chapter 14 - spinal cord and spinal nerves (exam 2)

where is the spinal cord located

it starts at the foramen magnum and ends L1 and L2 (does not go into the sacrum

conus medullaris

inferior most tip of the spinal cord (end)

cuada equina

bundle of nerves inferior to spinal cord

filum terminale 

inferior most spinal nerves that become the coccygeal ligament 

meninges

connective tissues membranes covering the CNS (brain and spinal cord)

epidural space

space between the meninges and vertebra that is usually filled with adipose tissue

dura mater 

outer meninge- very durable, stabilized by coccygeal ligament 

arachnoid mater

middle meninge, superficial to subarachnoid space

pia mater

inner meninge- firmly attached to brain and spinal cord and is impossible to remove

dorsal root of nerve 

brings sensory info into the spinal cord (have ganglion)

ventral root

bring motor nerves out of the spinal cord (have no ganglion)

what kind of nerve is a spinal nerve ?

mixed nerve - carries axon for sensory and motor information because the dorsal and ventral roots merge 

epineurium

surround the entire nerve and has the same consistency as the dura mater

perineurium

surrounds bundles of axons (aka the fascicles)

endoneurium 

areolar connective tissue that surrounds each individual axon of each neuron; if the nerve in myelinated, it covers the myelin sheath 

rami

offshoots of a nerve once it exits the vertebra

dorsal ramus

take sensory info from, and provides motor information to the back and neck

ventral ramus 

take sensory info from, and provides motor information to the skin and limbs 

ramus communicantes

part of the autonomic nervous system (white = myelinated, gray = unmyelinated)

dermatomes

represents an area of the body that is innervated by specific spinal nerves; allows drs to figure out where spinal cord damage occurs by identifying loss of sensation in particular locations

cervical plexus 

C1-C4 innervate of certain muscles of neck and torso (phrenic nerve : C3, C4, C5 branch and go to the diaphram)

brachial plexus

C4-C8 and T1- innervate the chest, upper back, and arm

lumbosacral plexus

innervate the gluteal and lower limb regions

obturator: adductors

femoral: motor/sensory or leg and thigh

sciatic: back of entire leg (largest and longest nerve)

ascending tract 

carries sensory impulse into the brain (dorsal ramus) 

descending tract

carries motor impulses out of the brain (ventral ramus) 

posterior column pathway of ascending tract

fasciculus gracilis (lower limbs) and fasciculus cuneatus (upper body) - carry sensory impulse such as touch, pressure, and movement from the skin, muscles, tendons and joint

** cross over in the medulla

what does crossing over mean

information from one side of the body goes to the opposite side of the brain or spinal cord for processing

spinothalamic tract of ascending tract 

anterior : senstation of touch and pressure 

lateral : senstation of pain and temperature 

** cross over as soon as the info hits the spinal cord 

spinocerebellar tract of ascending tract

posterior : dont cross over

anterior : cross over in spinal cord

impulses from legs and trunk that result in coordination

corticospinal tract of descending tract

lateral : crosses over in medulla

anterior : does not cross over

control voluntary movement - motor impulses from brain to spinal nerves to skeletal muscles

reticulospinal tract of descending tract 

lateral and anterior - controls muscle tone and activity of sweat glands from motor impulses in brain 

rubrospinal tract of descending tract

cross over in brain and pass through lateral funiculi - coordination and posture control from motor impulses of brain to skeletal muscles

reflexes

rapid automatic involuntary motor response to stimuli to help preserve homeostasis

does not require cerebral processing (not using thought centers) but can be modified by the cerebral center

reflex classification 

by development, by response, by processing site, by complexity of circuit 

reflexes by development

innate : genetically determined (what we are born with)

acquired : learned

reflexes by response

somatic : control skeletal muscle contractions (superficial and stretch reflexes)

visceral : control smooth/cardiac muscles and glands

reflexes by processing site 

spinal : processing in spinal cord

cranial : processing in brain 

reflexes by complexity of circuit

monosynaptic : one synapse

polysynaptic : multiple synapses

steps of a reflex arc

1. receptor is stimulated

2. sensory nerve sends signal to CNS

3. information is transmitted to appropriate interneurons for processing (polysynaptic)

4. motor neuron is stimulated and signals an effector

what is an effector

the muscle or gland that responds

stretch reflex 

a reflex is stimulated by the stretching of a muscle (muscle spindle fibers are receptors, effector is contraction) (monosynaptic) 

patellar reflex

stretch reflex that prevents muscles from being overstretched, or the individual from falling forward