The Peripheral Nervous System Flashcards
Sensory ( afferent ) division
CNS+PNS
PNS divides to sensory (afferent division): sensory neuron
getting info from skin and muscles to brain
and motor (efferent division)
Motor division divides to autonomic nervous system and somatic nervous system:voluntary control or automatic- skeletal muscles of the body
- we have 2 neurons, upper motor neuron ( CNS)
-lower motor neuron (PNS)
- synapse either in the brainstem or spinal cord.
Lower motor neuron will continue its way to the skeletal muscle.
Autonomic nervous system divides to sympathetic and parasympathetic.
Autonomic nervous system
divided into 2 components sympathetic and parasympathetic.
3 neurons
-1 neuron from hypothalamic nuclei to brain stem nuclei ( parasympathetic) or spinal cord (sympathetic), or sacral region ( parasympathetic sacral nerve)
- 2nd: preganglionic Neuron from brain stem nuclei/ or spinal cord to autonomic ganglia
-3rd: postganglionic Neuron from autonomic ganglia to Visceral Effectors
What is the equivalent of astrocytes in the PNS?
Satellite cells
Describe the packaging of nerve axons into nerves
Axons are packaged into fascicles and the fascicles are packaged into nerves.
What are the three layers of connective tissue found in nerves?
Endoneurium - wraps around individual axons
Perineurium - wraps around fascicles. Gives main tensile strength to nerve
Epineurium - wraps around nerves.
what is the difference between myelinated and unmyelinated axons?
unmyelinated axons also have Schwann cells wrapped around them, the difference is that they only have one layer of membrane around them and one Schwann cell can accommodate many axons
Describe the arrangement of the somatic motor neuron, autonomic motor neuron and sensory neuron
-Somatic motor neuron: have their cell bodies in the CNS.
CNS—–>SMN—>skeletal muscle
- Autonomic motor neuron: preganglionic neuron and post ganglionic motor neuron. There is an autonomic ganglionic in between the CNS and the effector.
CNS—> preganglionic—–> autonomic ganglion—-> post-ganglionic e.g. blood vessels, glands, viscera
Sensory neurons: have a ganglion in the middle.
CNS
Describe the arrangement of autonomic motor neurons.
Autonomic motor neurons have a preganglionic neuron and a postganglionic neuron with an autonomic ganglion in the middle. The location of the autonomic ganglion varies depending on whether it is sympathetic or parasympathetic.
What are the 4 types of neuron
- Somatic sensory: carries information in FROM the skin/muscles/joints
- somatic motor: controls striated muscle
- Autonomic sensory: brings sensory information from the internal organs
- Autonomic Motor: travels to glands to make them secrete or to smooth muscle in the wall of the gut etc
where are the somatic sensory and motor found and where are the autonomic nerves found
Somatic sensory and somatic motor: found in ALL spinal nerves
Autonomic: found in MOST spinal nerves.
where does the cell body of the somatic sensory axon and autonomic sensory come from and where is this found?
In the dorsal root ganglion.
this is found in the spinal nerve.
axon comes through the spinal nerve and it has a cell body in the Dorsal Root Ganglion.
How is the autonomic motor structured?
2 cells between the CNS and the effector instead of just one.
-preganglionic autonomic motor neuron sends its axon through the ventral root and into the spinal nerve.
-it will move towards the effector but at some stage in the journey it will move into an autonomic ganglion.
- in the autonomic ganglion, it will synapse with a postganlionic motor neuron and the axon of the post ganglionic motor neuron ill continue towards the target organ.
therefore the location of the autonomic ganglion is very variable
Which roots do motor and sensory nerves go out of?
Motor = ventral Sensory = dorsal
Where do autonomic sensory neurons have their cell bodies?
In the dorsal root ganglion
What is a myotome and dermatome?
Muscle= The muscle that a spinal nerve innervates Dermatome= the skin that a spinal nerve innervates
What spinal nerves make up the brachial plexus?
C5-T1
How is the brachial plexus different to thoracic nerves
some of the spinal nerves merge together then diverge later.
- this means you get mixing up of the individual spinal nerves so by the time you have 3 peripheral nerves emerging from the bottom of the plexus, each of these nerves will have axons which have originated from more than one spinal nerve.
- this is different from thoracic nerves which only have axons from a particular segment.
What are the nerves called that are leaving the brachial plexus and before the plexus?
Before the plexus= SPINAL NERVES
After the plexus= PERIPHERAL NERVES
Describe the differences in the dermatomes of spinal nerves and peripheral nerves.
Spinal nerves = stripey
Peripheral nerves = patchy
what is the clinical relevance of spinal nerve and peripheral nerve appearance?
If someone has sensory loss and you don’t know where the lesion is, plot out the area on the skin where the sensation is lost. If the pattern is a STRIPE you know the injury is to the spinal nerve. If a PATCH of skin has lost sensation, then it is most likely a peripheral nerve.
Describe the process of regeneration following peripheral nerve injury.
With compression injuries, the axoplasm is separated but the endoneurium is still in tact. The axon distal to the compression (further away from the cell body) degenerated - macrophages invade and phagocytose the cell debris. Schwann cells divides and increase in number. Axons sprouts then grow down the endoneurium. There is competition between the axonal sprouts to reach the target organ. When the first axon sprout reaches the target cell, the other axon sprouts regress. The axon then widens and a myelin sheath forms. The only difference is that the internodal distance is reduced so the conduction speed is reduced.
What could happen if the damage to the neuron is so severe that there are no guidance cues at all for the axonal sprouts?
A neuroma could form which is very painful and needs to be surgically removed.
what does the quality of regeneration depend on?
-distance between the point of injury and the cell body:
if the injury is close to the cell body, then the shock to the cell ma be so severe that the whole cell dies.
-also depends on the type of damage:
compression injury leave the endoneruial sheath intact, so you have a good conduit for the growth of axonal sprouts.
what is peripheral neuropathies?
-Progressive degeneration of nerves
-usually start distally and progress towards the CNS.
Mechanism:
-due to a direct problem with the axon or it will be due to a secondary effect of damage to the myelin sheath leading to damage to the axon.
May impair sensation, movement, gland or organ function
Sensory nerves (sensation): cause tingling, pain, numbness Motor nerves (movement): cause weakness to hands and feet Autonomic nerves (involuntary functions): cause changes in heart rate or blood pressure
