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Human Biology ATAR > endocrine and nervous > Flashcards

endocrine and nervous Flashcards

1
Q

endocrine glands x2

A

• Endocrine glands x2:
- Exocrine gland: secrete into a duct that carries the secretion to the body surface or to one of the body cavities
› E.g. Sweat glands, mucous glands, salivary glands, glands of the alimentary canal
- Endocrine gland: (aka ductless glands) secrete hormones into extracellular fluid that surrounds the cells that make up the gland. Secretions pass to capillaries to be transported via blood.
› Located in highly vascularised areas to ensure quick delivery

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2
Q

pineal gland

A 
•	Pineal gland: 
-	Deep inside brain
-	Size of pea then decreases
-	Secretes melatonin
›	regulation of sleep patterns
›	production of melatonin stimulated by darkness and inhibited by light
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3
Q

thymus gland

A

• Thymus gland:
- In chest above heart and behind sternum
- Shrinks after puberty
- Secretes thymosins
› Influence maturation of T-lymphocytes (disease fighting cells)

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4
Q

gonads

A
  • Androgens: male sex hormones. Development and maintenance of male sex characteristics. Made in testes, women also have but at much lower levels
    › Maintenance of muscle mass and bone density
    › Made in testes under control of LH and FSH
  • Oestrogen and Progesterone: female sex hormones. Development and maintenance of female sex characteristics.
    › With gonadotropic hormones of the pituitary gland, regulate menstrual cycle and changes that occur in pregnancy
    › Made in ovaries under control of LH and FSH
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5
Q

thyroid gland

A

• Thyroid gland:
- In neck below larynx, butterfly shape
- Two lobes on either side of trachea
› Joined by narrow piece of tissue across front of trachea (isthmus)
- Follicular cells secrete thyroxine and triiodothyronine in response to thyroid stimulating hormone
- Triiodothyronine: T3, 3 iodine atoms attached
- Thyroxine: (amine hormone) T4, 4 iodine atoms attached, 20%
› much less active bust lasts longer
› controls body metabolism
› regulates reactions in which complex molecules are broken down to release energy, and where complex molecules are made from simple ones
› brings about release of energy and maintains body temperature
- Calcitonin: released by C-cells. Regulate calcium and phosphate in the blood
› When calcium is high in blood, calcitonin reduces reabsorption of calcium by kidneys and reduces breakdown of bone.
› When phosphate in high in blood, calcitonin moves phosphate into bone and reduces reabsorption by kidneys
› Therefore, decrease calcium and phosphate concentration

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6
Q

parathyroid gland

A

• Parathyroid gland:
- Rear surface of lobes of thyroid gland
- Usually 4, pea sized, embedded in thyroid
- Secretes parathormone which increase calcium in blood and phosphate secretion in urine
› In bones: increased calcium released into blood
› In intestines: increased calcium absorbed from digested food
› In kidneys: increased calcium reabsorbed into blood from urine
- Negative feedback

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7
Q

adrenal gland

A

• Adrenal glands:
- 2 adrenal glands, sit on top of each kidney
› Adrenal medulla (inner)
› Adrenal cortex (outer)

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8
Q

adrenal medulla

A

• Adrenal medulla:
- Produces the catecholamine hormones:
› Adrenaline: (epinephrine) prepare body to react to threatening situations (flight/fight response)
› Noradrenaline: (norepinephrine) acts like a neurotransmitter in sympathetic nerves. Similar to adrenaline. Increases rate and force of the heart beat.

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9
Q

adrenal cortex

A

• Adrenal cortex: more than 20 hormones known as corticosteroids

  • Aldosterone: acts on kidney. Reduces amount of sodium, increases amount of potassium in urine. Hoemostasis of sodium and potassium
  • Cortisol: promotes normal metabolism, helps body withstand stress and repair damaged tissue. Anti-stress hormone, increase blood pressure and glucose metabolism, inhibits immune response
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10
Q

pancreas

A

• Pancreas:
- Below stomach, alongside duodenum
- Both exocrine and endocrine
› Exocrine: (99%) secretes digestive enzymes into small intestine using pancreatic duct
› Endocrine: made of clusters of cells called islets of Langerhans (aka pancreatic islets). Secretes insulin and glucagon
- Insulin: made by beta cells
› Decrease amount of glucose in blood by promoting uptake of glucose from the blood by body cells
› In liver: insulin causes glucose -> glycogen and fat
› In skeletal muscles causes glucose -> glycogen
› Fat storage tissue: glucose -> fat
› Controlled by a negative feedback system
- Glucagon: secreted by alpha cells, opposite to insulin
› Increase blood glucose level by promoting breakdown of glycogen -> glucose in the liver
› Also stimulates breakdown of fat in liver and fat storage sites

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11
Q

other endocrine tissues

A

• Other endocrine tissues:

  • Stomach and small intestine secrete hormones that coordinate exocrine glands of digestive system
  • Kidneys (erythropoietin) stimulates production of Red blood cells by the bone marrow
  • Heart secretes hormone that lowers BP
  • Placenta secretes hormones to maintain pregnancy, stimulate foetal development and mammary glands
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12
Q

hypothalamus and pituitary

A
  • Hypothalamus and pituitary gland work together to control the functioning of many other glands
  • The secretions of the pituitary gland are controlled by the hypothalamus by either neurosecretory cells or blood transport (via hypophyseal portal veins) of releasing or inhibiting factors
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13
Q

hypothalamus

A

• Hypothalamus:
- Connection between endocrine and nervous system
- Below thalamus and above pituitary gland
- Hypothalamus stimulates pituitary gland
- Many functions carried out through pituitary gland
- Secretes releasing factors which stimulate the secretion of a hormone, or inhibiting factors which slow down secretion of a hormone
› Factors travel through blood vessels to anterior lobe -> effects secretion of its hormones
› Other hormones produced by hypothalamus pass along nerve fibres to posterior lobe -> then release

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14
Q

pituitary gland

A

• Pituitary gland: (hypophysis) joined to hypothalamus by a stalk called the infundibulum

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15
Q

anterior lobe

A

• Anterior lobe: (adenohypophysis)

  • No nerves connecting it to the hypothalamus, but connected by a network of blood vessels in the infundibulum (capillary network) (hypophyseal portal system)
  • Secretions controlled by releasing and inhibiting factors released by hypothalamus
  • Gonadotropins: affects gonads, FSH and LH
  • Growth hormone: stimulates body growth, especially skeletal
  • Thyroid stimulating hormone: stimulate production and release of hormones from the thyroid gland
  • Adrenocorticotropic hormone (ACTH): control production and release of some hormones from adrenal cortex
  • Prolactin: initiate and maintain milk production
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16
Q

posterior lobe

A

• Posterior lobe: (neurohypophysis)
- Joined to hypothalamus by nerve fibres that come from nerve cell bodies in the hypothalamus and pass through infundibulum.
- Not a true endocrine gland as it doesn’t secrete substances, it stores and releases them
- Hormones are made in the hypothalamus by nerve cells. (in axon terminals)
› Nerve cells have long extensions that pass through the infundibulum to the posterior lobe
- Hormones stored here for release
› Triggered by nerve impulses initiated in the hypothalamus conducted along cell extensions
- Oxytocin: contraction of uterine muscles and milk letdown reflex
- ADH (vasopressin): kidneys, to remove water from urine, retain fluid. Increasing the permeability of the walls, allowing water to re-enter the blood capillaries.
› In high concentrations, ADH can cause constriction of small arteries (arterioles)

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17
Q

hormones

A

• Hormones:
- Chemicals secreted by endocrine glands, transported via blood
- Can change cell’s functioning by changing cell type, activities or quantities of proteins produced
- They can:
› Activate genes to produce certain enzymes
› Change shape or structure of enzyme
› Change rate of enzyme production by changing rate of transcription/ translation
- May effect:
› All body cells
› Target cells
› Target organs

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18
Q

steroid hormones

A

• Steroid Hormones:
- Lipid soluble, can’t dissolve in water
- Once released in the blood, bind to transport proteins to travel in bloodstream
- Once reaching target cells, they separate from the transport protein and diffuse across the cell membrane
- Inside cell: combine with receptor protein in cytoplasm/nucleus
› Hormone-receptor complex activates genes controlling formation of certain proteins
› Bind to promoter section of a gene and stimulate/inhibit protein synthesis
- Slow to have an effect but long lasting
- Secreted by adrenal cortex and gonads

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19
Q

protein and amine hormones

A

• Protein and Amine Hormones:
- Water soluble, can’t diffuse across -> attaches to receptor protein in membrane
- Combination of hormone and receptor causes a secondary messenger substance to diffuse through the cell to activate certain enzymes/ alter cell activities
› Increase/decrease rate of reactions
- Quick but short living
- Protein: secreted by pancreas and pituitary gland
- Amine: adrenaline and thyroxine

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20
Q

hormone receptors

A 
•	Hormone receptors: 
-	On surface of the target cell
-	Specific
›	Each type only bonds with one specific molecule
›	Limited number
›	“lock and key” analogy
-	Saturated:
›	Once all receptor molecules are occupied by hormone molecules, the addition of more hormones doesn’t increase the rate of the cell’s activity
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21
Q

enzyme amplification

A

• Enzyme Amplification:
- Hormone triggers a cascading effect
› Number of reacting molecules involved is increased x100 or x1000 for each step along metabolic pathway
- Series of chemical reactions, where product of one step is an enzyme that produces a greater number of products in the next step

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22
Q

hormone clearance

A

• Hormone clearance:
- Once hormone has produced required effect, it must be turned off -> by breaking down in target cells, most in liver/kidney
› Excreted in bile/urine

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23
Q

control of hormone secretions

A

• Control of hormone secretions:

  • Over/under secretion cause abnormal body functions
  • Regulated by negative feedback systems: response produced by secretion of hormone is the opposite of the stimulus that caused the secretion
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24
Q

nerve cells

A
  • Nervous system receives and processes information from sense organs and brings about responses to the information received
  • Nerve cells (neurons): basic structural and functional unit of the nervous system
    › Rapid communication
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25
Q

neuron structure

A
  • Neuron structure:
    › Cell body: contains nucleus, controls cell’s functioning, directs metabolism, no role in neural signalling. Holds the organelles (mitochondria, Golgi body, etc)
    › Dendrites: short extensions of the cytoplasm of the cell body. Increase surface area. Receive nerve messages. High branched and carry messages/nerve impulses into the cell body
    › Axon: single long extensions of cytoplasm. Carries nerve impulses away from the body of the cell to other cells. Length varies. At its end, axon divides into many small branches which terminates at the axon terminal
    › Myelin sheath: layer of white fatty material that covers axons.
  • Nerve fibres with myelin: myelinated fibres
  • Nerve fibres without myelin: unmyelinated fibres
  • Outside brain and spinal cord it is formed by Schwann cells (wrap around the axon)
  • Gaps in myelin sheath called nodes of Ranvier
  • In brain/spinal cord: made by oligodendrocytes
    › White matter: myelinated fibre appears white
    › Grey matter: areas made of cell bodies and unmyelinated fibres
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26
Q

functions of myelin sheath

A
  • Function of myelin sheath:
    1. Acts as an electrical insulator (stops nerve signal leakage)
    2. Protects axon from damage
    3. Speeds up movement of nerve impulses along axon
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27
Q

neurilemma

synapses

A
  • Outermost coil of Schwann cell forms neurilemma around myelin sheath
    › Helps in repair of injured fibres
  • Synapses:
    › Junction between the branches of adjacent neurons
    › Neurons don’t physically touch, small gap
    › Message carried across gap by movement of neurotransmitters
    › Axon and skeletal muscles cell = neuromuscular junction
28
Q

functional types of neutrons

A

• Functional types of neurons:

  • Sensory: (afferent/receptor) neurons that carry messages from receptors to CNS
  • Motor: (efferent/effector) neurons that carry message from CNS to effectors
  • Interneuron: (association/connector/relay) in CNS, link between sensory and motor
29
Q

Structural types of neurons:

A

• Structural types of neurons:
- Multipolar: have one axon and multiple dendrites extending from cell body.
› Interneurons and motor neurons
- Bipolar: one axon and one dendrite.
› Neurons in eye, ear and nose (from receptor cell to other neuron)
- Unipolar: only one extension, axon.
› Not in humans, insects
- Pseudo-unipolar: properties of both unipolar and bipolar. One axon separates into two. One connects to dendrites, while other ends in axon terminal. Cell body lies to one side of main axon.
› Sensory neuron

30
Q

nerve fibres

A

• Nerve fibres:

  • Axon and dendrites of nerve cells = nerve fibres
  • Nerve fibres arranged in bundles held together by connective tissue, with multiple bundles joining together to form nerve.
31
Q

central and peripheral

A
  • PNS is composed of
    › Nerve fibres that carry info to and from the CNS
    › Group of nerve cell bodies, ganglia, which lie outside brain and spinal cord
  • Cranial nerves:
    › 12 pairs (e.g., optic and auditory) that arise from the brain
    › Most are mixed nerves (both sensory and motor fibres), few carry only one
  • Spinal nerves:
    › 31 pairs arise from spinal cord
    › All mixed nerves
  • Each nerve is joined to the spinal cord by two roots
  • Ventral root: axons of motor neurons that have their cell bodies in grey matter of spinal cord
  • Dorsal root: contains axons of sensory neurons that have their cell bodies in a small swelling on the dorsal root, known as the dorsal root ganglion
32
Q

afferent and efferent

A

• afferent-efferent
- Afferent division: sensory division, has fibres that carry impulses into CNS by sensory neurons from receptors
› Somatic sensory neurons: bring impulses from skin and muscles
› Visceral sensory neurons: bring impulses from the internal organs
- Efferent division: motor division, has fibres that carry impulses away from the CNS
› Autonomic
- Parasympathetic
- Sympathetic
› Somatic

33
Q

autonomic and somatic

A

• autonomic-somatic
- Autonomic: carries impulses from CNS to heart muscle, involuntary muscles and glands
› Controls body’s internal environment
› Usually operates without conscious control
› Regulated by groups of neurons in medulla oblongata, hypothalamus and cerebral cortex
- Heart rate
- Blood pressure
- Pupil diameter
- Urination and defecation
› Nerve fibres of ANS make up part of spinal and cranial nerves.
› Impulse travels along 2 neurons from CNS to the effector
- First is myelinated and has its cell body in the CNS
- Second neuron is unmyelinated and has its cell body in a ganglion, outside CNS
› Neurotransmitter is either acetylcholine or noradrenaline
› Function: internal adjustment, homeostasis
› Usually involuntary control
› Two sets of nerves to target organ (parasympathetic and sympathetic)
› Effect of target organ: excitation and inhibition
- Somatic: takes impulses from CNS to the skeletal muscles
› Has one neuron from CNS to effector
› Neurotransmitter is acetylcholine
› Function: response to external environment
› Usually voluntary control
› Effect on target organ: always excitation

34
Q

sympathetic and parasympathetic

A

• sympathetic-parasympathetic
- Sympathetic: produce responses that that prepare body for strenuous physical activity (flight/fight)
› In threatening situations, sympathetic becomes dominant. Flight/fight response:
- Rate and force of heart increase, BP increases as well
- Blood vessels dilate in organs involved in strenuous activity (heart, skeletal muscles, liver)
- Blood vessels constrict in organ NOT involved in strenuous activity (kidney, stomach, intestines, skin)
- Airways in lung dilate, rapid breathing
- Blood glucose levels rise, as liver breaks down glycogen
- Secretions from sweat glands increase
- Adrenal medullae secrete adrenaline and noradrenaline which intensify and prolong above responses
- Parasympathetic: produces responses that maintain the body during relatively quiet conditions (rest)
› Both maintain stability of body functions
- Decreases rate and strength of heart contraction
- Constrict bronchioles
- Constrict pupil
- Constricts muscles of urinary bladder
- Increases movement of stomach and intestines
- Increase production of glycogen
- Increases secretion of saliva
- No effect on: sweat, blood vessels, adrenal medulla

35
Q

bone

A

• Cranium and vertebrae (bone):
- Outermost protective layer is bone
- Brain is protected by cranium
- Spinal cord runs through vertebral canal (opening in vertebrae)
› Bones provide strong, rigid structure that protects CNS

36
Q

meninges

A

• Meninges:
- Inside the bones and covering surface of brain and spinal cord.
- 3 layers of connective tissue forming membranes called meninges
› Dura mater: (outer) tough and fibrous and provides layer of protection
- Sticks closely to bones of skull, but on inside of vertebral canal it isn’t that close fitting
› Arachnoid mater: (middle) loose mesh of fibres
› Pia mater: (inner) contains many blood vessels and sticks closely to surface of brain and spinal cord.

37
Q

Cerebrospinal fluid

A

• Cerebrospinal fluid (CSF):
- Occupies space between middle and inner meninges layer
- Circulates through cavities in brain and through a canal in centre of spinal cord
- Clear watery fluid containing few cells and some glucose, proteins, salts and urea
- Functions:
› Protection: shock absorber, cushions blows/shocks sustained by CNS
› Support: the brain is suspended inside the cranium and floats in the fluid that surrounds it
› Transport: CSF formed from blood and circulates around and through CNS before re-entering capillaries. Takes nutrients to cells and carries away wastes.

38
Q

cerebrum

A

• Cerebrum:
- Biggest part of brain
- Outer surfaces thick of grey matter known as cerebral cortex
- Below cerebral cortex is white matter. Composed of nerve fibres surrounded by myelin. In CNS bundles of nerve fibres are called tracts (outside called nerves). Tracts in white matter
› Tracts that connect various areas of cortex to within same hemisphere
› Carry impulses between 2 hemispheres
› Connect the cortex to other parts of brain/spinal cord
- Deep inside cerebrum is additional grey matter called basal ganglia
› Consist of group of nerve cells associated with control of skeletal muscles
› Initiate desired movement, and inhibit unwanted movement.
- Folded to increase surface area (cortex contains 70% of all neurons CNS)
› Round ridges/convolutions (gyri)
› Convolutions separated by shallow downfolds (sulci)
› Convolutions separated by deep downfolds (fissures)
- Deepest fissure: longitudinal fissure, almost separates cerebrum into two hemispheres
- Fissures and sulci further divide each hemisphere into 4 lobes
- Frontal lobe: thinking, problem solving, emotions, personality, language (left hemisphere), control of movement
- Parietal lobe: processing temp, touch, taste, pain and movement
- Temporal lobe: processing memories and linking them with senses. Receives auditory information
- Occipital lobe: vision
- Insula: deep inside the brain. Recognition of different senses and emotions, addiction and psychiatric disorders.
- Cortex has three functional areas:
› Sensory: interpret impulses from receptors
› Motor: control muscular movements
› Association: intellectual and emotional processes

39
Q

corpus callosum

A

• Corpus callosum:

  • Wide band of nerve fibres that lies underneath the cerebrum at the base of the longitudinal fissure
  • Nerve fibres cross from one hemisphere to the other: allow the two sides to communicate with each other
40
Q

cerebellum

A

• Cerebellum:
- Under the rear part of cerebrum.
- Second largest
- Surface folded into a series of parallel ridges.
- Outer part is grey matter, inside is white matter that branches to all parts of cerebellum.
- Controls posture, balance and fine coordination of voluntary muscle movement
- Receives sensory info from:
› Inner ear about posture and balance
› Stretch receptors in skeletal muscles for information about length of muscles
- Without it movements would be spasmodic, jerky and uncontrolled

41
Q

hypothalamus

A 
•	Hypothalamus: 
-	Middle of brain
-	Concerned with homeostasis
›	Regulation of autonomic nervous system
›	Thermoregulation
›	Food and water intake
›	Emotional responses
›	Stimulates pituitary gland
42
Q

medulla oblongata

A

• Medulla oblongata:
- Continuation of spinal cord
› Cardiac centre: regulates rate and force of heartbeat
› Respiratory centre: control rate and depth of breathing
› Vasomotor centre: regulates diameter of blood vessels
- Influenced by higher centres in brain, especially hypothalamus

43
Q

spinal cord

A

• Spinal cord:
- 44 cm long
- From foramen magnum to second lumbar vertebra
- Space between outer meningeal layer and bone: contains fat, connective tissue and blood vessels
› Serves as padding around spinal cord
› Allows cord to bend when spine is bent
- grey matter is at centre surrounded by white matter
› grey matter is ‘H’ shape
› in centre of grey matter is central canal which holds CSF
- Myelinated fibres:
› Ascending tracts: sensory axons that carry impulses towards brain
› Descending tracts: motor axons that conduct impulses away from brain
- Takes messages between brain and peripheral nervous system

44
Q

receptors

A

• Receptors: structure that detects change in internal and external environment

45
Q

thermoreceptor

A

• Thermoreceptors: in skin and hypothalamus
- Respond to heat and cold
- Skin thermoreceptors: inform the brain (hypothalamus and cerebrum) of changes in temperature outside the body.
› Peripheral thermoreceptors in skin sensitive to heat or cold (not both)
- Thermoreceptors in the hypothalamus: monitors core temperature, detect temperature of the blood that is flowing through the brain
› Using info from skin AND hypothalamus receptors, hypothalamus can regulate body temperature
- Krause end bulbs: detect cold (in skin)
› Only in specialised regions
› Defined by capsules
- Ruffini endings: detect warmth (in skin)
› Can act as thermoreceptors
› Deep layers of skin
› Detect warmth

46
Q

Osmoreceptors

A

• Osmoreceptors: hypothalamus
- Sensitive to changes in osmotic pressure
› Osmotic pressure: concentration of substances dissolved in water of blood plasma. Higher the concentration -> higher osmotic pressure
- Stimulate hypothalamus so that body’s water content is maintained

47
Q

chemoreceptors

A

• Chemoreceptors:
- Stimulated by particular chemicals. Nose (sensitive to odours) and mouth (sensitive to taste), internal chemoreceptors (sensitive to composition of bodily fluid) e.g. Certain blood vessels (sensitive to blood pH and concentration of O2 and CO2)-> regulate heart rate and breathing

48
Q

touch receptor

A

• Touch/Mechanoreceptors: mainly in skin
- Some are close to skin surface and sensitive to light touch (lips, fingertips, eyelids, external genital organs)
- Hair receptor: nerve endings on base of hair follicle
› Respond to light touch that bends the hair
› Touch receptors close to skin and hair receptors: adapt rapidly, after a while no longer aware of the touch
- Some receptors are deeper in the skin and are sensitive to pressure and vibrations
- Merkel’s Disk: slow adapting, unencapsulated nerve endings that respond to light touch. Present in upper layers of the skin
- Ruffini endings: slow adapting, encapsulated receptors that respond to skin stretch and are present in both smooth and hairy skin
- Pacinian corpuscles: rapidly adapting, deep receptors that respond to deep pressure and high frequency vibration
- Meissner’s corpuscle: rapidly adapting, encapsulated neurons that respond to low frequency vibrations and fine touch. Located in glabrous (hairless) skin on fingertips and eyelids

49
Q

pain receptor

A

• Nociceptors: concentrated in skin and mucous membranes. Most organs, not in brain
- Stimulated by damage to the tissues by poor blood flow to tissue; or by excessive stimulation form stimuli (heat or chemicals)
- Pain warns us that damage to tissues is occurring so we can take evasive action/ seek medical action
- Pain receptors: adapt little or not at all, so pain continues as long as stimulus is present
› Failure to adapt keeps person aware

50
Q

reflexes

A

• Reflexes: rapid automatic response to a stimulus. Properties:
- Stimulus required to trigger reflex
- Involuntary: without conscious thought
- Rapid: only small number of neurons involved
- Stereotyped: occurs same way each type it happens
• Most are coordinated by spinal cord. Spinal reflex: reflex carried out by spinal cord without involvement of brain
- Impulses may be sent to brain, so we become aware of what is happening, awareness occurs after response has been initiated

51
Q

reflex arc

A

• Reflex arc: pathway a nerve impulse follows in travelling from a receptor to an effector

  • Receptor reacts to change in the internal and external environment by initiating nerve impulse in sensory neuron
  • Sensory neuron carries impulse from receptor to spinal cord or brain
  • There is at least one synapse: nerve impulse may be passed directly to motor neuron, or there may be one or more interneurons to direct impulse to correct motor neuron
  • Motor neuron carries nerve impulse to an effector
  • Effector receives impulse, and carries out appropriate response
52
Q

learnt reflexes

A

• Learnt reflexes:

  • Innate reflexes: acquired genetically, present at birth. Suckling, chewing, etc.
  • Acquired reflexes: response learnt through practise. Jamming car brakes, catching a ball, etc.
53
Q

nerve impulses

A

• Nerve impulses: electrochemical change that travels along a nerve fibre. Involves:

  • Change in electrical voltage
  • Brought about by changes in chemicals (concentration of ions around neuron cell membrane)
54
Q

electrical charge and potential difference

A

• Electrical charge and potential difference:

  • Like charges repel
  • Opposite charges attract
  • When positive and negative charges come together energy is released. If they are separated, they have potential to come together and release energy
  • Potential difference: difference in electrical charge between two locations
55
Q

potential difference across a cell membrane

A

• Potential difference across a cell membrane:
- Extracellular fluid: contains high concentration of NaCl. Positive Na ions and negative Cl ions
- Intracellular fluid: low concentration of Na ions and Cl ions. Mainly positive K ions, and negative ions come from a variety of organic substances made by the cell
- Differences in concentration of ions means there is a potential difference inside and outside cell membrane, membrane potential.
- Resting membrane potential = -70mV
› Potential of inside of membrane is 70mV less than that of outside

56
Q

sodium potassium pump

A

• Sodium- potassium pump:
- Ions are unable to diffuse through phospholipid bilayer
› Move through protein channels
- Leakage channels: channels that are open all the time
- Voltage-gated channels: only open when the nerve is stimulated
- Resting membrane potential is mostly due to Na and K ions. Extracellular more positively charged
› [Na ion] is 10x higher outside than inside. Limited number of sodium leakage channels, so this limits facilitated diffusion of Na ions
› [K ion] is 30x higher inside. Cell is very permeable to K ions due to lots of potassium leakage channels. More K ions able to diffuse than Na ions.
› [Cl ion] is higher outside than inside. Cell is highly permeable to Cl ions, allowing diffusion through protein channels
› Concentration of large, negatively charged organic ions is higher inside the neuron than outside. Cell membrane impermeable to these ions, so they stay inside
- Sodium-potassium pump is a carrier protein that lets Na and K move across membrane
› Uses ATP because it goes against concentration gradient
1. The S-P pump binds 3 Na ions and an ATP molecule
2. Splitting of ATP provides energy to change the shape of the channel. Na ions driven through the channel
3. Na ions released to outside of new membrane, and the new shape allows 2 K ions to bind
4. Release of phosphate allows the channel to revert to its original form, releasing the K ions on the inside of the membrane
› Net reduction of positive ions inside the cell
› Negative resting membrane potential, membrane is polarised

57
Q

action potential

A

• Action potential: opening and closing of voltage-gated channels, which cause rapid depolarisation and repolarisation of the membrane. Lasts a millisecond. Action potential triggers action potential in adjacent membrane
- 1. Depolarisation: sudden increase in membrane potential
› Level of stimulation exceeds around 15mV
› When a neuron is stimulated, some sodium channels are opened. More Na ions move into the cell, makes intracellular fluid less negative, increasing potential difference.
› If stimulus increased potential to -55mV, voltage-gated sodium channels open, and Na ions move into cells independently of stimulus
- Size of response is not related to strength of stimulus
- All or none response: nerve impulse is transmitted at full strength or not at all
› Inside more positive than outside, membrane is depolarised. Polarity reaches 40mV approximately
- 2. Repolarisation:
› Sodium channels close, stops influx of Na ions
› Voltage-gated potassium channels open, increasing flow of K out of cell
› Inside is more negative and decreases membrane potential- membrane is repolarised
› Potassium channels open for longer than needed, so membrane potential drops lower than resting membrane potential, membrane is hyperpolarised
- 3. Refractory period:
› Once sodium channels have opened, they quickly become inactivated: so, they are unresponsive to stimulus
› Brief period after being stimulated, membrane will not undergo another action potential.
› Lasts from -55mV to -70mV (returns to resting membrane potential)
› Period of time before another action potential can occur at same location

58
Q

Conduction along unmyelinated fibres:

A

• Conduction along unmyelinated fibres:
- Depolarisation of one area of membrane causes a movement of Na ions in adjacent areas
› Process repeats itself: action potential moves along the membrane away from point of stimulation
› Nerve impulse prevented from going backwards by refractory period

59
Q

Transmission along myelinated fibres:

A

• Transmission along myelinated fibres:
- Myelin sheath insulates the nerve fibre from extracellular fluid. Ions cannot flow between the inside and outside and action potential cannot form
- Doesn’t occur at nodes of Ranvier, no myelin there
› Action potential jumps from one node to the next
› Saltatory conduction: allows faster transmission in myelinated fibres
› (140m/s vs 2m/s)

60
Q

Size of nerve impulse:

A

• Size of nerve impulse:
- Nerve impulse that travels along a fibres is always the same size, regardless of stimulus size they produce same action potential (provided it exceeds threshold)
› Nerve impulse doesn’t become weaker with distance
- Strong impulse: causes depolarisation of more nerve fibres, and produces more nerve impulses in a given time

61
Q

Transmission across a synapse:

A

• Transmission across a synapse:
- 1. When the nerve impulse reaches the axon terminal, it activated voltage-gated calcium ion channels
- 2. Since there is a higher [Ca ion] in extracellular fluid, they flow into the cell at the pre-synaptic axon terminal
- 3. This causes synaptic vessels to fuse with the membrane, releasing neurotransmitters by exocytosis
- 4. Neurotransmitters diffuse across gap and attach to receptors on the membrane of the next neuron
- 5. This stimulates ligand-gated protein channel to open, which allows influx of Na ions and initiates an action potential in the post synaptic membrane
› Neurotransmitters are reabsorbed by presynaptic membrane, by being degraded by enzymes or diffusion
› One direction : Axon to dendrites or axon to cell body

62
Q

Effect of chemicals on transmission of nerve impulses:

A

• Effect of chemicals on transmission of nerve impulses:
- Stimulants: (caffeine) stimulate transmission at synapse
- Depressant: (alcohol) depress transmission at synapse
- Venom affects neuromuscular junction
› Nerve agents contain organophosphates, which cause build-up of acetylcholine at neuromuscular junction. All muscles then try to contract-> prevents breathing

63
Q

speed of action:

A

• speed of action:

  • nervous responses are more rapid than hormonal ones, because nerve impulses travel rapidly along nerve fibres, while hormones are transported in blood stream
  • nervous system responds to stimulus in milliseconds, while hormone release may take several seconds or days
64
Q

duration of action:

A

• duration of action:

  • when stimulus ceases: nervous system stops generating nerve impulse and the responses ceases almost immediately. So nerve impulses bring about an immediate response, which only lasts a short time
  • hormones are slower acting, and responses can last a considerable time (even years). May continue long after stimulus has stopped
65
Q

nature and transmission of the message:

A

• nature and transmission of the message:
- nervous messages are an electrochemical change (electrical impulses and neurotransmitters) that travels along membrane of neuron
- endocrine messages are chemical (hormones) that are usually transported by blood
› some substances function as both hormones and neurotransmitters (noradrenaline, ADH, dopamine)
› some neurotransmitters and hormones have the same effect on the same target cells. Noradrenaline and glucagon both act on liver cells to breakdown glycogen
› some hormones (oxytocin and adrenaline) are secreted by neurons into extracellular fluid

66
Q

specificity of message:

A

• specificity of message:
- nerve impulses travel along fibre to specific part of the body and often influence just one effector. Usually local and specific.
› Effects muscles, glands and other neurons
- hormones travel to all parts of the body, are carried by blood and often affect a number of different organs. May be very general and widespread
› can affect all body cells

Human Biology ATAR (22 decks)

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