SPINAL CORD AND SPINAL NERVES Flashcards
Dura mater (cranial meninges)
-tough, outermost layer made of dense connective tissue
-adheres to the skull
Arachnoid mater (cranial meninges)
-middle layer
-thin and translucent
-spiderweb like appearance
-contains no blood vessels or nerves, but has connective tissue projections that attaches to the pia mater
Pia mater (cranial meninges)
-delicate, innermost layer
-made of a single layer of cells, and blood vessels branch out from the subarachnoid space through the pia mater into the brain providing nutrients
Spinal cord
-nervous system structure that extends through the vertebral column
-part of the CNS
Functions:
-carries sensory input up the cord
-carries motor output down the cord
-involved in important spinal reflexes
Cauda equina
-lower root of the lower spinal nerves
Conus Medullaris
-terminal end of the spinal cord
-between L1 & L2
Spinal meninges
-surround the cord
-continuation of the cranial meninges
Dura mater (spinal meninges)
-outer protective layer
-though fibrous membrane sac that encloses the entire spinal cord
-thickest providing the most protection to the spine
Arachnoid mater (spinal meninges)
-middle layer
-not always there
-thin web like layer
-against the dura mater
Pia mater (spinal meninges)
-thin region up against the spinal cord
-inner layer
-supplies nutrients to the cord
Spaces formed between the meninges
-epidural
-subdural
-subarachnoid
Epidural space
-outside the dura matter
-an anesthetic is injected into the epidural space numbing the lower half of the body
Subdural space
-between dura and arachnoid mater
Subarachnoid space
-between pia mater (cord) and arachnoid mater
-where CSF circulates
Gray matter
-brain and spinal cord is formed by neuronal cell bodies and dendrites (no myelin)
Anterior horns
-cell bodies and dendrites of somatic motor neurons
Posterior horns
-somatic and autonomic sensory cell bodies
White mater
-formed by aggregations of myelinated axons from many neurons
-lipid part of myelin imparts white
appearance
Sensory pathways
-from sensory receptors to the brain
-ascending pathways
Primary neurons
-first neuron
-cell body in posterior root ganglion of spinal nerve
-extends to secondary
Secondary neurons
-second neuron
-interneuron between primary and tertiary
Tertiary neurons
-interneuron between secondary and cerebrum
Posterior funiculus-medial lemniscal pathway
-sensory tracts (afferent)
-conveys nerve impulses for discriminative touch, light pressure, vibration, and conscious proprioception
Anterolateral pathway
-sensory neuron (afferent) of spinothalamic tracts
-detect crude touch and pressure, pain and temperature, itch, tickling
Spinothalamic tracts
-sensory neuron (afferent)
-carry signal for proprioception to the cerebellum
Motor pathways
-from brain to effectors
-descending pathways
Upper motor neurons
-connect the brain to the appropriate level in spinal cord
Lower motor neurons
-take the information from upper motor neuron to effector
-performs movement
-descend to innervate skeletal muscles
Spinal reflexes
-integration of information takes place in the spinal cord, not the brain
Reflex arc
-pathway that a nerve impulse follows to produce a reflex
-includes a sensory receptor, sensory neuron, an integrating center in the spinal cord, an exiting motor neuron and an effector
Monosynaptic
-1 synapse
-only a sensory and motor neuron
-no interneuron
Polysynaptic
-more than one synapse
-includes interneurons
-has one or more interneurons between the sensory and motor neuron
Stretch reflex
-causes contraction of a skeletal muscle
-protects from over stretching
-monosynaptic reflex arc
Tendon reflex
-causes muscle relaxation
-controls muscle tension
-prevents muscles from tearing
-polysynaptic reflex arc
Flexor reflex
-causes muscles to contract to withdraw a body part from a painful stimulus
Crossed-extensor reflex
-maintain balance
-polysynaptic
-occurs in conjugation with withdrawal reflex
-when withdrawal reflex is happening in one limb the crossed extensor reflex is occurring in the other limb
There are 31 pairs of spinal nerves
-8 cervical, C1-C8
-12 thoracic, T1-T12
-5 lumbar, L1-L5
-5 sacral, S1-S5
-1 coccygeal
Roots
-2 bundles of axons connect the spinal nerve to the cord by rootlets
-short branches of spinal nerves
-1 motor and sensory
-motor=anterior
-sensory=posterior
Rootlets
-connect spinal cord to roots
Dermatomes
-area of skin that is innervated by a single spinal nerve
-indicated by the letter and number of a segmental nerve
-important dermatomes:
-C6/C7- thumb and index finger
-T4- nipple line
-T10- umbilicus
-L1-L5- lower extremities
Spinal nerves divide into branches known as peripheral nerves
-each nerve extends through the intervertebral column
-splits into 2 branches:
-consists of anterior and posterior
rami
Posterior ramus
-innervates deep muscles and skin of back
Anterior ramus
-splits into multiple other branches
-innervates skin and skeletal muscle of the anterior and lateral portions of the trunk, upper limbs and lower limbs
