Chapter 12: Spinal cord and spinal nerves part 2

what spinal roots are found in gray matter

ventral roots, dorsal roots, dorsal root ganglia, and spinal nerves

define ventral roots

bundle of motor fibers

define dorsal roots

sensory input to spinal cord

define dorsal root ganglia

cell bodies of sensory neurons

spinal nerves are formed by what

fusion of dorsal and ventral roots

in white matter, fibers allow what

communication between spinal cord and brain

in white matter, fibers run where

in three directions

what are the three direction the fibers run in white matter

ascending, descending, and transverse

Define fibers running in ascending direction in white matter

sensory inputs

Define fibers running in descending direction in white matter

motor outputs

Define fibers running in transverse direction in white matter

from one side to other (commissural fibers)

How is white matter divided in the spinal cord?

three white columns - the dorsal, lateral, and ventral columns.

**dorsal white column has which fibers**

ascending

lateral white column has which fibers

mixed fibers

Ventral white column has which fibers

descending

Define reflex

automatic response to stimulus without conscious thought

define reflex arc

neural pathway that controls reflex

What are the components of a reflex arc?

\

sensory receptor, sensory neuron, interneuron, motor neuron, and effector organ

what is the first step of a reflex arc

sensory receptor detects a stimulus, generating an action potential

what is the second step of a reflex arc

sensory neuron conducts action potential through dorsal root to spinal cord

what happens in the third step of reflex arc

action potential carried to integration center in spinal cord (example of interneuron) simple reflexes do not involve an interneuron

what happens in the fourth step of reflex arc

interneuron synapses with the motor neuron

what happens in the 5th step of reflex arc

motor neuron axon conducts action potential through ventral root and spinal nerve to an effector organ

muscles contract in response to what

stretching force applied to them

why is muscle contracting in response to stretching force applied to them considered unique

because no interneuron

define muscle spindle in stretch reflex

specialized muscle cells that respond to stretch

stretch reflex is innervated by what

specific motor neurons like gamma motor neurons that control sensitivity of muscle spindle

what are gamma motor neurons in stretch reflex

small diameter neurons

in the stretch reflex, these sensory neuron synapse with what

motor neurons of the spinal cord called alpha motor neurons which cause muscle to contract

function of golgi tendon reflex

prevent contracting muscles from applying excessive tension to tendons

stretch reflex, golgi tendon reflex, and withdrawal reflex are part of what

reflex arc

define golgi tendon organ

encapsulated nerve endings that have numerous terminal branches with small swellings associated with bundles of collagen fibers in tendon

where is golgi tendon organ located

in tendon near muscle

what goes golgi tendon reflex prevent

damage to tendons that could be caused by excessive tension

what does golgi tendon reflex produce

sudden relaxation of the muscles

function of withdrawal reflex

remove a body limb or other part from a painful stimulus

what is reciprocal innervation in withdrawal reflex

cause relaxation of extensor muscle when flexor muscle contracts

reciprocal innervation is also involved in what

stretch reflex

what happens when a withdrawal reflex is initiated in one lower limb in crossed extensor reflex of the withdrawal reflex

the crossed extensor reflex causes extension of opposite lower limbin

in crossed extensor reflex, signal are crossed over by what

interneurons

define spinal cord trauma

transection of spinal cord at any level results in total motor and sensory loss in regions inferior to cut

what are the 2 spinal cord trauma

paraplegia and quadriplegia

define paraplegia

transection between t1 and l1

define quadriplegia

transection in cervical region

define spinal shock

transient period of function loss

spinal nerves extend out from where

the vertebral column

how many pairs of spinal nerves are there

31

the spinal nerves are all what

mixed nerves

spinal nerves innervate body except for what

head and part of neck

how are spinal nerves named

according to region they are found in

define dermatomal map

skin area supplied with sensory innervation by spinal nerves

importance of dermatomes

help doctor identify which body part certain conditions affect like case of shingles, injury, and pinched nerves

what are the three connective tissue coverings in spinal nerves

endoneurium, perineurium, and epineurium

endoneurium, perineurium, and epineurium are what

connective tissue coverings in spinal nerves

define endoneurium

loose connective tissue that encloses axon and their myelin sheaths known as schwann cells

define perineurium

coarse connective tissue that bundle fibers into fascicles

define epineurium

tough fibrous sheath around all fascicles to form the nerve

define dorsal ramus

branch of spinal nerves that travel posteriorly

define ventral ramus

branch of spinal cords that travel anteriorly

ventral rami form what

5 plexuses

the thoracic region of the ventral ramus form what

intercostal nerves that innervate with intercostal muscles

define communicating rami

communicate with sympathetic chain of ganglia

where does cervical plexuses originate from

c1 to c4

cervical plexus innervate what

superficial neck structures, skin of neck, and posterior portion of head

where is the phrenic nerve

from c3 to c5 which is from the cervical and brachial plexuses

what does the phrenic nerve innervate

diaphragm involved in breathing

where does the brachial plexuses orginate from

spinal nerves c5 to t1

what are the branches in brachial plexus spinal nerves (in the upper limb)

axillary nerves, radial nerves, musculocutaneous nerve, ulnar nerve, median nerve, and smaller nerves also branch from this plexus

lumbar plexus give rise to what

femoral nerve

what does femoral nerve innervate

thigh and branches to nerves of legs

the two nerves in the thigh and branches of the leg are what

fibular and tibial

what does the fibular and tibial nerve referred to as

sciatic nerve

define neuralgia

sharp, shocking pain that follows the path of a nerve) of the sciatic nerve

Define neuralgia

sharp, shocking pain that follows the path of a nerve of the sciatic nerve in

in neuralgia, pain will radiate where

down the back of the leg

neuralgia is most common cause of what

it is a herniated lumbar disk