Spinal Cord Physiology Spinal Cord Physiology How does

Spinal Cord Physiology

Spinal Cord Physiology How does information travel in the spinal cord? – White matter tracts conduct nerve impulses to and from the brain – Gray matter receives and integrates incoming and outgoing information to perform spinal reflexes

Major Sensory and Motor Tracts Direct and Indirect Motor Pathways Posterior column: Central canal Gracile fasciculus Cuneate fasciculus Light touch / pressure, vibration, proprioception Lateral corticospinal tract Posterior spinocerebellar tract Rubrospinal tract Anterior spinocerebellar tract Lateral reticulospinal tract Spinal nerve Vestibulospinal tract Spinothalamic tract Medial reticulospinal tract Tectospinal tract Anterior median fissure Anterior corticospinal tract Sensory (ascending) tracts Motor (descending) tracts Pain, temp, itch, tickle, deep pressure

Reflexes and Reflex Arcs A reflex is a fast, predictable, automatic response to changes in the environment – Reflexes help maintain homeostasis – The spinal cord serves as the integrating center for spinal reflexes • Integration takes place in the gray matter of the spinal cord

TYPES OF REFLEXES Inborn Learned / Acquired LOCATION Cranial Spinal FUNCTION Autonomic (visceral) Somatic

General Components of a Reflex Arc

Reflex Arcs: Vocabulary Terms • • • Ipsilateral Contralateral Monosynaptic Polysynaptic Reciprocal innervation

Stretch Reflex Controls muscle length by causing muscle contraction Ipsilateral NMJ Monosynaptic vs. polysynaptic

Tendon Reflex Controls muscle tension by causing muscle relaxation

Flexor (Withdrawal) Reflex Moves a limb to avoid injury or pain Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Crossed-Extensor Reflex Maintains balance Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Reflexes Interactions Animation: n Reflexes

Clinical Connection Reflexes are often used for diagnosing disorders of the nervous system and locating injured tissue – If a reflex is absent or abnormal, the damage may be somewhere along a particular conduction pathway – Read page 467

Homeostatic Imbalances Damage that results from traumatic injuries depends on C 1 Cervical segment – Degree of spinal cord section Or – Degree of compression of the segments involved (A) C 7 T 1 Thoracic segment T 8 T 9 T 11 T 12 L 2 (B) Lumbar segment Sacral segment – Read pages 469 -470 (C) (D)