Nervous System Quiz

Spinal Cord Anatomy and Physiology

• The spinal cord is a long, almost cylindrical part of the central nervous system (CNS).
• It's located within the vertebral canal, extending from the foramen magnum (at base of skull) to the second lumbar vertebra.
• The spinal cord is protected by meninges and cerebral spinal fluid (CSF).
• Spinal nerves allow movement and sensation; damage can cause paralysis.
• Measures about 42-45 cm in length and the thickness of a little finger.
• It is shorter than the vertebral column.
• Spinal nerves that arise from lumbar, sacral, and coccygeal regions do not exit at the same level as the column; this collection is called the cauda equina.
• The spinal cord has two enlargements: cervical and lumbar.
• The cervical enlargement supplies nerves to the upper limbs.
• The lumbar enlargement supplies nerves to the lower limbs.
• White matter surrounds a centrally located H-shaped mass of gray matter within the spinal cord.

Spinal Cord Structure: Protection and Coverings

• Vertebrae protect the spinal cord.
• Spinal meninges are three layers of connective tissue:
  • Dura mater: tough, dense tissue extending to vertebra S2
  • Arachnoid mater: web-like structure
  • Pia mater: thin, delicate adheres to the surface of the spinal cord; contains blood vessels
• Continuous with cranial meninges.
• Cerebrospinal fluid (CSF) acts as a cushion to protect nerve tissues.

Spinal Cord Structure: Spinal Meninges and Spaces

• Epidural space is between the dura mater and the vertebrae.
• Dura mater is a tough, dense connective tissue that extends to vertebra S2.
• Arachnoid mater resembles a spider's web, extending into the subarachnoid space, where the CSF circulates.
• Pia mater is a thin, delicate layer that adheres to the spinal cord (and brain) and contains blood vessels.

Spinal Cord Structure: Internal Structure

• Gray matter forms an "H" shape (butterfly).
  • Has three horns on each side: posterior (dorsal) horns contain sensory neurons, anterior (ventral) gray horns contain somatic motor neurons, and lateral gray horns contain autonomic motor neurons.
• White matter (surrounds gray matter)
  • Consists primarily of myelinated axons organized into white columns (Posterior, anterior, and lateral).
  • Contains sensory (ascending) tracts carrying impulses toward the brain; and motor (descending) tracts carrying impulses from the brain down the spinal cord.
• Sensory and motor tracts are continuous with sensory and motor tracts in the brain.

Spinal Cord Nerve Tracts

• Sensory tracts carry impulses from the spinal cord toward the brain.
  • Examples include Gracile fasciculus, Cuneatus fasciculus, Dorsal spinocerebellar tract, Ventral spinocerebellar tract, Anterolateral system, Ventral corticospinal tracts, and Medial tectospinal tract.
• Motor tracts carry impulses from the brain down the spinal cord.
  -Examples include Lateral corticospinal tract, Lateral reticulospinal Tract, Medial Reticulospinal Tract, Lateral Tectospinal tract, Vestibulospinal tract, etc.
• 2 roots connect each spinal nerve to a segment of the cord: -Posterior (dorsal) root: input (afferent); contains sensory axons from sensory receptors in skin, muscles, and internal organs -Anterior (ventral) root, contains axons of motor neurons sending impulses from the CNS to effectors.

Functions of Spinal Cord

• Pathways for nerve impulses (ascending/descending).
• Reflexes: fast, involuntary responses to stimuli (simple, like withdrawal, or complex, like driving). -Spinal reflexes; simple, and cranial are more complex.

Functions of the Nerve Tracts: Somatic Sensory Pathways

• Sensory neurons transmit impulses towards the brain;
  • include cutaneous receptors (skin) and proprioceptors (tendons, muscles and joints).
• Sensory information travels from somatic sensory receptors to the primary somatosensory area (cerebral cortex).
• The majority of sensory input on one side of the body travels to the opposite side of the brain.

Functions of the Nerve Tracts: Somatic Sensory Pathways - Medial Lemniscus and Spinothalamic

• Crossing occurs either at the spinal cord entry point or in the medulla oblongata.
• Posterior column-medial Lemniscus Pathway: includes fine touch, body location, texture, size, proprioception (body position and movement), and vibration.
• Spinothalamic Pathways: includes pain, tickle, itch, hot, and cold sensations, carried through anterior and lateral spinothalamic tracts.

Functions of the Nerve Tracts: Somatic Motor Pathways

• Motor neurons transmit impulses away from the brain.
• Source of signals include upper motor neurons in the corticospinal tracts, basal ganglia (motor tone), cerebellum (coordination), sensory neurons, or interneurons via reflexes.
• Lower motor neurons in the anterior grey matter of the spinal cord move the signal to muscles through axons via the ventral root.

Voluntary Muscle Movement

• Voluntary movement originates in the cerebrum, regulating skeletal muscle activity through midbrain, brainstem and cerebellum output.
• Associated with coordination of muscle activity; including fine movement, posture, and balance.
• Motor pathways are made of two neurons, pyramidal (corticospinal) and extrapyramidal tracts. Within the brain, pyramidal tracts are found in the internal capsule and extrapyramidal neurons do not pass through the internal capsule.

Reflex Activity

• Reflexes: mechanisms by which sensory impulses are converted into motor responses.
  • Involve involuntary immediate responses to stimuli.
  • Basic defense mechanisms.
• Components of reflex arc: sensory receptor, sensory neuron, integrating center, motor neuron, effector.
• Types of reflexes: spinal reflexes and cranial reflexes.
• Deep tendon reflexes: elicited by tendon stroking (e.g., knee-jerk, ankle jerk); basically stretch reflexes.
• Visceral reflexes: autonomic reflexes (e.g., pupillary light reflex).
• Pathological reflexes: not normally present (e.g., Babinski's sign).

Test your knowledge on the structures and functions of the nervous system. This quiz covers topics such as sensory neurons, nerve tracts, and reflex arcs. Challenge yourself with matching terms and identifying functions related to neural pathways.