Human Body Systems

The Nervous System Chapter 21

Functions Responding to stimuli Homeostasis Stimuli is anything that elicits a response Homeostasis Ensuring that internal conditions stay constant

Neurons Basic functioning unit of the nervous system Neurons are cells that receive and carry messages Composed of Dendrites and Axons Dendrites receive messages and send them to the cell body Axons carry messages away from the cell body The messages carried by the neurons are called impulses

Types of Neurons Sensory neurons Motor neurons Interneurons Receive information from the external environment and send impulses to the brain Motor neurons Conduct impulses from the brain to your muscles and glands Interneurons Relay impulses from the brain to other neurons Synapses are areas between neurons When an impulse reaches the axon endings, they release chemicals called receptors that cross the synapse and reach the next dendrite

The Central Nervous System (CNS) Made up of the brain and spinal cord The brain Controls your body Made up of 100 billion neurons (10% of the total in your body) 3 main parts Cerebrum (Pink part) Where thinking occurs Largest part of the brain Cerebellum (tan part) Coordinates movement, interprets stimuli Brain Stem (Blue part) Connects parts of brain, and connects brain to spinal cord Controls involuntary actions

The Central Nervous System (CNS) The spinal cord Extension of brain stem Carries impulses throughout body

The Peripheral Nervous System (PNS) Made up of all of the nerves outside of the CNS Connects CNS to all of the other parts of the body Contains 2 systems Somatic System Controls voluntary actions Autonomic System Controls involuntary actions (automatic)

The circulatory System

The Heart Made up of cardiac tissue Contains 4 compartments Steps Right/Left Ventricle Right/Left Atrium Steps Blood enters the heart through the Vena Cava to the right atrium The right atrium contracts, sending blood into the right ventricle The right ventricle contracts, sending blood into lungs There, blood picks up oxygen Blood returns to the left atrium The left atrium contracts, sending blood to the left ventricle Left ventricle contracts, sending blood out of the heart through the aorta It then travels through the body, delivering blood, until it returns through the vena cava

Blood Vessels Arteries carry blood away from the heart Veins return oxygen-poor blood to the heart Capillaries connect arteries and veins

Blood Functions Carries oxygen to your cells Carries waste products to kidneys for disposal Transports nutrients Fight infections

Parts of Blood 55% of blood is plasma 45% is red blood cells Liquid portion of blood Carries nutrients and waste 45% is red blood cells Contain hemoglobin Carries oxygen and carbon dioxide Formed in long bones (such as the femur) Less than 1% is white blood cells Fight pathogens Also in blood is platelets which help clot blood

The Reproductive System and development

Maturity Warning We are going to talk about the male and female reproductive systems I expect you to act as if you are in middle school, not elementary. I will remove you from the class if needed.’ Let me teach, let others learn You have been warned!

The Male Reproductive System Made up of external organs The penis The scrotum Contains the testicles, which produce testosterone and sperm Sperm has a head and a tail The head contains the DNA, the tail helps them move Semen is the combination of sperm and fluids

The Female Reproductive System Internal structures Ovaries store eggs Females are born with all of the eggs that they will ever have Eggs are released from ovaries during ovulation They travel through an oviduct to the uterus If the egg is fertilized, the egg will implant in the uterus If a fetus develops, the child is born through the vagina, the muscular tube that reaches the outside of the body

The Menstrual Cycle Usually 28 days in length Phase 1: Menstrual flow begins Blood, tissues form the uterus, and the egg are expelled from the body Called the period Phase 2: Lining of the uterus is replenished and thickens An egg is released and travels to the uterus Phase 3: Uterus readies for conception If it happens, the uterus is ready to nourish the embryo If it doesn’t the cycle begins again Most females get their first period around 13. Continues until child-bearing years are over, around 45-55 years old

Human Life Stages Zygote formation: Sperm and egg fuse, and fertilized egg begins to undergo mitosis, forming an embryo The amniotic sac forms, along with the umbilical cord and placenta that will deliver nutrients to the fetus until birth After 2 months, the embryo becomes a fetus. Around the 3rd month, the fetus is about 9 cm long By the 9th month, the fetus is ready to be born, including being head-down Childbirth The first sign is contractions, which are the body preparing to push the newborn out Then, the amniotic sac breaks, releasing the contents (called “Water breaking” The uterus widens, contractions become more powerful

Human Life Stages Delivery Neonatal Stage Infancy The contractions and pushes by the mother force the baby out The placenta is also forced out shortly after Sometimes, a cesarean section is required An incision is made through the abdomen, then through the uterus, and the baby is delivered The umbilical cord is cut Neonatal Stage 0-4 weeks Newborn’s body begins to function, and gets used to the new environment Infancy 4weeks-18 months Baby becomes more aware of surroundings At about 8 months, the baby begins to crawl. They can sometimes walk at 10 months

Human Life Stages Childhood Adolescence Adulthood 18 months-12 or 13 years old Child grows, learns to use the bathroom, learns to speak, read, etc. Reaches puberty around 11-14 years old Adolescence 12 or 13-18 years old Puberty causes changes to the body Males: Voice deepens, hair growth, Females: breasts develop, body hair appears Adulthood 18-45 to 60 Growth stops, and body systems stop functioning as efficiently

Human Life Stages Late Adulthood Death 60+ Decline in body functions Bones become more fragile Hearing and eyesight deteriorate Death Currently, the human life span is about 79 years

Most common causes of death Heart disease: 611,105 Cancer: 584,881 Chronic lower respiratory diseases: 149,205 Accidents (unintentional injuries): 130,557 Stroke (cerebrovascular diseases): 128,978 Alzheimer's disease: 84,767 Diabetes: 75,578 Influenza and Pneumonia: 56,979

Other Body Systems

Lymphatic System Collects and returns fluids from tissues to the blood system

The Endocrine System Produces and regulates hormones Regulates metabolism, growth and development, bodily functions, reproduction, sleep, mood, etc. Negative-Feedback System When things in the body change, your body must compensate for this. Example: When you are cold, your body makes you shiver (move around) to keep warm. If you get too warm, you will begin to sweat. You do these until you are comfortable.