Skin, Skeleton, Muscle, and the Brain in Detail
Unit 1: Anatomy and Physiology. Lesson 6 of 60 in CBET Academy.
The exam's anatomy questions go one level deeper than "the heart pumps." They ask which layer of skin is deepest, which muscle type is not striated, where the parathyroid sits, and which part of the brain interprets sensation. This lesson supplies that level.
The integumentary system
Skin, hair, nails, and glands. Three layers, from the outside in: the epidermis (its innermost layer is the stratum basale, where new cells are born), the dermis (blood vessels, nerves, hair follicles, sweat and sebaceous glands), and the hypodermis (subcutaneous fat, technically beneath the skin but part of the system). Sebaceous glands secrete sebum, an oil that waterproofs the skin; sweat glands cool the body and excrete waste. Sensory receptors report pain, touch, pressure, and temperature. Skin makes vitamin D under ultraviolet light and absorbs some drugs, which is how transdermal patches work.
Muscle tissue
Three types, sharing excitability, contraction, and elongation:
- Skeletal: voluntary, striated (striped under a microscope), attached to bone, works in opposing pairs to move joints as levers.
- Cardiac: involuntary, striated, only in the heart.
- Smooth: involuntary, not striated, in the walls of hollow organs (stomach, intestines, bladder, uterus, blood vessels) and in sphincters. Smooth muscle is the one with a "disorderly" filament arrangement.
About 600 muscles in the body.
The skeleton
206 bones in the adult. The axial skeleton (80 bones) is the skull, vertebral column (33 vertebrae: cervical, thoracic, lumbar, sacral, coccygeal), rib cage (12 pairs, the sternum's manubrium, body, and xiphoid process), the middle-ear ossicles, and the hyoid bone that anchors the tongue. The appendicular skeleton (126 bones) is the pectoral girdle (scapula and clavicle), the pelvic girdle, and the limbs: humerus, radius, ulna, carpals, metacarpals, phalanges in the arm; femur, patella, tibia, fibula, tarsals, metatarsals, phalanges in the leg. Tendons join muscle to bone; ligaments join bone to bone; cartilage cushions joints.
The brain, region by region
Neurons pass signals as action potentials and hand them to the next cell across a synapse by releasing a chemical. The brain has three divisions:
- Forebrain: the cerebrum (two hemispheres joined by the corpus callosum, outer cortex of gray matter) with four lobes: frontal (planning, judgment, working memory, voluntary movement), parietal (sensory input and spatial sense; where sensation is interpreted), occipital (vision), temporal (hearing). The thalamus relays sensory signals and regulates sleep; the hypothalamus links the nervous system to the pituitary and controls temperature, hunger, and hormones.
- Midbrain: relays vision and hearing signals; sits above the pons.
- Hindbrain: the cerebellum (balance, coordination, smooth repetitive movement), the pons (relay and autonomic functions), and the medulla oblongata (breathing, heart rate, blood pressure).
The brain stem is the midbrain, pons, and medulla together; it connects to the spinal cord and keeps you alive without thinking.
Peripheral nerves, two ways to split them
The somatic system controls voluntary skeletal muscle (walking, typing). The autonomic system runs involuntary functions, with the sympathetic branch for fight or flight and the parasympathetic branch for rest and digest.
Skin, Skeleton, Muscle, and the Brain in Detail, explained slowly
Why the exam goes this deep
The anatomy section is only seven percent of the test, but its questions are cheap points if you know a layer of detail beyond the device connection. They are written like a biology quiz: which layer is deepest, which muscle is not striated, where a gland sits, which lobe does what. Treat the body as a building with named floors and rooms.
Skin, in layers
layer what is in it technician's angle epidermis dead outer cells; stratum basale at its base makes new ones the high-impedance barrier electrodes must cross dermis blood vessels, nerves, sweat and sebaceous glands, follicles where burns and pressure injuries happen hypodermis subcutaneous fat; deepest; anchors skin to muscle insulation and padding; the deepest layer on the exam
Sebaceous glands make oil; sweat glands cool and excrete; receptors report pain, touch, pressure, temperature; ultraviolet light makes vitamin D; some drugs cross the skin (patches).
Muscle, three kinds
type voluntary? striated? where note skeletal yes yes attached to bone, works in pairs about 600; levers around joints cardiac no yes heart only electrically self-driven smooth no no hollow organ walls, vessels, sphincters "disorderly" filaments; the uterus is smooth muscle
Common traps: the uterus and bladder are smooth (not striated); the quadriceps, triceps, and gastrocnemius are striated skeletal muscle.
Skeleton, by count
division bones contents axial 80 skull, 33 vertebrae (cervical, thoracic, lumbar, sacral, coccygeal), 12 rib pairs, sternum (manubrium, body, xiphoid), ossicles, hyoid appendicular 126 pectoral girdle (scapula, clavicle), pelvic girdle, arms (humerus, radius, ulna, carpals, metacarpals, phalanges), legs (femur, patella, tibia, fibula, tarsals, metatarsals, phalanges) total 206
The hyoid anchors the tongue; the ossicles are the three tiny bones of the middle ear; the xiphoid is the tip of the sternum that CPR hand placement avoids.
The brain as a building
division parts jobs forebrain cerebrum (frontal, parietal, occipital, temporal lobes), thalamus, hypothalamus thinking, sensing, seeing, hearing; relaying; hormones and temperature midbrain tectum, tegmentum vision and hearing relay; above the pons hindbrain cerebellum, pons, medulla coordination and balance; relay; breathing, heart rate, blood pressure brain stem midbrain + pons + medulla the trunk line to the spinal cord; keeps you alive
Lobe jobs: frontal plans and moves, parietal senses and locates the body in space, occipital sees, temporal hears. The parietal lobe is the answer to "where is sensory information interpreted." The cerebellum's failure shows as clumsy, uncoordinated movement and tremor.
Nerves, two splits
Central (brain and spinal cord) versus peripheral (everything else). Within the peripheral: somatic (voluntary skeletal muscle, such as walking) versus autonomic (involuntary), and within autonomic: sympathetic (fight or flight) versus parasympathetic (rest and digest). Neurons signal by action potentials and hand off at synapses.
Worked examples
- "Which layer of the integumentary system is deepest?" Hypodermis (the stratum basale is the deepest part of the epidermis only).
- "Which muscle has filaments arranged in a disorderly manner?" Smooth.
- "Which of these is not striated: quadriceps, uterus, triceps, gastrocnemius?" Uterus.
- "Which nervous system controls walking?" Somatic.
- "Within which part of the brain is sensory information interpreted?" The cerebrum (parietal lobe).
What to memorize
- Epidermis, dermis, hypodermis; stratum basale; sebaceous oil, sweat cooling, vitamin D.
- Skeletal striated voluntary, cardiac striated involuntary, smooth non-striated involuntary.
- 206 bones, 80 axial, 126 appendicular; the named bones.
- Forebrain, midbrain, hindbrain; lobe jobs; thalamus relay; hypothalamus to pituitary; cerebellum coordination; medulla vital functions; brain stem.
- Somatic voluntary; autonomic sympathetic and parasympathetic.