IX. Anatomy

Key focus of this chapter: 4 types of tissues

This chapter focuses on 4 types of tissues and gives concise summaries of the important things about glands in tissue cells, skeletal muscles, bone, ear, and eye.

A. Tissues

Groups of similar cells and their extracellular material organized to perform a common function

1. Four types of tissues

a. Epithelial

Covers body surfaces and lines organs and cavities; functions include protection, secretion, and absorption

Simple epithelium has one cell layer; stratified epithelium has two or more cell layers
Cuboidal epithelial cells are roughly cube shaped; squamous epithelial cells are flat

b. Connective

Functions to transport, support, connect, and protect the other three kinds of tissue

Types – Cartilage, bone, and blood

c. Muscle

Contains contractile cells that generate force for movement and other functions

Types – Smooth muscle, skeletal muscle, and cardiac muscle

d. Nerve

Receives and transmits signals in the central and peripheral nervous systems

Found in the brain, spinal cord, and peripheral nerves; includes neurons and supporting glial cells
Gray matter contains many neuronal cell bodies and synapses; white matter contains bundles of myelinated axons

2. Features and functions of each tissue

Tissues	Classification	Shapes	Features and functions
Epithelial	Cuboidal epithelia		• Cube shape • Lines many ducts and forms secretory portions of some glands
	Columnar epithelia		• Column and elongated shapes • Lines much of the digestive tract; specialized cells secrete and absorb substances
	Squamous epithelia		• Flat shape • Simple squamous epithelium lines alveoli, permitting gas diffusion
Connective	Cartilage		• Different cartilage types occur at joints, the external ear, nose, larynx, trachea, and bronchi • Chondrocytes maintain a collagen- and proteoglycan-rich matrix that provides support and resists compression • Avascular form
	Bone		• Supports body of vertebrates • Osteocytes – bone cells • Mineralized matrix, chiefly calcium phosphate, provides rigidity
	Blood		• Platelets – clotting aid • Leukocytes – white blood cells, immunity aid • Plasma – liquid matrix • Erythrocytes – red blood cells, carry oxygen, lack nuclei
	Fibrous connective tissue		• Tendons attach muscle to bone; the origin is generally the less mobile attachment and the insertion the more mobile attachment • Ligaments – connects bone to bone
Muscle	Skeletal muscle		• Voluntary and striated muscle • Muscle fibers contain actin and myosin filaments and multiple nuclei • Sarcomeres – Contractile units • Myofibrils are bundles of contractile filaments within muscle fibers
	Cardiac muscle		• Found in wall of heart • Involuntary and striated muscle • Branched cells • Intercalated discs mechanically and electrically connect adjacent cardiac muscle cells
	Smooth muscle		• Found in digestive tract, arteries, urinary bladder • Involuntary and not striated muscle • Thin and elongated cells with spindle shape

B. Glands in tissue cells

1. Exocrine gland

Release products through ducts onto epithelial surfaces, including the skin and the lumen of organs
Eg/ Sweat gland, mammary gland, salivary gland

2. Endocrine gland

Release hormones into interstitial fluid, from which they enter the bloodstream
Eg/ Adrenal gland, pituitary gland, thyroid gland

Sweating and changes in skin blood flow contribute to thermoregulation

C. Skeletal muscles

1. Structure of skeletal muscle

a. Sliding filament model of muscle contraction

Myofibril contains repeated sarcomeres
During contraction, thin (actin) filaments slide past thick (myosin) filaments, increasing their overlap
Thick filaments are anchored near the M line; thin filaments attach to Z discs
During muscle contraction, the width of I band and H zone are reduced but the width of A band is not changed

b. The process of the contraction of a skeletal muscle fiber

Acetylcholine (ACh) is released from synaptic terminal of motor neuron
Acetylcholine (ACh) is bound to ACh receptors on muscle fiber’s plasma membrane
Action potential spreads along sarcolemma and goes down T tubules
The action potential triggers Ca²⁺ release from the sarcoplasmic reticulum (SR) into the cytosol
Ca²⁺ binds to troponin, moving tropomyosin to expose myosin-binding sites on actin
Myosin heads bind to actin and pull thin filaments; ATP binding causes detachment so the cycle can repeat
After stimulation ends, Ca²⁺ is pumped back into the SR, dissociates from troponin, and the fiber relaxes

2. Neural control

a. Tetanus

Continuous muscular contraction

Summation of tension

At sufficiently high stimulation frequencies, individual twitches fuse into a sustained tetanic contraction.

Motor unit – one motor neuron and all the muscle fibers it innervates
Twitch – brief contraction and relaxation in response to a single stimulus
Muscle tone – low-level, involuntary tension present in a resting muscle

b. Isometric and isotonic muscle contractions

Isometric contraction – tension develops while overall muscle length remains approximately constant
Isotonic contraction – the muscle changes length while generating tension against a load

D. Bone

1. Functions

Blood cell production in red bone marrow
Framework for movement
Protection of organs

2. Bones of human skeleton

Axial skeleton

– Skull, vertebra, sternum, rib

Appendicular skeleton

– Arm bones: humerus, radius, ulna

– Hand bones: Carpals, phalanges, metacarpals

– Leg bones: femur, patella, tibia, fibula

– Foot bones: tarsals, metatarsals, phalanges

3. Structure of bone

Classification	Functions and features
Osteoclast	• Resorbs bone matrix, releasing calcium and phosphate into extracellular fluid
Osteoblast	• Produces osteoid and promotes mineral deposition during bone formation
Osteocyte	• Mature cell derived from an osteoblast; maintains bone matrix and senses mechanical strain
Haversian canal	• Central canal of an osteon containing blood vessels and nerves
Epiphyseal plates	• Cartilaginous growth plates near the ends of growing long bones, between epiphysis and diaphysis

E. Ear

1. Processing sound information

2. Structure of ear

a. Outer ear

Collects outside sounds
Consists of pinna and auditory canal

b. Middle ear (Ossicles)

Ossicles transmit and amplify eardrum vibrations toward the oval window
Contains three small bones: malleus, incus, and stapes

c. Inner ear

Fluid – filled chambers
Consists of semicircular canals and cochlea

Classification		Functions and features
Outer ear	Pinna	• Collecting sound
Outer ear	Auditory canal	• Transmission of sound to tympanic membrane
Tympanic membrane		• Eardrum • Dividing outer ear from middle ear • Transmission of sound to middle ear
Middle ear (Ossicles)	Malleus	• Hammer shaped small bone
	Incus	• Anvil shaped small bone
	Stapes	• Stirrup shaped small bone
Inner ear	Semicircular canals	• Three semicircular canals • Detect rotational movements of the head
Inner ear	Cochlea	• Hair cells transduce sound vibrations; different cochlear regions respond to different frequencies
Auditory nerve		• Transmission of sound signals to brain

F. Eye

1. Structure of eye

Classification	Functions and features
Sclera	• Tough white outer fibrous layer of the eye
Cornea	• Transparent anterior part of the fibrous outer coat of the eye • Admits and refracts incoming light
Choroid	• Inner pigmented vascular layer
Retina	• Innermost neural layer containing rod and cone photoreceptors
Iris	• Controls the amount of light by regulating pupil size
Pupil	• Opening in the center of the iris through which light enters
Lens	• Focuses light on the retina
Aqueous humor	• Clear fluid filling the anterior and posterior chambers in front of the lens
Vitreous humor	• Transparent gel filling the large cavity behind the lens
Optic disk	• Lacks photoreceptors, creating the blind spot • Site where retinal ganglion cell axons leave the eye as the optic nerve

2. Light response in retina

a. Rod and cone cells

Rod cells – sensitive in dim light; support low-light, non-color vision
Cone cells – support color vision and high acuity in brighter light

b. Light and dark responses

Response in light

– Activated photopigments (rhodopsin in rods)

– cGMP-gated Na⁺ channels close

– Rod and cone cells hyperpolarize

– Glutamate release decreases

Response in dark

– Photopigments are not activated by light

– cGMP-gated Na⁺ channels remain open

– Rod and cone cells remain relatively depolarized

– Glutamate is released continuously