Anatomy Notes

Skeletal System:

• 2 subdivisions of the skeleton

  • Axial Skeleton - made of 80 bones

  • Appendicular - made of 126 bones

• Parts of the skeletal system

  • Bones

  • Joints

  • Cartilage

  • Ligaments

Functions:

• Supports body

• Protects soft organs

  • Skull and vertebrae protect the brain and spinal cord

  • The rib cage protects thoracic cavity organs

• Attached skeletal muscles allow movement

• Store minerals and fat

  • Calcium and phosphorus

  • Fat in the internal marrow cavity

Bones:

• The adult skeleton has 206 bones

• Two basic types:

  • Compact

    • Dense, smooth, homogenous

  • Spongy

    • Small, needle-like pieces of bone

    • many open spaces

• Classified based on shape, as:

  • Long

  • Short

  • Flat

  • Irregular

Long Bones:

• Typically, longer than they are wide

• Shaft with heads situated at both ends

• Contains mostly compact bone

• All of the bones of limbs are long bones

  • (e.g. Femur and Humerus)

Short Bones:

• Generally, cube-shaped

• Contains mostly spongy bone

• Include bones of wrist and ankle

• Sesamoid bones are a type of short bone that form in the tendons

Flat Bones:

• Thin, flattened, usually curved

• 2 thin layers of compact bone surround a layer of spongy bone

  • (e.g. skull, ribs)

Irregular Bones:

• Irregular shape

• Don’t fit into other bone categories

  • (e.g. vertebrae and hip bones)

Long Bones:

• Diaphysis

  • Shaft

  • Makes up most of the length

  • Composed of compact bone

• Periosteum

  • Outside covering of diaphysis

  • Fibrous connective tissue membrane

  • Perforating (Sharpey’s) fibers secure

• Epiphysis

  • Ends of the bone

  • composed of mostly spongy bone, enclosed by a thin layer of compact bone

• Articular Cartilage

  • Covers the external joint surfaces

• Epiphyseal Plate

  • Flat bone of hyaline cartilage, seen in young bone

  • Causes lengthwise growth of long bone

• Epiphyseal Line

  • Remnant of the plate (seen in adult bone)

• Marrow Cavity

  • Cavity inside the shaft

  • Contains yellow marrow (mostly fat) in adults

  • Contains red marrow for blood cell formation in infants

• In adults, bone and epiphysis of some long bones

Compact Bones:

• Osteocytes are bone cells and are situated within cavities known as lacunae

• Lacunae are arranged in concentric rings called lamellae

• Lamellae are rings situated around the central (Haversian) Cave

  • Opening in the center of an osteon

  • Runs lengthwise through the bone

  • Carries blood vessels and nerves

• Osteon

  • A unit of bone containing a central canal

• Bone growth

  • Ossification

    • Process of bone formation

    • Occurs on hyaline cartilage models

    • Long bone growth

1. Osteoblasts

   • Bone forming cells

   • cover hyaline cartilage model

2. Enclosed cartilage is digested away, opening up as a medullary cavity

• By birth, most cartilage is converted to bone except:

  • Articular cartilage

  • Epiphyseal appendages

• New cartilage is formed continuously on the external face of these two cartilages

• Old cartilage is broken down and replaced by bony matrix

• Bones grow in length and width

  • Appositional growth

    • Growth in diameter

• Controlled by hormones such as growth hormone

• Epiphyseal plates are converted to bone during adolescence

Bone Remodeling:

• Bones are lengthened until growth stops

• Bones are remodeled throughout life in response to:

  • Blood calcium levels

  • Gravitational pull

• Parathyroid hormone (PTH)

  • Release when blood calcium levels are low

  • Activates osteoclasts

  • They break down bones and release calcium

• Hypercalcemia promotes calcium storage in bones

Bone Fracture:

• Break in a bone

  • Closed: Break that does not penetrate the skin

  • Open: Broken bone penetrates the skin (Compound)

Bone fractures are treated by reduction and immobilization

• Closed reduction: Bones are manually coaxed into position by the physician’s hands

• Open reduction: Bones are put back through surgery

Repair:

• Hematoma is formed

• Fibrocartilage callus is formed

  • Cartilage matrix, Bondy matrix, and collagen fibers splint the broken bone

• A bony callus replaces the fibrocartilage callus

  • Osteoblasts and osteoclasts migrate in

• Bone remodeling occurs in response to mechanical stresses

Types of Fractures:

• Comminuted: Bone breaks into many fragments

• Compression: Bone is crushed

• Depressed: Broken bone is pressed inward

• Impacted: Bone ends are forced into each other

• Spiral: Ragged breaks occur when excessive twisting forces are applied to a bone

• Greenstick: Bone breaks incompletely

Axial Skeleton:

• Forms the longitudinal axis of the body

• Divided into 3 parts:

  • Skull

  • Vertebral column

  • Bony thorax

The Skull:

• 2 sets of bones:

  • Cranium bones: Enclose the brain

  • Facial bones:

    • Hold eyelids in an anterior position

    • Allow facial muscles to express feelings

• Bones joined by sutures

• Only the mandible is attached by a freely movable

Cranial Bones:

• Frontal Bone: One bone that forms the forehead and upper part of the eye socket

• Parietal Bones: Two bones forming the bulging top sides of the cranium

• Occipital Bone: One bone that forms the back of the skull and has a large hole called the Foramen Magnum which allows the Spinal Cord to pass through

• Sphenoid Bone: One bone, which looks like a bat, forms the central part of the floor of the cranium, unites the cranium and facial bones, and holds the pituitary gland

• Temporal Bones: Two bones that form the lower sides of the cranium and House hearing

• Ethmoid Bone: One bone that forms the nasal cavity

Facial Bones:

• 14 types of bones

• Nasal Bones: Two bones that support the superior portion of the nose

• Lacrimal Bones: Two bones for the medial wall of the eye socket of the nasal and eye cavity

• Zygomatic Bones: Two bones that form the cheek and lateral side of the eye socket

• Inferior Nasal Cavity: Two small bones along the inside of the nose

• Vomer: One bone that forms the lower back part of the nasal septum

• Mandible: One bone that makes up the lower jaw and is freely movable

• Maxilla: Two bones that make up the upper jaw

• Palentine Bones: Two bones that are the posterior portion of the hard pallet and contribute to the floor of the eye socket

Sutures:

• Coronal Suture: Attaches the frontal bone to the parietal bones

• Squamous Suture: On either side of the skull between the temporal and parietal bones

• Sagittal Suture: Joins the two parietal bones

• Lambdoid Suture: Arches across the posterior surface of the skull and separates the occipital bone from the two parietal bones

Cleft Pallet: A birth defect in the early stages of embryonic development where the right and left maxillary bones do not unite. It may involve incomplete fusion of the Palatine bones.

Paranasal Sinuses:

• Hollow portions of bones surrounding the nasal cavity

• Lightens the skull

• Amplify sounds made as we speak

  • Frontal

  • Ethmoid

  • Sphenoidal

  • Maxillary

Hyoid Bone:

• Closely related to the mandible and temporal bones

• The only bone that does not articulate with another bone

• It serves as a movable base for the tongue

• Aids in swallowing and speech

Fetal Skull:

• Large compared to the rest of the body

• ¼ body length compared to an adult skull

• Fontanels are fibrous membranes connecting the cranial bone

  • Allow skull compression during birth

  • Allow the brain to grow during later pregnancy and into early childhood

  • Convert to bone within 24 months of birth

Vertebral Column:

• Provides axial support

  • Extends from skull to pelvis

• Intervertebral discs separate 26 single vertebral bones

  • 7 cervical (neck): C-(#)

  • 12 thoracic (chest): T-(#)

  • 5 lumbar (low back): L-(#)

• Surrounded by fibrocartilage

• Nine vertebrae fuse to form two composite bones

  • Sacrum formed by the fusion of five vertebrae

  • Coccyx (tailbone) formed by fusion of 3-5 vertebrae

• Atlas: C1 helps move the head up and down

• Axis: C2 helps move the head from side to side

• Primary Curvature: Form a C-shaped curve (baby)

  • Spinal curve of the thoracic and sacral regions

  • Present from birth

• Secondary Curvature: Form a S-shaped curve (adult)

  • Spinal curve of the cervical and lumbar region

  • Developed after birth

Bony Thorax:

• Forms a cage to protect major organs

• It consists of 3 parts

  • True ribs (1-7)

  • False ribs (8-10)

  • Floating ribs (11-12)

• Thoracic vertebrae

Appendicular Skeleton:

• Made of 126 bones

  • Limbs (Appendages)

  • Pectoral Girdle

  • Pelvic Girdle

Pectoral Girdle:

• It is composed of two bones that attach the upper limb to the axial skeleton

  • Scapula

  • Clavicle

• Light, poorly reinforced girdle

• Allows upper limb a great deal of freedom

• AC Joint: Joins the clavicle and scapula

Upper Limb Bones:

• Humerus

  • Forms the arm

  • Single bone

  • Proximal end articulation

    • The head articulates with the glenoid cavity of the scapula

  • Distal end articulation

    • Trochlea and capitulum articulate with forearm bones

• The forearm had two bones

  • Ulna: Longer, medial bone in anatomical position

    • Proximal end articulation

    • The coronoid process and olecranon articulate with the humerus

  • Radius: Lateral bone in anatomical position

    • In between the Radius and Ulna is a connective tissue called the inter-osseous membrane

    • Allows extra support

Hand:

• Carpals: Wrist

  • Eight bones arranged in two rows of four bones in each hand

• Metacarpals: Palm

  • Five per hand

• Phalanges: Fingers and thumb

  • 14 per hand

  • Three bones per finger

  • Two thumb bones

Pelvic Girdle:

• Formed by two coaxial bones

• Composed of three pairs of fused bones

  • Ilium: Flares

  • Ischium: Sit on

  • Pubis

• Bony Pelvis: Sacrum and Coccyx

• The total weight of the upper body rests on the Pelvis

• Protects vital organs

  • Reproductive

  • Urinary bladder

  • Part of the large intestine

Female Pelvis:

• The inlet is larger and more circular

• The pelvis as a whole is shallower, and bones are thinner and lighter

• Ilia flares more laterally

• The sacrum is shorter and less curved

• Ischial spines are shorter and farther apart

• The pubic arch is more round

Femur:

• Heaviest and strongest bone

• Proximal end articulation

  • The head articulates with the acetabulum of the coxal (hip) bone

• Distal end articulation

  • Lateral and medial condyles articulate with the tibia in the lower leg

Lower Leg:

• Tiba: Shinbone; larger and medially oriented

  • Proximal end articulation

    • Medial and lateral joints articulate with the femur to form the knee joint

• Fibula: Thin and stick-like; lateral to the tibia

  • It has no role in forming the knee joint

• The Foot

  • Tarsals: 7 bones

    • Two largest tarsals

      • Calcaneus (Heel)

      • Talus

  • Metatarsals: 5 bones form the sole

  • Phalanges: 14 bones form the toes

• Foot arches

  • The bones of the foot are arranged to form 3 strong arches

    • 2 longitudinal

    • 1 transverse

Joints:

• Articulations

  • 2 or more bones meet

• Functions

  • Holds bones together

  • Allows mobility

• Classifications

  • Functionally

  • Structurally

• Fibrous

  • Generally Immovable

• Cartilaginous

  • Slightly movable

• Synovial

  • Freely movable

Fibrous:

• Bones unite by fibrous tissue

• Types

  • Sutures

    • Immobile

  • Syndesmoses

    • Allows more movement than sutures

  • Gomphosis

    • Immobile

Cartilaginous:

• Connected by fibrocartilage

• Types

  • Synchondrosis

    • Immobile

  • Symphysis (pubic and intervertebral)

    • Slightly movable

Synovial:

• Articulating bones are separated by joint cavity

• Synovial fluid is found in the cavity

• Features

  • Articular cartilage

  • Articular capsule

  • Joint cavity

  • Reinforcing ligaments

• Bursae: Flattened fibrous sack

  • Lined with synovial membrane and fluid

• Tendon Sheath

Synovial Joints:

• Plane joint

  • found in the wrist and ankles and allows side-to-side movement

• Hinge joint (Knee and Elbow)

  • Like a door hinge with back-and-forth movement

• Pivot joint (Altas and Axis)

  • It has a rounded end and one sleeve fits in another

• Saddle joint

  • Concave and convex ends and found in the thumb

• Ball and socket joint

  • Most freely movable synovial joint and meant to go 360 degrees, most susceptible to injury

Overview:

• Muscles are responsible for all types of body movement

• Three basic muscle types are found in the body

  • Skeletal

  • Cardiac

  • Smooth

• Skeletal and smooth muscle cells are elongated

• Contraction and shortening of muscles are due to the movement of microfilaments

  • Prefixes ‘Myo’ and ‘Mys’ refer to muscle

  • Prefix ‘Sarco’ refers to flesh

Skeletal Muscle:

• Tendons attach most to bones

• Cells are multinucleate

• Striated - Visible bonding

• Voluntary - Subject to conscious control

• Cells are surrounded and bundled by connective tissue

• Endomysium - Wraps around a fascicle of muscle fibers

• Epimysium - Covers the entire skeletal muscle

• Fascia - On the outside of the epimysium

  • Tendons - Cord-like structures

    • Mostly collagen fibers

    • Often cross a joint due to toughness and small size

  • Aponeuroses - Sheet-like structures

    • Attach muscles indirectly to bones, cartilage, or connective tissue coverings

• Sites of muscle attachment

  • Bones

  • Cartilage

  • Connective tissue coverings

Smooth Muscle:

• Lacks striation

• Spindle-shaped cells

• Single nucleus

• Involuntary - No conscious control

• Found mainly in the walls of hollow organs

Cardiac Muscles:

• Striations

• Usually has a single nucleus

• Branching cells

• Joined to another muscle cell at an intercalated disc

• Involuntary

• Found only in the walls of the heart

Skeletal Muscle Functions:

• Produce movement

• Maintain posture

• Stabilize joints

• Generate heat

• Myofibrils are aligned to give distinct bands

  • 1 band = light bands

    • It contains only thin filaments

  • A band = dark band

    • Contains the entire length of thick filaments

  • Sarcomere - Contractile unit of a muscle fiber

  • Organization of the sarcomere

    • Myofilaments

      • Thick filaments - Myosin filaments

      • Thin filaments - Actin filaments

• Thick filaments

  • It is composed of protein myosin

  • Has ATPase enzymes

  • Myosin and actin overlap somewhat

• Thin filaments

  • Anchored to the Z disc

Cutaneous Membrane: Covers the body - made up of three parts:

• Epidermis

• Dermis

• Subcutaneous Layer (Hypodermis)

Accessory Structure: Other coverings of the body besides the skin:

• Hair

• Nails

• Exocrine Glands

Protection: Protects from impact, chemicals, infection, loss of body fluids

Temperature Maintenance: Regulates heat gain and loss to the environment

Synthesis and Storage of Nutrients: Makes Vitamin D3 and has a large reserve of lipids in the Adipose tissue

Sensory Reception: The receptor detects touch, pressure, pain, and temperature and sends the information to the nervous system

Excretion and Secretion: Excretes salt, water, and organic waste as well as producing milk

Epidermis:

• Made of stratified squamous epithelium in different layers

• Cells take 2-4 weeks to move through all of the layers; they remain another 2 weeks in the outermost layer until they shed

Thick Skin:

• Composed of 5 layers

• Found on the palms of the hands and soles of the feet

• It could be 0.5mm thick

• Keratinocytes

Thin Skin:

• Composed of 4 layers

• Covers the rest of the body

• It could be 0.08mm thick

  Avascular: Nutrients are delivered through dermal ridges

Functions of Body Membranes:

• Covers body surfaces

• Line body cavity

• Form protective sheets around organs

• Classified as tissue types

Epithelial Tissue:

• Cutaneous - Skin

• Mucous

• Serous - Heart/Lungs

• Connective Membrane

  • Synovial - Joints

Cutaneous Membrane:

• Dry membrane

• Outermost protective boundary

• Superficial epidermis is composed of keratinized stratified squamous epithelium

• The underlying dermis is mostly dense (fibrous) connective tissue

Integumentary System includes:

• Skin

• Skin derivatives

  • Oil Glands

  • Hair

  • Nails

Protects deeper tissue from:

• Mechanical damage

• Chemical damage

• Bacterial damage

• UV radiation (sunlight)

• Thermal damage (Hot/Cold)

• Desiccation (Drying out)

  • Keratin protects the skin from water loss

  • Aids in loss or retention of body heat

  • Aids in excretion of urea and uric acid

  • Synthesizes Vitamin D

• Cutaneous sensory receptors detect touch, temperature, pain, and pressure

Subcutaneous Tissue:

• Not technically part of the skin

• Anchors skin to underlying organs

• Composed of adipose tissue

• serves as a shock absorber and insulates deeper tissues

Stratum Basale:

• The deepest layer of the epidermis

• Next to the dermis

• Cells undergo mitosis

• Wavy borderline

Melanin:

• Pigment (melanin) produced by melanocytes

• Color is yellow to brown to black

• Melanocytes are mostly in the stratum Basale

Intermediate Strata: Cells move from one layer to the next as they move their way to the outer surface of the skin (composed of strata spinosum, granulosum, and lucidum)

Epidermal Dendric Cells:

• Alert and activate immune cells to a threat

Merkel Cells:

• Associated with sensory nerve endings

• Serves as a touch receptor called Merkel discs

Stratum Spinosum:

• Made of cells displaced from the stratum germinativum

• Cells continue to divide and add to the thickness of the epidermis

Stratum Granulosum:

• Made of cells displaced from the stratum spinosum

• Cells have stopped dividing and make large amounts of Keratin (water-resistant protein)

• Keratin is used to make the skin water-resistant and durable

• Keratin is found in hair, calluses, and nails

Stratum Corneum:

• Most superficial layer

• 15-30 layers of dead, flattened cells with high levels of Keratin

• Surface is generally dry, so it discourages the growth of microorganisms

Skin Color:

• Determined by epidermal pigmentation and dermal blood supply

• Pigmentation

• Carotene

  • Orange-yellow pigment

  • Can be converted into Vitamin A which is important in the epithelial tissue and synthesizing photoreceptors in the eye

Dermis:

• Two layers

  • Papillary layers (projections called dermal papillae)

    • Some contain capillary loops

    • Others house pain receptors (Free nerve endings)

    • Fingerprints are identifying films of sweat

  • Reticular layer

    • Blood vessels

    • Sweat and oil glands

    • Deep pressure receptors (lamellar)

• Overall dermis structure

  • Collagen fibers give skin its toughness

  • Elastic fibers give skin elasticity

• Blood vessels play a role in body temperature regulation

• Nerve supply sends messages to the central nervous system

Redness: Due to embarrassment, inflammation, hypertension

Pallor: Emotional stress, anemia, impaired blood flow (Paleness)

Jaundice: Liver disorder

Bruises: Hematoma

Sebaceous (Oil) glands:

• Provide sebum

  • Lubricant for skin

  • Prevents brittle hair

  • Kills bacteria

• Most have ducts that empty into hair follicles, while others open directly onto skin surface

• Glands are activated at puberty

Sweat (Sudoriferous) glands:

• Produce sweat

• Widely distributed in the skin

Eccrine gland: Opens via a duct to pores on skin surface and produces sweat

Sweat:

• Composition

  • Mostly water

  • Salts and Vitamin C

  • Some metabolic waste

  • Fatty acid and proteins (apocrine only)

• Function

  • It helps dissipate excess heat

  • Excretes waste products

  • Acidic nature inhibits bacteria growth

• Odor is from associated bacteria

Apocrine gland:

• Ducts empty into hair follicles

• Begin to function at puberty

• Release sweat that also contains fatty acid and proteins (milky/yellow color)

Hair:

• Produced by hair follicle

• Root is enclosed in the follicle

• Shaft projects from the surface of the scalp or skin

• Consists of hard keratinized epithelial cells

• Melanocytes provide pigment for hair color

• Hair grows in the matric of the hair bulb in the stratum Basale

Hair Anatomy:

• Central medulla

• Cortex surrounds the medulla

• Cuticle on the outside of cortex

  • Most heavily keratinized region of hair

Associated Hair Structure:

• Hair follicle

  • Dermal and epidermal sheath surround hair root

• Arrector pilli muscle

  • Pulls hairs upright when a person is cold or frightened

Nail Structure:

• Free edge

• Body is a visible attached portion

• Nail folds are skin from nail matrix (growth)

• Root of nail is embedded in the skin

• Cuticle is the proximal nail for that project onto the nail body

Burns:

• Tissue damage and cell death caused by heat, electricity, UV radiation, or chemicals

• Associated dangers:

  • Dehydration

  • Electrolyte imbalance

  • Circulatory shock

• Results in loss of body fluids and invasion of bacteria

Rule of Nines:

• Way to determine extent of the burns

• Body is divided into 11 areas for quick estimation

• Each area represents 9% of total body surface area

  • The area surrounding the genitals represents 1% of body surface

First-degree burns:

• Only epidermis is damaged

• Skin is red and swollen

Second-degree Burns:

• Epidermis and upper dermis are damaged

• skin is red with blisters

Third-degree burns:

• Destroys entire skin layer

• Burned area is painless

• Requires skin graft

• Burn is gray, white, or black

Critical burns:

• Burns are considered critical if:

  • Over 25% of body has 2nd degree burns

  • Over 10% of body has 3rd degree burns

  • There is 3rd degree burns of hands, feet, or face

Cancer: Abnormal cell mass

Skin Cancer:

• Classified in 2 ways

  • Benign - does not spread

  • Malignant - metastasized (moves)

• Skin cancer is the most common type

Basal Cell Carcinoma:

• Least malignant

• Most common type

• Arises from stratum basale

Squamous Cell Carcinoma:

• Metastasized to lymph nodes if not removed

• Early removal allows a good chance of cure

• Arises from stratum spinosum

(Malignant) Melanoma:

• Most deadly skin cancer

• Cancer of melanocytes

• Metastasizes rapidly to lymph nodes/blood vessels

• Detection uses ABCD rule

A = Asymmetry

• 2 sides of pigmented more do not match

B = Borders of Irregularity

• Borders of mole are not smooth

C = Color

• Different colors in pigmented area

D = Diameter

• Spot is larger than 6mm in diameter

CENTRAL OR PERIPHERAL

• Sensory Input - Gathering information

  • To monitor changes occurring inside and outside the body

    • Changes = Stimuli

• Integration

  • To process and interpret sensory input and decide if action is needed

• Motor Output

  • Response to integrated stimuli

  • Activates muscles or glands

• Central Nervous System (CNS)

  • Organs

    • Brain

    • Spinal Cord

  • Function

    • Integration - Command center

    • Interpret incoming sensory info

    • Issues outgoing instructions

• Peripheral Nervous System (PNS)

  • Nerves extending from the brain and spinal cord

    • Spinal Nerves - Carry impulses to and from the spinal cord

    • Cranial Nerves - Carry impulses to and from the brain

  • Functions

    • Serve as communication lines among sensory organs

• Sensory (afferent) Division

  • Nerve fibers that carry information to the central nervous system

• Motor (efferent) Division

  • Nerve fibers that carry impulses away from the central nervous system

• Support cells in the CNS are grouped together as ‘neuroglia’

• General Functions

  • Support

  • Insulate

  • Protect Neurons

• Astrocytes

  • Abundant, start-shaped cells

  • Brace neurons

  • Form barrier between capillaries and neurons

  • Control the chemical environment of the brain

• Microglia

  • Spiderlike phagocytes

  • Dispose of debris

• Ependymal Cells

  • Line cavities of the brain and spinal cord

  • Cilia assist with circulation of cerebrospinal fluid

• Oligodendrocytes

  • Wrap around nerve fibers in the CNS

  • Produce Myelin Sheaths

• Satellite Cells

  • Protect neuron cell bodies

• Schwann Cells

  • Form myelin sheaths in the PNS

• Neurons = Nerve cells

  • Cells specialized to transmit messages

  • Major regions of neurons

    • Cell body - Nucleus and metabolic center of the cell

    • Processes - Fibers that extended from the cell body

  • Dendrites - Conduct impulses toward the cell body

    • Neurons may have hundreds of dendrites

  • Axons - Conduct impulses away from the cell body

    • Neurons have only one axon arising from the cell body at the axon hillock

• Axons

  • End in axon terminals

  • Axon terminals contain vesicles with neurotransmitters

    • Axon terminals are separated from the next neuron by a gap

      • Synaptic cleft - Gap between adjacent neurons

      • Synapse - Junction between nerves

• Myelin sheath - Whitish, fatty material covering axons

  • Schwann cells - Produce myelin sheaths in jelly roll-like fashion around axons (PNS)

    • Nodes of Ranvier - Gaps in myelin sheath along the axon

    • Oligodendrocytes - Produce myelin sheaths around axons of the CNS

• Sensory (afferent) neurons

  • Carry impulses from the sensory receptors to the CNS

• Motor (efferent) neurons

  • Carry impulses from the CNS to viscera, muscles, or glands

• Interneurons (Association neurons)

  • Found in neural pathways in the CNS

  • Connect sensory and motor neurons

• Reflex - Rapid, predictable, and involuntary response to a stimulus

  • Occurs over pathways called reflex arcs

• Reflex arc - Direct route from a sensory neuron to an interneuron, to an effector

• Somatic reflexes

  • Stimulate the skeletal muscles

    (i.e. - Pull hand away from hot object)

• Autonomic reflex

  • Regulate the activity of smooth muscles, the heart, and glands

    (i.e. - regulation of smooth muscles, heart, and bp)

Brain:

• No more neurons are formed after birth

• Regions

  • Cerebral hemispheres (Cerebrum)

  • Diencephalon

  • Brain Stem

  • Cerebellum

• Cerebral Hemispheres

  • Paired (Left and Right) superior parts of the brain

  • Includes more than half of the brain mass

  • The surface is made of ridges (Gyri) and grooves (Sulci)

• Lobes of the Cerebrum

  • Fissures (Deep Grooves) divide the cerebrum

    • Surface lobes of the cerebrum

      • Frontal Lobe

      • Parietal Lobe

      • Occipital Lobe

      • Temporal Lobe

Cerebrum:

• Specialized areas

  • Primary somatic sensory area

    • Receives impulses from the body’s sensory receptors

    • Located in parietal lobe

  • Primary motor area

    • Sends impulses to skeletal muscles

    • Located in frontal lobe

  • Broca’s area - Ability to speak

• Cerebral areas involved in special senses

  • Gustatory area (Taste)

  • Visual area

  • Auditory area

  • Olfactory area (Smell)

• Interpretation areas

  • Speech / language region

  • Language comprehension region

  • General interpretation area

• Layers of the cerebrum

  • Gray matter - Outer layer in the cerebral cortex and composed of mostly neuron cell bodies

  • White matter - Fiber tracts deep to the gray matter

    • Corpus Callosum - Connects hemispheres

  • Basal Nuclei - Islands of gray matter buried within white matter

Diencephalon:

• Sits on top of the brain stem

• Enclosed by the cerebral hemispheres

• Made of 3 parts

  • Thalamus

  • Hypothalamus

  • Epithalamus

Thalamus: Surrounds the 3rd ventricle

• Relay station for sensory impulses

• Transfers impulses to the correct part of the cortex for localization and interpretation

Hypothalamus:

• Under the thalamus

• Important autonomic nervous system center

  • Helps regulate body temperature

  • Controls water balance

  • Regulates metabolism

• Houses limbic center

Epithalamus:

• Forms the root of the 3rd ventricle

• Houses the pineal body (Endo gland)

• Includes the Corid plexus - Forms the cerebrospinal fluid

Brain Stem:

• Attaches to the spinal cord

• Parts of the brain stem

  • Midbrain

  • Pons

  • Medulla Oblongata

• Midbrain

  • Mostly composed of tracts of nerve fibers

    (Reflex centers for vision / hearing)

• Pons

  • Bulging center part of the brain stem

  • Mostly composed of fiber tracts

  • Includes nuclei involved

• Medulla Oblongata

  • Lowest part of the brain stem

  • Merges into the spinal cord

  • Includes important fiber tracts

  • Contains important control centers

  • Heart rate control

  • Blood pressure regulation

  • Breathing

  • Swallowing

  • Vomiting

Cerebellum:

• 2 hemispheres with convoluted surfaces

• Provides involuntary coordination of body movements

Protection:

• Scalp / skin

• Skull / vertebral column

• Meninges

• Cerebrospinal fluid (CSF)

• Blood-brain barrier

Meninges:

• Dura matter

• Tough, outermost layer

• Double-layered external covering

• Periosteum - Attached to inner surface of the skull

• Meningeal layer - Outer covering of the brain

• Folders inwards in several areas

• Arachnoid layer

  • Middle layer

  • Web-like extensions span the subarachnoid space

  • Arachnoid villi reabsorb cerebrospinal fluid

• Pia mater

  • Internal layer

  • Clings to surface of the brain

Cerebrospinal Fluid (CSF):

• Similar to blood plasma composition

• Formed by the choroid plexus

  • Choroid plexus - Capillaries in the ventricles of the brain

• Forms a watery cushion to protect the brain

Hydrocephalus:

• CSF accumulated and exerted pressure on the brain if not allowed to drain

• Possible in an infant because the skull bones are not fused yet

• In adults, this situation results in brain damage

Blood-Brain Barrier:

• Includes the least permeable capillaries of the body

• Excluded many potentially harmful substances

• Useless as a barrier against some substances

  • Respiratory gases

  • Alcohol

  • Nicotine

  • Anesthesia

Traumatic Brain Injury (TBI):

• Concussion

  • Slight brain injury

  • No permanent brain damage

• Contusion

  • Nervous tissue destruction occurs

  • Nervous tissue does not regenerate

• Cerebral Edema

  • Swelling from the inflammatory response

  • May compress and kill brain tissue

CVA / Stroke:

• Result from a ruptured blood vessel supplying a region of the brain

• Brain tissue supplied with oxygen from that blood source dies

• Loss of some functions or death may result

  • Hemiplegia - One-sided paralysis

  • Aphasia - Damage to speech center in left hemisphere

  • Trans ischemia attack (TIA) - Temporary brain ischemia (Restriction of blood flow)

    • Warning signs for more severe CVA

Alzheimer’s Disease:

• Progressive degenerative brain tissue

• Mostly seen in the elderly, but may begin in middle age

• Structural changes in the brain include abnormal protein deposit and twisted fibers

Multiple Sclerosis (MS):

• Anyone can get it

• Deterioration of the myelin sheath

• Auto-immune disease where the immune system attacks the myelin sheath of nerve cells

• Can lead to paralysis

• Can be slowed down with immuno-suppressants

Meningitis:

• Inflammation of the meningeal layer of the brain

Spinal Cord:

• Extends from foramen magnum of the skull to the first or second lumbar vertebra

• Provides a 2-way conduction pathway to and from the brain

• 31 pairs of spinal nerves arise from the spinal cord

• Cauda Equina

• Internal gray matter is mostly cell bodies

  • Dorsal (posterior) horns

  • Anterior (ventral) horns

  • Gray matter surrounds the central canal

    • Central canal is filled with CSF

• Meninges cover the spinal cord

• Spinal nerves cover leave at each level of the vertebrae

Peripheral Nervous System (PNS):

• Mixed nerves

  • Both sensory and motor

• Sensory nerves

  • Carry impulses towards the CNS

• Motor nerves

  • Carry impulses away from the CNS

Cranial Nerves:

• Oh - Olfactory

• Oh - Optic

• Oh - Oculomotor

• To - Trochlear

• Touch - Trigeminal

• And - Abducens

• Feel - Facial

• Very - Vestibulocochlear

• Green - Glossopharyngeal

• Vegetables - Vagus

• A - Accessory

• H - Hypoglossal

• 12 pairs of nerves tat mostly serve the head and neck

• Only the pair of vagus nerves extend to thoracic and abdominal cavities

• Most are mixed nerves, but 3 are sensory only

• I Olfactory - Sensory for smell

• II Optic - Sensory for vision

• III Oculomotor - Motor fibers to the eye muscles

• IV Trochlear - Motor fibers to one eye muscle

• V Trigeminal - Sensory for face (chewing)

• VI Abducens - Motor fibers to eye muscles

• VII Facial - Sensory for taste

• VIII Vestibulocochlear - Sensory for balance and hearing

• IX Glossopharyngeal - Sensory for taste (throat)

• X Vagus - Sensory and motor fibers for pharynx, larynx, and viscera

• XI Accessory - Motor fibers to neck and upper back

• XII Hypoglossal - Motor fibers to the tongue

Spinal Nerves:

• There is a pair of spinal nerves at the level of each vertebra for a total of 31 pairs

• Formed by the combination of ventral and dorsal root of the spinal cord

• Named for the region from which they arise

• Spinal nerves divide soon after leaving the spinal cord

• Ramus - Branch of a spinal nerve; contains both motor and sensory fibers

  • Dorsal Rami - Serve the skin and muscles of the posterior trunk

  • Ventral Rami - Form a complex of networks (plexus)

• Plexus - Network of nerves serving motor and sensory needs of limbs

• Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions

  • Cervical - Shoulders / Neck

  • Brachial - Arm / Hand

  • Lumbar - Lower abdominal / Legs (thighs)

  • Sacral - Lower leg / Hip

The Senses:

• Smell

• Taste

• Sight

• Hearing

• Equilibrium

Eye and Vision:

• 70% of all sensory receptors are in the eyes

• Each eye has over one million nerve fibers

• Protection for the eye

  • Most of the eye is enclosed in a bony orbit

  • A cushion of fat surrounds most of the eye

Accessory Structures:

• Eyelids and eyelashes

• Conjunctiva

• Lacrimal apparatus

• Extrinsic eye muscles

• Eyelids

  • Meet at the medial and lateral commissure (Canthus)

• Eyelashes

  • Tarsal glands produce an oily secretion that lubricated the eye (Mohebian Gland)

  • Ciliary glands are located between the eyelashes

• Conjunctiva (Pink eye)

  • Membrane that lines the eyelids

  • Connects to the outer surface of the eye

  • Secretes mucus to lubricate the eye and keep it moist

• Lacrimal apparatus - Lacrimal gland and ducts

  • Lacrimal gland - Produces lacrimal fluid; situated on later aspect of each eye

  • Lacrimal canaliculi - Drain lacrimal fluid from eyes medially

  • Lacrimal sac - Provides passage of lacrimal fluid toward nasal cavity

  • Nasolacrimal duct - Empties lacrimal fluid into the nasal cavity

  • Functions:

    • Protects, moistens, and lubricates the eye

    • Empties into the nasal cavity

      • Lacrimal secretions (tears) contain:

        • Dilute salt solution

        • Mucus

        • Antibodies

        • Lysozyme (Enzyme that destroys bacteria)

• Excentric eye muscles

  • Six muscles attach to the outer surface of the eye

  • Produce eye movements

Structure:

• Layers forming the wall of the eyeball

  • Fibrous layer - Outside layer

  • Vascular layer - Middle layer

  • Sensory layer - Inside layer

• Humors are fluids that fill the interior of the eyeball

• Fibrous layer

  • Sclera

    • White connective tissue layer

    • Seen anteriorly as the white of the eye

  • Cornea

    • Transparent, central anterior portion

    • Allows for light to pass through

    • Repairs itself easily

    • The only human tissue that can be transplanted without fear of rejection

• Vascular layer

  • Choroid is a blood-rich nutritive layer in the posterior of the eye

    • Pigment prevents light from scattering

  • Modified anteriorly into 2 structures

    • Ciliary body - Smooth muscle attached to the lens by ciliary zonule (Suspensory ligament)

    • Iris - Regulates amount of light entering the eye

      • Pigmented layer that gives eye color

      • Pupil - Rounded opening in the iris

• Sensory layer

  • Retina contains two layers

    • Outer pigmented layer absorbs light and prevents it from scattering

    • Inner neural layer

      • Contains receptor cells (photoreceptors)

        • Rods

        • Cones

  • Signals pass from photoreceptors via a two-neuron chain

    • Bipolar neurons

    • Ganglion cells

  • Signals leave the retina toward the brain through the optic nerve

  • Optic disc (blind spot) is where the optic nerve leaves the eyeball

    • Cannot see images focused on the optic disc

  • Neurons of the retina and vision

    • Rods

      • Most are found toward the edges of the retina

      • Allow vision in dim light and peripheral vision

      • All perception is in gray tones

    • Cones

      • Allow for detailed color vision

      • Densest in the center of the retina

      • Fovea centralis - Lateral to the blind spot

        • Area of the retina with only cones

        • Visual acuity (sharpest version) is here

  • No photoreceptor cells are at the optic disc, or blind spot

  • Cone sensitivity

    • Three types of cones

    • Different cones are sensitive to different wavelengths

    • Color blindness is the result of the lack of one cone type

Lens:

• Biconvex crystal-like structure

• Held in place by a suspensory ligament attached to the ciliary body

• Cataracts result when the lens becomes hard and opaque with age

  • Vision becomes hazy and disoriented

  • Eventually causes blindness in affected eye

• Risk factors include:

  • Diabetes mellitus

  • Frequent exposure to intense light

  • Heavy smoking

Chambers of the Eye:

• Lens divides the eye into two chambers:

  • Anterior (aqueous) segment

    • Anterior to the lens

    • Contains aqueous humor

  • Posterior (vitreous) segment

    • Posterior to the lens

    • Contains vitreous humor

Anterior Segment:

• Watery fluid found between lens and cornea

• Similar to blood plasma

• Helps maintain intraocular pressure

• Provides nutrients for the lens and cornea

• Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm

Posterior Segment:

• Gel-like substance posterior to the lens

• Prevents the eye from collapsing

• Helps maintain intraocular pressure

Ophthalmoscope:

• Instrument used to illuminate the interior of the eyeball and fundus (posterior wall)

• Can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina

Pathway of Light:

• Light must be focuses to a point on the retina for optimal vision

• Light is bet, or refracted, by the cornea, aqueous humor, lens, and vitreous humor

• The eye is set for distance vision (over 20 feet)

• Accommodation - the lens must change shape to focus on closer objects (less that 20 feet away)

• Image formed on the retina is a real image

• Real images are:

  • Reversed from left to right

  • Upside down

  • Smaller than the object

• The pathway of light through the eye:

  • Cornea

  • Aqueous Humor

  • Pupil

  • Aqueous Humor

  • Lens

  • Vitreous Humor

  • Retina

Visual Fields and Pathways:

• Optic chiasma

  • Location where the optic nerves cross

  • Fibers from the medial side of each eye cross over the opposite side of the brain

• Optic tracts

  • Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye

• Overlap of the visual fields, and inputs from both eyes to each optic cortex provide for depth perception

Pathway of Nerves:

• The pathway of nerve impulses from the retina of the eye into the brain:

  • Optic nerve

  • Optic chiasma

  • Optic tract

  • Thalamus

  • Optic radiation

  • Visual cortex in occipital lobe of brain

Eye Reflexes:

• Internal muscles are controlled by the autonomic nervous system

  • Photopupillary reflex: Bright light causes pupils to constrict through action of radial, circular, and ciliary muscles

  • Accommodation Pupillary Reflex: Viewing close objects causes accommodation

• Viewing close objects causes convergence (eyes moving medially)

A Closer Look:

• Emmetropia - Eye focuses images correctly on the retina

• Myopia (nearsightedness)

  • Distant objects appear blurry

  • Light from those objects fails to each the retina and are focused in front of it

  • Results from an eyeball that is too long

• Hyperopia (farsightedness)

  • Near objects are blurry, whereas distant objects are clear

  • Distant objects are focused behind the retina

  • Results from an eyeball that is too short or from a ‘lazy lens’

• Astigmatism

  • Images are blurry

  • Results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens

Homeostatic Imbalances:

• Night blindness - Inhibited rod function that hinders the ability to see at night

• Color blindness - Genetic conditions that results in the inability to see certain colors

  • Due to lack of one type of cone (partial color blindness)

• Glaucoma - Can cause blindness due to increasing pressure within the eye

• Hemianopia - Loss of the same side of the visual field of both eyes; results from damage to the visual cortex on one side only