Overview
This lecture introduces the structure and function of the spine and spinal cord, focusing on spinal cord regions, associated nerves, and their motor and autonomic roles.
Structure of the Spine and Spinal Cord
- The spine consists of vertebrae enclosing the spinal cord, a major nervous tissue connecting brain and body.
- Spinal nerves branch out from the spinal cord to control movement and relay sensory information.
- Signals travel from the brain through spinal nerves for motor control and return for sensory input.
Regions of the Spinal Cord and Spinal Nerves
- The spinal cord is divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal.
- Cervical region (C1-C8): 8 nerves; controls neck, diaphragm (C3-C5), shoulder, arm, and hand (C5-C8).
- Thoracic region (T1-T12): 12 nerves; controls trunk muscles, intercostal (T1-T6), abdominals (T7-T12).
- Lumbar region (L1-L5): 5 nerves; controls hips, legs, and feet, forms lumbar plexus and cauda equina.
- Sacral region (S1-S5): 5 nerves; controls hips, legs, feet, forms sacral plexus, involved in parasympathetic control.
- Coccygeal nerve (Co1): provides tailbone sensation, no significant motor function.
Somatic and Autonomic Divisions
- Somatic division: voluntary motor and sensory control (e.g., moving limbs, feeling surfaces).
- Autonomic division: involuntary control (e.g., digestion, stress responses), includes sympathetic and parasympathetic branches.
- Cervical nerves: only somatic motor and sensory, no autonomic function.
- Thoracic and lumbar nerves: involved in sympathetic (stress) responses (e.g., increased heart rate).
- Sacral nerves: involved in parasympathetic (rest and digest) responses (e.g., bladder contraction, reproductive organ blood flow).
- Cranial nerves (not spinal): regulate parasympathetic responses in most of the body.
Spinal Cord Injury
- Complete spinal cord injury results in loss of function below the injury site; reflexes may remain.
- Example: Injury at C5 retains some neck and breathing control but loses arm/hand movement.
- Example: Injury at L2-L3 affects hips, legs, and feet motor control; reflexes may persist without conscious control.
Key Terms & Definitions
- Spinal cord — nervous tissue running from the brain through the spine, controlling body signals.
- Spinal nerves — nerves branching from the spinal cord, controlling movement and sensation.
- Plexus — network of nerves (e.g., brachial, lumbar, sacral).
- Somatic division — controls voluntary movements and conscious sensations.
- Autonomic division — controls involuntary body functions; includes sympathetic and parasympathetic systems.
- Cauda equina — bundle of nerve roots at the lower end of the spinal cord, resembling a horse's tail.
- Complete spinal cord injury — total loss of function below the injury point.
Action Items / Next Steps
- Practice labeling spinal cord regions and naming the number of nerves and functions in each section.
- Review related videos on the nervous system and cranial nerves for deeper understanding.