Anatomy and Physiology: Nervous System & Hormones

DNA and RNA Structure

• DNA is also called the "information molecule"
• Found within the nucleus of every cell
• Stands for deoxyribonucleic acid
• DNA has two strands arranged in a helical structure
• Contains the nucleotides Adenine (A), Thymine (T), Cytosine (C), and Guanine (G)
• DNA is double-stranded
• Chargaff's Rule states that the amount of adenine equals thymine and the amount of guanine equals cytosine.

Nucleotide Structure

• A nucleotide consists of a phosphate group, a sugar, and a nitrogenous base.
• The sugar in DNA is deoxyribose, and the sugar in RNA is ribose.
• The nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).
• The nitrogenous bases in RNA are adenine (A), uracil (U), cytosine (C), and guanine (G).

RNA Structure

• RNA is the working instruction of genes in building proteins.
• Found within the cytoplasm of every cell.
• Stands for ribonucleic acid.
• RNA is single-stranded

Learning Competencies

• Explain how protein is made using information from DNA.
• Describe the role and structure of DNA.
• Describe the role and structure of RNA.
• Compare the structures of DNA and RNA molecules.

Homeostasis

• Homeostasis is the ability of the body to maintain a stable internal state despite changes occurring in the external environment.
• It is maintained by feedback mechanisms.
• Feedback mechanisms bring the body either toward or away from its normal state.
• Negative feedback mechanisms negate change to maintain the normal range.
• Positive feedback mechanisms promote change.

Feedback Mechanisms

• A physiological loop that brings the body either toward or away from the normal, steady states.
• Can be either negative or positive feedback.
• The components of a feedback mechanism include sensors, control centers, and effectors.

Negative Feedback Mechanisms

• Negates change and keeps a variable within its normal range.
• The sensor detects a shift in a variable that is outside the normal range.
• The control center sets the normal range and sends signals to the effector.
• The effector brings about a response that moves the variable back to the normal range.
• Examples of negative feedback mechanisms include sweating in hot weather and shivering in cold weather.

Positive Feedback Mechanisms

• Promotes change.
• The sensor detects a shift in a variable that is outside the normal range.
• The control center sends signals to the effector, which creates a response. This response further amplifies the initial stimulus.
• The cycle continues until the change is complete.
• Examples of positive feedback mechanisms include childbirth and blood clotting.

The Nervous System

• Connects all body parts and transmits signals from one part to another.
• Involved in rapid but short-term responses.
• Sends signals to and receives responses from every organ and tissue of the body.
• Two main divisions: central nervous system (CNS) and peripheral nervous system (PNS).
• CNS is comprised of the brain and spinal cord which receive input, process that input in the brain, and send signals as a response back to the body.
• PNS includes all sensory receptors, neurons, and motor neurons.

CNS (Central Nervous System)

• Main processing center.
• Consits of the brain and the spinal cord.
• Protected by the skull and vertebral column.

Brain/Cerebrum

• Brain is the center of knowledge, emotions, learning and awareness.
• The cerebrum is divided into four lobes (frontal, parietal, temporal, and occipital).
• Each lobe is responsible for specific functions.

Cerebellum

• Responsible for posture, balance, and motor coordination.

Brain Stem

• Located between the brain and the spinal cord.
• Comprised of the hypothalamus, thalamus, pons, and medulla oblongata.

PNS (Peripheral Nervous System)

• Connects the CNS of the body to the organs and limbs.
• Contains nerves that include sensory and motor fibers.
• Two classifications: somatic or autonomic.

Somatic Nervous System

• Controls voluntary movements of the body.
• Sends motor signals through spinal nerves to muscles.
• Sends sensory signals through cranial nerves (face,eyes,head)

Autonomic Nervous System

• Controls involuntary movements of the body (internal organs).
• Two branches of this system are called sympathetic and parasympathetic.
• Sympathetic nervous system activates the "fight or flight" response.
• Parasympathetic nervous system activates the "rest and digest" response.

Nerve Cell

• Also called a neuron; the basic unit of the nervous system.
• Specialized cells for transmitting messages.
• Parts of a neuron consist of dendrites, which receive messages, a soma, which contains the nucleus, and an axon to transport messages to another neuron.
• The message is transmitted across synapses, which connect neurons.

Nerve Impulses

• Electrochemical charges occurring in neurons and transmitting between neurons at a speed of 120 m/s.
• Can pass across the synapses.

Menstrual Cycle

• Regular changes in the ovaries and endometrium that make reproduction possible.
• Usually takes about 28 days to complete.
• Consists of the ovarian cycle and the uterine cycle.

Ovarian Cycle

• Series of events wherein the ovaries prepare and release a mature ovum.
• Two phases: follicular and luteal.

Uterine Cycle

• Series of events wherein the uterine lining is prepared for possible pregnancy.
• Three phases: menstrual, proliferative, and secretory.

Ovaries

• About the size of an almond seed.
• Composed of ovarian follicles (sac-like structures).
• Contains egg cells at birth at the site of ovulation.
• Produce female hormones, including estrogen and progesterone.

Estrogen

• Produced by follicle cells.
• Causes secondary sex characteristics, uterine enlargement.
• Promotes sexual development and associated features.

Progesterone

• Produced by corpus luteum.
• Production continues until LH diminishes in the blood.
• Helps maintain pregnancy, thickens the lining of the uterus, and promotes maintenance of a successful pregnancy.

Oogenesis

• The process of formation of female gametes (ova) or egg cells.
• Happens within the ovaries.

Oviduct (Fallopian) Tubes

• Receive the ovulated oocyte (egg).
• Provide a site for fertilization.
• Connected to the uterus.
• Supported by broad ligaments.

Fimbria

• Finger-like projections at the distal end that receive the oocyte.
• Cilia move the oocyte towards the uterus (takes 3–4 days).
• Fertilization occurs inside the uterine tube.

Uterus

• Hollow, thick-walled organ located between the urinary bladder and rectum.
• Receives a fertilized egg
• Retains the fertilized egg
• Nourishes the fertilized egg
• Three main layers: perimetrium (outer layer), myometrium (middle layer of smooth muscle), endometrium (inner layer).

Endocrine System

• A system comprised of glands that regulate body activities through chemical messengers called hormones.
• Releases hormones into the blood to target cells or organs.
• Associated mechanisms are slow and long-lasting.

Endocrine Glands

• Pineal gland - located in the brain; produces melatonin, which regulates our internal clock, and sleep wake cycle.
• Hypothalamus - located in the brain; controls many endocrine processes associated with releasing hormones for the pituitary gland.
• Pituitary gland - located at the base of the brain; master gland; and controls other endocrine glands in the body, through releasing hormones.
• Thyroid gland - located below the voice box; produces thyroxine which controls metabolism in the body.
• Adrenal glands - located on top of the kidneys; produces adrenaline, which is associated with stress and other processes.
• Pancreas - located behind the stomach; produces insulin and glucagon for blood sugar control.

Reproduction

• Reproduction is the biological process through which new individual organisms – "offspring" – are produced from their "parents".
• Many factors contribute to reproductive success that include hormones (chemical messengers), fluids (necessary liquids), external genitalia, and accessory parts (complementary organs)

Parts of the Male Reproductive System

• Testes - produce sperm (gametes) and testosterone (hormone).
• Epididymis - stores and nourishes sperm cells.
• Vas deferens - carries sperm from the epididymis to the ejaculatory duct.
• Urethra - tube that carries urine and semen from the bladder to the outside of the body.
• Prostate gland - secretes an alkaline fluid into the semen to help sperm survive.
• Seminal vesicles - produce a fluid that nourishes sperm .
• Bulbourethral glands - secrete a mucus-like fluid to cleanse the urethra before ejaculation.
• Penis - copulatory organ.
• Scrotum - sac of skin that holds the testes.

Test your knowledge of positive feedback mechanisms, nervous system functions, brain structures, and hormonal effects. Topics include the central nervous system, brain stem, and ovarian and uterine cycles. Understand the roles of progesterone and other hormones.