Spinal Cord & Spinal Nerves: Anatomy Chapter 14

Ramus communicans (gray and white rami)

white ramus communicans: autonomic function -ANS only in thoracolumbar region -myelinated axons -Sensory and motor neurons gray ramus communicans: autonomic function -ANS only in thoracolumbar region -unmyelinated axons -motor neurons ONLY

Dorsal root

- has dorsal root ganglia (cluster of cell bodies in PNS) -cluster of SENSORY cell bodies -located between pedicles of adjacent vertebrae

Size and location of spinal cord

-45 cm long -starts at foramen magnum and ends between L1 and L2 -does not go into the sacrum

Stretch reflex

-a reflex stimulated by the stretching of a muscle -prevents muscles from being over stretched -muscle spindle fibers are usually the receptors -the effector is the contraction of the muscle -typically monosynaptic

Patellar reflex

-a type of stretch reflex -functions to prevent muscles from being overstretched -prevent one from falling forward

2 grooves of spinal cord

-anterior median fissure (ventral) -posterior median sulcus (dorsal)

Steps of a reflex arc

-arrival of a stimulus and activation of a receptor -relay of into to CNS (done by sensory neuron) -information processing (information transmitted to appropriate interneurons) -activation of motor neuron -response of peripheral effector -behavior

Nerve impulses: 2 types of tracts

-ascending: conducts impulses from body parts & carries info to the brain -descending: conducts motor impulses from brain & spinal cord to muscles & glands

Ventral root

-axons of both somatic & visceral MOTOR neurons -no ganglion

Gray commissure

-bar of gray matter around central canal -axons carry info from side to side (point of crossing over) -anterior and posterior commissure -connects 2 halves and surrounds central canal

Conus medullaris

-below lumbar enlargement -about L1 -inferior tip of spinal cord -cone shaped

Structure of spinal cord

-bilateral symmetry (mirror images) -gray and white matter -central canal -2 grooves (anterior median fissure and posterior median sulcus) -cervical and lumbar enlargements -conus medullaris -cauda equina -filum terminale

Nerve plexus

-braid of ventral rami -cervical, brachial, lumbar, sacral

Gray matter of spinal cord

-butterfly shapes core -contains cell bodies, dendrites, and synapses (things without myelin) -projections are called horns -cell bodies arranged in groups called nuclei -unmyelinated

Enlargements of spinal cord

-cervical: supplies nerves to pectoral region of body and arms -lumbar: supplies pelvic region and lower limbs enlargements are swollen regions of the spinal cord. Filled with cell bodies. Found in areas associated with lots of motor control

Functions of spinal cord

-conduct nerve impulses -act as a center for spinal reflexes

Rubrospinal tracts

-cross over in brain and pass through lateral funiculi (column) -carry motor impulses from brain to skeletal muscles concerned with coordination and posture control

Superficial to meninges

-epidural space (between outermost meninges and vertebra. May be filled with adipose tissue or BVs) -meninges connect to CT covering of spinal nerves.

Ascending tracts

-fasciculus gracilis and fasciculus cuneatus -spinothalmic tracts -spinocerebellar tracts -all sensory tracts

Central canal

-hole down the center of the spinal cord -continuous with ventricles of the brain -contains cerebrospinal fluid

Corticospinal tract (lateral and anterior)

-in lateral and anterior funiculi (column) -lateral tracts cross over in medulla -anterior tract doesn't cross -carry motor impulses from brain to spinal nerves & out to skeletal muscles -control voluntary movements -called pyramidal tracts

Cauda equina

-individual spinal nerve roots from conus medullaris to sacrum within spinal canal -nerves inferior to the spinal cord -translates to "horses tail"

Filum terminale

-inferior most spinal nerves -thin cord of meninges -becomes coccygeal ligament

Dermatomes

-innervation pattern of the body -sensory innervation by specific spinal nerves -spinal cord transection: will result in permanent loss of sensation -detection method

Lumbosacral plexus

-last thoracic, lumbar, sacral, and coccygeal nerves -gives rise to motor and sensory fibers associated with the abdominal wall, exterior genitalia, buttocks, thighs, and legs and feet obturator nerve: to adductors of the leg femoral nerve: motor impulses to leg and thigh & receive sensory from skin of leg and thigh sciatic nerve: to muscles and skin in thighs, legs, and feet (longest nerve in the body!)

Spinothalmic tracts (lateral & anterior)

-located in lateral and anterior funiculi (column) -cross over in spinal cord -lateral tract conduct impulses from various body parts and results in sensations of pain and temperature -anterior tract conducts impulses from various body parts and results in sensations of touch and pressure

Fasciculus gracilis and fasciculus cuneatus (posterior column pathway)

-located in posterior funiculi (column) -conduct sensory impulses from skin, muscles, tendons, and joints to brain -interpreted as touch, pressure, and body movement -"cross over" in medulla of brain

White matter

-made of tracts and columns (bunches of axons in CNS) -primarily made of myelinated axons

Spinal meninges

-membranes surrounding the CNS -layers of meninges called "mater"

Spinocerebellar tracts (posterior and anterior)

-posterior fibers do not cross over but anterior do in spinal cord -conduct impulses from legs and trunk to cerebellum -results in coordination

Tracts and columns in white matter

-posterior white column (posterior funiculi) -anterior white columns (anterior funiculi) -lateral white column (lateral funiculi) -ascending tract= sensory towards brain -descending tract= motor from brain

Ventral ramus

-provides sensory innervation from and motor innervation to segments of skin and muscles of body wall and limbs -B in picture

Dorsal ramus

-provides sensory innervation from and motor innervation to segments of skin and muscles of the back and neck -A in the picture

Reflexes

-rapid automatic involuntary motor response to stimuli -act to preserve homeostasis -occur at spinal cord or brain stem levels -no cerebral processing but can be modified by cerebral control

Reticulospinal tracts (lateral and anterior)

-some in lateral cross over, all others do not -carry motor impulses from brain to control muscle tone and activity of sweat glands -don't worry about crossing over of this tract

Spinal vs cranial reflexes

-spinal= spinal cord -cranial= brain (brain stem?)

Perineurium

-surrounds bundles of axons in a fascicle

Endoneurium

-surrounds individual axons/neurolemmocytes (Schwann cells) -areolar CT

Spinal nerves

31 pairs of nerves arising from the spinal cord 8 cervical 12 thoracic 5 lumbar 5 sacral -spinal nerves are both sensory and motor roots united -roots come out of spinal column -these roots go through the intervertebral foramina

Cervical plexus

C1-C4 and part of C5 C3-C5 fibers go into phrenic nerve (diaphragm)

Brachial plexus

C4-C8 and T1 lateral & medial pectoral nerve= to pectoralis major and minor dorsal scapular= to rhomboid major and levator scapulae subscapular= to subscapularis and teres major thoracodorsal nerve= to latissimus dorsi suprascapular nerve= to supraspinatus and infraspinatus musculocutaneous= to anterior muscles of arms and skin of forearm ulnar nerve= to muscles of forearm, hands, and skin of hands median nerve= same as ulnar radial nerve= to posterior muscles of arms and skin of forearms and hands axillary nerve= to muscles and skin of upper, lateral, and posterior regions of arm lower subscapular= subscapularis and teres major

Dura mater

Outermost layer of the meninges -tough mother -covered by epithelium -deep to epidural space and superficial to subdural space -subdural space (found in preps, probably not seen in life) -stabilized by coccygeal ligament and fusion with periosteum of cranial cavity

Nerve fibers in tracts are all _______

axons -names of tracts often identify origins & termination

Rami

branches of spinal nerves -dorsal ramus, ventral ramus, ramus comminucans (splitting in the ramus separating sensory and motor fibers)

Descending tracts

corticospinal, reticulospinal, rubrospinal tracts -motor

Innate vs acquired reflex

innate: genetic, built in acquired: learned through repetition or experience

Arachnoid mater

middle layer of the meninges -spidery looking -simple squamous -carries BVs -suspended by arachnoid trabeculae from dura -superficial to subarachnoid space -subarachnoid space contains CSF

Complexity of Neural Circuit

monosynaptic: 1 sensory and 1 motor neuron polysynaptic: involves interneurons -can be modified by higher centers

Interior horns of spinal cord (gray matter)

posterior horn= upper wings (somatic and visceral sensory nuclei) anterior gray horn = lower wings (somatic motor control) lateral gray horn= protrusion of gray matter between anterior and posterior (visceral motor control)

Sensory and motor nuclei of spinal cord

sensory nuclei= posterior/dorsal motor nuclei= anterior/ventral

Nature of motor response: somatic vs visceral

somatic- influences skeletal muscle system visceral (autonomic)- influences involuntary systems such as smooth muscles and glands

Epineurium

surrounds the entire nerve -outermost -dense irregular CT continuous with the dura

Pia mater

thin, delicate inner membrane of the meninges -delicate mother -adheres tightly to the surface of the spinal cord -astrocytes of spinal cord lock pia in place -denticulate ligaments: connect pia to the dura. stabilizing all 3 layers -forms part of filum terminale