Neural Control and Coordination

The One Thing

Neural control and coordination enable an organism to detect stimuli, process information, and produce suitable responses. This depends on specialised neurons, organised nervous-system divisions, synapses, reflex pathways, the brain, spinal cord, and sensory organs.

Reactions, Processes and Experiments

Key Terms

• Neuron: The structural and functional unit of the nervous system that receives and transmits nerve impulses.
• Cell body or cyton: The main part of a neuron containing the nucleus and most cell organelles.
• Dendrites: Short, branched processes that receive signals and carry them towards the cell body.
• Axon: A long process that carries nerve impulses away from the cell body.
• Myelin sheath: A protective, insulating covering around some axons that increases the speed of impulse conduction.
• Node of Ranvier: A small gap between successive myelin sheath segments where ion exchange occurs.
• Sensory neuron: A neuron that carries impulses from receptors to the central nervous system.
• Motor neuron: A neuron that carries impulses from the central nervous system to muscles or glands.
• Interneuron: A neuron within the central nervous system that connects sensory and motor neurons.
• Nerve impulse: An electrical signal produced by changes in the electrical state of a neuron's membrane.
• Resting potential: The polarised state of a neuron's membrane when it is not conducting an impulse, with the inside relatively negative compared with the outside.
• Action potential: A temporary reversal of membrane polarity caused mainly by the movement of sodium and potassium ions.
• Depolarisation: The phase in which sodium ions enter the neuron and the inner surface becomes less negative or positive.
• Repolarisation: The phase in which potassium ions leave the neuron and the membrane returns towards its resting state.
• Synapse: The junction between two neurons or between a neuron and an effector cell.
• Neurotransmitter: A chemical messenger released at a synapse that carries a signal across the synaptic gap.
• Reflex action: A rapid, automatic, and usually protective response to a stimulus.
• Reflex arc: The pathway followed by an impulse during a reflex action, generally involving a receptor, sensory neuron, central nervous system, motor neuron, and effector.
• Central nervous system: The brain and spinal cord, which receive, process, and coordinate information.
• Peripheral nervous system: All nerves and ganglia outside the brain and spinal cord that connect the central nervous system with the rest of the body.
• Somatic nervous system: The division of the peripheral nervous system involved mainly in voluntary control of skeletal muscles.
• Autonomic nervous system: The division that controls involuntary activities of internal organs, smooth muscles, cardiac muscles, and glands.
• Sympathetic nervous system: The autonomic division that prepares the body for emergencies by increasing activities such as heart rate and breathing.
• Parasympathetic nervous system: The autonomic division that promotes rest, digestion, and recovery after activity.
• Cerebrum: The largest part of the brain, responsible for conscious thought, intelligence, memory, sensations, and voluntary actions.
• Thalamus: A major relay centre that directs sensory information to appropriate regions of the cerebrum.
• Hypothalamus: A brain region involved in homeostasis, temperature regulation, hunger, thirst, emotions, and control of the pituitary gland.
• Cerebellum: The part of the brain that coordinates muscular activity, posture, and balance.
• Medulla oblongata: The lower part of the brainstem that controls involuntary functions such as breathing, heartbeat, swallowing, and blood pressure.
• Pons: A brainstem region that helps connect different brain parts and participates in the regulation of breathing.
• Spinal cord: A cylindrical nervous structure within the vertebral column that conducts impulses and coordinates many reflexes.
• Receptor: A specialised sensory structure or cell that detects a stimulus.
• Effector: A muscle or gland that carries out a response to a nerve impulse.
• Eye: A photoreceptor organ that detects light and forms visual signals through the retina.
• Retina: The light-sensitive inner layer of the eye containing rods and cones.
• Rods: Photoreceptor cells that function mainly in dim light and provide less detailed, non-colour vision.
• Cones: Photoreceptor cells that function best in bright light and enable colour and sharp vision.
• Ear: An organ responsible for hearing and maintaining equilibrium.
• Organ of Corti: The sensory structure in the cochlea containing hair cells that detect sound vibrations.
• Vestibular apparatus: A group of structures in the inner ear that detects head position and movement to maintain balance.

Easily Confused

• Sensory neuron and motor neuron: A sensory neuron carries impulses from receptors to the central nervous system, whereas a motor neuron carries impulses from the central nervous system to muscles or glands.
• Dendrites and axon: Dendrites generally carry signals towards the cell body, whereas the axon carries impulses away from it.
• Resting potential and action potential: Resting potential is the polarised state when the neuron is not conducting an impulse, whereas an action potential is the temporary reversal of membrane polarity during impulse transmission.
• Depolarisation and repolarisation: Depolarisation involves sodium ions entering the neuron; repolarisation involves potassium ions leaving it.
• Central nervous system and peripheral nervous system: The central nervous system consists of the brain and spinal cord, whereas the peripheral nervous system consists of nerves and ganglia outside them.
• Somatic and autonomic nervous systems: The somatic system mainly controls voluntary skeletal-muscle activity, whereas the autonomic system regulates involuntary functions.
• Sympathetic and parasympathetic nervous systems: The sympathetic division prepares the body for emergencies, whereas the parasympathetic division promotes rest, digestion, and recovery.
• Cerebrum and cerebellum: The cerebrum is associated with conscious thought, memory, sensations, and voluntary actions, whereas the cerebellum coordinates muscular activity, posture, and balance.
• Rods and cones: Rods function mainly in dim light and do not provide colour vision, whereas cones function best in bright light and provide colour vision and high visual acuity.
• Semicircular canals and utriculus and sacculus: The semicircular canals detect rotational movements, whereas the utriculus and sacculus detect linear acceleration and body position.
• Reflex action and conscious response: A reflex action prioritises speed and protection, whereas a conscious response involves more extensive processing in the brain.
• Chemical and electrical synapses: Chemical synapses use neurotransmitters and usually allow one-way transmission, whereas electrical synapses transmit signals directly between cells.

What Gets Asked

• Questions may require the three major functions of the nervous system: sensory input, integration or processing, and motor output. The mark-losing slip is omitting one of these stages.
• Neuron diagrams may require the structures and direction of impulse flow: dendrites or receptor -> cell body -> axon -> axon terminal. Confusing the direction of dendrites and the axon costs marks.
• Questions on nerve impulses may require the sodium-potassium pump, including 3 sodium ions out and 2 potassium ions in using ATP. Reversing these numbers or omitting ATP is an error.
• Action-potential questions may distinguish depolarisation from repolarisation. Sodium ions enter during depolarisation, whereas potassium ions move outward during repolarisation.
• Reflex-arc questions may require the complete sequence from receptor through sensory neuron, central nervous system, motor neuron, and effector. Leaving out the central nervous system or effector makes the pathway incomplete.
• Questions on sensory organs may compare rods with cones or identify the pathway of sound through the ear. The common slips are assigning colour vision to rods or omitting the malleus, incus, and stapes from sound transmission.