Chapter 13: The spinal cord, spinal nerves, and somatic reflexes

denticulate ligaments

extend through the arachnoid to the dura, anchoring the cord and limiting side-to-side movements

Tendon reflex

functions when some parts of a muscle contract more than others to spread the workload more evenly over the entire muscle

dorsal root (posterior)

gray matter that carries sensory nerve fibers, which ender the posterior horn of the cord and sometimes synapse with an interneuron there

ventral (anterior) root

gray matter that contain the large somas of the somatic motor neurons. Axons from here exit by way of the anterior root of the spinal nerve and lead to the skeletal muscles

gray commissure

gray matter that the right and left sides of the central core are connected by this

central canal

gray matter this is collapsed in most areas of the adult spinal cord, but in some places (and young children) it remains open, lined with ependymal cells and filled with CSF

white mater

has a bright, pearly white appearance due to an abundance of myelin

Gray matter

has relatively dull color because it contains little myelin

tendon reflex

inhibits alpha motor nurons to the muscle so that it does not contract as strongly

reflexes

play a vital roll in posture, motor coordination, and protective responses to pain or injury

neural integration

pools of spinal neurons receive input from multiple sources, integrate the information, and execute and appropriate output

somatosensory

meaning the nerve carries sensory signals from bones, joints, muscles and the skin

conus medullaris

medullary cone aka

locomotion

motor neurons in the brain initiate walking and determine its speed, distance, and direction

epineurium

protects the nerve from stretching and injury.

reflexes

quick, involuntary, stereotyped reactions of glands or muscles to stimulation

paraplegia

paralysis of both lower limbs resulting from spinal cord lesions at levels T1 to L1

hemiplegia

paralysis of one side of the body, usually resulting from a stroke or other brain lesion

somatic reflexes

reflexes of the skeletal muscle (also called spinal reflexes)

tendon reflex

serves to moderate muscle contraction before it tears the tendon or pulls it loose from the muscle or bone

epineurium

several fascicles are bundled together and wrapped in an ________ to compose the nerve as a whole

central pattern generators

simple repetitive muscle contractions over and over are coordinated by groups of these neurons in the spinal cord

muscle spindles

somatic reflexes involve stretch receptors called _______ ______ embedded in the muscles

subarachnoid space

space between arachnoid membrane and pia mater and is filled with CSF

myotatic

stretch reflex aka

posterior ramus

the _____ _______ innervates the muscles and joints in posterior region of the spin and the skin of the back.

coccygeal ligament

the ______ _____ is formed as the terminal filum and dura mater fuse.

flexor

the _______ reflex employs an ipsilateral reflex arc

spinal nerve proper

the anterior and posterior roots merge, leave the dural sheath and form:

crossed extension reflex

the contraction of extensor muscles in the limb opposite frm the one that is withdrawn. It extends that limb and enables you to keep balanced

extrafusal fibers

the fibers that make up the rest of the muscle and do its work (not intrafusal)

terminal filum

the fibrous strand that continues beyond the medullary cone within the lumbar cistern

intrafusal fibers

the modified muscle fibers within a spindle (at the ends of a muscle, near the tendon)

proprioception

the non visual sense of the position and movements of the body

quadriplegia

the paralysis of all four limbs resulting from lesions above level C5

flexor reflex

the quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus

gray matter

the site of all neural integration in the spinal cord

epidural space

the space between the sheath and vertebral bones which is occupied by blood vessels, adipose tissue, and loose connective tissue

conduction

the spinal cords contain bundles of nerve fibers that conduct information up and down the cord, connecting different levels of the trunk with each other and with the brain

meninges

the three fibrous membranes that encloses the brain and spinal cord

spinal nerves

there are 31 _____ ______

5

there are ______ sacral spinal nerves

tendon organs

these are proprioceptors located in a tendon near its junction with a muscle

lower motor neuron

these lead an axon the rest of the way to the muscle or other target organ

corticospinal tracts

these tracts were once called pyramidal tracts

muscle spindles

they inform the brain of muscle length and body movements, which enables the brain to send motor commands back to the muscles that control muscle tone, posture, coordinated movements, and corrective reflexes (balance)

lateral horn

this is present on each side of the gray matter in the spinal cord

lumbar cistern

this is where spinal taps take place

anterolateral system

this system passes up the anterior and lateral columns of the spinal cord

crude touch

touch whose location can only vaguely be identified

dura mater

tough, collagenous membrane that is thick and forms a loose fitting sleeve called the dural sheath around the spinal cord

columns

tracts are arranged in __________ or faniculi

stretch reflex

when a muscle is suddenly stretched and it "fights back"--contracts, increases tone, and feels stiffer than an unstretched muscle

ipsilateral

when a tract does not decussate, its origin and destination are on the same size of the body

monosynaptic reflex arcs

when fibers synapse directly with the alpha motor neurons that return to the muscle, this forms:

spinoreticular tract

Ascending tracts: These tract's third order neurons continue from the pons to the thalamus and fourth-order neurons complete the path to the cerebral cortex

spinothalamic tract

Ascending tracts: Third-order neurons in this tract lead to the cerebral cortex from the thalamus, and arrive in the cerebral hemisphere contralateral to their point of origin

medial lemniscus

Ascending tracts: a tract of nerve fibers that leads the rest of the way up the brainstem to the thalamus

gracile fasciculus

Ascending tracts: an ascending tract that carries signals from the midthoracic and lower parts of the body

spinoreticular tract

Ascending tracts: carries pain signals resulting from tissue injury

cuneate fasciculus

Ascending tracts: carries sensory signals from T6 and up (from the upper limbs and chest)

spinothalamic tract

Ascending tracts: carries signals for pain, temperature, pressure, tickle, itch, and light or crude tough

gracile fasciculus

Ascending tracts: first order nerves that travel up the ipsilateral side of the spinal cord and terminate at the gracile nucleus

spinothalamic tract

Ascending tracts: in this tract, first-order neurons end in the posterior horn of the spinal cord near the point of entry, where they synapse with second-order neurons

cuneate fasciculus

Ascending tracts: occupies the lateral potion of the posterior column and forces the gracile fasciculus medially

Posterior and anterior spinocerebellar tracts

Ascending tracts: their first order neurons originate in muscles and tendons and end in the posterior horn

Posterior and anterior spinocerebellar tracts

Ascending tracts: their second order neurons send their fibers up the spinocerebellar tracts and end in the cerebellum

gracile fasciculus

Ascending tracts: these fibers carry signals for vibration, visceral pain, deep and discriminative touch, and proprioception from lower limbs and trunk

spinothalamic tract

Ascending tracts: these form the anterolateral system

gracile nucleus

Ascending tracts: where gracile fasciculi terminate in the medulla oblongata of the brainstem

T6

At ____ the gracile fasciculus and cuneate fasciculus are joined

corticospinal tracts

Descending tract that carries motor signals from the cerebral cortex for precise, finely coordinated limb movements

tectospinal tract

Descending tract: begins in a midbrain region called the tectum and crosses to the contralateral side of the midbrain

Tectospinal tract

Descending tract: involved in reflex turning of the head, especially in response to sights and sounds

tectospinal tract

Descending tract: it descends through the brainstem to the upper spinal cord on that side, going only as far as the neck.

lateral corticospinal tract

Descending tract: most corticospinal fibers decussate in the lower medulla and for this tract on the contralateral side of the spinal cord

axon

The term "nerve fiber" refers to the ______ of a neuron.

5

There are ____ nerve plexuses.

31

There are ____ pairs of spinal nerves

12

There are ____ thoracic spinal nerves

8

There are _____ cervical spinal nerves

1

There are _____ coccygeal spinal nerve

5

There are _____ lumbar spinal nerves

upper motor neurons

These begin with a soma in the cerebral cortex or brainstem and has an axon that terminates on a lower motor neuron

stretch reflex

This reflex helps to maintain equilibrium and posture

polysynaptic reflex arc

a pathway in which signals travel over many synapses on thier way back to a muscle

reciprocal inhibition

a reflex that prevents muscles from working against each other by inhibiting antagonists

tendon reflex

a response to excessive tension on the tendon

dermatome

a specific area of the skin that sends sensory input to a spinal nerve

endoneurium

a thin sleeve of connective tissue that surrounds nerve fibers

brainstem

a vertical stalk that supports the large cerebellum at the rear of the head and the two cerebral hemispheres that dominate the brain

arachnoid membrane

adhering to the inside of the dura

lumbar puncture

aka spinal tap; a needle is inserted between vertebrae at level L3/L4 or L4/L5, where there is no risk for accidental injury to the spinal cord

coccygeal ligament

anchors the spinal cord and meninges to vertebra

epidural space

anesthetics are sometimes introduced to this space to block pain signals during childbirth or surgery

cauda equina

arising from the lumbar enlargement and medullary cone is a bundle of nerve roots that occupy the ventral canal

Posterior and anterior spinocerebellar tracts

both of these tracts provide the cerebellum with feedback needed to coordinate muscle action

faniculi

columns or _________ of tracts

white matter

composed of tracts that carry signals form one level of the CNS to another

arachnoid mater

consists of a simple squamous epithelium, the arachnoid membrane, and a loose mesh of collagenous and elastic fibers

tendon organ

consists of an encapsulated bundle of small, loose collagen fibers and one or more nerve fibers that penetrate the capsule and end in flattened leaflike processes between the collagen fibers

reflex arc

A somatic reflex employs a _____ _____, which signals travel along the following pathway

integrating center

(reflex arc) a point of synaptic contact between neurons in the gray matter of the cord or brainstem

afferent nerve fibers

(reflex arc) carry information from these receptors to the posterior horn of the spinal cord or to the brainstem

efferent nerve fibers

(reflex arc) carry motor impulses to the muscles and effectors

somatic receptors

(reflex arc) in the skin, muscles and tendons

effectors

(reflex arc) the muscles that carry out a response

reflexes

1. Require stimulation 2. They are quick 3. They are involuntary 4. They are stereotyped (response is very predictable)

gamma

A ________ motor neuron of the spinal cord innervates each end of an intrafusal fiber, preventing it from going slack

posterior and anterior spinocerebellar tracts

Ascending tracts that travel through the lateral column and carry proprioceptive signals from the limbs and trunk to the cerebellum

cuneate nucleus

Ascending tracts: Cuneate fasciculus fibers end here on the ipsilateral side of the medulla oblongata

spinoreticular tract

Ascending tracts: First-Order neurons in this tract immediately synapse with second-order neurons after they ender the posterior horn

medial lemniscus

Ascending tracts: In the medulla, second-order fibers from the gracile and cuneate fasciculi decussate and form this

spinoreticular tract

Ascending tracts: These decussate to the opposite anterolateral system, ascend the cord, and end in a loosely organized core of grey matter (reticular formation) in the medulla and pons

lateral

Descending tract: the ______ vestibulospinal tract passes down the anterior column of the spinal cord and facilitates neurons that control extensor muscles of the limbs, thus inducing the limbs to stiffen and straighten

medial

Descending tract: the _______ vestibulospinal tract splits into ipsilateral and contralateral fibers that descend through the anterior column of both sides of the cord and terminate in the neck. Plays a role in the control of head position

anterior cotricospinal tract

Descending tract: the few corticospinal fibers that do not decussate and remain uncrossed. These are on the ipsialteral side

lateral and medial vestibulospinal tracts

Descending tract: these begin in the brain stem vestibular nuclei, which receive signals for balance from the inner ear

lateral and medial reticulospinal tract

Descending tract: these contain descending analgesic pathways that reduce the transmission of pain signals to the brain

lateral and medial reticulospinal tracts

Descending tract: these control muscles of the upper and lower limbs, especially to maintain posture and balance

later and medial reticulospinal tracts

Descending tract: this originates in the reticular formation of the brainstem

corticospinal tract

Descending tract: this tract gets smaller as it descends and usually disappears by the mid thoracic level

corticospinal tracts

Descending tracts: most of these fibers decussate in the lower medulla and form the lateral corticospinal tract on the contralateral side of the spinal cord

corticospinal tracts

Descending tracts: these fibers form pyramids on the anterior surface of the medulla oblongata

fasciculi

Each column of white matter consists of subdivisions called tracts or ____________

roots; rami

Each spinal nerve branches on both ends into anterior and posterior _______ approaching the spinal cord and anterior and posterior _____ leading away from the vertebral column.

posterior; anterior

Fibers of the _______ tract travel up the ipsilateral side of the spinal cord, and _______ tract fibers cross over and travel up the contralateral side, but then cross back in the brain stem to enter the ipsilateral side of the cerebellum.

decussate

First order neurons synapse with second-order neurons, which ________ and form the contralateral ascending spinothalamic tract. These fibers lead all the way to the thalamus

nerve fibers

First-order neuron, second-order neuron, third order neurons can also be called (first, second, or third) ________ ________

medullary cone

Inferior to the lumbar enlargement is the cord that tapers to a point called the:

brachial

The _____ plexus is a nerve plexus near the shoulder.

meningeal branch

The ______ _____ reenters the vertebral canal and innervates the meninges, vertebrae, and spinal ligaments with sensory and motor fibers

denticulate ligaments

The ______ _______ ligaments are extensions of the pia mater that extend through the arachnoid to the dura mater to anchor the spinal cord.

coccygeal

The ______ plexus is a nerve plexus adjacent to the lower sacrum and coccyx.

cervical

The ______ plexus is a nerve plexus in the neck.

Intercostal nerve

The _______ _____ innervates the internal and external obliques and the transverse abdominal muscles

lumbar

The _______ plexus is a nerve plexus in the lower back

lumbar

The ________ enlargement fives rise to the pelvic region and lower limbs

Sacral

The ________ plexus is a nerve plexus immediately inferior to the lumbar plexus.

cervical

The _________ enlargement gives rise to nerves of the upper limbs.

intercostal nerve

The anterior ramus forms the _______ _____ in the thoracic region, which travels along the inferior margin of a rib and innervates the skin and intercostal muscles (breathing).

contralateral

The crossed extension reflex employs a _______________ reflex arc

anterior ramus

The larger _______ ______ innervates the anterior and lateral skin and muscles of the trunk, and gives rise to nerves of the limbs.

2

The number of nerves in a descending pathway

Foramen Magnum

What structure marks the beginning of the spinal cord?

general

______ fibers innervate widespread organs such as muscles, skin, glands, viscera, and blood vessles

secondary afferent fibers

_______ ______ _______ are sensory nerve fibers in intrafusal fibers in muscle that monitor the length only, not the rate of change

primary afferent fibers

_______ _______ _______ are sensory nerve fibers in intrafusal fibers in muscles that monitor muscle length and how rapidly it changes, which responds to sudden body movements

special

_______ fibers innervate more localized organs in the head, including the eyes, ears, olfactory, and taste receptors, and muscles of chewing, swallowing, and facial expression

alpha

_________ motor neurons supply the extrafusal muscle fibers

ipsilateral

_________ reflex arc: the sensory input and motor output are on the same side of the spinal cord

somatosensory

_________ sensory signals are for touch, heat, cold stretch, pressure, pain, and other sensations.

ascending

_________ tracts carry sensory information up the cord

descending

___________ tracts conduct motor impulses

intersegmental

____________ reflex arc: the input and output occur at different levels of the spinal cord

muscle spindle

a ______ ______ is usually seven or eight small, modified muscle fibers enclosed in an elongated fibrous capsule

nerve

a chordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue

ganglion

a cluster of neurosomas outside the CNS and nerve fibers

spinal cord

a cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull

pia mater

a delicate, transparent membrane that closely follows the contours of the spinal cord

ganglion

a knot in a thread of nerves

dural sheath

a loose-fitting sleeve around the spinal cord

tracts

bundles of axons in white matter

descending tracts

carry motor signals down the brainstem and spinal cord

ascending tracts

carry sensory signals up the spinal cord

perineurium

each fascicle is wrapped in a sheath called:

three

how many neurons does it take for a somatic sensation's nerve signal to complete the sensory pathway?

third-order neuron

in an ascending tract, this carries the signal the rest of the way to the cerebral cortex

second-order neuron

in an ascending tract, this continues as far as a gateway called the thalamus at the upper end of the brainstem

first-order neuron

in an ascending tract, this detects a stimulus and transmits a signal to the spinal cord or brainstem

rootlets

in each segment of the cord, six to eight nerve ______ emerge from the anterior surface and converge to form the ventral root of the spinal never

fascicles

in most nerves, the fibers are gathered in bundles called ________

lumbar cistern

inferior to the medullary cone, the subarachnoid space is called the ________ ________ and is occupied by the cauda equine and CSF

perineurium

is composed of up to 20 layers of overlapping, squamous, epithelium-like cells

gray matter

it contains the somas, dendrites, and proximal parts of the axons and neurons

contralateral

when the origin and destination of a tract are on opposite sides of the body

decussation

when tracts cross over from the left side of the body to the right or vice versa