Chapter 16: Spinal Cord and Spinal Nerves Flashcards
Describe the spinal cord and be able to label it’s features on a diagram.
(Diagram Pg. 486 & 488)
- Link between body and brain
- Spinal cord and spinal nerves serve 2 important functions
- Pathway for sensory and motor impulses
- Reflexes
- External surface has 2 longitudinal depressions:
- Posterior median sulcus
- Anterior median fissure
List the (5) regions of the spinal cord and how many pairs of spinal nerves are in each region.
Cervical Region (8 pairs) Thoracic Region (12 pairs) Lumbar Region (5 pairs) Sacral Region (5 pairs) Coccygeal region (1 pair)
(Total: 31 pairs of nerves)
What is the conus medullaris and why is it significant?
It’s the tapering end of the spinal cord.
It marks the official end of the spinal cord proper (approx. L1).
What is the caudal equina and what does it mean?
Cauda equina means “horses tail.”
Inferior to the conus medullaris, is the caudal equina which is nerve roots that protect inferiorly from the spinal cord.
What is the filum terminale?
- thin strand of pia mater that anchors the conus medullaris to coccyx
- within caudal equina
White Matter vs Gray Matter
(in the spinal cord)
Be able to identify the structures in the diagram.
(Diagram Pg. 490)
Gray matter
- In the middle of spinal cord
- Cell bodies of motor neurons
- Horns (anterior, posterior, and lateral)
- Gray Commisure
White Matter
- Outside of gray matter
- Funiculus (anterior, posterior, and lateral)
- White Commisure
Describe the arrangement and function of the meninges in the spinal cord.
(Outermost to innermost)
Be able to identify these layers on the diagram.
(Diagram Pg. 488)
Vertebra
Epidural Space
- between outermost meninge (dura mater) and periosteum covering the inner walls of vertebra
DURA MATER
- fuses the connective layers that surround the spinal nerves
Subdural space
- potential space between dura mater and arachnoid mater
ARACHNOID MATER
Subarachnoid space
- Real space filled with CSF
PIA MATER
- Innermost layer adheres directly to the spinal cord
Describe the components contributing to a spinal nerve.
Be able to identify the structures in the diagram on Pg. 492.
Anterior rootlets - from spinal cord come together to form anterior roots
Anterior roots - contain motor axons only (voluntary movement, efferent)
Cell bodies of the motor axons are in the anterior and lateral horn (gray matter in spinal cord)
Posterior rootlets
Posterior roots - contain sensory axons only (sensory, afferent)
Cell bodies of the sensory axons are in the posterior root ganglion
Anterior and posterior roots combine in the intervertebral foramen to form a spinal nerve (obviously containing both motor and sensory axons)
Define dermatome. Be able to label and describe them.
(Diagram Pg. 493)
A specific segment of skin supplied by a single spinal nerve.
- The skin of the body is may be divided into sensory segments that collectively make up a “dermatome map”
(Pg. 493)
Define myotomes.
Why do you think they are significant to our field?
A group of muscles primarily innervated by the motor fibers of a single nerve root.
My guess:
Based on muscle function tests, we can tell where an injury is located (what nerve is not functioning properly). ie. If a patient has weakness while performing dorsiflexion, it can be an indication that something is wrong with spinal nerve L4.
ie. This is why on intake forms it asks if you have trouble controlling bladder/bowel. It can be a red flag for injury to S3-5.
Myotomes!
List what muscle groups are innervated by these nerves: C3-5: C5: C6: C7: C8, T1: T1-T12: L1, 2: L3: L4: L5: S1: S3-5:
C3-5: Diaphragm/breathing"C3-5 keep the diaphragm alive!" C5: Shoulders, bicep C6: Elbow flexors, wrist extensors C7: Elbow extensors, wrist flexors C8, T1: Finger flexors/abductors T1-T12: Chest wall and back mm L1, 2: Hip flexor L3: Knee extensor L4: Ankle dorsiflexor L5: Great toe extensor, hamstrings S1: Ankle plantar flexors, hamstrings S3-5: Bowel, bladder
What do intercostal nerves innervate?
Travel in the intercostal space between two adjacent ribs.
Innervate
Define a nerve plexus and list the primary nerve plexuses in the body (4).
Nerve plexus: network of interweaving anterior rami of spinal nerves; occurs on both sides of the body;
Nerve plexuses split into multiple named nerves which innervate various body structures.
Primary Plexuses:
- Cervical Plexus
- Brachial Plexus
- Lumbar Plexus
- Sacral Plexus
Describe the structure of the brachial plexus.
Brachial plexuses - (right and left - one on each side) network of nerves that innervates the pectoral girdle and entire upper limb
Formed by anterior rami of C5-T1
List the peripheral nerves that come off of the brachial plexus (5) with their sensory (S) and motor (M) innervations.
- Axillary Nerve
M: Deltoid Muscles
S: Skin over deltoid - Musculocutaneous Nerve
M: Anterior upper arm muscles
S: Lateral forearm - Median Nerve
M: Forearm flexors, thenar group muscles
S: Palm and thumb through half of 4th finger; dorsal tips of fingers - Radial Nerve
M: Extensors upper and lower arm
S: Posterior arm, posterior forearm, dorsal aspect of lateral 3 digits (but not tips) - Ulnar Nerve
M: Anterior forearm muscles and intrinsic hand muscles
S: Lateral half of of 4th finger and the pinky
List the peripheral nerves that come off of the lumbar plexus (2) with their sensory (S) and motor (M) innervations.
- Femoral Nerve
M: Anterior Thigh Muscles
S: Anterior thigh down medial leg down to medial part of foot - Obturator Nerve
M: Adductors muscles of the thigh
S: Superior medial thigh
List the peripheral nerves that come off of the sacral plexus (4 sorta) with their sensory (S) and motor (M) innervations.
Sciatic Nerve (made up by #’s 1 and 2)
1. Tibial Nerve
M: Posterior thigh muscles, posterior lower leg muscles, plantar foot muscles
S: Heel of foot
- Common Fibular Nerve (splits into #’s 3 and 4)
M: Short head of biceps femoris
S: - (See 3 and 4) - Deep Fibular Nerve
M: Anterior lower leg muscles, dorsum of foot
S: Between great toe and second toe - Superficial Fibular Nerve
M: Lateral lower leg muscles
S: Dorsum of foot
What is a reflex? What similar properties do all reflexes have in common? (3)
Rapid, automatic, involuntary reacts of muscles or glands to a stimulus.
Properties:
- Stimulus is required
- Rapid response is produced with few neurons involved and minimal synaptic delay
- Automatic response occurs the same way every time
Discuss components and function of a reflex arc. Give an example.
- Begins at a receptor in the PNS
- Communicates with the CNS
- Ends at a peripheral effector cell (muscles or gland)
ie. Patellar reflex
List and describe the (3) types of spinal reflexes.
Diagrams Pg. 509
- Withdrawl or Flexor Reflex
- Polysynaptic
- Initiated by painful stimulus
- Receptor organ sends sensory info to spinal cord, received by interneuron which stimulate motor neurons to contract, causing you to pull away from the sharp stimulus - Stretch Reflex
- Monosynpatic
- Monitors and regulates skeletal muscle length
- Stimulus results in stretching of a muscle and the muscle reflexively contracts to protect itself from over stretching
- ie. Patellar Reflex - Golgi Tendon Reflex
- Polysynaptic
- Prevent skeletal muscles from tensing excessively
- Nerve endings located within tendons near a muscle-tendon junction (golgi tendon organs) when activated send a signal to interneurons in the spinal cord which intern inhibit the action of the motor neurons
(So if tension on the muscles is too much, this reflex inhibits the the muscle from working so the muscle is not overloaded and damaged/torn from the tendon/bone)
Distinguish between ipsilateral and contralateral reflex arcs.
Ipsilateral
- Receptor and effector organ are on the same side of the spinal cord
- ie. muscles in your left arm contract to pull your left hand away from hot object
Contralateral
- Sensory impulses from receptor organ cross over through the spinal cord to activate effector organs on the opposite limb
- ie. step on sharp object with your left foot, contract muscles in your right leg to maintain balance while you draw your left leg away from sharp object
Distinguish between monosynaptic and polysynaptic reflexes.
Diagram Pg. 509
Monosynpatic
- Simplest reflex
- Interneurons NOT involved
- ie. Patellar reflex
Polysynaptic
- More complex
- Interneurons ARE involved
- Also a number of synapses involved (as indicated in the name)
- More of a delay between stimulus and response (due to involvement of multiple synapses)
