Human Anatomy: Spinal Cord and Vertebrae

Quiz Information

• A 12-minute quiz will be given in two weeks.
• The quiz will cover all five lectures.

Central Nervous System

• The central nervous system contains the cerebrum, diencephalon, brain stem, cerebellum, and spinal cord.
• The cerebrum is composed of cerebral hemispheres.
• The brain stem includes the midbrain, pons, and medulla.
• The cerebellum is located at the back of the brain.
• The spinal cord transmits messages between the brain and the rest of the body.

Spinal Cord

• The spinal cord is a long, thin, tubular bundle that extends from the base of the brain down the back.
• It transmits messages between the brain and the rest of the body.
• The spinal cord is protected by bones, discs, ligaments, and muscles.
• The spine is made of bones called vertebrae.
• The vertebrae provide flexibility of motion, while maintaining strength and stability.

Spinal Cord Vertebrae

• Vertebrae have different shapes
• Different shapes allow for a range of motion
• Different shapes provide strength and stability

Spinal Cord and Vertebral Foramen

• The spinal cord is located in the vertebral foramen.
• Vertebrae are stacked on top of each other, creating a space for the spinal nerves to enter and exit.

Spinal Cord Segments

• There are 31 spinal segments in the spinal cord.
• Each segment gives rise to a pair of spinal nerves.
• The cervical region contains 8 pairs of nerves.
• The thoracic region contains 12 pairs of nerves.
• The lumbar region contains 5 pairs of nerves.
• The sacral region contains 5 pairs of nerves.
• The coccygeal region contains 1 pair of nerves.

Spinal Cord and Cauda Equina

• The spinal cord tapers at the lumbar region to become the conus medullaris.
• Spinal nerves arising from the conus medullaris and below continue down the vertebral column as the cauda equina.
• The cauda equina resembles a horse's tail, hence the name.

Development of Spinal Cord

• In the fetus, the spinal cord and vertebral column are the same length until the third month.
• Spinal nerves pass through the neural foramina as the embryo grows, and the spinal cord lengthens.
• The spinal cord gradually recedes from below, as vertebral column growth is faster.

Human Brain Growth

• The human brain grows much less than other parts of the body after birth.
• As a result, the brain is proportionally smaller in adults compared to children.

Cauda Equina

• The cauda equina is the collection of spinal nerve roots that extend from the conus medullaris.
• The cauda equina resembles a horse's tail, hence the name.
• The spinal cord ends approximately at the level of L1 or L2.

Spinal Cord Organization and Function

• The spinal cord is organized into a butterfly shape.
• The grey matter is in the center, and white matter surrounds it.
• The cervical and lumbosacral regions of the spinal cord are enlarged.
• The enlargements contain more grey matter where motor neurons and sensory neurons reside, and allows for greater control of muscle movement and sensory input from limbs.

Spinal Cord and Grey and White Matter Organization

• There are areas of grey matter (collection of neuron cell bodies)
• There are areas of white matter (collection of bundles of myelinated nerve fibers/axons)
• The shape of grey matter is often described as a butterfly or an 'H' shape
• The grey matter is centrally located in the spinal cord, surrounded by white matter.

Sympathetic and Parasympathetic Nervous System

• The sympathetic nervous system controls "fight or flight" responses.
• The parasympathetic nervous system controls "rest and digest" functions.
• The sympathetic nervous system originates in the thoracic and lumbar regions of the spinal cord.
• The parasympathetic nervous system originates in the cranial and sacral regions of the spinal cord.

Spinal Cord White Matter Tracts

• The ascending tracts carry sensory information up to the brain.
• The descending tracts carry motor commands from the brain.
• White matter is organized into tracts (bundles of axons) with a common origin and destination.
• Different tracts are designated to sensory or motor functions in the spinal cord
• Several types of sensory tracts and motor tracts exist, carrying specific types of information to and from the brain
• The dorsal column is more recent in terms of evolutionarily, than the spinal-thalamic tract, because it has more myelination
• The amount of white matter in the cervical and lumbosacral regions of the spinal cord is different from the thoracic region. This is due to the need for higher density of fibres and neurons in the control of the limbs.
• The spinal-thalamic tract conveys sensory information about pain, temperature, and crude touch to the brain.
• The dorsal/posterior column carries sensory information about fine touch, pressure, vibration, and proprioception to the brain.
• The spinocerebellar tract carries proprioceptive information to the cerebellum.

Spinal Cord and Reflexes

• Spinal reflexes do not require input from the brain.
• Spinal reflexes involve sensory neuron, interneurons, and motor neurons
• The brain can send orders down the spinal cord but it not needed for spinal reflexes.
• Some reflexes involve direct connections between the dorsal and ventral horns.