Chapter 13- Spinal Cord and Spinal nerves

Cervical enlargements

extends from the 4th cervical vertebra to the 1st thoracic vertebra -nerves to upper limbs arise from this

spinal reflex

when integration takes place in the spinal cord grey matter- it's a spinal reflex (the knee jerk patellar reflex- doctor taps your knee). * Does not require input from your brain

muscle tone

which is the small degree of contraction present while the muscle is at rest

Epineurium

the outermost covering over the entire nerve and consists of fibroblasts and thick collagen fibers

Meningitis

inflammation of the meninges due to an infection. Usually caused by a bacterium or virus, symptoms include fever, headache, and stiff neck, vomiting confusion, lethargy and drowsiness. Bacterial meningitis is much more serious and is treated with antibiotics. Viral meningitis has no specific treatment. Bacterial meningitis may be fatal if not treated promptly, viral meningitis usually resolves on its own in 1-2 weeks. A vaccine is available to help protect against some types of bacterial meningitis

posterior median sulcus

is a narrow furrow on the posterior (dorsal side) little cuts are sulcus

anterior median fissure

is a wide groove on the anterior (ventral side) grand canyon is a fissure

muscle spindle

slight stretching of a muscle stimulates sensory receptors in the muscle. The spindles moniter changes in the length of the muscle

Rootlets

smaller bundles of axons

subarachnoid space

space between arachnoid mater and pia mater -containing shock absorbing cerebrospinal fluid

anterior (ventral/front) gray horn

contains somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles * location of somatic motor neuron cell bodies

Reflexes and why are they important

* Clinical connection- reflexes are often used to diagnosing disorders of the nervous system and locating injured tissue. Many somatic reflexes can be tested by simply tapping or stroking the body.

subdural space

-between dura mater and the arachnoid mater -interstitial fluid filled

anterior (ventral) root

contains axon of motor neurons * joint together to form a spinal nerve and pass through intervertebral foramen

posterior (dorsal) root

contains axons of sensory neuron/back

Sensory (ascending) tract

consists of axons that conduct nerve impulses toward the brain

Tracts

-bundles of axons in the CNS -carry nerve impulses up or down the spinal cord. --- -originating in the white column (nerves are bundles of Axons in the PNS)

reciprocal innervation

in which the component of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonist. This prevents conflict between opposing muscles and is vital in coordination body movements.

indirect pathways

include rubrospinal, tectospinal, vestinbulospinal and lateral reticulospinal and medial reticulospinal tracts. These tracts convey nerve impulses from the brain stem to cause automatic movements and help coordinate body movements with visual stimuli. They also maintain skeletal muscle tone, sustain contraction of postural muscles and play a major role in equilibrium by regulating muscle tone in response to movements of the head. Brain stem to nerve impluse to automatic movemnts coordinate body movement with visual stimuli/ equilibrium

shingles

is an acute infection of peripheral nervous system caused by herpes zoster (virus also causes chicken pox). After a person recovers from chickenpox, the virus retreats to a posterior root ganglion. If the virus is reactivated, the immune system usually prevents it from spreading. From time to time, however the reactivated virus overcomes a weekend immune system leaves the ganglion and travels down sensory neurons of the skin by fast axonal transport. The result is pain, discoloration of the skin, characteristic line of skin blisters. The line of blisters makes the distribution (dermatome) of the particular cutaneous sensory nerve belonging to the infected posterior root ganglion.

Poliomyelitis

is caused by a virus called poliovirus. The onset of the disease is marked by fever, severe headache, a stiff neck and back, deep muscle pain and weakness and loss of certain somatic reflexes. It in its most serious form, the virus produces paralysis by destroying cell bodies of motor neurons, specifically those in the anterior horns of the spinal cord and in the nuclei of the cranial nerves.

cervical plexus

is formed by the roots of the 1st 4 cerivcal nerves with contributions from c5. There is one on each side of the neck along the 1st 4 vertebrae. Supplies the skin and muscles of the head, neck and superior part of the shoulders and chest. The phrenic nerves arise from the cervical plexuses and supply motor fibers to the diaphragm.

Tendon organ or Golgi tendon organ

sensory receptors for this reflex which lie within a tendon near its junction with a muscle. -inhibitory/ polysynpatic reflex -tendon organs detect and respond to changes in muscle tension that are caused by passive stretch or muscle contraction. -as tension on the tendon organ increases, the frequency of inhibitory impulses increases, inhibition of the motor neurons to the muscle developing excess tension (effectors) causes relaxation of the muscle. -this way the tendon reflex protects the tendon and muscle from damage due to excessive tension.

patellar reflex (knee jerk reflex)

stretch reflex involves extension of the leg at the knee joint by contraction of the quadriceps femoris muscle in response to tapping on the patellar ligament. This reflex is blocked by damage to the sensory or motor nerves supplying the muscle or to the integrating centers in the 2nd, 3rd, or 4th lumbar segments of the spinal cord. Often absent in people with chronic diabetes mellitus or neurosyphilis - both causes nerve degeneration. It is exaggerated in disease or injury involving certain motor tracts descending from the higher centers of the brain to the spinal cord.

intercostal or thoracic nerves

the anterior rami of spinal nerves T2-T12 do not enter into the formation of plexuses and are known as intercoastal or thoracic nerves. These nerves directly connect to the structures they supply in the intercostal spaces.

arachnoid mater

-middle layer, thin avascular covering comprised of cells -looks spider web like in the collagen /elastic fiber arrangement

Stimulus

a change in the internal or external environment

filum terminale

thin thread of fibrous tissue at end of conus medullaris -attaches to coccygeal ligament

posterior or dorsal root ganglion

swelling of posterior/dorsal root containing the cell bodies of sensory neurons.

lateral grey horn

between poster and anterior grey horns which are present only in thoracic and upper lumbar segments of spinal cord. Contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscles, smooth muscle and glands * where autonomic motor neurons originate

reflex

the second way the spinal cord promotes homeostasis by serving as an integrating center for some reflexes. A reflex is a fast, involuntary unplanned sequence of actions that occurs in response to a particular stimulus, some are inborn- (pulling hand away from hot surface before you feel it is hot) Others are learned or acquired, (ones while driving, slamming on breaks while driving to avoid accident)

Babinski reflex

this reflex results from gentle stroking of the lateral outer margin of the sole. The great toe extends with or without a lateral fanning of the other toes. This phenomenon normally occurs in children under 1.5 years and is due to incomplete myelination of fibers in the corticospinal tract. -A positive babinski sign after age 1.5 is abnormal and indicates an interruption of the corticospinal tract as the result of a lesion of the upper neuron tract. -The normal response after 1.5 years is the plantar flexion reflex or negative babinski -curling under of all the toes.

Motor (descending) tract

tract consists of axons that carry nerve impulses from the brain

Roots

2 bundles of axons called roots connect each spinal nerve to a segment of the cord by smaller bundles of axons called rootlets

Perineurium

the middle layer wrapped around each fasicle, thicker layer of CT.

posterior or dorsal root

-contain only sensory axons from sensory receptors in -skin, muscles and interal organs

Plexus

a network of axons is called plexus

cauda equina

-nerve roots extending below conus medullaris

Lumbar enlargements

-from 9th to 12th thoracic vertebra. -nerves to and from lower limbs arise from this

Pia Mater

-(delicate) inner thin transparent CT layer that adheres to the surface of the spinal cord and the brain -Consists of thin squamous to cuboidal cells with interlacing bundles of collagen fibers and some fine elastic fibers. -piamater has many blood vessels that supply oxygen and nutrients to the spinal cord.

anterior or ventral root

contain axons of motor neurons -conduct nerve impulses from the CNS to effectors (muscles and glands)

posterior (dorsal/posterior) gray horn

contain cell bodies and axons of interneuron's as well as axons of incoming sensory neurons. * sensory nerve fibers synapse onto interneuron's

Anterior (ventral) white column, Posterior (dorsal) white column, Lateral white column

contain distinct bundles of axons having a common origin or destination and carrying similar information

polysynaptic reflex arc

involves more than 2 types of neurons and more than 1 CNS synapse.

epidural space

-spinal cord protected by a cushion of fat and CT -located in epidural space (space between the dura-mater and wall of the vertebral canal)

Fascicle

group of axons with their endoneurium are held together in bundles

1. stretch reflex

-causes contraction of a skeletal muscle (the effector) in response to stretching of a muscle. -monosynaptic reflex arc. -it occurs by activation of a single motor neuron. -Stretch reflexes can be elicited by tapping on tendons attached to muscles at the elbow, wrist, knee and ankle joints. (knee jerk- knee tap at docotrs office)

cranial reflex

if integration occurs in the brain stem rather than the spinal cord- it's a cranial reflex ( tracking movements of your eyes as you read this sentence)

central canal

-in center of gray commissure -small space extends entire length of the spinal cord -and is filled with cerebrospinal fluid

nuclei

-in the gray matter of spinal cord/brain -clusters of neuronal cell bodies from functional groups called nuclei Sensory nuclei -receive input from receptors via sensory neurons and motor nuclei provide output to effectors tissues via motor neurons.

Dura Mater

-outer layer of 3 meninges -is a thick strong layer of dense irregular CT

spinal nerve

-paths of communication between the spinal cord and specific regions of the body. -31 pairs of spinal nerves emerge from intervertebral foramina.

3. flexor or withdrawal reflex

-polysynaptic reflex arc results when for instances, you step on a tack. -in response to such a painful stimulus, you immediately withdraw your leg. *The flexor reflex like stretch is ipsilateral- the incoming and outgoing impulses propagate into and out of the same side of the spinal cord. the flexor reflect also illustrates another feature of the polysnpatic reflex arcs. -Moving your entire lower or upper limb away from a painful stimulus involves contraction of more than 1 muscle group, hence several motor neurons must simultaneously convey impulses to several limb muscles.

Mixed nerve

-posterior root contains sensory axons -anterior root contains motor axons, -a spinal nerve is classified as a mixed nerve. -the posterior root contains a posterior root ganglion in which cell bodies of sensory neurons are located.

ramus (plural is rami)

-the posterior (dorsal) ramus (RA ̄-mus; singular form) serves the deep muscles and skin of the posterior surface of the trunk. -the anterior (ventral) ramus serves the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk

4. Motor neuron

impulses triggered by the integrating center propagate out of the CNS along a motor neuron to the part of the body that will respond

3. integrating centre

1 or more regions of grey matter within the CNS act as an integrating center. In the simplest type of reflex, the Integrating center is a single synapse between a sensory neuron and a motor neuron.

spinal meninx (plural is meninges)

3 membranes that like between the bony encasement and the nervous tissue in both the brain and spinal cord

reflex arc

The pathway followed by nerve impulses that produce a reflex- 5 components Sensory Receptor Sensory Neuron Integrating Center Motor Neuron Sensory Effector

Dermatome

The surface of the skin is divided in to specific areas called dermatomes. Area of skin supplied by a specific nerve. They are clinically important and necessary for assessing & diagnosing the level of spinal cord injury Ex: Herpes zoster viral infection, that can migrates along the spinal nerve to affect the area of the skin served by that nerve.

Inside spinal nerve

Visceral sensory neuron (internal organs) and somatic sensory neuron (skin and skeletal muscles) + somatic motor neuron (sending voluntary commands to skeletal muscle) and autonomic motor neuron (sending automatic commands to internal organs)

monosynaptic reflex arc

a reflex pathway having only 1 synapse in the CNS. More often the integrating center consists of 1 or more interneuron's, which may relay impulses to other interneuron's as well as to a motor neuron

4. crossed extensor reflex

along with the reflex arch, as you step on a tack, and withdraw the limb, the pain impulses from stepping on the tack also initiate a crossed extensor reflex to help you maintain your balance

spinal nerves

are associated with the spinal cord (in PNS) are barallel bundles of axons and their associated neuroglial cells wrapped in several layers of CT. Spinal nerves connect the CNS to sensory receptors, muscles and glands in all parts of the body.

direct pathways

direct pathways- include the lateral corticospinal, anterior corticospinal and corticobulbar tracts that convey nerve impluses that originate in the cerebral cortex and are destined to cause voluntary movements of skeletal muscles Cerebral cortex to nerve impluse to voluntary skeletal muscles

grey commissure

forms crossbar of the H (grey matter) -consists of dendrites and cell bodies of neurons, unmyelinated axons and neuroglia, * a lot of cell bodies of neurons (millions)

spinal cord physiology 2 functions

has 2 principal functions in maintaining homeostasis: 1. nerve impulse propagation- White mater tracts in the spinal cord are highways for nerve impulse propagation. Sensory input travels along these tracts towards brain, and motor output travels from the brain along these tracts towards skeletal muscles and other effector tissues. 2. integration of information- the grey matter of the spinal cord receives and integrates incoming and outgoing information.

spinothalamic tracts

myelinated nerve fibers, sensory pathway and it is sending info from spinal cord level to area of brain called the thalamus (pain temp itch and crude touch) * sensory information sent to the thalamus before the cerebral cortex

sensory and motor tracts

often the name of the tract indicates its position in the white matter and where it begins and ends. Nerve impluses from sensory receptors propagate up the spinal cord to the brain along 2 main routes on each side. The spinothalamic tract conveys nerve impluses for sensing pain, warmth, coolness, itching, tickling, deep pressure and crude touch.

2. Tendon reflex

operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn. (ipsilateral) (Example: making your drop a very heavy weight)

Contralateral reflex arc

sensory impulses enter 1 side of the spinal cord and motor impulses exit on the opposite side. This a crossed extensor reflex synchronizes the extension of the contralateral limb with the withdrawal (flexion) of the stimulated limb. Reciprocal innervation also occurs in both the flexor reflex and the crossed extensor reflex- because of reciprocal innervation, 1 set of muscles contracts while the other relaxes.

ipsilateral reflex arc

sensory nerve impluses enter the spinal cord on the same side from which motor nerve impluses leave it- all monosynaptic reflexes are ipsilateral.

1. sensory receptor

the distal end of a sensory neuron or an associated sensory structure serves as a sensory receptor. It responds to specific stimulus (internal/external enviro change) by producing a graded potential called a generator (or receptor) potential. It reaches threshold level of depolarization it will trigger one or more nerve impulses in the sensory neuron.

Endoneurium

the inner most layer consisting of a mesh collagen fibers, fibroblasts, and macrophages surrounding individual axon with a nerve, myelinated or unmyelinated

2. sensory neuron

the nerve impulses propagate from the sensory receptor along the axon of the sensory neuron to the axon terminals which are located in the gray matter of the spinal cord or brain stem. From here, relay neurons send nerve impulses to the area of the brain that allows conscious awareness that the reflex has occurred

5. Effector

the part of the body that responds to the motor nerve impulse such as a muscle or gland is the effector. Its action is called a reflex. If the effector is skeletal muscle, the reflex is a somatic reflex, if the effector is smooth muscle, cardiac muscle or a gland, the reflex is an autonomic (visceral) reflex.

lumbar plexus

the roots anterior rami of spinal nerves L1-L4 from the lumbar plexus and there is minimal intermingling of fibers in the lumbar plexus. It then gives rise to its peripheral nerves, it supplies the anterolateral abdominal wall, external genital and part of the lower limbs|

brachial plexus

the roots of spinal nerves from the brachial plexus. It provides almost the entire nerve supply of the shoulder and upper limbs. Axillary, musculocutaneous, radial median and ulnar nerves arise from the brachial plexus

sacral plexus

the roots of the spinal nerves L4-L5 and S1-S4 form the sacral plexus. This plexus is situated largely anterior to the sacrum. The sacral plexus supplies the buttocks, perineum, and lower limbs, The largest nerve in the body, the sciatic nerve arises from the sacral plexus. The roots of spinal nerves S4-S5 and the coccygeal nerves form a small coccygeal plexus which supplies a small area of skin in the coccygeal region

autonomic reflex or visceral reflex

which generally are not consciously perceived. The involve responses of smooth muscle, cardiac muscle and glands. (body functions such as heart rate, digestion, urination, and defecation are controlled by the autonomic nervous system through autonomic reflexes)

somatic reflex

which involve contraction of skeletal muscles