ANS 1 Flashcards
describe the organisation of the nervous system
- CNS - brain and spinal cord
- PNS - motor & sensory neurons, somatic and ANS divisions
- ANS - parasympathetic vs sympathetic
what is the peripheral NS?
where are the cell bodies and peripheral nerves?
- anything not in the brain or spinal cord
- cell bodies are located in the spinal cord or in ganglia (collection of cell bodies)
- peripheral nerves are either - somatic NS (sensory and motor nerves) or autonomic NS (controls smooth muscle and gland secretions and enteric NS)
what is the ANS and briefly describe what it controls
- ANS controls multiple systems that maintain homeostasis
- eg it controls blood pressure, metabolism, gut mobility, digestion, reproductive function etc
- involuntary - subconscious
what does the NTS stand for?
nucleus tractus solitarri - nuclei in the brainstem that receives many inputs from the cranial nerves
how are the efferent nerves organised in the ANS?
- two distinct branches
- pre and post ganglionic neurons
what 2 branches is the ANS divided into?
- parasympathetic
- sympathetic
Describe the parasympathetic system PNS
eg functions
- rest and digest functions
- GI acid secretion
- GI motility - increases motility
- pupil constriction and lens adjustment
- heart rate - reduces
- often overridden by the SNS
describe the sympathetic NS
- often described as ‘fight or flight’
- functions include increasing the hr, airway dilation (bronchodilation), dilates pupil of eye, decreases gut motility and secretions
what are the **3 different types of interaction **between the SNS and the PSNS?
- **antagonistic **- act in opposing directions
- **complementary **- both act similarly
- co -operative - both play a role at some stage in overal function
describe the **antagonistic effects **of the SNS and PSNS
- heart rate - SNS increases it and PNS decreases it
- gut motility - SNS decreawes contraction and PNS increases contraction
- pupil pf the eye - SNS dilates the pupil and PSNS constricts the pupil
what is an example of a **complimentary effect **of SNS and PNS?
- saliva
- primarily controlled by the PNS in response to various stimuli - eg if there is food in the mouth etc
- SNS input changes the composition of saliva but not the volume made (makes it thicker and conatin more protein)
Describe the **co-operative effects **of the SNS and PNS
2 examples
- **pupil of the eye and lens **
* sns causes dilation of the pupil and pns causes focussing of the lens - reproduction
* PNS causes erection through the dilation of blood vessels
* SNS causes ejaculation by constriction of smooth muscle
what is a pre-ganglionic vs post ganglionic neuron?
- pre-ganglionic neuron - cell body in the brain stem or spinal cord
- post ganglionic neuron - collection of cell bodies outside the CNS
what is the anatomical definition of the SNS?
- thoraco-lumbar (T1-L2)
What is the** anatomical definition** of the PSNS?
- cranio-sacral
- crain nerves III,VII,IX and X)
- sacral segments S2-S4
describe the length of the pre and post ganglionic fibres in the PSNS
- in the PNS, ganglia are **close to the target tissue **
- therefore there are** long pre-ganglionic fibres**
*** short post ganglionic fibres **
describe the length of the pre and post ganglionic fibres in the SNS
- fibres in the SNS are arranged in a **chain close to and on either side of the spinal cord **
-
short pre-ganglionic fibres
* long post-ganglionic fibres
what neurotransmitters do the post ganglionic fibres of the PSNS and the SNS release?
- PNS post-ganglionic fibres release Ach
- SNS post-ganglionic fibres release noradrenaline (NA)
- NB - some SNS fibres tp sweatglands and pilorector muscles are cholinergic
what do pre-ganglionic neurons of both the PNS & the SNS release?
Acetylcholine
where are the adrenal glands located and what NT’s do they release & what area of the gland is an extension of the SNS & how?
- the adrenal medulla of the adrenal glands is an extension of the SNS
- adrenal glands sit next to the kidney (ad renal) and secrete catecholmines (NA & Adr) from the medulla
- sympathetic pre-ganglionic fibres stimulate chromaffin cells in the medulla leading to release of adr and NA
what is neural tone in the ANS?
- it is not the case that the ANS is switched on or off as required
- at rest, there is basal activity in both the SNS and PNS known as neural tone
- ie the SNS tone keeps the blood vessels slightly constricted and the PNS tone keeps the HR under 100bpm
what centre of the CNS is the site of cardio and resp control?
- the brain stem - pons & medulla
- they receive afferents from both baro and chemo receptors
what is the function of the hypothalamus in terms of the ANS?
- set point control in a number of negative feedback control systems including temperature, osmolality and hunger
- describe briefly G protein coupled receptors
- seven transmembrane domain receptors linked to a membrane bound protein complex
- different subunits
- Gs - stimulatory
- Gq- stimulatory
- Gi- inhibitory
what are nicotonic cholinergic receptors?
- ionotrophic receptors that open in response to Ach binding to them
- they are linked to a cation channel - normally Na+, but also can be k+
- found in muscle (n1) and nerves (n2)
- it is the receptor on all post ganglionic fibres
what is a muscarinic cholinergic receptor?
- Ach receptors
- g protein coupled receptors
- 5 sub types M1-M5
- odd numbered sub types are stimulatory and linked to Gq
- even numbered are inhibitory and linked to Gi
what are alpha 1 adrenoceptors?
- type of adrenoceptor
- stimulatory (Gq)
- found on vascular smooth muscle
what are alpha 2 adrenoceptors?
- linked to Gi - inhibitory
- found on some vascular beds, GI smooth muscle and platekets
what type of receptors are adrenergic receptors?
g protein coupled receptors
- remember if linked to Gs (stimulatory), if linked to Gq (stimulatory) and if linked to Gi (inhibitory)
which NT of the SNS do alpha adrenoceptors preferably bind to?
noradrenaline > adrenaline
what NT of the SNS do the beta adrenoceptors bind to?
- adrenaline > noradrenaline
what g protein are beta 1 adrenoceptors linked to and where are they found?
- Gs - stimulatory
- found in the heart
what g protein are beta 2 adrenoceptors linked to and where are they found?
- Gs - stimulatory protein
- found in smooth muscle where they dilate
