chapter 11, sections 11.5-11.8

spinal cord

slender column of nervous tissue continuus with brain and brainstem

where is spinal cord

extends downward through vertebral canal, begins and the foramen magnum and terminates at the first and second lumbar vertebrae space

how many segments does the spinal cord have

31, each gives rise to a pair of spinal nerves

how are spinal nerves grouped

according to the level of the vertebra with which they are associated

how are pairs of spinal nerves numbered

in sequence from superior to inferior

portions of the spinal cord (longitudinal section)

cervical enlargement, lumbar enlargement, conus medullaris, filum terminale, cauda equina

cervical enlargement

supplies nerves to upper limbs

lumbar enlargement

supplies nerves to lower limbs

conus medullaris

tapering region below lumbar enlargement

filum terminale

cord of connective tissue that anchors spinal cord to coccyx

cauda equina

group of lumbar and sacral nerves extending downward from conus medullaris in vertebral canal

structures of the spinal cord (cross section)

white matter surround core of gray matter

how is gray matter arranged in the spinal cord

in horns

anterior median fissure and posterior median sulcus

grooves that extend whole length of spinal cord

how is white matter arranged in spinal cord

in funiculi

what do posterior roots contain

sensory neurons

where are cell bodies in spinal cord

outside spinal cord, in posterior root ganglia

what do anterior roots of spinal cord contain

motor neurons

what does the gray commissure surround

central canal

2 main functions of the spinal cord

center for spinal reflexes, pathway for impulses to and from the brain

how do reflexes maintain homeostasis

controlling involuntary processes, such as heart rate, blood pressure, swallowing, coughing

reflex arc

neural pathway, consisting of a sensory receptor, 2 or more neurons, and an effector

simple reflex arc

contains only sensory and motor neurons

what does the most common reflex arc contain

sensory neuron, interneurons, motor neurons

monosynaptic (stretch) reflex

contains 2 neurons, sensory and motor, has only 1 synapse in spinal cord

example of monosynaptic reflex

patellar or knee-jerk reflex

what does a monosynaptic reflex do

helps maintain an upright posture

withdrawal reflex

occurs when a person touches something painful, limits tissue damage

postsynaptic withdrawal reflex

contains sensory neuron, interneuron, motor neuron

reciprocal innervation

flexors contract, extensors are inhibited

crossed extensor reflex

during withdrawal reflex, flexors on affected (ipsilateral) side contract, and extensors are inhibited; at same time, extensors on opposite (contralateral) side contract, flexors are inhibited (also shifts body weight so person remains upright)

uses of reflexes

used to assess condition of nervous system, routinely performed in neurological testing, effectiveness of anesthetic during surgery can be assessed through reflex testing

ascending tracts

conduct sensory impulses to the brain (pink)

descending tracts

conduct motor impulses from the brain via motor neurons reaching muscles and glands (light brown)

what are tracts composed of

axons

major ascending (sensory) spinal cord tracts

fasciculus gracilis, fasciculus cuneatus, spinothalamic tracts, spinocerebellar tracts

major descending (motor) spinal cord tracts

corticospinal tracts, reticulospinal tracts, rubrospinal tract

fasciculus gracilis and fasciculus cuneatus

conduct sensory impulses associated with touch, pleasure, and body movement from skin, muscles, tendons, and joints to the brain

spinothalamic tracts (lateral and anterior)

conduct sensory impulses associated with the senses of pain, temp, touch, and pressure from various body regions to the brain

fasciculus gracilis and fasciculus cuneatus location

posterior funiculi

spinothalamic tracts (lateral and anterior) location

lateral and anterior funiculi

spinocerebellar tracts (posterior and anterior)

conduct sensory impulses required for the coordination of muscle movements from muscles of the lower limbs and trunk to the cerebellum

spinocerebellar tracts (posterior and anterior) location

lateral funiculi

corticospinal tracts (lateral and anterior)

conduct motor impulses associated with voluntary movements from brain to skeletal muscles

corticospinal tracts (lateral and anterior) location

lateral and anterior funiculi

reticulospinal tracts (lateral, anterior, and medial)

conduct motor impulses associated with the maintenance of muscle tone and the activity of sweat glands from the brain

reticulospinal tracts (lateral, anterior, and medial) location

lateral and anterior funiculi

rubrospinal tracts

conduct motor impulses associated with muscular coordination from the brain

rubrospinal tracts location

lateral funiculi

where are spinal cord injuries most common

workplace and motor vehicle accidents

what is the result of compression or distortion of the spinal cord

damage to or death of neurons, leading to pain, weakness, loss of sensation, and muscular atrophy

what neurons do not regenerate

cns

injury to ascending tracts

can result in loss of sensation

damage to descending tracts

can result in loss of motor function, paralysis

what are potential ways to limiting damage of spinal cord after injury

growth factors, stem cells

nerves of pns

cranial and spinal nerves arising from the brain or spinal cord

somatic nervous system

cranial and spinal nerves that connect the cns to skin and skeletal muscles

autonomic nervous system

cranial and spinal nerves that connect cns to viscera (subconcious activities)

what are nerve fibers

axons

what are nerves

bundles of axons

endoneurium

loose connective tissue that surrounds individual axons

perineurium

loose connective tissue that surrounds fascicles

epineurium

dense connective tissue that surround a group of fascicles

mixed nerves

contain both sensory and motor nerve fibers

what kind of nerves are most nerves

mixed nerves

what kind of nerves are spinal nerves (except the first pair)

mixed nerves

cranial nerves

originate from brain

spinal nerves

originate from spinal cord

how many pairs of nerves on underside of brain

12

where is the first pair of cranial nerves

fibers start in the nasal cavity

where is the second pair of cranial nerves

originates in eyes, fibers synapse in thalamus

how are cranial nerves numbered

with roman numerals from anterior to posterior (for the two pairs associated with the cerebrum) and from superior to inferior for the remaining pairs

olfactory nerve

sensory only, sense of smell, bipolar neurons

olfactory process (I)

bipolar neurons, the olfactory receptor cells, pass through cribriform plate of ethmoid bone and enter olfactory bulbs

optic nerve (II)

sensory only, vision

optic process

neuron cell bodies form ganglion layers of retina, and pass through optic foramina of the orbits

oculomotor nerve (III)

primarily motor nerve, motor impulses to voluntary muscles that move eyes and eyelids, involuntary muscles that focus lens, adjust light entering eye, small sensory component (proprioceptive fibers)

trochlear nerve (IV)

primarily motor, small pair of cranial nerves, motor impulses to one pair of muscles that move the eyes, small sensory component (proprioceptive fibers)

trigeminal nerve (V)