Nervous control: neurones, reflex arcs and synapses — Combined Science 0653 - Biology Revision Notes & Topical Questions

Section 1 of 43Structure of the nervous system

Structure of the nervous system

Central nervous system (CNS)

• Central nervous system (CNS) the brain and spinal cord.

Peripheral nervous system (PNS)

• Peripheral nervous system (PNS) all of the nerves in the body.

Role

• Role the nervous system makes sense of the surroundings and responds to them and coordinates and regulates body functions.

Nerve impulses

• Nerve impulses information is sent as electrical signals along nerve cells called neurones.

Nerve

• Nerve a bundle of neurones.

Section 2 of 43Types of neurone

Neurone	Carries impulses	Notes
Sensory	From sense organs to the CNS	Long, with the cell body branching off the middle of the axon
Relay (intermediate)	Between sensory and motor neurones	Found inside the CNS
Motor	From the CNS to effectors (muscles or glands)	Long, with a large cell body at one end and long dendrites

Section 3 of 43Neurone structure

Neurone structure

Dendrites

• Dendrites short, branched extensions that carry impulses towards the cell body.

Axon

• Axon a longer extension that carries impulses away from the cell body.

Fatty sheath

• Fatty sheath it insulates the axon, with small uninsulated sections called nodes.

Jumping impulses

• Jumping impulses the impulse jumps from node to node, which speeds it up.

Section 4 of 43Voluntary responses

Voluntary response

Voluntary response a response in which a conscious decision is made to carry out a particular action.

Brain

• Brain voluntary responses start in the brain, as when reaching for a cup.

Section 5 of 43Reflex responses

Reflex responses

Reflex

Reflex an automatic and rapid response to a stimulus that does not involve the brain as coordinator.

Awareness

• Awareness a person is aware of the response only after it has happened.

Speed

• Speed it is quicker than any other nervous response, which helps to minimise damage.

Features

• Features reflex actions are automatic, fast and protective.

Section 6 of 43The reflex arc

1

The pin, which is the stimulus, is detected by a pain or touch receptor in the skin.

2

A sensory neurone sends electrical impulses to the spinal cord, the coordinator.

3

The impulse passes to a relay neurone in the spinal cord.

4

The relay neurone connects to a motor neurone.

5

The motor neurone carries the impulse to a muscle in the leg, the effector.

6

The muscle contracts and pulls the foot away, which is the response.

Section 7 of 43Synapses

Synapse

• Synapse the junction where two neurones meet, with a small gap between them.

Importance

• Importance synapses let the nervous system function as a connected network and direct impulses along the right route.

Section 8 of 43Events at a synapse

1

An impulse arrives at the end of an axon.

2

The impulse triggers release of neurotransmitter from vesicles into the synaptic gap.

3

The neurotransmitter molecules diffuse across the gap.

4

They bind with receptor proteins on the membrane of the next neurone.

5

An impulse is stimulated in the next neurone.

One direction

• One direction synapses make sure impulses travel one way only, which avoids confusion.

Drugs

• Drugs synapses are a common target for drugs that affect the nervous system, such as heroin.

Section 9 of 43Reaction time practical

1

A partner holds a 30 cm ruler vertically with the zero mark between your open thumb and finger.

2

The partner drops the ruler without warning.

3

Catch it as quickly as possible and read the distance fallen.

4

Repeat at least five times and calculate a mean.

5

Keep other variables controlled, such as the hand used and the starting gap.

Section 10 of 43More from the specification

1Reflex arc

• Reflex arc a sensory neurone, relay neurone and motor neurone link a receptor to an effector for a fast automatic response.

2Synapse

• Synapse a gap where an electrical impulse triggers neurotransmitter release that diffuses across to the next neurone.

3Pupil reflex

• Pupil reflex in bright light the iris muscles constrict the pupil to protect the retina.

4Negative feedback

• Negative feedback responses that reverse a change, as insulin lowers blood glucose and sweating restores body temperature.

5Auxin

• Auxin a plant hormone that moves to the shaded side of a shoot and promotes growth there, causing bending towards light.

6Gravity

• Force of attraction between objects with mass.

7Retina

• The layer at the back of the eye with light receptors.

8Pupil reflex

• The automatic change in pupil size in response to light.

9Ciliary muscle

• Muscle that changes the lens shape

10Suspensory ligaments

• Fibres joining the lens to the ciliary muscles

11Negative feedback

• A control that reverses a change to restore the set point.

12Glucose

• Sugar that is the fuel for respiration.

13Temperature

• Average energy of the particles in an object.

14Growth

• Permanent increase in size.

15Hormone

• A chemical messenger carried in the blood.

16Concentration

• Amount of solute dissolved in a volume of solution.

17Homeostasis

• Maintaining a constant internal environment.

18Glycogen

• The storage carbohydrate in animals.

Section 11 of 43More on this topic

Stimulus	Receptor	Coordinator	Effector	Response
Hot object	Heat receptor in skin	Spinal cord	Arm muscle	Hand withdrawn
Bright light	Retina	Brain	Iris muscles	Pupil constricts
High blood glucose	Pancreas cells	Pancreas	Liver and muscle cells	Glucose stored as glycogen
Light from one side	Shoot tip	Auxin distribution	Cells in the shoot	Shoot bends towards the light

Section 12 of 43Divisions of the nervous system

Divisions of the nervous system

Central nervous system (CNS)

Central nervous system (CNS) the brain and spinal cord.

Peripheral nervous system (PNS)

Peripheral nervous system (PNS) all the nerves of the body, connecting the CNS to receptors and effectors.

Nerve

Nerve a bundle of neurones.

Nerve impulse

Nerve impulse an electrical signal that passes along a neurone.

Section 13 of 43Pathway of information

1

A receptor detects the stimulus.

2

An impulse travels along a sensory neurone to the CNS.

3

The CNS coordinates the response.

4

An impulse travels along a motor neurone to an effector.

5

The effector, a muscle that contracts or a gland that secretes, responds.

Section 14 of 43Types of neurone

Neurone	Position	Structure and role
Sensory	Receptor to CNS	Long, with the cell body branching off the middle of the axon; carries impulses to the CNS
Relay (intermediate)	Inside the CNS	Short, with a small cell body at one end and many dendrites; connects sensory and motor neurones
Motor	CNS to effector	Long, with a large cell body at one end and long dendrites; carries impulses to muscles or glands

Section 15 of 43Structure of a neurone

Structure of a neurone

Cell body

• Cell body contains the nucleus and makes the proteins the cell needs.

Dendrites

• Dendrites short branched extensions that carry impulses towards the cell body.

Axon

• Axon a long extension that carries impulses away from the cell body.

Myelin sheath

• Myelin sheath a fatty sheath that insulates the axon.
• Small uninsulated gaps, the nodes, lie along it.
• The impulse jumps from node to node, which speeds it up.

Section 16 of 43Adaptations of neurones

Long axon

• Long axon carries impulses over long distances, for example from the toe to the spinal cord.

Myelin sheath

• Myelin sheath insulates the axon and speeds up the impulse.

Many dendrites

• Many dendrites allow connections with many other neurones.

Section 17 of 43Receptors and effectors

Receptors

• Receptors specialised cells that detect stimuli such as light, sound, touch and chemicals.

Sense organs

• Sense organs eye (light), ear, nose and tongue (chemicals) and skin (touch, pressure, pain and temperature).
  • (sound and balance)

Effectors

• Effectors muscles, which contract, and glands, which secrete.

Section 18 of 43Nervous and hormonal control compared

Feature	Nervous system	Endocrine system
Made up of	Neurones, brain and spinal cord	Glands
Type of message	Electrical impulse	Chemical hormone
Speed	Very fast	Slower
Length of effect	Short, until impulses stop	Longer, until the hormone is broken down
Area affected	Precise, e.g. one muscle or gland	Widespread, wherever target cells have receptors

Section 19 of 43More from the specification

1Reflex Arcs and Rapid Responses

• Involuntary reflex actions bypass conscious brain areas to provide swift, protective responses.
  • (such as pupil constriction or withdrawing from pain)

2Homeostatic Negative Feedback

• Negative feedback systems continuously monitor blood glucose levels and other vital physiological parameters, counteracting deviations from ideal set points.

3Hormonal vs Neural Coordination

• Neural signals transmit rapid, short-lived electrical impulses along neurones,
• whereas hormonal signals regulate blood glucose concentration via chemical messengers.

4Auxin-Regulated Growth in Shoots

• In plant phototropism, auxin accumulates on the darker side of young shoots, stimulating cell elongation and directional growth towards light.

5Synapse

• A junction between two neurones.

6Pupil reflex

• The automatic change in pupil size in response to light.

7Ciliary muscle

• Muscle that changes the lens shape

8Suspensory ligaments

• Fibres joining the lens to the ciliary muscles

9Negative feedback

• A control that reverses a change to restore the set point.

10Glucose

• Sugar that is the fuel for respiration.

11Growth

• Permanent increase in size.

12Concentration

• Amount of solute dissolved in a volume of solution.

13Homeostasis

• Maintaining a constant internal environment.

14Glycogen

• The storage carbohydrate in animals.

15Gravity

• Force of attraction between objects with mass.

16Retina

• The layer at the back of the eye with light receptors.

Section 20 of 43Reflex actions

Reflex action

Reflex action a rapid, automatic response to a stimulus that involves no conscious decision.

Speed

• Speed the pathway is short and the brain is not the coordinator, so the response is very fast.

Protection

• Protection it limits damage, for example withdrawing a hand from a hot object.

Awareness

• Awareness the person knows about the event only after the response.

Section 21 of 43Steps of the reflex arc

1

A receptor detects the stimulus.

2

A sensory neurone carries impulses to the spinal cord (the coordinator).

3

A relay neurone in the spinal cord passes the impulse on.

4

A motor neurone carries the impulse to an effector.

5

The effector, a muscle or gland, produces the response.

Section 22 of 43Reflex compared with voluntary action

Feature	Reflex	Voluntary
Brain involvement	Not the coordinator	Conscious decision made in the brain
Speed	Very fast	Slower
Purpose	Protection	Planned action
Example	Withdrawing a hand from a hot object	Kicking a ball

Section 23 of 43Voluntary actions

1Voluntary response

• Voluntary response it starts in the brain after a conscious decision, for example picking up a cup.

2Pathway

• Pathway impulses pass from the brain down the spinal cord to motor neurones and on to the muscles.

3Overriding a reflex

• Overriding a reflex the brain can sometimes override a reflex, which shows it can control the spinal pathway.

Section 24 of 43Pupil reflex

Pupil reflex

• Pupil reflex a reflex that controls the light entering the eye by changing the pupil diameter.

Iris muscles

• Iris muscles circular muscles form rings around the pupil and radial muscles radiate outwards from it.

Antagonistic action

• Antagonistic action when one set contracts the other relaxes.

Light level	Radial muscles	Circular muscles	Pupil	Light entering the eye
Dim	Contract	Relax	Dilates (wider)	More
Bright	Relax	Contract	Constricts (narrower)	Less, so the retina is protected

Section 25 of 43Examples of reflexes

Reflex	Stimulus	Effector	Protective effect
Withdrawal	Heat or sharp object	Arm or leg muscle	Avoids burns or cuts
Blinking	Object near the eye	Eyelid muscle	Protects the eye
Pupil constriction	Bright light	Iris muscles	Protects the retina
Coughing	Irritant in the airway	Chest and diaphragm muscles	Clears the airway

Section 26 of 43Direction of impulses in the arc

Sensory neurone

• Sensory neurone enters the spinal cord at the back.

Motor neurone

• Motor neurone leaves the spinal cord at the front.

Relay neurone

• Relay neurone lies in the grey matter between them.

Arrows

• Arrows they point in the direction the impulse travels, from receptor to effector.

Section 27 of 43More from the specification

1

Reflex Arc Pathway

• A rapid, automatic response pathway of the nervous system where receptor cells detect stimuli and pass impulses through sensory, relay,
• and motor neurones to effector muscles or glands.

2

Nervous vs Endocrine Coordination

• The nervous system delivers rapid electrical impulses along neurones for immediate localized reactions,
• whereas the endocrine system releases hormones into the blood to regulate slower, body-wide processes.

3

Homeostasis and Blood Glucose Regulation

• Pancreatic cells monitor blood glucose levels;
• when levels rise, beta cells secrete insulin to stimulate glucose uptake into liver and muscle cells for glycogen storage.

4

Chemical Coordination Across Organisms

• While animal homeostasis coordinates core body temperature and blood sugar via negative feedback loops, plant coordination relies on hormones like auxin to regulate cell elongation and growth.

5

Homeostasis

• Maintaining a constant internal environment.

6

Glycogen

• The storage carbohydrate in animals.

7

Gravity

• Force of attraction between objects with mass.

8

Synapse

• A junction between two neurones.

9

Ciliary muscle

• Muscle that changes the lens shape

10

Suspensory ligaments

• Fibres joining the lens to the ciliary muscles

11

Negative feedback

• A control that reverses a change to restore the set point.

12

Glucose

• Sugar that is the fuel for respiration.

13

Temperature

• Average energy of the particles in an object.

14

Growth

• Permanent increase in size.

15

Insulin

• The hormone that lowers blood glucose.

16

Hormone

• A chemical messenger carried in the blood.

17

Concentration

• Amount of solute dissolved in a volume of solution.

Section 28 of 43Structure of a synapse

Structure of a synapse

Synapse

Synapse the junction (gap) between the end of one neurone and the start of the next neurone or an effector.

No contact

• No contact neurones are not directly connected.

Chemical message

• Chemical message an electrical impulse cannot cross the gap, so a chemical transmitter carries the message.

Section 29 of 43Transmission across a synapse

1

An impulse arrives at the end of the axon of the first neurone.

2

Vesicles release neurotransmitter into the synaptic gap.

3

The neurotransmitter molecules diffuse across the gap.

4

They bind to receptor proteins on the membrane of the next neurone.

5

A new impulse is stimulated in the next neurone.

6

The neurotransmitter is then broken down by enzymes or taken back up.

Section 30 of 43Why synapses matter

One direction

• One direction transmitter is released from one side only, so impulses cannot travel backwards.

Network

• Network synapses let the nervous system work as a connected network and direct impulses along the correct route.

Integration

• Integration many neurones can connect to one neurone, so signals can be combined.

Section 31 of 43Synapses in the reflex arc

Positions

• Positions one synapse lies between the sensory and relay neurones and another between the relay and motor neurones.

Speed

• Speed each crossing is chemical but the gap is tiny, so the whole response takes only a few milliseconds.

Section 32 of 43Drugs and synapses

Target of drugs

• Target of drugs the synapse is where messages pass chemically, so it is a common target.
• Heroin acts at synapses.
• Some chemicals mimic a transmitter and bind to its receptors.
• Others block receptors so the signal is not passed on.

Removal of transmitter

• Removal of transmitter if it were not removed, the receiving neurone would be stimulated continuously.

Section 33 of 43More from the specification

Reflex arc and involuntary responses

• A reflex arc provides a rapid, automatic protective response to a stimulus;
  • sensory neurones transmit impulses from receptor cells to the spinal cord,
• and motor neurones stimulate effector muscles to contract.

The pupil reflex to light intensity

• In the pupil reflex, radial and circular muscles in the iris contract antagonistically to regulate pupil diameter, constricting in bright light to protect retinal cells from damage.

Homeostatic control of blood glucose levels

• In mammals, blood glucose concentration is maintained through negative feedback;
  • the pancreas secretes insulin to lower elevated glucose levels and glucagon to elevate low levels.

Auxin regulation in plant phototropism

• In plants, the plant hormone auxin coordinates growth responses;
  • unequal auxin distribution away from light stimulates cell elongation on the shaded side of shoots, bending them toward light.

Negative feedback

• A control that reverses a change to restore the set point.

Concentration

• Amount of solute dissolved in a volume of solution.

Homeostasis

• Maintaining a constant internal environment.

Glycogen

• The storage carbohydrate in animals.

Gravity

• Force of attraction between objects with mass.

Retina

• The layer at the back of the eye with light receptors.

Pupil reflex

• The automatic change in pupil size in response to light.

Ciliary muscle

• Muscle that changes the lens shape

Suspensory ligaments

• Fibres joining the lens to the ciliary muscles

Glucose

• Sugar that is the fuel for respiration.

Muscle

• Tissue that contracts to cause movement.

Temperature

• Average energy of the particles in an object.

Growth

• Permanent increase in size.

Insulin

• The hormone that lowers blood glucose.

Control

• A set-up kept the same except for the factor being tested.

Hormone

• A chemical messenger carried in the blood.

Section 34 of 43Neurones

Neurones

Neurone

Neurone a specialised cell that carries electrical impulses, and some are over a metre long.

• Sensory neurone
  • carries impulses from receptors to the CNS.
• Relay neurone
  • short, connects sensory and motor neurones in the CNS.
• Motor neurone
  • carries impulses from the CNS to effectors.

Structure

• Structure a cell body with nucleus, dendrites that receive signals and an axon, often insulated by a fatty myelin sheath that speeds up the impulse.

Section 35 of 43Reflex arc

1

A receptor in the skin detects the stimulus, for example a hot object.

2

A sensory neurone carries impulses to the spinal cord.

3

A relay neurone passes the signal to a motor neurone.

4

The motor neurone carries the impulse to the effector.

5

The effector, a muscle, contracts and pulls the hand away.

Reflexes

• Reflexes rapid, automatic and protective, for example withdrawal, blinking, the pupil reflex and the knee jerk.

Brain

• Brain it is informed, but the response occurs before the brain is aware.

Section 36 of 43Synapse

1

An impulse reaches the end of the first neurone.

2

Vesicles release neurotransmitter into the gap.

3

Neurotransmitter diffuses across and binds to receptor proteins on the next neurone.

4

A new impulse is triggered in the second neurone.

5

The neurotransmitter is broken down or reabsorbed.

Gap

• Gap a synapse is a gap of about 20 nm that an electrical impulse cannot cross.

One direction

• One direction only the first neurone releases transmitter and only the second has receptors.

Section 37 of 43Voluntary actions

1Pathway

• Pathway sensory neurone, brain and motor neurone, so the response is chosen, not automatic.

2Speed

• Speed processing in the brain makes it slower than a reflex.

3Spinal cord damage

• Spinal cord damage it cuts communication between the brain and the body below the injury.

Section 38 of 43Reaction time

1

One person drops a ruler without warning.

2

The other catches it as fast as possible.

3

Record the distance the ruler fell before it was caught.

4

Repeat several times and take a mean.

Interpretation

• Interpretation a shorter distance means a faster reaction.

Factors

• Factors practice, caffeine, tiredness and drugs change results, so other conditions must be controlled.

Section 39 of 43Drugs and reaction time

Heroin

• Heroin it mimics or blocks neurotransmitters at synapses.

Alcohol

• Alcohol it slows responses, so reaction times are longer, which is why drinking and driving is dangerous.

Section 40 of 43Reflexes with fewer synapses

Knee jerk

• Knee jerk it has no relay neurone, only one synapse between the sensory and motor neurones.

Number of synapses

• Number of synapses each synapse adds a small delay, so more synapses mean a slower response.

Section 41 of 43More from the specification

Organization of the Mammalian Nervous System

• The nervous system consists of the central nervous system and peripheral nerves, coordinating rapid, short-term responses via electrical impulses conducted along specialised nerve cells (neurones).
  • (brain and spinal cord)

Reflex Arc Pathway and Synapses

• In a reflex arc, receptor cells detect a stimulus and transmit impulses along sensory neurones to relay neurones in the spinal cord,
• and then via motor neurones to muscle effectors, with chemical neurotransmitters diffusing across synapses.

Homeostasis and Blood Glucose Levels

• The endocrine and nervous systems collaborate in homeostasis;
• when blood glucose levels fluctuate, pancreatic cells secrete insulin to stimulate glucose uptake or glucagon to trigger glycogen breakdown, maintaining constant internal blood glucose concentration.

Auxin and Phototropism in Plants

• Unlike mammalian nervous control, plants coordinate directional growth through plant growth hormones like auxin;
• when shoots are exposed to unilateral light, auxin diffuses to the shaded side, promoting cell elongation and positive phototropic growth.

Organization of the Mammalian Nervous System

• The nervous system consists of the central nervous system and peripheral nerves, coordinating rapid, short-term responses via electrical impulses conducted along specialised nerve cells (neurones).
  • (brain and spinal cord)

Reflex Arc Pathway and Synapses

• In a reflex arc, receptor cells detect a stimulus and transmit impulses along sensory neurones to relay neurones in the spinal cord,
• and then via motor neurones to muscle effectors, with chemical neurotransmitters diffusing across synapses.

Homeostasis and Blood Glucose Levels

• The endocrine and nervous systems collaborate in homeostasis;
• when blood glucose levels fluctuate, pancreatic cells secrete insulin to stimulate glucose uptake or glucagon to trigger glycogen breakdown, maintaining constant internal blood glucose concentration.

Auxin and Phototropism in Plants

• Unlike mammalian nervous control, plants coordinate directional growth through plant growth hormones like auxin;
• when shoots are exposed to unilateral light, auxin diffuses to the shaded side, promoting cell elongation and positive phototropic growth.

Reflex arc coordination

• Reflex arc coordination sensory and motor neurones coordinate rapid involuntary responses through the central nervous system.

Pupil reflex to light

• Pupil reflex to light circular iris muscle cells contract in bright light, reducing pupil diameter to protect the retina.

Blood glucose homeostasis

• Blood glucose homeostasis endocrine cells in the pancreas monitor circulating glucose levels, releasing insulin or glucagon to maintain setpoints.

Homeostasis

• Maintaining a constant internal environment.

Glycogen

• The storage carbohydrate in animals.

Gravity

• Force of attraction between objects with mass.

Retina

• The layer at the back of the eye with light receptors.

Ciliary muscle

• Muscle that changes the lens shape

Suspensory ligaments

• Fibres joining the lens to the ciliary muscles

Negative feedback

• A control that reverses a change to restore the set point.

Glucose

• Sugar that is the fuel for respiration.

Temperature

• Average energy of the particles in an object.

Growth

• Permanent increase in size.

Hormone

• A chemical messenger carried in the blood.

Concentration

• Amount of solute dissolved in a volume of solution.

Section 42 of 43Key terms

Term	Meaning
Neurone	A nerve cell that carries electrical impulses.
Sensory neurone	A neurone carrying impulses from a sense organ to the CNS.
Relay neurone	A neurone inside the CNS connecting sensory and motor neurones.
Motor neurone	A neurone carrying impulses from the CNS to an effector.
Reflex arc	The pathway of a reflex from receptor to response.
Synapse	The junction between two neurones.
Neurotransmitter	A chemical that carries the signal across a synapse.
Effector	A muscle or gland that carries out a response.

Term	Meaning
Central nervous system	Brain and spinal cord
Sensory neurone	Carries impulses from receptors to the CNS
Motor neurone	Carries impulses from the CNS to effectors
Relay neurone	Connects sensory and motor neurones inside the CNS
Myelin sheath	Fatty insulation around an axon
Effector	Muscle or gland that responds

Term	Meaning
Reflex action	Rapid automatic response to a stimulus
Reflex arc	Pathway from receptor to effector in a reflex
Stimulus	Change detected by receptors
Relay neurone	Neurone linking sensory and motor neurones
Effector	Part that produces a response
Pupil reflex	Change in pupil size in response to light

Term	Meaning
Synapse	Gap between two neurones
Neurotransmitter	Chemical released at a synapse
Vesicle	Small sac holding the transmitter
Receptor protein	Protein on the next neurone that binds the transmitter
Impulse	Electrical signal along a neurone
Diffusion	Net movement from high to low concentration

Term	Meaning
Neurone	A nerve cell that carries impulses
Reflex arc	Pathway of a rapid automatic response
Synapse	The gap between two neurones
Neurotransmitter	Chemical released at a synapse
Myelin	Fatty insulation around some axons
Relay neurone	Neurone linking sensory and motor neurones in the CNS

Section 43 of 43Exam technique

1

Saying the brain controls a reflex — the spinal cord coordinates it.

2

Saying sensory neurones carry impulses from the CNS — they carry impulses to it.

3

Saying impulses cross the synapse as electrical signals — a chemical neurotransmitter crosses the gap.

4

Saying reflexes are voluntary — they are automatic.

1

Saying all neurones carry impulses to the brain — motor neurones carry them away from the CNS.

2

Saying effectors detect stimuli — receptors detect, effectors respond.

3

Saying impulses are chemical signals along an axon — they are electrical.

4

Saying the peripheral nervous system includes the spinal cord — the spinal cord belongs to the CNS.

1

Saying the brain decides in a reflex — the spinal cord coordinates it.

2

Missing out the relay neurone from the arc.

3

Saying the effector detects the stimulus — the receptor does.

4

Saying a reflex is slower than a voluntary action — it is faster.

1

Saying the impulse itself jumps the gap — a chemical carries the message.

2

Saying the transmitter travels along the axon — it diffuses across the gap.

3

Saying synapses speed up transmission — they add a small delay.

4

Saying impulses travel both ways across a synapse — only one way.

1

Saying impulses cross a synapse as electrical signals — a chemical carries them.

2

Saying the reflex arc passes through the brain — the spinal cord coordinates it.

3

Confusing sensory and motor neurones — sensory go to the CNS, motor go away from it.

4

Saying the synapse is a physical connection between neurones — there is a gap.

5

Saying neurotransmitters pass in both directions — only from the first neurone to the second.