1. 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

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

3. 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

4. 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

5. 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

6. 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

7. Nerve Impulses
Chapter 48

8. 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)

9. 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

10. 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)

11. 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

12. 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

13. 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

14. 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

15. 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