Cranial Nerve V - Trigeminal Nerves

The trigenimal nerves are the general sensory nerves of the face and motor nerves of the chewing muscles, and are the largest of all the cranial nerves. These nerves are grouped into three divisions:

1. OPHTHALMIC (V1)
Origin: Face
Pathway: To pons via superior orbital fissure
Oorgans/structures served: Skin of frontal scalp, upper eyelid, nose, nasal cavity, cornea, lacrimal gland
Function: Conveys sensory impulses from touch, temperature, and pain receptors
Sensory or motor: Sensory
Visceral or somatic: Visceral

2. MAXILLARY (V2)
Origin: Face
Pathway: To pons via foramen rotundum
Organs/structures served: Nasal cavity, palate, upper teeth, skin of cheeck, upper lip, lower eyelid
Function: Conveys sensory impulses from touch, temperature, and pain receptors.
Sensory or motor: Sensory
Visceral or somatic: Visceral

3. MANDIBULAR (V3)
Origin: Face
Pathway: To pons through skull via formaen ovale
Organs/structures served: Anterior tongue, lower teeth, skin of chin, temporal region of scalp, chewing muscles
Function: Conveys sensory impulses from touch, temperature, and pain receptors. Supplies motor fibers to chewing muscles.
Sensory or motor: Both
Visceral or somatic: Both

I like this image (from the University of Manitoba website), because it helps me visualize the target areas of each division. V1 innervates the forehead and eye, while V2 innervates the cheek area, and V3 innervates the lower face and jaw muscles. I also like this image because it reminds me that even though Cranial Nerve V has 3 divisions, each division brings sensory info back to the same spot (or sends motor direction out from the same spot).

The Upper Limb - AKA "The Arms"

This blog entry will present a comprehensive view of the upper limb, including discussion of the bones, joints, and major muscles of the upper limb. It will also discuss the underlying structures, ie. tissues, that make up each of these elements - bony tissue, cartilage in joints, and muscle tissue. Finally, it will discuss the nerves that trigger the muscles of the upper limb, which in turn move the skeleton.

BONES OF THE UPPER LIMB
-32 bones in each arm, 3 regions of arm

1. Arm
- Humerus

2. Forearm
- Ulna (pinky side)
- Radius (thumb side)

3. Hand
- Carpus (wrist)
- Metacarpus (palm)
- Phalanges (fingers)
***Metacarpus & phalanges
together form the digits

We should also note that pectoral girdle (or shoulder girdle) attach the upper limb to the axial skeleton and also provide points of attachment for many of the muscles which move the upper limb. The pectoral girdle consists of the the scapulae (or shoulder blades) and clavicles (or collarbones).

In the image of the upper limb bones at below, you can see that the humerus, radius, ulna, clavilcle, metacarpal bones, and phalanges are all long bones. The carpal bones are short bones, and the scapula is a flat bone.

Image is from the Christine M. Kleinert Institue for Hand &
Microsurgery website.

Each of bones of the upper limb, along with all the bones of the skeleton, are composed of bony tissue. Bony tissue has 4 main functions:
1. Support & movement
2. Protection
3. Mineral storage, especially calcium
4. Blood cell development in long bone marrow

Bony tissue consists of:
- 35% collagen, ground substance, and cells
- 65% inorganic calcium

There are 3 types of bone cells:
1. Osteoblasts which make & deposit the components of bone's extracellular matrix
2. Osteoclasts which break down and resorb bone for remodeling (become phagocytes and degrade calcium)
3. Osteocytes which are mature, spider shaped bone cells that monitor the environment

Furthermore, there are 2 main textures of bony tissue:
1. Compact tissue which is dense tissue containing the Haversian canals (canals through which blood vessels and nerves pass, and surrounded by layer of bone), which is found at the surface of bones. Compact tissue is highly vascularized. In the image of compact bone at right, you can see the Haversian canals and the layers of bone. The image is from McGraw Hill Higher Education website.

2. Spongy tissue, found in the interior of long and skull bones and at the ends of long bones, which provides spaces for bone marrow formation in the trabeculae.

The picture below gives a clear view of where both spongy and compact bones can be found in a typical long bone. Note the spongy tissue is at the end and the inteior of the bone, while the compact bone is at the surface of the bone. The image is from medco.com

And, there are four classes of bones:

1. Long bones are longer than they are wide, and consist of a shaft plus two ends.

2. Short bones are cube-shaped bones.

3. Flat bones are thin, flat, and somewhat curved, such as the skull, ribs, and sternum.

4. Irregular bones have complicates shapes, like the vertebrae and the hip bones.
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JOINTS OF THE UPPER LIMB

Now that we know a little about bones, we can talk about joints. Joints are important because they are the sites where two or more bones meet. Joints give the skeleton mobility while holding it together. Joints usually, but not always, allow for movement.

Cartilage is a type of skeletal tissue that is found at the end of bones and often forms joints. It is mostly made of water, but is stil very resilient, maintaing its shape and form, and it does not contain nerves. Cartilage grows very quickly, and forms most of the embryonic skeleton. There are 3 types of cartilage that we should know about:

1. Hyaline cartilage is the most common type of cartilage found in joints. It is made of fine collagen fibers and provides support with flexibility and resilience. It forms the skeleton of the voicebox and support the external nose.

2. Elastic cartilage contains many stretchy fibers and is only found in the epiglottis and the ear.

3. Fibrocartilage which has great tensile strength and is highly compressible - it contains thick collagen fibers. It is found in the menisci of the knee and in the intervertebral discs.

There are some other joint basics we need to talk about before we discuss the specific joints of the upper limb. We should know that joints are classified by structure and by function. Functionally, there are 3 types of joints:

1. Synarthroses are immovable joints

2. Amphiarthroses are slightly movable joints

3. Diarthroses are freely movable joints, which predominate in the limbs, and are of most concern to us for the purposes of this blog entry.

Structurally, there are also 3 main classes of joints:

1. Fibrous joints

- Sutures are found in the skull only, and are bones tightly bound by minimal fiber

- Syndemos are bones connected by ligaments (such as the radius and ulna)

- Gomphoses are peg in socket joints and are found only in the teeth

2. Cartilaginous joints

- Synchondrosis are composed of hyaline cartilage and unites bones. Found in such places as the epiphyseal growth plates. No joint cavity.

- Symphyses are composed of fibrocartilage united bones. Found in the pubic sympheses. No joint cavity.

C. Synovial joints are the most common joint in the body and have a fluid filled joint cavity, allowing for freedom of movement. All the joints of the limb are synovial joints. This image, from webschoolsolutions.com, shows the key components of a typical synovial joint.

Synovial joints are classified into six major categories:

- Plane

-Hinge

- Pivot

- Condyloid

- Saddle

- Ball & Socket

OKAY! Now we have a foundation in place, we can talk about the specific joints of the upper limb. For each joint, we'll learn the type of joint, the bones that the joint is between, and the type of movement the joint is capable of. We'll start at the shoulder joint and work our way down the arm. Let's go!!

The shoulder is a ball & socket joint. As show at right, it is located between the scapula and humerus, and can perform all of the angular movements (rotation, abducation, adduction, flexion, and extension). Image courtesty of www.kettering.edu.

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The elbow is a hinge joint. It is between the humerus and the radius/ulna. The elbow can only flex and extend.

The proximal/distal radio-ulnar joint is a pivot joint. It is located between the radius and ulnar, and allows supination and pronation.

The metacarpal-phalangeal joints are condyloid joints located between...you guessed it...the metacarpals and phalages. Flexion, extension, abduction, and adduction can all be performed.

The interphalangeal joints are located in the phalanges. There are two interphalangeal joints per finger (the proximal and distal joints). These are hinge joints which allow for flexion and extension.

*The image at right (from www.cms.depuy.com) is a great view of both the metacarpal-phalangeal joints and the interphalangeal joints. Notice the distal ip joints are at the fingertips.

The metacarpal-carpal joint is located in the thumb and is a saddle joint and has freedom of movement.

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MUSCLES OF THE UPPER LIMB

We have bones, we have joints....now we need the eer...muscle....to make them move! Each skeletal muscle is an organ, made of skeletal muscle fibers (hundred or thousands of contractile elements called myofibrils per fiber), blood vessels, nerve fibers (1 nerve, 1 artery and one or more veins), and connective tissue (several layers). Skeletal muscle tissue contains the longest muscle cells, and have obvious stripes called striations. Skeletal muscles are under voluntary control. Skeletal muscles attach to and cover the bony skeleton, producing movement, maintaining posture, stabilizing joints, and generating heat.

The major muscles of the upper limb include:

The biceps and biceps brachialis (anterior) and triceps (posterior) in the arm region. The biceps allow for flexion of the arm, and the triceps allow for extension of the arm.

The forearm flexors and the flexor carpi ulanris (anterior) and anconeus and brachioradialis in the forearm (posterior).

The digit extensors (posterior) in the hand.

The muscles of the scapula, which also provide movement to the upper limb, include:

The subscapularis, the supraspinatus, the infraspinatus, the teres minor, the teres major, the latissimus dorsi, and the coracobrachialis. Each of these muscles have their point of origins (meaning they are attached to the movable or less movable bone) on the scapula and point of insertion (attachment to movable bone) on bones of the upper limbs.

Muscles of the scapula which move the scapula include,

The rhomboids, trapezius, pectoralis minor, serratus ventralis, and levator scapulae.

Below is a great picture -a posterior view of the upper limb muscles.From www.discovery-services.net

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With all the elements of the upper limb in place - bones, joints, and muscles, we need to talk about the nerves and the motor unit which enable all the elements to work together! Let's get moving!

A motor unit is made of a motor neuron and all the muscle fibers it supplies. Remember, motor neurons (both somatic and visceral) are found in the ventral horns of spinal nerves. The axon of each motor neruos divides as it enters the msucles, and each separate ending forms a neuromuscular junction with each individual muscle fiber. When a motor neuron fires (ACTION POTENTIAL!!) all the muscle fibers it innervates contract. When a skeletal muscle of the upper limb contracts, the biceps on the anterior compartment of the arm, for instance, causing the elbow joint to flex and the forearms bones to move. The image below is from coursewareobjects.com, and is the best image I could find that shows a motor unit - from the spinal cord right to a muscle.

The major nerves of the upper limb anteriorly are:

- The M-C (musculocutaneous) nerve, located between the biceps brachii and the brachialis

- The median nerve , which is medial/posterior to the biceps, and branches into the forearm flexors at the elbow, continuing to the hand through the carpel tunnel

- The ulnar nerve, which is medial in the arm, posterior to the humberus and down the middle of the forearm to the carpal tunner into the palm.

Posteriorly, there is one major nerve of the upper limb, the radial nerve. The radial nerve is deep in the posterior arm around the humerus, extending to the forearm.

NERVOUS SYSTEM I - The Vertebral Column, Structure of Vertebrae, and the Peripheral Nervous System

The nervous system consists of two main divisions - the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves that branch out of the spinal cord and into the body). This blog will discuss the vertebral column (that protects the spinal cord), the structure of individual vertebrae, and give an overview of the peripheral nervous system. Due to its complexity, the CNS will not be discussed here.

I. THE VERTEBRAL COLUMN

A. Characteristics

• Flexible and curved structure
• Also known as "the spine"
• Axial support of the trunk, keeps body upright
• Extends from the skull to the pelvis
• 26 irregular bones

B. Functions

• Surrounds and protects the spinal cord
• Acts as point of attachment for the ribs and neck and back muscles

C. Three Main Components

- 1.Vertebrae (5 divisons)

• Cervical region (7 vertebrae, C1-C7)
• Thoracic region (12 vertebrae, T1-T12)
• Lumbar region (5 vertebrae, L1-L5)
• Sacrum region (5 fused vertebrae)
• Cocyx region (4 fused vertebrae)
• In the image at right, you can clearly see each vertebral region, and note that each region becomes larger from the cervical region to the lumbar region. This is because the lower regions must support more body weight. You should also note the different curves in the spine, which form an "s" shape. The curves provide flexibility to the spine.

- 2. Ligaments

• Continuous bands that run down the front (anterior longitudinal ligament) and back (posterior longitudinal ligament) surfaces of the spine
• Keep the spine upright
• Prevent hyperextension and hyperflexion
• Also connect vertebrae to those above and below
• Image from Walden University website

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- 3. Discs

• Act like shock absorbers during activity
• Allow the spine to flex and extend, and move from side to side
• Cushionlike pads made of 2 parts
• - a. Nucleus pulposus is the inside of the disc.
• - Jello like
• - Provides elasticity and compressibility
• - b. Annulus fibrosus forms the exterior portion of disc
• - Made of collagen fibers and fibrocartilage
• - Hold the nucleus together when the spine is compressed
• In the image at right, you can see how the discs fit nicely in between each vertebrae, providing cushioning for the entire vertebrae. When I think of discs, I think of the shoe inserts that you put into your shoes to provide extra support and cushioning!
• Image from chiropractic-care.com.

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II. STRUCTURE OF VERTEBRAE

• All vertebrae have common elements
• Regional variations depending on function and movement (flex/extend, bend side to side, or rotate)

A. Common Elements

• The body is the disc-shaped, weight bearing, anterior portion of the vertabrae. It combines with the .....
• Posterior vertebral arch to form the...
• Vertebral foramen (formamen meaning "hole"). All of the vertabral foramen on successive vertabrae make up the...
• Vertebral canal, through which the spinal cord passes.
• The vertebral arch consists of 4 parts...
• Two pedicles (pedicle meaning "little foot"), forming the sides of the arch, and
• Two laminae, or flattened plates that fuse together.
• The spinous process (process meaning "piece sticking off") is a centered, posterior projection in between the two laminae.
• There are two transverse processes, which stick out laterally on either side of the vertebral arch.
• The spinous and transverse process are the sites for muscle and ligament attachment.
• The superior and inferior articular processes stick out from the junction of the pedicle and lamina.
• Finally, the intervertebral foramina are lateral openings between adjacent vertebrae where spinal nerves pass thorugh. These nerves as well as the cranial nerves, are part of the peripheral nervous system, or PNS, and are a great starting point for our discussion of the PNS!
• Image from Owensboro Community & Technical college website.

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III. PERIPHERAL NERVOUS SYSTEM

• All nerves that leave the CNS and branch out into the body
• Includes 12 pairs of cranial nerves and 31 pairs of spinal nerves
• Link body parts to CNS

A. 2 Main Divsions

-1. Sensory/afferent system

• Touch and proprioception (positional info)
• Collects info for CNS

-2. . Motor/efferent system

• Muscle movement and gland secretion
• 2 subdivisions
• Somatic (voluntary) - allows conscious control of skeletal muscles
• Autonomic (involuntary) - regulates heart, smooth muscles, glands. 2 branches
• Sympathetic and parasympathetic

• I recreated the organizational flow chart from our textbook which diagrams the PNS using MS Word. I find this type of diagram most helpful in understanding the many levels of the PNS.
  

B. Components

• All neural strucutures outside the CNS

-1. Supporting cells, or neuroglia - 2 types in PNS

• Schwann cells - Form myelin sheath around nerve fibers, acting as insulator
• (Image of Schwann cells & neuron from www.sciencedaily.com.)
• Satellite cells - Function unknown

-2. Neurons

• Characteristics
• - Highly specialized
• - Conduct impulses that transmit messages
• - Longevity
• - Do not divide/can't replace
• - High metabolic rate
• - Usually large and complex
• - Made of a cell body, slender processes (axons or dendrites), and an axonal terminus

• Cell body, or soma
• - Contain clear, round nucleus
• - Most somas are in CNS

• Processes
• - Most are in PNS
• - 2 types, dendrites and axons

• Dendrites
• - Short, branching extensions
• - Hundreds per cell body
• - Receptors
• - Receive info toward the body

• Axons
• - Can be short or long
• - One per neuron
• - May have branches
• - Generate nerves impulses and carry messages away

• Image at right from the University of Baltimore clearly illustrates that each neuron has only one axon, but multiple dendrites.

• Axonal terminus

C. CLASSES OF NEURONS

- 1. Structural Classes

• Multipolar
• - 3 or more processes
• - Most common, especially in CNS
• - Motor neurons

• Bipolar
• - 2 processes
• - 1 axon and 1 dendrite opposite each other
• - Rare
• - Found only in special sense organs

• Unipolar
• - One single, short process
• - Mostly found in PNS
• - Sensory neurons

- 2. Functional Classes

• Sensory neurons
• - Transmit from receptors in skin or organs to CNS
• - Mostly unipolar structure
• - Mostly in PNS

• Motor neurons
• - Carry impulses from CNS to muscles and glands
• - Multipolar structure
• - CNS

• Interneurons
• - Multipolar
• - Mostly in CNS
• - Lie between sensory and motor neurons

TISSUE

TISSUE

Tissues are a group of cells that are similar in structure and work together to perform a related function.

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The four primary types of tissue and their primary functions are:

1. Epithelial (covering)
2. Connective (support)
3. Muscle (movement)
4. Nervous (control)

This blog entry will focus on the first two types of tissue - epithelial and connective tissue, their components, functions, and examples of each.

I.Epithelial Tissue - Sheets of cells that cover a body surface or line a body cavity

A. Special Characteristics of Epithelial Tissue

-1. Cellularity

- a. Epithelia cells are closely packed together, side by side, with very little space between them.

-2. Specialized contacts/cell junctions

- a. Desmosomes are cell junctions composed of thickened plasma membranes joined by filaments. In the image of a desmosome below, you can see the connecting filaments that hold the cells together - they remind me of paper clips.

(from the University of Arizona - The Biology Project website)

- b. Tight junctions are the areas where cell membranes of adjacent cells are actually fused together. In the image below, you can see where the junctional proteins join the cell membranes. In this case, the proteins remind me of staples!

(from the University of Arizona -The Biology Project website)

- c. Gap junctions are passageways between two adjacent cells, formed by transmembrane proteins. Below, you can see the hydrophilic channels binding the two cells. The channels look like little roads!

(from the University of Arizona - The Biology Project website)

3. Polarity

- a. The apical part of the cell which is exposed to the body's exterior or to the internal organ cavity has a different function than the lower, attached basal surface. I remember this by thinking of polarity = north pole vs. south pole = apical vs. basal.

4. Supported by connective tissue

5. Supplied by nerve fibers (innervated), but does not have blood vessels (avascular)

6. Regeneration

- a. High capacity for fast regeneration if receiving adequate nutrition

7. Cell extensions on apical surface

- a. Microvilli are finger-like extensions of the cell membrane. They increased the cell's surface area for absorption purposes. Think of fingers reaching out to grab (absorb) as much as possible.

- b. Cilia are small, hair-like projections on cell surfaces that move in a wave-like manner, propelling substances across the cell's surface.

- c. Flagellum are long,whip-like extensions of the cell membrane which actually move the cell.

B. Classes of Epithelia - Epithelia tissue are classified by their shape and by the number of layers.

1. Simple Epithelia (Single layer)

- a. Simple squamous (squamous from the root "squash", being flat and scalelike)

• Simplest epithelia
• Single layer of flat cells
• Function: Allows passage of materials by diffusion and filtration in sites where protection is not important
• Locations: Air sacs in lung, lining of heart, kidneys
• Two special types: Endothelium found in lymphatic vessels, blood vessels, and the heart Mesothelium is found in serous membranes lining the ventral body cavity and covering its organs.
• Picture:Surface view of simple squamous (mesothelium). From The JayDoc Histoweb.

- b. Simple cuboidal (cube, or boxlike)

• Single layer of cells that are equally tall as they are wide
• Have dark staining nuclei
• Function: Secretion and absorption
• Locations: Kidney tubules, ovary surface, ducts
• Image: Clearly shows one layer of box shaped cells. (from the University of Delaware website)

- c. Simple columnar (tall and column shaped)

• Single layer of tall, closely packed cells
• Function: Mostly absorption and secretion
• Location: Lining of digestive tract
• Image: One row of tall, elongated cells can clearly be seen.

(from the University of Delaware website)

- d. Pseudostratified columnar

• Single layer of columnar cells resting on basement membrane, but having vary heights, giving the impression of several cell layers
• Function: Secretion and absorption
• Image: You can see how the nuclei of the cells are at different levels, making it look like there could be more than one row of cells in some spots.

(from University of Delaware website)

2. Stratified Epithelia (2 or more stacked layers - classified by the cell layer at the apical surface).

- a. Stratified squamous

• Most widespread stratified tissue
• Surface cells are squamous; deeper layers are cuboidal or columnar
• Function: Protection from wear and tear
• Location: Epidermis of skin (contains keratin, a tough protective protein)
• Image: Several rows of stratified squamous are clear visible at surface, with columnar layers below.

(from the University of Delaware website).

- b. Stratified cuboidal

• Rare
• Usually 2 or more layers of cuboidal cells
• Location: Ducts of some large glands such as sweat and mammary glands
• Image:MANY layers of cuboidal cells in the vaginal lining.

(from Brown University Medical School website)

- c. Stratified columnar

• Scarce
• Only apical cells are columnar
• Location: Pharynx, male urethra, some gland ducts, also found at junction between other epithelia
• Image: You can see one row of columnar cells on the apical surface, and what appears to me to be a row of cuboidal cells below, inside a kidney tubule. (from McGraw Hill Higher Education website)

3. Transitional Epithelia

• Basal layer cells are cuboidal or columnar.
• Apical cells vary depending on degree of distension
• Function: Form linings of hollow urinary organs, which stretch as they fill with urine
• Location: Bladder
• Image: Transitional cells in the bladder (From McGraw Hill Higher Ed website)

4. Glandular Epithelia

- a. Glands are one or more cells that secrete a particular water based product.

- b. Endocrine

• Internally secrete into the bloodstream
• Ductless
• structurally diverse
• Hormones travel to target organ to increase response
• Examples: Adrenal glands
• Image: Parathryoid gland that is rich in capillaries (bright red). From pathguy.com

- c. Exocrine

• Secrete onto body surface or into body cavity
• Have ducts
• Examples: Mucous, sweat, oil and salivary glands, liver, pancreas
• i. Unicellular - Goblet cells which are in the epithelial linings of the intestinal and respiratory tracts. Produce mucin, which dissolves into mucus
• ii. Multicellular - Have duct and secretory unit.
• Image: Mucous gland.(from Univ. of CA at Davis website)

II. Connective Tissue - Found everywhere in body. Most abundant tissue

A. Functions of Connective Tissue

1. Binding and support (primary function)

2. Protection

3. Insulation

4. Transportation of substances

B. Common Characteristics of Connective Tissue

1. Arise from mesenchyme (embryonic tissue)

2. Degree of vascularity

3. Extracellular matrix

• Comprises most connective tissue
• Non-living
• Bears weight

C. Structural Elements of Connective Tissue

1. Ground substance

• Unstructured material between cells
• Contains fibers
• Holds large amounts of fluids which aids in diffusion

2. Fibers

- a. Collagen fibers give structure and are glistening white in appearance.

- b. Elastic fibers give elasticity and are long, thin and yellow. Found in skin, lungs, and blood vessel walls.

- c. Reticular fibers give order and branch extensively to form delicate networks.

3. Cells

- a. Fibroblasts (in connective tissue proper)

- b. Chondroblasts (in cartilage)

- c. Osteoblast (in bone)

- d. Hematopoetic stem cells (in blood)

- e. Immune cells

• Macrophages
• Plasma cells
• Mast cells
• Neutrophils, lymphocytes

D. Types of Connective Tissue

1. Embryonic Connective: Mesenchyme

- a. First tissue formed from mesoderm layer

- b. Made of mesenchymal cells and fluid ground substance

- c. Turns into all other connective tissue

- d. Some remains and is a source of new cells in mature connective tissues

• Image is of embryonic mesenchyme with a capillary running through it. You can also see red blood cells inside the capillary. (from Loyola University Medical Center website).

2. Connective Tissue Proper

- a. Loose connective

- i. Areolar connective

• mostly widely distributed connective tissue
• Soft packing material
• Functions: Supporting and binding other tissue, holding body fluids, defending against infection, storing nutrients as fat
• Example: Mucous membranes
• Picture: Areolar connective tissue, with thick(collagen) and thin(elastic) fibers visible in ground substance. (from Red Deer College website)

- ii. Adipose (Fat)

• High metabolic activity
• 18% of average person's weight is fat
• Functions: Prevents heat loss, source of stored food
• Exampes: Fat depots at hips and abdomen, behind eyes, behind kidneys
• Image: Adipose fat tissue (from City University London website)

- iii. Reticular

• Limited to certain sites.
• Function: Forms stroma, or internal labyrinth like framework which supports free blood cells
• Example: Lymph nodes, spleen, bone marrow
• Image: Stroma of the lymph node. (from Univ. Of California @San Diego Med School web site)

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b. Dense connective

- i. Dense regular

• Collagen fibers are predominant element.
• Fibers are aligned parallel to pulling force
• Function: Resist tension in one direction, attach and bind
• Examples: Tendon (cords that attach muscle), ligaments (bind bones at joints)
• Image of dense regular connective tissue with fibers that run parallel. (from McGraw Hill Higher Education website).

- ii. Dense irregular

• Collagen fibers are thick and arranged irregular in many planes.
• Function: Resist tension in many directions
• Examples: Forms joint capsules and fibrous coverings that surround testes, kidneys, bones, cartilage, muscles, and nerves. *Dermis of skin*
• Image: Dense irregular connective tissue with fibers running in many directions. (from McGraw Hill Higher Education website)

3. Cartilage (covered later in a&p)

- a. Hyaline

- b. Elastic

- c. Fibrocartilage

4. Bone (coveraed later in a&p)

5. Blood (covered later in a&p)

III. Tissue Repair

A. Inflammation

1. Body's response to injury

2. Repair beings during inflammatory process

3. Regeneration (replacement of destroyed tissue), fibrosis (forming of scar tissue), or both

Human Development and Organizational Structure

The following outline is my attempt at summarizing the complex process of human fertilization and the phenomenal growth and development that occurs during the human gestation period, as well as an overview of the resulting organizational structure.

PART I - HUMAN DEVELOPMENT

The events that occur from conception until birth are all part of pregnancy. The human gestation period is normally 280 days, from the start of the females last menstrual period until birth. Preembryonic development takes place from fertilization until 2 weeks after fertilization. Embryonic development occurs from 3 to 8 weeks after fertilization. Fetal development takes place from 9 weeks after fertilization until birth.

I. Fertilization

A. Accomplishing fertilization

1. Fertilization occurs when a sperm fuses with an egg to form a fertilized egg, or a zygote.

2. Sperm transport & capacitation

- a. Millions of sperm are expelled during copulation.

- b. A few thousand reach the uterine tubes.

- c. Capacitation is the process of the sperms' membranes becoming fragile so that enzymes can be released. (6-8 hours).

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3. Acrosomal reaction and sperm penetration

- a. Hundreds of sperm must release their acrosomes to break down an eggs zona pellucida.

- b. ONE sperm binds to the receptors on an egg and inserts itself into the eggs membrane.

- c. The egg and sperm membranes open and the two fuse together.

4. Polyspermy

- a. Polyspermy is the entry of several sperm into one egg.

- b. Polyspermy does not occur in humans.

5. Completion of Meiosis II and Fertilization

- a. The sperm loses its tail and midpiece and migrates to the center of the ooctye.

- b. The ovum and sperm nuclei swell and approach.

- c. Mitotic spindle develops and membranes rupture, releasing chromosomes.

- d. Chromosomes combine and a zygote is produced.

B. Preembryonic Development (Fertilization through implantation in uterine wall)

1. Cleavage and blast formation

- a. Cleavage is a period of rapid mitotic divisions of the zygote, which eventually results in the formation of a blastocyst, or fluid-filled sphere made of a single-layer of flat cells.

2. Implantation

- a. Implantation of blastocysts into uterine wall takes place about 6-7 days after ovulation.

- b. Lasts for period of 1 week.

- c. Blastocysts buries itself deep into endometrium.

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3. Placentation

- a Placentation is the forming of the placenta the temporary organ that originates from embryonic and maternal tissues.

- b. The fetal side of the placenta is slick and smooth.

- c. The maternal side of the placenta is lumpy.

- d. The placenta detaches after birth and is expelled from the mother in the afterbirth.

- e. The placenta functions as the developing fetus' nutritive, respiratory, excretory, and endocrine organ.

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II. Events of Embryonic Development

A. Formation & Roles of Embryonic Membranes

1. Blastocyst is converted to a gastrula, where the germ layers form and embryonic membranes are made.

2.Embryonic membranes include the amnion, or bag of waters, yolk sac, allantois, and chorion. - a. The amnion is filled with amniotic fluid, and it protects against physical trauma, maintains homeostatic temperature, and prevents embryonic parts from fusing together.

- b. The yolk sac forms part of the digestive tube, produces early blood cells and vessels, and is the source of germ cells that seed the gonads.

- c. The allantois is a small outpocket at the end of the yolk sac, and is the structural base for the umbilical cord. It becomes part of the adult bladder.

- d. The chorion is the outermost membrane that encloses the embryonic body and all other membranes.

3. The first germ cells are two flat sheets of cells stacked on one another.

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B. Gastrulation: Germ Layer Formation

1. Gastrulation is the forming of a 3 layered embryo from the 2 flat layers of stacked cells. The flat layers roll up and form a tube.

- a. At least 50% and up to 80-90% of all embryos do not survive gastrulation, and are released in the womens menstrual flow.

- b. Three germ layers serve as the tissue from which all other body organs will be made.

- c. The notochord forms, which is a rod representing the long axis of the body. The notochord becomes the vertebrae and ribs.

- d. The neural tube also develops, which eventually becomes the brain and the spinal cord.

2. The endoderm is the most inferior layer.

3. The mesoderm is the middle layer.

4. The ectoderm is on the embryos dorsal surface.

C. Organogenesis: Differentiation of Germ Layers

1. Organogenesis is the formation of body organs and systems from the three germ layers.

2. Specialization of Ectoderm

- a. Neuralation is the differentiation of the ectoderm, which forms the brain and spinal cord from the neural tube.

- b. Remainder of the ectoderm forms the epidermis of the skin.

3. Specialization of the Endoderm

- a. Forms epithelial linings of digestive and respiratory systems, and related glands.

4. Specialization of Mesoderm

- a. Forms just about everything else in the body, including bones and muscles.

- b. The mesoderm splits during gastrulation, and some sticks to the inside of the tube, and some to the outside. The outer tube is the somatic or parietal tube, and will form the skin, skeleton, skeletal muscles, and nervous system. The inside of the tube is the gut or viscera, and will form the digestive system, liver, pancreas, and lungs.

- c. The coelem is formed between the 2 mesodermal layers, which becomes the ventral cavity.

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D. Development of Fetal Circulation

1. Cardiovascular system is basis for early circulation.

- a. Endothelial cells form vascular networks, which will eventually be the heart, blood vessels, and lymphs.

- b. By end of week 3, the heart is working.

- c. Ductus arteriosus, foramen ovale, ductus venosus, umbilical arteries, and umbilical cord are all structures that are only present during fetal development.

- d. The circulatory pattern & cardiovascular system changes at birth.

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By birth, an average human fetus weighs about 6-10 pounds, and is about 22 inches long. By examining the process of human development above, we can observe that there are many levels of structural organization in the human body, which have developed as part of evolution.

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PART II. ORGANIZATIONAL STRUCTURE

A. Chemical Level

1. Atoms combine to form molecules.

2. Molecules combine to form organelles, the basic unit of living cells.
Example: An atom of carbon

B. Cellular Level

1. Basic unit of structure/function.

2. Many different types.
Example: Smooth muscle cell

C. Tissue Level

1. Group of cells having a common function. 4 major types:
- a. Skeletal tissue
- b. Muscle tissue
- c. Epithileal tissue
- d. Connective tissue

D. Organ Level

1. Structures made of at least 2 tissue groups, working together on a specific function.
Example: Heart (made of cardiac muscle tissue)

E. Organ System level

1. Groups of organs that have a common function.
- a. Integumentary: of skined ofskin, hair, nails. Protects from injury.
- b. Skeletal: Composed of bones and joints. Frame for muscles to provide movement, site of blood cell formation, and stores minerals.
- c. Muscular: Made of skeletal muscles. Locomotion, expression, posture, and heat production. - - d. Nervous: Brain, spinal cord, nerves, sensory receptor. Control center of body.
- e. Endocrine: Glands. Secrete hormones that regulate body processes.
- f. Cardiovascular: Heart and blood vessels. Transportation and pumping of blood.
- g. Lymphatic: Lymph nodes, spleen, red bone marrow, thymus, lymphatic vessels, and thoracic duct. Immunity.
- h. Respiratory: Nasal cavity, pharynx, larynx, trachea, lungs, and bronchus. Supplies blood with O2 and removes CO2.
- i. Digestive: Oral cavity, esophagus, liver, stomach, small intestine, large intestine, rectum, anus. Breaks down food and eliminates feces.
- j. Urinary: Kidney, ureter, urinary bladder, and urethra. Eliminates nitrogen containing waste from body, regulates water, and regulates electrolytes and acid-bases in blood.
- k. Reproductive: In the male, penis, testis, prostate gland, ductus deferens, and scrotum. In the female, mammary glands, ovary, uterine tube, uterus, and vagina. Production of offspring.

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F. Organismal level

1. All structures working together in order for the organism to live.
Example: ME!

Once the human body is formed, there are eight functions that must take place in order for the body to function properly:

1. Maintain boundaries to allow an organism to maintain separate and internal & external environments.
2. Movement allows the organism to travels the transport of molecules within the organism.
3. Responsiveness is the ability to detect changes in the internal or external environment and respond to them.
4. Digestion is the process of breaking down food into molecules that are usable by the body.
5. Metabolism includes all chemical reactions that occur.
6. Excretion is the process of removing wastes.
7. Reproduction is the process of producing more cells or organisms.
8. Growth is an increase in size of body parts or of the whole organism.

Furthermore, in order for these life functions to take place, an organism needs:

1. Nutrients that are used by the organism for energy and cell building.
2. Oxygen for chemical reactions that release energy from foods.
3. Water for chemical reactions and as an outlet for secretions and excretions.
4. Normal body temperature for chemical reactions to occur normally.
5. Atmospheric pressure for normal breathing.

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With all of these elements in place, the body works to maintain homeostasis.

A.Homeostasis
1. Homeostasis is the ability of the body to maintain a stable internal environment, regardless of external changes. Imbalance in body often results in disease.

2. There are 4 parts of the control mechanism:
- a. The variable is the regulated factor or event.
- b. The receptor is the structure that monitors changes in the environment and sends information to the control center.
- c. The control center determines the set point for a variable, analyzes input, and coordinates responses.
- d. The effector is the structure that carries out the response directed by the control center.

3. Positive Feedback Mechanisms
- a. Cause variable to change in the same directions as the original change, resulting in a greater deviation from the set point.
- b. Most positive feedback mechanisms are not related to homeostatic maintenance.

4. Negative Feedback Mechanisms
- a. Most mechanisms are negative.
- b. Cause the variable to change in a way that opposes the initial change. Goal is to prevent sudden, severe change.

Intro Information

1. Jennifer Clark
2. Born in New Bedford, MA on 06/1976
3. Arthur Moniz, George Strait
4. Change careers
5. Married for 2.5 years
Have an 18 month old son
Have 1 brother and 1 sister