Spinal Cord & Spinal Nerves

• Cervical - 8
• Throacic - 12 
• Lumbar - 5
• Sacral - 5
• Coccygeal - 1

• All mixed in function
• Emerge from intervertebral foramina

• Varies
• Generally narrows inferiorly

• Inferior cervical part of spinal cord 
• Innervate upper limbs

Extends through the lumbar and sacral parts of spinal cord and innervates the lower limbs

• Tapering inferior tip
• Marks the official end of spinal cord proper

• Nerve roots from lumbar, sacral & Coccygeal region with vertebral cavity 
• "Horses tail"

Thin strand of pia mater that helps anchor the conus medullaris to the coccyx

• Cell bodies, dendrites, unmyelinated axons
• Horns & gray commissure
• Synapses occur

• Finiculi
• White commissure

Sensory axons

• Cell bodies of sensory neurons 
• attached to posterior root

Motor axons

• Interneuron cell bodies
• Sensory neuron axons
• Synapses occur

• Motor(Somatic) neuron cell bodies
• Interneuron axons
• Synapses Occur

Lateral gray horns- Motor neuron cell bodies (ANS)Throacic & upper lumbar regions (t1-L2)

• Unmyelinated axons
• Path between R&L sides of cord (Site of central canal)

C1-C4: Neck, portions of head and shoulder

C5-T1: Upper limbs

L1-L4: Anterior/medial thigh

L4-S4: Most of lower limb & lower pelvis

• Innervates deep muscle/skin of back 
• Smallest of the 2 branches

• Largest branch
• Innervates limb muscles & structures, skin of anterior and lateral trunk 
• May form spinal nerve plexus

• Between spinal nerve & sympathetic trunk ganglia 
• Innervates glands, cardiac & smooth muscle

Spinal Nerves

• Specific area of skin whose sensations are carried by a single spinal nerve 
• Some overlap
• Involved in referred visceral pain
• Can be used diagnostically (indicate spinal damage or level or spinal cord injury)

A network of interweaving anterior rami of spinal nerves 

(posterior nerves are smaller and do not form plexus)

• Shortest pathway; result in reflex
• Fast automatic, involuntary response to a specific stimulus

• Receptor - Excited by stimulus 
• Sensory Neuron- Transmits to CNS
• Interneuron- Integrates (in CNS)
• Motor Neurons- Transmit to effector 
• Effector- Performs reflexive action; muscle or gland

• Integration in spinal cord
• Withdrawal 
• Never reach the brain

• Integration in brainstem
• Eye tracking movements during reading

Effects skeletal muscle

Effects glands, cardiac & smooth muscle

• Ipsilateral- When both receptor and effector are on the same side of spinal cord (pull hand from hot  object)
• Contralateral- When sensory impuls from receptor cross over to activate effector on opposite limb