Anatomy of the PNS Flashcards
What is the basic unit of the nervous system?
Neuron
What is a collection of nerve cell bodies called in the CNS?
Nucleus
What is a collection of nerve cell bodies called in the PNS?
Ganglion
What produces the myelin sheath in the PNS?
Schwann cells
What produces the myelin sheath in CNS?
Oligodendrocytes
What are the two main types of neurones?
Multipolar
Unipolar
Describe a multipolar neuron
2 or more dendrites
All motor neurones of skeletal muscle and ANS
Cell body found in CNS
Describe a unipolar neuron
Double process
Aka psedounipolar/sensory
Cell body found in PNS
In which direction do impulses travel in motor (efferent) nerves?
Impulse move towards the body wall, cavity or organ
In which direction do impulses travel in sensory (afferent) nerves?
Impulses move towards the brain
What can a nerve be defined as?
A collection of axons surrounded by connective tissue and blood vessels
What is another name for a nerve in the CNS?
Tract
What are the two modalities of nerves?
Single modality
Mixed modality
Give examples of nerves with single modality
Somatic motor, somatic sensory, special sensory, sympathetic, parasympathetic, visceral afferent
Give examples of nerves with mixed modality
Somatic motor, somatic sensory and sympathetic all together in one nerve
Give examples of ‘named’ peripheral nerves
Trigeminal
Femoral
Radial
Where are CN I and II found?
Forebrain
Where is CN V found?
Pons
Where are CN VI, VII, VIII found?
Junction between pons and medulla
Where are CN IX, X and XII found?
Directly from medulla
Where is CN XI found?
Spinal cord
How many pairs of spinal nerves are there?
31 pairs
Where are spinal nerves only ever found?
Intervertebral foramina
From the spinal cord describe the path of the spinal nerve
Anterior and posterior rootlets converge to become anterior and posterior roots
The anterior and posterior root converge to become the spinal nerve
The spinal nerve then divides into anterior and posterior rami
Describe the path that all sensory axons take
Sensory axons pass from spinal nerve into POSTERIOR root then into posterior rootlets then into posterior horn of spinal cord
Describe the path that all motor axons take
Motor axons pass from anterior horn of spinal cord into anterior rootlets then into anterior root then into spinal nerve
Which type of nerves pass through the spinal nerve?
Both sensory and motor!
Each spinal nerve pair supplies a body segment with….
General sensory supply to all structures
Somatic motor supply to skeletal muscles
Sympathetic nerve supply to skin and smooth muscle of arterioles
Do spinal nerves contain parasympathetic?
Never!
Only contain sympathetic nerves
What is a dermatome?
Area of skin supplied with sensory innervation from single spinal nerve
Also supplies sensory innervation to deeper structures
What is a myotome?
Skeletal muscles supplied with motor innervation from a single spinal nerve
May be deep to dermatome of same spinal nerve (not always)
Give an example of a myotome that is not deep to the same dermatome
The diaphragm
Innervated by phrenic nerve- C3,4,5- the dermatome does not match the myotome on the surface
What are 2 landmarks on the trunk of the dermatome map
Male nipple- T4 segment
Umbilicus- T10 segment
Which dermatomes cover posterior scalp, neck and shoulder?
C2-C4
Which dermatomes cover upper limb?
C5-T1
Which dermatomes cover lower limb, gluteal region and perineum?
L2-S3
Which spinal nerves form the cervical plexus?
C1-C4
Which spinal nerves form the brachial plexus?
C5-T1
Which spinal nerves form the lumbar plexus?
L1-L4
Which spinal nerves form the sacral plexus?
L5-S4
Describe sympathetic outflow
Originates from autonomic control centres in brain, passes down spinal cord
Exits spinal cord with T1-L2 spinal nerves
Where do presynaptic axons that innervate the heart originate?
Presynaptic axons synapse in T1 or cervical paravertebral ganglia
Where do postsynaptic axons that innervate the heart synapse?
Postsynaptic axons pass in cardiopulmonary splanchnic servers to the SA & AV nodes and the myocardium
Describe parasympathetic outflow
Presynaptic parasympathetic axons leave CNS via cranial nerves III, VII, IX and X and sacral spinal nerves
From the cranial and spinal nerves where does parasympathetic travel via?
Ciliary ganglion in eye
Parasympathetic ganglia in head- lacrimal gland and salivary gland
Vagus nerve- organs of neck, chest and abdomen
Sacral spinal nerves- handgun, pelvis and perineum
