Spinal Cord 1/14 CNS tissue is enclosed within vertebral column; begins at foramen magnum and ends at L 1 or L 2 Functions – Provides two-way communication to and from brain – Contains spinal reflex centers – Protected by bone, meninges, and CSF BIO 105--Lab 10--Spinal Cord1

Ends in conus medullaris Filum terminale (fibrous extension of conus medullaris) covered with pia mater which extends to coccyx and anchors the cord so it is not damaged by movements Cauda equina – Collection of nerve roots at inferior end of vertebral canal BIO 105--Lab 10--Spinal Cord2

Spinal nerves (Part of PNS) – 31 pairs Spinal nerves split into dorsal and ventral branches or “rami” almost as soon as they leave vertebral column. – Spinal nerves are often named for bone or structure they pass near Plexuses are groups of spinal nerves. BIO 105--Lab 10--Spinal Cord3

Cervical plexus ( C1 to C4) serves muscles and skin of neck, except for phrenic nerve which stimulates diaphragm. Brachial plexus (C5-8, T1): serves skin and muscles of arm & shoulder area Lumbar plexus (L1-4): serves skin and muscles of (upper) leg & pelvic area. Sacral plexus ( L4, L5, S1-4) : serves skin and muscles of (lower) leg & pelvic area. BIO 105--Lab 10--Spinal Cord4

Cross-sectional Anatomy Two lengthwise grooves partially divide cord into right and left halves – Ventral or Anterior median fissure – Dorsal or Posterior median sulcus BIO 105--Lab 10--Spinal Cord5

Gray Matter-consists of cell bodies, non-myelinated processes and neuroglia In cross section, looks like “H” or a butterfly Gray commissure—connects masses of gray matter; encloses central canal Dorsal horns - interneurons that receive somatic and visceral sensory input Ventral horns - some interneurons; somatic motor neurons; axons exit cord via ventral roots Lateral horns (only in thoracic and superior lumbar regions) - sympathetic neurons Dorsal roots – sensory input to cord Dorsal root (spinal) ganglia—cell bodies of sensory neurons BIO 105--Lab 10--Spinal Cord6

White Matter Divided into three white columns (funiculi) on each side – Dorsal, lateral, and ventral – Each spinal tract composed of axons with similar destinations and functions The tracts in funiculi are typically named for start and end points of their axons  Ascending=spinal cord  brain; Descending=brain  spinal cord. – Lateral funiculi have a mix of ascending and descending tracts. Distribution: primarily sensory tracts in posterior; descending motor tracts in the anterior; ( recall that sensory information comes in back side (dorsal root), and motor responses go out front door (ventral root). 7

BIO 105--Lab 10--Spinal Cord Spinothalamic Pathways (Ascending) Lateral and ventral spinothalamic tracts Provide discriminatory touch (pain, temperature, coarse touch, pressure) and conscious proprioception Spinocerebellar Tracts (Ascending) Ventral and dorsal tracts terminate in cerebellum Convey information about muscle or tendon stretch to cerebellum – Used to coordinate muscle activity 8

BIO 105--Lab 10--Spinal Cord Dorsal Column–Medial Lemniscal Pathways (Ascending) Composed of paired fasciculus cuneatus and fasciculus gracilis in spinal cord and medial lemniscus in brain (medulla to thalamus) Transmit input to somatosensory cortex for discriminative touch and vibrations 9

BIO 105--Lab 10--Spinal Cord Descending Pathways Reticulospinal and vestibulospinal tracts—maintain balance Rubrospinal tracts—control flexor muscles Tectospinal tracts mediate head movements in response to visual stimuli 10

Reflexes rapid, involuntary, predictable motor response to stimulus – Can involve just peripheral nerves and spinal cord or may also involve higher brain centers Direct transfer of stimulus from sensory neuron to motor neuron (sometimes with an interneuron in between) allows for rapid response to stimuli. May be: – Inborn (intrinsic) Example – maintain posture, control visceral activities Can be modified by learning and conscious effort --Learned (acquired) reflexes result from practice or repetition, Example – driving skills BIO 105--Lab 10--Spinal Cord11

Input travels along one pathway, called a reflex arc, to a specific destination System works in all-or-none manner to produce specific response Particular stimulus always causes same response BIO 105--Lab 10--Spinal Cord12

Reflex Arc Components 1.Receptor—site of stimulus action 2.Sensory neuron—transmits afferent impulses to CNS 3.Integration center—either monosynaptic or polysynaptic region within CNS 4.Motor neuron—conducts efferent impulses from integration center to effector organ 5.Effector—muscle fiber or gland cell that responds to efferent impulses by contracting or secreting BIO 105--Lab 10--Spinal Cord13

Stretch and Tendon Reflexes To smoothly coordinate skeletal muscle, nervous system must receive constant proprioceptor input about – Length of muscle (from muscle spindles) – Muscle tone: Amount of tension in muscle and tendons – allows muscle to maintain correct muscle tone and adjust it reflexively BIO 105--Lab 10--Spinal Cord14

LABWORK 1.Describe the important structures of spinal cord. 2. Describe cross-sectional features of spinal cord (models and cross-section slide). 3. Describe spinal nerves and plexuses associated with the spinal cord (models). 4. Describe reflexes and basics of reflex physiology. BIO Lab 10--Spinal Cord15