T1L18: Principles of the Nervous System 2 Flashcards
Peripheral nerves arise [2]
Brain/brainstem = cranial nerves
Spinal cord = spinal nerves
Spinal nerves overview [4]
Sympathetic supply to whole body
Motor and sensory supply to whole body except head and neck
Excellent segmental organisation
1 pair at each vertebrae
31 pairs of nerves
8 Cervical: Upper limb/head/neck 12 thoracic 5 lumbar 5 sacral 1 coccylgeal
Dorsal and ventral roots [4]
Nerve roots connect spinal nerves to spinal cord
Ventral root = efferent (motor/sympathetic)
Dorsal root = afferent (sensory)
Root sit within vertebral canal
Spinal nerves [4]
Dorsal and ventral roots merge to form spinal nerves
Mixed nerves (motor/sensory and sympathetic)
Mixed = efferent and afferent nerves
Exit through intervertebral foramen
Primary rami [3]
Spinal nerve divide into
Dorsal/posterior primary ramus
Ventral/anterior primary ramus
Mixed nerves
Dorsal primary ramus [3]
Skin over paravertebral gutter
Erector spinae muscles
Facet joints of vertebral column
Ventral primary ramus [2]
Supply rest of body
Larger nerves
Map of ventral primary rami [4]
• From intercostal nerves and 4 nerve plexuses
• Nerve plexus is where ventral primary rami merge
• Formed nerves contain axions from multiple spinal nerves
Important for innervation to limbs
Dermatomes and myotomes
Dermatome: Individual area of skin innervated by single spinal nerve (primary ramus)
Myotome: An individual muscle group innervated by a single spinal nerve (primary ramus)
Embryonic development of dermatomes and myotomes [2]
Dermatomes and myotomes develop from somites (mesoderm) during embryonic week 3
Somites are paired blocks from horizontal bands
One pair of spinal nerves (ectoderm) grow into one pair of somites
Dermatome: Clinical importance [2]
Loss/altered sensation/pain from dermatome indicates injury to spinal cord, nerve root or spinal nerve
○ Easy to determine location of injury from dermatomes
○ E.g. loss of sensation from skin over umbilicus may indicate damage to……
Also, visceral (organ) pain can be referred to skin (dermatomes) as cutaneous pain
§ E.g. Diaphragm irritation referred to shoulder
(C3-C5 dermatomes)
Myotomes [3]
Conserved in thorax
Intercostal muscles supplied by intercostal nerves (T1-T11)
More complicated in limbs
Autonomic component [4]
Involuntary part of peripheral nervous systems
○ Regulate operation of internal organs ○ Maintains internal environment
Sympathetic or parasympathetic
Sympathetic vs parasympathetic
Sympathetic function
• Flight or fight
• Maximise use of metabolic resources
Parasympathetic function
• Opposite to sympathetic division
• Switched on during resting
Increases/conserves metabolic resources
