Human Embryology Study Guide PDF

HUMAN EMBRYOLOGY I. Period of the Ovum (0 - 2 weeks) Germinal Period: WEEK 1 Fertilization - a sperm cell penetrates an egg cell, creating a zygote, a fertilized egg cell Cleavage - forms a ball of around...

HUMAN EMBRYOLOGY I. Period of the Ovum (0 - 2 weeks) Germinal Period: WEEK 1 Fertilization - a sperm cell penetrates an egg cell, creating a zygote, a fertilized egg cell Cleavage - forms a ball of around 16 - 32 cells known as a morula Blastocyst - forms after the morula continues to divide & develop; consists of: a. Embryoblast - inner cell mass b. Trophoblast - outer cell layer WEEK 2 Adplantation - initial adhesion to uterine epithelium Implantation - happens at the uterine wall Embedding - blastocyst embeds itself Coagulation Plug - forms at the site where implantation occurs II. Period of the Embryo (2 weeks - 2 months) WEEK 3 Fertilization - a sperm cell penetrates an egg cell, creating a zygote, a fertilized egg cell Cleavage - forms a ball of around 16 - 32 cells known as a morula Blastocyst - forms after the morula continues to divide & develop; consists of: c. Embryoblast - inner cell mass d. Trophoblast - outer cell layer WEEK 4 Adplantation - initial adhesion to uterine epithelium Implantation - happens at the uterine wall Embedding - blastocyst embeds itself Coagulation Plug - forms at the site where implantation occurs WEEK 5 Size of Embryo: 2mm long (poppy seed) Nervous System - developing Heart - has blood vessels; blood begins to circulate Neural tube - baby’s brain & spinal cord WEEK 6 Size: 6mm (pea) Tiny dents that will be arms and legs; dents form: ears Bump: heart; bulge: head WEEK 7 Size: 10 mm, “crown-rump length” Brain: grows faster than the body Inner ear - start to develop Cartilage: arms & legs begin to form WEEK 8 Size: 16mm (raspberry) Head begins to uncurl Arms grow longer, bigger than legs Legs begin to form Embryo turns into a “fetus” (Latin for offspring) III. Period of the Fetus (2 months - birth) Fetal Period WEEK 9 Size: 22mm long Development of face, limbs, and internal organs Body begins to look more human Cartilage begins to develop into bones WEEK 10 “Fetal Developmental Stage” (transition from embryo - fetus) Size: 30mm Organogenesis - development of internal organs by the: - Ectoderm - nervous system, skin - Mesoderm - muscle, skeleton, kidneys, reproductive system - Endoderm - endocrine glands, lungs, digestive tract, liver WEEK 11 Development and refinement of the fetus’s features Size: 41mm WEEK 12 Completion of 1st trimester Size: 5.4cm Internal organs and muscles have developed Digestive system - more functional Kidneys - functioning; fetus drinks and peed amniotic fluid WEEK 13 Beginning of 2nd trimester Size: 7.4cm Bone ossification - bone formation WEEK 14 Skin starts to thicken Fetal bones: cartilage → bone Fingerprints are formed WEEK 15 Fetus develops hearing Size: 10.1cm Body is covered in lanugo - soft, fine hair Has light sensitivity and is about to develop hearing Organs: in permanent location WEEK 16 Fetus develops ears and lips WEEK 17 Fetus reacts to different noises Skin is covered in vernix - biofilm, protects newborn skin WEEK 18 Fetus’ reflexes develop Size: 14.2cm Hearing, feeling, swallowing, and sucking reflexes develop WEEK 19 Fetus gains some weight Size: 15.3cm WEEK 20 Fetus’ senses develops Size: 25.6cm WEEK 21 Fetus grows some hair Size: 26.7cm Bone marrow - helps produce blood WEEK 22 Fetus’ grasp is getting stronger Size: 27.8cm, 1lb Testes begin to descend Taste buds develop WEEK 23 Brain activity is growing Size: 28.9cm Limbs are proportionate Baby becomes more active, causing kicking movements WEEK 24 Baby’s skin is wrinkled, translucent Size: 30cm, 1⅓ lbs WEEK 25 Baby grows more hair Size: 34.6cm Responds to familiar sounds by moving Rapid Eye Movement in sleep WEEK 26 Baby’s lungs develop more Size: 35.6cm, 2 lbs Lungs produce surfactant - allows air sacs to inflate properly & prevents them from collapsing Eyes start to open WEEK 27 2nd trimester ends Size: 36.6cm Nervous system - matures Skin - smoother Lungs - can breathe WEEK 28 3rd trimester Size: 37.6 2¼ lbs Eyelashes form Heartbeat can be heard through a stethoscope WEEK 29 Baby’s kicks and punches feel more evident Regular activity cycles emerge (movement once a minute) WEEK 30 Size: 10 ½ in, 3 lbs Eyes can open wide Bone marrow begin to form red blood cells WEEK 31 Major developments finished Rapid weight gain begins Baby can process more information & stimuli WEEK 32 Size: 11 in, 3 ¾ lbs Begins to practice breathing Lanugo - starts to fall off Organs are well-formed WEEK 33 Bones harder, except skull Own immune system WEEK 34 Vernix - thickens Size: 18 in, 5 ½ lbs Testiles make their own way down from abdomen → scrotum WEEK 35 Majority of weight comes from fat Skull remains soft WEEK 36 Hearing - sharpens Bones & cartilages - soft Blood circulation - perfect Lungs - fully formed Digestion - not fully mature WEEK 37 Inhalation & exhalation of amniotic fluids Dexterity develops  WEEK 38 Lungs - stronger Vocal cords develop WEEK 39 Full-term WEEK 40 End of the pregnancy Placenta - provides antibodies to the baby Treacher Collins Syndrome - deformities of the ears, eyes, cheekbones, and chin Pierre Robin Sequence - Glossoptosis - backward positioned tongue - Micrognathia - underdevelopment of lower jaw Development of Upper Lip: - 2 external nares come closer together - 2 medial nasal processes fuse with each other to form the philtrum of the upper lip - The lateral portions of the upper lip are formed by the maxillary processes Formation of the Palate: - Primary Palate - formed by palatal component of the merged medial nasal process - Definitive Palate - palatine shelves fuse with triangular primary palate - Incisive Fossa - represents junction between the two ^ in adults - Hard Palate - ossified ventral ¾ of definitive palate - Soft Palate - unossified dorsal ¼  MUSCLE AND NERVE PHYSIOLOGY Mobility - Muscular system provides the ability to move - Muscles contract → gross & fine movement - Gross Movement - large coordinate motions (walking, swimming) - Fine Movement - smaller movements (speaking, facial expression) Muscle Contraction - begins when the nervous system generates a signal; followed by muscle relaxation Stability - ability of muscles to maintain body position & control movement; ensures balance, prevents injury a. Mover muscles - executing movement b. Stabilizer muscles - provide stability c. Relaxer muscles - work in opposition to the movers; gradual relaxing Circulation - pumping blood inside the body (heart) a. Cardiac muscles - specialized muscle of the heart; primary pump b. Skeletal muscles - muscle pump assist with venous return c. Smooth muscles - lining of blood vessels & vasoconstriction - Allows blood vessels to constrict = let less blood go through - Allows blood vessels to dilate = increase diameter, lets more blood flow through Heat Production/Regulation + 85% of heat comes from contracting muscles Metabolism - process of changing food into energy to fuel body function Homeostasis - maintains body temperature; state of balance Thermoregulation - regulating temperature Respiration - For inspiration - contraction of external intercostals & diaphragm to increase chest cavity - For expiration - relaxation of the same muscles reduces the size of the chest cavity Diaphragm - contracts & flattens to expand the thoracic cavity during inhalation Intercostal muscles - assist by elevating rib cage to expand the chest cavity Types of Muscles: 1. Skeletal Muscle - Function: - For voluntary movements, attached to one another and work in pairs - Control: - Voluntary 2. Cardiac Muscle - Function: - Pumps blood throughout the body - Control: - Involuntary; regulated by ANS and heart pacemaker cells 3. Smooth Muscle - Function: - Controls involuntary movements (contraction of blood vessels, food movement, etc) - Control: - Involuntary; controlled by ANS and hormones Different Abilities of the Skeletal Muscle a. Excitability - ability of a muscle to respond to stimuli b. Contractility - ability of a muscle to contract/shorten c. Extensibility - ability of a muscle to stretch without damage d. Elasticity - ability of muscles to return to their original length after stretching Action Potential - brief reversal of membrane potential Membrane Potential - changes from -70mV to +30mV Threshold: -55mV = all or nothing  + 2K3Na 1. Depolarization: when Na+ rush into a neuron with the opening of voltage-gated Na channels 2. Repolarization: closing of Na ion channels and the opening of voltage-gated K ion channels 3. Hyperpolarization: excess of open K channels & K efflux from the cell; Na channels reset Refractory Period - Amount of time needed for neurons and muscle fibers to recuperate from one action potential before producing the next - Secures one-way flow of the signal - Regulates the rate of signal transmission Absolute Refractory Period - Spans from depolarization to initial repolarization - NO action potential can occur; Na+ channels are inactivated Relative Refractory Period - Spans from late repolarization to hyperpolarization - Needs a stronger-than-normal stimulus Myelin Sheaths - Prevents ion leakage, enables faster transmission - Myelin - produced by glial cells a. CNS: Oligodendrocytes b. PNS: Schwann cells Saltatory Conduction - AP jumps node to node; faster transmission compared to continuous conduction Axon Diameter - larger diameter = faster signal transmission Sliding Filament Theory - Sarcomeres must shorten in order to facilitate muscle contraction; lengths of myofibril’s filaments don’t change Sarcomeres - Form the myofibril of muscle fibers, contains contractile proteins called myofilaments that serve as the primary units of muscle contraction Actin - structured with other proteins that assist with myosin head attachment to the actin Troponin - anchored to the actin; responsible for binding with Ca2+ to stimulate the beginning of muscle contraction Tropomyosin - Covers the active sites of actin, moves to expose attachment sights when troponin binds with Ca2+ - Regulatory protein, stabilizes the conditions for muscle relaxation Myosin - contains myosin heads protruding laterally; acts as attachment sites for cross-bridges with actin myofilaments SYNAPSE NEUROMUSCULAR JUNCTION Neuron to neuron Neuron to skeletal muscle cell Postsynaptic stimulation leads to action potential in Postsynaptic stimulation leads to depolarisation of postsynaptic neuron: muscle/gland sarcolemma muscle contraction Either excitatory or inhibitory Always excitatory Synaptic knob is smooth and rounded End plate has brushed appearance: microvilli and is flattened up to muscle fiber Neurotransmitter in vesicles in presynaptic cytoplasm Neurotransmitter in vesicles in presynaptic cytoplasm Vesicles release neurotransmitter into cleft on stimulation: Vesicles release neurotransmitter into cleft on stimulation: synaptic cleft neuromuscular cleft Neurotransmitter diffuses across synaptic cleft and binds Neurotransmitter diffuses across synaptic cleft and binds to postsynaptic receptor to postsynaptic receptor: sarcolemma Binding of neurotransmitter results in opening of sodium Binding of neurotransmitter results in opening of sodium channels and depolarisation of the postsynaptic channels and depolarisation of the postsynaptic membrane membrane: T-system tubules Enzymes present to breakdown neurotransmitter to avoid Enzymes present to breakdown neurotransmitter to avoid continual stimulation of postsynaptic membrane continual stimulation of postsynaptic membrane, and muscle contraction  ANATOMY OF HEARING OUTER EAR - Made up of fibrocartilage covered by skin and attached to the temporal bone by many extrinsic muscles and ligaments - Internal ligaments connect the auricular structures Auricle/Pinna Flap-like structure that helps send sound waves into the external auditory meatus and facilitates sound localization Helix Curved outer rim Crus of Helix Divides the concha; inferior portion being the entrance to the external auditory meatus Auricular Small projection that can be seen on the lateral border of the helix Tubercle Anti-helix A second semicircular hill rim that is anterior to the helix + Crura of antihelix - 2 divisions of antihelix that are in the anterior section of the helix’ Concha of Cup-shaped/concave depression Auricle Triangular fossa Between the 2 crura of the antihelix Scaphoid fossa Between the helix and antihelix Tragus Flap partly hiding the entrance to the external auditory meatus Antitragus Smaller flap opposite the tragus Intertragic notch Space between the tragus and the antitragus Lobule of the Non-cartilaginous and extremely vascular inferior extremity auricle External Auditory - Ear canal; where the sound waves enter and reach the tympanic membrane, or eardrum Meatus - S-shaped tube, around 25-35 mm length and 6-8 mm in diameter that extends from the auricle to eardrum - Outer third is composed of cartilage and this cartilage is directly continuous to the cartilage of the auricle - Inner ⅔ are made up of osseous - Contains cilia and glands (produce wax & oils: ceruminous glands, sebaceous glands) - Earwax - sticky trap for foreign objects while preventing insects Tympanic - Vibrates in reaction to auditory energy Membrane - Positioned obliquely at the end of the external auditory meatus MIDDLE EAR  - Commonly known for the 3 smallest bones in the body (malleus, incus, and stapes = ossicles) Tympanic 3 layers of tissue: Membrane 1. Outer Layer - aka cuticular layer; continuation of the epithelial lining of the EAM & Pinna 2. Intermediate or Fibrous Layer a. Superficial Layer - fibers that radiate out from the handle of the malleus to the periphery b. Deep Layer - circular fibers that are found mostly in the periphery of the membrane 3. Inner Mucous Layer - continuous with the mucosa of the middle ear Ossicles - Provide the means for transmission of acoustic energy impinging on the tympanic membrane to the inner ear  1. Malleus - In charge of providing the point of attachment with the tympanic membrane - Parts: - Manubrium or handle - long process, separated from the head by a thin neck - Anterior lateral processes - provides points of attachments for ligaments + As the manubrium attaches to the tympanic membrane, it terminates with the lateral process; this forms the anterior and posterior malleolar folds with the pars flaccida - Superior ligament - in charge of holding the head within the epitympanic recess - Anterior ligament - binds the neck to the anterior wall - Lateral ligament - attaches the head to the lateral wall 2. Incus - Mainly responsible for providing the intermediate communication link of the ossicular chain - The long process is nearly parallel with the manubrium of the malleus - The short process projects posteriorly forming the lenticular process with which the stapes articulates 3. Stapes - The smallest - Forms the incudostapedial joint with the incus - Its head articulates with the lenticular process of the incus, neck bifurcates to become the crura Tympanic Muscles Stapedius Muscle - Inserts into the posterior next to the stapes; when it contracts, stapes is rotated posteriorly - Reduces vibrations caused by loud sounds - Innervated by CN VII Tensor Tympani - At the anterior wall of the middle ear space, superior to the eustachian tube - Dampens loud sounds - Innervated by CN V Landmarks Medial Wall Oval Window - Impedance-matching function, allowing sound to be transferred from air (outer ear) to liquid (cochlea) Round Window - Decompress acoustic energy that enters the cochlea via stapes movement against the oval window Anterior Wall Displays the entrance to the auditory tube and within that wall is where the internal carotid artery Pharyngotympanic Tube - aids the transmission of oxygen to the middle ear space  Canal for the tensor tympani - arises from the medial aspect of the wall, marked by the trochlear form process Posterior Wall This is where the prominence of the stapedial pyramid or pyramidal eminence can be found, and Floor along with the aditus to the mastoid antrum Jugular fossa - lies beneath the floor of the middle ear INNER EAR - Consists of the sense mechanism for balance and hearing and houses the vestibulocochlear organs Bony Labyrinth - Its epithelial lining releases perilymph, an extracellular fluid that can be found in the scala tympani and the scala vestibuli - Composed of: a. Vestibule - Entryway to the cochlea - Helps maintain balance by sending signals to the brain about the changes in position or movement - Interior prominent recesses: 1. Spherical recess - has tiny holes, macula cribrosa media, which allow parts of the vestibular nerve to pass through to the saccule of the inner ear 2. Cochlear recess - connects the vestibule to the base of the cochlear duct 3. Elliptical recess - has openings that allow connection between the utricle & ampullae of the superior & lateral semicircular canals b. Semicircular Canals - Contains the sense organs for the movement of the body in space a. Anterior vertical canal - detects movement in a plane mostly perpendicular to the temporal bone; detects movement like nodding your head b. Posterior vertical semicircular canal - detect movements like tilting your head towards your shoulder c. Lateral semicircular canal - senses movement roughly in the transverse plane; detects movements like shaking your head c. Cochlea - Thickest at the base, gets thinner until it ends at the cochlear cupula - Twists around a central bone area called the modiolus, forming a cone shape - Spiral lamina - extends from the modiolus and supports the cochlear duct Membranous - Filled with endolymph Labyrinth - Composed of: a. Cochlear duct 1. Scala vestibuli - helps transmit sound waves from the oval window into the cochlear duct + Reissner’s membrane - extend obliquely from the osseous spiral lamina to the outer bony wall and above the basilar membrane; separates the scala vestibuli from the cochlear duct and the stria vascularis + Basilar membrane - contains the Organ of Corti (responsible for hearing) 2. Scala tympani - helps dissipate sound waves back into the middle ear via the round window b. Saccule and Utricle - Expanded region of the semicircular canals - Saccule & utricle = endolymph → endolymphatic duct → vestibular aqueduct → back of the temporal bone = sac: fluid is secreted and absorbed 1. Utricle - sensory organ with hair cells & cilia; covered by a membrane that has tiny crystals called otoliths 2. Saccule - connects with the utricle through the endolymphatic duct (in dura mater) c. Semicircular ducts - inside the semicircular canals and have the same orientation; fluid inside changes speed/direction when the head moves  PHYSIOLOGY OF HEARING Sound Sound is produced → Eardrum vibrates → Ossicles (amplify sounds) → Cochlea → Hair cells Transmission vibrate → Auditory nerve → Brain (temporal lobe) Sound 1. Vibrations at the stapes footplate creates pressure in the scala vestibuli Processing 2. Waves move around through the helicotrema into the scala tympani (Cochlea) 3. Wave is transmitted into the endolymph 4. The basilar membrane vibrates, so Organ of Corti moves against tectorial membrane Sound waves are converted into electrical impulses, auditory nerve sends this to the brain. AUDITORY PATHWAYS Afferent Central Function: Auditory Carries auditory information from the peripheral auditory system to the central nervous system Pathway Path: Cochlea → Sound waves - Electrical signals → Auditory nerve → Brainstem → Thalamus (processed & relayed) → Auditory cortex (temporal lobe) → Brain + Carries info from periphery to center + Responsible for hearing and sound perception + Essential for hearing; carries the auditory signals to the brain Efferent Central Function: Auditory Carries neural signals from the central nervous system back to the peripheral auditory system Pathway (cochlea). These signals help to modulate or regulate the incoming auditory information Path: Brainstem → Auditory nerve → Cochlea → Synapse on hair cells → influenced sensitivity to sound + Carries info from center to periphery + Plays a role in regulating auditory sensitivity and attention + Involved in refining & modulating auditory input; not essential for basic hearing HEARING IMPAIRMENTS Sensorineural Inner ear or auditory nerve is damaged Hearing Loss Conductive Obstruction of sound wave transmission (external & middle ear) Hearing Loss Mixed Hearing Either external ear, middle ear, or inner ear Loss VESTIBULOCOCHLEAR NERVE - Sensory nerve that carries auditory & vestibular information to the brain Cochlear nerve - Carries auditory information from the cochlea to the brain - Responsible for hearing Vestibular nerve - Carries vestibular information from the vestibular system to the brain - Responsible for balance and spatial orientation  IMPEDANCE MATCHING - Process of optimizing the transfer of sound energy from the external environment to the inner ear 1. Sound waves vibrate the tympanic membrane 2. Auditory ossicles vibrate, pressure is amplified 3. Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli 4. Sounds with frequencies below the hearing range travel through the helicotrema and do not excite hair cells 5. Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells SOUND ACOUSTICS - Human auditory mechanism has a frequency range of approximately 10 octaves, spanning 20 to 20,000 Hz - High frequency, high pitch = short wavelength - Low frequency, low pitch = long wavelength TONOTOPIC ARRANGEMENT Low-frequency Can’t move, stiff fibers sounds Continue to the longer, floppier apex fibers Medium-frequenc Vibrate the basilar membrane near its middle y sounds High-frequency Vibrate the basilar membrane near its base sounds