Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 13 The Spinal Cord & Spinal Nerves Together with brain forms the CNS Functions spinal cord reflexes integration (summation of inhibitory and excitatory) nerve impulses highway for upward and downward travel of sensory and motor information 1 Spinal Cord Protection By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments. 2 Structures Covering the Spinal Cord Vertebrae Epidural space filled with fa Dura mater dense irregular CT tube Subdural space filled with interstitial fluid Arachnoid = spider web of collagen fibers Subarachnoid space = CSF Pia mater 3 External Anatomy of Spinal Cord Flattened cylinder 16-18 Inches long & 3/4 inch diameter In adult ends at L2 In newborn ends at L4 Growth of cord stops a age 5 Cervical enlargement upper limbs Lumbar enlargement lower limbs 4 Inferior End of Spinal Cord Conus medullaris Filum terminale thread-like extension of pia mater stabilizes spinal cord in canal Caudae equinae (horse’s tail) cone-shaped end of spinal cord dorsal & ventral roots of lowest spinal nerves Spinal segment area of cord from which each5 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 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 neuron cell bodies, unmyelinated axons & dendrites paired dorsal and ventral gray horns lateral horns only present in thoracic spinal cord 8 White Matter of the Spinal Cord White matter covers gray matter 9 Tracts of the Spinal Cord 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 pyramidal tract (corticospinal) ---spinothalamic tract extrapyramidal tract ---posterior column 11 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 nerves12 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 Stretch Reflex (patellar reflex) 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) 14 Illustration of the Stretch Reflex 15 Tendon Reflex Controls muscle tension by causing muscle relaxation that prevents tendon damage Both tendon & muscle are protected 16 Illustration of Tendon Reflex 17 Flexor (withdrawal) Reflex Step on tack (pain fibers send signal to spinal cord More than one muscle group activated to lift foot off of tack 18 Crossed Extensor Reflex Lifting left foot requires extension of right leg to maintain one’s balance Pain signals cross to opposite spinal cord 19 Clinical Considerations 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) 20 Spinal Nerves 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 21 Branching of Spinal Nerve Spinal nerves formed from dorsal & ventral roots Spinal nerves branch into dorsal & ventral rami 22 A Nerve Plexus Joining of ventral rami of spinal nerves to form nerve networks or plexuses Found in neck, arm, low back & sacral regions No plexus in thoracic region 23 Cervical Plexus Ventral rami of spinal nerves (C1 to C5) Supplies parts of head, neck & shoulders Phrenic nerve (C3-C5) keeps diaphragm alive Damage to cord above C3 causes respiratory arrest 24 Brachial Plexus Ventral rami from C5 to T1 Supplies shoulder & upper limb Passes superior to 1st rib & under clavicle Axillary n. = deltoid & teres m. Musculocutaneous n. = elbow flexors Radial n. = shoulder & elbow extensors Median & ulnar nn. = flexors of wrist & hand 25 Clinical Correlations Erb-Duchene palsy Radial nerve injury improper deltoid injection or tight cast wrist drop Median nerve injury waiter’s tip position fall on shoulder numb palm & fingers; inability to pronate & flex fingers Ulnar nerve injury (clawhand) inability to adduct/abduct fingers, 26 Lumbar Plexus Ventral rami of L1 to L4 Supplies abdominal wall, external genitals & anterior/medial thigh Injury to femoral nerve causes inability to extend leg & loss of sensation in thigh Injury to obturator nerve causes paralysis of thigh adductors 27 Sacral Plexus Ventral rami of L4-L5 & S1S4 Anterior to the sacrum Supplies buttocks, perineum & part of lower limb Sciatic nerve = L4 to S3 supplies post thigh & all below knee Peroneal nerve injury produces foot drop or numbness Tibial nerve injury produces calcaneovalgus (loss of 28 function on anterior leg & Sciatic Nerve Branches Notice: Common Peroneal nerve and Tibial nerve behind the knee Notice: Sciatica pain extends from the buttock down the leg to the foot may be sign of 29 Dermatomes & Myotomes 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 30 Dermatomes 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 31 Neuritis inflammation of nerves caused by injury, vitamin deficiency or poison Shingles Disorders 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 32 respiratory arrest