A Reflex Happens Before Your Brain Knows About It
Label a neuron and follow an impulse across a synapse, trace a reflex arc and see why it bypasses the brain, match each part of the brain to what it controls, and find out how a muscle turns a nerve signal into movement.
Why does your hand pull back before you feel the pain?
Touch something unexpectedly hot and your hand is already moving before you have registered what happened. The pain arrives a moment after the withdrawal, not before it.
That order of events is not an illusion. The signal that moved your hand never went to the thinking part of your brain at all. It travelled up to the spinal cord, was switched straight across to a motor nerve there, and came back to the muscle — while a separate copy of the signal carried on up to the brain, where it became the sensation of pain.
The reason for that shortcut is speed. Thinking takes time, and some situations do not allow any. A reflex is a hard-wired connection made in advance, so that the response needs no decision.
But most of what a body does is not a reflex, and for everything else the nervous system has to receive information, carry it a long way, compare it with other information and then act. That needs:
- Receptors to detect a change — in the eyes, ears, nose, tongue and skin
- Neurons to carry the information as an electrical impulse
- A brain and spinal cord to process it
- Muscles and glands to carry out the response
This page covers the first part of the CBSE Class 10 Science chapter on control and coordination: the neuron and the synapse, the reflex arc, the parts of the brain and spinal cord, and how muscles produce movement.
That order of events is not an illusion. The signal that moved your hand never went to the thinking part of your brain at all. It travelled up to the spinal cord, was switched straight across to a motor nerve there, and came back to the muscle — while a separate copy of the signal carried on up to the brain, where it became the sensation of pain.
The reason for that shortcut is speed. Thinking takes time, and some situations do not allow any. A reflex is a hard-wired connection made in advance, so that the response needs no decision.
But most of what a body does is not a reflex, and for everything else the nervous system has to receive information, carry it a long way, compare it with other information and then act. That needs:
- Receptors to detect a change — in the eyes, ears, nose, tongue and skin
- Neurons to carry the information as an electrical impulse
- A brain and spinal cord to process it
- Muscles and glands to carry out the response
This page covers the first part of the CBSE Class 10 Science chapter on control and coordination: the neuron and the synapse, the reflex arc, the parts of the brain and spinal cord, and how muscles produce movement.
How does an impulse travel along a neuron and across a synapse?
Electrically along the neuron, chemically across the gap between two neurons.
The parts of a neuron, in the order the information travels:
- Dendrites — short branched extensions that receive the information from a receptor or from another neuron
- Cell body — where the information sets off an electrical change
- Axon — a long fibre that carries the electrical impulse away from the cell body
- Nerve endings — the fine branches at the far end of the axon
Along the axon the signal is electrical. A chemical change at the dendrite tip sets up an electrical impulse, which travels to the cell body and then all the way down the axon to its end.
At the end the signal has to change form. Two neurons do not touch — there is a tiny gap between the nerve ending of one and the dendrite of the next, and that junction is called a synapse. The electrical impulse cannot jump the gap, so it releases a chemical at the nerve ending, the chemical diffuses across, and it starts a fresh electrical impulse in the next neuron.
That is the point of the whole design. A synapse converts electrical to chemical and back again, which means:
- The signal can travel in one direction only, since only one side releases the chemical
- The signal can be filtered — a weak input may not produce enough chemical to fire the next neuron
- Many neurons can feed into one, so information can be combined
A similar junction ends the journey. The last nerve ending meets a muscle cell or a gland rather than another neuron, and releases its chemical there to trigger the response.
The everyday consequence of one-way synapses. You cannot think a sensation into existence, and a message cannot run backwards down a motor nerve. The nervous system is built from one-way links, which is why a pathway has to be traced in a fixed order and why a reflex diagram has arrowheads.
One limitation worth knowing. The electrical impulse and the chemical diffusion both take time. Nervous control is fast but not instant, and it cannot reach every cell of the body — only those a nerve fibre actually arrives at. That is exactly the gap the hormones of Part 2 fill.
The parts of a neuron, in the order the information travels:
- Dendrites — short branched extensions that receive the information from a receptor or from another neuron
- Cell body — where the information sets off an electrical change
- Axon — a long fibre that carries the electrical impulse away from the cell body
- Nerve endings — the fine branches at the far end of the axon
Along the axon the signal is electrical. A chemical change at the dendrite tip sets up an electrical impulse, which travels to the cell body and then all the way down the axon to its end.
At the end the signal has to change form. Two neurons do not touch — there is a tiny gap between the nerve ending of one and the dendrite of the next, and that junction is called a synapse. The electrical impulse cannot jump the gap, so it releases a chemical at the nerve ending, the chemical diffuses across, and it starts a fresh electrical impulse in the next neuron.
That is the point of the whole design. A synapse converts electrical to chemical and back again, which means:
- The signal can travel in one direction only, since only one side releases the chemical
- The signal can be filtered — a weak input may not produce enough chemical to fire the next neuron
- Many neurons can feed into one, so information can be combined
A similar junction ends the journey. The last nerve ending meets a muscle cell or a gland rather than another neuron, and releases its chemical there to trigger the response.
The everyday consequence of one-way synapses. You cannot think a sensation into existence, and a message cannot run backwards down a motor nerve. The nervous system is built from one-way links, which is why a pathway has to be traced in a fixed order and why a reflex diagram has arrowheads.
One limitation worth knowing. The electrical impulse and the chemical diffusion both take time. Nervous control is fast but not instant, and it cannot reach every cell of the body — only those a nerve fibre actually arrives at. That is exactly the gap the hormones of Part 2 fill.
What is a reflex arc, and why does it skip the brain?
A reflex arc is the shortest possible nerve pathway from a receptor to a muscle, completed in the spinal cord instead of the brain.
The pathway, in order.
- A receptor in the skin detects the heat or the prick
- A sensory neuron carries the impulse to the spinal cord
- A relay neuron inside the spinal cord passes it straight across
- A motor neuron carries the instruction out to the muscle
- The muscle contracts and the hand is withdrawn
That is the whole arc, and the brain is not part of it. A separate branch carries the same information up to the brain, which is why you also feel the pain — but the movement has already happened by then.
Why the arrangement exists. The thinking parts of the brain are at the top of the spinal cord, and sending the signal up, having it processed as a decision, and sending it back down would take noticeably longer. For a response that must be immediate, that delay could be the difference between a small burn and a serious one. So the connection is made permanently in the spinal cord instead of being worked out each time.
Familiar examples of reflex actions.
- Withdrawing a hand from something hot or sharp
- Blinking when something comes towards the eye
- Watering of the mouth at the smell of food
- Sneezing and coughing
- The knee-jerk response a doctor tests with a small hammer
The distinction that is examined. A reflex is involuntary — it happens without your deciding, and you cannot easily stop it. Picking up a hot vessel deliberately, using a cloth, is voluntary, and that decision does go through the brain. Both use the same neurons; only the route differs.
A boundary case worth naming. Some reflexes can be partly overridden with practice — you can hold your hand steady for an injection, or keep your eyes open when something approaches. The brain can inhibit a reflex, but it cannot make one faster, which tells you the arc is real and the brain's role is supervisory.
And one detail that makes the design clearer. Reflex arcs evolved in animals whose thinking apparatus was limited, and even in animals with large brains the arcs were kept, because there is no advantage in slowing down a response that never needs a decision. Efficient design keeps what works, and the spinal cord is where that shortcut lives.
The pathway, in order.
- A receptor in the skin detects the heat or the prick
- A sensory neuron carries the impulse to the spinal cord
- A relay neuron inside the spinal cord passes it straight across
- A motor neuron carries the instruction out to the muscle
- The muscle contracts and the hand is withdrawn
That is the whole arc, and the brain is not part of it. A separate branch carries the same information up to the brain, which is why you also feel the pain — but the movement has already happened by then.
Why the arrangement exists. The thinking parts of the brain are at the top of the spinal cord, and sending the signal up, having it processed as a decision, and sending it back down would take noticeably longer. For a response that must be immediate, that delay could be the difference between a small burn and a serious one. So the connection is made permanently in the spinal cord instead of being worked out each time.
Familiar examples of reflex actions.
- Withdrawing a hand from something hot or sharp
- Blinking when something comes towards the eye
- Watering of the mouth at the smell of food
- Sneezing and coughing
- The knee-jerk response a doctor tests with a small hammer
The distinction that is examined. A reflex is involuntary — it happens without your deciding, and you cannot easily stop it. Picking up a hot vessel deliberately, using a cloth, is voluntary, and that decision does go through the brain. Both use the same neurons; only the route differs.
A boundary case worth naming. Some reflexes can be partly overridden with practice — you can hold your hand steady for an injection, or keep your eyes open when something approaches. The brain can inhibit a reflex, but it cannot make one faster, which tells you the arc is real and the brain's role is supervisory.
And one detail that makes the design clearer. Reflex arcs evolved in animals whose thinking apparatus was limited, and even in animals with large brains the arcs were kept, because there is no advantage in slowing down a response that never needs a decision. Efficient design keeps what works, and the spinal cord is where that shortcut lives.
Which part of the brain controls which activity?
Match the activity to the region: thinking to the cerebrum, balance to the cerebellum, involuntary vital functions to the medulla, and reflexes to the spinal cord.
The cerebrum — the largest part, the seat of everything you are aware of:
- Voluntary actions, such as writing or lifting an arm deliberately
- Thinking, reasoning, memory and learning
- Sensation — the regions that receive impulses from the eyes, ears, nose, tongue and skin, and where you actually feel things
The cerebellum — responsible for precision of voluntary actions and for posture and balance. Walking in a straight line, riding a bicycle, picking up a pencil without knocking it over, and standing upright all depend on it.
The medulla — in the hindbrain, controlling involuntary actions that must never stop:
- Blood pressure
- Salivation
- Vomiting
The spinal cord — the site of reflex arcs, and the cable carrying every signal between the body and the brain.
Worked matching. Which part is responsible for each of these?
- Deciding to pick up a glass — cerebrum, a voluntary action
- Not spilling it while walking — cerebellum, precision and balance
- The heartbeat continuing while you sleep — medulla, involuntary
- Dropping it the instant it turns out to be scalding — spinal cord, a reflex
Four regions, four kinds of control, and a question describing an activity is asking you to decide which kind it is.
How the brain is protected. It sits inside the bony skull and is cushioned by a fluid-filled balloon of membranes, which absorbs shocks. The spinal cord runs inside the vertebral column for the same reason. Soft tissue that cannot be repaired is protected by bone, which is why a helmet matters.
One consequence of the division of labour. Damage to the cerebellum does not stop you from moving — it stops you from moving accurately, so the walk becomes unsteady. Damage to the medulla is far more serious, because breathing and blood pressure depend on it. The severity of an injury depends on which region it affects, not only on how large it is.
And the limitation that carries into Part 2. All of this control needs a nerve to reach the target. Cells with no nerve supply cannot be controlled this way at all, and plants have no nervous system whatsoever — which is why the next part of the chapter is about chemical messengers.
The cerebrum — the largest part, the seat of everything you are aware of:
- Voluntary actions, such as writing or lifting an arm deliberately
- Thinking, reasoning, memory and learning
- Sensation — the regions that receive impulses from the eyes, ears, nose, tongue and skin, and where you actually feel things
The cerebellum — responsible for precision of voluntary actions and for posture and balance. Walking in a straight line, riding a bicycle, picking up a pencil without knocking it over, and standing upright all depend on it.
The medulla — in the hindbrain, controlling involuntary actions that must never stop:
- Blood pressure
- Salivation
- Vomiting
The spinal cord — the site of reflex arcs, and the cable carrying every signal between the body and the brain.
Worked matching. Which part is responsible for each of these?
- Deciding to pick up a glass — cerebrum, a voluntary action
- Not spilling it while walking — cerebellum, precision and balance
- The heartbeat continuing while you sleep — medulla, involuntary
- Dropping it the instant it turns out to be scalding — spinal cord, a reflex
Four regions, four kinds of control, and a question describing an activity is asking you to decide which kind it is.
How the brain is protected. It sits inside the bony skull and is cushioned by a fluid-filled balloon of membranes, which absorbs shocks. The spinal cord runs inside the vertebral column for the same reason. Soft tissue that cannot be repaired is protected by bone, which is why a helmet matters.
One consequence of the division of labour. Damage to the cerebellum does not stop you from moving — it stops you from moving accurately, so the walk becomes unsteady. Damage to the medulla is far more serious, because breathing and blood pressure depend on it. The severity of an injury depends on which region it affects, not only on how large it is.
And the limitation that carries into Part 2. All of this control needs a nerve to reach the target. Cells with no nerve supply cannot be controlled this way at all, and plants have no nervous system whatsoever — which is why the next part of the chapter is about chemical messengers.
How does a muscle turn a nerve signal into movement?
The muscle cell changes shape. Its protein filaments slide over one another and the cell becomes shorter, and a shorter cell pulls on what it is attached to.
The sequence, from signal to movement.
- The motor neuron's ending releases a chemical at the junction with the muscle cell
- The muscle cell responds by taking up that chemical, which sets off an electrical change in it
- Inside the cell are special proteins arranged in a regular pattern
- The electrical change makes those proteins change their arrangement and their shape
- The cell becomes shorter, and because it is anchored at both ends, it pulls
That shortening is what we call contraction, and it is the only thing a muscle can do. A muscle can pull but it cannot push, which is why muscles are arranged in opposing pairs — one to bend a joint and another to straighten it. Your arm has a muscle on the front to bend the elbow and one at the back to straighten it, and neither could do the other's job.
Where the energy comes from. Changing the shape of those proteins is work, and the energy is supplied by respiration inside the muscle cell — which is exactly why a muscle working hard runs short of oxygen, respires anaerobically and accumulates lactic acid. The cramp of the respiration chapter is this chapter's muscle running out of supply.
Two kinds of muscle to keep apart.
- Voluntary muscles, attached to bones, which you control through the cerebrum — the muscles of the arms, legs and face
- Involuntary muscles, in the walls of the gut, the blood vessels and the heart, which you cannot control by deciding to. Peristalsis and the heartbeat are involuntary muscle at work, directed by the medulla and by the heart's own rhythm
The misconception to clear. A nerve does not move anything. It only delivers a signal; the movement is produced by the muscle changing shape. So paralysis can result from damage to the nerve, to the spinal cord or to the muscle itself — three different causes producing the same outward effect, which is why the site of an injury matters so much.
And here is the limitation the whole chapter is driving towards. This entire system needs cells specialised for conduction and cells specialised for contraction. A plant has neither — no neurons, no muscles — and yet a plant shoot bends towards light and a root grows downwards. Something else must be doing the controlling, and that is where Part 2 begins.
The sequence, from signal to movement.
- The motor neuron's ending releases a chemical at the junction with the muscle cell
- The muscle cell responds by taking up that chemical, which sets off an electrical change in it
- Inside the cell are special proteins arranged in a regular pattern
- The electrical change makes those proteins change their arrangement and their shape
- The cell becomes shorter, and because it is anchored at both ends, it pulls
That shortening is what we call contraction, and it is the only thing a muscle can do. A muscle can pull but it cannot push, which is why muscles are arranged in opposing pairs — one to bend a joint and another to straighten it. Your arm has a muscle on the front to bend the elbow and one at the back to straighten it, and neither could do the other's job.
Where the energy comes from. Changing the shape of those proteins is work, and the energy is supplied by respiration inside the muscle cell — which is exactly why a muscle working hard runs short of oxygen, respires anaerobically and accumulates lactic acid. The cramp of the respiration chapter is this chapter's muscle running out of supply.
Two kinds of muscle to keep apart.
- Voluntary muscles, attached to bones, which you control through the cerebrum — the muscles of the arms, legs and face
- Involuntary muscles, in the walls of the gut, the blood vessels and the heart, which you cannot control by deciding to. Peristalsis and the heartbeat are involuntary muscle at work, directed by the medulla and by the heart's own rhythm
The misconception to clear. A nerve does not move anything. It only delivers a signal; the movement is produced by the muscle changing shape. So paralysis can result from damage to the nerve, to the spinal cord or to the muscle itself — three different causes producing the same outward effect, which is why the site of an injury matters so much.
And here is the limitation the whole chapter is driving towards. This entire system needs cells specialised for conduction and cells specialised for contraction. A plant has neither — no neurons, no muscles — and yet a plant shoot bends towards light and a root grows downwards. Something else must be doing the controlling, and that is where Part 2 begins.
Exam tip
What layout keeps a nervous-system answer complete?
Name the structure, then its function, then the direction of the signal. Most marks in this chapter are for a correctly ordered pathway rather than for a description.
- Trace a pathway in order with arrows: receptor, sensory neuron, spinal cord, relay neuron, motor neuron, muscle. Missing one step loses the mark for the whole arc
- Say that the synapse is a gap and that the signal crosses it as a chemical. That word is the answer to how does an impulse cross from one neuron to the next
- Explain the one-way rule by saying that only one side releases the chemical
- State the reason a reflex skips the brain — speed — rather than only stating that it does
- Match each brain region to its kind of control: cerebrum voluntary and thinking, cerebellum balance and precision, medulla involuntary, spinal cord reflex
- **Say that a muscle cell changes shape and contracts, and that it can only pull
- Label a neuron diagram with dendrite, cell body, axon and nerve ending, and mark the direction of the impulse
- Give the protective structures: skull for the brain, vertebral column for the spinal cord, fluid to cushion both
The distinction to state carefully. Reflex action is the involuntary response; the reflex arc** is the pathway it travels along. A question asking what is a reflex arc wants the pathway, and one asking what is a reflex action wants the involuntary quick response. Two different answers, and they are frequently swapped.
- Trace a pathway in order with arrows: receptor, sensory neuron, spinal cord, relay neuron, motor neuron, muscle. Missing one step loses the mark for the whole arc
- Say that the synapse is a gap and that the signal crosses it as a chemical. That word is the answer to how does an impulse cross from one neuron to the next
- Explain the one-way rule by saying that only one side releases the chemical
- State the reason a reflex skips the brain — speed — rather than only stating that it does
- Match each brain region to its kind of control: cerebrum voluntary and thinking, cerebellum balance and precision, medulla involuntary, spinal cord reflex
- **Say that a muscle cell changes shape and contracts, and that it can only pull
- Label a neuron diagram with dendrite, cell body, axon and nerve ending, and mark the direction of the impulse
- Give the protective structures: skull for the brain, vertebral column for the spinal cord, fluid to cushion both
The distinction to state carefully. Reflex action is the involuntary response; the reflex arc** is the pathway it travels along. A question asking what is a reflex arc wants the pathway, and one asking what is a reflex action wants the involuntary quick response. Two different answers, and they are frequently swapped.
Did you know
Why can a doctor test your spinal cord with a small hammer?
Sit with your legs hanging free and have someone tap the tendon just below the knee. The lower leg kicks forward, and there is nothing you can do about it.
That kick is a reflex, and its arc is unusually simple: a receptor in the tendon, a sensory neuron into the spinal cord, and a motor neuron straight back out to the thigh muscle. The brain is not consulted at all — which is exactly what makes it useful to a doctor.
Because the pathway is short and entirely within the spinal cord, the test checks that one specific stretch of cord and its two nerves are working. If the kick is absent, the fault is somewhere in that arc; if it is present, that segment is intact even in a patient who cannot answer questions. A response that needs no cooperation from the person being tested is a valuable thing in medicine.
And the same logic explains a familiar experience. The blink reflex protects the eye long before you could decide to close it, and you cannot stop it by trying — which is why it is hard to keep your eyes open when a hand moves towards your face, even when you know the hand belongs to a friend.
Notice what the reflex cannot do. It cannot learn, judge or adapt. A hand jerks away from anything sufficiently hot, including the handle of a vessel you were deliberately lifting — which is why a careful cook uses a cloth: the cloth prevents the receptor from being triggered at all, rather than trying to overrule the reflex once it is.
The general design principle is worth keeping. Responses that must be fast and never need judgement are wired in permanently; responses that need judgement go through the brain and are slower. A nervous system is a mixture of hard-wired shortcuts and flexible decisions, and this chapter is really about where the boundary between them falls.
That kick is a reflex, and its arc is unusually simple: a receptor in the tendon, a sensory neuron into the spinal cord, and a motor neuron straight back out to the thigh muscle. The brain is not consulted at all — which is exactly what makes it useful to a doctor.
Because the pathway is short and entirely within the spinal cord, the test checks that one specific stretch of cord and its two nerves are working. If the kick is absent, the fault is somewhere in that arc; if it is present, that segment is intact even in a patient who cannot answer questions. A response that needs no cooperation from the person being tested is a valuable thing in medicine.
And the same logic explains a familiar experience. The blink reflex protects the eye long before you could decide to close it, and you cannot stop it by trying — which is why it is hard to keep your eyes open when a hand moves towards your face, even when you know the hand belongs to a friend.
Notice what the reflex cannot do. It cannot learn, judge or adapt. A hand jerks away from anything sufficiently hot, including the handle of a vessel you were deliberately lifting — which is why a careful cook uses a cloth: the cloth prevents the receptor from being triggered at all, rather than trying to overrule the reflex once it is.
The general design principle is worth keeping. Responses that must be fast and never need judgement are wired in permanently; responses that need judgement go through the brain and are slower. A nervous system is a mixture of hard-wired shortcuts and flexible decisions, and this chapter is really about where the boundary between them falls.
Exam relevance
Why does NEET keep returning to the neuron and the reflex arc?
This is foundation work for one of the most detailed Class 11 Biology chapters, and it is examined in NEET every kind of way.
Where the neuron leads. Class 11 Neural Control and Coordination takes the same cell much further: the resting potential, the action potential, the sodium and potassium channels, the myelin sheath and saltatory conduction. The chemical crossing of the synapse becomes named neurotransmitters and the mechanism of release, and NEET asks directly about the sequence of events at a synapse.
Where the reflex arc leads. The same arc is drawn in Class 11 with the dorsal and ventral roots of the spinal nerve named, and the distinction between a monosynaptic reflex such as the knee-jerk and a polysynaptic one such as withdrawal. The order of the five components is examined as a sequence question, and the marks go to getting the order exactly right.
Where the brain regions lead. Class 11 expands the forebrain, midbrain and hindbrain with the thalamus, hypothalamus, pons and the limbic system. The four functions you learn here remain the core, and NEET sets match-the-column questions pairing a region with a function.
Where the muscle leads. Class 11 Locomotion and Movement explains the shape change as the sliding filament theory, with actin and myosin named and the role of calcium and ATP described. The Class 10 statement that the proteins change their arrangement is the outline of that theory, and knowing it as a mechanism rather than a phrase makes the later chapter far easier.
Question types to expect. At this level: label a neuron, trace an arc, match a region to an activity. In competitive papers: sequence-the-steps questions on synaptic transmission, assertion-reason items on why the impulse is one-way, and diagram-based questions on the brain and the reflex pathway.
The single trap that costs marks. Saying that the impulse jumps the synapse electrically. It crosses as a chemical, and that fact is the reason the transmission is one-way and can be blocked by drugs — a point NEET examines. An answer that says the electrical impulse passes to the next neuron has missed the whole mechanism.
A second trap. Confusing the reflex arc with the reflex action, or leaving the relay neuron out of the pathway. Five components, in order, with the relay neuron inside the spinal cord is what the marking scheme looks for.
Board versus competitive emphasis. The CBSE paper marks the labelled diagram, the ordered pathway and the stated function; a competitive paper marks a matched pair or a correct sequence. The transferable asset is the order of the pathway — it appears again in Class 11 and in every question about how a response is produced.
Where the neuron leads. Class 11 Neural Control and Coordination takes the same cell much further: the resting potential, the action potential, the sodium and potassium channels, the myelin sheath and saltatory conduction. The chemical crossing of the synapse becomes named neurotransmitters and the mechanism of release, and NEET asks directly about the sequence of events at a synapse.
Where the reflex arc leads. The same arc is drawn in Class 11 with the dorsal and ventral roots of the spinal nerve named, and the distinction between a monosynaptic reflex such as the knee-jerk and a polysynaptic one such as withdrawal. The order of the five components is examined as a sequence question, and the marks go to getting the order exactly right.
Where the brain regions lead. Class 11 expands the forebrain, midbrain and hindbrain with the thalamus, hypothalamus, pons and the limbic system. The four functions you learn here remain the core, and NEET sets match-the-column questions pairing a region with a function.
Where the muscle leads. Class 11 Locomotion and Movement explains the shape change as the sliding filament theory, with actin and myosin named and the role of calcium and ATP described. The Class 10 statement that the proteins change their arrangement is the outline of that theory, and knowing it as a mechanism rather than a phrase makes the later chapter far easier.
Question types to expect. At this level: label a neuron, trace an arc, match a region to an activity. In competitive papers: sequence-the-steps questions on synaptic transmission, assertion-reason items on why the impulse is one-way, and diagram-based questions on the brain and the reflex pathway.
The single trap that costs marks. Saying that the impulse jumps the synapse electrically. It crosses as a chemical, and that fact is the reason the transmission is one-way and can be blocked by drugs — a point NEET examines. An answer that says the electrical impulse passes to the next neuron has missed the whole mechanism.
A second trap. Confusing the reflex arc with the reflex action, or leaving the relay neuron out of the pathway. Five components, in order, with the relay neuron inside the spinal cord is what the marking scheme looks for.
Board versus competitive emphasis. The CBSE paper marks the labelled diagram, the ordered pathway and the stated function; a competitive paper marks a matched pair or a correct sequence. The transferable asset is the order of the pathway — it appears again in Class 11 and in every question about how a response is produced.
Key takeaways
What should you know about nervous control before plant hormones?
One cell type, one pathway, four brain regions and one kind of response.
- Control needs receptors, neurons, a processing centre and an effector — a muscle or a gland
- A neuron has dendrites, a cell body, an axon and nerve endings, and the impulse travels in that order
- Along the axon the signal is electrical; across the synapse it is chemical, which makes transmission one-way
- A reflex arc: receptor, sensory neuron, spinal cord with a relay neuron, motor neuron, muscle — the brain is not part of it
- Reflexes skip the brain for speed, and the sensation arrives afterwards
- Cerebrum — voluntary action, thinking, memory and sensation; cerebellum — balance and precision; medulla — involuntary actions such as blood pressure and vomiting; spinal cord — reflexes
- The brain is protected by the skull and the spinal cord by the vertebral column, both cushioned by fluid
- A muscle cell changes shape and contracts, using energy from respiration, and it can only pull — which is why muscles work in opposing pairs
- Reflex action is the response; reflex arc is the pathway — not the same thing
- Nervous control needs a nerve to reach the target, which is why chemical control is also necessary
The sharpest self-test is the arc. Draw the five components of a reflex arc in order with arrows, mark where the brain's copy of the signal branches off, and explain in one sentence why the hand has already moved before the pain is felt.
- Control needs receptors, neurons, a processing centre and an effector — a muscle or a gland
- A neuron has dendrites, a cell body, an axon and nerve endings, and the impulse travels in that order
- Along the axon the signal is electrical; across the synapse it is chemical, which makes transmission one-way
- A reflex arc: receptor, sensory neuron, spinal cord with a relay neuron, motor neuron, muscle — the brain is not part of it
- Reflexes skip the brain for speed, and the sensation arrives afterwards
- Cerebrum — voluntary action, thinking, memory and sensation; cerebellum — balance and precision; medulla — involuntary actions such as blood pressure and vomiting; spinal cord — reflexes
- The brain is protected by the skull and the spinal cord by the vertebral column, both cushioned by fluid
- A muscle cell changes shape and contracts, using energy from respiration, and it can only pull — which is why muscles work in opposing pairs
- Reflex action is the response; reflex arc is the pathway — not the same thing
- Nervous control needs a nerve to reach the target, which is why chemical control is also necessary
The sharpest self-test is the arc. Draw the five components of a reflex arc in order with arrows, mark where the brain's copy of the signal branches off, and explain in one sentence why the hand has already moved before the pain is felt.