Peripheral Nervous System Flashcards
What is the PNS composed of?
The cranial and spinal nerves, and ganglia outside the spinal cord and brain
What is the role of the PNS?
Communicates information between the limbs and organs with the spinal cord and brain
What are the 2 major divisions of the PNS?
Afferent (sensory) and Efferent (motor) divisions
What are 2 further divisions of the Efferent PNS?
Autonomic and Somatic Nervous Systems (ANS and SNS)
What are 2 further divisions of the ANS?
Sympathetic and Parasympathetic Nervous Systems
How many pairs of cranial nerves are there, and how many pairs of spinal nerves are there?
What are the 5 major segments of the spinal nerves?
12 and 31 respectively
Cervical, Thoracic, Lumbar, Sacral and Coccygeal
What is a plexus?
What is the brachial plexus?
Collection of nerves coalescing (coming together to form one)
A collection of spinal nerves that come together, divide up and then rejoin to form peripheral nerves
If only one segment of the spinal cord is damaged, why are multiple muscles impacted?
A plexus can go in through a single spinal segment, but afterwards, come out with multiple divisions (ie. multiple routes via which the plexus comes out from - forming different named nerves)
How are the spinal, cranial, peripheral and plexus nerves named (for shorthand)?
Spinal: Has a letter (depending on which spinal segment) and a number
Cranial: CN followed by roman numerals (to represent which number of the CNs)
Peripheral: A name
Plexus: Name based on where it is going, or what it is innervating (supplying) e.g. brachial plexus comes from brachium, meaning arm
What / Where are the 2 enlargements in the spinal segments?
To do with the physical sizes of the cord - if a spinal cord is sliced along a tranverse plane, these areas of the spinal cord physically have a larger circumference due to a larger volume of grey matter compared to the rest of the spine
Cervical (C3 to T1) and Lumbar enlargements (L1 to S2)
What is the cauda equina?
Known as the ‘horse’s tail’
A collection of nerves that have come from the spinal cord segment and are on their way to exit via the intervertebral foramina - sends and receives messages between the lower limbs and the pelvic organs
What information does the afferent branch of the somatic nerves carry?
Do skeletal muscles have sensory receptors?
Information from the skin, skeletal muscles and joints
Yes, hence why the knee jerk reflex takes place.
What type of sensations do the sensory receptors in skeletal muscles detect and why might they be important?
What information does the efferent branch of the Somatic nerves carry?
Detect how much and how quickly the muscle is being stretched / how much tension is on it - prevents us from over stretching our muscles to the point where tendons are torn etc.
Also, propioception - brain knows the positioning of our muscles e.g. whether our arms are stretched out or relaxed even if we cannot see them due to these sensory receptors inside joints and muscles
Nerves going to skeletal muscles, which we have voluntary control over
What are dermatomes?
Why is it if a single spinal nerve is damaged, sometimes there is not a strip of skin that is non-functioning?
How and why are the dermatomes different in the trunk than the limbs?
Dermatome - An area / strip of skin that is supplied by a single spinal nerve
Spinal nerves often somewhat overlap in the area they supply [Yeah, I don’t really understand this point either]
Trunk and limbs develop differently, so the trunk’s dermatomes are segmented
Why are dermatomes important clinically? (3 major reasons)
As an anaethesist - e.g. delivering epidurals, certain organs at certain vertebral levels etc. Dermatomes are tested to know when the anesthesia is adequate enough to begin surgery
Neuropathies / Injuries that affect single spinal nerves - can correlate symptoms to the nerve damaged
Nerve compression - sometimes major issue, sometimes e.g. ‘sleeping funny’ or ‘pins and needles’
What is the difference between anaesthesia and paraesthesia?
Anaesthesia - no sensation
Paraesthesia - altered sensation
For an overview - where do each of these nerves go / come from?
How are peripheral nerves arranged?
What are the 3 layers of connective tissue that cover the fasciculi and what are the order of these layers?
Into fasciculi (bundle of nerves)
Individual axons (outside the myelin sheath) are covered in endoneurium
Individual fasicles are covered in perineurium
The entire nerve bundle and surrounding all the fasicles (AKA external vascular layer) is the epineurium
Which are the fastest and slowest conducting in this image?
Left to right = fastest to slowest
What two branches is the autonomic nervous system split into? And then which 2 further branches?
Where does the parasympathetic nerve supply come out of?
Where does the sympathetic nerve supply come out of?
Has visceral afferent and efferent parts, the efferent part if further split into the sympathetic and parasymathetic nervous system
The brain and the sacral spinal cord (craniosacral)
Between the T1 and L2 spinal cord segments (thoracolumbar)
What is the anatomy of the sympathetic outflow from the spinal cord to the periphery?
Pre-ganglionic neurons of the sympathetic system are in the spinal cord, in the intermediate horn found between T1 and L2
Highest level of outflow is at T1
They come out and go into the paravertebral / sympathetic trunks (which run either side of the spinal cord)
Into the white (myelinated) or grey (unmyelinated) ramus communicans
Why are the sympathetic trunks enlarged?
Following along the green nerve, where does it travel?
What does that section of the spinal nerve consist of?
They contain the post-ganglionic neurons in them
Out of the spinal cord, into the spinal nerve (for a small distance), into an enlargement where it synapses, and then continues along the post-ganglionic neuron, which can go up to the head, down to the limbs, or straight across to that region on the body
Efferent, afferent and some sympathetic pre-ganglionic neurons
What is the anatomy of the sympathetic outflow to the heart?
Similar to the nerves going to the skin - nerve comes out of the spinal cord, synapses in the enlargements of the sympathetic branch, then travels to the heart
What is the anatomy of the sympathetic outflow to the viscera?
Where does the pre-ganglionic nerve synapse if travelling to the viscera?
Pre-ganglionic nerve comes out of the spinal cord and carries along via the sympathetic trunk without synapsing until it arrives at the pre-aortic ganglia, which is synapses and the post-ganglionic nerve continues to the organ
Not in the sympathetic trunks like for the skin or heart, but instead, in front of the aorta in the pre-aortic ganglia
What is the anatomy of the parasympathetic outflow to the viscera?
i.e. which CNs and where do they synapse?
Outflow from the base of the spinal cord?
CNs III, VII, IX, and X are associated with parasympathetic outflow?
CN III (occulomotor) - goes to the eye for pupillary constriction
CN VII (facial) - goes to lacrimal gland and sub mandibular salivary glands
CN IX - Parotid gland
CN X - Salivary glands
Sacral outflow that goes to the pelvic organs
What are the actions of the Autonomic NS?
In terms of eyes, salivary glands, heart rate, lungs, stomach, liver, intestines, and bladder?
