Neural Control and Coordination: questions with answers

Coordination lets organs interact and complement one another to maintain homeostasis. Neural coordination uses an organised point-to-point network for rapid responses, while endocrine coordination provides chemical integration through hormones. Neurons detect, receive and transmit stimuli; organisation ranges from a diffuse neural network in Hydra to a brain with ganglia in insects and a more developed vertebrate system.

Coordination lets organs interact and complement one another to maintain homeostasis. Neural coordination uses an organised point-to-point network for rapid responses, while endocrine coordination provides chemical integration through hormones. Neurons detect, receive and transmit stimuli; organisation ranges from a diffuse neural network in Hydra to a brain with ganglia in insects and a more developed vertebrate system.

The CNS comprises brain and spinal cord and processes information and control. The PNS includes nerves associated with the CNS. Afferent fibres carry impulses from tissues and organs to the CNS, while efferent fibres carry regulatory impulses from the CNS outward. Somatic pathways serve skeletal muscle; autonomic pathways serve involuntary organs and smooth muscle and include sympathetic and parasympathetic divisions. The visceral nervous system comprises PNS routes between CNS and viscera.

The CNS comprises brain and spinal cord and processes information and control. The PNS includes nerves associated with the CNS. Afferent fibres carry impulses from tissues and organs to the CNS, while efferent fibres carry regulatory impulses from the CNS outward. Somatic pathways serve skeletal muscle; autonomic pathways serve involuntary organs and smooth muscle and include sympathetic and parasympathetic divisions. The visceral nervous system comprises PNS routes between CNS and viscera.

A neuron has a cell body, dendrites and an axon. Cell body and dendrites contain Nissl's granules; dendrites conduct toward the cell body, whereas the axon conducts away to a synapse or neuromuscular junction. Terminal branches end in synaptic knobs containing neurotransmitter vesicles. Multipolar, bipolar and unipolar neurons differ in axon-dendrite number. Schwann cells form myelin around myelinated axons, interrupted at nodes of Ranvier; in non-myelinated fibres Schwann cells enclose the axon without forming a myelin sheath.

A neuron has a cell body, dendrites and an axon. Cell body and dendrites contain Nissl's granules; dendrites conduct toward the cell body, whereas the axon conducts away to a synapse or neuromuscular junction. Terminal branches end in synaptic knobs containing neurotransmitter vesicles. Multipolar, bipolar and unipolar neurons differ in axon-dendrite number. Schwann cells form myelin around myelinated axons, interrupted at nodes of Ranvier; in non-myelinated fibres Schwann cells enclose the axon without forming a myelin sheath.

At rest, the axonal membrane is more permeable to K+ and nearly impermeable to Na+ and intracellular negatively charged proteins. Axoplasm has high K+, low Na+ and negatively charged proteins; extracellular fluid has low K+ and high Na+. The sodium-potassium pump actively moves 3 Na+ outward for 2 K+ inward, maintaining gradients. The exterior is positive and interior negative; this potential difference is the resting potential.

At rest, the axonal membrane is more permeable to K+ and nearly impermeable to Na+ and intracellular negatively charged proteins. Axoplasm has high K+, low Na+ and negatively charged proteins; extracellular fluid has low K+ and high Na+. The sodium-potassium pump actively moves 3 Na+ outward for 2 K+ inward, maintaining gradients. The exterior is positive and interior negative; this potential difference is the resting potential.

A stimulus briefly increases Na+ permeability at an excited site, causing Na+ influx and reversal of polarity: inside becomes positive and outside negative. This action potential is the nerve impulse. Local currents flow internally from the active site toward the next resting site and externally in the reverse direction, depolarising the next segment. A subsequent rise in K+ permeability lets K+ diffuse outward and restores resting potential.

A stimulus briefly increases Na+ permeability at an excited site, causing Na+ influx and reversal of polarity: inside becomes positive and outside negative. This action potential is the nerve impulse. Local currents flow internally from the active site toward the next resting site and externally in the reverse direction, depolarising the next segment. A subsequent rise in K+ permeability lets K+ diffuse outward and restores resting potential.

At a chemical synapse, the arriving impulse triggers neurotransmitter release from the pre-synaptic terminal. The transmitter binds receptors on the post-synaptic membrane and opens ion channels. Depending on the channels affected, the resulting potential can be excitatory or inhibitory. Direct current transfer between neurons characterises electrical synapses.

A synapse joins pre- and post-synaptic neuronal membranes, which may or may not be separated by a cleft. At electrical synapses the membranes lie close and current passes directly; transmission is faster and these synapses are rare in humans. At chemical synapses, an arriving action potential drives vesicle fusion and neurotransmitter release into the cleft. Transmitter binds specific post-synaptic receptors, opens ion channels and generates an excitatory or inhibitory potential.

The brain is protected by skull and cranial meninges: dura mater, arachnoid and pia mater. The forebrain contains cerebrum, thalamus and hypothalamus. Cerebral hemispheres are linked by corpus callosum; cortex is folded grey matter rich in cell bodies, while inner myelinated tracts form white matter. Association areas support complex integration. Thalamus coordinates sensory and motor signalling; hypothalamus regulates temperature, hunger and thirst and has neurosecretory cells. Limbic structures with hypothalamus participate in emotion, sexual behaviour and motivation.

The brain is protected by skull and cranial meninges: dura mater, arachnoid and pia mater. The forebrain contains cerebrum, thalamus and hypothalamus. Cerebral hemispheres are linked by corpus callosum; cortex is folded grey matter rich in cell bodies, while inner myelinated tracts form white matter. Association areas support complex integration. Thalamus coordinates sensory and motor signalling; hypothalamus regulates temperature, hunger and thirst and has neurosecretory cells. Limbic structures with hypothalamus participate in emotion, sexual behaviour and motivation.

Midbrain lies between thalamus/hypothalamus and pons, contains the cerebral aqueduct and has four dorsal corpora quadrigemina. Hindbrain comprises pons, cerebellum and medulla. Pons contains tracts interconnecting brain regions; cerebellum has a highly convoluted surface; medulla continues into spinal cord and controls respiration, cardiovascular reflexes and gastric secretions. Midbrain, pons and medulla form the brain stem connecting brain and spinal cord.