Unit 5 - Homeostasis Flashcards
1
Q
steady state of being in organisms
A
homeostasis
2
Q
optimal body temp
A
37 degrees
3
Q
optimal blood sugar
A
4 mmol/L
4
Q
optimal blood pH
A
7.35
5
Q
All homeostatic control systems have three functional components:
A
A receptor (or monitor) A coordinating centre A regulator (or effector)
6
Q
what do all homeostatic control systems start and end with
A
stimulus and response
7
Q
conscious responses
A
behavioural response
8
Q
unconscious responses
A
physiological responses
9
Q
Negative feedback systems
A
(also called negative feedback loops) are mechanisms that make adjustments to bring the systems of the body back to within an acceptable range. The system reacts to stimulus by doing the opposing action (i.e. when the body gets too hot the system cools it by sweating).
10
Q
Positive feedback system
A
A positive feedback system is the opposite of a negative feedback system. It reinforces small changes to make them larger or amplified. Positive feedback moves the target variable even further away from its steady state or increases the magnitude of the change away from the steady state resulting in a change in the body’s status, rather than a return to homeostasis.
11
Q
thermoregulation
A
maintenance of body temperature within a range that enables cells to function efficiently
12
Q
ectotherms
A
organisms with metabolic rates are dependent on external temperatures and other external elements. Invertebrates, as well as most fish, amphibians, and reptiles, are ectotherms.
13
Q
endotherms
A
organisms able to maintain a constant internal body temperature, regardless of their surroundings. They have evolved metabolic processes that generate internal heat from organs such as the kidney and liver. As a consequence, they are less vulnerable to changes in external temperatures.
14
Q
“thermostat” for thermoregulation is located in
A
hypothalamus
15
Q
excretory system has three main jobs:
A
to remove waste
monitor water balance
control pH
16
Q
Main organs of the excretory system
A
kidneys (remove metqbolic waste, maintain blood chemistry + water levels)
liver (transforms ingested toxins into soluble compounds that can be eliminated in kidneys, or create metabolites which are hazardous products of protein metabolism)
large Intestine (removes toxic waste from digestive system)
17
Q
There are two types of waste produced by the human body:
A
Digestive waste
Cellular waste (byproducts of cell respiration e.g. carbon dioxide and nitrogenous waste)
18
Q
nitrogenous waste + 3 types
A
cellular waste based in nitrogen (typically proteins)
Ammonia
Urea
Uric acid
19
Q
Ammonia waste
A
- a water-soluble toxic gas.
- type of waste that is a by-product of protein digestion.
- amino group is removed through a process called deamination.
20
Q
Deamination
A
occurs in the liver of humans. The by-product of deamination is ammonia
21
Q
Urea
A
two molecules of ammonia combined with co2, is created to detoxify ammonia in the body
22
Q
uric acid
A
waste product created through breakdown of nucleic acids
23
Q
human urinary system
A
- most important waste-removal system in your body
- removes waste from blood, and balances levels
24
Q
what tubes empty urine into the bladder
A
ureters
25
on average how much can a bladder hold and at what volume does it typically signal to eliminate
- 600ml
- signalled between 200-400mL
26
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name parts of kidney and identify where nephrons would be
located in the cortex and extend into the medulla, surrounded by capillaries
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Each nephron consists of five main parts:
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Bowman’s capsule (containing the glomerulus)
Proximal tubule
Loop of Henle
Distal tubule
Collecting duct
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afferent arteriole
blood in
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efferent arteriole
blood out
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artery vs vein
Arteries carry blood away from the heart, and veins carry blood towards the heart. With the exception of pulmonary blood vessels, arteries carry oxygenated blood and veins carry deoxygenated blood.
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path of blood flow in nephron
- afferent arteriole brings blood to nephron
- blood branches into glomerulus (capillary bed) which is enclosed in bowman's capsule
- fluid from blood is squeezed into the capsule
- filtered blood leaves via efferent arterioles which branches into pertibular capillaries which will reabsorb the non waste that is filtered out from the blood during urine formation
32
3 steps in urine filtraion
- Filtration (in glomerulus and bowmans capsule - fluid is filtered out blood in glomerus and flows into the bowmans capsule)
- Reabsorption (in proximal tube, filtrate from b capsule are selctively reabsorbed via active/passive transport, descending side of loop of Henle water is lost through osmosis, and ascending loop of henle the Na+ is actively tansported into the medulla)
- Secretion (starts in distal tube where H+, Na+, K+ are selectively reabsorbed into nephron via active transport, water is removed which regulates concentration of pH and electrolytes. The remainder is urine which moves to collecting duct to be secreted into the bladder)
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substances transported in 1st step of urine filtration
Na+, Cl-, water, H+, glucose, amino acids, vitamins, minerals, urea, uric acid via pressure
34
substances transported in 2nd step of urine filtration
Water at descending side of loop of Henle through osmosis, and NaCl at ascending loop of Henle via active transport
35
substances transported in 3rd step of urine filtration
Water, Salt, Urea, Uric Acids, K+, bicarbonate, H+
36
what to systems are required for the urinary system to maintain homeostatis and why
endocrine and nervous, nerves will pick up signals to activate hormones that activate negative feedback systems used to maintain balance
37
Antidiuretic hormone (ADH),
helps to regulate the osmotic pressure of body fluids by causing the kidneys to increase water reabsorption. ADH moves along specialized fibres from the hypothalamus to a gland called the pituitary gland, which stores and releases ADH into the blood.
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osmoreceptors
specialized nerve receptors in the hypothalamus that picks up changes in osmotic pressure in the blood
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acts on the nephrons to increase Na+ reabsorption
aldosterone
40
Aldosterone is produced in
the cortex of the adrenal glands
41
Describe how the bicarbonate buffer helps the kidneys to regulate blood pH through negative feedback when pH is too high
The carbonate ion bonds to any excess H+ ions to form carbonic acid ( H2CO3 ) and so lowers the blood pH.
The carbonic acid breaks down into carbon dioxide and water, and the CO2 is transported to the lungs, where much of it is exhaled.
42
Describe how the bicarbonate buffer helps the kidneys to regulate blood pH through negative feedback when pH is too low
The carbonic acid breaks down into H+ ions and water, in order to raise the blood pH.
43
what test is conducted to detect kidney disorders
urinalysis
44
Diabetes insipidus
occurs when the ADH-producing cells of the hypothalamus, or the nerve tracts leading from the hypothalamus to the pituitary gland, are destroyed. Without ADH to regulate water reabsorption, urine output increases considerably, so none of the remaining 15% (after the other 85% has been reabsorbed at the proximal tubule), is recovered. As much as 20 L of dilute urine may result, creating a strong thirst response, and a severe need to replace lost water.
45
Urology Glomerulonephritis
This disease is also known as nephritis or the inflammation (swelling) of the nephrons. one type of nephritis affects the tiny blood vessels of the glomerulus. Toxins produced by invading microbes destroy the tiny blood vessels, altering the permeability of the nephron. This means that proteins and other large molecules are able to pass into the nephron. When the nephrons are destroyed, no mechanism occurs in the nephron membrane to reabsorb protein; instead, the protein remains in the nephron and draws water from the neighbouring peritubular capillaries, which, in turn, increases the output of urine.
46
diabetes mellitus
When a deficiency of insulin occurs because of a defect in the pancreas, blood sugar levels tend to rise. The cells of the proximal tubule are supplied with enough ATP to reabsorb 0.1% of blood sugar. When higher blood sugar concentrations exist, such as in a person with diabetes, the excess sugar remains in the nephron. This excess sugar in the nephron draws water into the nephron, increasing the volume of urine. Individuals with diabetes mellitus expel large volumes of urine, which explains why they are often thirsty and have to replace the lost water.
47
UTI
If bacteria accumulates in the urethra it may cause an infection in the bladder. Once it is in the urinary tract, the infection may cause an immune response which may include increased white blood cells and/or fever. If the infection spreads upwards through the ureter into the kidney, there can be more severe health complications such as kidney failure or the bacteria entering the bloodstream (a condition known as sepsis).
48
Kidney stones
occur when solutes from the blood precipitate (solidify) out of the urine. These solutes can accumulate and lodge themselves in the renal pelvis or move into the narrow ureter. As the kidney stones move into the bladder, they can tear delicate tissue and cause severe pain and discomfort. They can also work their way further down the excretory passage and lodge in the urethra, causing a burning sensation, along with excruciating pain.
49
Dialysis Technology
The term “dialysis” means the exchange of substances across a semipermeable membrane. A dialysis machine is used for people whose kidneys cannot effectively process bodily wastes. The principles of diffusion and blood pressure both influence the operation of a dialysis machine.
50
Dialysis Technology
The term “dialysis” means the exchange of substances across a semipermeable membrane. A dialysis machine is used for people whose kidneys cannot effectively process bodily wastes. The principles of diffusion and blood pressure both influence the operation of a dialysis machine.
51
6 things the endocrine system is instrumental in:
regulating mood
growth and development
tissue function
metabolism
sexual function
reproductive processes
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endocrine system
is a system of glandular tissues that produce and secrete special messenger molecules called hormones, into the blood
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hormones
special messenger molecules. The word “hormone” means “to excite or set into motion.” Hormones are often produced in one part of the body and then travel in the blood to a target tissue cell, bind to it, and affect it in some way.
54
Target hormones + 2 examples
Target specific tissues and cells of the body, rather than all cells.
Parathyroid hormone—regulates calcium levels in the body (targets bone tissue)
Gastrin—stimulates cells of the stomach to produce digestive enzymes
55
Non-Target hormones + 3 examples
Impact many cells of the body, instead of just one specific cell type.
Growth hormone (GH) or somatotropin (STH)—regulates the development of long bones and cell division
Insulin—regulates blood sugar by increasing the permeability of all cells to glucose
Epinephrine (adrenalin)—is produced in times of stress to
56
There are two types of hormones that differ, both in chemical structure and action:
steroid and protein hormones.
57
There are two types of hormones that differ, both in chemical structure and action:
steroid and protein hormones.
58
Steroid hormones are
derivatives of cholesterol
- 3 types: male + female sex hormones, and cortisol
- composed of complex, fused rings of carbon, hydrogen, and oxygen molecules. Steroid hormones are not soluble in water but are soluble in fat.
59
The mechanism of action for steroid hormones
- hormones diffuse from the capillaries into the interstitial fluid and then into the target cell.
1. The hormones combine with receptor molecules located in the cytoplasm.
2, This hormone-receptor complex then moves into the nucleus of the cell.
3. The hormone-receptor complex and attaches to a segment of DNA that has a complementary shape, causing transcription of an mRNA strand.
4. The newly produced mRNA diffuses out of the nucleus and into the cytoplasm where it is translated into a specific protein.
60
Protein hormones
They contain chains of amino acids that vary in length.
They are soluble in water.
They bind at specific receptor sites
e.g. insulin and GH
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The mechanism of action for protein hormones
- must work in a different way from steroid hormones as cannot cross the phospholipid bilayer easily.
- Some form a hormone-receptor complex that activates the production of an enzyme called adenyl cyclase, which, in turn, causes the cell to convert ATP into cyclic adenosine monophosphate (cyclic AMP).
- The cyclic AMP functions as a messenger, activating enzymes in the cytoplasm to carry out their normal functions.
62
describe the pituitary gland
- often called “the master gland,” because it exercises control over other endocrine glands.
- produces and stores several hormones. (ADH, oxytocin)
- small sac-like structure that is connected to the hypothalamus.
- has two lobes: the posterior lobe and the anterior lobe.
- controlled by the hypothalamus, which is part of the brain and the nervous system.
63
antidiuretic hormone
ADH, hormone responsible for increasing water reabsorbtion in urinary system
64
Thyroid-stimulating hormone (TSH)
- p gland hormone / anterior lobe
- impacts Thyroid gland
- Stimulates release of thyroxine from the thyroid. Thyroxine regulates cell metabolism
65
Adrenocorticotropic hormone (ACTH)
- p gland hormone / anterior lobe
- impacts Adrenal cortex
- Stimulates release of hormones involved in stress responses
66
Somatotropin (STH) or growth hormone (GH)
- p gland hormone / anterior lobe
- impacts most cells
- Promotes growth and cell division
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Follicle-stimulating hormone (FSH)
- p gland hormone / anterior lobe
- impacts ovaries+testes
- In females, stimulates follicle development in ovaries
In males, promotes the development of sperm cells in testes
68
Luteinizing hormone (LH)
- p gland hormone / anterior lobe
- impacts ovaries, testes
- In females, stimulates ovulation and formation of the corpus luteum
In males, stimulates the production of sex hormone testosterone
69
Prolactin
- p gland hormone / anterior lobe
- impacts mammary glands
- Stimulates and maintains milk production in lactating females
70
Oxytocin
- p gland hormone / posterior lobe
- impacts Uterus, mammary glands
- Initiates strong contractions for childbirth
- Triggers milk release in lactating females
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Antidiuretic hormone (ADH)
- p gland hormone / posterior lobe
- impacts Kidneys
- Increases water reabsorption by kidneys
72
4 major types of hormone functions
Hormones that regulate blood sugar levels
Hormones that respond to stress
Reproductive hormones
Hormones affecting metabolism
73
the kinds of hormones involved in regulated blood sugar
- pancreatic hormones + stress hormones (adrenal glands)
74
Explain the roles of the hormones insulin and glucagon in maintaining blood sugar homeostasis
Glucagon and insulin have opposite effects. Insulin is released from the beta cells in the pancreas when blood sugar levels are high (such as after a meal), causing the cells of the muscles, liver, and other organs to draw glucose out of the blood.
When blood levels are low (such as between meals or when fasting), glucagon is released by the alpha cells of the islets of Langerhans and promotes the conversion of glycogen to glucose, which is released into the blood, thus raising the blood sugar level.
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Hormones that have opposite effects are called
antagonistic hormones
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hormone released for hyperglycemia
insulin
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hormone released for hypoglycemia
glucagon
78
The cells that produce hormones in the pancreas are located in structures called the
islets of Langerhans. There are more than 2000 tiny islets, each containing thousands of beta or alpha cells. The beta cells produce the hormone insulin, and the alpha cells produce the hormone glucagon.
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bodys response to insulin
Cells in your muscles, liver, and other organs to become more permeable to glucose.
When the glucose is drawn out of your blood, this lowers your blood glucose level.
Once in your liver, the glucose is converted to glycogen (the storage form of glucose).
80
bodys response to glycagon
During periods of fasting, glucagon is released and promotes the conversion of glycogen to glucose, which is released into the blood, thus raising the blood sugar level.
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Diabetes mellitus
An individual with diabetes mellitus cannot produce enough insulin to regulate blood glucose levels. If left untreated, diabetes can cause blindness, kidney failure, nerve damage, and in extreme cases, the need for limb amputation.
If a deficiency of insulin exists, blood sugar rises substantially, resulting in hyperglycemia or high blood sugar.
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The symptoms associated with hyperglycemia are:
Glucose in the urine.
Dehydration and thirst caused by glucose in the nephron, which in turn draws water out of the blood through osmosis.
Low energy levels because of a lack of insulin, the permeability of glucose into the cells does not increase, so less glucose is burned and less ATP is made.
There are three types of diabetes mellitus. Read more about each type in the table below.
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describe type 1 diabetes
Represents 10% of all diabetes cases.
Inability to produce insulin, due to an early degeneration of the beta cells in the islets of Langerhans.
Occurs in early childhood
Insulin must be taken daily in order to survive
84
difference between type 1 diabetes, and type 2 + gestational diabetes
type 2: most common, decrease in insulin production or ineffective use of insulin being produced in body (resistance), can be managed with diet and exercise or preveneted
gestational - occurs in 2-4% of pregnant women, increases chance of type 2 in woman, and type 1 in baby, can be controlled with diet and exercise
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adrenal gland
above each kidney
- releases stress hormones
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short term stress response
- medulla of adrenal gland releases epinephrine and norepinephrine when signalled by the hypothalamus to rise blood sugar quickly, increasing circulatory flow to allow quicker cellular respirations, iris dilates to increase awareness
87
long term stress response
- cortex of adrenal gland
- after hormone ACTH from pitutiary gland is released, eleases Glucocorticoids (e.g. cortisol) and Mineralocorticoids (e.g. aldosterone) are released and carried to liver and muscle to raise blood sugar and maintain fluid levels
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Glucagon
Converts glycogen to glucose
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Epinephrine
Mobilizes energy release from stored carbohydrates and fats
Increases blood glucose and fatty acids
Accelerates heart rate and breathing
90
Insulin
Decreases the breakdown of glycogen in the liver
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3 problems due to longterm stress
Higher blood sugar
(Alters osmotic balance between blood and extracellular fluids; can lead to increased fluid uptake by the blood and increased blood pressure. Increases water loss from nephron)
Increased blood pressure
(Can rupture blood vessels due to higher pressure. Increases blood clotting)
Increased heart rate
(Can lead to higher blood pressure;Can damage heart muscle)
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Reproductive hormones
control the development of reproductive systems during growth, as well as their use when sexually mature. Each sex has its own set of reproductive hormones.
93
androgens
(male sex hormone). The main androgen is testosterone.
94
Testosterone:
is manufactured by the interstitial cells of the testes.
secretion increases sharply at puberty and is responsible for the development of the so-called secondary sexual characteristics (for example, beard growth, deepening of the voice, pubic hair development, and so on) of men.
is also essential for the production of sperm (spermatogenesis). Testosterone is also associated with sex drive.
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gonadotropin-releasing hormone (GnRH).
hormone in hypothalmus that when secreted activates pituitary gland to release FS and LH to produce testosterone levels to increase follicle production
96
oogenesis
process of female follicles being developed
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Ovulation
process of releasing a mature haploid egg (which contains 23 chromosomes instead of 46
98
describe 4 phases of menstrual cycle
Flow phase—this is the shedding of the endometrium, or menstruation. This phase marks the beginning of the menstrual cycle and lasts for approximately 5 days.
Follicular phase—this phase is characterized by the development of the follicles within the ovary. As the follicle cells develop, the hormone estrogen is secreted, and its concentration increases. This takes place during days 6 to 13 of the cycle.
Ovulatory phase—estrogen levels decline and the egg bursts from the ovary and follicle cells differentiate into the corpus luteum.
Luteal phase—in this phase, estrogen levels are restored as the corpus luteum develops. This occurs between days 15 and 28 and prepares the uterus to receive a fertilized egg, as the corpus luteum releases both estrogen and progesterone. These hormones stimulate the endometrium (lining of the uterus or womb) and prepare the uterus for an embryo. They also inhibit further ovulation and prevent uterine contractions from occurring. If progesterone levels fall, uterine contractions begin. If fertilization does not occur, the concentration of estrogen and progesterone drops, causing the endometrium to shed. This shedding marks the end of the cycle and the beginning of the next.
99
There are three different kinds of glands that affect metabolism:
Thyroid gland - at base of neck near trachea ; regulates body metabolism and the rate at which blood glucose is metabolized (hormones: triiodothyronine, thyroxine, and calcitonin)
Parathyroid glands - regulate calcium ion levels in the blood (hormone: parathyroid hormone)
Anterior pituitary gland - influences the growth of long bones and accelerates protein synthesis (hormone: growth hormone (somatotropin))
100
The thyroid secretes three hormones:
Thyroxine (T4) and triiodothyronine (T3) which both regulate body metabolism and the growth and differentiation of tissues.
Calcitonin which acts on the bone cells to lower the level of calcium ions found in the blood. More on this in the next section.
101
t4 and t5 negative feedback process
Receptors in the hypothalamus are activated when the metabolic rate decreases.
Nerve cells secrete thyroid-releasing hormone (TRH).
TRH stimulates the pituitary gland to release TSH.
TSH is carried through the blood and reaches the thyroid gland, which, in turn, releases T4 and T3.
T4 and T3 concentrations increase in the blood and stimulate sugar oxidation.
When levels of thyroxine and triiodothyronine increase to a critical point, they cause the pathway to be “turned off ” by inhibiting the release of TRH from the hypothalamus, thus stopping the production of TSH in the pituitary gland (negative feedback).
102
Hyperthyroidism
Individuals who produce high levels of T4 and T3 have a condition called hyperthyroidism. These people may lose weight and may often feel warm, due to the higher respiratory rates they experience because of increased glucose oxidation.
103
Hypothyroidism
Conversely, those who gain weight easily due to low levels of T4 and T3 production have hypothyroidism. In this condition, glucose is not consumed at normal rates, and it gets stored in the liver. Once the liver reserves are full, the body converts sugar into fat. People who secrete low levels of T4 and T3 often experience muscle weakness, cold intolerance, and have dry skin and hair.
104
Parathyroid glands
The parathyroid glands secrete parathyroid hormone (PTH). PTH regulates blood calcium levels and is another example of a negative feedback system. Low blood calcium levels trigger the release of PTH.
105
What happens when there is a decrease in blood calcium levels?
Parathyroid hormone will work to increase the calcium levels using three methods:
Bones: It increases the blood calcium levels by accelerating the breakdown of bones to produce higher calcium levels.
Kidneys: causes reabsorb calcium ions from the filtrate to increase levels.
Small intestine: causes absorption of calcium ions from undigested food to increase levels.
106
What happens when there is an increase in blood calcium levels?
The thyroid gland produces calcitonin which acts on bone cells to decrease the loss of calcium from bones. Thus, decreasing the levels of calcium in the blood.
107
nervous system
- is a specialized organ system that connects the external environment to the internal environment and helps to maintain homeostasis.
- network of specialized cells that communicate information about your surroundings and your internal state. It processes this information and causes reactions throughout your body. - linked to all systems of the body, including the cardiovascular, respiratory, and endocrine systems.
108
The nervous system has two main divisions:
The Central Nervous System (CNS)
The Peripheral Nervous System (PNS)
109
The CNS
acts as a coordinating centre for incoming and outgoing information. The CNS consists of the brain and spinal cord.
110
The PNS
The PNS carries information between the organs of the body and the CNS. The PNS consists of nerves.
The PNS is further subdivided into the somatic nervous system and the autonomic nervous system.
111
The somatic nervous system controls the:
skeletal muscle
bones
skin
112
Somatic nerves can be either:
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sensory nerves (which relay sensory information)
motor nerves (which generate muscle responses)
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113
autonomic nervous system + its 2 parts
controls the internal organs of the body.
- sympathetic nervous system which controls, for example, the “fight or flight” reaction
- parasympathetic nervous system which controls functions such as sleep and digestion
114
The nervous system contains two types of nerve cells:
Glial cells
- non-conducting cells
- provide structural support and perform metabolic functions for the nervous system.
Neurons
- functional units of the nervous system
115
myelin sheath
a glial cell that surround nerves act as a kind of insulation, ensuring efficient transmission of electric charge. formed by special glial cells called Schwann cells
116
three types of neurons:
Sensory neurons
These neurons sense and relay information from the environment to the CNS for processing. They are located in clusters called ganglia.
Interneurons
These neurons link neurons within the body and are found mostly throughout the brain and spinal cord. They integrate and interpret the sensory information and connect neurons to outgoing motor neurons.
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Motor neurons (also known as efferent neurons)
These neurons send information to the “effectors.” Effectors are muscles, organs, and glands.
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All neurons are made up of three parts:
dendrites - parts of a neuron that receive information. This comes either from sensory receptors or from other nerve cells, such as motor neurons. Dendrites conduct nerve impulses toward the cell body.
the cell body- portion of the neuron that contains the nucleus and the majority of the cytoplasm.
axon - extension of a neuron. It carries nerve impulses away from the cell body towards other neurons or effectors.
118
describe an axon
- Axons are extremely thin;
- often covered with a white coat of fatty protein called the myelin sheath.
- areas between the sections of myelin sheath are known as the nodes of Ranvier. Nerve impulses jump from node to node, which speeds up the conduction process. Nerve impulses move much faster along myelinated nerve fibres than they do along non- myelinated nerve fibres.
119
Communication among nerves results in
neural circuits
120
A reflex arc
is a simple neural circuit that runs through the spinal cord. It provides a way for a reflex action to occur.
Stimulus → Sensory neuron → Interneuron → Motor neuron → Response
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Nerve impulses
are electrochemical messages created by the movement of ions through the nerve cell membrane. When a nerve gets stimulated (for example, by a pinprick or the sight of someone’s face), a rapid change occurs in the electrical potential difference (commonly just called “potential”) across the nerve membrane.
122
electrical potential difference/potential across an axon at rest + stimulated
-70mV(inside axon is negative) and +40mV (inside axon is positive)
123
action potential
the voltage difference across a nerve cell membrane when the nerve is excited.
124
voltage difference across the membrane during the resting stage is called the
resting potential
125
potential of a resting neuron is about –70 mV, which indicates
the difference between the number of positive charges found on the inside of the membrane in relation to the outside.
126
membrane becomes negatively charged due to the movement of two positive ions out of the cell:
Sodium (Na+)
Potassium (K+)
127
polarization
process of charging neuron membrsne via active transport pumping out Na and in K ions at a 3:2, losing more positive charge than it gains creating a negative resting potential/aka polarization
128
The rapid influx of sodium ions causes a charge reversal known as
depolarization
129
When the nerve is excited by a stimulus
The gates of the sodium channel open
The gates of the potassium channel close.
130
refractory period
The time required for the nerve cell to become repolarized and be able to activate again
131
stimulus must generate a depolarization at or above a certain voltage in order to produce a response in the nerve. This critical level is known as
the threshold level.
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intensity of the nerve impulse and speed of transmission
constant / all or none response
133
how does a brain now the intensity of a stimulus if nerve cells have an all or none response
by counting the amount of nerve impulses it received, a more intense stimulus will generate high nerve impulses
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synaptic transmission
The process by which one nerve cell communicates with another nerve cell
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synapsess
small spaces between neurons, or between neurons and effectors
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Synapse structure
The neuron transmitting the impulse is called the presynaptic neuron.
The neuron receiving the impulse is called the postsynaptic neuron.
At the end of the axon in the presynaptic neuron is a plate where small vesicles containing chemicals called neurotransmitters are released.
137
Neurotransmitters
diffuse across the synapse and attach to receptors on the postsynaptic neuron, where they cause depolarization.
many different types of neurotransmitters
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Acetylcholine
is a common neurotransmitter found in the end plates of many nerve cells. Acetylcholine acts as an excitatory neurotransmitter on many postsynaptic neurons by opening their sodium ion gates and causing depolarization. After depolarization has occurred, the postsynaptic neuron releases the enzyme, cholinesterase, to destroy acetylcholine. This allows the sodium gates to close so that the postsynaptic neuron can begin its recovery phase.
139
Describe, in detail how a nerve impulse is formed.
When the nerve is excited because of a stimulus, the cell membrane becomes more permeable to sodium than potassium.
The sodium gates open, while the potassium gates close.
Sodium ions rush into the nerve cell because of the electrochemical gradient. This process is known as depolarization.
Once the charge on the inside becomes positive, the sodium gates close, stopping the influx of sodium.
The sodium- potassium pump restores the condition of the resting membrane by transporting sodium ions out of the neuron while moving potassium ions into the neuron, at a ratio of 3 Na+ to 2 K+ ions.
The energy for the pump comes from ATP, and the process of restoring the original polarity of the nerve membrane is called repolarization.
During synaptic transmission, a neurotransmitter travels through the synaptic cleft (the gap between neurons) and binds to a receptor on the post-synaptic membrane.
This results in the nerve impulse being transmitted down the next neuron.
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describe the brain
a concentration of nervous tissue that acts as the coordinating centre of the nervous system. The brain is covered by a three-layered protective membrane known as meninges. These three membrane layers form the blood-brain barrier, which determines what chemicals in the blood will reach the brain.
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spinal cord
carries sensory nerve messages from receptors in the body to the brain, as well as carrying nerve messages from the brain to the muscles, organs, and glands.
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cerebrospinal fluid
is found between the innermost and middle layers of the meninges of the brain, and also through the central canal of the spinal cord.
- functions as both a shock absorber and a transport medium for carrying nutrients to the brain cells, while it takes wastes from the brain cells to the blood.
143
spinal nerve tissues
White matter
The outside edge of the cord contains both sensory and motor neurons that are covered in myelin, which makes this nerve tissue look white.
Grey matter
The core of the spinal cord consists of unmyelinated interneurons, which makes them look grey.
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brain can be divided into three main regions:
the forebrain, the midbrain, and the hindbrain.
145
The forebrain contains:
The cerebral cortex
Two halves or hemispheres,
There are four main lobes of the forebrain:
Frontal
Parietal
Temporal
Occipital
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The cerebral cortex,
made of grey matter and contains many folds and fissures. This is the region of the brain where higher-level thinking occurs.
147
Describe forebrain hemispheres
2 halves, each with its own special functions:
=The right-hand side of the forebrain is linked to visual patterns or spatial awareness.
-The left-hand side of the brain is linked to verbal skills.
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corpus callosum
bundle of nerves that allow hemispheres to communicate to each other
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Lobes of forebrain
Sections called lobes are responsible for processing information from your senses, as well as higher-order thinking.
Frontal
Parietal
Temporal
Occipital
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Frontal lobe
responsible for movement of voluntary muscles (walking/speech)
linked to intellectual activities, mood and personality, especially self- control, reasoning, and abstract thought
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Temporal lobe
responsible for vision and hearing
linked to memory and interpretation of sensory information
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Parietal lobe
responsible for touch and temperature awareness
linked to emotions and interpretation of speech
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Occipital lobe
responsible for vision
linked to interpretation of visual information
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The midbrain:
Consists of four spheres of grey matter.
Acts as a relay centre for some eye and ear reflexes.
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The hindbrain
Joins with the spinal cord.
Controls breathing movements, the diameter of blood vessels, and heart rate.
Consists of the cerebellum, pons, and medulla oblongata.
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cerebellum
controls limb movements, balance, and muscle tone.
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The pons,
which means “bridge,” relays information between the two regions of the cerebellum, and between the cerebellum and the medulla oblongata.
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The medulla oblongata is the
connection between the peripheral and central nervous systems. It controls involuntary muscle action and acts as the coordinating centre for the autonomic nervous system.
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The autonomic system is
part of the peripheral nervous system that regulates organs of the body without conscious control. It works with the endocrine system to adjust the body to changes that take place in the external and internal environments.
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2 subsections of the autonomic system, and main difference in responses
Sympathetic system → fight or flight
Parasympathetic system → rest and digest
