Anatomy 2 - Clinical anatomy of the spinal nerves Flashcards
What does each pair of spinal nerves supply ?
They supply everything in one segment of the body wall
What type of nerve fibres are carried within spinal nerves ?
- Somatic general sensory
- Somatic motor & sympathetics - for motor functions
Describe what somatic general sensory fibres supply
They transmit sensations form the body to the CNS; this can be sensations from the skin or pain & proprioceptive sensations from the muscles, tendons & joints
Describe the supply of somatic motor fibres
They transmit impulses to skeletal (voluntary) muscles
Describe the supply of sympathetic motor fibres to the body wall
They are conveyed by all spinal nerves to the smooth muscle of blood vessels & to sweat glands & arrector pili muscles of the skin.
What type of nerve fibres do you need to remember are NOT associated with spinal nerves ?
Parasympathetics
On spinal nerve testing what are the different somatic general sensory symptoms a patient may experience ?
Pain (neuralgia), pins & needles (paraesthesia), numbness (anaesthesia), sensitivity (hyperaesthesia), temperature perceptions, loss of co-ordination/balance/clumsiness (e.g. ataxia)
On spinal nerve testing what are the different somatic motor symptoms a patient may experience ?
Muscle stiffness, tightness or spasm (cramp), muscle floppiness or looseness, (reduced tone or hypotonia), muscular weakness (reduced power), loss of co-ordination/balance/clumsiness (e.g. ataxia)
How do you test each of the following for spinal nerve segments:
- Sensory function
- Motor function
- Both sensory and motor function
- Sensory function - test the corresponding dermatome
- Motor function - test the corresponding myotome
- Both sensory and motor function - test spinal cord reflexes as in a reflex you have to be able to sense muscle stretch and then react (reflex) with motor function
What type of nerve fibres are contained within each of the following in a spinal nerve:
- Posterior root
- Anterior root
- The actual spinal nerve
- Anterior and posterior rami
- Posterior root - sensory fibres = somatic general sensory
- Anterior root - motor fibres = sympathetics and somatic motor fibres
- The actual spinal nerve - mixed fibres (sensory and motor) = all 3
- Anterior and posterior rami - mixed fibres (sensorry and motor) = all 3
Go over the spinal nerve dermatomes
Describe the route a general sensory AP takes starting at the dermatome
- AP’s generated in the axons of the receptors of the dermatome
- AP’s conducted along axons within the anterior ramus/ or posterior ramus depending on if its a dermatome on the anterior or posterior wall which is stimulated
- AP’s then pass into the posterior root (as these are sensory AP’s)
- AP’s pass into the posterior rootlets
- AP’s arrive at the posterior horn of the specific spinal cord segment e.g. if T10 dermatome stimulated it would arrive at T10 spinal cord segment
Define a named nerve
- Named nerves = nerves that often (not always) have >1 spinal nerve root & ==> overlap more than one ‘true’ dermatome e.g. femoral nerve (L2,3,4)
- The area of cutaneous innervation by the femoral nerve corsses 3 true dermatomes
Label the peripheral cutaneous nerve supply of the head and neck
Where is the nerve point of the neck located ?
Just above midpoint of posterior border of SCM
Label the peripheral cutaenous nerve supply of the upper limb
Label the peripheral cutaneous innervation of the lower limb
Describe the pathway of testing sensory function of a peripheral nerve
- right femoral nerve “area” is stimulated (at the point shown)
- APs in the axons of the receptors of the L2 dermatome part of the femoral nerve “area” (L2 area is what is stimulated)
- APs conducted centrally along the same axons within the L2 anterior ramus
- the same L2 axons weave their way through the lumbar plexus to the L2 spinal nerve
- APs conducted via the same axons which are now in the L2 posterior root
- APs conducted via the same axons which are now in the L2 posterior rootlets
- APs arrive at the posterior horn of the L2 spinal cord segment
- APs are conducted via an ascending tract to the primary somatosensory cortex
Describe the pathway of spinal cord reflexes using patellar reflex as an example
- 1.patellar ligament tapped
- 2.stretches quadriceps fibres
- 3.muscle stretch receptors initiate APs in the anterior rami axons within the femoral nerve
- 4.sensory APs conducted to dorsal horn of L4
- 5.axons pass into anterior horn to synapse on LMNs that supply quadriceps
- 6.APs conducted via the LMN axons in the femoral nerve to reach the quadriceps NMJ
- 7.muscle contracts to extend knee joint
Note reflex muscle reactions controlled by descending pathways so AP does not travel to the brain
Label the spinal nerve levels for the reflexes
- Biceps - C5, 6
- Triceps - C7, (8)
- supinator / brachioradialis - C5, (6)
- Knee - L3, 4
- Ankle - S1 (2)
