Lesson 16 The Spinal Cord and Spinal Nerves Spinal Reflexes Controlled by spinal cord alone not the brain Rapid automatic nerve responses triggered by specific stimuli Can involve a single spinal segment or multiple segments The spinal cord is part of the CNS and the spinal nerve is part of the PNS In a spinal reflex information flows from PNS to CNS to PNS q Describe the gross anatomy of the spinal cord q Is it symmetrical along the entire length Gross Anatomy of the Spinal Cord 18 inches 45cm long inch 14mm wide Ends between vertebra L1 and L2 Bilateral symmetry Grooves divide the spinal cord into left and right Anterior median fissure deeper groove on anterior Posterior median sulcus on posterior side side Enlargements of the Spinal Cord Caused by amount of gray matter in segment involvement with sensory and motor nerves of limbs Cervical enlargement nerves of shoulders and upper limbs Lumbar enlargement nerves of pelvis and lower limbs The Distal End Conus medullaris thin conical spinal cord below lumbar enlargement Filum terminale thin thread of fibrous tissue at end of conus medullaris attaches to coccygeal ligament provides longitudinal support to spinal cord Cauda equina nerve roots ventral and dorsal extending below conus medullaris and into sacrum q Explain how spinal nerves are numbered 31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age Cervical nerves named for inferior vertebra except for cervical nerve 8 since cervical vertebrae 8 does not exist All other nerves named for superior vertebra q Describe the difference between the ventral and dorsal root q Which carries information to the CNS Which carries information away from the CNS Where are the cell bodies of these Two branches of spinal nerves 1 Dorsal root contains axons of sensory neurons a Carries info to the CNS afferent b Cell bodies of sensory neurons are located in dorsal root ganglia c The dorsal root ganglia consist mainly of cell bodies of unipolar neurons 2 Ventral Root contains axons of motor neurons somatic and visceral effectors a Carries info away from the CNS efferent b Cell bodies of motor neurons that extend axons through ventral root are located in the gray matter of the spinal cord The Spinal Nerve Each side of spine dorsal and ventral roots join to form a spinal nerve Mixed nerves carry both afferent sensory and efferent motor fibers 1 q Describe the meninges covering the spinal cord q How is it anchored to prevent lateral movement The Spinal Meninges Specialized membranes isolate spinal cord from surroundings continuous with cranial meninges Functions protect spinal cord carry blood supply Meningitis Viral or bacterial infection of meninges spinal meningitis or cerebral meningitis can disrupt CSF flow damage or kill neurons and neuroglia later stages of meningitis affects entire meningeal system Three Meningeal Layers 1 Dura mater outer layer of spinal cord 2 Arachnoid mater middle meningeal layer 3 Pia mater inner meningeal layer 1 Dura Mater Tough and fibrous Cranially Fuses with periosteum of occipital bone Is continuous with cranial dura mater Caudally Tapers to dense cord of collagen fibers Joins filum terminale in coccygeal ligament Epidural space Between spinal dura mater and walls of vertebral canal o Contains loose connective and adipose tissue adipose tissue acts as protective padding o Anesthetic injection site epidural block temporary sensory loss and possibly some motor paralysis mostly just sensory though used at inferior lumbar sacral region for pain control during childbirth only affects spinal nerves in immediate area Subdural Space between arachnoid mater and dura mater 2 Arachnoid Mater Middle meningeal layer Arachnoid membrane simple squamous epithelia covers arachnoid mater Subarachnoid space between arachnoid mater and pia mater contains collagen elastin fiber network arachnoid trabeculae extends to filum terminale filled with cerebrospinal fluid Cerebrospinal fluid CSF carries dissolved gases nutrients and wastes lumbar puncture or spinal tap withdraws CSF The cerebrospinal fluid CSF circulates within the subarachnoid space The CSF is confined between the pia mater and the arachnoid mater Spinal anesthesia injection of local anesthetics to subarachnoid space spreads as CSF distributes along spinal cord breathing is not affected since upper cervical spinal nerves controlling respiration are not affected 3 Pia Mater The innermost meningeal layer Mesh of collagen and elastic fibers Is bound to underlying neural tissue Blood vessels serving the spinal cord run along surface of spinal Pia mater within the subarachnoid space Structure of the Spinal Cord Paired denticulate ligaments found on each side of the spinal cord extend from pia mater to dura mater stabilize side to side movement lateral movement Blood vessels along surface of spinal pia mater within subarachnoid space q Describe the difference between the gray and white matter found in the spinal cord White matter Gray matter Superficial Contains myelinated and unmyelinated axons Surrounds the central canal of spinal cord Contains neuron cell bodies neuroglia unmyelinated axons Has projections gray horns 2 q Explain the function of the gray horns of the spinal Control and Location cord Gray horns Posterior gray horns contain somatic and visceral sensory nuclei Lateral gray horns are in thoracic and lumbar segments contain visceral motor nuclei Anterior gray horns contain somatic motor nuclei The dorsal gray horns contain sensory nuclei The gray horns of the spinal cord contain neuroglia neuron cell bodies unmyelinated axons Sensory or motor nucleus location within the gray matter determines which body part it controls Ex Cervical enlargement from medial to lateral somatic motor nuclei control pectoral girdle muscles of arm forearm hand and fingers q Explain the function of the white columns of the spinal cord Refer to image on left for location Organization of White Matter Posterior white columns lie between posterior gray horns and posterior median sulcus Proprioception fine touch ventral pressure vibrations Lateral white columns located on each side of spinal cord between anterior and posterior columns Proprioception Anterior white columns lie between anterior gray horns and anterior median fissure Crude touch and pressure Anterior white commissure is area where axons cross from one side of spinal cord to the other Tracts or fasciculi
View Full Document
Unlocking...