The Nervous and Endocrine Systems Flashcards
Neurons
- Nerve cells. Soma contains usual organelles.
- Carries impulses from place to place, received at dendrites (spiky things) and transmitted to axon.
- The inside of a neuron is more negatively charged than the outside.
Resting membrane potential
- Inside of a cell is more negative
- A neuron is polarized when resting
- -70 mV in humans
Impulse
An electrical signal.
Membrane proteins
Na/K ATPase and K leak channel, help to set up resting membrane potential.
Leak channels
K channels that are always open and allow K to leak out of the cell according to its gradient.
How is the inside of a neuron more negative?
- Na/K ATPase uses a molecule of ATP to move 3 Na ions out of the cell, while moving 2 K ions into the cell.
- Eventually there is more Na outside the cell and more K inside the cell. These molecules are charged and can’t cross the membrane without a channel.
- Leak channels and pumps allow Na and K to leave the cell, leaving negatively charged items inside the cell, like DNA and proteins.
Charge of K and Na
Positive
Voltage Gated Channels
- Channels in a neuron that open when the cell membrane reaches a particular voltage.
- 2 types: Na voltage gated and K voltage gated
- Will open if a neuron is polarized and depolarizes slightly.
Threshold potential
Point at which voltage gated channels open (-50 mV)
Action potential
- Movement of ions to restore resting membrane potential
- Causes a chain of action potentials down the axon of the cell.
- During this, the membrane is positive on the inside and negative on the outside.
Depolarization
Membrane potential moves in the positive direction.
Repolarization
Membrane potential returns to its resting value (negative direction).
Efflux
Leaving
Influx
Entering
Process
Something sticking off of something else.
Process of an action potential
- If a neuron is polarized and depolarizes slightly, VGC open.
- Na channels open first, and Na enters according to concentration gradient.
- Na depolarizes the cell further, reaches a max of +35 mV before Na channels close.
- K channels open, K enters cell according to concentration gradient.
- Exiting K ions repolarize the cell, bypassing resting membrane potential to min -90 mV before channels close.
- Na/K ATPase and K leak channels return membrane to resting polarized state.
Myelin sheath
Wrapping of Schwann cells, which wrap some axons, increases speed of an impulse.
Nodes of Ranvier
Space between Schwann cells.
Saltatory Conduction
Only nodes of Ranvier conduct impulses, so impulses jump from node to node.
Refractory Period
- For a short period of time after firing an action potential, that portion of the membrane can’t fire a second
- This ensures the action potential will only travel away from the cell body.
Synapse
Point where an impulse is transferred.
Synaptic cleft
Small gap between neurons.
Summation
A neuron receives multiple impulses, and will add them up. More stimulatory impulses will cause an action potential.
Stimulate
To depolarize toward threshold, can cause an action potential.
Inhibit
Move away from threshold.
When an impulse reaches the end of an axon
- An impulse will be transferred to another neuron’s dendrite or to an organ.
- Most neurons use a neurotransmitter to transfer impulses, acetylcholine being the most common.
- Terminal end of axon 1 contains vesicles with neurotransmitter
- When the action potential reaches them, vesicles fuse with the cell membrane and nt is released by exocytosis
- It crosses synaptic cleft and binds with receptors on neuron 2.
- Receptors are usually connected to ion channels that open when nt binds.
Central nervous system
- Brain and spinal cord.
- Like a command center where information is processed and decisions are made.
- Composed of interneurons
Peripheral nervous system
- Neurons outside the brain and spinal.
- Connects CNS to all other centers
- Composed of sensory and motor neurons
- Subdivided into somatic and autonomic nervous systems.
Interneurons
Connect sensory and motor neurons.
What causes strength of sensation?
The more frequently the action potentials are fired, the stronger the sensation.
Spinal cord
Involved in primitive, reflex actions.
Cerebrum
- Conscious mind
2. Voluntary actions such as movement, speech, and problem solving. Awareness of sensations such as sight or heat.
Cerebellum
Coordinates muscle movement and balance.
Medulla
Involuntary acts such as breathing and blood pressure.
Hypothalamus
Maintains body homeostasis- monitors hormone levels, temperature, and controls the pituitary gland.
Somatic Nervous System
- Subdivision of PNS
- Voluntary system controlling skeletal muscle
- Uses acetylcholine as a neurotransmitter.
How is a muscle stimulated?
- A motor neuron releases acetylcholine onto a muscle
2. Ach binds to receptors, muscle depolarizes and contracts.
Autonomic Nervous System
- Subdivision of PNS
- Involuntary actions, controlling heart, blood vessels, etc.
- Subdivided into sympathetic and parasympathetic nervous systems.
Sympathetic Nervous System
- Prepares you for stressful situations by increasing heart rate, blood pressure, etc.
- Uses neurotransmitter epinephrine
- Epinephrine remains in blood for longer than norepinephrine, and therefore has a prolonged effect.
Parasympathetic Nervous System
- Most active at rest, diverting blood to digestive organs, away from skeletal muscle
- Uses acetylcholine.
Endocrine System
Controls the body through hormones secreted into the blood by endocrine glands.
Why do hormones only have an effect on certain organs?
Only some organs have receptors for specific organs.
Target organs
Organ affected by a specific hormone.
2 classes of hormones
Steroid and peptide
Steroid hormones
- Lipids that cross membranes and bind to receptors inside the cell.
- Cause effects more slowly, because they bind to DNA and change which genes are transcribed.
Ex: estrogen and testosterone.
Peptide hormones
- Protein molecules, can’t cross membranes so they bind to receptors outside the cell.
- Cause effects rapidly by turning cell enzymes on or off. Ex: insulin
Pituitary gland
- “master” endocrine organ- controls many other endocrine glands.
- Controlled by the hypothalamus, and consists of the anterior and posterior pituitary
Growth Hormone
- Anterior pituitary
2. Causes tissues and organs to grow in children, stimulates cell turnover rate in adults.
Thyroid Stimulating Hormone
- Anterior pituitary
2. Stimulates thyroid to secrete thyroid hormones
Adrenocorticotropic Hormone
- Anterior pituitary
2. Stimulates adrenal cortex to secrete hormones
Follicle Stimulating Hormone
- Anterior pituitary
- Targets the ovaries in females, maturing eggs and causing the release of estrogen, and the testes to make sperm in males.
Luteinizing Hormone
- Anterior pituitary
- In females, stimulates the ovaries to develop the corpus luteum. In males, stimulates the testes to make testosterone.
Prolactin
- Anterior pituitary
2. Released after childbirth, stimulates mammary glands to make breast milk.
Oxytocin
- Posterior pituitary
2. Causes the uterus to contract during childbirth, stimulates the mammary glands, bonding hormone.
Antidiuretic Hormone/Vasopressin
- Posterior pituitary
2. Causes the kidneys to retain water
Thyroid Hormone/Thyroxine
- Thyroid
- Increases all cells’ rate of metabolism
- Need iodine to secrete it, so not enough causes hypothyroidism.
Calcitonin
- Thyroid
2. Activates special cells in bone to remove calcium from the blood to build new bone. Reduces blood calcium levels.
Parathyroid glands
4 glands found on the back of the thyroid gland.
Parathyroid Hormone/Parathormone
- Parathyroid glands
- Activates cells in bone to dissolve it and increase blood calcium levels. Calcium levels need to be constant, because it’s used for impulse conduction and blood clotting.
Adrenal glands
Sit on top of the kidneys. Adrenal medulla is the inner part and adrenal cortex is the outer part. Can be stimulated by the sympathetic nervous system to secrete epinephrine or norepinephrine.
Epinephrine/adrenaline
- Adrenal medulla
- Epi secreted by the AM lasts longer than that secreted by the sympathetic nervous system, and therefore the effects of the sympathetic nervous system are prolonged.
Norepinephrine
- Adrenal medulla
- Similar structure to epi, and can therefore bind to the same receptors and have the same effects.
- Affects all cells
Glucocorticoids
- Adrenal cortex
- Causes gluconeogenesis as the liver produces glucose from fat or proteins.
- Targets other body cells to use fats instead of glucose, increasing glucose levels and metabolism.
- Strong anti inflammatory agents such as Cortisol
Gluconeogenesis
Release of new glucose into blood.
Aldosterone
- Mineralocorticoids secreted by the adrenal cortex
2. Targets the kidneys, causing them to retain sodium, which leads to an increase in blood pressure.
Insulin
- Secreted by islet cells of the pancreas when glucose levels are high.
- Allows all cells to take glucose out of the blood to use in respiration to produce energy.
- Stimulates liver to store glucose as glycogen.
Glucagon
- Islet cells of the pancreas
- Released when glucose is low
- Allows liver to break down glycogen (stored glucose) and release it into blood.
Testosterone
- Testes
- Develops male secondary sex characteristics such as deep voice and facial hair.
- Necessary for adequate sperm production
Estrogen
- Ovaries, which also produce progesterone
- Develops female secondary sex characteristics such as breasts and wide hips
- Estrogen regulates the menstrual cycle by stimulating the growth of the uterine lining during the first half, and progesterone maintains the lining.
