Chapter overview: neural coordination
Coordination is the interaction of two or more organs so that their functions complement one another and maintain homeostasis. The neural and endocrine systems jointly integrate organ activities.
Two complementary systems Neural coordination uses organised point-to-point connections for rapid responses; endocrine coordination provides chemical integration through hormones.
Neurons are specialised cells that detect, receive and transmit stimuli. Neural organisation progresses from a nerve net in Hydra to brain, ganglia and neural tissues in insects, and a highly developed vertebrate neural system.
18.1-18.2 Human neural system
| Division | Components and function |
|---|---|
| Central neural system (CNS) | Brain and spinal cord; information processing and control centre. |
| Peripheral neural system (PNS) | All nerves associated with CNS. |
| Afferent fibres | Carry impulses from tissues and organs to CNS. |
| Efferent fibres | Carry regulatory impulses from CNS to peripheral tissues and organs. |
| Somatic neural system | Relays CNS impulses to skeletal muscles. |
| Autonomic neural system | Transmits CNS impulses to involuntary organs and smooth muscle; includes sympathetic and parasympathetic systems. |
| Visceral nervous system | Complex PNS nerves, fibres, ganglia and plexuses linking CNS with viscera in both directions. |
18.3 Neuron: structure and types
A neuron is the structural and functional unit of the neural system. It has a cell body, dendrites and axon. The cell body contains organelles and Nissl’s granules.
| Part / type | NCERT details |
|---|---|
| Dendrites | Short, repeatedly branching fibres containing Nissl’s granules; transmit impulses towards cell body. |
| Axon | Long fibre with branched distal end. Synaptic knobs contain neurotransmitter-filled synaptic vesicles; axon conducts away from cell body to synapse or neuromuscular junction. |
| Multipolar neuron | One axon and two or more dendrites; found in cerebral cortex. |
| Bipolar neuron | One axon and one dendrite; found in retina. |
| Unipolar neuron | Cell body with one axon only; usually present during embryonic stage. |
Myelinated and non-myelinated nerve fibres
| Feature | Myelinated fibre | Non-myelinated fibre |
|---|---|---|
| Schwann-cell covering | Schwann cells form a myelin sheath around axon. | Enclosed by a Schwann cell, but no myelin sheath forms around axon. |
| Nodes of Ranvier | Gaps between adjacent myelin sheaths. | Absent as there is no segmented myelin sheath. |
| Common occurrence | Spinal and cranial nerves. | Common in autonomic and somatic neural systems. |
18.3.1 Resting potential and nerve-impulse conduction
At rest, the axonal membrane is more permeable to K+ and nearly impermeable to Na+ and negatively charged proteins. Axoplasm contains more K+ and proteins but less Na+; external fluid has more Na+ and less K+.
| State / event | Ion movement and electrical result |
|---|---|
| Polarised resting membrane | Sodium-potassium pump moves 3 Na+ out for every 2 K+ in. Outer surface is positive, inner surface negative: resting potential. |
| Depolarisation | Stimulus opens Na+ permeability at a point. Rapid Na+ influx reverses polarity, producing action potential / nerve impulse. |
| Conduction | Current flows inside from depolarised site to next resting site and outside in reverse direction. This sequentially depolarises the axon. |
| Repolarisation | Na+ permeability rise is brief; K+ permeability rises, K+ diffuses out, and resting potential is restored. |
18.3.2 Synaptic transmission
A synapse is the junction between pre- and post-synaptic neurons. Their membranes may be separated by a synaptic cleft.
| Type | Mechanism and significance |
|---|---|
| Electrical synapse | Pre- and post-synaptic membranes are extremely close. Current flows directly, similar to single-axon conduction; transmission is faster and these synapses are rare in humans. |
| Chemical synapse | Fluid-filled synaptic cleft separates membranes. Action potential causes synaptic vesicles to fuse with pre-synaptic membrane and release neurotransmitter. It binds specific post-synaptic receptors, opens ion channels and generates excitatory or inhibitory potential. |
18.4 Central nervous system and protection
The brain is the command-and-control centre for voluntary movement, balance, vital involuntary organs, thermoregulation, hunger, thirst, circadian rhythms, endocrine activity, vision, hearing, speech, memory, intelligence, emotions and thought.
| Protective structure | Detail |
|---|---|
| Skull | Encloses and protects brain. |
| Cranial meninges | Three coverings: outer dura mater, thin middle arachnoid, and inner pia mater in contact with brain tissue. |
| Major brain divisions | Forebrain, midbrain and hindbrain. |
Forebrain: cerebrum, thalamus and hypothalamus
| Part | Structure and function |
|---|---|
| Cerebrum | Largest brain part. Deep cleft forms left and right cerebral hemispheres, linked by corpus callosum. Cortex (grey matter) has neuron cell bodies and motor, sensory and association areas; inner myelinated tracts form white matter. |
| Association areas | Neither clearly sensory nor motor; perform intersensory association, memory and communication. |
| Thalamus | Wrapped by cerebrum; major coordinating centre for sensory and motor signalling. |
| Hypothalamus | At thalamus base; controls temperature, eating and drinking, and contains neurosecretory cells releasing hypothalamic hormones. |
| Limbic system | Inner hemispheric regions plus deep structures such as amygdala and hippocampus. With hypothalamus regulates sexual behaviour, emotion, motivation, excitement, pleasure, rage and fear. |
Midbrain and hindbrain
| Region | Key NCERT facts |
|---|---|
| Midbrain | Between thalamus/hypothalamus and pons. Cerebral aqueduct passes through it; dorsal portion has four rounded corpora quadrigemina. |
| Pons | Fibre tracts interconnect different brain regions. |
| Cerebellum | Highly convoluted surface accommodates many neurons; integrates information related to balance and coordination. |
| Medulla oblongata | Connects with spinal cord; contains centres for respiration, cardiovascular reflexes and gastric secretions. |
| Brain stem | Midbrain, pons and medulla oblongata; links brain and spinal cord. |
NCERT revision prompts
- Explain neural and endocrine coordination during physical exercise.
- Compare CNS, PNS, somatic and autonomic neural systems.
- Differentiate afferent and efferent fibres.
- Draw and label a neuron; compare dendrites with axon.
- Compare myelinated and non-myelinated fibres.
- Explain polarisation, depolarisation, repolarisation and impulse conduction.
- Compare electrical and chemical synapses; explain chemical transmission.
- Describe brain protection and its three major divisions.
- Compare cerebrum, thalamus, hypothalamus, midbrain, cerebellum, pons and medulla.