Menstrual Cycle Chapter 46 Because the hormonal control of menstruation is rich in examples of feedback and illustrates so well the circulation of hormones in the blood affecting target tissues, this is a good process to understand in detail. Menstrual Cycle Chapter 46

Female Reproductive Cycles Females have 2 closely related cycles: Menstrual cycle Ovarian cycle Controlled by hormones released by the pituitary gland

Menstruation Menstruation occurs when the endometrium is shed from the uterus through the cervix and vagina 3 Phases: Menstrual flow – endometrium is shed and bleeding occurs Proliferative phase – endometrium begins to regenerate and thicken Secretory phase – the endometrium continues to thicken and if an embryo doesn’t implant, menstrual flow occurs

Ovarian Cycle Occurs in the ovary 3 Phases: Follicular phase – growth and development of the follicle and oocyte (egg) Ovulation – release of the secondary oocyte into the fallopian tube Luteal phase – development of corpus luteum and secretion of estradiol and progesterone

FSH and LH stimulate follicle to grow and mature 8 Hypothalamus releases GnRH (Gonadotropin-releasing hormone) based on the amount of estradiol and progesterone in the blood Anterior pituitary is stimulated by GnRH to secrete FSH and LH into the blood FSH and LH stimulate follicle to grow and mature Growing follicle secretes estradiol into the blood When estradiol concentration peaks, it stimulates the release of more GnRH → FSH and LH release (positive feedback) LH level peaks and ovulation occurs Follicular tissue forms corpus luteum which secretes progesterone and estradiol Increased levels of progesterone and estradiol inhibit hypothalamus and anterior pituitary gland from producing GnRH and FSH and LH Low levels of FSH and LH cause corpus luteum to disintegrate allowing the hypothalamus and pituitary gland to secrete GnRH, FSH, and LH again Cycle starts over 5 1 2 6 3 9 7 4 8 5

Rapid drop in levels of estradiol and progesterone cause endometrium to tear away from uterus wall and menstrual flow begins Increased estradiol and progesterone levels signal the endometrium to thicken

Nerve Impulses Chapter 48

The Nervous System Function The nervous system controls and coordinates activities throughout the body and responds to internal and external stimuli (signals) Organization Neurons Central nervous system (CNS) Peripheral nervous system (PNS)

Neurons Cell body – contains the nucleus Dendrites – receives messages and relays them to the cell body Axons – sends message away from cell body to another neuron

Types of Neurons Sensory – send messages to the CNS Motor – receive messages from the CNS Interneurons – relay messages between the sensory and motor neurons (spinal cord & brain only)

Neurons at Rest Neuron membrane potential at rest = positively charged outside the cell and negatively charged inside the cell More Na+ ions outside of cell and more K+ ions inside of cell Resting potential is between -60 & -80 mV Changes in the membrane potential of a neuron give rise to nerve impulses

Action Potentials I An action potential (nerve impulse) is an all-or-none response to depolarization of the membrane (change in charge) A stimulus must exceed a threshold to generate an action potential ( -55 mV for mammals) If exceeded, Na+ ions will rush into the nerve cell through voltage-gated sodium channels causing the charge inside the neuron to become positive The membrane potential is restored by opening voltage-gated K+ channels allowing K+ ions to leave the neuron Action potential travels down the axon

Action Potentials II The speed of an action potential increases with the axon’s diameter The evolutionary adaptation that enables fast conduction in vertebrate axons is electrical insulation, analogous to the plastic insulation that covers many electrical wires Electrical insulation is called a myelin sheath and is found in Schwann cells Allows the depolarizing current to spread farther along the axon anterior so that distant regions can reach the threshold sooner

Neuron to Neuron Between two neurons there is a gap called a synapse When an action potential reaches the end of the axon it is converted from an electrical impulse into a chemical impulse so it can “jump” the gap The axon terminal releases neurotransmitters into the synapse and they diffuse across to receptors on the dendrites of the next neuron When the receptors are full, the action potential is initiated in the next neuron

Types of Neurotransmitters Acetylcholine – aids in muscle stimulation, memory formation, and learning Dopamine & Serotonin – affect sleep, mood, attention, and learning Endorphins – pain relief, decrease urine output, depress respiration, and produce euphoria Dopamine Video Zoloft Commercial