Anatomy: The Nervous System (stud notes pt 3)

The Nervous System: The Information Superhighway

• The brain is in the cranial cavity
• The spinal cord is in the spinal cavity
• The cranium (skull) and the vertebral column protect the brain and spinal cord
• The spinal cord can be thought of as the main highway carrying impulses from the brain which is the control center
• Spinal nerves that go out from the spinal cord are like smaller highways

Cerebrospinal Fluid (CSF)

• CSF is a fluid cushion that protects the brain and spinal cord from shock

Meninges

• The brain and spinal cord are surrounded by meninges which act as cushions and shock absorbers

Spinal Cord

• The spinal cord is an extension of the brain stem
• It sends information from the brain stem which controls important functions for staying alive
• The spinal cord exits the skull through the foramen magnum located at the base of the skull
• The spinal cord remains intact as the main highway, leading to the conus medularis

Conus Medularis and Cauda Equina

• The conus medularis is where the spinal cord tapers down to a pointed structure in the lumbar region
• From the tip of the conus medularis, nervous tissue hangs downward, forming multiple spinal nerves
• These nerves together are called the cauda equine
• The cauda equine are surrounded by CSF

Spinal Nerves

• Spinal nerves are connected to the spinal cord
• Spinal roots are ramps for the spinal cord
• Each spinal nerve is covered with connective tissue, containing axon bundles and blood vessels
• Each spinal nerve carries both sensory and motor information
• Sensory information goes to the brain
• Motor information goes from the brain to the muscles

Spinal Nerve Pairs

• There are 31 pairs of spinal nerves, each named for the spinal cord segment they come from
• There are:
  • 8 cervical nerves (C1-C8)
  • 12 thoracic nerves (T1-T12)
  • 5 lumbar nerves (L1-L5)
  • 5 sacral nerves (S1-S5)
  • 1 coccygeal nerve (Co1)
• Nerves innervate specific areas of the body, carrying information to and from that area

Reflexes

• Reflexes are the simplest form of motor output
• Reflexes are a protective mechanism
• Sensory impulses do not go to the brain
• Impulses are sent to the gray matter (sensory horn) in the spinal cord and messages are sent to the motor neuron in the gray matter (motor horn), then out to the motor neuron in the nerve

Spinal Cord Injury

• The spinal cord is protected by structures like vertebra and meninges, but trauma can damage the nervous tissue
• Spinal cord injuries result in paralysis of the area related to and below the injury location
• There is no sensory input or motor output below the level of the injury
• Spinal cord injury in the cervical region results in quadriplegia (paralysis of all four limbs)
• If the spinal cord is completely cut at the C5 spinal nerve, no impulses can be sent to and from the brain below C5
• Injuries in the thoracic region and below result in paraplegia, paralysis of the lower extremity

Stroke (Cerebral Vascular Accident)

• A stroke occurs when blood flow is disrupted to a portion of the brain, due to blockage or hemorrhage
• When blood stops flowing, the area no longer receives oxygen, and brain tissue dies
• Stroke symptoms are related to the affected brain area, and symptoms appear suddenly

Aging and the Nervous System

• With aging, reaction time slows, and impulses do not travel as fast
• This makes individuals more prone to injury, like falls, burns, and trauma