Nervous system Flashcards
What are the components of the human nervous system?
- Central nervous system
2. Peripheral nervous system
What are the components of the central nervous system?
The brain and spinal cord
What are the components of the peripheral nervous system
The cranial and spinal nerves
The autonomic nerves
What are nerves?
Bundles of axons in the PNS, some percentage of them will be myelinated by Schwann cells
What are tracts?
Bundles of axons in the CNS, some of them will be myelinated by oligodendrocytes
What is white matter?
Areas of the CNS composed of neural cell bodies
What is grey matter?
Areas of the CNS composed of neural cell bodies
What does afferent refer to?
CNS/individual nerve cell that projects inward
What does efferent refer to?
CNS/individual nerve cell that projects outward
What is a plexus?
An interwoven mass of nerves and axons making up these nerves
What is a ganglion?
A swelling on a nerve which usually contains cell bodies
What is a ramus?
A branch of a nerve
How many cranial nerves are there?
12 pairs
Where do cranial nerves originate?
In the brain
What are the different roles of cranial nerves?
Sensory - CN1/2/8
Motor - CN3/6/11/12
Mixed - CN5/7/9/10
How many spinal nerves are there?
31 pairs
Describe the origin of the spinal nerves
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
Why are spinal nerves commonly stretched downwards?
Spinal cord stops at around level L1
After this, the nerves angle down since the spinal cord stays the same length, but the vertebral column continues growing, stretching the nerves downwards
Describe the spatiolocation of the vertebral column and spinal nerves
For cervical nerves 1-7, the nerve number corresponds to the vertebrae below the nerve
After C8, the vertebrae come before the nerve
Where does sensory afferent information enter the vertebral column?
Through the dorsal root ganglion
Where does the motor efferent information exit the vertebral column?
Through the anterior ventral root ganglion
What are dermatomes?
Nerves supply a particular territory of the skin
This segmental innervation originates in the somites
Describe the nerve supply in each dermatome
Each dermatome is supplied by one main spinal nerve, but is also partially covered by the nerve below and above
What are the dermatomes of the body?
Cervical
Thoracic
Lumbar
Sacral
Describe which spinal nerves form which plexus
C2-C5 = cervical plexus
C5-T1 = brachial plexus
T12-L4 = lumbar plexus
L5-S5/Cox1 = sacral plexus
What is the largest nerve in the body?
Which plexus does it contribute to?
Sciatic nerve
Sacral plexus
Describe the functional divisions of the peripheral nervous system
The first 2 divisions are:
- Sensory (afferent)
- Motor (efferent)
Sensory is divided into viscerosensory, somatosensory and special sensory
Motor is divided into somatomotor and visceromotor (parasympathetic, sympathetic, enteric)
Give examples to each functional division of the peripheral nervous system
Somatosensory - skeletal muscle and skin
Viscerosensory = viscera/organs
Special sensory = ears, eyes, nose and tongue
Somatosenory = skeletal muscle/voluntary
Visceromotor = smooth muscle/involuntary
Describe the spinal reflex arc
Involves one sensory and one motor neurons
- Sensory neuron sends information via dorsal root to motor neurons
- Motor neurons send information to the same muscle
- The muscle contracts
- Other antagonistically paired muscles may help this reflex to relax the antagonistic muscle
What type of synapses is involved in the reflex arc?
It is monosynaptic
What are the two divisions of the autonomic nervous system?
- Parasympathetic
2. Sympathetic
Which spinal nerves are involved in the sympathetic nervous system?
Thoracolumnar
T1 - L2
Which spinal nerves are involved in the parasympathetic nervous system?
Craniosacral
Cranial nerves 3, 7, 9 and 19
Sacral nerves 2-4
Vagus nerve - originates from CN10
Describe the ganglia of the sympathetic system
Associated with chain of ganglia
Can go up into the neck area and lumbar/sacral region
Ganglia near the spinal cord and far from target
What is the sympathetic chain?
A chain of ganglia lateral to the vertebral column.
Extends from the neck to the sacrum, but sympathetic outflow from the spinal cord is only between T1 and L2
This allows sympathetic innervation to extend beyond levels T1 and L2
Describe the ganglia of the parasympathetic system
Ganglia are near the target organs
How many sympathetic chains are there?
2
One on each side of the body
Describe the myelination of pre and post-ganglionic nerves
Preganglionic are myelinated
Postganglionic are unmyelinated
Describe the exit and entry roots of the nerves
Preganglionic = white ramus comunicans
Post-ganglionic = grey ramus comunicans
What is the origin of the splanchnic nerves?
T5 - T12
What is an important quality about some splanchnic nerves?
Some pass through their ganglia without synapsing and instead synapse in collateral ganglia close to abdominal organs
Pass through the ganglion and have a peripheral ganglion
Examples of these include: Greater splanchnic (T5 - T9) Lesser splanchnic (T10 - T11) Least splanchnic (T12)
What is the function of the enteric nervous system?
Controls gut function:
- secretion
- gut mobility
- gut reflexes
What is unique about the enteric nervous system
Can operate in 3 ways:
- CNS - via parasympathetic and sympathetic system
- Isolation
- In response to hormones
What are the two important plexuses in the enteric nervous system?
Myenteric plexus - mostly controls gut mobility
Submucosal plexus - mostly controls gut secretions
What is referred pain?
Some of the innervation via the visceromotor and viscerosensory can synapse into similar nerves, so the brain develops the body image referring to the inner organs
Clinically important examples of referred pain
T1 - T4 = associated with the heart
T5 - T7 = stomach
T10 = uterus/appendix
