Sunday, October 25, 2009

Ch 14, spinal cord

Material for this chapter is difficult, lectures go very fast, and it can be tough to follow and write quickly - he is going over this material VERY fast and it is very conceptual, my notes are not entirely complete thus far. Seriously recommend getting a copy of the power points to study with if you don't already have one.

Exam note:
The test will be on Wednesday the 4th at 10:30 am. It will probably not include much in the way of models, he has said several times to focus on learning to label the illustrations in the book and study off pictures, as they will comprise a lot of the practical material. As he holds reviews, I am compiling a study guide for the class, this will be available next MOnday.


WEDNESDAY and FRIDAY's lectures, combined

Spinal Cord
1. It is the link between the brain and the PNS.
2. pathway for sensory and motor impulses
3. roughly cylindrical


Regions of the spinal cord

1. Cervical
2. Thoracic
3. Lumbar
4. Sacral


Anatomical landmarks of the spinal cord that you absolutely need to know

1. 2 longitudinal depressions
a. Posterior Median Sulcus - PMS
b. Anterior Median Fissure - AMF
2. 2 enlargements of the spinal cord
a. Cervical enlargement (biggest) - supplies and innervates pectoral girdle - lies at about C6, the plexus is between C4 and C8 (spinal nerve)
b. Lubrosacral enlargement - supplies and innervates lower limbs
3. Conus Medullaris - L1 - tapering end of the spinal cord proper.
4. Cauda Equina - L1 to sacrum - "Horse Tail" this is made up of bundles of nerves/axons. Looks like a horse's tail.
5. Filum Terminale - one terminal fiber which anchors the spinal cord to the end of the sacrom, comes off the cauda equina.

Spinal Nerves
there are 31 pairs - please note that the cervical spinal nerves have an extra set, C8. All the others correspond to the number of vertebra in that particular spine.
Know: diagram on page #363 (be able to fill it in)
a. Dorsal Root - posterior - paired structures of sensory nerves
b. Dorsal Root Ganglion (contains sensory nerve cell bodies)
c. Ventral Root - anterior - paired axons of motor neurons
"AMPS" anterior/motor and posterior/sensory
1. Spinal nerves start where the dorsal root ganglia and ventral root come together and join to become a mixed nerve/exit the spine at the intervertebral foramen.

DAP - 3 layers of meninges - page #364
1. Dura mater
- outer meningeal layer, has two actual layers of it's own
a. periosteal (this is the outermost layer, next to the bone, thus 'osteal')
b. meningeal (inner layer)
2. Arachnoid mater
a. thin, spiderwebby
3. Pia mater
a. innermost meningeal layer, has blood supply, extensions that anchor the cord come off the pia matter and are known as "denticulate ligaments".

The order basically goes like this, from outside in:
Dura Mater outermost
a. periosteal
b. meningeal
SUBdural space - space between dura mater and arachnoid mater
Arachnoid mater middle layer
Subarachnoid space - this is the largest of the spaces between maters and this one is full of CerebroSpinalFluid (CSF) which bathes the spinal cord.
Pia Mater - inner most layer
Spinal cord.

The Spinal Cord proper:
see slide #20 and also page #368 for a good diagram of this. Memorize it.
So there's white matter which is around the outside and grey matter inside, which looks a lot like a butterfly or a Honda logo. The grey matter is made up of unmyelinated dendrites, axons and neurons. The front, side and back parts of the "butterfly" are called the "horns". You want to know them and what they do.
1. Anterior Horn:
cell bodies of somatic motor neurons (anterior motor)
2. Posterior Horn:
cell bodies of somatic sensory neurons and visceral sensory neurons (posterior sensory)
3. Lateral Horns
cell bodies of autonomic nervous neurons
4. know also the "grey commisure"
this is where nerve impulses cross over - remember that the right side of the brain deals with the left side of the body, etc. impulses cross over contralaterally at some point in the spine.

Page #368 has an important diagram that you need to memorize about somatic motor and somatic sensory impulses and where they are located on the "butterfly".

NOTE: You MUST get the power points or use the diagrams in the book to learn this. The diagrams are crucial to understanding this visually. slide 47-48
PLEXUS - this stuff is really important
A plexus is:
a. a group of spinal nerves that do a specific job
b. divided into groups
cervical, brachial, lumbar and sacral
Note: the Thoracic nerves are NOT A PLEXUS. They're different.

Cervical plexus
- C1-C4 - deep to SCM muscle, innervates the muscles and skin of the face
a. Know the "Phrenic nerve" at C4 - innervates the diaphragm via the thoracic cavity, with a little assistance from C3 and C5.
Brachial Plexus C5-T1 (anterior rami) - innervates the upper limbs and pectoral girdle.
1. "Trunks" know these and in what order, what they do, etc. SLIDE #58-60- It's kind of like a tree, right? The spinal cord is the root of the tree, then the spinal nerves exit and branch out to:
a. superior trunk
b. middle trunk
c. inferior trunk
to
a. posterior cord
b. lateral cord
c. medial cord
to 5 major terminal branches (know these terms and functions)
a. axillary (armpit, shoulder)
b. median (down the middle of the arm)
c. musculocutaneous - high and shoulder, biceps brachii, some skin
d. radial - along the radial bone, thumb, fingers 2-3, underlying muscles
e. ulnar - along ulna, little finger, skin to little finger
Lumbar Plexus - ant rami L1-L4 SLIDE #64
give rise to
1. Femoral Nerve - posterior (refers to how it is relative to other nerves exiting spine, NOT where it lies in the leg)
a. lies beneath the inguinal ligament
b. primary nerve to the anterior thigh/leg
c. fibular, foot and gluteal innervation
2. Obdurator nerve - anterior
Sacral Plexus - L4-S4 anterior rami
1. Sciatic nerve
largest nerve in the body
longest nerve in the body
Distally, it has 2 divisions in a common sheath
a. common fibular divison
b. tibial division
Branches
a. Tibial
b. common fibular nerve
c. deep fibular nerve
d. superficial fibular nerve
Thoracic nerves - remember, these are not a plexus, see slide #45
T1-T11 and T12 subcostally
T1 is actually part of the brachial plexus, so T2 is where the thoracic nerves officially 'start'.
Intercostal nerves - along each rib, the lower border of the rib margin
innervated along ganglia

Dermosomes
a. each pair of spinal nerves controls a region of body surface sensation - the exception to this is C1, which does not.
b. from dorsal and ventral rami fibers
c. damage to the spinal nerve results in loss of sensation to a region of skin
d. this is a helpful diagnostic tool, sometimes pain is referred from one nerve to a corresponding region of skin.

Reflexes
a reflex is a specific, rapid and involuntary response to a specific stimulus (which is required, to elicit the reflex)
3 types:
a. rapid
b. automatic
c. involuntary
can be:
a. ipsilateral - receptor and effector are on the same side
b. contralateral - crosses over, receptor and effector cross over at commisure

Reflex arcs are either monosynaptic or polysynaptic
Steps of a Reflex Arc - slide 75-78, know these steps
1. peripheral stimulation
2. sensory neuron
3. dorsal root
4. posterior horn
5. activates motor neuron
6. response by effector muscle
EXAMPLES:
Withdrawal reflex - #79
polysynaptic reflex arc
Stretch reflex - #80
monosynaptic reflex arc

Slide #82, ignore, he said it will not be on the test.

1 comment:

  1. That was a really knowledgeable post. I often find that this topic is complicated to get your head round but you have summed it up really well.
    http://www.youtube.com/watch?v=EyuUyN5RVTI

    ReplyDelete