The Chapter in One Page

The functions of the organs and organ systems in our body must be coordinated to maintain homeostasis, and coordination is the process through which two or more organs interact and complement the functions of one another. During physical exercise the energy demand rises to maintain the increased muscular activity, the supply of oxygen is increased, and that increased oxygen supply necessitates an increase in the rate of respiration, in the heart beat and in the blood flow via the blood vessels; when the exercise is stopped, the activities of the nerves, lungs, heart and kidney gradually return to their normal conditions. The NEURAL SYSTEM and the ENDOCRINE SYSTEM jointly coordinate and integrate all the activities of the organs so that they function in a synchronised fashion. The neural system provides an ORGANISED NETWORK OF POINT-TO-POINT CONNECTIONS for quick coordination; the endocrine system provides CHEMICAL INTEGRATION through HORMONES.

The neural system of all animals is composed of highly specialised cells called NEURONS, which can DETECT, RECEIVE and TRANSMIT different kinds of stimuli. In lower invertebrates such as Hydra the neural organisation is very simple - a NETWORK OF NEURONS. In insects it is better organised - a BRAIN is present, along with A NUMBER OF GANGLIA AND NEURAL TISSUES. Vertebrates have a MORE DEVELOPED neural system.

The human neural system is divided into two parts - the CENTRAL NEURAL SYSTEM (CNS) and the PERIPHERAL NEURAL SYSTEM (PNS). The CNS includes the BRAIN and the SPINAL CORD and is the SITE OF INFORMATION PROCESSING AND CONTROL. The PNS comprises all the nerves of the body associated with the CNS. The nerve fibres of the PNS are of two types - AFFERENT fibres, which transmit impulses from tissues and organs TO the CNS, and EFFERENT fibres, which transmit regulatory impulses FROM the CNS TO the peripheral tissues and organs. The PNS is divided into the SOMATIC NEURAL SYSTEM, which relays impulses from the CNS to SKELETAL MUSCLES, and the AUTONOMIC NEURAL SYSTEM, which transmits impulses from the CNS to the INVOLUNTARY ORGANS AND SMOOTH MUSCLES of the body. The autonomic neural system is further classified into the SYMPATHETIC and the PARASYMPATHETIC neural systems. The VISCERAL NERVOUS SYSTEM is the part of the PNS that comprises the whole complex of NERVES, FIBRES, GANGLIA AND PLEXUSES by which impulses travel from the CNS to the VISCERA and from the viscera to the CNS. 12 PAIRS OF CRANIAL NERVES arise from the brain and 31 PAIRS OF SPINAL NERVES arise from the spinal cord.

A neuron is a microscopic structure composed of THREE MAJOR PARTS - the CELL BODY, the DENDRITES and the AXON. The cell body contains cytoplasm with typical cell organelles and certain granular bodies called NISSL'S GRANULES. Short fibres which branch repeatedly and project out of the cell body also contain Nissl's granules and are called DENDRITES; these fibres TRANSMIT IMPULSES TOWARDS THE CELL BODY. The AXON is a long fibre, the DISTAL END OF WHICH IS BRANCHED; each branch terminates as a bulb-like structure called the SYNAPTIC KNOB, which possesses SYNAPTIC VESICLES CONTAINING CHEMICALS CALLED NEUROTRANSMITTERS. The axons TRANSMIT NERVE IMPULSES AWAY FROM THE CELL BODY to a synapse or to a NEURO-MUSCULAR JUNCTION.

Based on the number of axons and dendrites, neurons are divided into three types - MULTIPOLAR, with ONE AXON AND TWO OR MORE DENDRITES, found in the CEREBRAL CORTEX; BIPOLAR, with ONE AXON AND ONE DENDRITE, found in the RETINA OF THE EYE; and UNIPOLAR, with a CELL BODY BEARING ONE AXON ONLY, found usually in the EMBRYONIC STAGE. There are two types of axons - MYELINATED and NON-MYELINATED. The myelinated nerve fibres are ENVELOPED WITH SCHWANN CELLS, WHICH FORM A MYELIN SHEATH around the axon; the GAPS BETWEEN TWO ADJACENT MYELIN SHEATHS are called NODES OF RANVIER; myelinated nerve fibres are found in SPINAL AND CRANIAL NERVES. The unmyelinated nerve fibre IS ENCLOSED BY A SCHWANN CELL THAT DOES NOT FORM A MYELIN SHEATH, and is commonly found in the AUTONOMOUS AND THE SOMATIC NEURAL SYSTEMS. In a myelinated fibre the impulse JUMPS FROM ONE NODE OF RANVIER TO THE NEXT, which makes conduction MUCH FASTER AND LESS COSTLY IN ENERGY than the STEP-BY-STEP conduction along the whole membrane of an unmyelinated fibre.

Neurons are EXCITABLE CELLS BECAUSE THEIR MEMBRANES ARE IN A POLARISED STATE. Different types of ION CHANNELS are present on the neural membrane, and these channels are SELECTIVELY PERMEABLE TO DIFFERENT IONS. When a neuron is not conducting any impulse, that is, when it is RESTING, the axonal membrane is COMPARATIVELY MORE PERMEABLE TO POTASSIUM IONS K+\mathrm{K^+} AND NEARLY IMPERMEABLE TO SODIUM IONS Na+\mathrm{Na^+}, and it is also IMPERMEABLE TO THE NEGATIVELY CHARGED PROTEINS present in the axoplasm. Consequently the AXOPLASM INSIDE THE AXON CONTAINS A HIGH CONCENTRATION OF K+\mathrm{K^+} AND NEGATIVELY CHARGED PROTEINS AND A LOW CONCENTRATION OF Na+\mathrm{Na^+}, while the FLUID OUTSIDE THE AXON CONTAINS A LOW CONCENTRATION OF K+\mathrm{K^+} AND A HIGH CONCENTRATION OF Na+\mathrm{Na^+}, and thus a CONCENTRATION GRADIENT is formed. These ionic gradients across the resting membrane are maintained by the ACTIVE TRANSPORT of ions by the SODIUM-POTASSIUM PUMP, which transports 3 Na+\mathrm{Na^+} OUTWARDS FOR 2 K+\mathrm{K^+} INTO THE CELL. As a result the OUTER SURFACE of the axonal membrane possesses a POSITIVE CHARGE while its INNER SURFACE becomes NEGATIVELY CHARGED and therefore is POLARISED. The ELECTRICAL POTENTIAL DIFFERENCE ACROSS THE RESTING PLASMA MEMBRANE IS CALLED THE RESTING POTENTIAL, and the standard exam figure for it is about -70 millivolts.

When a stimulus is applied at a site on the polarised membrane - call it SITE 'A' - the membrane at that site becomes FREELY PERMEABLE TO Na+\mathrm{Na^+}. This leads to a RAPID INFLUX OF Na+\mathrm{Na^+} followed by the REVERSAL OF THE POLARITY at that site, that is, the OUTER SURFACE of the membrane becomes NEGATIVELY CHARGED and the INNER SIDE becomes POSITIVELY CHARGED, and the membrane at site 'A' is said to be DEPOLARISED. The ELECTRICAL POTENTIAL DIFFERENCE ACROSS THE PLASMA MEMBRANE AT SITE 'A' IS CALLED THE ACTION POTENTIAL, WHICH IS IN FACT TERMED AS A NERVE IMPULSE. At SITE 'B', immediately ahead, the axonal membrane has a POSITIVE CHARGE ON THE OUTER SURFACE AND A NEGATIVE CHARGE ON THE INNER SURFACE. As a result a CURRENT FLOWS ON THE INNER SURFACE FROM SITE 'A' TO SITE 'B', and ON THE OUTER SURFACE THE CURRENT FLOWS FROM SITE 'B' TO SITE 'A' to complete the circuit of current flow. Hence the POLARITY AT SITE 'B' IS REVERSED, AND THEREFORE AN ACTION POTENTIAL IS GENERATED AT SITE 'B'. Thus the impulse, that is the action potential, generated at site 'A' arrives at site 'B'; the SEQUENCE IS REPEATED ALONG THE LENGTH OF THE AXON AND CONSEQUENTLY THE IMPULSE IS CONDUCTED. The rise in the stimulus-induced permeability to Na+\mathrm{Na^+} is EXTREMELY SHORT-LIVED, and it is QUICKLY FOLLOWED BY A RISE IN PERMEABILITY TO K+\mathrm{K^+}. Within a fraction of a second, K+\mathrm{K^+} DIFFUSES OUTSIDE THE MEMBRANE AND RESTORES THE RESTING POTENTIAL of the membrane at the site of excitation, and the FIBRE BECOMES ONCE MORE RESPONSIVE TO FURTHER STIMULATION.

A NERVE IMPULSE IS TRANSMITTED FROM ONE NEURON TO ANOTHER THROUGH JUNCTIONS CALLED SYNAPSES. A synapse is formed by the MEMBRANES OF A PRE-SYNAPTIC NEURON AND A POST-SYNAPTIC NEURON, WHICH MAY OR MAY NOT BE SEPARATED BY A GAP CALLED THE SYNAPTIC CLEFT. There are two types of synapses - ELECTRICAL SYNAPSES and CHEMICAL SYNAPSES. At an electrical synapse the MEMBRANES OF THE PRE- AND POST-SYNAPTIC NEURONS ARE IN VERY CLOSE PROXIMITY; the ELECTRICAL CURRENT CAN FLOW DIRECTLY FROM ONE NEURON INTO THE OTHER ACROSS THESE SYNAPSES; transmission of an impulse across them is VERY SIMILAR TO IMPULSE CONDUCTION ALONG A SINGLE AXON; impulse transmission across an electrical synapse is ALWAYS FASTER than that across a chemical synapse; and ELECTRICAL SYNAPSES ARE RARE IN OUR SYSTEM. At a chemical synapse the membranes of the pre- and post-synaptic neurons are SEPARATED BY A FLUID-FILLED SPACE CALLED THE SYNAPTIC CLEFT; CHEMICALS CALLED NEUROTRANSMITTERS ARE INVOLVED IN THE TRANSMISSION OF IMPULSES at these sites; and the AXON TERMINALS CONTAIN VESICLES FILLED WITH THESE NEUROTRANSMITTERS. When an impulse arrives at the axon terminal, it STIMULATES THE MOVEMENT OF THE SYNAPTIC VESICLES TOWARDS THE MEMBRANE, WHERE THEY FUSE WITH THE PLASMA MEMBRANE AND RELEASE THEIR NEUROTRANSMITTERS IN THE SYNAPTIC CLEFT. The released neurotransmitters BIND TO THEIR SPECIFIC RECEPTORS PRESENT ON THE POST-SYNAPTIC MEMBRANE; this BINDING OPENS ION CHANNELS ALLOWING THE ENTRY OF IONS, WHICH CAN GENERATE A NEW POTENTIAL IN THE POST-SYNAPTIC NEURON; and the NEW POTENTIAL DEVELOPED MAY BE EITHER EXCITATORY OR INHIBITORY.

Our brain is the CENTRAL INFORMATION PROCESSING ORGAN of our body, and acts as the 'COMMAND AND CONTROL SYSTEM'. It CONTROLS THE VOLUNTARY MOVEMENTS, THE BALANCE OF THE BODY, THE FUNCTIONING OF VITAL INVOLUNTARY ORGANS such as the LUNGS, HEART and KIDNEYS, THERMOREGULATION, HUNGER AND THIRST, CIRCADIAN (24-HOUR) RHYTHMS OF OUR BODY, THE ACTIVITIES OF SEVERAL ENDOCRINE GLANDS AND HUMAN BEHAVIOUR; it is also the SITE FOR PROCESSING OF VISION, HEARING, SPEECH, MEMORY, INTELLIGENCE, EMOTIONS AND THOUGHTS. The brain is PROTECTED BY THE SKULL, and inside the skull it is covered by CRANIAL MENINGES consisting of an OUTER LAYER CALLED THE DURA MATER, A VERY THIN MIDDLE LAYER CALLED THE ARACHNOID, and an INNER LAYER, IN CONTACT WITH THE BRAIN TISSUE, CALLED THE PIA MATER. The brain can be divided into THREE MAJOR PARTS - the FOREBRAIN, the MIDBRAIN and the HINDBRAIN.

The FOREBRAIN consists of the CEREBRUM, the THALAMUS and the HYPOTHALAMUS. The CEREBRUM FORMS THE MAJOR PART OF THE HUMAN BRAIN. A DEEP CLEFT DIVIDES THE CEREBRUM LONGITUDINALLY INTO TWO HALVES, WHICH ARE TERMED AS THE LEFT AND RIGHT CEREBRAL HEMISPHERES, and these are CONNECTED BY A TRACT OF NERVE FIBRES CALLED THE CORPUS CALLOSUM. The LAYER OF CELLS WHICH COVERS THE CEREBRAL HEMISPHERE IS CALLED THE CEREBRAL CORTEX, AND IS THROWN INTO PROMINENT FOLDS; the cerebral cortex is referred to as the GREY MATTER DUE TO ITS GREYISH APPEARANCE, WHICH IS CAUSED BY THE CONCENTRATION OF NEURON CELL BODIES THERE. The cerebral cortex CONTAINS MOTOR AREAS, SENSORY AREAS AND LARGE REGIONS THAT ARE NEITHER CLEARLY SENSORY NOR MOTOR IN FUNCTION; these ASSOCIATION AREAS are RESPONSIBLE FOR COMPLEX FUNCTIONS LIKE INTERSENSORY ASSOCIATIONS, MEMORY AND COMMUNICATION. FIBRES OF THE TRACTS ARE COVERED WITH THE MYELIN SHEATH, WHICH CONSTITUTES THE INNER PART OF THE CEREBRAL HEMISPHERE; they give an OPAQUE WHITE APPEARANCE to the layer and hence it is called the WHITE MATTER.

The CEREBRUM WRAPS AROUND A STRUCTURE CALLED THE THALAMUS, WHICH IS A MAJOR COORDINATING CENTRE FOR SENSORY AND MOTOR SIGNALLING. Another very important part of the brain, the HYPOTHALAMUS, LIES AT THE BASE OF THE THALAMUS; it CONTAINS A NUMBER OF CENTRES WHICH CONTROL BODY TEMPERATURE AND THE URGE FOR EATING AND DRINKING, and it also CONTAINS SEVERAL GROUPS OF NEUROSECRETORY CELLS, WHICH SECRETE HYPOTHALAMIC HORMONES. The INNER PARTS OF THE CEREBRAL HEMISPHERES AND A GROUP OF ASSOCIATED DEEP STRUCTURES LIKE THE AMYGDALA AND THE HIPPOCAMPUS FORM A COMPLEX STRUCTURE CALLED THE LIMBIC LOBE OR LIMBIC SYSTEM; ALONG WITH THE HYPOTHALAMUS IT IS INVOLVED IN THE REGULATION OF SEXUAL BEHAVIOUR, IN THE EXPRESSION OF EMOTIONAL REACTIONS such as EXCITEMENT, PLEASURE, RAGE and FEAR, AND IN MOTIVATION, and the chapter summary adds OLFACTION and AUTONOMIC RESPONSES.

The MIDBRAIN IS LOCATED BETWEEN THE THALAMUS AND THE HYPOTHALAMUS OF THE FOREBRAIN AND THE PONS OF THE HINDBRAIN. A CANAL CALLED THE CEREBRAL AQUEDUCT PASSES THROUGH THE MIDBRAIN. THE DORSAL PORTION OF THE MIDBRAIN CONSISTS MAINLY OF FOUR ROUND SWELLINGS, THAT IS LOBES, CALLED CORPORA QUADRIGEMINA. The midbrain RECEIVES AND INTEGRATES VISUAL, TACTILE AND AUDITORY INPUTS. The HINDBRAIN COMPRISES THE PONS, the CEREBELLUM and the MEDULLA, also called the MEDULLA OBLONGATA. PONS CONSISTS OF FIBRE TRACTS THAT INTERCONNECT DIFFERENT REGIONS OF THE BRAIN. THE CEREBELLUM HAS A VERY CONVOLUTED SURFACE IN ORDER TO PROVIDE ADDITIONAL SPACE FOR MANY MORE NEURONS, and it INTEGRATES THE INFORMATION RECEIVED FROM THE SEMICIRCULAR CANALS OF THE EAR AND THE AUDITORY SYSTEM. THE MEDULLA OF THE BRAIN IS CONNECTED TO THE SPINAL CORD, AND THE MEDULLA CONTAINS CENTRES WHICH CONTROL RESPIRATION, CARDIOVASCULAR REFLEXES AND GASTRIC SECRETIONS. THE MIDBRAIN AND THE HINDBRAIN FORM THE BRAIN STEM - MIDBRAIN, PONS AND MEDULLA OBLONGATA, THREE REGIONS IN ALL - AND THE BRAIN STEM FORMS THE CONNECTIONS BETWEEN THE BRAIN AND THE SPINAL CORD.

Two answers the exercise set wants that the body text only implies. The MOST DEVELOPED PART OF THE HUMAN BRAIN IS THE CEREBRUM. The part that acts as the MASTER CLOCK is the HYPOTHALAMUS, the part responsible for the circadian, that is 24-hour, rhythms of the body.

What Each Section Covers

Seventeen sections, and what each one carries. Use this as the index when you are hunting a fact and do not want to read the whole chapter again.

Section Title What it covers
1 Coordination and the Neural System Coordination defined - two or more organs interact and complement the functions of one another; the physical-exercise chain; the neural and endocrine systems acting jointly; point-to-point connections against chemical integration; neurons as cells that detect, receive and transmit stimuli; Hydra, insects and vertebrates.
2 The Human Neural System - Central and Peripheral The two parts of the human neural system - CNS (brain + spinal cord, the site of information processing and control) and PNS (all the nerves associated with the CNS); afferent and efferent fibres and their directions; the split of the PNS into somatic and autonomic; 12 pairs of cranial nerves and 31 pairs of spinal nerves.
3 The Autonomic Neural System - Sympathetic and Parasympathetic The somatic system to skeletal muscles and the autonomic system to the involuntary organs and smooth muscles; the visceral nervous system - nerves, fibres, ganglia and plexuses running to and from the viscera; the sympathetic and parasympathetic divisions of the autonomic system.
4 The Neuron - Structure and Parts The three major parts of a neuron - cell body, dendrites, axon; Nissl's granules in the cell body and dendrites; the direction rule - dendrites towards, axon away; the branched distal end of the axon, the synaptic knob and the synaptic vesicles containing neurotransmitters; the neuro-muscular junction.
5 Types of Neurons and Types of Axons The three types of neuron by number of axons and dendrites - multipolar (cerebral cortex), bipolar (retina of the eye), unipolar (embryonic stage); the two types of axon - myelinated with Schwann cells forming a myelin sheath and nodes of Ranvier, and non-myelinated with a Schwann cell that forms no sheath; saltatory conduction.
6 The Resting Potential - Why a Neuron is Polarised Why neurons are excitable - their membranes are in a polarised state; the selectively permeable ion channels; the resting membrane more permeable to K+\mathrm{K^+}, nearly impermeable to Na+\mathrm{Na^+}, impermeable to the negatively charged proteins; the concentration gradient; the sodium-potassium pump at 3 Na+\mathrm{Na^+} out for 2 K+\mathrm{K^+} in; the resting potential, about -70 millivolts.
7 The Action Potential and Conduction of the Impulse The stimulus at site 'A', free permeability to Na+\mathrm{Na^+}, the rapid influx, the reversal of polarity and depolarisation; the action potential, which is in fact termed a nerve impulse; the current flowing inside from 'A' to 'B' and outside from 'B' to 'A'; the short-lived sodium permeability followed by the rise in K+\mathrm{K^+} permeability and the restoration of the resting potential.
8 Synapses and the Transmission of Impulses The synapse defined - the membranes of a pre-synaptic and a post-synaptic neuron which may or may not be separated by a synaptic cleft; the electrical synapse, always faster and rare in our system; the chemical synapse and its fluid-filled cleft; the six ordered events of chemical transmission; the new potential, either excitatory or inhibitory.
9 The Brain - Protection and Major Divisions The brain as the central information processing organ and the 'command and control system'; everything it controls, from voluntary movements to circadian rhythms; the skull and the cranial meninges - dura mater, arachnoid, pia mater; the three major parts - forebrain, midbrain, hindbrain.
10 The Forebrain - Cerebrum The forebrain - cerebrum, thalamus, hypothalamus; the deep cleft, the two cerebral hemispheres and the corpus callosum; the cerebral cortex as grey matter from the concentration of neuron cell bodies, against the myelinated inner tracts as white matter; the motor, sensory and association areas.
11 Thalamus, Hypothalamus and the Limbic System The thalamus, which the cerebrum wraps around - the major coordinating centre for sensory and motor signalling; the hypothalamus at the base of the thalamus - body temperature, eating and drinking, neurosecretory cells secreting hypothalamic hormones, and the master clock of the 24-hour rhythm; the limbic system with the amygdala and hippocampus.
12 The Midbrain and the Hindbrain The midbrain between the thalamus and hypothalamus and the pons - the cerebral aqueduct and the four round swellings, the corpora quadrigemina; the hindbrain - pons, cerebellum, medulla; the brain stem as midbrain + pons + medulla oblongata, forming the connections between the brain and the spinal cord.
13 Which Part Controls What - The Functional Map of the Neural System The address grid - every control centre of the neural system in one place, with the part in one column and its function in the next; the route a signal takes from stimulus to response; the three divisions of the brain set against the three regions of the brain stem.
14 Important Questions and Answers The full worked set for the chapter - the divisions of the neural system, the neuron and the impulse, the synapse, the brain, and a closing set of mixed and harder problems.
15 NEET Corner - Neural Control and Coordination the NEET Way The chapter rewritten for the NEET pattern - the four shapes this chapter is asked in, every number in the chapter in one block, one name one line, and the negatives and the pairs that get swapped.
16 NEET-Pattern Practice Questions Forty exam-pattern questions covering the whole chapter in proportion, including assertion-and-reason items, 'which is incorrect' items, sequence-ordering items and match-the-column items, with pacing and guessing advice.
17 Summary and Exam Tips This page - the chapter in one page, a section-by-section map, every number in one table, the exam tips, the last-minute revision list, and a closing set of worked examples.

The chapter has one natural break in the middle. Sections 1 to 8 are the machinery - the divisions of the system, the neuron, and the three mechanisms by which an impulse is made, moved and handed over. Sections 9 to 13 are the map - the brain, part by part, and then the whole address grid in one place. Sections 14 to 17 are the practice and the revision. If you have time for one half only, the mechanisms are the half that must be walked in order and the map is the half that can be revised as a table, so start with the mechanisms and leave the map for last.

Every Number and Name in the Chapter

The whole numeric set of the chapter in one table, because the paper builds its wrong options out of this same list.

Number What it counts
2 Parts of the human neural system - CNS and PNS
2 Types of PNS nerve fibre - afferent and efferent
2 Divisions of the PNS - somatic and autonomic
2 Divisions of the autonomic neural system - sympathetic and parasympathetic
12 pairs Cranial nerves, arising from the brain
31 pairs Spinal nerves, arising from the spinal cord
3 Major parts of a neuron - cell body, dendrites, axon
3 Types of neuron by number of axons and dendrites - multipolar, bipolar, unipolar
1 axon, 2 or more dendrites A multipolar neuron - found in the cerebral cortex
1 axon, 1 dendrite A bipolar neuron - found in the retina of the eye
1 axon only A unipolar neuron - found usually in the embryonic stage
2 Types of axon - myelinated and non-myelinated
3 out, 2 in The sodium-potassium pump - 3 Na+\mathrm{Na^+} outwards for 2 K+\mathrm{K^+} into the cell
about -70 millivolts The resting potential
2 Types of synapse - electrical and chemical
6 Ordered events of transmission across a chemical synapse
3 Cranial meninges - dura mater, arachnoid, pia mater, outer to inner
3 Major parts of the brain - forebrain, midbrain, hindbrain
3 Parts of the forebrain - cerebrum, thalamus, hypothalamus
3 Parts of the hindbrain - pons, cerebellum, medulla
3 Regions of the brain stem - midbrain, pons, medulla oblongata
2 Cerebral hemispheres, joined by the corpus callosum
4 Corpora quadrigemina - the four round swellings on the dorsal midbrain
24 hours The circadian rhythm the brain runs, with the hypothalamus as the master clock

Two swaps in that table cost more marks than everything else in it. The pump is 3 Na+\mathrm{Na^+} out for 2 K+\mathrm{K^+} in - reverse the figures and the sentence still reads perfectly, which is exactly why the reversed version is offered. The nerves are 12 pairs cranial and 31 pairs spinal - and the same applies. Say both aloud once with the direction and the source attached: three sodium OUT, two potassium IN; twelve from the BRAIN, thirty-one from the SPINAL CORD.

And the name set, one line each.

Name What it is
Nissl's granules Granular bodies in the cell body and the dendrites - never in the axon
Synaptic knob The bulb-like end of each branch of the axon, holding synaptic vesicles with neurotransmitters
Node of Ranvier The gap between two adjacent myelin sheaths on a myelinated fibre
Schwann cell The cell that wraps the axon; it forms a myelin sheath in a myelinated fibre and does not in an unmyelinated one
Axoplasm The cytoplasm inside the axon - high K+\mathrm{K^+}, high negatively charged proteins, low Na+\mathrm{Na^+}
Synaptic cleft The fluid-filled space between the two membranes at a chemical synapse
Corpus callosum The tract of nerve fibres connecting the two cerebral hemispheres
Cerebral cortex The layer of cells covering the cerebral hemisphere, thrown into prominent folds - the grey matter
Association areas Cortical regions neither clearly sensory nor motor - intersensory associations, memory and communication
Limbic system The inner parts of the cerebral hemispheres plus amygdala and hippocampus
Cerebral aqueduct The canal passing through the midbrain
Corpora quadrigemina The four round swellings on the dorsal midbrain
Brain stem Midbrain + pons + medulla oblongata - the connection between the brain and the spinal cord

Exam Tips - What Gets Asked, What Gets Confused, and How to Write It

What gets asked. Strip the whole chapter down and the questions come in five shapes, and they come in roughly this order of frequency.

  1. A direction. Afferent or efferent? Dendrite or axon? Inside from 'A' to 'B' or outside from 'B' to 'A'? Three sodium out or three sodium in? Every one of these has a reverse that reads just as fluently, so the reverse is always on offer.
  2. An address. Which part of the brain does this? The answer is one of a small closed set - cerebrum, thalamus, hypothalamus, cerebellum, pons, medulla - and the wrong options are the other members of that same set.
  3. A step in a sequence. What happens immediately after the neurotransmitter binds to its receptor? What follows the rapid influx of sodium ions? These are answered by walking the list, not by recognising the option.
  4. A definition, word for word. Coordination, resting potential, action potential, synapse. The chapter's own wording is the marking scheme.
  5. A negative. Which of the following is NOT a part of the brain stem? Which statement about the resting membrane is incorrect? Read the stem twice - half the marks lost on these are lost to a student who found the true statement and ticked it.

What gets confused. Eight pairs, and they account for most of the marks that go missing while the material is perfectly well known.

  1. Afferent against efferent. Afferent brings information IN to the CNS. Efferent carries regulation OUT to the tissues. Fix it with the vowel: A for arriving, E for exiting.
  2. Dendrite against axon. Dendrites carry impulses TOWARDS the cell body; the axon carries them AWAY. And Nissl's granules are in the cell body and the dendrites, never in the axon.
  3. Somatic against autonomic. Somatic goes to SKELETAL muscle. Autonomic goes to the INVOLUNTARY organs and SMOOTH muscle.
  4. The two permeability states of the same membrane. At rest: MORE permeable to K+\mathrm{K^+}, NEARLY IMPERMEABLE to Na+\mathrm{Na^+}. On stimulation: FREELY PERMEABLE to Na+\mathrm{Na^+}. The same membrane, two states, and a question will give you one state and ask for the other.
  5. Depolarisation against repolarisation. Depolarisation is the Na+\mathrm{Na^+} INFLUX and the reversal of polarity. Repolarisation is the K+\mathrm{K^+} OUTFLOW and the restoration of the resting potential.
  6. Electrical against chemical synapse. The electrical one is ALWAYS FASTER and yet RARE. Both halves of that sentence are examinable and the second half surprises students who have only learnt the first.
  7. Thalamus against hypothalamus. Thalamus - coordinating centre for SENSORY AND MOTOR SIGNALLING. Hypothalamus - BODY TEMPERATURE, EATING AND DRINKING, NEUROSECRETORY CELLS, and the MASTER CLOCK.
  8. Cerebellum against medulla. Cerebellum - BALANCE, and the input from the semicircular canals. Medulla - RESPIRATION, CARDIOVASCULAR REFLEXES and GASTRIC SECRETIONS. And the cerebellum is NOT part of the brain stem.

How to write a two-mark answer. Two marks means two marked points, and nothing more is read. Give the name first and the function second, in one sentence each, and stop.

  • Where are Nissl's granules found? - "Nissl's granules are granular bodies present in the cytoplasm of the CELL BODY of a neuron. They are also present in the DENDRITES, but never in the axon."
  • What is the resting potential? - "The electrical potential difference across the resting plasma membrane of a neuron is called the RESTING POTENTIAL. It exists because the OUTER SURFACE of the membrane is POSITIVELY CHARGED and the INNER SURFACE is NEGATIVELY CHARGED, that is, the membrane is POLARISED."
  • Do not open a two-mark answer with a sentence of background. The marker is looking for two specific phrases, and a paragraph of run-up buys nothing.

How to write a five-mark answer. Five marks means five marked points, and the structure is what makes them findable. Three rules.

  1. If the question names a process, write it as a NUMBERED LIST of events in order. Transmission across a chemical synapse, the generation and conduction of an action potential, the setting up of the resting potential - all three are marked step by step, and a paragraph hides the steps from the marker even when every step is present. One event per line.
  2. If the question names a structure, write a table or a labelled list, part by part. The brain, the neuron, the divisions of the neural system - name the part, then its position, then its function, and keep the same three columns for every part. A part named without its function scores half.
  3. If the question says "differentiate" or "distinguish", draw a two-column table with a Feature column. Give the same features in the same order on both sides, because a difference is awarded only when both halves of it are on the page. CNS against PNS, resting against action potential, myelinated against unmyelinated, dendrite against axon, thalamus against hypothalamus, cerebrum against cerebellum, afferent against efferent, cranial against spinal nerves - eight comparisons in this chapter's exercise set alone, and every one of them is a table.

Three habits that pay across the whole exercise set. When a count is asked, give the number with its unit of counting - 12 PAIRS of cranial nerves, not 12; 3 Na+\mathrm{Na^+} OUT for 2 K+\mathrm{K^+} IN, with the directions written in. When a figure-point is named, use the chapter's own labels - site 'A' and site 'B' - because the marker is reading for them. And when the chapter gives two names for one thing, write both - medulla or medulla oblongata, limbic lobe or limbic system, action potential or nerve impulse, non-myelinated or unmyelinated - because a marking scheme that accepts either will always accept both.

Class 11 has no board paper, but the chapter-end exercises and your school tests are still written answers, marked by a person reading for particular words. Every rule above is about making those words easy to find.

The Night Before - What to Revise, in Order

Read in this order and stop when the list runs out. Nothing new goes in tonight.

1. The three mechanisms, walked out loud from the top. Twenty-five minutes, and the most valuable twenty-five in the chapter.

  • The resting potential. More permeable to K+\mathrm{K^+}, nearly impermeable to Na+\mathrm{Na^+}, impermeable to the proteins; inside high K+\mathrm{K^+} and proteins, outside high Na+\mathrm{Na^+}; gradients held by the pump at 3 out, 2 in; outer surface positive, inner negative, membrane polarised.
  • The action potential and its conduction. Stimulus at site 'A'; membrane freely permeable to Na+\mathrm{Na^+}; rapid influx; polarity reversed, outside negative and inside positive; that potential difference is the action potential, which is the nerve impulse; site 'B' ahead is still positive outside; current flows inside from 'A' to 'B' and outside from 'B' to 'A'; polarity at 'B' reverses; the sequence repeats along the axon.
  • The chemical synapse. Impulse arrives at the axon terminal; vesicles move towards the membrane; vesicles fuse with the plasma membrane; neurotransmitters released into the cleft; bind to specific receptors on the post-synaptic membrane; ion channels open and the entry of ions generates a new potential, which may be excitatory or inhibitory.

If you can walk all three without stopping, most of this paper is already answered.

2. The brain address grid. Fifteen minutes. Say the division, then the part, then the job - forebrain: cerebrum, thalamus, hypothalamus; midbrain: cerebral aqueduct, corpora quadrigemina; hindbrain: pons, cerebellum, medulla. Then say the four addresses that are asked most: thalamus - sensory and motor coordination; hypothalamus - temperature, hunger, thirst, hormones, master clock; cerebellum - balance and the semicircular canals; medulla - respiration, cardiovascular reflexes, gastric secretions.

3. The numbers table. Ten minutes. 3 out and 2 in. 12 pairs and 31 pairs. 3 meninges, 3 divisions, 3 in the forebrain, 3 in the hindbrain, 3 in the brain stem, 4 corpora quadrigemina, 24 hours. Say each number with what it counts, never on its own.

4. The eight confused pairs from the exam-tips block. Ten minutes. These are the marks you are most likely to lose while knowing the material perfectly well, which makes them the cheapest to save. Spend longest on afferent against efferent, the two permeability states of the resting and the stimulated membrane, and thalamus against hypothalamus.

5. The definitions, word for word. Five minutes. Coordination - two or more organs interact and complement the functions of one another. Resting potential - the electrical potential difference across the resting plasma membrane. Action potential - the potential difference across the membrane at the stimulated site, which is in fact termed a nerve impulse. Synapse - formed by the membranes of a pre-synaptic and a post-synaptic neuron, which may or may not be separated by a synaptic cleft.

6. The two answers the exercises want but the body text only implies. Two minutes. Most developed part of the human brain - the CEREBRUM. Master clock of the central neural system - the HYPOTHALAMUS.

7. The negatives. Five minutes. The spinal cord is CNS, not PNS. The cerebellum is not part of the brain stem. The corpora quadrigemina are on the midbrain, not the hindbrain. Nissl's granules are not in the axon. An electrical synapse is faster but rare. A synapse does not always have a cleft. The new post-synaptic potential is not always excitatory. The unmyelinated fibre does have a Schwann cell.

If you have ten minutes and no more, walk the chemical synapse in six steps and say the four brain addresses. This chapter rewards a correctly ordered mechanism and a correctly filed address over everything else, and a student who has those will out-score one who has read the whole chapter through again.

Solved Examples

Question 1

Q. Define coordination, and name the two systems that carry it out in the human body.

Answer. Coordination is the process through which two or more organs interact and complement the functions of one another. It is what keeps homeostasis. The two systems that do the work are the neural system and the endocrine system, and they act jointly so that all the organs function in a synchronised fashion. The neural system provides an organised network of point-to-point connections for quick coordination; the endocrine system provides chemical integration through hormones.

Question 2

Q. Distinguish between the central and the peripheral neural systems.

Answer.

Feature Central neural system Peripheral neural system
What it includes The brain and the spinal cord All the nerves of the body associated with the CNS
Its role The site of information processing and control Carrying impulses to and from the CNS
Its fibres The processing tissue itself Afferent and efferent fibres
Its divisions Brain and spinal cord Somatic and autonomic, the autonomic further into sympathetic and parasympathetic

The single difference that gets marked: the CNS processes and controls, while the PNS carries - it brings information in along afferent fibres and takes regulation out along efferent fibres.

Question 3

Q. Write the resting potential as a numbered list of events, from the permeability of the membrane to the final polarised state.

Answer.

  1. The neural membrane carries different types of ion channels, and these channels are selectively permeable to different ions.
  2. When the neuron is resting, the axonal membrane is comparatively more permeable to K+\mathrm{K^+} and nearly impermeable to Na+\mathrm{Na^+}, and it is also impermeable to the negatively charged proteins of the axoplasm.
  3. Consequently the axoplasm holds a high concentration of K+\mathrm{K^+} and negatively charged proteins and a low concentration of Na+\mathrm{Na^+}, while the fluid outside the axon holds a high concentration of Na+\mathrm{Na^+} and a low concentration of K+\mathrm{K^+}. A concentration gradient is thus formed.
  4. These gradients are maintained by the active transport of ions by the sodium-potassium pump, which transports 3 Na+\mathrm{Na^+} out for every 2 K+\mathrm{K^+} in.
  5. As a result the outer surface of the membrane is positively charged and the inner surface is negatively charged, so the membrane is polarised.
  6. The electrical potential difference across this resting plasma membrane is the resting potential, about -70 millivolts.

Question 4

Q. A student says the resting membrane is impermeable to potassium ions. Correct the statement and give the reason it matters.

Answer. That is wrong. The resting axonal membrane is comparatively MORE permeable to K+\mathrm{K^+} and nearly impermeable to Na+\mathrm{Na^+}. It matters because that permeability is half of what sets the resting potential up - K+\mathrm{K^+} can leave and Na+\mathrm{Na^+} cannot enter, so the inside is left negative and the outside positive. Make the membrane impermeable to K+\mathrm{K^+} instead and the polarisation the whole chapter depends on does not happen.

Question 5

Q. Distinguish between the resting potential and the action potential.

Answer.

Feature Resting potential Action potential
When it exists When the neuron is not conducting an impulse When a stimulus has been applied at that site
Permeability More permeable to K+\mathrm{K^+}, nearly impermeable to Na+\mathrm{Na^+} Freely permeable to Na+\mathrm{Na^+}
Ion movement Gradients held by the sodium-potassium pump Rapid influx of Na+\mathrm{Na^+}
Charge outside Positive Negative
Charge inside Negative Positive
State of the membrane Polarised Depolarised
Its other name - It is in fact termed a nerve impulse

The single difference that gets marked: the action potential is a reversal of the polarity that the resting potential maintains.

Question 6

Q. How does an impulse generated at site 'A' reach site 'B'? Write it as a sequence.

Answer.

  1. A stimulus at site 'A' makes the membrane there freely permeable to Na+\mathrm{Na^+}, so there is a rapid influx of Na+\mathrm{Na^+} and the polarity is reversed - outer surface negative, inner surface positive. Site 'A' is depolarised, and the potential difference there is the action potential.
  2. At site 'B', immediately ahead, the membrane has not been stimulated, so it is still positive on the outer surface and negative on the inner surface.
  3. Because the two sites now differ, a current flows on the inner surface from site 'A' to site 'B'.
  4. On the outer surface the current flows from site 'B' to site 'A', completing the circuit.
  5. The polarity at site 'B' is therefore reversed, and an action potential is generated at site 'B'.
  6. The sequence is repeated along the length of the axon, and the impulse is conducted.

Question 7

Q. What restores the resting potential after an impulse has passed, and why does it matter that it happens quickly?

Answer. The stimulus-induced rise in permeability to Na+\mathrm{Na^+} is extremely short-lived, and it is quickly followed by a rise in permeability to K+\mathrm{K^+}. Within a fraction of a second K+\mathrm{K^+} diffuses outside the membrane and restores the resting potential at the excited site. It matters because only then does the fibre become once more responsive to further stimulation - a fibre that stayed depolarised could carry one impulse and no more.

Question 8

Q. Distinguish between impulse conduction in a myelinated and in an unmyelinated nerve fibre.

Answer.

Feature Myelinated fibre Unmyelinated fibre
The sheath Schwann cells form a myelin sheath around the axon A Schwann cell encloses the axon but forms no myelin sheath
Gaps Nodes of Ranvier between two adjacent myelin sheaths No nodes
How the impulse moves It jumps from one node of Ranvier to the next It travels step by step along the whole membrane
Speed Much faster Slower
Energy Less costly in energy More costly in energy
Where found Spinal nerves and cranial nerves Autonomous and somatic neural systems

The single difference that gets marked: the impulse in a myelinated fibre jumps between the nodes instead of travelling along every point of the membrane.

Question 9

Q. Explain the mechanism of transmission of a nerve impulse across a chemical synapse.

Answer. At a chemical synapse the membranes of the pre-synaptic and the post-synaptic neuron are separated by a fluid-filled space called the synaptic cleft, and the message is carried across it by chemicals called neurotransmitters. The axon terminals contain vesicles filled with these neurotransmitters. The transmission runs in six steps:

  1. An impulse arrives at the axon terminal of the pre-synaptic neuron.
  2. It stimulates the movement of the synaptic vesicles towards the membrane.
  3. The vesicles fuse with the plasma membrane.
  4. They release their neurotransmitters into the synaptic cleft.
  5. The released neurotransmitters bind to their specific receptors present on the post-synaptic membrane.
  6. This binding opens ion channels, and the entry of ions generates a new potential in the post-synaptic neuron.

The new potential developed may be either excitatory or inhibitory - that last clause is a separate mark, and it is the one most often left out.

Question 10

Q. Which type of synapse is faster, and which type is more common in our body?

Answer. The electrical synapse is faster - impulse transmission across an electrical synapse is always faster than across a chemical synapse, because the electrical current flows directly from one neuron into the other. But the electrical synapse is rare in our system, so the chemical synapse is the common one. Both halves are examinable together, because a student who remembers only the speed assumes the fast one must also be the common one.

Question 11

Q. Describe the protection of the brain, from the outside inwards.

Answer. The brain is protected by the skull, the hard bony box that encloses it. Inside the skull the brain is covered by cranial meninges, which are three layers:

  1. The outer layer, the DURA MATER.
  2. The very thin middle layer, the ARACHNOID.
  3. The inner layer, the PIA MATER, which is in contact with the brain tissue.

The order dura, arachnoid, pia runs from outside to inside, and it is asked as an order.

Question 12

Q. Distinguish between grey matter and white matter in the cerebrum.

Answer.

Feature Grey matter White matter
What it is The cerebral cortex - the layer of cells covering the cerebral hemisphere The fibres of the tracts, which are covered with the myelin sheath
Where it lies The outer layer, thrown into prominent folds The inner part of the cerebral hemisphere
Why it looks as it does The concentration of neuron cell bodies gives it a greyish appearance The myelin sheath gives an opaque white appearance
What it contains functionally Motor areas, sensory areas and association areas Connecting fibre tracts

The single difference that gets marked: grey matter is cell bodies on the outside, white matter is myelinated fibres on the inside.

Question 13

Q. Fill in the address for each part: thalamus, hypothalamus, cerebellum, medulla, pons.

Answer.

Part Division What it does
Thalamus Forebrain A major coordinating centre for sensory and motor signalling
Hypothalamus Forebrain Centres controlling body temperature and the urge for eating and drinking; neurosecretory cells secreting hypothalamic hormones; the master clock of the 24-hour rhythm
Cerebellum Hindbrain A very convoluted surface giving space for many more neurons; integrates the input from the semicircular canals of the ear and the auditory system - the balance of the body
Medulla Hindbrain Connected to the spinal cord; centres controlling respiration, cardiovascular reflexes and gastric secretions
Pons Hindbrain Fibre tracts that interconnect different regions of the brain

Question 14

Q. Why is the cerebellum not counted as part of the brain stem, and what is the brain stem made of?

Answer. The brain stem is made of the midbrain, the pons and the medulla oblongata - three regions - and it forms the connections between the brain and the spinal cord. The cerebellum is a part of the hindbrain but it is not one of those three regions, so it is not part of the brain stem. The trap is that the pons and the medulla are hindbrain parts and are in the stem, which makes it easy to sweep the third hindbrain part in with them.

Question 15

Q. Name the most developed part of the human brain, and the part that acts as the master clock. Give one line of justification for each.

Answer. The most developed part of the human brain is the CEREBRUM - it forms the major part of the human brain, it is divided into two cerebral hemispheres joined by the corpus callosum, and its cortex carries the motor, sensory and association areas that handle memory, intelligence, speech and communication.

The part that acts as the master clock is the HYPOTHALAMUS - the brain runs the circadian, that is 24-hour, rhythms of the body, and the hypothalamus is the part that holds the centres controlling body temperature, eating and drinking and the neurosecretory cells, so it is the part that keeps the body on its daily cycle.