ANS Flashcards
What two sub-nervous systems makes up the anatomic nervous system, and which bodily states do they work under?
Parasympathic- controls organs in times when the body is at rest.
Sympathetic- controls organs in times of stress.
What is different between the SNS and ANS?
SNS- voluntary. Relays information to and from skin and skeletal muscles.
ANS- involuntary. Relays information to internal organs.
What three categories can sum up the differences betweent the parasympathic and sympathetic nervous systems?
Anatomical
Functional
Chemical (neurotransmitter)
Describe the basic anatomy of the ANS:
The preganglionic neuron lies in the spinal cord and synapses at the ganglion (a peripheral cluster of neuronal cell bodies), where the post-ganglionic neuron lies, and transmits signals to organs.
What is the function of the vertebrae?
To protect the spinal cord.
What ANS division has its pre-ganglion clustered in the lumbar region?
How does this differ in the other division?
The sympathetic nervous system has its pre-ganglion clustered in the lumbar region.
In the parasympathetic nervous system pre-ganglion cluster at both ends of the spinal cord.
What is the difference in location of cell bodies of the PSNS and SyNS relative to their target organs and spinal cord.
The PSNS has its cell bodies closer to the target organ. The SyNS has its cell bodies closer to the spinal cord.
Describe two anatomical characteristics of the parasympathetic nervous system:
- Pre-ganglionic fibres leave CNS in cranial nerves (III, VII, IX, X) and sacral spinal roots.
- Post-ganglionic neurons usually lie close to or within the target organ.
Describe two anatomical characteristics of the sympathetic nervous system:
- Pre-ganglionic fibres leave the CNS in thoracic and lumbar spinal roots.
- Post-ganglionic neurons form two paravertebral chains on either side of the spinal cord, plus midline ganglia.
Do all organs have a sympathetic and parasympathetic division of their ANS?
No- blood vessels only have sympathetic input.
What is the function of the parasympathetic NS?
To accumulate, store and preserve resources (rest and digest).
What is the function of the sympathetic NS?
To prepare the body for strenuous activity and stress emergencies (fight or flight).
List some effects the parasympathetic nervous systems has on the body:
Decreases heart rate
Increases GI tract activity
Glands stimulated to secrete (e.g. saliva)
Pupils constrict
List some effects the sympathetic nervous system has on the body:
Increases heart rate Decreases GI tract activity Increases blood flow to skeletal muscle Decreases blood flow to skin and visceral organs Increases glycogen and lipid breakdown Pupils dilate
Define a synapse:
This is the junction between the axonal ending of a neuron with another neuron, a muscle cell or a glandular cell.
What is synaptic transmission?
The process by which neurons signal to the next cell via the release of neurotransmitters.
How are neurotransmitters stored, and how do they act?
They are stored (and synthesised) in vesicles on the nerve terminal and then released. Neurotransmitters then bind to cellular receptors before their action can be terminated.
Describe the 10 steps involved in neurotransmission?
- Precursor is transported into the nerve terminal.
- Enzymes convert the precurson to a transmitter.
- Transmitter stored in vesicles.
- Action potential reaches terminal and depolarises cell.
- Voltage-gated ion channels open, leading to Ca2+ influx.
- Vesicles fuse with membrane and release transmitter.
- Transmitter diffuses into synapse, acts on post-synaptic receptors AND
- Acts on pre-synaptic receptors to act as an autoinhibitory feedback loop, hyperpolarising the terminal and preventing further transmitter release.
Transmitter terminated by two mechanisms: - Enzymic degradation to give recyclable degradation product.
- Transmitter transported back into nerve terminal.
How many potential places are there for drugs to act and change normal events of synaptic transmission, and what do these places correspond to?
There are 10 places, which correspond to the 10 steps involved in neurotransmission.
What neurotransmitter is involved in parasympathetic neurotransmission, and what receptors does it bind to?
Acetylcholoine (ACh) in both pre and post neurons.
ACh binds to nicotinic (Nn and Nm) and muscarinic (M1-M3) receptors.
What neurotransmitter is involved in sympathetic neurotransmission for the pre-ganglion neuron, and what receptor does it bind to?
ACh.
It binds to nicotinic receptors (Nn).
What neurotransmitter is involved in sympathetic neurotransmission for the post-ganglion neuron, and what receptor does it bind to?
Noradrenaline (NA).
It binds to receptors alpha1, alpha2, beta1 and beta2.
Describe a situation where the post-ganglionic receptor for sympathetic neurotransmission is not NA:
In sweat glands post-ganglionic neurotransmitter is ACh, and binds to muscarinic receptors.
What does neuromodulation describe?
The effects of other chemical mediators on synaptic transmission.