Spinal Cord and Spinal Cord

Dermatomes

=Segment of skin supplied by single spinal nerve =Some overlap in innervated regions =Can help localize damage to one or more spinal nerves =Involved in referred visceral pain

Somatic

effector a skeletal muscle

lumbar enlargement

extends through lumbar and sacral parts of the spinal cord and innervates the lower limbs

gray commissure

horizontal bar of gray matter that surrounds central canal; connects left and right sides of the gray matter

median nerve

innervates flexor muscles

musculotaneous nerve

innervates flexors; come off lateral cord

integration center

interprets input and elicits response

Reflexes

involuntary responses A stimulus is required to initiate Response is rapid; involves a chain of only a few neurons The response is preprogrammed; always the same The response is involuntary; no intent or awareness of the reflex before it happens is a survival mechanism

femoral nerve

posterior division of lumbar plexus

monosynaptic

sensory neurons synapse directly with motor

brachial plexus

spinal nerves C5-T1; supply upper limbs and pectoral girdle

lumbar plexus

spinal nerves L1-L4; subdivided into anterior (obturator) and posterior division (femoral)

sacral plexus

spinal nerves L4-S4;

spinal cord

the cylindrical bundle of nerve fibers and associated tissue that is enclosed in the spine and connects nearly all parts of the body to the brain, with which it forms the central nervous system

polysynaptic

the interneurons in the reflex arc

reflex arcs

the nerve pathway involved in a reflex action including at its simplest a sensory nerve and a motor nerve with a synapse between (PNS > CNS > PNS)

axillary nerve

diverges from posterior cord

Golgi tendon reflex

-Prevents muscles from contracting excessively =detect excessive tension =They are proprioceptors with sensory ending at muscle tendon junction =Their sensory axons excite interneurons in the spinal cord =Some excited interneurons inhibit motor neurons of same muscle =Muscle relaxes (polysynaptic reflex), preventing it from damage =Some excited interneurons excite motor neurons of antagonist muscle (reciprocal activation) =Antagonist muscle contracts (polysynaptic reflex)

common fibular nerve

L4-S2; posterior division of sciatic nerve

tibial nerve

L4-S3; anterior division of sciatic nerve

Nerve plexus

Network of interweaving anterior rami of spinal nerves Four main plexuses occur bilaterally: cervical, brachial, lumbar, and sacral plexuses Most thoracic spinal nerves and nerves S5-Co1 do not form plexuses Individual rami branch repeatedly Damage to one nerve or spinal segment does not deprive a muscle or skin region of all innervation

Crossed-extensor reflex

Occurs in conjunction with withdrawal reflex Some interneurons excited by the nociceptor sensory neuron cross midline and excite extensor motor neurons on other side E.g. as left leg is withdrawn, right leg's quadriceps is excited Allows the opposite side limb to support body weight while the hurt limb withdraws

Withdrawal reflex

Pulls a body part away from a painful stimulus Stimulus excites nociceptor sensory neuron that transmits signal to spinal cord and excites interneurons Interneurons excite motor neurons of flexors so flexor muscles (e.g., hamstrings) contract and limb is withdrawn Simultaneously, other interneurons reciprocally inhibit motor neurons of extensors so that extensor muscles (e.g., quadriceps) relax and withdrawal happens quickly

shingles

Reactivation of chickenpox infection Virus remaining latent in posterior root ganglia Reactivated, travels through sensory axons to dermatome Rash and blisters along the dermatome Burning and tingling pain Antiviral medication to reduce severity Vaccine to prevent or reduce disease severity

Stretch reflex

Reflexive contraction of a muscle after it is stretched is detected by a muscle spindle receptor Spindle contains intrafusal muscle fibers innervated by gamma motor neurons and wrapped by sensory neurons Fibers not within spindle are extrafusal muscle fibers innervated by large alpha motor neurons When stretched, spindle's sensory axon fires impulses that are conducted to the spinal cord In spinal cord, the sensory axon excites alpha motor neurons of the same muscle, causing contraction (monosynaptic) Simultaneously, the sensory axon excites interneurons that inhibit motor neurons of antagonist muscle (polysynaptic reciprocal inhibition) classified as: spinal, somatic, ipsilateral, innate

obturator nerve

anterior division of lumbar plexus

Hyperactive reflex

abnormally strong response May indicate damage to brain or spinal cord, especially if accompanied by clonus (rhythmic oscillating movements with reflex testing)

dermatomes

area of skin innervated by all the sensory neurons of a single spinal nerve

sacral spinal nerves

bowel, bladder, sexual function, and feet (PNS)

lateral cord

brachial plexus division, C5-C7 (#5)

posterior cord

brachial plexus division, C5-T1 (#17)

medial cord

brachial plexus division, C8-T1 (#18)

thoracic spinal nerves

chest and abdominal muscles (PNS)

motor neuron

conducts efferent impulse to effector

anterior (ventral) root

contains motor neurons

posterior (dorsal) root

contains sensory axons only

posterior root ganglion

contains sensory neuron (cell) bodies

paraplegia

damage btw T1 and L2; lower limbs

quadriplegia

damage in cervical region; all limbs

motor pathways

descending) pathways Control effectors such as skeletal muscles Start in brain and include at least two neurons

Hypoactive reflex

diminished or absent May indicate damage to spinal cord, or muscle disease, or damage to neuromuscular junction

cauda equina

group of axons that project ineriorly from the spinal cord

sciatic nerve

largest and longest nerve in sacral plexus

anterior (ventral) horns

left and right anterior masses of gray matter

posterior (dorsal) horns

left and right posterior masses of gray matter

lumbar spinal nerves

leg muscles (PNS)

cervical plexus

located deep on each side of the neck, immediately lateral to cervical vertebrae (C1-C4). innervates anterior neck muscles, head, and shoulders

cervical enlargement

located in the inferior cervical part of the spinal cord, contains the neurons that innervate the upper limb

paralysis

loss of motor function

conus medullaris

marks the official end of the spinal cord proper

effector

muscle or gland that responds

cervical spinal nerves

nerves to the head, neck, diaphragm, and arms (PNS)

lateral horn

occurs in T1-L2, contain cell bodies of autonomic motor neurons

phrenic nerve

originated from C4 and some contributing axons of C3 and C5

radial nerve

posterior to musculotaneous

shingles

reactivation of chickenpox; virus invades dorsal root ganglia of spinal cord

contralateral

receptor and effector on the opposite sides

Ipsilateral

receptor and effector on the same side of the body

central cannal

runs the entire length of the spinal cord and contains cerebrospinal fluid (CSF)

sensory neuron

transmit afferent impulse to CNS