Anatomy and function of spinal cord | Neuromuscular system

Primary function of the spinal cord

Acts as a relay pathway between the peripheral system and the brain
- Provides sensory information regarding the environment to the brain
- Manages motor commands to the peripheral system in reaction to the environment
- Coordinates simple reflexes that do not need to go to the brain, such as withdrawal from pain, patellar reflex, etc

Cervical spine
- Eight (8) nerves that provide innervation to the neck and upper extremity
Thoracic spine
- Twelve (12) nerves that provide innervation to the upper chest, chest, abdomen, and upper back
Lumbar spine
- Five (5) nerves that provide innervation to the legs and feet
Sacral spine
- Five (5) nerves that provide innervation to the sacrum and pelvis
Coccygeal spine
- One (1) nerve that provides innervation to the perineal area

Dura mater
- Outermost protective layer
- Space between dura and bony vertebral body referred to as epidural space, which contains adipose tissue and blood vessels
Arachnoid
- Middle layer with a web-like appearance
- Space between arachnoid and Pia referred to as subarachnoid space and contains cerebrospinal fluid
Pia mater
- Innermost layer that is in direct contact with the spinal cord

Definitions

Dorsal root: Sensory nerve that carries information from the spinal cord to the brain
Ventral root: Motor nerve that carries information from the brain to the spinal cord
Spinal nerve: Pathway for sensory and motor information to move between the peripheral system and the spinal cord
Denticulate ligament: Ligament that provides stabilization of the spinal cord
Posterior (dorsal) gray horn: Nerve fibers containing sensory information from the body
Lateral gray horn: Nerve fibers containing sympathetic nervous system information are only found in the thoracic, upper lumbar, and sacral regions of the spinal cord
Anterior (ventral) gray horn: Nerve fibers containing motor neurons that control skeletal muscles
Posterior (dorsal) white column: Nerve fibers containing sensory information from the body, such as two-point discrimination, fine touch, vibration, and proprioception
Lateral white column: Nerve fibers that contain sensory information such as pain, temperature, and crude touch
Anterior (ventral) white column: Nerve fibers containing sensory and motor nerve fibers that provide information to the contralateral brain
Sympathetic nervous system: A network of nerves that are enacted to aid in the response to physical activity, stress, or danger (fight or flight response)
Parasympathetic nervous system: A network of nerves that provides relaxation after the body has responded to a stressful or dangerous situation (rest and digest response)

Ascending tracts
- Carry sensory information such as touch, pain, and temperature from the peripheral system to the brain
- Names of tracts/pathways:
  - Dorsal column-medial lemniscal: transmits light touch, deep pressure, two-point discrimination, and vibratory information to the cerebrum via the thalamus - crosses in the medulla to the contralateral side
  - Anterior and lateral spinothalamic: transmit pain, crude touch, and temperature information to cerebrum via the thalamus - crosses in the medulla to the contralateral side
  - Spinocerebellar: transmit proprioceptive information to the cerebellum- does not cross; stays on the same side
Descending tracts
- Carry motor information from the brain to the peripheral system to give voluntary commands of movement of axial and skeletal muscles
- Names of tracts/pathways
  - Anterior and lateral corticospinal: transmit commands to move axial and/or skeletal muscles
    Pathways of spinal cord

Two (2) primary arteries of the spinal cord
- Anterior spinal artery
  - Supplies blood to the anterior two-thirds of the spinal cord, except the dorsal column
- Posterior spinal artery
  - Provides blood supply to the posterior spinal cord via two (2) branches that supply the dorsal sensory column, dorsal gray matter, and posterior columns