Human Neural System

BiologyNeural Control and CoordinationFor NEET aspirants

The human neural system coordinates the activities of all organs through a network of neurons that carry electrical impulses. This page covers neural coordination, the central and peripheral neural systems, the structure and types of neurons, the generation and conduction of a nerve impulse, synaptic transmission and the parts of the human brain. It follows the NCERT Class 11 chapter Neural Control and Coordination. NEET often tests the human neural system through match lists on brain parts and their functions, and through statements on resting and action potentials.

On this page1Neural coordination2Neural system in animals3CNS and PNS4Neuron5Nerve impulse6Synapse7The brain8Forebrain9Midbrain and hindbrain10Exam essentials11Quick revision12Solved examples13Practice

Key Points at a Glance

★ Must learn Neural and endocrine systems jointly coordinate all organ activities; the neural system gives quick point-to-point coordination.
CNS = brain + spinal cord (information processing and control); PNS = all nerves associated with the CNS.
★ Must learn Afferent fibres: tissues or organs to the CNS. Efferent fibres: CNS to tissues or organs.
PNS: somatic (CNS to skeletal muscles) and autonomic (CNS to involuntary organs and smooth muscles); autonomic = sympathetic + parasympathetic.
★ Must learn Neuron = cell body + dendrites + axon. Multipolar: cerebral cortex; bipolar: retina; unipolar: embryonic stage.
Schwann cells form the myelin sheath; the gaps between sheaths are nodes of Ranvier.
★ Must learn Resting membrane: more permeable to $K^{+}$ ; the pump sends 3 $N a^{+}$ out for 2 $K^{+}$ in; outside positive, inside negative.
Stimulus: $N a^{+}$ influx reverses polarity (depolarisation) giving the action potential; $K^{+}$ outflow restores the resting potential.
Electrical synapse: direct current, faster, rare. Chemical synapse: neurotransmitters cross the synaptic cleft and bind receptors.
★ Must learn Meninges (outer to inner): dura mater, arachnoid, pia mater. Brain: forebrain, midbrain, hindbrain.
Forebrain: cerebrum, thalamus, hypothalamus. Hindbrain: pons, cerebellum, medulla. Brain stem: midbrain, pons, medulla.
Medulla: centres for respiration, cardiovascular reflexes and gastric secretions.

1. Neural Coordination

The functions of the organs and organ systems of the body must be coordinated to maintain homeostasis.
Coordination: the process through which two or more organs interact and complement the functions of one another.
★ Exam imp The neural system and the endocrine system jointly coordinate and integrate the activities of all organs.
As a result, 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.
The neural system also integrates the metabolic and homeostatic activities of all organs.

1.1 Example: coordination during physical exercise

Physical exercise raises the energy demand for the increased muscular activity.
The supply of oxygen to the muscles also increases.
This needs a higher rate of respiration, a faster heart beat and increased blood flow through the blood vessels.
When exercise stops, the activities of nerves, lungs, heart and kidney gradually return to normal.

Thus the muscles, lungs, heart, blood vessels, kidney and other organs work in a coordinated way during exercise.

Neural system

Organised network of point-to-point connections
Gives quick coordination
Works through neurons and nerve impulses

Endocrine system

Provides chemical integration
Works through hormones
Jointly integrates organ activities with the neural system

Key idea

Coordination lets organs work together for homeostasis; the neural system does it quickly through point-to-point connections, the endocrine system chemically through hormones.

2. Neural System in Animals

The neural system of all animals is made of highly specialised cells called neurons.
Neurons can detect, receive and transmit different kinds of stimuli.
★ Exam imp Neural organisation is very simple in lower invertebrates. In Hydra, it is a network of neurons.
It is better organised in insects, where a brain is present along with a number of ganglia and neural tissues.
Vertebrates have a more developed neural system.

Examples to Remember

Animal group	Neural organisation
Hydra (lower invertebrate)	Network of neurons (very simple)
Insects	Brain + a number of ganglia and neural tissues (better organised)
Vertebrates	More developed neural system

Key idea

Neural organisation grows more complex from the nerve net of Hydra to the brain and ganglia of insects and the developed system of vertebrates.

3. Human Neural System

The human neural system has two parts: the central neural system (CNS) and the peripheral neural system (PNS).
★ Exam imp The CNS includes the brain and the spinal cord. It is the site of information processing and control.
The PNS comprises all the nerves of the body associated with the CNS.

3.1 Afferent and efferent fibres

The nerve fibres of the PNS are of two types: afferent fibres and efferent fibres.
★ Exam imp Afferent fibres transmit impulses from tissues or organs to the CNS.
Efferent fibres transmit regulatory impulses from the CNS to the concerned peripheral tissues or organs.

Memory Trick

Afferent Arrives, Efferent Exits: afferent fibres bring impulses in to the CNS; efferent fibres carry impulses out from the CNS.

3.2 Divisions of the PNS

The PNS has two divisions: the somatic neural system and the autonomic neural system.
The somatic neural system relays impulses from the CNS to skeletal muscles.
★ Exam imp The autonomic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles.
The autonomic neural system is further classified into the sympathetic and the parasympathetic neural systems.
Visceral nervous system: the part of the PNS made of the whole complex of nerves, fibres, ganglia and plexuses.
Through it, impulses travel from the CNS to the viscera and from the viscera to the CNS.

Organisation of the human neural system

Part	Made of or carries impulses
Central neural system (CNS)	Brain and spinal cord; information processing and control
Peripheral neural system (PNS)	All nerves of the body associated with the CNS
Somatic neural system (PNS)	From the CNS to skeletal muscles
Autonomic neural system (PNS)	From the CNS to involuntary organs and smooth muscles
Divisions of the autonomic system	Sympathetic and parasympathetic neural systems
Visceral nervous system (PNS)	Nerves, fibres, ganglia and plexuses; CNS to viscera and viscera to CNS

Central neural system (CNS)

Brain and spinal cord
Site of information processing and control
Receives impulses through afferent fibres

Peripheral neural system (PNS)

All nerves associated with the CNS
Afferent and efferent fibres
Somatic and autonomic divisions

Extra Depth: Nerves that arise from the brain are cranial nerves, and nerves that arise from the spinal cord are spinal nerves. Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves; both belong to the PNS.

Key idea

CNS = brain + spinal cord; PNS = all the nerves, with afferent and efferent fibres and somatic and autonomic divisions.

4. Neuron: The Structural and Functional Unit

4.1 Parts of a neuron

★ Exam imp A neuron is a microscopic structure with three major parts: the cell body, dendrites and the axon.
The cell body contains cytoplasm with typical cell organelles and granular bodies called Nissl's granules.
Dendrites: short fibres that branch repeatedly and project out of the cell body. They also contain Nissl's granules.
Dendrites transmit impulses towards the cell body.
The axon is a long fibre whose distal end is branched.
Each branch ends as a bulb-like structure called the synaptic knob.
Synaptic knobs possess synaptic vesicles containing chemicals called neurotransmitters.
★ Exam imp Axons transmit nerve impulses away from the cell body to a synapse or to a neuro-muscular junction.

Test yourself: hide labels

Figure 1: Structure of a neuron. Dendrites carry impulses towards the cell body, and the axon carries them away to the synaptic knobs at its branched end.

Memory Trick

Dendrites Deliver, Axons carry Away: dendrites deliver impulses to the cell body; the axon carries them away from it.

Dendrites

Short fibres that branch repeatedly
Contain Nissl's granules
Carry impulses towards the cell body

Axon

A long fibre, branched at its distal end
Branches end in synaptic knobs with neurotransmitter vesicles
Carries impulses away from the cell body

4.2 Types of neurons

Neurons are grouped by the number of axons and dendrites into three types.

Type	Axon and dendrites	Found in
Multipolar	One axon and two or more dendrites	Cerebral cortex
Bipolar	One axon and one dendrite	Retina of the eye
Unipolar	Cell body with one axon only	Usually the embryonic stage

Memory Trick

Multi in the Mind, Bi in the eye, Uni in the Unborn: multipolar neurons in the cerebral cortex, bipolar neurons in the retina, unipolar neurons usually in the embryonic stage.

4.3 Myelinated and non-myelinated axons

Axons are of two types: myelinated and non-myelinated.
★ Exam imp Myelinated nerve fibres are enveloped by Schwann cells, which form a myelin sheath around the axon.
Nodes of Ranvier: the gaps between two adjacent myelin sheaths.
Myelinated nerve fibres are found in spinal and cranial nerves.
An unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon.
Unmyelinated fibres are commonly found in the autonomic and the somatic neural systems.

Myelinated fibre

Schwann cells form a myelin sheath
Nodes of Ranvier between adjacent sheaths
Found in spinal and cranial nerves

Non-myelinated fibre

Enclosed by a Schwann cell, but no myelin sheath
No nodes of Ranvier
Common in autonomic and somatic neural systems

Extra Depth: In a myelinated fibre the impulse jumps from one node of Ranvier to the next (saltatory conduction), so it travels much faster. In a non-myelinated fibre the impulse moves step by step along the whole membrane, which is slower.

Quick Recall: tap to check

Name the granular bodies found in the cell body and dendrites of a neuron.

Nissl's granules.

Name the bulb-like structure at the end of each axon branch.

The synaptic knob. It contains synaptic vesicles filled with neurotransmitters.

Which type of neuron is found in the retina of the eye?

Bipolar neuron: one axon and one dendrite.

What are the gaps between two adjacent myelin sheaths called?

Nodes of Ranvier.

Which cells form the myelin sheath around an axon?

Schwann cells.

Key idea

A neuron receives impulses through its dendrites and sends them away along its axon; Schwann cells myelinate the axon, leaving nodes of Ranvier between sheaths.

5. Generation and Conduction of Nerve Impulse

5.1 Resting membrane: the polarised state

Neurons are excitable cells because their membranes are in a polarised state.
Different types of ion channels are present on the neural membrane. They are selectively permeable to different ions.
★ Exam imp At rest, the axonal membrane is comparatively more permeable to $K^{+}$ and nearly impermeable to $N a^{+}$ .
The membrane is also impermeable to the negatively charged proteins present in the axoplasm.
So the axoplasm has a high concentration of $K^{+}$ and negatively charged proteins, and a low concentration of $N a^{+}$ .
The fluid outside the axon has a low concentration of $K^{+}$ and a high concentration of $N a^{+}$ . This forms a concentration gradient.
These ionic gradients are maintained by active transport by the sodium-potassium pump.
★ Exam imp The pump sends 3 $N a^{+}$ outwards for every 2 $K^{+}$ that it brings into the cell.
As a result, the outer surface of the axonal membrane becomes positive and its inner surface negative. The membrane is polarised.

Ion or particle	Inside the axon (axoplasm)	Outside the axon
$K^{+}$	High	Low
$N a^{+}$	Low	High
Negatively charged proteins	High; cannot leave (membrane impermeable)	-
Surface charge at rest	Negative (inner surface)	Positive (outer surface)

★ Very important Resting potential: the electrical potential difference across the resting plasma membrane of a neuron. It exists because of the unequal distribution of ions across the membrane.

Memory Trick

Pump ratio 3 out, 2 in: three $N a^{+}$ leave for every two $K^{+}$ that enter. More positive charge leaves than enters, so the outer surface stays positive.

Think of the sea outside: sodium (common salt) is high outside the cell, while potassium is kept high inside.

5.2 Generation of the action potential

A stimulus is applied at a site, say point A, on the polarised membrane.
The membrane at A becomes freely permeable to $N a^{+}$ .
A rapid influx of $N a^{+}$ follows.
The polarity at A is reversed: the outer surface becomes negative and the inner surface positive. The membrane at A is depolarised.
The electrical potential difference across the membrane at A is now the action potential, also termed the nerve impulse.

★ Very important Action potential: the electrical potential difference across the plasma membrane at a depolarised site, after the influx of $N a^{+}$ reverses its polarity. It is the nerve impulse.

5.3 Conduction along the axon

At a site just ahead, say point B, the membrane is still positive outside and negative inside.
So a current flows on the inner surface from A to B.
On the outer surface, current flows from B to A, completing the circuit.
The polarity at B is reversed and an action potential is generated at B. The impulse has moved from A to B.
The sequence repeats along the length of the axon, and so the impulse is conducted.

Test yourself: hide labels

Figure 2: Conduction of a nerve impulse through an axon at points A and B. Entry of

N a^{+}

at A reverses the polarity there; local currents then flow to B, which depolarises next.

5.4 Restoring the resting potential

The stimulus-induced rise in permeability to $N a^{+}$ is extremely short-lived.
It is quickly followed by a rise in permeability to $K^{+}$ .
Within a fraction of a second, $K^{+}$ diffuses outside the membrane and restores the resting potential at the site of excitation.
The fibre then becomes responsive to further stimulation once more.
★ Exam imp Thus a nerve impulse is conducted along the axon membrane as a wave of depolarisation and repolarisation.

Memory Trick

Sodium In, then Potassium Out: $N a^{+}$ rushes in to depolarise; $K^{+}$ moves out to repolarise and restore the resting potential.

Feature	Resting potential	Action potential
State of membrane	Resting, polarised	Excited, depolarised
Outer surface	Positive	Negative
Inner surface	Negative	Positive
Permeability	More permeable to $K^{+}$ , nearly impermeable to $N a^{+}$	Freely permeable to $N a^{+}$ (short-lived)
Cause	Ionic gradients kept by the sodium-potassium pump	Rapid influx of $N a^{+}$

NEET Focus

At rest the membrane is more permeable to $K^{+}$ , not to $N a^{+}$ .
The pump ratio is 3 $N a^{+}$ out : 2 $K^{+}$ in, not the other way round.
At rest the inside is negative; during the action potential the inside becomes positive.
Inside the axon, current flows from A to B (the direction of the impulse); outside, it flows from B back to A.
Repolarisation is due to $K^{+}$ moving out, not $N a^{+}$ moving out.

Tips and Tricks

To fix the direction of local currents, follow the impulse: inside goes forward, outside comes back. Inside the axon the current runs from A to B; outside it returns from B to A.

Quick Recall: tap to check

Which ion rushes in when a stimulus is applied to the membrane?

Sodium ions (

N a^{+}

What is the potential difference across the resting membrane called?

The resting potential.

How many

N a^{+}

and

K^{+}

does the sodium-potassium pump move per cycle?

It moves 3

N a^{+}

out and 2

K^{+}

in.

In which direction does current flow on the inner surface of the axon?

From the excited site A to the site ahead, B.

Which ion restores the resting potential, and how?

K^{+}

, by diffusing out of the membrane.

Key idea

At rest the membrane is polarised (outside positive, inside negative); a stimulus lets

N a^{+}

in, the polarity reverses and local currents spread the impulse, while

K^{+}

outflow restores the resting state.

6. Transmission of Impulses: The Synapse

A nerve impulse passes from one neuron to another through junctions called synapses.
★ Exam imp A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron.
These membranes may or may not be separated by a gap called the synaptic cleft.
Synapses are of two types: electrical synapses and chemical synapses.

6.1 Electrical synapse

The membranes of the pre- and post-synaptic neurons are in very close proximity.
Electrical current can flow directly from one neuron into the other.
Transmission across it is very similar to impulse conduction along a single axon.
★ Exam imp Transmission across an electrical synapse is always faster than across a chemical synapse.
Electrical synapses are rare in our system.

6.2 Chemical synapse

The membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space, the synaptic cleft.
Chemicals called neurotransmitters carry the impulse across this synapse.
The axon terminals contain vesicles filled with neurotransmitters.

Test yourself: hide labels

Figure 3: Axon terminal and synapse. Synaptic vesicles release neurotransmitters into the synaptic cleft, and the neurotransmitters bind to receptors on the post-synaptic membrane.

Steps of transmission at a chemical synapse

An impulse (action potential) arrives at the axon terminal.
It stimulates the movement of synaptic vesicles towards the membrane.
The vesicles fuse with the plasma membrane.
They release their neurotransmitters into the synaptic cleft.
The neurotransmitters bind to their specific receptors on the post-synaptic membrane.
The binding opens ion channels, allowing the entry of ions.
A new potential is generated in the post-synaptic neuron. It may be excitatory or inhibitory.

Memory Trick

After the impulse arrives, the vesicle steps run My Friend Ravi Buys Oranges: Move, Fuse, Release, Bind, Open channels. A new potential follows.

★ Very important Neurotransmitters: chemicals stored in the synaptic vesicles of axon terminals that carry the impulse across a chemical synapse by binding to receptors on the post-synaptic membrane.

Feature	Electrical synapse	Chemical synapse
Gap between membranes	Membranes in very close proximity	Separated by a fluid-filled synaptic cleft
How the impulse crosses	Electrical current flows directly	Neurotransmitters released into the cleft
Speed	Always faster	Slower
Occurrence in our system	Rare	Common
Effect on post-synaptic neuron	Similar to conduction along one axon	New potential, excitatory or inhibitory

Key idea

At a chemical synapse, neurotransmitters released from the axon terminal cross the synaptic cleft and bind receptors, creating an excitatory or inhibitory potential in the next neuron.

7. Central Neural System: The Brain

★ Exam imp The brain is the central information processing organ of the body. It acts as the command and control system.
It is also the site for processing vision, hearing, speech, memory, intelligence, emotions and thoughts.

The brain controls

Voluntary movements and the balance of the body
Functioning of vital involuntary organs, such as the lungs, heart and kidneys
Thermoregulation, hunger and thirst
Circadian (24-hour) rhythms of the body
Activities of several endocrine glands, and human behaviour

7.1 Cranial meninges

The human brain is well protected by the skull.
Inside the skull, the brain is covered by the cranial meninges, which have three layers.

Dura mater: the outer layer.
Arachnoid: a very thin middle layer.
Pia mater: the inner layer, in contact with the brain tissue.

Memory Trick

The brain is PADded from the inside out: Pia mater, Arachnoid, Dura mater. Read it backwards for the outside-in order.

7.2 Three parts of the brain

The brain can be divided into three major parts: the forebrain, the midbrain and the hindbrain.

Test yourself: hide labels

Figure 4: Sagittal section of the human brain. The forebrain (cerebrum, thalamus, hypothalamus), the midbrain and the hindbrain (pons, cerebellum, medulla) lie in sequence above the spinal cord.

Test yourself: hide labels

Figure 5: The human brain in position inside the head. The skull and the cranial meninges protect it, the cerebral aqueduct runs through the midbrain, and the medulla continues below as the spinal cord.

Part of the brain	Consists of
Forebrain	Cerebrum, thalamus and hypothalamus
Midbrain	Region between the thalamus or hypothalamus and the pons; cerebral aqueduct passes through it; corpora quadrigemina on its dorsal side
Hindbrain	Pons, cerebellum and medulla (medulla oblongata)

Key idea

The brain, protected by the skull and three meninges, is the command and control system; it has a forebrain, a midbrain and a hindbrain.

8. Forebrain

★ Exam imp The forebrain consists of the cerebrum, the thalamus and the hypothalamus.

8.1 Cerebrum

The cerebrum forms the major part of the human brain.
A deep cleft divides the cerebrum longitudinally into two halves: the left and right cerebral hemispheres.
★ Exam imp The hemispheres are connected by a tract of nerve fibres called the corpus callosum.
Cerebral cortex: the layer of cells covering the cerebral hemisphere. It is thrown into prominent folds.
The cortex is called the grey matter because of its greyish appearance. Neuron cell bodies are concentrated here and give it this colour.
The cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor.
These regions are the association areas. They handle complex functions: intersensory associations, memory and communication.
Fibres of the tracts are covered with myelin sheath and form the inner part of the cerebral hemisphere.
They give this layer an opaque white appearance, so it is called the white matter.

Grey matter

The cerebral cortex (outer layer)
Neuron cell bodies concentrated
Greyish appearance

White matter

Inner part of the cerebral hemisphere
Fibres of tracts covered with myelin sheath
Opaque white appearance

8.2 Thalamus and hypothalamus

The cerebrum wraps around a structure called the thalamus.
The thalamus is a major coordinating centre for sensory and motor signalling.
The hypothalamus lies at the base of the thalamus.
★ Exam imp The hypothalamus has centres that control body temperature and the urge for eating and drinking.
It contains several groups of neurosecretory cells, which secrete hypothalamic hormones.

Feature	Thalamus	Hypothalamus
Position	The cerebrum wraps around it	At the base of the thalamus
Part of	Forebrain	Forebrain
Main role	Major coordinating centre for sensory and motor signalling	Centres for body temperature, eating and drinking; neurosecretory cells secrete hypothalamic hormones; works with the limbic system

Memory Trick

The four H's of the Hypothalamus: Heat (body temperature), Hunger (eating), Hydration (drinking) and Hormones (hypothalamic hormones).

8.3 Limbic system

The inner parts of the cerebral hemispheres and associated deep structures, such as the amygdala and hippocampus, form a complex structure.
This structure is called the limbic lobe or limbic system.
★ Exam imp Along with the hypothalamus, it regulates sexual behaviour, the expression of emotional reactions and motivation.
Emotional reactions include excitement, pleasure, rage and fear.
The limbic system is also concerned with olfaction and autonomic responses.

Tips and Tricks

Hypo means below: the hypothalamus sits at the base of the thalamus. If a statement mentions body temperature, eating, drinking or hormone secretion, the answer is the hypothalamus; sensory and motor signalling points to the thalamus.

Key idea

Forebrain = cerebrum (two hemispheres, grey cortex outside, white matter inside), thalamus (sensory and motor coordination) and hypothalamus (temperature, eating, drinking, hormones).

9. Midbrain and Hindbrain

9.1 Midbrain

The midbrain lies between the thalamus or hypothalamus of the forebrain and the pons of the hindbrain.
★ Exam imp A canal called the cerebral aqueduct passes through the midbrain.
The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called the corpora quadrigemina.
The midbrain receives and integrates visual, tactile and auditory inputs.

Memory Trick

Quadri means four, as in quadrilateral: the corpora quadrigemina are four round lobes on the dorsal side of the midbrain.

9.2 Hindbrain

The hindbrain comprises the pons, the cerebellum and the medulla (medulla oblongata).
Pons: consists of fibre tracts that interconnect different regions of the brain.
Cerebellum: has a very convoluted surface, which provides additional space for many more neurons.
The cerebellum integrates information received from the semicircular canals of the ear and the auditory system.
The medulla of the brain is connected to the spinal cord.
★ Exam imp The medulla contains centres that control respiration, cardiovascular reflexes and gastric secretions.

Memory Trick

The medulla keeps you alive with Breathe, Beat, Digest: respiration, cardiovascular reflexes and gastric secretions.

9.3 Brain stem

Three major regions make up the brain stem: the midbrain, the pons and the medulla oblongata.
The brain stem forms the connections between the brain and the spinal cord.

★ Very important Brain stem = midbrain + pons + medulla oblongata. It links the brain with the spinal cord. The cerebellum is part of the hindbrain but not of the brain stem.

Memory Trick

Brain stem from top to bottom: My Pet Mouse = Midbrain, Pons, Medulla oblongata.

Cerebrum

Part of the forebrain; forms the major part of the brain
Two hemispheres joined by the corpus callosum
Cortex with motor, sensory and association areas

Cerebellum

Part of the hindbrain
Very convoluted surface for more neurons
Integrates input from semicircular canals and auditory system

NEET Focus

The cerebral aqueduct passes through the midbrain.
Corpora quadrigemina are on the dorsal side of the midbrain; there are four.
Pons = fibre tracts interconnecting brain regions; it is part of both the hindbrain and the brain stem.
Medulla, not the hypothalamus, controls respiration, cardiovascular reflexes and gastric secretions.
Corpus callosum joins the two cerebral hemispheres, not the cerebrum and cerebellum.

Quick Recall: tap to check

Name the tract of nerve fibres that connects the two cerebral hemispheres.

Corpus callosum.

Which part of the brain contains centres for body temperature, eating and drinking?

Hypothalamus.

Name the four round swellings on the dorsal side of the midbrain.

Corpora quadrigemina.

Which canal passes through the midbrain?

The cerebral aqueduct.

Name the three regions of the brain stem.

Midbrain, pons and medulla oblongata.

Name the parts of the brain marked as the hindbrain in a sagittal section.

Pons, cerebellum and medulla.

Key idea

Midbrain: cerebral aqueduct and corpora quadrigemina. Hindbrain: pons (fibre tracts), cerebellum (convoluted; ear and auditory inputs) and medulla (vital centres). Brain stem: midbrain, pons, medulla.

10. Exam Essentials

Pairs to Match

Structure or term	Feature, location or function
Multipolar neuron	Cerebral cortex
Bipolar neuron	Retina of the eye
Unipolar neuron	Usually the embryonic stage
Nissl's granules	Cell body and dendrites
Nodes of Ranvier	Gaps between adjacent myelin sheaths
Myelinated nerve fibres	Spinal and cranial nerves
Corpus callosum	Connects the two cerebral hemispheres
Association areas	Intersensory associations, memory and communication
Thalamus	Coordinating centre for sensory and motor signalling
Hypothalamus	Body temperature, eating and drinking; hypothalamic hormones
Limbic system (with hypothalamus)	Sexual behaviour, emotional reactions and motivation
Corpora quadrigemina	Four round swellings on the dorsal midbrain
Pons	Fibre tracts interconnecting different regions of the brain
Cerebellum	Integrates information from the semicircular canals and auditory system
Medulla	Respiration, cardiovascular reflexes and gastric secretions

Exceptions

Unipolar neurons (cell body with one axon only) are found usually only in the embryonic stage.
Nissl's granules occur not only in the cell body but also in the dendrites.
A non-myelinated fibre is still enclosed by a Schwann cell, but the cell does not form a myelin sheath.
The resting membrane is nearly impermeable to $N a^{+}$ and impermeable to the negatively charged proteins of the axoplasm.
In an electrical synapse the membranes are in very close proximity, with no fluid-filled cleft between them; such synapses are rare in our system.
The new potential in a post-synaptic neuron is not always excitatory; it may be inhibitory.
The cerebellum belongs to the hindbrain but is not part of the brain stem.
The pons is part of the hindbrain and also of the brain stem.

Numbers to Remember

Major parts of a neuron: 3 (cell body, dendrites, axon).
Neuron types by number of axons and dendrites: 3. Multipolar: 1 axon, 2 or more dendrites; bipolar: 1 axon, 1 dendrite; unipolar: 1 axon only.
Sodium-potassium pump: 3 $N a^{+}$ out for 2 $K^{+}$ in.
Layers of cranial meninges: 3. Major parts of the brain: 3. Cerebral hemispheres: 2.
Corpora quadrigemina: 4 round swellings (lobes) on the dorsal midbrain.
Circadian rhythm: a 24-hour rhythm controlled by the brain.
Regions of the brain stem: 3 (midbrain, pons, medulla oblongata).
Types of synapses: 2. PNS fibre types: 2. PNS divisions: 2. Autonomic divisions: 2.

11. Quick Revision

Neural and endocrine systems jointly coordinate organs; neural = quick point-to-point, endocrine = chemical integration through hormones.
Hydra: network of neurons. Insects: brain with ganglia. Vertebrates: more developed system.
CNS = brain + spinal cord (processing and control); PNS = all nerves associated with the CNS.
Afferent fibres: organs to CNS. Efferent fibres: CNS to organs.
Somatic: CNS to skeletal muscles. Autonomic: CNS to involuntary organs and smooth muscles; sympathetic and parasympathetic.
Neuron: cell body and dendrites with Nissl's granules; dendrites carry impulses in, the axon carries them out.
Axon branches end in synaptic knobs with vesicles of neurotransmitters.
Multipolar: cerebral cortex. Bipolar: retina. Unipolar: usually embryonic stage.
Schwann cells form the myelin sheath; nodes of Ranvier are the gaps; myelinated fibres in spinal and cranial nerves.
Resting membrane: $K^{+}$ high inside, $N a^{+}$ high outside; pump sends 3 $N a^{+}$ out for 2 $K^{+}$ in; outside positive, inside negative.
Stimulus: $N a^{+}$ influx reverses polarity, giving the action potential; $K^{+}$ outflow restores the resting potential.
Local currents: inside from A to B, outside from B to A; the impulse is a wave of depolarisation and repolarisation.
Electrical synapse: direct, always faster, rare. Chemical synapse: neurotransmitters, receptors, excitatory or inhibitory potential.
Meninges: dura mater, arachnoid, pia mater. Forebrain: cerebrum, thalamus, hypothalamus.
Midbrain: cerebral aqueduct, corpora quadrigemina. Hindbrain: pons, cerebellum, medulla. Brain stem: midbrain, pons, medulla.

12. Solved Examples

Solved Example 1

Match List I with List II.
List I: A. Multipolar neuron, B. Bipolar neuron, C. Unipolar neuron, D. Myelinated nerve fibres
List II: I. Embryonic stage, II. Retina of the eye, III. Spinal and cranial nerves, IV. Cerebral cortex
Choose the correct answer:
(A) A-II, B-IV, C-I, D-III
(B) A-IV, B-I, C-II, D-III
(C) A-IV, B-II, C-I, D-III
(D) A-III, B-II, C-I, D-IV

Solution:

Answer: (C). Multipolar neurons occur in the cerebral cortex (IV), bipolar neurons in the retina (II) and unipolar neurons usually in the embryonic stage (I). Myelinated fibres are found in spinal and cranial nerves (III).

Solved Example 2

Read the statements about a resting neuron.
A. The axonal membrane is more permeable to

K^{+}

than to

N a^{+}

.
B. The axoplasm has a high concentration of

N a^{+}

.
C. The sodium-potassium pump moves 3

N a^{+}

outwards for 2

K^{+}

inwards.
D. The membrane is impermeable to the negatively charged proteins of the axoplasm.
E. The inner surface of the membrane is positively charged.
Choose the correct answer:
(A) A, B and C only
(B) A, C and D only
(C) B, D and E only
(D) A, C, D and E only

Solution:

Answer: (B). B is wrong: the axoplasm has a low $N a^{+}$ and a high $K^{+}$ concentration. E is wrong: at rest the inner surface is negative and the outer surface positive. A, C and D are correct.

Solved Example 3

Arrange the events at a chemical synapse in the correct order.
A. Neurotransmitters bind to receptors on the post-synaptic membrane
B. Synaptic vesicles move towards the membrane and fuse with it
C. An action potential arrives at the axon terminal
D. Ion channels open and ions enter the post-synaptic neuron
E. Neurotransmitters are released into the synaptic cleft
Choose the correct answer:
(A) C, B, E, A, D
(B) C, E, B, A, D
(C) B, C, E, A, D
(D) C, B, A, E, D

Solution:

Answer: (A). The impulse arrives (C), vesicles move and fuse (B), neurotransmitters are released (E), they bind receptors (A), and ion channels open to create a new potential (D).

Solved Example 4

Match List I with List II.
List I: A. Hypothalamus, B. Medulla, C. Pons, D. Corpus callosum
List II: I. Fibre tracts that interconnect regions of the brain, II. Connects the two cerebral hemispheres, III. Controls body temperature and the urge for eating and drinking, IV. Centres for respiration and cardiovascular reflexes
Choose the correct answer:
(A) A-III, B-I, C-IV, D-II
(B) A-IV, B-III, C-I, D-II
(C) A-III, B-IV, C-II, D-I
(D) A-III, B-IV, C-I, D-II

Solution:

Answer: (D). Hypothalamus: temperature, eating and drinking (III). Medulla: respiration and cardiovascular reflexes (IV). Pons: interconnecting fibre tracts (I). Corpus callosum: joins the two hemispheres (II).

Solved Example 5

Statement I: Impulse transmission across an electrical synapse is always faster than across a chemical synapse.
Statement II: At an electrical synapse, the pre- and post-synaptic membranes are separated by a fluid-filled synaptic cleft.
(A) Both Statement I and Statement II are correct
(B) Statement I is correct but Statement II is incorrect
(C) Statement I is incorrect but Statement II is correct
(D) Both Statement I and Statement II are incorrect

Solution:

Answer: (B). At an electrical synapse the membranes are in very close proximity and current flows directly. A fluid-filled synaptic cleft separates the membranes at a chemical synapse.

Solved Example 6

Which of the following is NOT a part of the brain stem?
(A) Midbrain
(B) Pons
(C) Cerebellum
(D) Medulla oblongata

Solution:

Answer: (C). The brain stem is made of the midbrain, pons and medulla oblongata. The cerebellum belongs to the hindbrain but is not part of the brain stem.

13. Practice Questions

Practice Questions

Match List I with List II.
List I: A. Dura mater, B. Arachnoid, C. Pia mater, D. Cerebral aqueduct
List II: I. Canal passing through the midbrain, II. Inner layer in contact with brain tissue, III. Outer layer of the cranial meninges, IV. Very thin middle layer
Choose the correct answer:
(A) A-IV, B-III, C-II, D-I
(B) A-III, B-IV, C-II, D-I
(C) A-III, B-II, C-IV, D-I
(D) A-II, B-IV, C-III, D-IAnswer: (B). The meninges run dura mater (outer), arachnoid (thin middle), pia mater (inner); the cerebral aqueduct passes through the midbrain.
Read the statements about the forebrain.
A. The cerebral cortex is called grey matter because neuron cell bodies are concentrated in it.
B. The corpus callosum connects the cerebrum with the cerebellum.
C. Association areas handle intersensory associations, memory and communication.
D. The hypothalamus lies at the base of the thalamus.
E. The thalamus contains neurosecretory cells that secrete hypothalamic hormones.
Choose the correct answer:
(A) A, C and D only
(B) A, B and D only
(C) B, C and E only
(D) A, C, D and E onlyAnswer: (A). The corpus callosum joins the two cerebral hemispheres (B wrong); the neurosecretory cells are in the hypothalamus (E wrong).
Arrange the events in the correct order.
A. The polarity at site A is reversed
B. The membrane at A becomes freely permeable to $N a^{+}$
C. A stimulus is applied at site A
D. A rapid influx of $N a^{+}$ occurs
E. $K^{+}$ diffuses out and the resting potential is restored
Choose the correct answer:
(A) C, D, B, A, E
(B) C, B, D, A, E
(C) B, C, D, A, E
(D) C, B, A, D, EAnswer: (B). Stimulus, $N a^{+}$ permeability, $N a^{+}$ influx, reversal of polarity, then $K^{+}$ outflow restores the resting potential.
The medulla contains centres that control all of the following EXCEPT:
(A) Respiration
(B) Cardiovascular reflexes
(C) Gastric secretions
(D) Body temperatureAnswer: (D). Body temperature is controlled by centres in the hypothalamus.
Statement I: Afferent nerve fibres transmit impulses from the CNS to the peripheral tissues.
Statement II: The somatic neural system relays impulses from the CNS to skeletal muscles.
(A) Both Statement I and Statement II are correct
(B) Statement I is correct but Statement II is incorrect
(C) Statement I is incorrect but Statement II is correct
(D) Both Statement I and Statement II are incorrectAnswer: (C). Afferent fibres carry impulses from tissues or organs to the CNS; efferent fibres carry them from the CNS.
Nissl's granules are present in:
(A) The cell body only
(B) The cell body and dendrites
(C) The synaptic knob only
(D) The myelin sheathAnswer: (B). Nissl's granules occur in the cell body and also in the dendrites.
Arrange the parts in the order in which an impulse passes through a neuron to the next neuron.
A. Axon
B. Dendrites
C. Synaptic knob
D. Cell body
E. Synapse
Choose the correct answer:
(A) D, B, A, C, E
(B) B, D, C, A, E
(C) B, D, A, C, E
(D) B, A, D, C, EAnswer: (C). Dendrites carry the impulse to the cell body, the axon carries it away to the synaptic knob, and it crosses the synapse to the next neuron.
Briefly describe the structure of the brain.Answer: The brain lies in the skull, covered by three cranial meninges (dura mater, arachnoid, pia mater). It has three parts. The forebrain has the cerebrum (two hemispheres joined by the corpus callosum, with outer grey matter and inner white matter), the thalamus and the hypothalamus. The midbrain carries the cerebral aqueduct and, dorsally, the corpora quadrigemina. The hindbrain has the pons, cerebellum and medulla. The midbrain, pons and medulla form the brain stem.
Compare: (a) the central neural system (CNS) and the peripheral neural system (PNS); (b) the resting potential and the action potential.Answer: (a) The CNS is the brain and spinal cord, the site of information processing and control. The PNS is all the nerves associated with the CNS, with afferent and efferent fibres and somatic and autonomic divisions. (b) The resting potential is the potential difference across a resting, polarised membrane (outside positive, inside negative). The action potential is the potential difference at a depolarised site after $N a^{+}$ influx (outside negative, inside positive).
Explain: (a) polarisation of the membrane of a nerve fibre; (b) depolarisation of the membrane of a nerve fibre; (c) transmission of a nerve impulse across a chemical synapse.Answer: (a) At rest the membrane is more permeable to $K^{+}$ , nearly impermeable to $N a^{+}$ and impermeable to the negative proteins. The pump sends 3 $N a^{+}$ out for 2 $K^{+}$ in, so the outside is positive and the inside negative. (b) A stimulus makes the membrane freely permeable to $N a^{+}$ ; rapid $N a^{+}$ influx reverses the polarity (outside negative, inside positive). (c) The impulse makes synaptic vesicles fuse with the membrane and release neurotransmitters into the cleft; these bind receptors on the post-synaptic membrane, ion channels open and a new excitatory or inhibitory potential arises.
Draw labelled diagrams of: (a) a neuron; (b) the brain.Answer: (a) Follow Figure 1 and label dendrites, Nissl's granules, cell body, nucleus, Schwann cell, axon, myelin sheath, node of Ranvier, axon terminal and synaptic knob. (b) Follow Figures 4 and 5 and label the cerebrum, cerebral hemisphere, corpus callosum, thalamus, hypothalamus, midbrain, cerebral aqueduct, pons, cerebellum, medulla and spinal cord, with forebrain, midbrain and hindbrain marked.
Write short notes on: (a) neural coordination; (b) forebrain; (c) midbrain; (d) hindbrain; (e) synapse.Answer: (a) The neural system gives quick, point-to-point coordination of organs, working with the endocrine system to keep homeostasis. (b) Cerebrum, thalamus and hypothalamus; the cortex has motor, sensory and association areas. (c) Between the thalamus or hypothalamus and the pons; has the cerebral aqueduct and corpora quadrigemina; integrates visual, tactile and auditory inputs. (d) Pons, cerebellum and medulla; the medulla controls respiration, cardiovascular reflexes and gastric secretions. (e) A junction between pre- and post-synaptic neurons; it is electrical or chemical.
Give a brief account of the mechanism of synaptic transmission.Answer: An impulse reaches the axon terminal and moves the synaptic vesicles to the membrane. They fuse and release neurotransmitters into the synaptic cleft. The neurotransmitters bind specific receptors on the post-synaptic membrane, ion channels open, ions enter, and a new excitatory or inhibitory potential develops. At electrical synapses current passes directly instead.
Explain the role of $N a^{+}$ in the generation of an action potential.Answer: A stimulus makes the membrane freely permeable to $N a^{+}$ . Since $N a^{+}$ is high outside, it rushes in. This influx reverses the polarity at that site (inside positive, outside negative), which is the action potential.
Differentiate between: (a) myelinated and non-myelinated axons; (b) dendrites and axons; (c) thalamus and hypothalamus; (d) cerebrum and cerebellum.Answer: (a) Myelinated axons have a myelin sheath formed by Schwann cells, with nodes of Ranvier, and occur in spinal and cranial nerves; non-myelinated axons are enclosed by a Schwann cell that forms no sheath, common in autonomic and somatic systems. (b) Dendrites are short, repeatedly branched and carry impulses towards the cell body; the axon is long and carries them away to the synaptic knobs. (c) The thalamus coordinates sensory and motor signalling; the hypothalamus, at its base, controls temperature, eating and drinking and secretes hormones. (d) The cerebrum (forebrain) is the largest part, with two hemispheres and the cortex; the cerebellum (hindbrain) is highly convoluted and integrates input from the semicircular canals and auditory system.
(a) Which part of the human brain is the most developed? (b) Which part of our central neural system acts as a master clock?Answer: (a) The cerebrum, which forms the major part of the brain. (b) The hypothalamus, which holds the centre that sets the body's 24-hour (circadian) rhythms.
Distinguish between: (a) afferent and efferent neurons; (b) impulse conduction in a myelinated and an unmyelinated nerve fibre; (c) cranial nerves and spinal nerves.Answer: (a) Afferent neurons carry impulses from tissues or organs to the CNS; efferent neurons carry regulatory impulses from the CNS to tissues or organs. (b) In a myelinated fibre the impulse jumps from node to node of Ranvier and travels faster; in an unmyelinated fibre it moves along the whole membrane and is slower. (c) Cranial nerves arise from the brain (12 pairs); spinal nerves arise from the spinal cord (31 pairs).

Common Mistakes to Avoid

Watch out

Saying the resting membrane is more permeable to $N a^{+}$ . It is more permeable to $K^{+}$ and nearly impermeable to $N a^{+}$ .
Reversing the pump ratio. The pump sends 3 $N a^{+}$ out for 2 $K^{+}$ in.
Writing that the inside of a resting axon is positive. At rest the outer surface is positive and the inner surface negative.
Saying dendrites carry impulses away from the cell body. Dendrites carry them towards it; the axon carries them away.
Placing bipolar neurons in the cerebral cortex. Multipolar neurons are in the cerebral cortex; bipolar neurons are in the retina.
Calling electrical synapses slower or common. They are always faster than chemical synapses but rare in our system.
Including the cerebellum in the brain stem. The brain stem is the midbrain, pons and medulla oblongata.
Placing the hypothalamus in the midbrain. It is part of the forebrain, at the base of the thalamus.

Frequently Asked Questions

What are the central and peripheral neural systems?

The central neural system (CNS) is the brain and spinal cord, the site of information processing and control. The peripheral neural system (PNS) is all the nerves associated with the CNS. Its afferent fibres carry impulses to the CNS, and its efferent fibres carry regulatory impulses from the CNS to tissues and organs.

What is resting potential in a neuron?

Resting potential is the electrical potential difference across the resting membrane of a neuron. At rest the membrane is more permeable to potassium ions than to sodium ions, and the sodium-potassium pump moves three sodium ions out for two potassium ions in. So the outer surface is positive and the inner surface negative.

How is an action potential generated?

When a stimulus is applied at a site, the membrane there becomes freely permeable to sodium ions. Sodium ions rush in, and the polarity reverses: the outer surface becomes negative and the inner surface positive. This potential difference at the depolarised site is the action potential, also called the nerve impulse.

How is a nerve impulse conducted along an axon?

Next to the depolarised site, the membrane is still positive outside and negative inside. So current flows on the inner surface from the excited site to the next site, and on the outer surface back again. The next site depolarises, and this repeats along the axon. Potassium ions then diffuse out to restore the resting potential.

What is the difference between electrical and chemical synapses?

At an electrical synapse, the two membranes are very close, and current flows directly from one neuron to the next. It is always faster but rare in our system. At a chemical synapse, a fluid-filled synaptic cleft separates the membranes, and neurotransmitters released from vesicles carry the impulse by binding to receptors.

What are the functions of the hypothalamus?

The hypothalamus lies at the base of the thalamus in the forebrain. It has centres that control body temperature and the urge for eating and drinking. Its neurosecretory cells secrete hypothalamic hormones. Along with the limbic system, it regulates sexual behaviour, emotional reactions such as rage and fear, and motivation.

What is the limbic system?

The limbic system, or limbic lobe, is formed by the inner parts of the cerebral hemispheres and associated deep structures such as the amygdala and hippocampus. With the hypothalamus, it regulates sexual behaviour, the expression of emotions such as excitement, pleasure, rage and fear, and motivation. It is also concerned with olfaction and autonomic responses.

Which parts make up the brain stem and the hindbrain?

The hindbrain has the pons, the cerebellum and the medulla oblongata. The brain stem is made of the midbrain, pons and medulla oblongata, and it connects the brain with the spinal cord. The cerebellum belongs to the hindbrain but not to the brain stem. The medulla controls respiration, cardiovascular reflexes and gastric secretions.

Previous year questions on Human Neural System

9 questions from past papers, each with a step-by-step solution.

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