is to maintain homeostasis

Question 27

describe the pupillary light reflex

Answer 27

- organised in the pretectal area of the midbrain - uses ON and OFF afferents to luminance and darkness detectors respectively - too bright = parasympathetic reflex via 3rd cranial nerve to ciliary ganglion and circular iris muscles - too dark = sympathetic reflex via thoracic cord, sympathetic chain to radial muscles

Question 28

brightness illusion

Answer 28

brightness illusions occur because the visual system encodes contrast and context via lateral inhibition and scene interpretation, causing identical luminance to be perceived as different brightness.

Question 29

where is the baroreflex controlled?

Answer 29

- controlled by the cardiovascular center in the ventrolateral medulla - located adjacent to the respiratory center - sensory input is processed in the Nucleus of the Solitary Tract (NTS)

Question 30

what is the purpose of the baroreflex?

Answer 30

a cardiovascular reflex that regulates blood pressure

Question 31

describe how a baroreflex takes place

Answer 31

1. NTS receives input from the baroreceptors (stretch-sensitive pressure receptors located in specific large arteries) 2. NTS sends information to the VLM 3. Caudal ventrolateral medulla inhibits the rostral ventrolateral medulla, dropping BP. The rostral half excites sympathetic efferents, raising BP and HR.

Question 32

give a flow chart for the baroreflex

Answer 32

baroreceptors -> nucleus solitary tract -> ventrolateral medulla -> sympathetic output

Question 33

what are the sympathetic effects on skeletal muscle blood vessels?

Answer 33

- the major influence is noradrenergic vasoconstriction, which is tonically active to maintain blood pressure - this is part of the baroreflex

Question 34

autonomic control centres

Answer 34

- sensory information (somatosensory and visceral) feeds the autonomic control centres: hypothalamus, pons, medulla - these centres then regulate important functions (blood pressure, HR, body temperature)

Question 35

what are the control centres present in the brainstem?

Answer 35

- cardiovascular centre - respiratory pattern generator (lateral medulla/pons)

Question 36

what is the function of the brainstem?

Answer 36

receives sensory input and relays output to the muscles, glands, etc

Question 37

PAG

Answer 37

periaqueductal gray - found in the midbrain - functions as coordinator of autonomic behaviours (fight, fear, feeding, vocalisation, sex)

Question 38

how is the PAG organised?

Answer 38

- organised into longitudinal columns, according to behavioural pattern - heavy interactions with the hypothalamus - PAG acts through the reticular formation and hypothalamus

Question 39

give an example of the organisation of the PAG

Answer 39

fight (rage) column projects to the cardiovascular centre in the medulla, and raphé which releases serotonin in the spinal cord, depolarising all motoneurons. this inhibits pain transmission in the dorsal horn

Question 40

what is the effect of the reticular activating system?

Answer 40

results in a global shift in CNS activity via the diffuse modulatory system

Question 41

what is the function of the diffuse modulatory system?

Answer 41

causes a global shift in CNS activity, mainly through metabotropic mechanisms

Question 42

five types of metabotropic mechanisms of the modulatory system

Answer 42

cholinergic, serotonergic, noradrenergic, dopaminergic, histaminergic

Question 43

cholinergic

Answer 43

determines level of attention, and sleep-wake cycle through the thalamus; mainly ascending

Question 44

serotonergic

Answer 44

for stressful situations; influences mood, sleep-wake cycle

Question 45

noradrenergic

Answer 45

for stressful situations, vigilance

Question 46

dopaminergic

Answer 46

reward centre

Question 47

histaminergic

Answer 47

sleep-wake control, supports the waking state - originate in the posterior thalamus - projects throughout forebrain and others

Question 48

distinguish between the reticular activating system and the diffuse modulatory system

Answer 48

RAS is a functional arousal network, while diffuse modulatory systems are specific neuromodulatory pathways that contribute to arousal and other brain states.