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Sensory (ascending) Tracts

consist of axons that conduct nerve impulses from the spinal cord toward the brain

Motor Nuclei

provide output to effector tissues via motor neurons

Rami Communicantes

Also form the autonomic pathways to smooth muscle and glandular tissue and are components of the ANS

supraclavicular nerve (cervical plexus)

C3-C4 Skin over superior portion of chest and shoulder

Axillary nerve (brachial plexus)

C5-C6 Deltoid and teres minor muscles; skin over deltoid and superior posterior aspect of arm

Brachial Plexus cords

In the axillae, the divisions unite to form this. Lateral, medial, and posterior Are so named for their relationship to the axillary artery, a large artery that supplies blood to the upper limb.

Nuclei (of brain/spinal cord)

In the gray matter of the spinal cord and brain, clusters of neuronal cell bodies form functional groups

Conus Medullaris

Inferior to the lumbar enlargement, the spinal cord terminates as a tapering, conical structure which ends at the level of the intervertebral disc between the first and second lumbar vertebrae (L1-L2) in adults.

Genitofemoral nerve (lumbar plexus

L1-L2 Cremaster muscle; skin over middle anterior surface of thigh, scrotum in male, and labia majora in female

Obturator nerve (lumbar plexus)

L2-L4 Adductor muscles of hip joint; skin over medial aspect of thigh

femoral nerve (lumbar plexus)

L2-L4 Largest nerve arising from the lumbar plexus, distributed to the flexor muscles of hip joint and extensor muscles of knee joint, and to skin over anterior and medial aspect of thigh and medial side of leg and foot

Pudendal nerve (sacral plexus)

S2-S4 Muscles of perineum; skin of penis and scrotum in male and clitoris, labia majora, labia minora, and vagina in female

reflex arc

The pathway followed by nerve impulses that produce a reflex

Epidural Space

The spinal cord is also protected by a cushion of fat and connective tissue located in the space between the dura mater and the wall of the vertebral canal.

Vertebral Column as a protective structure

The spinal cord is located within the vertebral canal of the vertebral column. The vertebral foramina of all the vertebrae, stacked one on top of the other, form the vertebral canal. The surrounding vertebrae provide a sturdy shelter for the enclosed spinal cord. The vertebral ligaments provide additional protection.

Rootlets

The spinal nerves arise from the spinal cord as a series of small tree like branches The two types of rootlets are anterior (ventral) rootlets and posterior (dorsal) rootlets

Tracts

These bundles of axons along columns, which may extend long distances up or down the spinal cord

ansa cervicalis (cervical plexus)

This nerve divides into superior and inferior roots: Superior root C1 Infrahyoid and geniohyoid muscles of neck Inferior root C2-C3 Infrahyoid muscles of neck

Motor (descending) Tracts

Tracts consisting of axons that carry nerve impulses away from the brain down the spinal cord and continuous along the brain

reflex

a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus. Some are inborn, learned or required,

Nerves

bundles of axons and their associated neuroglial cells wrapped in layers of connective tissue. Like skeletal muscles, consist of long cells.

posterior columns

carry nerve impulses for several types of sensations. These include (1) proprioception, awareness of the positions and movements of muscles, tendons, and joints; (2) discriminative touch, the ability to feel exactly what part of the body is touched; (3) two-point discrimination, the ability to distinguish the touching of two different points on the skin, even though they are close together; (4) light pressure sensations; and (5) vibration sensations

Cranial Meninges

encircle the brain

Fasciculi

holds many nerve fibers together into bundles

cranial reflex

if integration occurs in the brain stem rather than the spinal cord

white matter tracts

in the spinal cord are highways for nerve impulse propagation. Along these tracts, sensory impulses from receptors flow toward the brain, and motor impulses flow from the brain toward skeletal muscles and other effector tissues.

Indirect pathways

include the rubrospinal tract, tectospinal tract, vestibulospinal tract, lateral reticulospinal tract, and medial reticulospinal tract. These tracts convey nerve impulses from the brain stem and other parts of the brain that govern automatic movements and help coordinate body movements with visual stimuli. Indirect pathways 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.

Sensory Nuclei

receive input from receptors via sensory neurons

Meningeal Branch

reenters the vertebral canal through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges and form the autonomic pathways to smooth muscle and glandular tissue

somatic reflex

reflexes which involve contraction of skeletal muscles

autonomic (visceral) reflexes

reflexes, which generally are not consciously perceived. These reflexes involve responses of smooth muscle, cardiac muscle, and glands.

Posterior (dorsal) Roots

series of posterior rootlets converges to form larger sets of branches

Posterior (dorsal) Ramus

serves the deep muscles and skin of the posterior surface of the trunk.

Anterior (ventral) Ramus

serves the muscles and structures of the upper and lower limbs and the muscles and skin of the lateral and anterior regions of the trunk.

Spinal Meninges

surround spinal cord

Dermatome

the area of the skin that provides sensory input to the CNS via one pair of spinal nerves Knowing which spinal cord segments supply each of this makes it possible to locate damaged regions of the spinal cord

Components and steps of a reflex arc (ex. patellar reflex: Knee jerk)

➊ Sensory receptor. The distal end of a sensory neuron (dendrite) or an associated sensory structure serves as a sensory receptor. Sensory receptors respond to a specific type of stimulus (a change in the internal or external envi- ronment) by generating one or more nerve impulses. In the patellar reflex, sensory receptors known as muscle spin- dles detect slight stretching of the quadriceps femoris mus- cle (anterior thigh) when the patellar (knee cap) ligament is tapped with a reflex hammer. ➋ Sensory neuron. The nerve impulses conduct from the sensory receptor along the axon of a sensory neuron to its axon terminals, which are located in the CNS gray matter. From here, relay neurons send nerve impulses to the area of the brain that allows conscious awareness that the reflex has occurred. ➌ Integrating center. One or more regions of gray matter in the CNS act as an integrating center. In the simplest type of reflex, such as the patellar reflex in our example, the integrating center is a single synapse between a senso- ry neuron and a motor neuron in the spinal cord. A reflex pathway in the CNS that involves one synapse is called a monosynaptic reflex arc (mon′-oˉ-sı ̄=NAP-tik; mono-=one). In other types of reflexes, the integrating center includes one or more interneurons and thus more than one synapse. These reflex pathways are referred to as polysynaptic reflex arcs (poly-=many). ➍ Motor neuron. Impulses triggered by the integrating center pass out of the spinal cord (or brain stem, in the case of a cranial reflex) along a motor neuron to the part of the body that will respond. In the patellar reflex, the axon of the motor neuron extends to the quadriceps femoris muscle. While the quadri- ceps femoris muscle is contracting, the antagonist hamstring muscles are relaxed. ➎ Effector. The part of the body that responds to the motor nerve impulse, such as a muscle or gland, is the effector. The patellar reflex is a somatic reflex because its effector is a skeletal muscle, the quadriceps femoris muscle, which contracts and thereby relieves the stretching that initiated the reflex. In sum, the patellar reflex causes extension of the knee by contraction of the quadriceps femoris muscle in response to tapping the patellar ligament. If the effector is smooth muscle, cardiac muscle, or a gland, the reflex is an autonomic (visceral) reflex

Cervical Enlargement

The superior enlargement, which extends from the fourth cervical vertebra (C4) to the first thoracic vertebra (T1). Nerves to and from the upper limbs arise from the cervical enlargement.

Filum Terminale

Arising from the conus medullaris is the extension of the pia mater that extends inferiorly and fuses with the arachnoid mater and dura mater to anchor the spinal cord to the coccyx.

Posterior (dorsal) rootlets

Projecting from the posterolateral sulcus of the spinal cord is another series of rootlets which contain the central processes of the sensory unipolar neurons. These neurons transmit action potentials from peripheral receptor organs to the central nervous system.

Brachial Plexus divisions

Posterior to the clavicles, the trunks divide into these called the anterior and posterior

Anterior White Commissure

Anterior to the gray commissure which connects the white matter of the right and left sides of the spinal cord.

Anterior Rootlets

From the anterolateral aspect of the cord, these emerge in two or three irregular rows. They contain the axons of multipolar motor neurons arising from cell bodies in the anterior regions of the spinal cord gray matter. These axons transmit action potentials to the muscles and glands of the body.

Leptomeninges

The arachnoid mater and pia mater are often referred to collectively

Horns

The gray matter on each side of the spinal cord is subdivided into regions

Spinal Cord

roughly oval in shape, being flattened slightly in the anterior-posterior axis. In adults, it extends from the medulla oblongata (the most inferior part of the brain) to the superior border of the second lumbar vertebra. In newborn infants, the spinal cord extends to the third or fourth lumbar vertebra. Elongation stops around age 4 or 5, but growth of the vertebral column continues, which explains why the spinal cord does not extend the entire length of the vertebral column.

Dura Mater

(DOO-ra MA-ter=tough mother). The most superficial of the three spinal meninges is a thick, outermost, strong layer composed of dense irregular connective tissue called the dura mater. Mater meaning mother was chosen because early anatomists erroneously believed that all of the tissues of the body arose from the dura mater and other meningeal layers. The dura mater 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. The dura mater is also continuous with the epineurium, the outer covering of spinal and cranial nerves.

Pia Mater

(PE-a MA-ter; pia=delicate). This is the innermost meninx, a thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain. It consists of thin squamous to cuboidal cells within interlacing bundles of collagen fibers and some fine elastic fibers. Within the pia mater are many blood vessels that supply oxygen and nutrients to the spinal cord. Triangular-shaped membranous extensions (denticulate ligaments) of the pia mater suspend the spinal cord in the middle of its dural sheath.

Arachnoid Mater

(a-RAK-noyd MA-ter; arachn-=spider; -oid=similar to). This layer, the middle of the meningeal membranes, is a thin, avascular covering comprised of cells and thin, loose arrays of collagen. It is called the arachnoid mater because of its spider's web arrangement of delicate collagen fibers and some elastic fibers. It is deep to the dura mater and is continuous through the foramen magnum with the arachnoid mater of the brain.

Coccygeal Nerves

1 pair (Co1) Resemble lower sacral spinal segments, but much smaller

Thoracic Nerves

12 pairs (T1-T12) Small diameter is due to relatively small amounts of gray matter; except for first thoracic segment, anterior and posterior gray horns are relatively small; a small lateral gray horn is present

Lumbar Nerves

5 pairs (L1-L5) Nearly circular; very large anterior and posterior gray horns; relatively less white matter than cervical segments

Sacral Nerves

5 pairs (S1-S5) Relatively small, but with relatively large amounts of gray matter; relatively small amounts of white matter; anterior and posterior gray horns are large and thick

Cervical Nerves

8 pairs (C1-C8); The first cervical pair emerges between the atlas (first cervical vertebra) and the occipital bone. Relatively large diameter, relatively large amounts of white matter, oval in shape; in upper cervical segments (C1-C4), posterior gray horn is large, but anterior gray horn is relatively small; in lower cervical segments (C5 and below), posterior gray horns are enlarged and anterior gray horns are well-developed

Perineurium

A thicker sheath of connective tissue holding fasciculi together. This consists of collagenous sheaths with up to 15 layers of fibroblasts distributed in a meshwork of collagen. This important sheath functions as a diffusion barrier that, along with the tight junctions in the capillaries (blood-nerve barrier), maintains the osmotic environment and fluid pressure within the endoneurium. It terminates by blending with the connective tissue capsules of various types of nerve endings and muscle junctions.

Lateral Gray Horns

Between the anterior and posterior gray horns which are present only in the thoracic, upper lumbar, and sacral segments of the spinal cord. The lateral horns contain the cell bodies of autonomic motor nuclei that regulate activity of smooth muscle, cardiac muscle, and glands

Subdural Space

Between the dura mater and the arachnoid mater is a thin space, which contains interstitial fluid.

Subarachnoid Space

Between these two meninges of arachnoid and pia mater (leptomeninges) is a space containing the shock-absorbing CSF

Suprascapular nerve (brachial plexus)

C5-C6 Supraspinatus and infraspinatus muscles

Musculocutaneous nerve (brachial plexus)

C5-C7 Coracobrachialis, biceps brachii, and brachialis muscles

Long thoracic nerve (brachial plexus)

C5-C7 Serratus anterior muscle

median nerve (brachial plexus)

C5-T1 Flexors of forearm, except flexor carpi ulnaris: the ulnar half of the flexor digitorum profundus, and some muscles of the hand (lateral palm); skin of lateral two-thirds of palm of hand and fingers

radial nerve (brachial plexus)

C5-T1 Triceps brachii, anconeus, and extensor muscles of forearm; skin of posterior arm and forearm, lateral two-thirds of dorsum of hand, and fingers over proximal and middle phalanges

ulnar nerve (brachial plexus)

C8-T1 Flexor carpi ulnaris, ulnar half of the flexor digitorum profundus, and most muscles of the hand; skin of medial side of hand, little finger, and medial half of ring finger

Epineurium

Completing the structure of the nerve is an outer connective tissue sheath. The bundles all the fasciculi together to form a single nerve. This is continuous with the dura mater and consists of fibroblasts and thick collagen strands that primarily parallel the long axis of the nerve. Extensions fill the spaces between fascicles. It makes up, on average, 50 percent of the cross-sectional area of a nerve. This important sheath gives the nerve the necessary tensile strength to resist the forces that can so easily damage the delicate nervous tissue. The strong collagenous sheaths protect the neurons from being torn apart by the strong tensile forces generated by muscular activities and movements of the body. This outer part of the nerve also contains the small blood vessels and lymphatic vessels for the nerve.

Ramus

Each large spinal nerve branch follows a specific course to different peripheral regions. The two largest branches, the anterior (ventral) ramus and posterior (dorsal) ramus, are somatic branches that run in the musculoskeletal wall of the body.

Endoneurium

Each nerve fiber sits in a loose connective tissue covering which consists of a mesh of collagen fibers, fibroblasts, and macrophages surrounded by endoneurial fluid (extracellular fluid) derived from the capillaries. This fluid nourishes the neuron and provides the necessary environment for its function of propagating action potentials.

Anterior (ventral) Roots

Each series of anterior rootlets converges to form larger sets of branches

Posterior (dorsal) Ganglion

Each series of posterior rootlets has a swelling which contain cell bodies of sensory neurons

Plexus

Forms networks on both the left and right sides of the body by joining with various numbers of axons from anterior rami of adjacent nerves. Such a network of axons is called this. Cervical, Brachial, Lumbar, Sacral, Coccygeal

Cauda Equina

However, because the spinal cord is shorter than the vertebral column, nerves that arise from the lum- bar, sacral, and coccygeal regions of the spinal cord do not leave the vertebral column at the same level they exit the cord. The roots of these lower spinal nerves angle inferiorly alongside the filum terminale in the vertebral canal like wisps of hair; meaning "horse's tail".

Superior gluteal nerve (sacral plexus)

L4-L5 and S1 Gluteus minimus, gluteus medius, and tensor fasciae latae muscles

Common Fibular

L4-S2 Divides into a superficial fibular and a deep fibular branch

Sciatic Nerve (sacral plexus)

L4-S3 Actually two nerves—tibial and common fibular—bound together by common sheath of connective tissue; it splits into its two divisions, usually at the knee (see below for distributions); as it descends through the thigh, sends branches to hamstring muscles and the adductor magnus

tibial nerve (sacral plexus)

L4-S3 Gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles; branches in foot are medial plantar nerve and lateral plantar nerve

Inferior gluteal nerve (sacral plexus)

L5-S2 Gluteus maximus muscle

Columns

The anterior and posterior gray horns divide the white matter on each side into three broad areas that in turn contains distinct bundles of axons having a common origin or destination and carrying similar information.: (1) anterior (ventral) white columns, (2) posterior (dorsal) white columns, and (3) lateral white columns.

Spinal nerve trunk

The anterior and posterior roots on each side of the spinal cord correspond to one developmental segment or level of the body. As the sensory posterior root and motor anterior root project laterally from the spinal cord, they converge to form a mixed nerve (mixed nerve contains both motor and sensory axons.). The spinal nerve trunk runs for a short distance before branching into two large branches and a variable series of smaller branches

Two grooves penetrate the white matter of the spinal cord and divide it into right and left sides

The anterior median fissure - wide groove on the anterior (ventral) side posterior median sulcus - narrow groove on the posterior (dorsal) side.

Brachial Plexus

The anterior rami of spinal nerves C5-C8 and T1 form the roots which extends inferiorly and laterally on either side of the last four cervical and first thoracic vertebrae. It passes above the first rib posterior to the clavicle and then enters the axilla. Provides almost the entire nerve supply of the shoulders and upper limbs

Lumbar Plexus

The anterior rami of spinal nerves L1-L4 form these roots. Unlike Brachial plexus, the intricate intermingling of fibers is minimal. On either side of the first 4 Lumbar vertebrae, this passes obliquely outward, between the superficial and deep heads of the psoas major muscle and anterior to the quadratus lumborum muscle. Between the heads of the psoas major, these roots split into anterior and posterior divisions, which then give rise to the peripheral branches of the plexus. This plexus supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs.

Sacral Plexus

The anterior rami of spinal nerves L4-L5 and S1-S4 form these roots; situated largely anterior to the sacrum. supplies the buttocks, perineum, and lower limbs.

Intercostal Nerves

The anterior rami of spinal nerves T2-T12 do not enter into the formation of plexuses and are known as these; Thoracic Nerves; Because these nerves connect directly to the structures they supply in the intercostal spaces and are mainly distributed to a single body segment, they are referred to as segmental nerves.

Protective structures of the spinal cord

The first layer of protection for the central nervous system is the hard bony skull and vertebral column. The skull encases the brain and the vertebral column surrounds the spinal cord, providing strong protective defenses against damaging blows or bumps. The second protective layer is the meninges, three membranes that lie between the bony encasement and the nervous tissue in both the brain and spinal cord. Finally, a space between two of the meningeal membranes contains cerebrospinal fluid, a buoyant liquid that suspends the central nervous tissue in a weightless environment while surrounding it with a shock-absorbing, hydraulic cushion.

Lumbar Enlargements

The inferior enlargement extends from the ninth to the twelfth thoracic vertebra (T9-T12). Nerves to and from the lower limbs arise from the lumbar enlargement.

Coccygeal Plexus

The roots (anterior rami) of spinal nerves S4-S5 and the coccygeal nerves form a small. From this plexus arises the anococcygeal nerves, which supply a small area of skin in the coccygeal region.

Brachial Plexus trunks

The roots of several spinal nerves unite to form these in the inferior part of the neck. These are the superior, middle, and inferior

spinal reflex

When integration takes place in the spinal cord gray matter

Nerve Fiber

Within the nerve are many axons of neurons with their surrounding neurilemma and myelin sheaths. The axon and its associated glial cells form this structure

phrenic nerve (cervical plexus)

arise from the cervical plexuses (C3-C5) and supply motor fibers to the diaphragm. Complete severing of the spinal cord above the origin of these nerves causes respiratory arrest. Breathing stops because the these nerves no longer send impulses to the diaphragm. The these nerves may also be damaged due to pressure from malignant tumors in the mediastinum, such as tracheal and esophageal tumors.

Posterior (Dorsal) Gray Horns

contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons.

Anterior (ventral) Gray Horns

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

lateral and anterior spinothalamic tracts

convey nerve impulses for sensing pain, warmth, coolness, itching, tickling, and deep pres- sure, and a crude, poorly localized sense of touch

denticulate ligaments

den-TIK-u ̄ -la ̄ t=small tooth), are thickenings of the pia mater. They project laterally and fuse with the arach- noid mater and inner surface of the dura mater between the anterior and posterior nerve roots of spinal nerves on either side. These extensions protect the spinal cord against sudden displacement that could result in shock.

direct pathway

descending pathway that includes the lateral corticospinal tract, the anterior corticospinal tract, and the corticobulbar tract. Each of these tracts conveys nerve impulses that originate in the cerebral cortex and are destined to cause precise, voluntary movements of skeletal muscles.

Brachial Plexus branches

form the principal nerves of the brachial plexus.

Cervical Plexus

formed by the roots (anterior rami) of the first four cervical nerves (C1-C4), with contributions from C5 supplies the skin and muscles of the head, neck, and superior part of the shoulders and chest. Branches also run parallel to two cranial nerves, the accessory (XI) nerve and hypoglossal (XII) nerve.

Gray Commissure

forms the crossbar of the H (or body of the butterfly)

Meninges

me-NIN-jeˉz; singular is meninx (ME-ninks)) are three protective, connective tissue coverings that encircle the spinal cord and brain. From superficial to deep they are the: (1) dura mater; (2) arachnoid mater; and (3) pia mater

Central Canal

n the center of the gray com- missure is a small space that it extends the entire length of the spinal cord and contains cerebrospinal fluid. At its superior end, the central canal is continuous with the fourth ventricle (a space that also contains cerebrospinal fluid) in the medulla oblongata of the brain.

Spinal Nerves

nerves associated with the spinal cord and, like all nerves of the peripheral nervous system (PNS), are parallel bundles of axons and their associated neuroglial cells wrapped in several layers of connective tissue. In addition, connect the CNS to sensory receptors, muscles, and glands in all parts of the body. There are 31 pairs. All other spinal nerves emerge from the vertebral column through the intervertebral foramina between adjoining vertebrae.

gray matter tracts

of the spinal cord receives and integrates incoming and outgoing information.

Cutaneous Fields

on the other hand, are regions of skin supplied by a specific nerve arising from a plexus