Spinal Cord PDF

The spinal cord and spinal nerves  Learning Objectives Describe the structure of the spinal cord (both gross and sectioned) Identify spinal tracts and contrast 3 spinal reflexes Compare the spinal nerve plexuses  Spinal cord Spinal Cord Thumbnail...

The spinal cord and spinal nerves  Learning Objectives Describe the structure of the spinal cord (both gross and sectioned) Identify spinal tracts and contrast 3 spinal reflexes Compare the spinal nerve plexuses  Spinal cord Spinal Cord Thumbnail Spinal Cord conducts impulses from body to brain conducts impulses from brain to body controls reflex activities  Spinal Cord flattened cylinder 42-45cm long, 2cm diameter lies within the spinal canal  External Anatomy of Spinal Cord foramen cervical magnum enlargement (nn. to upper limbs) lumbosacral enlargement (nn. to lower L1 limbs) conus cauda medullaris equina filum terminale conus medullaris cone-shaped end of spinal cord cauda equina dorsal, ventral roots of lowest spinal nerves filum terminale thread-like extension of pia mater stabilizes spinal cord in spinal canal  gray matter posterior horn shaped like butterfly (sensory axons, interneurons) (or letter H) divided into horns anterior central horn canal (cell bodies of LMN) gray commissure lateral horn © John Wiley & Son Inc (in thoracic s.c. only; autonomic motor cell bodies)  lateral funiculus posterior funiculus anterior funiculus lateral funiculus white matter surrounds gray matter divided into funiculi (columns) contains sensory and motor nerve tracts  Spinal Nerves spinal nerves emerge from s.c. as roots: – root contains sensory fibers – root contains motor fibers spinal ganglia (dorsal root ganglia) contain cell bodies of sensory neurons  Tracts of the Spinal Cord bundles of axons highways for sensory and motor information (sensory tracts ascend, motor tracts descend) forms the white matter of the spinal cord  Tracts of the Spinal Cord Brain Ascending tract Afferent neuron Receptor Spinal cord Tracts of the Spinal Cord Descending Brain tract Spinal cord Efferent neuron Effector  Spinal tracts © John Wiley & Son Inc tracts sensory tracts direct (pyramidal) posterior funiculi indirect (extrapyramidal) spinothalamic spinocerebellar  Function of Spinal Tracts Tracts Posterior funiculi – proprioception, discriminative touch, two- point discrimination, pressure, vibration Spinothalamic tracts – pain, temperature, deep pressure, crude touch Spinocerebellar tracts – unconscious proprioception  Function of Spinal Tracts Tracts Direct pathways (pyramidal tracts) – precise, voluntary movements Indirect pathways (extrapyramidal tracts) – “programmed” automatic movements – co-ordinate gross movements and visual reflexes  Motor Tracts indirect pathways direct pathways (extrapyramidal tracts) (pyramidal tracts)  Spinal Integration integrating centres - regions in CNS that relay impulses from sensory to motor neurons - fast, predictable, automatic responses to environmental changes s.c. serves as an integrating centre for spinal reflexes (promotes homeostasis)  Reflex Arc association receptor neuron afferent neuron efferent spinal cord neuron effector © John Wiley & Son Inc  Spinal reflexes some examples: –stretch reflex –tendon reflex –flexor (withdrawal) reflex  Stretch Reflex (patellar reflex) synaptic reflex prevents over-stretching injury Tendon Reflex Tendon organs activated when tendon stretched → muscle relaxes, antagonistic muscle contracts prevents tendon damage Flexor (withdrawal) Reflex polysynaptic reflex pain signals activate motor fibers in several s.c. segments >1 muscle group activated to lift foot away from painful stimulus Physiological Role of Reflexes - minimizes duration of exposure to noxious stimuli maintain posture, balance co-ordination Spinal Nerves branch from s.c., emerge through intervertebral foramina mixed nerves (contain sensory and motor fibers) Spinal Nerve Coverings nerve wrapped in epineurium (continuation of dura) fascicle wrapped in perineurium nerve fibers (individual axons) wrapped in endoneurium  blood epineurium vessels perineurium 900x endoneurium axons fascicle  Spinal Nerves 8 cervical 12 thoracic 5 lumbar 5 sacral © John Wiley & Son Inc 1 coccygeal  Branching of Spinal Nerve posterior and anterior roots join to form spinal nerves posterior root spinal nerve anterior root Branching of Spinal Nerve spinal nerves branch into posterior and anterior rami posterior ramus posterior root (supplies skin, muscles of back) spinal nerve anterior ramus (supplies limbs, anterior root ant. neck, trunk) form plexuses  Plexus complex of nerves “junction box” for anterior rami of spinal nerves found in cervical, brachial, lumbar and sacral regions  Cervical Plexus C1 C2 C3 C4 © John Wiley & Son Inc anterior rami of s.n. C5 C1 to C5 innervates skin and muscles of head and neck, and superior phrenic n. (C3-C5) shoulders and chest to diaphragm  Brachial Plexus C5 C6 C7 C8 T1 anterior rami of s.n. C5 to T1 innervate shoulder and upper limb  Lumbar Plexus L1 anterior rami of L2 s.n. L1 to L4 L3 innervates L4 abdominal wall, external genitals L5 and anterior- medial thigh femoral n.  Sacral Plexus L4 L5 anterior rami of S1 s.n. L4 to S4 S2 S3 innervates buttocks, S4 perineum and part of lower limb sciatic n.