Neural Control and Coordination ISC Class 11: Neuron, Brain and Nerve Impulse

What Neural Control and Coordination is about

Weightage: Neural Control and Coordination belongs to the unit Human Physiology, which CISCE weights at 18 of the 70 marks in the ISC Class XI Biology Paper I (Theory). Class XI is examined by the school, so your school sets the paper within this weightage.Source: CISCE ISC Biology syllabus, examination year 2028, Class XI unit weightage

Key concepts

Structure of a neuron and nerves

A neuron has three parts. (1) Cell body (cyton): contains cytoplasm with the usual organelles and granular bodies called Nissl's granules (rich in ribosomes, for protein synthesis). (2) Dendrites: short, branched fibres projecting from the cell body; they also contain Nissl's granules and carry impulses towards the cell body. (3) Axon: a long fibre whose far end branches; each branch ends in a bulb-like synaptic knob containing synaptic vesicles filled with neurotransmitters. Axons carry impulses away from the cell body to a synapse or a neuromuscular junction. Axons may be myelinated, enveloped by Schwann cells that form a fatty myelin sheath with gaps called nodes of Ranvier (found in spinal and cranial nerves), or non-myelinated, enclosed by a Schwann cell that does not form a myelin sheath (common in autonomic and somatic nerves). A nerve is a bundle of axons wrapped in connective tissue. Sensory (afferent) nerves carry impulses from receptors to the CNS; motor (efferent) nerves carry impulses from the CNS to effectors (muscles, glands); mixed nerves contain both.

Worked example

Why are Nissl's granules found in the cell body and dendrites but not in the axon?

Try it first, then show the solutionSolution

1. Nissl's granules are clusters of rough ER and ribosomes that make proteins
2. Protein synthesis takes place in the cell body and dendrites; the axon depends on proteins transported from the cell body

Answer: Because the axon does not synthesise proteins itself

Types of neurons: unipolar, bipolar, pseudounipolar and multipolar

Neurons are classified by the number of processes arising from the cell body. (1) Multipolar: one axon and two or more dendrites; the most common type, found in the cerebral cortex, spinal cord (motor neurons) and elsewhere. (2) Bipolar: one axon and one dendrite at opposite ends of the cell body; found in the retina of the eye and in the olfactory epithelium. (3) Unipolar: the cell body has only one process (an axon); usually found in the embryonic stage. (4) Pseudounipolar: a single short process leaves the cell body and then divides into two branches, one going to the periphery (acting like a dendrite) and the other entering the CNS (acting as an axon); typical of sensory neurons in the dorsal root ganglia of spinal nerves. Neurons are also classified by function as sensory, motor and interneurons (association neurons within the CNS).

Worked example

A neuron in a spinal ganglion has a single process that splits like a T into a peripheral branch and a central branch. Name the type and its role.

Try it first, then show the solutionSolution

1. One process that divides into two is the pseudounipolar arrangement
2. These are sensory neurons carrying impulses from receptors into the spinal cord

Answer: Pseudounipolar sensory neuron

Divisions: CNS, PNS, somatic, autonomic and visceral nervous systems

The central nervous system (CNS) is the brain and spinal cord, the site of information processing and control. The peripheral nervous system (PNS) consists of all the nerves associated with the CNS: 12 pairs of cranial nerves and 31 pairs of spinal nerves. Nerve fibres of the PNS are afferent (CNS-bound, from tissues and organs) or efferent (carrying regulatory impulses from the CNS to tissues and organs). The PNS is divided into: (1) the somatic nervous system, which relays impulses from the CNS to skeletal muscles (largely voluntary); and (2) the autonomic nervous system, which relays impulses from the CNS to involuntary organs and smooth muscles. The autonomic system has two divisions with generally opposite effects: sympathetic (prepares the body for emergencies: increases heart rate, dilates pupils, inhibits digestion) and parasympathetic (restores the body at rest: slows the heart, stimulates digestion). The visceral nervous system is the part of the PNS that serves the internal organs: its nerves, fibres, ganglia and plexuses carry signals in both directions, outwards from the CNS to the viscera and back from the viscera to the CNS.

Worked example

When you are frightened, your heart races and your mouth goes dry. Which division is responsible?

Try it first, then show the solutionSolution

1. These are involuntary changes in internal organs, controlled by the autonomic nervous system
2. Faster heartbeat and reduced salivation prepare the body for action: sympathetic division

Answer: Sympathetic division of the autonomic nervous system

Brain: meninges, forebrain, midbrain and hindbrain

The brain is the central information-processing organ. It is protected by the cranium and covered by three meninges: an outer tough dura mater, a very thin middle arachnoid and an inner pia mater in contact with the brain tissue. Forebrain: (1) Cerebrum, the largest part, divided by a deep cleft into left and right cerebral hemispheres, joined by a tract of nerve fibres, the corpus callosum. Its outer layer, the cerebral cortex, is grey matter (cell bodies), thrown into folds; it contains motor areas, sensory areas and large association areas responsible for complex functions such as intersensory associations, memory, communication and thinking. The inner part is white matter (myelinated fibres). (2) Thalamus, wrapped by the cerebrum, a major coordinating centre for sensory and motor signals. (3) Hypothalamus, at the base of the thalamus, with centres controlling body temperature, hunger and thirst; it also has neurosecretory cells that release hypothalamic hormones. The inner parts of the hemispheres and associated deep structures (such as amygdala and hippocampus) form the limbic system, which with the hypothalamus regulates emotions (excitement, pleasure, rage, fear), motivation and sexual behaviour. Midbrain: between the thalamus/hypothalamus and the pons; a canal, the cerebral aqueduct, runs through it; its dorsal part has four round swellings, the corpora quadrigemina, which control visual and auditory reflexes. Hindbrain: (1) Pons: fibre tracts linking different regions of the brain; contains a centre that helps regulate breathing (pneumotaxic centre). (2) Cerebellum: very convoluted surface (to fit many neurons); coordinates voluntary movements, balance and posture. (3) Medulla oblongata: continuous with the spinal cord; contains centres controlling respiration, cardiovascular reflexes and gastric secretion, and reflexes such as swallowing, coughing, sneezing and vomiting. The midbrain, pons and medulla together form the brain stem, which connects the brain to the spinal cord.

Worked example

After a head injury, a person walks unsteadily and cannot touch the nose accurately with eyes closed, though muscle strength is normal. Which part of the brain is likely affected?

Try it first, then show the solutionSolution

1. Strength is fine, so motor pathways work; the problem is coordination and balance
2. Coordination of voluntary movement, balance and posture is the job of the cerebellum

Answer: The cerebellum

Spinal cord and reflex action

The spinal cord lies in the neural canal of the vertebral column, running from the medulla down to about the first or second lumbar vertebra, and is covered by meninges. In cross-section, the grey matter is inside (butterfly or H-shaped, with dorsal and ventral horns) and the white matter outside (the reverse of the cerebrum), with a narrow central canal in the middle. Each spinal nerve joins the cord by a dorsal (sensory) root, which carries a dorsal root ganglion of sensory cell bodies, and a ventral (motor) root. Functions: (1) conduction of impulses to and from the brain through ascending and descending tracts in the white matter; (2) a centre for reflex actions. A reflex action is a quick, automatic (involuntary) response to a stimulus that involves a part of the CNS but not conscious thought. Its pathway, the reflex arc, is: receptor → afferent (sensory) neuron → through the dorsal root into the spinal cord (sometimes via an interneuron) → efferent (motor) neuron → through the ventral root to the effector (muscle or gland). The knee-jerk reflex is a simple example in which the sensory neuron synapses directly with the motor neuron.

Worked example

When your hand touches a hot pan, you pull it away before you feel pain. Explain why.

Try it first, then show the solutionSolution

1. The withdrawal is a spinal reflex: impulses go from receptor to spinal cord to motor neuron to muscle along a short path
2. Signals to the brain, which create the sensation of pain, travel further and are processed later, so the hand moves first

Answer: The reflex arc through the spinal cord is shorter and quicker than the pathway to conscious awareness

Generation of the nerve impulse: resting and action potentials

Neurons are excitable because their membranes are polarised. Resting potential: in a resting neuron, the axon membrane is more permeable to K⁺ and nearly impermeable to Na⁺ and to the negatively charged proteins inside. The axoplasm has a high K⁺ concentration and negative proteins, and low Na⁺; the fluid outside has high Na⁺ and low K⁺. These gradients are kept up by the sodium–potassium pump, which actively moves 3 Na⁺ out for every 2 K⁺ in, using ATP. As a result the outer surface is positive and the inner surface negative: the membrane is polarised, with a resting potential of about −70 mV. Action potential: when a stimulus is applied at a site (A), the membrane there becomes freely permeable to Na⁺. Na⁺ rushes in, and the polarity reverses: the outer surface becomes negative and the inner surface positive (about +30 mV); the membrane is depolarised. This reversed potential difference is the action potential, i.e. the nerve impulse. The rise in Na⁺ permeability is short-lived; it is quickly followed by a rise in K⁺ permeability: K⁺ moves out, restoring the resting charge (repolarisation), and the pump re-establishes the ion distribution. For a brief refractory period the membrane cannot fire again, which keeps impulses moving in one direction.

Worked example

If the resting potential is −70 mV and the action potential peaks at +30 mV, by how much does the membrane potential change, and which ion causes the rise?

Try it first, then show the solutionSolution

1. Change = +30 − (−70) = 100 mV
2. The rise is caused by the rapid inflow of Na⁺

Answer: 100 mV, due to Na⁺ influx

Conduction along non-myelinated and myelinated fibres

Non-myelinated fibre: when site A is depolarised, the next site (B) is still at rest (inside negative, outside positive). On the inner surface, current flows from A to B (from positive to negative); on the outer surface, current flows from B to A, completing a local circuit. This depolarises site B, generating an action potential there; meanwhile site A repolarises. The process repeats along the whole axon, so the impulse travels as a continuous wave. Conduction is relatively slow (about 0.5–2 m s⁻¹). Myelinated fibre: the myelin sheath is an insulator and ion flow cannot occur across it; ion channels are concentrated at the nodes of Ranvier. Local currents therefore flow from one node to the next, and the action potential jumps from node to node: saltatory conduction. This is much faster (up to about 100 m s⁻¹ or more) and uses less energy, because ions are exchanged only at the nodes, so less pumping is needed to restore them.

Worked example

An impulse must travel 1 m. How long does it take along a myelinated fibre at 100 m s⁻¹ and a non-myelinated fibre at 1 m s⁻¹?

Try it first, then show the solutionSolution

1. Myelinated: 1 ÷ 100 = 0.01 s = 10 ms
2. Non-myelinated: 1 ÷ 1 = 1 s = 1000 ms, i.e. 100 times slower

Answer: 10 ms versus 1000 ms

Transmission across a synapse

A synapse is the junction between the pre-synaptic neuron and a post-synaptic neuron (or effector), which may be separated by a fluid-filled gap, the synaptic cleft. Electrical synapses: the membranes are very close; current flows directly from one neuron to the next, so transmission is very fast (as along a single axon); they are rare in our system. Chemical synapses (most common): the membranes are separated by a cleft. When the impulse reaches the axon terminal, it causes (via Ca²⁺ entry) the synaptic vesicles to move towards and fuse with the membrane, releasing neurotransmitters (for example acetylcholine) into the cleft by exocytosis. The neurotransmitters bind to specific receptors on the post-synaptic membrane, which opens ion channels; the entry of ions produces a new potential in the post-synaptic neuron that may be excitatory (depolarising) or inhibitory (hyperpolarising). The neurotransmitter is then broken down (e.g. acetylcholine by acetylcholinesterase) or taken back, ending its effect. Because only the pre-synaptic side releases transmitters and only the post-synaptic side has receptors, chemical synapses conduct in one direction only, and they cause a small synaptic delay.

Worked example

A drug blocks acetylcholinesterase at synapses. What happens to transmission, and why?

Try it first, then show the solutionSolution

1. Acetylcholine is no longer broken down in the synaptic cleft
2. It keeps binding receptors, so the post-synaptic membrane is repeatedly or continuously stimulated (over-stimulation, which can cause spasms)

Answer: Continuous stimulation of the post-synaptic cell, since the signal is not switched off

Neural Control and Coordination in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Human Brain, Spinal Cord and Reflex Action
• Neuron, Nerve Impulse and Synaptic Transmission

Neural Control and Coordination: key facts

Membrane potentials

$\text{resting}\approx -70\text{mV};\text{peak}\approx +30\text{mV};\Delta V\approx 100\text{mV}$

Inside relative to outside.

Sodium–potassium pump

$3N{a}^{+}\text{out}+2K^{+}\text{in per ATP}$

Maintains ion gradients.

Conduction time

$t=\frac{\text{distance}}{\text{velocity}}+(\text{number of synapses}\times \text{synaptic delay})$

Myelinated up to about 100 m/s; non-myelinated about 0.5–2 m/s.

Reflex arc

$\text{receptor}\to \text{sensory neuron}\to \text{spinal cord (interneuron)}\to \text{motor neuron}\to \text{effector}$

Involuntary; involves the CNS.

Peripheral nerves

$12\text{pairs cranial}+31\text{pairs spinal}=43\text{pairs}$

86 nerves in all.

Neural Control and Coordination: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Neural Control and Coordination

The question patterns to expect, and the method that works for each.

Tricks to remember Neural Control and Coordination

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Dendrites Deliver In, Axons Away

  Dendrites carry impulses towards the cell body; axons carry them away.

  Use it when: Neuron direction.

• Many, Bi, Uni, Pseudo

  Multipolar in cortex; bipolar in retina; unipolar in embryo; pseudounipolar in dorsal root ganglia.

  Use it when: Neuron types.

• Salt in, Potassium out

  Na⁺ in = depolarisation; K⁺ out = repolarisation; pump: 3 Na⁺ out, 2 K⁺ in.

  Use it when: Action potential.

• Salta = jump

  Saltatory conduction jumps from node to node in myelinated fibres.

  Use it when: Myelinated conduction.

• Brain stem = Mid + Pons + Medulla

  'My Pet Mouse': midbrain, pons, medulla.

  Use it when: Brain stem parts.

Neural Control and Coordination: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Neural Control and Coordination

The slips examiners see most often, and what to write instead.

• ✗Mistake: Reversing ion movements

  Na⁺ and K⁺ roles are swapped.

  Wrong working

  Depolarisation is caused by K⁺ entering the axon.

  Right working

  Depolarisation is caused by Na⁺ entering; repolarisation by K⁺ leaving.

  ✓Do this: Salt in, potassium out.

  Usually costs: 1-2 marks.

• ✗Mistake: Saying the inside of a resting axon is positive

  Charges are guessed.

  Wrong working

  At rest the axoplasm is positive.

  Right working

  At rest the inside is negative (about −70 mV) relative to the outside.

  ✓Do this: Resting: inside negative.

  Usually costs: 1 mark.

• ✗Mistake: Grey and white matter positions mixed up

  Brain and spinal cord are assumed identical.

  Wrong working

  In the spinal cord grey matter is outside.

  Right working

  Spinal cord: grey matter inside, white outside; cerebrum: grey cortex outside, white inside.

  ✓Do this: Cord is the reverse of the cortex.

  Usually costs: 1 mark.

• ✗Mistake: Wrong neuron type examples

  Bipolar and pseudounipolar are confused.

  Wrong working

  Dorsal root ganglion neurons are bipolar.

  Right working

  They are pseudounipolar; bipolar neurons are in the retina.

  ✓Do this: Learn a location with each type.

  Usually costs: 1 mark.

• ✗Mistake: Assigning functions to the wrong part of the brain

  Hindbrain parts are mixed up.

  Wrong working

  The cerebellum controls breathing.

  Right working

  The medulla controls breathing and heart reflexes; the cerebellum coordinates movement and balance.

  ✓Do this: Cerebellum = balance; medulla = vital reflexes.

  Usually costs: 1 mark.

Practice questions on Neural Control and Coordination

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   The resting membrane potential of a neuron is about:
   (a) +70 mV
   (b) −70 mV
   (c) +30 mV
   (d) 0 mV

   Hint

   Inside negative.

   Answer

   (b)

2. Q2 · 1 mark · MCQExam level

   The part of the brain that coordinates balance and posture is the:
   (a) medulla
   (b) pons
   (c) cerebellum
   (d) thalamus

   Hint

   Hindbrain, convoluted.

   Answer

   (c)

3. Q3 · 1 mark · Very short answerExam level

   Name the gaps in the myelin sheath.

   Hint

   Ranvier.

   Answer

   Nodes of Ranvier

4. Q4 · 1 mark · Very short answerExam level

   How many pairs of spinal nerves are there in humans?

   Hint

   Thirty-something.

   Answer

   31 pairs

5. Q5 · 2 marks · Short answerExam level

   Distinguish between afferent and efferent nerve fibres.

   Hint

   Direction.

   Answer

   Afferent (sensory) fibres carry impulses from receptors in tissues and organs to the CNS; efferent (motor) fibres carry impulses from the CNS to effectors (muscles and glands).

6. Q6 · 2 marks · Short answerHarder exam level

   What is the function of the limbic system?

   Hint

   Emotions.

   Answer

   Along with the hypothalamus, it regulates emotional reactions such as excitement, pleasure, rage and fear, motivation and sexual behaviour.

7. Q7 · 2 marks · Short answerHarder exam level

   Distinguish between sympathetic and parasympathetic systems with two effects each.

   Hint

   Fight or rest.

   Answer

   Sympathetic prepares for emergencies: increases heart rate, dilates pupils (also inhibits digestion). Parasympathetic restores at rest: slows heart rate, constricts pupils, stimulates digestion.

8. Q8 · 3 marks · Short answerHarder exam level

   Describe the structure of the spinal cord in transverse section.

   Hint

   Grey inside.

   Answer

   A central canal surrounded by H- or butterfly-shaped grey matter with dorsal and ventral horns, and an outer zone of white matter of myelinated fibres; covered by meninges; dorsal roots (with ganglia) enter dorsally and ventral roots leave ventrally to form spinal nerves.

9. Q9 · 3 marks · Short answerHarder exam level

   Describe the functions of the medulla oblongata, pons and midbrain.

   Hint

   Brain stem.

   Answer

   Medulla: centres for respiration, cardiovascular reflexes, gastric secretion; reflexes of swallowing, coughing, sneezing, vomiting. Pons: fibre tracts linking brain regions; helps regulate breathing. Midbrain: corpora quadrigemina controlling visual and auditory reflexes; cerebral aqueduct passes through.

10. Q10 · 3 marks · Short answerHarder exam level

    What is a reflex arc? Name its components in order.

    Hint

    Five parts.

    Answer

    The pathway of a reflex action: receptor → sensory (afferent) neuron → spinal cord (with or without an interneuron) → motor (efferent) neuron → effector (muscle or gland).

11. Q11 · 5 marks · Long answerHarder exam level

    (a) Describe the structure and functions of the forebrain. [3]
    (b) Why is the cerebral cortex folded? [2]

    Hint

    Cerebrum, thalamus, hypothalamus.

    Answer

    (a) Cerebrum: two hemispheres joined by corpus callosum; grey cortex with motor, sensory and association areas (thinking, memory, communication); inner white matter. Thalamus: major coordinating centre for sensory and motor signals. Hypothalamus: controls body temperature, hunger and thirst; neurosecretory cells release hormones; with limbic system regulates emotions. (b) Folding greatly increases the surface area of the cortex, so many more neurons fit inside the skull, allowing complex functions.

12. Q12 · 5 marks · Long answerHarder exam level

    (a) Explain saltatory conduction. [3]
    (b) Give two advantages of myelination. [2]

    Hint

    Node to node.

    Answer

    (a) In myelinated fibres the myelin sheath insulates the axon; ion channels are concentrated at the nodes of Ranvier; local currents flow from one node to the next, so the action potential jumps from node to node. (b) Much faster conduction; less energy used, since ions are exchanged only at nodes, so less pumping is needed.

13. Q13 · 2 marks · Short answerHarder exam level

    An impulse travels 30 cm along a fibre in 250 ms. Calculate its velocity in m s⁻¹ and say whether the fibre is likely to be myelinated.

    Hint

    Convert units.

    Answer

    v = 0.3 m ÷ 0.25 s = 1.2 m s⁻¹. This lies in the range of non-myelinated fibres (about 0.5–2 m s⁻¹) and is far below myelinated fibres (tens of m s⁻¹, up to about 100 m s⁻¹), so the fibre is probably non-myelinated.

14. Q14 · 3 marks · Short answerHOTS / competency

    Some snake venoms block acetylcholine receptors at neuromuscular junctions. Explain why this can cause death by respiratory failure.

    Hint

    Diaphragm.

    Answer

    Acetylcholine released by motor neurons cannot bind its receptors, so no action potential arises in the muscle fibres and they do not contract. The diaphragm and intercostal muscles are skeletal muscles controlled this way, so breathing stops and the victim dies of lack of oxygen.

15. Q15 · 3 marks · Short answerHOTS / competency

    If a nerve is stimulated twice within 1 ms, only one impulse is produced. Explain, and state the maximum number of impulses per second if the refractory period is 2 ms.

    Hint

    Refractory period.

    Answer

    After an action potential the membrane is refractory: Na⁺ channels cannot reopen until the membrane repolarises, so a second stimulus within this time produces no impulse. Maximum frequency = 1 ÷ 0.002 s = 500 impulses per second. The refractory period also keeps impulses moving in one direction.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Granules in the cell body of a neuron?Show answer

   Nissl's granules.

2. 2.Cells forming myelin in peripheral nerves?Show answer

   Schwann cells.

3. 3.Neuron with T-shaped process?Show answer

   Pseudounipolar.

4. 4.Innermost meninx?Show answer

   Pia mater.

5. 5.Band linking cerebral hemispheres?Show answer

   Corpus callosum.

6. 6.Four swellings of the midbrain?Show answer

   Corpora quadrigemina.

7. 7.Ion causing depolarisation?Show answer

   Na⁺.

8. 8.Common neurotransmitter at neuromuscular junction?Show answer

   Acetylcholine.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you label a myelinated neuron?
• ☐Can you name a location for each neuron type?
• ☐Can you draw a flowchart of the nervous system's divisions?
• ☐Can you give one function each for cerebrum, thalamus, hypothalamus, cerebellum and medulla?
• ☐Can you draw a reflex arc?
• ☐Can you explain the resting potential with ion distributions?
• ☐Can you explain saltatory conduction?
• ☐Can you describe chemical synaptic transmission step by step?

Neural Control and Coordination: frequently asked questions