Human Biology: Nervous System, Senses, and Reproduction
1. Organization of the Nervous System
1.1 Central Nervous System
- Brain:
- Cerebrum (Cerebral Cortex and Limbic System)
- Cerebellum
- Brainstem
- Hypothalamus
- Epithalamus
- Thalamus
- Spinal Cord
1.2 Peripheral Nervous System
- Autonomic Nervous System:
- Sympathetic
- Parasympathetic
- Somatic Nervous System:
- Sensory Nerves
- Motor Nerves
2. Nerve Impulse
2.1 Along a Neuron
The nerve impulse travels in the form of an electric current from the dendrite to the soma (cell body) to the axon.
2.2 Neuron to Neuron
Transmission occurs via connections called synapses. The nerve impulse reaches the end of the presynaptic neuron’s axon, where neurotransmitters are released from synaptic vesicles into the synaptic cleft. These neurotransmitters cross the cleft and bind to specific receptors on the postsynaptic neuron’s membrane, generating a new impulse that travels along the axon.
3. Functions of the Brain
- Cerebral Cortex: Processes information, controls voluntary motor responses, governs intellectual and mental functions, and regulates the rest of the nervous system.
- Limbic System: Regulates the endocrine system, emotions, feelings, and basic instincts.
4. Nervous vs. Endocrine Systems
- Nervous System: Quick response
- Endocrine System: Slower response
5. Hypothalamic-Pituitary Axis
The hypothalamus releases hormones that stimulate the pituitary gland, which in turn releases hormones that act on endocrine glands, producing further hormones. These hormones can then inhibit the pituitary gland and hypothalamus through negative feedback.
6. Pituitary Hormones
- Vasopressin: Increases water reabsorption, leading to concentrated urine.
- Oxytocin: Stimulates smooth muscle contractions in the uterus.
- Growth Hormone (GH): Promotes bone growth and lengthening.
- Luteinizing Hormone (LH): Stimulates milk production and release.
7. Ear Structure
- Outer Ear: Auricle and ear canal
- Middle Ear: Eardrum and ossicles (malleus, incus, stapes)
- Inner Ear: Cochlea and vestibular system (semicircular canals, utricle, and saccule)
8. Hearing
Sound waves enter the auricle and travel through the ear canal, causing the eardrum to vibrate. This vibration is transmitted through the ossicles to the inner ear, where it creates waves in the cochlea’s endolymph fluid. These waves stimulate sensory cells in the organ of Corti, generating nerve impulses that are sent to the brain via the auditory nerve.
9. Balance
- Dynamic Balance: Maintained by the semicircular canals, which detect movement through the endolymph fluid and send nerve impulses to the brain.
- Static Balance: Maintained by the utricle and saccule, which detect the body’s position.
10. The Eyeball
The eyeball has three layers: sclera (outermost), choroid (middle), and retina (innermost). Key structures include the aqueous humor, crystalline lens, iris, pupil, vitreous humor, and the anatomical blind spot.
11. Skin Structure
- Epidermis: Outer layer (epithelial tissue)
- Dermis: Inner layer (connective tissue)
- Hypodermis: Deepest layer, primarily composed of adipose cells, with protective and thermoregulatory functions.
14. Types of Bones
Long, short, and flat bones.
15. Structure of a Long Bone
- Epiphysis: Ends of the bone
- Endosteum: Lining of the medullary cavity
- Cartilage: Covers the ends of the bone
- Diaphysis: Shaft of the bone
- Periosteum: Outer covering of the bone
16. Skeleton Types
- Axial Skeleton: Skull, thorax, and spinal column
- Appendicular Skeleton: Upper and lower limbs
17. Muscle Structure
Muscles are connected to bones by tendons. They are composed of muscle fascicles, which contain muscle fibers. The epimysium surrounds the entire muscle, the perimysium surrounds each fascicle, and the endomysium surrounds each fiber.
18. Types of Muscles
Fusiform (movement), flat (cover organs), and circular (open and close).
19. Stages of Human Development
Childhood, adolescence, and adulthood.
20. Physical Changes During Puberty
Secondary sex characteristics develop due to hormones released by the pituitary gland and gonads.
21. Male Reproductive System
- Penis: Deposits sperm in the vagina
- Testicles: Produce sperm and testosterone
- Genital Tract: Epididymis (stores sperm), vas deferens, and urethra (expels semen and urine)
- Accessory Glands: Seminal vesicles, prostate gland, and Cowper’s gland (produce seminal fluid and lubricating fluid)
22. Formation of Gametes (Gametogenesis)
Gametogenesis (spermatogenesis in males and oogenesis in females) produces gametes with half the number of chromosomes (23) compared to normal body cells (46) through meiosis.
23. Fertilization
Fertilization involves the approximation of gametes, fusion, zygote formation, and implantation. The ovarian cycle (follicular phase, ovulation, and luteal phase) corresponds to the uterine cycle (proliferative phase, secretory phase, and menstruation).