Organisation of the Peripheral Nervous System Flashcards
Somatic nerves innervate what?
Skeletal muscle
What does the autonomic nervous system regulate?
Cardiac muscle, smooth muscle and glands
What cells secrete epinephrine and norepinephrine?
Chromaffin cells
What neurotransmitter do somatic neurons release?
Acetylcholine
Explain the anatomy of a preganglionic neuron.
The axon of a preganglionic neuron has a small diameter and consists of myelinated type B fibers.
Explain the anatomy of postganglionic neurons.
The axon of a postganglionic neuron has a small diameter and consists of unmyelinated type C fibers.
What do preganglionic neurons do?
Relay nerve impulses from the CNS to autonomic ganglia.
What do postganglionic neurons do?
Relay impulses from autonomic ganglia to visceral effectors.
Which ganglia are associated with the parasympathetic division of the nervous system?
Terminal ganglia
Which ganglia are associated with the sympathetic division of the nervous system?
Prevertebral ganglia
Why do sympathetic ganglions have widespread effects over the entire body?
A sympathetic preganglionic fiber has many axon branches that synapse with 20 or more postganglionic neurons.
The postganglionic axons terminate in several visceral effectors thus leading to widespread effects over the whole body.
Where do the cell bodies of the preganglionic sympathetic neurons located?
Lateral gray horns of the thoracic segments of the spine.
Through what pathway do preganglionic sympathetic neurons run?
White ramus
Through what pathway do postganglionic sympathetic neurons run?
Gray ramus
Where are the cell bodies of parasympathetic preganglionic neurons found?
Nuclei of the brainstem
Lateral gray matter of the second and fourth sacral segments of the spine.
Pelvic splanchnic nerves branch from which spinal nerves?
Second through to fourth sacral spinal nerves
Muscarinic receptors bind to what?
ACh
What receptor does norepinephrine stimulate most strongly?
Norepinephrine stimulates alpha receptors more strongly than beta receptors.
Sweat glands receive what type of innervation?
Sympathetic innervation only
What are the associated ganglia of the sympathetic nervous system?
Sympathetic trunk ganglia and prevertebral ganglia.
What are the associated ganglia of the parasympathetic nervous system?
Terminal ganglia
Explain the anatomy of A nerve fibers.
Large diameter, myelinated and are the fastest nerve fiber.
B nerve fibres are found where?
Preganglionic ANS neurons
C nerve fibres are found where?
Postganglionic ANS neurons
C nerve fibres detect what?
Sensory/Pain fibres
What are somatic senses?
Tactile sensation eg touch, pressure, pain, temperature, vibration.
What are proprioceptive sensations?
Sense of the position of your limbs in space
What do nociceptors do?
Respond to painful stimuli
What receptor detects vibration?
Lamellated aka pacinian corpuscle
What detects skin stretching and pressure?
Ruffini corpuscle
What receptor detects onset of tight and light vibration?
Meissner corpuscle
What receptor detects continuous touch and pressure?
Tactile disc
What does bradykinin do?
Vasodilator also involved in detection of pain
What is the neurotransmitter at the neuromuscular junction?
ACh
Where are the acetylcholine receptors found at the NMJ?
On the motor end plate
Outline the basic steps of how a nerve action potential initiates a muscle action potential at the NMJ.
- Release of acetyl choline
- Activation of ACh receptors
- Production of the muscle action potential
- Termination of ACh activity
How is acetylcholine released into the synaptic cleft?
Arrival of a nerve impulse stimulates the opening of Ca2+ ion channels. Influx of calcium triggers exocytosis of vesicles containing ACh.
What happens when ACh bind to it’s receptor.
ACh receptors are ligand gated ion channels and so the ion channels open allowing influx of sodium across the membrane.
How does the muscle action potential cause contraction?
Influx of Na+ makes the inside of the muscle fibre more positively charged thus triggering an action potential.
The action potential then propagates along the sarcolemma of the muscle fibre to a system of T tubules, causing the sarcoplasmic reticculum to release it’s stored Ca2+.
Ca2+ causes the muscle fibre to contract.
How is ACh activity terminated?
ACh is rapidly broken down by acetylcholinesterase in the synaptic cleft.
How does Ca2+ cause muscle contraction?
Ca2+ binds to troponin causing tropmyosin to unwind and expose the myosin-binding sites on the actin filament.
Myosin heads bind to actin and undergo power strokes and release. This causes muscle contraction.
What lie in the lateral gray horns of the thoracic segments of the spine?
Preganglionic sympathetic neurons
