Nervous System: Spinal Cord and Nerves

• Information highway between brain and body.
• Extends through vertebral canal from foramen magnum to L1
• Each pair of spinal nerves receives sensory information and issues motor signals to muscles and glands
• Spinal cord is part of the central nervous system, while nerves are part of the peripheral nervous system

• Conduction: Pass information between brain and nerves
• Locomotion: Repetitive, coordinated actions of muscle groups
• Reflexes: Involuntary responses to stimuli

• 31 pairs of spinal nerves among the cervical, thoracic, lumbar, and sacral regions
• Cervical and lumbar enlargements
• Medullary cone tapers at the end
• Cauda Equina: (Horse's Tail) L2-S5 nerves

Fibrous Layers covering spinal cord like the Dura Mater, Arachnoid Mater, and Pia Mater

Tough membrane made of collagen

Squamous epithelial cells create loose mesh of fibers filled with cerebral spino fluid

Delicate membrane

• Failure of vertebral arch to close covering of spinal cord
• Often causes paralysis below affected area
• Folic acid as part of a healthy diet (before conception) drastically decreases risk

Neuron cell bodies

Myelinated axons

• or Dorsal Column-medial Lemniscus Pathway
• Carries touch, movement, and limb position information up the spinal cord to the brain

Crossing over to other side of brain

Carries pain and temperature information up spinal cord to the brain

Carries planned movement information to motor neurons in spinal cord

• Bundles of axons
• Epineurium covers nerves, perineurium surrounds a bundle of nerves (fascicle), endoneurium surrounds individual axons
• Blood vessels penetrate perineurium

• Cluster of neuron cell bodies in PNS
• Dorsal root ganglion is cluster of sensory neuron cell bodies

• 31 Pairs
• Mixed with sensory and motor neurons

• Dorsal root is sensory input
• Ventral root is motor output

Sensory neuron entry into spinal cord

Motor neuron exit from spinal cord

Muscles and joints on dorsal surface

Muscles and joints of trunk and limbs

• Ventral rami branch and come together to form 5 nerve plexi
• Cervical in the neck: C1-C5 (neck and diaphragm)
• Brachial in armpit: C5-T1 (arm and some of shoulder and neck)
• Lumbar in lower back: L1-L4 (abdominal wall, anterior thigh, and genitalia)
• Sacral in pelvis: L4-S4 (lower trunk and legs)
• Coccygeal: S4-S5

• Sensory: ear, chin, neck, shoulder, anterior chest
• Motor: diaphragm

Sensory and motor for lower abdomen, anterior thigh

Sensory and motor for remainder of leg (posterior thigh, distal portion), foot, genitals, and gluteal region

Sciatic nerve gets pinched and pain from sciatica radiates from the buttock down the leg and can travel as far as the feet and toes

• Virus that can enter CNS and destroy motor neurons
• Muscle weakness and paralysis

Degeneration of motor neurons, which leads to muscle weakness and paralysis

• Each nerve sends and receives information to and from a band of the body
• There's lots of overlap between adjacent nerves
• Total loss of sensation requires 3 adjacent nerves to be damaged

• Chicken pox virus remains dormant in dorsal root ganglia for life
• Can become active in one dorsal root ganglion in older adults
• Only parts of the body receiving input from that nerve are affected

• Require sensory input
• Occur very quickly
• Involuntary
• Stereotyped

• Muscle spindle sensory fibers fire action potentials when muscle is stretched
• This causes motor neurons to induce muscle contraction

• Pain receptor stimulation can induce flexor reflex
• Allows withdrawal from painful stimulus
• Crossed-extension reflex does opposite in other leg
• Prevents falling on face

• GTO sensory fibers fire action potentials when muscle contracts
• This stops motor neuron from firing so that muscle won't contract further

Alertness, heart rate, blood pressure, pulmonary air flow, blood glucose, blood from to muscles

Blood flow to skin and digestive tract, reproductive processes, and immune system funtions

• Complementary of sympathetic NS
• Digestion and reproductive processes occur
• Heart rate, blood pressure etc. decreases