Spinal cord

• The spinal cord is a long, tubular structure that extends from the base of the brain (medulla oblongata) down to the lower back, protected by the vertebral column and encased in meninges.
• It is a crucial part of the central nervous system (CNS) and serves as a conduit for transmitting neural signals between the brain and the rest of the body.
• The spinal cord plays a key role in reflex activities and motor control.

Gross Structure

• The spinal cord is cylindrical, with two noticeable enlargements: the cervical enlargement, which corresponds to the limbs’ sensory input and motor output needs, and the lumbar enlargement, which handles signals to and from the legs.
• The cord is divided into segments according to the vertebral column’s bones, with each segment giving rise to a pair of spinal nerves.

The Spinal cord is further divided into gray and white matter:

1. Gray matter is located in the center, forming an H or butterfly shape on cross-section. It contains neuron cell bodies, dendrites, and axons of interneurons as well as the beginnings of motor neurons.
2. White matter surrounds the gray matter and consists of myelinated axons, which are divided into ascending (sensory) and descending (motor) tracts.

Functions of Afferent and Efferent Nerve Tracts

Afferent (Sensory) Tracts:

• Carry sensory information from the body to the brain.
• Enter through the dorsal root, transmitting signals such as touch, temperature, pain, and proprioception to brain centers.

Efferent (Motor) Tracts:

• Convey motor commands from the brain to the body.
• Exit through the ventral root, controlling voluntary and involuntary movements, posture, and balance.

Reflex Activity of Spinal Cord

Reflexes:

• Automatic, rapid responses to stimuli that involve the spinal cord.
• They are crucial for survival, providing immediate reactions to potential threats without routing signals to the brain.

Reflex Arc:

• The simplest form of a neural pathway, involving:
  1. Sensory Receptor: Responds to a stimulus.
  2. Sensory Neuron: Carries the message to the spinal cord.
  3. Integration Center: May be a single synapse (monosynaptic reflex) or involve one or more interneurons (polysynaptic reflex).
  4. Motor Neuron: Conducts the impulse from the integration center to an effector.
  5. Effector: The muscle or gland that responds by contracting or secreting a product.

Types of Reflex Activities:

• 1. Somatic Reflexes: Involving skeletal muscles.
  2. Autonomic Reflexes: Involving internal organs.
• Reflexes are essential for maintaining homeostasis and enabling the body to make rapid adjustments to environmental changes.

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