Anatomy of the Peripheral Nervous System Flashcards
What is the difference between a nucleus and a ganglion?
A collection of nerve cell bodies in the CNS is known as a nucleus; while a collection of nerve cell bodies in the PNS is known as a ganglion
What are neurones?
Nerve cells which receive and conduct impulses
What are the 3 main parts of a neurone?
Body, dendrites, axon
Which is longer, a dendrite or an axon?
Axon
Dendrites travel in which direction with regards to the neurone cell body?
Towards
Dendrites are effectively extensions of the neurone cell body, what is their function?
To increase surface area to allow the neurone to connect with other neurones
Axons travel in which direction with regards to the neurone cell body?
Away
What is the role of the axon?
To communicate with other neurones or effectors (muscles/glands)
What would be the main difference in the myelin sheath surrounding an axon in the PNS vs the CNS?
In the CNS, the myelin sheath will be composed of oligodendrocytes; in the PNS, it will be composed of Schwann cells
What are the two main different types of neurone?
Multipolar and unipolar
Out of multipolar and unipolar, which is the most common type of neurone?
Multipolar
How many dendrites must a neurone have to be classed as multipolar?
Two or more
Are motor neurones (either of skeletal muscle or the ANS) multipolar or unipolar?
Multipolar
Usually, where is the cell body of a multipolar neurone found?
In the CNS (with the axon extending into the PNS)
Usually the cell body of a multipolar neurone is found in the CNS. What is the exception to this?
In the ANS: the cell body of the presynaptic neurone is located in the CNS, but the cell body of the postsynaptic neurone is located within autonomic ganglia in the PNS
Are sensory neurones multipolar or unipolar?
Unipolar
Most unipolar neurones are located where?
In the dorsal root ganglion
Where is the cell body of a unipolar neurone found?
In the PNS
In a motor (efferent) neurone, where does the impulse move towards?
The body wall, body cavity or an organ
In a sensory (afferent) neurone, where does the impulse move towards?
The brain
What are nerves?
A collection of axons surrounded by connective tissue and blood vessels
What is the CNS equivalent of a nerve?
A tract
What are the two main subtypes of nerve?
Single modality and mixed modality
Which is more common - single modality or mixed modality nerves?
Mixed (single modality nerves are quite rare)
Single modality nerves can be composed of one of what modalities?
Somatic motor, somatic sensory, special sensory, sympathetic, parasympathetic or visceral afferent
All spinal nerves are which type: single or mixed modality?
Mixed
Mixed modality nerves contain what 3 modalities?
Somatic motor, somatic sensory and sympathetics all together in one nerve
How man pairs of spinal nerves are there? How are these divided up?
31 pairs, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal
What is important to remember about the cervical spinal nerves and cervical vertebrae?
There are only 7 cervical vertebrae so C1 starts above the first vertebrae
Spinal nerves are only found where in the body?
Intervertebral foramina
The spinal nerves become what to travel to structures of the soma?
Rami
Before they become spinal nerves, what do they travel from the spinal cord as?
Rootlets and roots
Are rami single or mixed modality?
Mixed
Which is larger, anterior or posterior rami?
Anterior
What do anterior and posterior rami supply respectively?
Anterior rami supply the anterior body wall, posterior rami supply the posterior body wall
Describe the path of a sensory axon?
Spinal nerve, posterior root, posterior rootlets, posterior horn of the spinal cord
Describe the path of a motor axon?
Anterior horn of the spinal cord, anterior rootlets, anterior root, spinal nerve
What is found in the dorsal root ganglion?
The cell bodies of primary afferent neurones
Each spinal nerve pair supplies its particular body segment with what?
General sensory supply to all structures, somatic motor supply to skeletal muscles and sympathetic supply to skin and smooth muscle of arterioles
What is a dermatome?
An area of skin supplied with sensory innervation from a single spinal nerve
What is a myotome?
The skeletal muscles supplied with somatic motor innervation from a single spinal nerve
Is the myotome always deep to the dermatome of the same spinal nerve?
No, it sometimes can be but isn’t always
What is the dermatome level of the male nipple?
T4
What is the dermatome level of the umbilicus?
T10
What range of dermatomes supply the scalp, neck and shoulder?
C2, C3, C4
What range of dermatomes supply the upper limb?
C5-T1
What range of dermatomes supply the lower limb, gluteal region and perineum?
L2-S4
What is a nerve plexus?
Intermingled anterior rami from a number of adjacent spinal nerves
The anterior rami of a nerve plexus contribute to the formation of multiple what?
Peripheral nerves
What spinal nerves form the cervical plexus? What does this supply?
C1-C4, the scalp, neck and diaphragm
What spinal nerves form the brachial plexus? What does this supply?
C5-T1, the upper limb
What spinal nerves form the lumbar plexus? What does this supply?
L1-L4, the lower limb
What spinal nerves form the sacral plexus? What does this supply?
L5-S4, the lower limb, gluteal region and perineum
Where does sympathetic outflow originate from? It passes down the spinal cord and exits at what spinal levels?
Control centres in the brain / T1-L2
What additional feature of the spinal cord allows sympathetics to leave at T1-L2 levels?
Lateral horns
The presynaptic sympathetic axons is motor innervation, so after leaving the spinal cord it passes through where to reach the spinal nerve?
Anterior roots and rootlets
How does sympathetic supply reach the body wall structures?
Via anterior and posterior rami of spinal nerves
How does sympathetic supply reach the thoracic viscera?
Cardiopulmonary splanchnic nerves
How does sympathetic supply reach the abdominopelvic viscera?
Abdominopelvic splanchnic nerves
Once sympathetics pass into the anterior and posterior rami of spinal nerves, how do they reach organs of he head and neck, and the body wall?
By ‘hitching a ride’ with arteries
Describe where presynaptic sympathetic fibres would be found?
Leaving the spinal cord in anterior roots/rootlets
Describe where postsynaptic sympathetic fibres would be found?
Within anterior and posterior rami of spinal nerves
Where are paravertebral sympathetic ganglia found?
Associated with the sympathetic chain
Where are prevertebral sympathetic ganglia found?
Infront of the abdominal aorta
Do sympathetics to the heart and lungs synapse paravertebral or prevertebral sympathetic ganglia?
Paravertebral
Do sympathetics to the abdomen and pelvis synapse paravertebral or prevertebral sympathetic ganglia?
Prevertebral
Where do presynaptic parasympathetic axons leave the CNS?
CNs III, VII, IX and X, and sacral spinal nerves
How do parasympathetics travel to the eye?
Via the ciliary ganglion
How do parasympathetics travel to the lacrimal and salivary glands?
Via parasympathetic ganglia in the head and neck
How do parasympathetics travel to organs of the neck chest and abdomen (to the midgut)?
Vagus nerve
How do parasympathetics travel to the hindgut, pelvis and perineum?
Sacral spinal nerves
Horner’s syndrome is caused by what?
Impaired sympathetic innervation to the head and neck
What is the clinical picture of Horner’s syndrome?
Ipsilateral miosis, ptosis, anhydrosis and increased redness and warmth
