Neural Control and Coordination Class 11 Notes

The nervous system is the coordinating system of the body. It receives information from the environment through receptors, integrates it, and then sends an appropriate response through effectors such as muscles and glands. Structurally it splits into the central nervous system and the peripheral nervous system.

• Somatic nervous system — the nerves of voluntary action, supplying skeletal muscles, and carrying impulses from the CNS to the effectors and back.
• Autonomic nervous system — the nerves of involuntary action, supplying smooth muscles, cardiac muscle and glands, and governed entirely by the CNS without conscious control.
• Sympathetic division — prepares the body for emergency, increasing heart rate, dilating the bronchi and redirecting blood to the muscles.
• Parasympathetic division — returns the body to its normal resting state, slowing the heart and promoting digestion.

A neuron is the structural and functional unit of the nervous system. It is built from a cell body with branching dendrites that receive the impulse, and a single long axon that carries the impulse away to its terminal.

Neurons are classified by the number of processes arising from the cyton, and nerve fibres are further classified by whether the axon carries a myelin sheath.

• Multipolar neuron — has many dendrites and one axon, and is the most common type, found wherever both motor and sensory function are combined.
• Bipolar neuron — one dendrite and one axon, found in the retina of the eye and the olfactory epithelium, and in the embryo.
• Unipolar or pseudounipolar neuron — a single process that splits into a peripheral and a central branch, with the cyton placed off to one side. It is the commonest sensory neuron in the body.

• Myelinated nerve fibre — carries impulses faster and is found in the white matter of the CNS and in the somatic nerves.
• Unmyelinated nerve fibre — slower, and found in the grey matter of the CNS and in the autonomic nerves.

A synapse is the junction where one neuron communicates with the next neuron, or with a muscle cell or a gland. The neuron that carries the impulse towards the synapse is the presynaptic neuron, and the one that receives it is the postsynaptic neuron.

The impulse arriving at the synaptic knob opens calcium channels in the presynaptic membrane, and calcium influx causes the vesicles already present in the knob to fuse with the membrane and release their neurotransmitter by exocytosis. The neurotransmitter diffuses across the synaptic cleft and binds receptors on the postsynaptic membrane, opening channels there and generating the next impulse.

A receptor is a specialised sensory cell or organ that detects a particular stimulus and converts it into an electrical impulse. NCERT highlights the gustatory, olfactory and photoreceptor systems.

The brain is the master coordinator of the body, and it is divided into three major regions — the forebrain, the midbrain and the hindbrain. Each of these arises from a cavity within the brain that is filled with cerebrospinal fluid.

• Cerebrum — the largest part, made of two hemispheres joined by the corpus callosum. It holds the sensory, motor and association areas, and the cerebral hemispheres govern intelligence, memory and reasoning.
• Limbic system — a ring of tissue with the hippocampus and the amygdala; it is the centre of emotional expression, controlling fear, anger, pleasure, sexual behaviour and maternal behaviour.
• Thalamus — a relay centre for sensory information; almost all of it passes through here before reaching the cortex.
• Hypothalamus — contains centres for body temperature, urge for food and drink, and the endocrine control that links the nervous system to the pituitary.
• Pineal gland — an endocrine gland of the forebrain that secretes melatonin.
• Midbrain — the dorsal part forms the corpora quadrigemina, whose superior colliculi control visual reflexes and inferior colliculi control auditory reflexes; the ventral part forms the cerebral peduncles.
• Cerebellum — has two hemispheres with many folds called folia, and maintains balance, posture and the precision of voluntary movement. Its white matter branches in a pattern called the arbor vitae.
• Pons — a bridge between the cerebrum and the cerebellum, containing centres that regulate respiration.
• Medulla oblongata — controls blood pressure, salivation, vomiting, heart rate and respiration, and so holds the vital involuntary centres.

The spinal cord runs from the base of the skull at the foramen magnum down to the first lumbar vertebra in the adult. It is cylindrical and lies within the vertebral column, protected by the vertebrae and the meninges.

There are two enlargements in the spinal cord, a cervical enlargement supplying the upper limbs and a lumbar enlargement supplying the lower limbs. Internally the grey matter forms a butterfly or H shape around the central canal and is surrounded by the white matter — the reverse of the arrangement in the brain.

• Posterior or dorsal horn — receives sensory information, since the axons of the afferent neurons end here.
• Anterior or ventral horn — sends motor commands out, since it contains the cell bodies of the efferent neurons that supply the skeletal muscles.
• Lateral horn — present in the thoracic and upper lumbar segments, and contains the cell bodies of the sympathetic neurons, which is why it is called the thoracic horn as well.

A reflex action is a sudden, rapid, involuntary and automatic response to a stimulus, and it is mediated by the spinal cord without any conscious thought. The path of this response is called the reflex arc.

A nerve impulse is an electrical signal. At rest the axonal membrane is polarised, sitting at about minus 70 millivolts, maintained by the sodium and potassium pump which pushes three sodium ions out for every two potassium ions brought in. When the impulse arrives, sodium channels open and sodium rushes in, so the membrane becomes depolarised. Potassium channels then open, potassium flows out and the membrane repolarises, after which the sodium and potassium pump restores the resting distribution.

Plants have neither a nervous system nor specialised receptor cells, yet they still respond to their environment. They do so through a system of plant neuroids and plant hormones, which NCERT treats as a chemical rather than an electrical equivalent of nerves. Auxin mediates the bending of a shoot towards light, and photoperiodic flowering is timed by phytochromes.

Exercises (NCERT Q1–Q10)

• 1) Briefly describe the structure of the Brain
• 2) Compare the following: (a) Central neural system (CNS) and Peripheral neural system (PNS) (b) Resting potential and action potential
• 3) Explain the following processes: (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
• 4) Draw labelled diagrams of the following: (a) Neuron (b) Brain
• 5) Write short notes on the following: (a) Neural coordination (b) Forebrain (c) Midbrain (d) Hindbrain (e) Synapse
• 6) Give a brief account of Mechanism of synaptic transmission.
• 7) Explain the role of Na+ in the generation of action potential.
• 8) Differentiate between: (a) Myelinated and non-myelinated axons (b) Dendrites and axons (c) Thalamus and Hypothalamus (d) Cerebrum and Cerebellum
• 9) Answer the following: (a) Which part of the human brain is the most developed? (b) Which part of our central neural system acts as a master clock?
• 10) Distinguish between: (a) afferent neurons and efferent neurons (b) impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre (c) cranial nerves and spinal nerves

Answers at a glance

1. 1
   Q1 → The brain has three protective meninges and is filled with cerebrospinal fluid. It is divided into the forebrain (cerebrum with its two cerebral hemispheres, corpus callosum and cerebral cortex, plus the diencephalon containing thalamus and hypothalamus), the midbrain (cerebral peduncles and corpora quadrigemina, with reflex centres), and the hindbrain (pons, cerebellum and medulla oblongata), which together control voluntary action, sensory integration, balance, posture and vital reflexes.
2. 2
   Q2 → (a) The CNS is the brain and spinal cord, the centre of integration and command, with no subdivision; the PNS is all nervous tissue outside it, subdivided into somatic and autonomic parts, and serves only to conduct impulses to and from the CNS. (b) The resting potential is a steady −60 to −90 mV, inside negative, caused by K⁺ efflux and maintained by the Na⁺/K⁺ pump; the action potential is a brief all-or-none reversal to about +30 to +40 mV caused by Na⁺ influx followed by K⁺ efflux.
3. 3
   Q3 → (a) Polarisation is the resting state in which the membrane is more permeable to K⁺ than to Na⁺, so the inside is negative at about −60 to −90 mV. (b) Depolarisation occurs when threshold is reached, Na⁺ channels open and Na⁺ rushes in, making the inside positive at about +30 to +40 mV. (c) Across a chemical synapse the impulse triggers exocytosis of neurotransmitter from the presynaptic terminal; it diffuses across the cleft, binds receptors on the postsynaptic membrane and generates a new signal, and transmission is unidirectional because release and reception occur on opposite membranes.
4. 4
   Q4 → (a) The neuron should be labelled dendrites, cell body with nucleus, axon hillock, axon with myelin sheath and nodes of Ranvier, and axon terminals, with the impulse travelling from dendrites to terminals. (b) The brain should be labelled with the three meninges, the cerebral hemispheres, the diencephalon with thalamus and hypothalamus, the midbrain, and the hindbrain with pons, cerebellum and medulla oblongata leading to the spinal cord.
5. 5
   Q5 → (a) Neural coordination is the nervous system integrating sensory input and issuing motor commands through impulses and reflex action. (b) The forebrain comprises the cerebrum, whose cortex carries sensory, motor, association and language areas, and the diencephalon with thalamus (relay and master clock) and hypothalamus (homeostasis, pituitary control). (c) The midbrain is a small region with the cerebral peduncles and corpora quadrigemina that carries reflex centres for the pupil, vision and hearing. (d) The hindbrain comprises pons, cerebellum and medulla, controlling respiration and salivation, balance and motor precision, and vital cardiovascular and respiratory reflexes. (e) A synapse is the cleft-separated junction between two neurons, transmitting impulses chemically in one direction from presynaptic terminal to postsynaptic receptors.
6. 6
   Q6 → The impulse reaching the axon terminal opens Ca²⁺ channels; Ca²⁺ influx makes the synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter by exocytosis. The transmitter diffuses across the synaptic cleft, binds specific receptors on the postsynaptic membrane and opens ion channels, giving a depolarising excitatory potential if threshold is reached. The transmitter is then removed by enzymatic degradation or reuptake. Since release and reception occur on opposite membranes, transmission is one-way.
7. 7
   Q7 → Na⁺ supplies the charge for the rising phase. When a stimulus brings the axonal membrane to threshold, voltage-gated Na⁺ channels open and Na⁺ rushes in down its electrochemical gradient, reversing the membrane potential from about −70 mV to about +30 to +40 mV. The channels then inactivate, K⁺ efflux repolarises the membrane, and the Na⁺/K⁺ pump restores the gradients using ATP. Blocking or removing Na⁺ prevents the action potential, which confirms its role.
8. 8
   Q8 → (a) A myelinated axon has a Schwann-cell or oligodendrocyte sheath interrupted at the nodes of Ranvier and conducts by saltatory conduction, faster and with less energy use; a non-myelinated axon conducts continuously and more slowly. (b) Dendrites are short, branched and receive signals; an axon is a single long uniform fibre arising at the axon hillock and conducts impulses away from the cell body. (c) The thalamus relays and integrates sensory information and acts as the master clock; the hypothalamus maintains homeostasis and controls the pituitary and sex drive. (d) The cerebrum is the large convoluted centre of voluntary action, sensation and intelligence; the cerebellum is the smaller posterior centre of balance, posture and motor precision.
9. 9
   Q9 → (a) The cerebrum is the most developed part of the human brain, and its cerebral cortex carries the areas for sensation, voluntary action, memory, reasoning and speech. (b) The pineal gland, lying on the dorsal side of the forebrain, acts as the master clock; it secretes melatonin, whose secretion depends on day length and so regulates the diurnal rhythm and the sleep–wake cycle.
10. 10
    Q10 → (a) An afferent neuron carries impulses from receptors to the CNS, with its cell body in the dorsal root ganglion and long dendrites; an efferent neuron carries impulses from the CNS to effectors, with its cell body in the ventral horn and a long axon. (b) In a myelinated fibre the impulse leaps node to node by saltatory conduction, which is fast and economical; in an unmyelinated fibre it travels continuously and is slow. (c) Cranial nerves arise from the brain, are 12 numbered pairs, and supply the head and neck; spinal nerves arise from the spinal cord, are 31 pairs, are not named, and are mixed because a dorsal sensory root joins a ventral motor root.

MCQ Questions

1 Mark Questions

1. 1
   What is a nerve impulse? (Ans: an electrical disturbance that travels along a neuron)
2. 2
   Name the neurotransmitter released at the neuro-muscular junction of a skeletal muscle. (Ans: acetylcholine)
3. 3
   Which part of the ear maintains body balance? (Ans: vestibular apparatus — semicircular canals and vestibule)
4. 4
   Define a reflex arc. (Ans: the pathway of a reflex: receptor → sensory neuron → CNS → motor neuron → effector)

2 Mark Questions

1. 1
   Differentiate between a myelinated and a non-myelinated nerve fibre.
2. 2
   What are rods and cones? How do they differ? (Ans: rods for scotopic/sensitivity in dim light; cones for colour and photopic vision)
3. 3
   Write two functions of the cerebellum. (Ans: coordination of muscles, maintenance of posture/balance)

3 Mark Questions

1. 1
   Describe the generation and conduction of a nerve impulse in terms of resting and action potential.
2. 2
   Describe the structure of a synapse and the transmission of an impulse across it. (Ans: presynaptic terminal, synaptic cleft, postsynaptic membrane; neurotransmitter diffusion e.g. acetylcholine)
3. 3
   Explain the mechanism of vision, from light entering the eye to the formation of the image and its transmission to the brain.

5 Mark Questions

1. 1
   Describe the structure of the human ear (external, middle, inner), explaining the functions of the cochlea (hearing) and the vestibular apparatus (balance).
2. 2
   Describe the structure of the human eye with a labelled diagram and explain accommodation and the formation of a real, inverted image on the retina. (Ans: cornea, pupil/iris, lens, retina; accommodation by ciliary muscles)