8.24.11+-+Peripheral+Nervous+System


 * Peripheral Nervous System**


 * 1) Define the Following terms** [REARRANGE TERMS IN CONCEPTUAL ORDER RATHER THEN ALPHABETICAL THEN ADD PICTURES]
 * **afferent nerve fiber** - nerve fiber which carries signals towards the central nervous system. sensory nerve fiber. Two kinds, visceral afferent nerve fiber (non-localized sensations such as hunger or stomach cramps). These nerves arrive in the spinal cord via dorsal root of the spine. Recall: //**a**fferent connection **a**rrives// and an //**e**fferent connection **e**xits//
 * **arachnoid mater -** The brain and spinal cord are surrounded by (3) layers of protective meninges. Arachnoid mater is interposed between the more superficial dura mater and the deeper pia mater. The arachnoid mater is separated from the pia mater by the subarachnoid space, which is where the Cerebralspinal fluid (CSF) is located.
 * **axon -** A long slender projection of a nerve cell which carries the electrical action potential away from the cell body (soma). Axons differ from dendrites in both shape (axons are much longer then dendrites), function (axons typically transmit signals while dendrites receive signals) and number (nerve cells can have many dendrites but only one axon).
 * **cardiac muscle cell** - Also called a myocardiocyte, one of three types of muscle cells. cardiac muscle contracts involuntarily. a major difference from other muscle cells is that myocardiocytes have only one or two nuclei, as opposed to skeletal muscle which is multinucleated
 * **cauda equina** - Because the vertebrae continue to grow after the spinal cord is fully developed, the spinal cord ends at around L2/L3. The nerve fibers themselves continue to descend inferiorly till they exit at their proper levels through the intervertebral foramina. This bundle of nerves is known as the cauda equina. The cauda equina exists in the space called the lumbar cistern, which is contained by the dural sac. When a lumbar puncture is performed to extract CSF, it is done here
 * **cervical enlargement** - An enlargement of the spinal cord (in terms of diameter) from C5-T1. This enlargement is caused by the many nerves that innervates the upper limbs.
 * **conus medullaris** - The terminal end of the spinal cord, around L2/L3. The nerve fibers extend inferiorly from this point in the cauda equina
 * **dendrite** - Branched protrusions from a nerve cell which act to conduct the electrical impulses into the soma. Electrical impulses are received across a synapse from pre-synaptic axon.
 * **denticulate ligament** - protrusions extending from the deeper pia mater to the more superficial arachnoid mater and dura mater**.** comes in pairs, helps to stabalize the spinal cord within the vertebral column.
 * **dorsal (spinal) root -** There are (4) catagories of spinal nerve fiber: somatic afferent, somatic efferent, visceral afferent and visceral efferent. The dorsal (spinal) root is a grouping of visceral and somatic afferent nerve fibers. The nerves within the dorsal root are pseudo unipolar; their cell bodies are within the dorsal root ganglion; they conduct their signals from from sensory receptors through the axon to a synapse with cns neurons in the dorsal horn of the gray matter of the spinal cord.
 * **dorsal root ganglion -** Distal to the dorsal root is a bundle of nerve cell bodes called the dorsal root ganglion. These cell bodies are all associated with afferent nerve fibers.
 * **dura mater -** The outermost layer of the meninges**.** Latin for the hard mother
 * **dural sac** - The area enclosed by the dura mater. The dural sac ends at the S2 level.
 * **efferent nerve fiber** - Nerve fiber which carries nerve pulses away from the central nervous system to effectors such as glands (visceral efferent) or muscles (somatic efferent). These nerves arise in the ventral root of the spine. Recall: //**a**fferent connection **a**rrives// and an //**e**fferent connection **e**xits//
 * **epidural space** - The outermost portion of the spinal canal. It is between the vertebral canal and the dura mater.
 * **filum terminale** - Fibrous tissue extending downward from the conus medullaris. Helps to stabilize the spinal cord
 * **ganglion** - a mass of nerve cell bodies outside of the CNS. Note: a mass of neural cell bodies in the CNS is called a "nucleus" (COA7th p47).
 * **intervertebral foramina** - openings formed between two adjacent vertebrae which allow for the passage of the spinal nerve root
 * **lumbar cistern** - the subarachnoid space inferior to the conus medullaris
 * **lumbar enlargement** - The attachment point for the nerves which innervate the lower limbs. Immediately superior to the conus medullaris
 * **meninges** - system of membranes enveloping the central nervous system. In order of superficial to deep, the three meninges are the dura mater, the arachnoid mater and the pia mater.
 * **multipolar neuronal morhoplogy -** One of three major morphologies of neurons in the peripheral nervous system. Has a single axon and many dendrites extending from the cell body. All motor neurons that control skeletal muscles and those comprising the autonomic nervous system are multipolar (COA7th pg46). The most common neural cell morphology in the CNS (~100%) is multipolar, whereas 50% of neurons in the PNS are multipolar (lecture audio).
 * **nerve cell body (somata) -** The cell body contains all of the normal intracellular organelles (nucleus, mitochondria, golgi, etc.). Its placement is important for determining the cell type (morphology). For more information on cell types, see #2 below.
 * **nerve fiber -** threadlike extension from a neuron which contains both an axon and possibly a myelin sheath. Note that "a nerve " is an anatomical description for a collection of cells. The "fiber" includes the axon, the myelin sheath (if myelinated), and the endoneurium. These components have different cell lineages and are not all true nerve cells (neurons) even though they compose the nerve fiber. A nerve fiber consists of a single axon, its neurolemma, and surrounding endoneurial connective tissue (COA7th pg47), thus it represents only a single neural cell.
 * **nerve plexus** - Network of nerve fibers**.**
 * **neuron** - an electrically excitable cell which can transmit electrical and chemical signals.
 * **pia mater** - The deepest level of meninges. Impermeable to fluid, which allows it to contain CSF. Anchored to arachnoid and dura mater via denticulate ligaments.
 * **post-synaptic cell** - A cell on the receiving end of an action potential that can include neurons as well as other effectors such as motor cells.
 * **pre-synaptic terminal** - A neuron that forms a synapse to another cell (neuronal or non-neuronal). When the electrical signal of an action potential travel reaches the axon terminal, the signal is transduced into a chemical signal (neurotransmitter) that leaves the pre-synaptic terminal, crosses the synapse, and binds to receptors on the post-synaptic cell.
 * **pseudounipolar neuronal morphology** - A neuron that makes up afferent nerve fibers. Pseudounipolar neurons have no dendrites and one branched axon. The cell body is located in the doral root ganglion. The central axon branch joins the spinal cord in the dorsal horn of the spinal cord. The peripheral axon branch travels through the distal dorsal root into the periphery.
 * **smooth muscle cell -** involuntary non-striated muscle tissue. Innervated by visceral afferent and visceral efferent nerves.
 * **spinal cord -** A long bundle of nervous tissue and support cells extending inferiorly from the brain to the conus medullaris.
 * **spinal nerve** - A mixed spinal nerve which carries all four types of nerve fibers between the spinal cord and the body. A spinal nerve is formed by the combination of the dorsal root and the ventral root. There are 31 pairs which roughly correspond to the vertebrae: 8 cervical pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs and 1 coccygeal pair. Each pair innervates a dermatome and a myotome.
 * **striated (skeletal) muscle cell** - Multinucleated muscle cells that are innervated by efferent somatic nerves. Typically under voluntary control, although also susceptible to involuntary control (e.g., subpatellar tendon stretch reflex).
 * **subarachnoid space** - The space between the arachnoid mater and the pia mater. Contains CSF
 * **subdural space** - An artificial space between the dura mater and the arachnoid mater**.** Called artificial because typically does not exist outside of a cadaver or severe trauma.
 * **synapse** - a junction which permits a nerve to pass a signal to another cell via neurotransmitters.
 * **ventral (spinal) root** - Efferent root of the spinal nerve.
 * **vertebral canal** - The space in the vertebrae through which the spinal cord passes.


 * 2) Describe the 3 general types of neuronal morphologies. Name those neuronal types that have axons and those that have dendrite. Describe the typical ultrastructural features of a synapse.**

There are three main morphological types of neurons in the peripheral nervous system: multipolar, pseudounipolar, and bipolar neurons.
 * Multipolar neurons compose efferent nerve fibers, have dendrites and a single axon (the axon plus the many dendrites are the "mutiple poles" of the multipolar neuron.
 * Pseudounipolar compose afferent nerve fibers, lack dendrites and have a single branched axon. Thus it appears to be a "unipolar" neuron because of the single process that exits the soma, but since the axon is bifurcated it is referred to as a "**//pseudo//**unipolar neuron."
 * Bipolar neurons are relatively rare and carry signals for specialized sensory nerves (such as sight, smell, taste, hearing etc), have two axons and dendrites. They are found in the sensory (afferent) neurons of the 8th cranial nerve ganglia. [Figure 1]

Peripheral nerves are composed of axons (afferent and efferents), schwann cells (myelin), blood vessels, connective tissue. There are four categories of nerve fibers in spinal nerves, specifically: Somatic nerves innervates tissues such as skin, muscle, bone, joints and dura mater. Visceral nerves innervates smooth muscle, cardiac muscle, glands, and adult derivatives of the embryonic cut and embryonic cardiovascular system. The two can be distinguished by the fact that somatic nerves affect mostly voluntarily controlled tissue whereas visceral nerves innervate involuntarily controlled tissue.
 * 3) Describe the contents of a peripheral nerve. Name the four catagories of nerve fibers found in spinal nerves. Compare and contrast the properties of the two types of afferent fibers (ie somatic and visceral) and the properties of the two types of efferent fibers (ie somatic and visceral) found in spinal nerves. In these comparisons, list the locations of their respective neuronal cell bodies, the sorts of information carried by the fibers, and the pathways that these fibers follow to reach their targets. Describe the types of cells that receive synaptic input from efferent fibers.**
 * 1) Somatic afferent
 * 2) Somatic efferent
 * 3) Visceral afferent
 * 4) Visceral efferent
 * 1) Afferent:
 * 2) Both somatic and visceral have pseudounipolar cell body located in spinal ganglion (DRG) and central axon innervates neurons in the CNS (look identical)
 * 3) Somatic: peripheral axon innervates one of the "somatic tissues," conveying touch, vibration, temperature, proprioception, somatic pain (burning like quality, highly localized, due to trauma)
 * 4) Visceral: pheripheral axon innervates viscera (eg smooth or cardiac muscle, lungs, etc) and conveys visceral pain (unpleasant, poorly localized, due to ischemia or distention) and other visceral sensations
 * 5) Efferent:
 * 6) Somatic moter neurons (lower motor neurons) is only 1 neuron, large, multipolar cell body, cell body located in CNS, axon directly innervates skeletal muscle, causes skeletal muscle to fire causing volitional movements. Neuron cell bodies are located in the ventral horn gray matter.
 * 7) Visceral motor neurons (autonomic neurons) have 2 neurons in a chain. The cell body is small, multipolar, and also located in the CNS. Another cell body that is also small and multipolar is located in the peripheral ganglion. Axon of more distal neuron innervates smooth muscle, cardiac muscle, glandular epithelium, causing contraction of smooth and cardiac muscle and increases secretion of glandular epithelia. Neuron cell bodies are located in the intermediolateral cell column and in peripheral ganglia.

There are 31 pairs of spinal nerves, which roughly correspond to the vertebrae. There are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral and 1 coccygeal [ Figure 2] 4 sets of spinal rootlets emerge from each spinal cord segment--2 sets of dorsal, 2 sets of ventral. Ventral roots contain efferent axons and arise from spinal cord neurons in the ventral horn gray matter and intermediate zone. Dorsal roots have afferent axons and the cell body is in the dorsal root ganglion. [Figure 3] Dorsal and ventral roots on each side pass through the intervertebral foramina to merge and form the spinal nerve. First branching external to intervetebral foramina yields the dorsal ramus and ventral ramus. Both contain all 4 types of nerve fibers, but dorsal rami turn dorsally to innervate dorsal midline structures and the back of the head. The ventral rami continue laterally and innervate structures in the body wall of the thorax and abdomen, as well as upper and lower limbs. Ventral rami are proportionally thicker because they innervate a substantially larger area. 2 Rami communicantes branch from the ventral rami, which serve the autonomic nervous system. [Figure 4]
 * 4) Name the number of spinal nerve pairs. Describe how these spinal nerves originate from the dorsal (posterior) and ventral (anterior) roots and how they branch to form the dorsal (posterior) and ventral (anterior) primary rami, as well as the white and grey rami communicantes. describe the make up and function of the dorsal and ventral spinal roots.**


 * 5) Define the terms "dermatome" and "myotome". Explain how a clinical evaluation of sensory and motor deficits can provide clues as to the location of peripheral nervous system injury - ie. whether the deficits follow dermatomal/myotomal patters or peripheral nerve patterns.**
 * 1) Dermatome- a patch of skin innervated by the somatic sensory neurons found in particular dorsal root ganglia. [Figure 5]
 * 2) Myotome- the group of muscles innervated by the somatic motor neurons whose axons exit the spinal cord in a particular spinal nerve.


 * 6) Describe the structure of grey and white matter regions of the spinal cord. Describe which regions of the gray matter of the cord produce efferent fibers and which regions receive afferent fibers. Explain what is meant by the term "segment of the spinal cord".**
 * 1) Grey matter - inner region of the spinal cord containing nerve cell bodies and dendrites. In the shape of a butterfly "H", subdived into...
 * 2) dorsal horn gray matter: neuron cell bodies that receive synaptic input from sensory neurons in the dorsal root ganglion and are involved in further processing of somatosensory info
 * 3) ventral horn grey matter: contains neuron cell bodies that send axons out along peripheral nerves to form synapses with skeletal muscles)
 * 4) intermediate zone: neuron cell bodies that also send their axons along spinal nerves to form synapses with ganglionic neurons in autonomic ganglia, which in turn, form synpases with glandular epithelial cells, cardiac muscle cells, and smooth muscle cells.
 * 5) White matter - outer region that contains axons
 * 6) Segment of the spinal cord- short regions of the spinal cord associated with a particular spinal nerve. As mentioned above, there are 31 distinct segments.

Nerve plexuses are networks of intersecting nerves originating from the ventral rami. Because the dermatomes and myotomes served by the lumbar and sacral nerve plexuses interconnect so much they are often grouped as a single lumbosacral plexus. Note that L4 is associated with both the lumbar and sacral plexi.
 * 7) Define the term "nerve plexus". State whether nerve plexuses originate from the dorsal rami, the verntral rami or both. Describe the levels of the spinal cord involved in the cervical, brachial, lumbar and sacral nerve plexuses. Explain why the lumbar and sacral nerve plexuses are sometimes considered to be combined as the "lumbosacral plexus".**
 * The cervical nerve plexus involves the ventral rami of C1-C4 and the superior part of C5. It innervates muscles of the neck and areas of skin on the head, neck and chest.
 * The brachial nerve plexus involves the ventral rami of C5 - T1 and it innervates the chest, shoulders, arms and hands
 * The lumbar nerve plexus involves the ventral rami of L1 - L4 and it innervates the back, abdomen, groin, thighs, knees, and calves
 * The sacral nerve plexus involves the ventral rami of L4 - S3 and it innervates the pelvis, buttocks, genitals, thighs, calves, and feet


 * 8) Identify the location of neuron cell bodies forming the ventral and dorsal roots of spinal nerves.**
 * 1) Ventral: ventral horn of the gray matter of spinal cord
 * 2) Dorsal: dorsal root ganglion

During early human development, the spinal cord is similar in length to the bony vertebral canal. During the 3rd trimester the vertebral column extends past the spinal cord. At birth the caudal tip of the spinal cord is at about L2/L3. By adulthood the caudal tip, the conus medullaris, is at L1. The remainder of the vertebral column contains only the filum terminale and the cauda equine.
 * 9) Describe the relative lengths of the spinal cord and vertebral canal at different stages of development - ie. in embryos, at birth and in adults**


 * 10) Describe the three layers of the meninges surrounding the spinal cord. Name which layers contribute to the filum terminale, arachnoid trabeculae, denticulate ligaments and the dural sac.**
 * 1) Dura mater - tough outermost covering. Defines the border of the dural sac. Extends to the intervertibral foramina as sleeves that cover ventral and dorsal nerve roots.
 * 2) Dural sac - long tube around the spinal cord
 * 3) Epidural space lies between outside of dura mater and vertebral canal wall. (loose fat, loose connective tissue, venous plexuses)
 * 4) Subdural space - potential space between dura mater and memanous portion of arachnoid mater.
 * 5) Arachnoid mater - includes membranous sheet of cells that is adjacent to the inner serface of the dura mater, and the arachnoid trabeculae
 * 6) Arachnoid trabeculae - forms a multitude of delicate cellular structures bridging the gap between the membranous portion of arachnoid mater and pia mater
 * 7) Subarachnoid space - gap is filled with cerebrospinal fluid and arties and veins subserving CNS
 * 8) Pia mater - very thin and delicate layer of meninges in direct contact with surface of CNS
 * 9) Inferior to the conus medullaris, the pia mater tapers to become the Filum terminale, a slender filament that stretches from caudal tip of conus medullaris to the end of the dural sac at the S2 vertebrae. Serves to anchor the caudal end of the spenal cord (reduces swaying)
 * 10) Denticulate ligaments - thin membrane that stretches laterally from two lateral edges of spinal cord to arachnoid mater. Lateral edges continuous along lateral surface of spianl cord--lateral etches attached at 21 or so attachment points along the vertebral canal - gives a "sawtooth' appearance at the lateral edge. Helps anchor spinal cord within vertebral canal, preventing it from swaying back and forth. Also distinguishes between dorsal and ventral roots.



New Learning Objectives - Joints/Periosteum [ Dr. Ciment added these after the handouts were distributed. ]


 * 1) Describe the periosteum, its general location, it's anatomical relationship to ligaments and tendons, and what type of nerve fiber innervates it (i.e., somatic versus visceral, afferent versus efferent).**
 * The periosteum is a membrane made of dense connective tissue that lines the outer surface of bone (except at articulating surface of synovial joints).
 * It attaches to tendons and ligaments.
 * It is heavily innervated by somatic pain receptors.
 * Periosteum is continuous with joint capsule in synovial joints.
 * Note: It is analogous to the perichondrium which covers the surface of most pieces of cartilage (except at articulating surfaces of synovial joints).


 * 2) Name the three general types of joints, and describe the features that distinguish between these types. Name the subcategories of each type of joints, and describe the features that distinguish between them. Describe how much movement each type and subcategory of joint allows. Name the type and subcategory of joint that disappears during either late fetal or postnatal life (i.e., isn't present in the adult).**
 * 1) __Synovial Joints__- with synovial cavity (and cartilage). 6 general types (depending of shapes of articulating surfaces and types of movement allowed). May allow considerable movement.
 * Pivot - e.g. atlas (C1) pivots around the dens of the axis (C2)
 * Ball & Socket - e.g. Hip/shoulder
 * Plane - e.g. between articular processes of vertebrae
 * Hinge - e.g. Knee/Elbow
 * Saddle - e.g. Carpometacarpal joint of the thumb
 * Condyloid - e.g. Metacarpophalangeal joints
 * 1) __Cartilaginous Joints__- 2 types made of cartilage. Allow for little movement.
 * Primary (synchondrosis) - usually transient development
 * Secondary (symphyses) - persistent structure e.g. costal (rib) cartilage, intervertebral disc, pubic symphysis
 * 1) __Fibrous joints__- 3 types made of fibrous tissue connecting two bones. Allow for little or no movement. No synovial cavity, no articular cartilage.
 * Syndesmosis - Gap between bones is wide. Some movement. e.g. interosseus membranes of forearm, leg
 * Suture - Gap between bones is narrow. No movement. e.g. joints between flat bones of the skull
 * Gomphosis - Associated with teeth. No movement.


 * 3) With synovial type of joints, name the two features that restrict the types of movements these joints are capable of.** [ MORE? ]
 * The joint capsule consists of a fibrous capsule on the outside to provide strength, protection, and to limit movement, as well as an inner, synovial membrane that produces lubricant.
 * The periosteum, which is continuous with the joint capsule, is innervated by somatic afferent receptors and is sensitive to pain.


 * 4) Name and describe the two layers of the joint capsule around synovial joints, and describe which layer is innervated by sensory neurons. State which type of sensory fiber innervates this layer -- i.e., somatic versus visceral.**
 * The outer layer is called the **fibrous layer.**
 * The inner layer is called the **synovial membrane**, which secretes synovial fluid to lubricate the joint.
 * Joint are innervated by somatic afferent (sensory) nerves.