W7 Functioning Of The Autonomic Nervous System Flashcards
Autonomic sensory components
Sensory receptors within the viscera (soft internal tissues)
Somatosensory/external environment
Does sensory input control somatic or autonomic changes?
A single piece of sensory input might result in somatic and autonomic changes, because information is integrated within the CNS.
How are autonomic motor components different to somatic motor components?
- the effectors innervated
- the number of neurones between CNS and effector
- neurotransmitter release and the nature of neurotransmitters
What are the effectors of the autonomic nervous system?
Autonomic neurones will innervate smooth and cardiac muscles, and glands (viscera).
What can the autonomic nervous system be split into?
Sympathetic, parasympathetic, enteric
How do neurones communicate with effectors in the autonomic NS?
There is a 2-neurone chain between the CNS and effector tissue
Pre-ganglionic and Post-ganglionic neurones communicating at a synapse existing in collections known as ganglia
What is a preganglionic neurone?
The neurone whose cell body is in the CNS and terminals in the ganglia.
What is a postganglionic neurone?
Cell bodies in the ganglia and terminates in the effector tissue
What is the functional important of having a 2-neurone chain between the CNS and effector tissue?
Preganglionic neurones might branch and be in contact with multiple postganglionic neurones, resulting in widespread activation of postganglionic neurones and thus can control a large area of effector tissue.
What acts like the NMJ a of the somatic NS in the autonomic NS?
There are a series of small swellings, which each contrail vesicles of neurotransmitter. ‘Beads on a string’. Refer to image. Allows a single postganglionic neurone to release neurotransmitter at many sites and thus over a large area.
What are the functional implications of the ‘beads on a string’ arrangement?
A small number of postganglionic autonomic neurones can influence a large number of effector cells. So within an organ we can organise the change in activity in a large number of smooth muscle cells, allowing a high level of coordination.
Sympathetic neurotransmitters
Within the ganglion = ACh
Released at nerve endings = NA
Parasympathetic neurotransmitters
Within the ganglion = ACh
Release at nerve terminals = ACh
What exceptions are there to the sympathetic and parasympathetic neurotransmitters.
Sweat glands and adrenal medulla
How are the sweat glands exceptions to the autonomic NS?
They have sympathetic function however release ACh at the postganglionic nerve endings.
How is the adrenal medulla an exception to the autonomic NS?
Receives normal sympathetic input via ACh. But adrenal medulla cells are endocrine cells which release adrenaline (and NA in humans), not postganglionic cells (neuroendocrine organ).
So NA and Ad are released and able, via blood transport, to activate non-innervated receptors. They act at adrenergic receptors. Can be found in smooth muscle of bronchioles/blood vessels etc.
Role of the sympathetic and parasympathetic NS
Homeostasis, vision, reproduction
When are the SNS or PNS responsible?
SNS = responsible when we are alert and active. In emergency or as a defence (fight or flight) PNS = rest and digest. Energy conservation, digestion and emptying.
How are most organs innervated by the autonomic NS? Give example
Most organs and tissues are dual innervated with an antagonistic SNS and PNS
E.g., GIT, activation of the SNS decreases motility due to action on the smooth muscle cells of the GIR but activation of PNS increases motility
What are the different ways the autonomic NS can innervate structures?
Dual innervation with antagonistic SNS and PNS
Overall antagonistic dual innervation but innervation is of different parts of the structure
Dual innervation but not antagonistic
Single innervation
Give an example of where an overall structure has antagonistic dual innervation but the innervation is of different parts of the structure
The pupil (smooth muscle)
Describe the arrangement of the iris
Formed of 2 layers of muscle:
- inner layer next to pupil where the long smooth muscles are arranged point to point in circular arrangement, circular muscle
- outside layer where smooth muscle cells are labelled end to end, radial muscle
What causes pupil dilation?
SNS is activated causing contraction of the radial muscle
Smooth muscle cell contraction in the outer layer will pull open the pupil
What causes pupil constriction?
PNS aids activated causing contraction of the circular muscle.
Smooth muscle cell contraction in the inner layer will constrict the pupil.
