Ch. 13 - Spinal Cord and Spinal Nerves

filum terminale (external SC anatomy)

- arising from the conus meduallaris - extension of the pia mater and extends inferiorly, fuses with the arachnoid mater and the dura mater, anchors the spinal cord to the coccyx

lateral gray horn (internal SC anatomy)

-between posterior and anterior gray horn -present ONLY IN thoracic and upper lumbar segments of spinal cord -contain autonomic motor nuclei- regulate activity of cardiac muscle, smooth muscles and glands

lateral white column (internal SC anatomy)

-contains distinct bundles of axons having a common origin or destination and carrying similar info

posterior median sulcus (internal SC anatomy)

-narrow furrow on the posterior (dorsal) side

tract (internal SC anatomy)

-nerve bundles of axons in CNS -extend up or down spinal cord (called nerve bundles in PNS)

conus medullaris (external SC anatomy)

-inferior to lumbar enlargement, the spinal cord terminates as a tapering, conical structure called this -ends between L1-L2

posterior or dorsal root ganglion (spinal nerve connection to SC)

-has a swelling -contains the cell bodies of sensory neurons

spinal nerves

31 pairs, connect CNS to PNS

anterior or ventral root (spinal nerve connection to SC)

- contain motor axons, conducts nerve impulses to skeletal muscles - contain autonomic motor neuron, conducts nerve impulses from the CNS to effectors (muscles and glands)

posterior or dorsal root (spinal nerve connection to SC)

- contain only sensory axons - conduct nerve impulses from sensory receptors in the skin, muscles and internal organs into the CNS

crossed extensor reflex

- reflex arc that is intersegmental and contralateral and where opposite limb supports body during withdrawal of injured limb - i.e. extending limb to catch a fall or shifting the weight to it for support of the other 1.) Stepping on a tach stimulates sensory receptor (dendrites of pain-sensitive neuron) in R foot 2.) Sensory neuron are excited 3.) Sensory neuron activates several interneurons (SC integration center) 4.) Motor neurons are excited 5.) Extensor muscles contract and extend L leg (effectors)

spinal nerves (external SC anatomy)

- the paths of communication between the spinal cord and specific regions of the body -segmented: 31 pairs of spinal nerves cervical nerves 8 pairs; C1- C8 thoracic nerves 12 pairs; T1-T12 lumbar 5 pairs; L1-L5 sacral nerves 5 pairs; S1-S5 coccygeal nerves 1 pair; Co1

contralateral reflex arc

-OPPOSITE SIDE -reflex arc where sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side -Sensory impulses from receptor on opposite sides of spinal cord. (e.g. step on object with left foot). Contract right leg to maintain balance (as withdraw left leg).

epidural space

-a place between dura mater and the wall of the vertebral canal -spinal cord protected by a cushion of fat and connective tissue located in this space

distribution of spinal nerves

-a short distance after passing though its intervertebral foramen, a spinal nerve divides into several branches

shingles

-acute infection of the PNS caused by herpes zoster -after recovering from chicken pox the virus retreats to a posterior root ganglion. if the virus is reactivated, the immune system usually prevents from spreading but can overcome a weak system -then it leaves the ganglion and travels down sensory neurons of the skin by fast axonal transport -result is pain, discoloration of skin, a characteristic line of skin blisters (marks like like of distribution=dermatome) of the particular cutaneous sensory nerve belonging to the infected posterior root ganglion

anterior or ventral white commissure (internal SC anatomy)

-anterior to gray commissure -connects the white matter of the right and left sides of the spinal cord

motor (descending) tract (internal SC anatomy)

-consist of axons that conduct nerve impluses AWAY from the brain -spinal tracts contd with sensory and motor tracts in the brain

sensory (ascending) tract (internal SC anatomy)

-consist of axons that conduct nerve impulses TOWARD the brain -spinal tracts contd with sensory and motor tracts in the brain

posterior (dorsal) gray horn (internal SC anatomy)

-contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons RECALL: that cell bodies of sensory neurons are located posterior (dorsal) root ganglion of a spinal nerve

anterior (ventral) gray horn (internal SC anatomy)

-contain somatic motor nucleo, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles

anterior (ventral) white column (internal SC anatomy)

-contains distinct bundles of axons having a common origin or destination and carrying similar info

posterior (dorsal) white column (internal SC anatomy)

-contains distinct bundles of axons having a common origin or destination and carrying similar info

gray commissure (internal SC anatomy)

-grey matter of the spinal cord is shaped like an H or butterfly gray commissure forms the CROSSBAR of the H

fascicle (connective tissue coverings - spinal nerve)

-groups of axons with their endoneurim held together is called this

nuclei (internal SC anatomy)

-in the gray matter of the spinal cord and the brain, clusters of neuronal cell bodies form functional groups called this -sensory nuclei receive input from receptors via sensory neurons, and motor nuclei provide output to effector tissues via motor neurons

reflex

-is a fast involuntary, unplanned sequence of action that occur in response to a particular stimulus inborn: pulling hand from hot surface learned/acquired: when driving, slamming on breaks.

muscle spindle (reflex)

-slight stretching of a muscles stimulates sensory receptors in the muscle called this. -this monitor changes in the length of the muscle.

subarachnoid space (epidural space)

-space between arachnoid mater and pia mater -contains shock-absorbing cerebrospinal fluid.

meningeal branch (spinal nerve)

-spinal nerve also branches into this in addition of rami -reenters the vertebral cavity through the interbertebral foramen and supplies the vertebrae, ligaments, blood vessels of the spinal cord and meninges -C in pic -posterior ramus- A in pic -anterior ramus- B in pic

roots (spinal nerve connection to SC)

-two (posterior and anterior) bundles of axons called this -connect each spinal nerve to a segment of the cord by even smaller bundles of axons called rootlets

stretch reflex

-type of reflex that causes contraction of a skeletal muscle (the effector) - via monosynaptic and ipsilateral reflex arc (ie: tapping knee for reflex) 1.) Stretching stimulates sensory receptor (i.e. muscle spindle) 2.) Sensory neuron is excited 3.) Sensory neuron activates motor neuron (SC integration center) 4.) Motor neuron is excited 5.) Same muscle contracts and relieve stretching (effector) - via AP triggered by Ach, released by nerve impulse at the NMJ

columns (internal SC anatomy)

-white matter that is divided into areas called this

2 principles functions in maintaining homeostasis with spinal cord

1.) nerve impulse propagation of information - the white matter tracts in the spinal cord are highways for this. sensory input travels along these tracts toward the brain, and motor output travels from the brain along these tracts toward skeletal muscles 2.) integration of information - the grey matter of the spinal cord receives and integrates incoming and outgoing information. the effector = tissue. - i.e. serve as integration center for some reflexes

5 functional components (reflex arc)

1.)*sensory receptor* -distal end (dendrite) receptor receives stimulus. if graded potential reaches threshold level of depolarization it will trigger nerve impulse in the sensory neuron 2.)*sensory neuron* -impulse propagates from sensory receptor along axon to terminal which are located in the grey matter of spinal cord or brain stem. from here relay neurons sends them to the area of the brain 3.)*integration center* grey matter in the CNS, simple reflex with one synapse (monosynaptic reflex arc) or many synapse and more than 1 neuron type (polysynaptic reflex arc) in the CNS 4.)*motor neuron* impulses triggered by integration center propagate out if the CNS along motor neurons to the part of the body that will respond 5.) *effector* part of the body that responds to the motor nerve impulse action is called a reflex - if effector is a skeletal muscle: somatic reflex - if effector is a smooth muscle: autonomic reflex

pia mater (epidural space)

DELICATE -deepest, thin, transparent, connective tissue-squamous to cubodial cells with interlacing bundles of collagen and elastic fibers. -adheres to the surface of spinal cord and brain -many blood vessels and supply O2 and nutrients to spinal cord Denticulate ligaments - triangle shaped extensions that suspend into the spinal cord in the middle of its dura sheath. -they are thickenings of the pia mater -project and fuse with arachnoid mater and dura mater -protect spinal cord against sudden displacement that could result in shock

plexus

Formed from axons of the anterior rami (spinal nerves; except for thoracic T2-T12) that do not go directly to the body structures they supply but instead form this and innervate: -networks on both L and R sides of the body via joining with various numbers of axons from anterior rami of adjacent nerves Main plexus: cervical brachial lumbar sacral (coccygeal)

spinal cord compression

SC normally protected by vertebral column but certain disorders may put pressure and disrupt its normal function - fracture vertebrae - herniated intervertebral discs - tumors - osteoporosis - infections if compression source is determined before tissue is destroyed, SC function usually returns to normal

arachnoid mater (epidural space)

SPIDER - middle , thin, avascular, loosely arrangement collagen and elastic fibers -contd though the foramen magnum with arachnoid mater of the brain

dura mater (epidural space)

TOUGH MOTHER -most superficial layer -thick, strong, dense irreg. connective tissue -forms a sac from the level of the foramen magnum in the occipital bone, where it is continuous with the meningeal dura mater of the brain, to the second sacral vertebra -also continuous with the epineurium- the outer covering of the spinal and cranial nerves

cauda equina (external SC anatomy)

The wisp-like roots of the nerves at the end of the spinal cord are called the:

poliomyelitis

a highly contagious viral disease by the poliovirus that affects the anterior horn cells of the gray matter in the spinal cord. Characteristics - fever, severe headaches, stiff neck and back, deep muscle pain and weakness and loss of certain somatic reflexes - paralyze by destroying cell bodies of motor neurons -can cause death by resp or heart failure Post-polio syndrome (survivors) - slow break down of motor units causing muscle weakness, fatigue, muscle pain, joint pain, cold intolerance, atrophy, & loss of functional skills, triggers can be a fall, minor accident, surgery, prolonged bed rest Causes overuse of surviving neurons, reactivation of dormant polio virus, immune response, hormone deficiencies, environment toxins Treatment strength exercises, admin of pyrifostigmine to enhance action of acetylcholine in stimulation muscle contractions and admin of nerve growth factors

reciprocal innervation (reflex)

an innervation arrangement where the components of a neural circuit or reflex simultaneously cause contraction of one muscle and relaxation of its antagonist -prevents conflict between opposing muscles and is vital in coordinating body movements

mixed nerve (spinal nerve)

because posterior root contains sensory (afferent) axons and the anterior root contains motor (efferent) axons, a spinal nerve is called this

subdural space (epidural space)

between dura mater and arachnoid mater is a space called this -contains interstitial fluid

ramus (plural is rami) (spinal nerve)

branches of spinal nerve after passing through its intervertebral foramen: Posterior ramus - serves the deep muscles and skin of the posterior surface of the truck - posterior ramus shown as nerve above yellow in pic Anterior ramus - serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk - anterior ramus shown in yellow in pic

cervical and lumbar enlargements (external SC anatomy)

cervical enlargement: -superior -extends from C4-T1 -nerves to and from the upper limbs arise from this lumbar enlargement: -inferior -extends from T9-12 -nerves to and from lower limbs arise from this

perineurium (connective tissue coverings - spinal nerve)

each fasical is wrapped in a thick layer of tissue called this

central canal (internal SC anatomy)

in the center of the gray commissure is a small space called this -it extends the entire length of the spinal cord and is filled with cerbrospinal fluid -at its superior end the central canal is continous with the 4th ventreal-space with cerebrospinal fluid in the medualla oblongata

indirect motor pathways (motor tracts -descend)

motor tracts that convey nerve impulses from the brain stem to cause automatic and involuntary movements and help coordinate body movements with visual stimuli Function -maintain skeletal muscle tone, sustain postural muscles and play major role in equilibrium by regulating muscle tone in response to movements of the head.

direct motor pathways (motor tracts -descend)

motor tracts that convey nerve impulses that originate in the cerebral cortex and are destined to cause voluntary movements of skeletal muscles consists of 2 tracts: (1) lateral (#2) and anterior corticospinal (#8 in pic) (2) cortcobulbar tracts

epineurium (connective tissue coverings - spinal nerve)

outer most layer covering of the entire nerve

brachial plexus

plexus formed by the roots (anterior rami) and spinal nerves C5-C8 and T1 Location: -extends below and to the side of the last four cervical and first thoracic vertebrae. it passes above the first rib posterior to the clavicle and enters the axilla. Function: provides almost the entire nerve supply of the shoulder and upper limbs. 5 large terminal branches arise from: 1.) axillary nerve 2.) musculocutaneous nerve 3.) radial nerve 4.) median nerve 5.) ulnar nerve Subunits: Roots-Trunks-Divisions-Cords-Branches "Risks takers don't cautiously behave"

cervical plexus

plexus formed by the roots (anterior rami) of cervical nerves C1-C4, C5 also contributes; the phrenic nerve (diaphragm) arises this plexus Location: there is one on each side of the neck alongside the first four vertebrae Function: supplies the skin and head muscles, neck, and superior part of shoulders and chest, and diaphragm (if damaged = can't breath)

lumbar plexus

plexus formed by the roots (anterior rami) of spinal nerves L1-L4; minimal intermingling of fibers Location on either side the plexus passes obliquely outward, between the psoas major and anterior quadratus lumborum muscle. between the heads of the psoa major the roots of the plexus divide and give rise to the peripheral branches of the plexus. Function supplies the anterolateral abdominal wall, external genitals, and part of the lower limb.

sacral plexus

plexus formed by the roots (anterior rami) of the spinal nerves L4-L5 and S1-S4; give rise to the sciatic nerve (largest nerve in the body) Location situated largely anterior to the sacrum Function supplies the butt, perineum, and lower limbs

Babinski reflex

reflex from gentle stroke of lateral outer sole of foot usually occurs in children less then 1.5 yo due to incomplete myelination of fibers in the corticospinal tract Negative test (normal) - toes curling under Positive test (abnormal past 1.5 yo) - great toe extends with or without lateral fanning of other toes - indicates an interruption of the corticospinal tract as a result of a lesion of the tract.

tendon organ or Golgi tendon organ (reflex)

sensory receptors for a tendon reflex are -tendon lies near the junction with the muscle - this detect and respond to changes in muscle tension that are cause by passive stretch or muscular contraction

posterior column (sensory tracts -ascend)

sensory tract that conveys nerve impulses for discriminative touch, light pressure, vibration, and conscious proprioception (awareness of the positions and movements of muscles, tendons, and joints) consists of 2 tracts: (1) gracile fasiculus (#9 in pic) (2) cuneate fasciculus (#10 in pic)

spinothalamic tracts (sensory tracts -ascend)

sensory tract that conveys nerve impulses for sensing pain, warmth, coolness, itching, tickling, deep pressure, and crude touch - located within the white matter from spine to brain (anterior and posterior)

muscle tone (reflex)

small degree of muscle contraction that makes normal posture, coordination, and movement possible

coccygeal plexus

small plexus formed by the roots (anterior rami) of the spinal nerves S4-S5 and the coccygeal nerves; gives rise to the anococcygeal nerves Function supply a small area of skin in coccygeal region

rootlets

smaller bundles of axons; each nerve root is composed of multiple what?

spinal meninges (singular is meninx)

surround spinal cord and are continuous with the cranial meninges which encircle brain. 3 protective, connective tissue coverings that encircle the spinal cord and brain: #3: deep- pia mater #4: middle - arachnoid mater #5: superficial - dura mater

intercostal or thoracic nerves

the anterior rami of spinal nerves T2-T12 do not enter into the formation of the plexuses and are known as these nerves instead Function directly connect to the structures they supply in the intercostal spaces (i.e. muscle and skin)

dermatome

the areas of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal (V) nerve is called this; nerve supply in adjacent of ___ overlaps somewhat clinical sig.: know which SC segments supply each of ____ makes it possible to locate damaged regions of the SC i.e. if the skin of that region is stimulated but the sensation is not perceived, the nerves supply that of ___ are probably damaged

reflex arc/circuit

the pathway followed by a nerve impulse that produces a reflex 5 functional components (see detail notes): 1. sensory receptor 2. sensory neuron 3. integration center 4. motor neuron 5. effector

ipsilateral reflex arc

the reflex arc when the sensory input and motor output are on the same side of the spinal cord - all monosynaptic reflexes have this arc

patellar reflex (knee jerk reflex)

the stretch reflex involves extension of the leg at the knee joint by contraction the quadriceps femoris muscle in response to tapping on knee ligament. Blocked - damage to sensory or motor nerves supplying the muscle or to integration centers in the L2, L3, or L4 segments Absent - chronic diabetes mellitus - neurosyphilis = nerve degeneration Exagerated - diseases or injury involving certain motor tracts descending from higher centers of the brain to the spinal cord.

autonomic or visceral reflex

type of reflex involved in response of smooth muscles, cardiac muscles, and glands - not usually consciously perceived

somatic reflex

type of reflex involving contraction of skeletal muscles

flexor or withdrawal reflex

type of reflex that is a polysynaptic, intersegmental, and ipsilateral reflex and results when i.e. you step on a tack and immediatel withdraw your leg 1.) Stepping on tac stimulates sensory receptors (dendrites of pain-sensitive neuron) 2.) Sensory neuron is excited 3.) Sensory neuron activates interneurons in several SC segments (SC integration center) 4.) Motor neuron is excited 5.) Flexor muscles contract and withdraw the leg - via Ach, released by motor neurons

tendon reflex

type of reflex that operates as a feedback mechanism to control muscles tension by causing muscle relaxation before force becomes so great that the tendons tear - ipsilateral reflex arc Compared to stretch reflex: - stretch reflex controls muscle length by causing muscle contraction - less sensitive then the stretch reflex, it can override the stretch reflex when tension is too great, like dropping a heavy weight. 1.) Increased tension stimulates sensory receptor (i.e. tendon organ) 2.) Sensory neuron excited 3.)Sensory neuron activates inhibitory interneuron that synapse with motor neuron (SC integration center) 4.) Motor neuron is inhibited via inhibitory NTs (hyperpolarizes) 5.) Muscle attached to the same tendon relaxes and relieves excess tension (effector)

spinal reflex

type of reflex when integration takes place in spinal cord gray matter ie: patellar reflex (knee jerk)

cranial reflex

type of reflex when integration takes place in the brain stem ie: tracking movements of your eyes reading this sentence.

intersegmental reflex arc

type of reflex where nerve impulses from one sensory neuron ascend and descend in the SC and activate interneurons in MULTIPLE segments of the SC (monosynaptic stretch reflex is only ONE segment of SC) - single sensory neuron can activate several motor neurons, thereby stimulating more than one effector

anterior median fissure (internal SC anatomy)

wide groove on the anterior (ventral) side

endoneurium (connective tissue coverings - spinal nerve)

wraps individual axons within a nerve whether myelinated or unmyelinated; innermost layer - mesh of collagen fibers, fribroblasts, and macs