Spinal Cord Protection Chapter 13 The Spinal Cord & Spinal Nerves We are only going to cover Pages 420-434 and 447 Together with brain forms the CNS Functions spinal cord reflexes integration (summation of inhibitory and excitatory) of nerve impulses highway for upward and downward travel of sensory and motor information By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments. 1 2 External Anatomy of Spinal Cord Structures Covering the Spinal Cord Vertebrae Epidural space filled with fat Dura mater dense irregular CT tube Subdural space filled with interstitial fluid Arachnoid = spider web of collagen fibers Subarachnoid space = CSF Pia mater thin layer with many BV s denticulate ligs hold in place Flattened cylinder 16-18 Inches long & 3/4 inch diameter In adult ends at L2 In newborn ends at L4 Growth of cord stops at age 5 Cervical enlargement upper limbs Lumbar enlargement lower limbs 3 Inferior End of Spinal Cord Conus medullaris cone-shaped end of spinal cord Filum terminale thread-like extension of pia mater stabilizes spinal cord in canal Caudae equinae (horse s tail) dorsal & ventral roots of lowest spinal nerves Spinal segment area of cord from which each pair of spinal nerves arises 4 Spinal Cord & Spinal Nerves Spinal nerves begin as roots Dorsal or posterior root is incoming sensory fibers dorsal root ganglion (swelling) = cell bodies of sensory nerves Ventral or anterior root is outgoing motor fibers 5 6
Spinal tap or Lumbar Puncture Technique long needle into subarachnoid space safe from L3 to L5 Purpose sampling CSF for diagnosis injection of antibiotics, anesthetics or chemotherapy measurement of CSF pressure 7 Gray Matter of the Spinal Cord Note: colors in reverse due to staining of tissue Gray matter is shaped like the letter H or a butterfly contains cell bodies, unmyelinated axons & dendrites paired dorsal and ventral gray horns lateral horns only present in thoracic spinal cord gray commissure crosses the midline Central canal continuous with 4th ventricle of brain 8 White Matter of the Spinal Cord Tracts of the Spinal Cord White matter covers gray matter Anterior median fissure deeper than Posterior median sulcus Anterior, Lateral and Posterior White Columns contain axons that form ascending & descending tracts 9 Function of tracts highway for sensory & motor information sensory tracts ascend motor tracts descend Naming of tracts indicates position & direction of signal example = anterior spinothalamic tract impulses travel from spinal cord towards brain (thalamus) found in anterior part of spinal cord 10 Location of Tracts inside Cord Motor tracts!!!! Sensory tracts Direct (pyramidal) tract ---spinothalamic tracts Indirect(extrapyramidal) tract! ---posterior columns see page 515 ---spinocerebellar 11 Function of Spinal Tracts Spinothalamic tract pain, temperature, deep pressure & crude touch Posterior columns proprioception, discriminative touch, two-point discrimination, pressure and vibration Direct pathways (corticospinal & corticobulbar) precise, voluntary movements Indirect pathways (rubrospinal, vestibulospinal) programming automatic movements, posture & muscle tone, equilibrium & coordination of visual reflexes 12
Spinal Reflexes Automatic response to change in environment Integration center for spinal reflexes is gray matter of spinal cord Examples somatic reflexes result in skeletal muscle contraction autonomic (visceral) reflexes involve smooth & cardiac muscle and glands. heart rate, respiration, digestion, urination, etc Note: cranial reflexes involve cranial nerves Reflex Arc Specific nerve impulse pathway 5 components of reflex arc receptor sensory neuron integrating center motor neuron effector 4 important somatic spinal reflexes stretch, tendon, flexor(withdrawal) & crossed extensor reflexes 13 14 Stretch Reflex (patellar reflex) Illustration of the Stretch Reflex Monosynaptic,ipsilateral reflex arc Prevents injury from over stretching because muscle contracts when it is stretched Events of stretch reflex muscle spindle signals stretch of muscle motor neuron activated & muscle contracts Brain sets muscle spindle sensitivity as it sets muscle tone (degree of muscle contraction at rest) Reciprocal innervation (polysynaptic- interneuron) antagonistic muscles relax as part of reflex 15 16 Tendon Reflex Illustration of Tendon Reflex Controls muscle tension by causing muscle relaxation that prevents tendon damage Golgi tendon organs in tendon activated by stretching of tendon inhibitory neuron is stimulated (polysynaptic) motor neuron is hyperpolarized and muscle relaxes Both tendon & muscle are protected Reciprocal innervation (polysynaptic) causes contraction of ipsilateral muscle group 17 18
Flexor (withdrawal) Reflex Crossed Extensor Reflex Step on tack (pain fibers send signal to spinal cord Interneurons branch to different spinal cord segments Motor fibers in several segments are activated More than one muscle group activated to lift foot off of tack Lifting left foot requires extension of right leg to maintain one s balance Pain signals cross to opposite spinal cord Contralateral extensor muscles are stimulated by interneurons to hold up the body weight Reciprocal innervation when extensors contract flexors relax, etc 19 Connective Tissue Coverings of the Spinal Nerves 20 Connective Tissue Coverings of the Spinal Nerves Endoneurium - around individual nerve fibers - Fascicles - a bundle of axons/nerve fibers Perineurium - around fascicles Epineurium - the superficial covering around the whole nerve Endoneurium - around individual nerve fibers - Fascicles - a bundle of axons/nerve fibers Perineurium - around fascicles Epineurium - the superficial covering around the whole nerve 21 22 Clinical Considerations Dermatomes & Myotomes Checking a patient s reflexes may help to detect disorders/injury Plantar flexion reflex -- stroke the lateral margin of the sole normal response is curling under the toes abnormal response or response of children under 18 months is called Babinski sign (upward fanning of toes due to incomplete myelination in child) Each spinal nerve contains both sensory & motor nerve fibers Dermatome area of skin supplied by one spinal nerve overlap prevents loss of sensation if one damaged sensory anesthesia requires 3 spinal nerves to be blocked Skin on face supplied by Cranial Nerve V 23 24
Dermatomes Disorders Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region Infusing local anesthetics or cutting roots must be done over 3 adjacent spinal nerves. Spinal cord transection injury that severs the cord loss of sensation& motor control below the injury Neuritis inflammation of nerves caused by injury, vitamin deficiency or poison Shingles infection of peripheral nerve by chicken pox virus causes pain, skin discoloration, line of skin blisters Poliomyelitis viral infection causing motor neuron death and possible death from cardiac failure or respiratory arrest 25 Spinal Nerves 26 The End 31 Pairs of spinal nerves Named & numbered by the cord level of their origin 8 pairs of cervical nerves (C1 to C8) 12 pairs of thoracic nerves (T1 to T12) 5 pairs of lumbar nerves (L1 to L5) 5 pairs of sacral nerves (S1 to S5) 1 pair of coccygeal nerves Mixed sensory & motor nerves 27 28