Spinal Cord and Reflexes

Spinal Cord & Nerves

Spinal Cord Connects the PNS with the brain Produces spinal reflexes Passes down the foramen magnum and descends to T12-L3 In children, spinal cord is as long as the spine Two enlarged regions: Cervical Enlargement: supplies nerves to upper limbs Lumbar Enlargement: supplies nerves to lower limbs Conus Medullaris: where the spinal cord ends Cauda Equina (“horse’s tail”): group of spinal nerves that branch from the end of the conus medullaris

Introduction The spinal cord is composed of white matter surrounding a gray matter core The gray matter is arranged with a left and right dorsal horn and a left and right ventral horn.

Sectional Anatomy Cord is divided by deep anterior median fissure and surface posterior median sulcus White Matter: contains many myelinated axons Divided into columns Grey Matter: contains many glial cells and cell bodies Divided into “horns” Posterior Gray Horn: carry sensory neurons in spinal cords Anterior Gray Horn: carry somatic motor neurons to skeletal muscle Lateral Gray Horn: occur in T1=L2 and consists of visceral motor neurons Axons can cross opposite side of spinal cord at the crossbars called “commissures”

Spinal Meninges Dura Mater – outer membrane, tough connective tissue Epidural space – contains adipose tissue to pad the spinal cord Arachnoid space Subdural space – separates the dura mater from the arachnoid Subarachnoid space – contains the CSF to protect and cushion the spinal cord Pia Mater – thin, inner meningeal layer directly over spinal cord; hold the blood vessels in place

Spinal and Peripheral Nerves 12 pairs of cranial nerves 31 pairs of spinal nerves 8 cervical nerves – 12 thoracic nerves 5 lumbar nerves 1 coccygeal nerve

Spinal Nerve Plexus Plexus: groups of spinal nerves Four regions Cervical Brachial Lumbar Sacral **Thoracic  NOT part of any plexus but make up the intercostal nerves that innervate the intercostal and abdominal muscles

Spinal Reflexes Reflexes – automatic neural responses to certain stimuli CNS has little involvement in these reflexes Many type of reflexes Reflex Arc – a stimulus does not to be recognized to elicit a response to it