Spinal Cord Anatomy Quiz

Organization of the Nervous System (Part 3)

• The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS)
• The CNS consists of the brain and spinal cord
• The PNS includes nerves that connect the CNS to the rest of the body
• The brain has protective coverings: cerebrum, cerebellum, brainstem, and diencephalon.

Structural Classification of Neurons

• Neuroglia are supportive cells in the nervous system
• Astrocytes are star-shaped glial cells
• Ependymal cells line cavities of the CNS
• Microglial cells are phagocytic cells
• Oligodendrocytes produce myelin sheath in the CNS
• Schwann cells produce myelin sheath in the PNS

Spinal Cord

• Elongated cylinder extending from the brainstem through the foramen magnum of the skull
• Contains grey matter (interior) and white matter (surrounding)
• Has 31 pairs of spinal nerves attached by dorsal and ventral nerve roots
• Lies within the spinal canal, extends to the first lumbar vertebra, and tapers from above downward
• Bulges in cervical and lumbar regions
• Two deep grooves: anterior median fissure & posterior median sulcus; anterior fissure is deeper

Spinal Cord Nerve Roots

• Dorsal nerve root fibers carry sensory information into the spinal canal
• Dorsal root ganglion houses cell bodies of unipolar sensory neurons forming a gray matter region in the dorsal nerve root
• Ventral nerve root fibers carry motor information out of the spinal cord
• Ventral nerve root houses cell bodies of multipolar motor neurons in the gray matter of the spinal cord

Spinal Cord

• Interneurons are located in the spinal cord's gray matter core
• Spinal nerve is a single mixed nerve on each side of the spinal cord, merging dorsal and ventral nerve roots
• Cauda equina is a bundle of nerve roots extending from the conus medullaris (inferior end of the spinal cord)

Cauda Equina

• Collection of spinal nerves descending from the spinal column's lower part (distal end)
• Extends to the lower third of the spinal canal
• Resembles a horse's tail, hence the name (Latin)

Grey Matter

• Composed of nerve cell bodies, dendrites, axon terminals (unmyelinated), and neuroglia
• Pinkish-gray color due to a rich network of blood vessels
• Forms an H shape, consisting of posterior, anterior, and lateral horns
• Projections of gray matter toward the outer surface of the spinal cord are called horns

Grey Matter

• Dorsally-running posterior horns handle afferent input
• Ventrally-running anterior horns oversee efferent somatic output
• Laterally-running lateral horns are involved in autonomic function
• Function: integration of spinal reflexes & filtering of info to higher centers
• Cross reflexes function within the gray commissure

White Matter

• Composed primarily of myelinated nerve fibers, appearing whitish
• Divided into three pairs of columns (funiculi): anterior, posterior, and lateral
• Within each funiculus, bundles of fibers are called fasciculi
• Ascending tracts carry sensory impulses to the brain
• Descending tracts transmit motor impulses from the brain

Learning Outcome 4

• Describe the structure and function of spinal nerves
• Define dermatome and myotome (skin & muscle areas supplied)
• Compare somatic (voluntary) & autonomic (involuntary) structure & function
• Compare sympathetic & parasympathetic structure & function
• Differentiate the effects of the autonomic nervous system
• Describe membrane potentials and impulse transmission processes

Spinal Nerve

• Mixed nerve carrying motor, sensory, & autonomic signals between spinal cord & body
• 31 pairs roughly corresponding to vertebral column segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal)

Types of Spinal Nerves

• Cervical nerves supply movement & feeling to arms, neck, & upper trunk; control breathing
• Thoracic nerves supply the upper back & trunk
• Lumbar nerves supply the lower back, abdomen, thighs, knees, and calves
• Sacral nerves supply lower back, legs, bladder, bowel, sexual organs
• Coccygeal nerves innervate the coccygeal region

Dermatomes

• Regions of skin surface supplied by sensory fibers of a specific spinal nerve

Myotomes

• Skeletal muscle or muscle groups supplied by motor fibers of a given spinal nerve

Cranial Nerves

• 12 pairs of cranial nerves arising from the brain and controlling functions like sight, smell, taste, facial expressions, etc.
• Identified by Roman numerals and names
• Afferent & efferent nerve fibers run in pairs within them
• Cranial nerve nuclei: cell groupings within the brain stem housing termination of sensory fibers & origin of motor fibers in cranial nerves.

Somatic vs. Autonomic

• Somatic controls voluntary body functions (skeletal muscles) with input from sense organs
• Autonomic controls involuntary body functions (smooth muscles, glands) with input from internal receptors

Comparison of Somatic & Autonomic Nervous Systems

• Autonomic has two neurons, somatic one
• Autonomic innervates smooth, cardiac muscle, glands; somatic, skeletal muscles
• Autonomic often has dual antagonistic innervation; somatic does not

Autonomic Nervous System (Sympathetic vs. Parasympathetic)

• Sympathetic and parasympathetic systems work antagonistically on many organs
• The sympathetic nervous system is dominant during danger and stressful events and promotes fight or flight response while parasympathetic is dominant during rest and control routine body activities

Comparison of Sympathetic & Parasympathetic Systems

• Structure: Origin, length of fibers, position of ganglia, transmitters
• Function: Types of responses (increase vs. decrease), general effects (increase vs. decrease in metabolic levels, rhythmic activities)

Difference in Effect of Autonomic Nervous System

• Specific responses of various organs to sympathetic and parasympathetic stimulations. (e.g., pupil dilation/constriction, heart rate increase/decrease).

Learning Outcome 5

• Describes the concept of membrane potentials
• Explains the formation of resting and action potentials
• Describes the mechanism of impulse transmission & spreading along the axon
• Explains the propagation of action potential along axon

Action Potential

• Resting Potential: Nerve at rest, holding a negative charge
• Depolarization: A shift from negative to positive charge
• Repolarization: A return to the negative resting potential
• Refractory period: Period to recover from the action
• Threshold: Level of stimulation required to produce an action potential

Transmission of Impulse Along Axon

• Action potential moves along axon automatically (without external stimulation)
• Voltage-gated channels detect the reversal of membrane potential and respond
• Refractory period prevents propagation backwards, ensuring unidirectional movement
• Threshold triggers the opening of voltage-gated channels, leading to action potential propagation