Neural Control and Coordination: common doubts, answered
The questions students ask most often about Neural Control and Coordination, each with a short answer. For the full chapter, read the Neural Control and Coordination notes.
Coordination
Read this section in the notes →How does the nervous system differ from the endocrine system in coordinating the body?
The neural system provides quick, short-lived and point-to-point coordination through nerve impulses, while the endocrine system works through chemical messengers called hormones, which usually act more slowly and over longer periods. Together they integrate the activities of organs so that the body works as one unit.
Neural system in animals
Read this section in the notes →How is the neural system different in Hydra, insects and vertebrates?
Hydra has a network of neurons, the simplest form. Insects have a brain and a number of ganglia, and a ventral nerve cord. Vertebrates have a more developed neural system, in which the brain and spinal cord handle control. The complexity of the system increases up the animal groups.
Human neural system
Read this section in the notes →What is the difference between the central and peripheral nervous system?
The central nervous system consists of the brain and spinal cord and is the site for information processing and control. The peripheral nervous system includes all the nerves that connect to the CNS. Afferent fibres carry impulses from tissues to the CNS, and efferent fibres carry impulses from the CNS to tissues.
What is the difference between the somatic and autonomic neural systems?
The somatic neural system relays impulses from the CNS to skeletal muscles, while the autonomic neural system relays them to the involuntary organs and smooth muscles of the body. The autonomic system has two divisions, sympathetic and parasympathetic, which usually have opposite effects on an organ.
Structure of a neuron
Read this section in the notes →What are the parts of a neuron?
A neuron has a cell body containing the nucleus and Nissl's granules, short fibres called dendrites that carry impulses toward the cell body, and a long axon that carries them away, ending in synaptic knobs containing vesicles of neurotransmitter. So dendrites receive and axons transmit.
What are unipolar, bipolar and multipolar neurons?
They are classed by the number of processes arising from the cell body. Multipolar neurons have one axon and two or more dendrites, as in the cerebral cortex. Bipolar neurons have one axon and one dendrite, as in the retina. Unipolar neurons have a cell body with only one axon and are usually found in the embryo.
What is the myelin sheath and what are nodes of Ranvier?
The myelin sheath is an insulating covering around some axons, formed by Schwann cells. The small uncovered gaps between adjacent sheath segments are the nodes of Ranvier. Myelinated nerve fibres are found in spinal and cranial nerves. Unmyelinated fibres are enclosed by a Schwann cell with no myelin around them.
Resting potential
Read this section in the notes →How is the resting membrane potential maintained?
The axon membrane at rest is permeable to potassium and almost impermeable to sodium, so the inside holds high potassium and negatively charged proteins, and the outside holds high sodium. The sodium-potassium pump moves 3 sodium ions out for every 2 potassium ions in, leaving the outer surface positive and the inner surface negative.
Nerve impulse
Read this section in the notes →Which ion rushes in during an action potential?
Sodium ions rush in. When a stimulus is applied, the membrane becomes freely permeable to sodium, whose entry reverses the polarity, so the outside becomes negative and the inside positive. This depolarisation is the action potential, or nerve impulse. Potassium moves out afterwards to restore the resting state.
How does the nerve impulse travel along an axon?
At the site of the action potential, current flows on the inner side from the active region to the neighbouring resting region and on the outer side in the reverse direction, which completes a circuit. This depolarises the next site and the impulse moves forward. The previous site is meanwhile brought back to resting potential by potassium leaving.
Transmission of impulses
Read this section in the notes →What is the difference between an electrical synapse and a chemical synapse?
At an electrical synapse the pre- and post-synaptic membranes are very close and current flows directly, so transmission is always faster, but these are rare in our system. At a chemical synapse a synaptic cleft separates the membranes and a neurotransmitter carries the signal, so the new potential can be excitatory or inhibitory.
How does a chemical synapse transmit an impulse?
When an impulse reaches the axon terminal, it makes synaptic vesicles fuse with the pre-synaptic membrane and release a neurotransmitter into the cleft. The neurotransmitter binds receptors on the post-synaptic membrane, opening ion channels, and this produces a new potential in the next neuron, which may be excitatory or inhibitory.
The brain
Read this section in the notes →What are the three meninges, from outside to inside?
The brain is covered by three layers, from outermost to innermost: the dura mater, the arachnoid and the pia mater. The dura is tough and fibrous, the arachnoid is thin and web-like, and the pia mater is closely attached to the brain tissue. They protect the brain together.
What are the three major parts of the human brain?
The brain has the forebrain, midbrain and hindbrain. The forebrain includes the cerebrum, thalamus and hypothalamus. The midbrain lies between the thalamus and hypothalamus of the forebrain and the pons of the hindbrain. The hindbrain includes the pons, cerebellum and medulla oblongata. The pons and cerebellum are not forebrain parts.
Forebrain
Read this section in the notes →What is the difference between grey matter and white matter?
Grey matter is the outer layer of the cerebral cortex, made of neuron cell bodies, and it gives the grey colour. White matter is the inner part, made of myelinated nerve fibres that run in tracts. So the cortex is grey matter, not white matter. The two cerebral hemispheres are connected by the corpus callosum.
What does the hypothalamus do?
The hypothalamus contains centres that control body temperature and the urge for eating and drinking, and it also secretes hypothalamic hormones. Together with the limbic system it takes part in the regulation of sexual behaviour, expression of emotional reactions and motivation. It is a part of the forebrain, lying at the base of the thalamus.
What are the functions of the thalamus and the corpus callosum?
The thalamus is the major coordinating centre for sensory and motor signalling, and it lies at the centre of the forebrain, wrapped by the cerebrum. The corpus callosum is a bundle of fibres that connects the two cerebral hemispheres, so they can exchange information. They are separate structures with different roles.
Midbrain and hindbrain
Read this section in the notes →What are corpora quadrigemina?
The corpora quadrigemina are four round swellings, called lobes, on the dorsal side of the midbrain. The midbrain also contains the cerebral aqueduct, a passage that runs through it. Together with the pons and medulla, the midbrain forms the brain stem, which connects the brain to the spinal cord.
What is the role of the medulla oblongata?
The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions. It connects to the spinal cord and forms the lowest part of the brain stem. The cerebellum, in contrast, has very convoluted surface and controls balance and coordination of movement, while the pons has fibre tracts connecting different brain regions.
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