1. Chapter at a glance
- Neural system and endocrine system jointly coordinate and integrate organ functions for homeostasis; neural system provides quick point-to-point connections via neurons.
- Human neural system comprises CNS (brain and spinal cord) for information processing and control, and PNS (all nerves associated with CNS) with afferent fibres (to CNS) and efferent fibres (from CNS).
- PNS divided into somatic neural system (to skeletal muscles) and autonomic neural system (to involuntary organs/smooth muscles), further split into sympathetic and parasympathetic.
- Neuron (structural and functional unit) consists of cell body (with Nissl’s granules), dendrites (impulses toward cell body) and axon (impulses away; ends in synaptic knobs with neurotransmitters); classified as multipolar, bipolar or unipolar; axons are myelinated (with nodes of Ranvier) or non-myelinated.
- Resting membrane is polarised (more permeable to K⁺, nearly impermeable to Na⁺); Na⁺-K⁺ pump maintains gradients (3 Na⁺ out : 2 K⁺ in).
- Stimulus causes depolarisation (Na⁺ influx) generating action potential (nerve impulse) that propagates along axon; repolarisation follows via K⁺ efflux.
- Impulse transmission at chemical synapses involves neurotransmitters released into synaptic cleft; electrical synapses allow direct current flow (rare in humans).
- Brain (protected by skull and meninges: dura mater, arachnoid, pia mater) divided into forebrain (cerebrum, thalamus, hypothalamus, limbic system), midbrain (corpora quadrigemina) and hindbrain (pons, cerebellum, medulla).
2. Definitions and laws
- Resting potential: “The electrical potential difference across the resting plasma membrane.”
- Action potential: “The electrical potential difference across the plasma membrane at the site A is called the action potential, which is in fact termed as a nerve impulse.”
- Synapse: “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 synaptic cleft.”
- Neurotransmitters: Chemicals contained in synaptic vesicles that transmit impulses across chemical synapses.
- No mathematical formulas or SI units are stated in the chapter.
3. Important diagrams and activities
- Figure 18.1 Structure of a neuron — shows cell body, dendrites, axon, synaptic knob, Nissl’s granules, myelin sheath and nodes of Ranvier.
- Figure 18.2 Diagrammatic representation of impulse conduction through an axon — illustrates depolarisation at site A, current flow and generation of action potential at site B.
- Figure 18.3 Diagram showing axon terminal and synapse — depicts synaptic vesicles, synaptic cleft, neurotransmitter release and receptors on post-synaptic membrane.
- Figure 18.4 Diagram showing sagittal section of the human brain — labels forebrain, midbrain, hindbrain, cerebrum, thalamus, hypothalamus, pons, cerebellum and medulla.
4. Common misconceptions and exam pitfalls
- Confusing afferent fibres (tissues to CNS) with efferent fibres (CNS to periphery) or somatic with autonomic divisions.
- Mixing resting potential (polarised, K⁺ permeable) with action potential (depolarised, Na⁺ influx); forgetting Na⁺-K⁺ pump ratio or sequence of repolarisation.
- Assuming all axons are myelinated or that nodes of Ranvier occur in non-myelinated fibres.
- Placing hypothalamus or limbic system outside forebrain; misattributing functions (e.g., medulla vs hypothalamus centres).
- Describing electrical synapses as common or chemical transmission without mentioning synaptic cleft and receptors.
5. Formula sheet
No formulas present in the chapter.