Chapter 13 Spinal Cord Functions Surface anatomy Conduction of information up and down the cord Integration of received information and deciding an appropriate output Locomotion coordinating the simple repetitive muscle contractions Reflexes Cylinder of nervous tissue from foramen magnum to L1 From L2 to S5 cauda equina a bundle of nerve roots pelvic organs lower limbs Here subarachnoid space is called lumbar cistern Here pia mater becomes terminal filum fibrous strand There are 31 pairs of spinal nerves 1st pair passes b w the skull and C1 2 enlargements cervical nerves of the upper limbs and lumbar lower limbs Lumbar enlargement medullary cone cauda equina Cross sectional anatomy Gray matter White matter Tracts Ascending Horns posterior sensory input anterior motor output Lateral horn T2 L1 sympathetic nervous system Gray commissure connects right and left sides central canal in the middle Columns funiculi posterior lateral anterior Gracile fasciculus joined by cuneate fasciculus at T6 and up Pressure proprioception 1st order nerve fibers go to medulla oblongata 2nd order fibers decussate thalamus cerebral cortex Spinothalamic tract Temperature pain 1st order fibers end at posterior horn 2nd order decussate thalamus cortex Spinocerebellar tract Proprioception 1st order fibers end at posterior horn 2nd order travel ipsilateral side cerebellum Anterior crosses over but then crosses back in the brainstem Descending Corticospinal pyramidal tracts Motor coordination for limb movements Lateral tract decussate in the lower medulla Anterior in the spinal cord Tectospinal extrapyramidal tract Controls the head during visual auditor reflexes Begins in midbrain decussates neck Nerve anatomy Peripheral nervous system Nerve fiber Schwann cells neurilemms myelin basil lamina endoneurium fascicle perineurium epineurium dense irregular connective tissue Ganglion cluster of neurosomas outside the CNS Spinal Nerves Proximal branches 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal anterior rootlets anterior root motor posterior rootlets posterior root with ganglion sensory merge Distal branches emerging from the intervertebral foramen anterior ramus larger innervates anterior and lateral skin muscles of the trunk gives rise to nerves of the limbs In thoracic region also forms an intercostal nerve posterior ramus innervates muscles and joints in that region of the spine and skin of the back meningeal branch reenters the vertebral canal Reflexes quick involuntary stereotyped reactions of muscles and glands to stimulation Somatic reflexes unlearned skeletal muscles reflexes mediated by brain brainstem spinal cord Reflex arc Somatic receptors skin muscles tendons afferent nerve fibers intergrating center gray matter of cord or brainstem efferent nerve fibers effectors muscles that carry out the response Muscle spindle the body s proprioceptor in the perimusium of a muscle Made up of intrafusal fibers have sarcomeres only at the ends Nuclear chain fibers single file of nuclei in the noncontractile region Nuclear bag fibers flatter longer have nuclei clustered in the baglike middle region Nerve fibers Sensory one Primary afferent group Ia fiber coils around the middle of fibers Large fast 8 Secondary afferent group II fibers coild adjacent to Smaller slower Motor adjusts the length sensitivity Gamma motor neurons connect to contractile ends of the intrafusal fibers Relatively small and slow Monosynaptic arc there is only one synapse b w afferent and efferent neuron in spinal cord Stretch reflex when muscle is suddenly stretched it fights back contracts increases tone stiffens Usually an action of synergists and antagonists Mediated primarily by the brain postural stability but if the stretch is very sudden spinal component is more pronounced Tendon reflex reflexive contraction of the muscle when the tendon is tapped Polysynaptic reflex arc signals travel over many synapses on their way back to the muscle Withdrawal reflex quick contruction of flexor muscles to withdraw a limb from injurious stimulus Requires sustained contraction parallel after discharge circuit prolonged output ipsilateral reflex arc Crossed extension reflex contraction of extensor muscles in the limb opposite from the one that is withdrawn enables to keep the balance Branches of the afferent nerve fibers cross from the stimulated side of the body to the contralateral side of spinal cord exite inhibit muscles of the contralateral limb contralateral reflex arc input and output are on opposite sides intersegmental reflex arc input and output occur at different levels of the spinal cord Nerve Plexuses Name Sensory innervation distal Motor innervation proximal Cervical plexus C1 to C5 Phrenic nerve Diaphragm pleura pericardium Diaphragm Brachial plexus C4 to T1 Musculocutaneous Skin of anterolateral forearm Elbow joint Skin of lateral shoulder and arm Shoulder joint Brachialis biceps bracii coracobrachialis Deltoid and teres minor Axillary Radial Median Ulnar Skin of posterior arm Posterior and lateral forearm and wrist Joints of elbow wrist and hand Mainly extensor muscles of posterior arm and forearm triceps bracii extensor carpi radialis longus Skin of lateral hand Tips of digits I IV Joints of hand Skin of palmar and median hand Digits II V Joints of elbow and hand Mainly forearm flexors Some forearm flexors Lumbar plexus L1 to L4 Femoral Skin of anterior medial and lateral thigh and knee Skin of medial leg and foot Hip and knee joints Illiacus Quadriceps femoris Sartorius Obturator Skin of medial thigh Hip and knee joints Obturator externus Adductors Sacral L4 L5 S1 and Coccygeal plexuses S4 S5 Co Skin of posterior leg Plantar skin Sciatic Knee and foot joints nerve Tibial Fibular common Skin of anterior distal leg Dorsum of foot Toes 1 2 Knee joint Hamstrings Semitendinosus semimembranosis Gastrocnemius soleus Tibialis anterior Toe extensors dorsiflexors Pudental Skin of penis scrotum Clitoris labia lower vagina Bulbospongiosus levator ani Sphincters anal urethral