Lecture 19 - Anatomy and function of spinal cord and spinal nerves

Question 1

Where does the spinal cord start?

Answer 1

Foramen magnum = the opening at the base of the skull

Transition of brain to spinal cord

Question 2

Where does the spinal cord end?

Answer 2

Inferior border of first lumbar vertebra (L1)

Question 3

What is the spinal cord within?

Answer 3

Within a sack that fits inside the spinal cavity and the spinal cavity is within vertebrae

Question 4

Vertebrae - ventral and dorsal side

Answer 4

Dorsal side = spinous process

Ventral side = body

Question 5

What is the spinal cord extended within?

Answer 5

Extends with a meningeal sack which is filled with fluid

Question 6

Conus medularis

Answer 6

the tapered cone like end of the spinal cord (this is non-neural tissue). The tip of this ends at the level of L1/L2

Question 7

Filium terminale

Answer 7

Fibrous, non-neural tissue which extends from the conus medullar is to the end of the spinal cavity - anchors the spinal cord. This makes the spinal cord taut within the spinal cavity - it cannot move and be damaged

Question 8

Spinal nerves

Answer 8

The spinal cord has 31 segments. One pair (left and right) of spinal nerves comes off each segment. There are 8 cervical spinal nerves even though only 7 cervical vertebrae.

Spinal nerves exit the vertebral column at the level appropriate to their origin e.g. nerves originating in the lumbar spinal cord exit between lumbar vertebrae

Question 9

Number of spinal nerves

Answer 9

The spinal cord has 31 pairs of spinal nerves :

8 pairs of cervical spinal nerves (there are 8 cervical nerves and only 7 cervical vertebrae) 
12 pairs of thoracic spinal nerves 
5 pairs of lumbar spinal nerves 
5 pairs of sacral spinal nerves 
1 pair of coccygeal spinal nerves

There is therefore one nerve coming out of each segment of the spinal cord
The spinal nerves exit the vertebral column at the level appropriate to their origin (so nerves originating in the lumbar region of the spinal cord will exit between the lumbar vertebrae)
The C1 nerve exits above the C1 vertebrae, all other spinal nerves exit below their corresponding vertebrae

Question 10

Cauda equina

Answer 10

Large collection of long nerves inferior to the end of the spinal cord

Looks like a horse’s tail

Composed of nerve roots extending from the ends of the spinal cord (conus medullaris)

Question 11

Spinal cord

Answer 11

Part of the CNS

One long continuous structure

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column.

Question 12

Anatomy of the spinal cord - internal features (Point to these features on an unlabelled image)

Answer 12

CNS
Grey matter (cell bodies) 
White matter (axons) 
Posterior (dorsal) median sulcus
Central canal 
Anterior (ventral) median fissure 
Dorsal grey horn (cell bodies) 
Ventral grey horn (cell bodies) 
Ventral white columns (axons) 
Dorsal white columns (axons) 
Lateral grey horn (cell bodies) 
Lateral white column (axons) 

PNS
Dorsal nerve root (axons) contains afferent sensory neurons
Ventral nerve root (axons) contains efferent motor neurons
Dorsal root ganglion (cell bodies)
Spinal nerve

Question 13

Sulcus

Answer 13

Furrow

Question 14

Fissure

Answer 14

A deep sulcus

Question 15

Anatomy of the spinal cord - flow of information

Answer 15

Dorsal half of the spinal cord is the sensory (afferent) part (gets information from PNS to CNS)

Ventral half of the spinal cord is the motor (efferent) pathway (takes information from the CNS into the PNS

Question 16

Dorsal (posterior)

Answer 16

Sensory/afferent information comes into the dorsal aspect of the spinal cord from the PNS

1. Sensory information is detected at the periphery and travels up the dendrites of the peripheral nerve, 2. It travels into the dorsal root ganglion, then travels down the axons (in the dorsal nerve root), 3. Synapses in the 2nd order neuron in the dorsal horn (where the second order neurons’ cell body/dendrites are), 4. Travels up the icons in the dorsal column (white matter) to the brain

Question 17

Ventral (anterior)

Answer 17

Motor/efferent information goes out of the ventral aspect of the spinal cord to the PNS
1. Efferent information leaves the spinal cord through the ventral roots, sending motor commands to effectors in the body
The somatic motor neuron cell bodies are located in the ventral horn
The autonomic motor neuron cell bodies are located in the lateral horn

Question 18

Flow of information out of the spinal cord

Answer 18

Efferent (moto) information leaves through ventral roots - motor commands go to the effectors in the body
Somatic motor neurons (cell bodies) are in the ventral horn
Autonomic motor neurons (cell bodies) are in the lateral horn

Question 19

Damage to the ventral horn

Answer 19

Paralysis of muscles supplied by spinal nerves from this level, on the same side only

If they die then there is no more motor neuron going out to command the skeletal muscle which effectively means there are no commands to the skeletal muscle that it was previously able to control

Question 20

Flow of information into the spinal cord

Answer 20

Cell bodies of sensory neurons are in dorsal root ganglion
Dendrite (input zone) out in body contains receptors for sensory stimulus
Axon (carriers information IN = afferent) enters the spinal cord through dorsal roots

Question 21

Damage to the dorsal root ganglion

Answer 21

Loss of sensation from regions of the body supplied by spinal nerves from this level and on the same side only

Question 22

Dorsal nerve roots

Answer 22

Carry only afferent information

Question 23

Ventral nerve roots

Answer 23

Carry only efferent information

Question 24

Spinal nerve

Answer 24

Carries both efferent and afferent information (it has two way traffic)

Question 25

What happens to the spinal nerves once they leave the spinal column?

Answer 25

Spinal nerve = both afferent and efferent

Dorsal ramus - efferent to back (to control muscles of the back), afferent from the back (about heat, touch etc from the back)

Ventral ramus - efferent to ventral body, afferent from the ventral body

Rami communicantes
Sympathetic ganglion
Synthetic nerve

Question 26

Structure of a peripheral nerve

Answer 26

Bundles of axons in the PNS are called a nerve

Individual axons may be myelinated or unmyelinated
Axons are covered with endoneurium
Endoneurium-covered axons are bundled together to form a fascicle.
Fascicles are covered with perineurium
Fascicles bundle with each other and with blood vessels to form a nerve (blood vessels supply blood to the internal path of the peripheral nerve so the axons here have the energy and oxygen that they need)
Nerves are covered by epineurium

Question 27

Dorsal white columns are part of the …

Answer 27

Sensory system

Question 28

Are ventral root axons myelinated?

Answer 28

Yes they are myelinated

Question 29

What is the sympathetic ganglia comprised of?

Answer 29

Chains of sympathetic ganglia which contain cell bodies of post synaptic neurons of the sympathetic nervous system which is connected by neural fibres

Question 30

What happens when spinal nerves leave the spinal column?

Answer 30

The spinal nerve carriers both efferent and afferent information

Dorsal ramus - carries efferent (motor) output to the BACK (muscles), afferent (sensory) input from the BACK

Ventral Ramus - carries efferent (motor) output to the ventral body, a fferent (sensory) input from the ventral body

There is also a rami communicantes which branches from the sympathetic ganglion to the spinal nerve. These contain postganglionic nerve fibres of the sympathetic nervous system

Question 31

Spinal nerve anatomy

Answer 31

Three layers of connective tissue

• Axons are covered in endometrium
• Fascicles are covered in perineum
• Nerves are covered in epineurium

Axons can be myelinated or unmyelinated
Multiple axons are bundles to form fascicles
Fascicles bundle together to form a nerve