Coordination, Response & Homeostasis

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レッスンノート

Mammalian Nervous System

The nervous system consists of the central nervous system (CNS) (brain & spinal cord) and the peripheral nervous system (PNS) (all nerves).
It allows us to sense surroundings, respond, and coordinate body functions.
Information travels as nerve impulses – electrical signals along neurones.
A bundle of neurones is called a nerve.

A nerve is a bundle of neurones

Types of Neurones

Sensory neurones carry impulses from sense organs to the CNS.
Relay neurones (intermediate) connect sensory and motor neurones inside the CNS.
Motor neurones carry impulses from the CNS to effectors (muscles or glands).
Neurones have a long axon insulated by a fatty sheath with nodes – impulses jump between nodes for speed.
Dendrites on the cell body connect to many other neurones.

Structure of a neurone showing dendrite, cell body and axon

The Reflex Arc

A reflex is an automatic, rapid, involuntary response to a stimulus.
It does not involve the brain as coordinator – only the spinal cord.
Pathway: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.
Reflexes are protective and minimise damage (e.g., pulling hand from heat).

The reflex arc pathway

The Synapse (Extended)

A synapse is the junction between two neurones where they do not touch.
The electrical impulse triggers release of neurotransmitters from vesicles in the presynaptic neurone.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
This stimulates a new electrical impulse in the second neurone.
Neurotransmitters are then destroyed to prevent repeated stimulation.
Synapses ensure one-way transmission and are sites where drugs (e.g., heroin) can act.

Structure of a synapse

Sense Organs & The Eye

Sense organs contain receptors that detect specific stimuli and generate impulses.
The eye is a sense organ with light-sensitive receptors.
Key structures: cornea (refracts light), iris (controls pupil size), lens (focuses light), retina (contains rods & cones), optic nerve (carries impulses to brain).
Pupil reflex: In dim light, radial muscles contract, circular muscles relax → pupil dilates. In bright light, opposite occurs.
Accommodation: For near objects, ciliary muscles contract, suspensory ligaments loosen, lens becomes fatter. For distant objects, ciliary muscles relax, ligaments tighten, lens becomes thinner.
Rods detect low light (night vision); cones detect colour (concentrated in fovea).

Cross-section of the eye

Hormones in Humans

A hormone is a chemical substance produced by a gland, carried by the blood, altering target organ activity.
Endocrine glands (e.g., pancreas, adrenal, pituitary) secrete hormones directly into the blood.
Adrenaline ('fight or flight') increases blood glucose, heart rate, breathing rate, diverts blood to muscles, dilates pupils.
Insulin lowers blood glucose by converting excess glucose to glycogen in liver and muscles.
Glucagon raises blood glucose by converting glycogen to glucose.
Nervous system: fast, short-lived, electrical impulses. Hormonal system: slower, longer-lasting, chemical signals in blood.

The endocrine glands

Homeostasis & Negative Feedback (Extended)

Homeostasis is the maintenance of a constant internal environment.
Negative feedback reverses changes: if a level rises, mechanisms reduce it; if it falls, mechanisms raise it.
Blood glucose control: high glucose → insulin released → glucose converted to glycogen → glucose falls. Low glucose → glucagon released → glycogen converted to glucose → glucose rises.
Type 1 diabetes: pancreas cannot produce insulin; treated by insulin injections, diet control, and exercise.

Negative feedback control of blood glucose

Temperature Control (Extended)

Body temperature is maintained at ~37°C for optimal enzyme function.
When hot: vasodilation (skin capillaries widen, more heat lost), sweat production (evaporative cooling), hairs lie flat.
When cold: vasoconstriction (skin capillaries narrow, less heat lost), sweat stops, hairs stand up (trap insulating air), shivering generates heat.

Negative feedback control of body temperature

Tropisms

Tropisms are plant growth responses to stimuli.
Phototropism: shoots grow towards light (positive), roots grow away (negative).
Gravitropism: shoots grow away from gravity (negative), roots grow towards gravity (positive).
Auxin is a plant hormone produced in shoot tips that stimulates cell elongation.
Unequal light distribution causes auxin to accumulate on the shaded side of shoots, causing faster growth there and bending towards light.
In roots, higher auxin concentration inhibits cell elongation, causing downward bending.

Auxin distribution and phototropism

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練習問題

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1.Which of the following is the correct order of components during a nervous response?
Easy
- Astimulus → receptor → coordinator → effector → response
- Bstimulus → effector → coordinator → receptor → response
- Creceptor → stimulus → coordinator → effector → response
- Dstimulus → receptor → effector → coordinator → response
2.What is the name of the junction between two neurones?
Easy
- Asynapse
- Baxon
- Cdendrite
- Dnode of Ranvier
3.Which part of the eye contains light receptor cells?
Easy
- Aretina
- Bcornea
- Clens
- Diris
4.Which hormone is released by the adrenal glands in response to danger?
Easy
- Aadrenaline
- Binsulin
- Cglucagon
- Dauxin
5.In a reflex arc, which type of neurone carries impulses from the receptor to the spinal cord?
Easy
- Asensory neurone
- Bmotor neurone
- Crelay neurone
- Dintermediate neurone
6.In bright light, what happens to the circular and radial muscles of the iris?
Easy
- Acircular muscles contract, radial muscles relax
- Bcircular muscles relax, radial muscles contract
- Cboth contract
- Dboth relax
7.Which of the following is an effect of adrenaline on the body?
Easy
- Aincreased pulse rate
- Bdecreased breathing rate
- Cconstricted pupils
- Ddecreased blood glucose concentration
8.Which plant hormone stimulates cell elongation in shoots?
Easy
- Aauxin
- Binsulin
- Cglucagon
- Dadrenaline

もっと問題

9.In negative feedback control of blood glucose, what is the role of glucagon?
Easy
- Aconverts glycogen to glucose
- Bconverts glucose to glycogen
- Cincreases glucose uptake by cells
- Ddecreases blood glucose concentration
10.In a synapse, neurotransmitters are released from which part of the neurone?
Easy
- Apresynaptic membrane
- Bpostsynaptic membrane
- Ccell body
- Daxon hillock
11.Which part of a neurone contains the nucleus and receives connections from many dendrites?
Easy
- Acell body
- Baxon
- Cdendrite
- Dmyelin sheath
12.In a reflex arc, which structure carries out the response, such as a muscle contracting to move a body part away from a stimulus?
Easy
- Amuscle
- Bsensory neurone
- Crelay neurone
- Dreceptor
13.Which part of a neurone is a fatty sheath that insulates the axon and speeds up impulse conduction?
Easy
- AMyelin sheath
- BDendrite
- CCell body
- DNucleus
14.In an experiment, a plant shoot is placed horizontally. After 24 hours, the shoot bends upward. Which statement explains this response?
Medium
- AAuxin accumulates on the lower side of the shoot, causing faster cell elongation there.
- BAuxin accumulates on the upper side of the shoot, causing faster cell elongation there.
- CAuxin is evenly distributed, so the shoot grows straight.
- DAuxin inhibits cell elongation on the lower side of the shoot.
15.A student investigates the effect of light on seedling growth. Three seedlings are placed in a box with a slit on one side. After 5 days, the seedlings bend toward the slit. Which conclusion is supported by this result?
Medium
- ALight causes auxin to accumulate on the shaded side, stimulating cell elongation.
- BLight destroys auxin on the illuminated side, reducing growth there.
- CAuxin is produced only in the tip and diffuses equally to both sides.
- DThe seedlings are responding to gravity, not light.
16.2,4-D is a synthetic auxin used as a selective weedkiller: it is sprayed on cereal crop fields to kill broad-leaved weeds. Which statement best explains why 2,4-D kills the weeds but does not harm the cereal crop?
Medium
- ABroad-leaved weeds are far more sensitive to synthetic auxin than narrow-leaved cereal plants, so 2,4-D causes uncontrolled, damaging growth in the weeds only.
- B2,4-D only dissolves in the broad, flat leaves of weeds and cannot enter the narrow leaves of cereal plants.
- CCereal plants produce an enzyme that breaks down 2,4-D before it reaches their shoot tips.
- D2,4-D kills weeds by blocking photosynthesis, which cereal plants do not need to survive.
17.Which gland releases the hormone adrenaline?
Easy
- AAdrenal gland
- BPancreas
- CThyroid gland
- DPituitary gland
18.A person with Type 1 diabetes has a blood glucose concentration of 12 mmol/L after a meal. Which treatment would most directly reduce this level?
Medium
- AInjecting insulin
- BInjecting glucagon
- CEating more carbohydrates
- DDrinking more water
19.Which of the following describes the role of the iris in the eye?
Easy
- AIt controls the amount of light entering the eye.
- BIt refracts light onto the retina.
- CIt contains light-sensitive cells.
- DIt carries impulses to the brain.
20.When viewing a near object, which changes occur in the eye?
Medium
- ACiliary muscles contract, suspensory ligaments loosen, lens becomes fatter.
- BCiliary muscles relax, suspensory ligaments tighten, lens becomes thinner.
- CCiliary muscles contract, suspensory ligaments tighten, lens becomes thinner.
- DCiliary muscles relax, suspensory ligaments loosen, lens becomes fatter.
21.In an experiment to investigate phototropism, three plant shoots are set up as follows: A - tip removed, B - tip covered with opaque cap, C - tip covered with transparent cap. All are exposed to light from one side. Which shoot will bend towards the light?
Medium
- AShoot A
- BShoot B
- CShoot C
- DNone of the shoots
22.A student investigates the effect of gravity on root growth. Four bean seedlings are placed in a petri dish with damp cotton wool: seedling 1 - radicle pointing down, seedling 2 - radicle pointing up, seedling 3 - radicle horizontal, seedling 4 - radicle horizontal on a clinostat. After 48 hours in darkness, which seedling's radicle will have grown horizontally?
Medium
- ASeedling 1
- BSeedling 2
- CSeedling 3
- DSeedling 4
23.In a reflex arc, which neurone is located inside the spinal cord and connects the sensory neurone to the motor neurone?
Easy
- ARelay neurone
- BSensory neurone
- CMotor neurone
- DReceptor
24.Which of the following is an effect of adrenaline on the heart?
Easy
- ADecreased heart rate
- BIncreased heart rate
- CNo change in heart rate
- DIrregular heart rate
25.A person with Type 1 diabetes has a blood glucose concentration of 15 mmol/L after a meal. Which treatment would most directly reduce this level?
Medium
- AInject glucagon
- BInject insulin
- CEat a carbohydrate-rich snack
- DDrink plenty of water
26.Farmers spray 2,4-D on cereal (grass) crop fields to kill broad-leaved weeds. A single application controls weeds for a few weeks, but repeated applications over the growing season keep weed density lower for longer. Which statement best explains why repeated applications are more effective?
Easy
- AA single application kills existing weeds, but new weed seedlings germinate later and need their own dose of 2,4-D to be killed.
- B2,4-D breaks down the cereal crop's own auxin, so repeated doses are needed to keep the crop's growth suppressed.
- CEach application makes the weeds more resistant, so a stronger dose is needed the next time.
- D2,4-D has no effect on weeds until it has been applied at least twice.
27.A student sets up an experiment to investigate the effect of temperature on the rate of a reflex response. Which of the following is the most appropriate method to measure the response time?
Medium
- AMeasure the distance a ruler falls before being caught by the subject.
- BCount the number of times the subject blinks in one minute.
- CRecord the time taken for the pupil to constrict in bright light.
- DMeasure the change in heart rate after exercise.
28.Which of the following is the definition of a hormone?
Easy
- AA chemical substance produced by a gland and carried by the blood that alters the activity of target organs
- BAn electrical impulse that travels along nerve cells
- CA chemical substance released at a synapse to transmit a signal
- DA protein that speeds up a chemical reaction
29.At a synapse, neurotransmitters are released from which part of the neurone?
Easy
- APresynaptic membrane
- BPostsynaptic membrane
- CAxon hillock
- DNode of Ranvier
30.In tropism investigations, very high concentrations of applied auxin can stop root growth altogether, while the same concentrations promote shoot growth. Which statement is consistent with this?
Medium
- ARoots are far more sensitive to auxin than shoots, so a concentration that stimulates cell elongation in a shoot can be high enough to inhibit it in a root.
- BRoots do not respond to auxin at all, so any change in root growth must be caused by a different hormone.
- CHigh auxin concentrations destroy root cells, while shoot cells are unaffected by auxin at any concentration.
- DAuxin only affects growth in the dark, so the difference is caused by roots growing underground.
31.A student sets up an experiment to investigate phototropism in bean seedlings. Three seedlings are placed in a box with a slit on one side. Seedling A has its tip removed, seedling B has its tip covered with an opaque cap, and seedling C is untreated. After 5 days, which seedling will show the greatest curvature towards the light?
Medium
- ASeedling A
- BSeedling B
- CSeedling C
- DAll three will curve equally
32.In an experiment investigating gravitropism, four bean seedlings are placed in a petri dish with damp cotton wool: seedling 1 with radicle pointing downwards, seedling 2 placed horizontally, seedling 3 with radicle pointing upwards, and seedling 4 attached to a clinostat. After 48 hours in darkness, which seedling's radicle will show the greatest downward curvature?
Medium
- ASeedling 1
- BSeedling 2
- CSeedling 3
- DSeedling 4
33.A student investigates the effect of temperature on the rate of a reflex response. Which of the following is the most appropriate method to ensure reliable results?
Medium
- ATest each temperature on a different person and compare results
- BTest the same person at each temperature, repeating several times and calculating a mean
- CTest each temperature only once to avoid habituation
- DUse a different reflex for each temperature
34.In an experiment to investigate phototropism, three plant shoots are set up as follows: A - tip removed, B - tip covered with opaque cap, C - tip uncovered. All are exposed to light from one side. After 48 hours, which shoot(s) will show curvature towards the light?
Medium
- AA only
- BB only
- CC only
- DA and C
35.In an experiment investigating gravitropism, four bean seedlings are placed in a petri dish with damp cotton wool: seedling 1 with radicle pointing downwards, seedling 2 horizontal, seedling 3 with radicle pointing upwards, seedling 4 on a clinostat. All are kept in the dark. After 48 hours, which seedling shows no gravitropic response?
Medium
- ASeedling 1
- BSeedling 2
- CSeedling 3
- DSeedling 4
36.Which part of the nervous system consists of the brain and spinal cord?
Easy
- ACentral nervous system
- BPeripheral nervous system
- CAutonomic nervous system
- DSomatic nervous system
37.What is the name of the chemical messenger released at a synapse?
Easy
- ANeurotransmitter
- BHormone
- CEnzyme
- DAntibody
38.In the control of blood glucose, which hormone is secreted when blood glucose levels fall?
Easy
- AInsulin
- BGlucagon
- CAdrenaline
- DGlycogen
39.Which of the following describes a reflex action?
Easy
- AA conscious decision to move away from a stimulus
- BA rapid, automatic response that does not involve the brain
- CA slow response coordinated by the brain
- DA voluntary action that protects the body
40.Which part of a neurone carries nerve impulses away from the cell body towards the axon terminals?
Easy
- AAxon
- BDendrite
- CCell body
- DNucleus
41.The central nervous system consists of the brain and the spinal cord.
Easy
True or false?
42.Which type of neurone carries impulses from a sense organ to the central nervous system?
Easy
- Asensory neurone
- Brelay neurone
- Cmotor neurone
- Dintermediate neurone
43.What is the name of the gap between two neurones where chemical messengers are released?
Easy
- Asynapse
- Baxon
- Cdendrite
- Dnode of Ranvier
44.Which of the following is a function of the iris in the eye?
Easy
- Acontrols the amount of light entering the eye
- Bfocuses light onto the retina
- Cconverts light into nerve impulses
- Dcarries impulses to the brain
45.Adrenaline is produced by the adrenal glands and is transported in the blood to target organs.
Easy
True or false?
46.When blood glucose concentration falls, which hormone is secreted to raise it?
Easy
- Aglucagon
- Binsulin
- Cadrenaline
- Dthyroxine
47.In a reflex arc, the effector is always a muscle.
Medium
True or false?
48.Which of the following statements about the pupil reflex is correct?
Medium
- AIn bright light, circular muscles contract and radial muscles relax.
- BIn bright light, circular muscles relax and radial muscles contract.
- CIn dim light, circular muscles contract and radial muscles contract.
- DIn dim light, circular muscles relax and radial muscles relax.
49.In a synapse, what is the role of neurotransmitters?
Medium
- AThey diffuse across the synaptic gap and bind to receptors on the postsynaptic membrane.
- BThey carry electrical impulses directly across the gap.
- CThey are released by the postsynaptic neurone.
- DThey destroy the receptors on the presynaptic membrane.
50.Match each structure of the eye with its function.
Medium
- cornea
- lens
- retina
- optic nerve
- refracts light
- focuses light onto retina
- contains light receptor cells
- carries impulses to brain
51.Complete the sentence.
Easy
The three types of neurone are sensory, relay and ____.

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