Spinal Nerves contain axons from Somatic and Autonomic Components.
What parts of the body does it supply? (2)
- The Somatic components (motor and sensory) supply the whole body except except head and parts of neck.
- The Spinal nerves contain the sympathetic components of the ANS which supplies whole body.
How many pairs of Spinal Nerves are there?
How are this arranged? (5)
There are 31 pairs of Spinal nerves.
Cervical - 8 (there are only 7 C vertebrae where nerves all exit above vertebrae, last nerve exits below)
**Rest of nerves exit between respective vertebrae
Thoracic - 12
Lumbar - 5
Sacral - 5
Coccygeal - 1
How do Spinal nerves connect to Spinal Cord? What’s the arrangement? (3)
Where do they exit? (1)
Nerve roots which sit within vertebral canal.
- The Dorsal Root (posterior) contains Afferent nerves (Somatosensory axons)
- Ventral Root (anterior) contains Efferent nerves (somatic motor and sympathetic axons).
- They exit via Intervertebral Foramen
How long at Spinal Nerves? What about the nerve roots? (3)
They are generally very short.
However the NERVE ROOTS of Lumbar and sacral roots are long as they have to travel to their respective vertebrae.
The Dorsal Primary Ramus . Where does it supply? (3)
- Skin over paravertebral gutter
- Erector Spinae Muscles
- Facet Joints of Vertebral Column
Ventral Primary RAMUS. Where does it supply?
It is much larger Ramus. It supplies rest of body except Head and parts of neck.
What group of nerves are formed from Ventral Primary Rami? (5)
- Inter coastal Nerves
- Four Nerve Plexus:
- Cervical Plexus
- Brachial Plexus
- Lumbar Plexus
- Sacral Plexus
What is a Dermatome and Myotome? Why is T10 Dermatome important? (3)
How are these developed during Embryology? (2)
Dermatome - Strip of Skin that is innervated by Single Spinal Nerve. T10 runs over UMBILICUS.
Myotome - Individual Muscle group innervated by a Single Spinal nerve.
Embryology: Dermatome and Myotomes develop from Somites (blocks of mesoderm). Spinal Nerves are formed from Ectoderm.
What is an example of when Visceral Pain is ‘referred’ (2)
Diaphragm Irritation referred to Shoulder (c3-c5 Dermatomes) as cutaneous pain in skin.
(ANS): What are the origins of the Parasympathetic and Sympathetic Nervous systems? (2)
Parasympathetic: Brainstem and Sacral Spinal Cord
Sympathetic: Thoraic and lumbar Spinal Cord (T1 to L2 only)
How are Neurons arranged in a circuit in the ANS. (4)
- Usually two neurons in a circuit. A myelinated Preganglionic Neuron which reaches a Synapse at Autonomic Ganglia, and then passes into Postganglionic Neuron.
- Exception is SYMPATHETIC Supply to ADRENAL MEDULLA. This just have one line preganglionic axon.
Where do the Sympathetic preganglionic neurons start and where do they insert? (4)
- Start from Ventral Roots from T1 to L2
- Insert into Sympathetic Trunk: This is an interconnected paravertebral ganglia and extends the whole length of the vertebral column.
- Most carry on into spinal nerves, while some pass through Sympathetic trunk and insert into SPLANCHIC nerves into Prevertebral ganglia in abdomen.
Where do the Sympathetic postganglionic exit into MSK + Heart, lungs and head + Abdomen.
- They exit via Primary Rami into MSK.
- Also exit via Branches into Heart, lungs or head.
- The postganglionic neurons in abdomen pass directly into organs.
Cranial Parasympathetic Axons: Where do they originate?
What organs do they affect? (3)
The preganglionic axon pass through Cranial Nerves to reach ganglion near effector organ; then synapse unto postganglionic axon.
Effector Organs: Pupil, Tear gland, Salivary gland
What nerve connects Preganglionic Axons from Brainstem to Thoracic/abdominal viscera?
What are the effector organs? (2)
- Via Vagus Nerve
2. Lungs, Heart and Abdomen
For Sacral Parasympathetic preganglionic axons, where do they originate?
What are its effector organs?
- Originate from Sacral Spinal Cord
- They pass through Pelvic Splanchic Nerves.
Effector organs - Bladder, Rectum, Sexual Function.