Chapter 6: Neural Control and Coordination

Main Parts

• Cell body: Contains cytoplasm, cell organelles and Nissl’s granules.
• Nissl’s granules: Irregular masses of rough endoplasmic reticulum with attached and free ribosomes and polysomes; they probably synthesise proteins.
• Dendrites: Short, repeatedly branched fibres containing Nissl’s granules; they conduct impulses towards the cell body.
• Axon: A long fibre with branched distal ends; it carries impulses away from the cell body to a synapse or neuromuscular junction.
• Synaptic knobs: Bulb-like endings of axon branches containing vesicles filled with neurotransmitters.

Resting State

• Selective permeability: At rest, the axonal membrane is more permeable to \(K^+\) and nearly impermeable to \(Na^+\); it is impermeable to negatively charged proteins in the axoplasm.
• Ion distribution: Inside the axon, \(K^+\) and negatively charged proteins are concentrated, while \(Na^+\) is low. Outside, \(Na^+\) is high and \(K^+\) is low.
• Sodium–potassium pump: By active transport, it maintains ion gradients by moving \(3Na^+\) out for every \(2K^+\) moved into the cell.
• Polarisation: The outer membrane surface is positive and the inner surface negative; the resting potential inside is about \(-70\,\text{mV}\).

Electrical Synapse

• Structure: Presynaptic and postsynaptic membranes lie very close together.
• Transmission: Electrical current passes directly from one neuron to the other, much like conduction along one axon.
• Occurrence and speed: Electrical synapses are rare in our nervous system and transmit faster than chemical synapses.

Chemical Synapse Transmission

• Neurotransmitters: Synaptic vesicles in axon terminals store neurotransmitters. Acetylcholine is excitatory and GABA inhibitory; acetylcholine and noradrenaline are major neurotransmitters in vertebrates.
• Arrival: An action potential at the axon terminal stimulates vesicles to move towards and fuse with the plasma membrane.
• Release and binding: Neurotransmitters enter the synaptic cleft and bind to specific receptors on the postsynaptic membrane.
• Postsynaptic response: Receptor binding opens ion channels, allowing ions to enter and generate a new potential that may be excitatory or inhibitory.

• Controls: voluntary movements, body balance, vital involuntary organs such as the heart, lungs and kidneys, and human behaviour.
• Regulates: thermoregulation, hunger, thirst, 24-hour circadian rhythms and activities of several endocrine glands.
• Processes: vision, hearing, speech, memory, intelligence, emotions and thoughts.
• Protection: the skull encloses the brain; cranial meninges cover it inside the skull.

Cerebrospinal Fluid (CSF)

• Location: clear fluid in the brain’s ventricles and the subarachnoid space around the brain and spinal cord.
• Function: acts as a shock-absorbing medium for the brain.

• Major divisions: forebrain, midbrain and hindbrain.

• Components: olfactory lobes, cerebrum and diencephalon.
• Limbic system: the inner part of the cerebral hemispheres and associated deep structures, including the amygdala and hippocampus, form the limbic lobe/system.
• Role: with the hypothalamus, it regulates sexual behaviour, emotional reactions such as excitement, pleasure, rage and fear, and motivation.

• Location: between the thalamus/hypothalamus of the forebrain and the pons of the hindbrain.
• Cerebral aqueduct: a canal that passes through the midbrain.
• Corpora quadrigemina: four lobes on the dorsal midbrain; the superior colliculi are associated with sight and the inferior colliculi with hearing.
• Crura cerebri: relay impulses to and from the cerebrum, cerebellum, pons and medulla.

• Components: pons, cerebellum and medulla oblongata (medulla).
• Pons: lies below the midbrain; its fibre tracts interconnect different brain regions. Its pneumotaxic centre regulates breathing.
• Cerebellum: its highly convoluted surface provides space for many neurons; it regulates and coordinates movement, posture and balance.
• Medulla: connected to the spinal cord; contains centres controlling respiration, cardiovascular reflexes and gastric secretions.

• Parts: midbrain, pons and medulla oblongata; it connects the brain to the spinal cord and supports life-sustaining functions.
• Functions: coordinates and integrates incoming information and forms the connection between the brain and spinal cord.
• Cranial nerves: serves as the entry or exit point for 10 of the 12 cranial nerves.

• Extent and size: extends from the medulla oblongata to the level of the second lumbar vertebra; it is about 42–45 cm long and weighs about 35 g.
• Functions: conducts impulses to and from the brain, controls most reflex activities and enables communication between spinal nerves and the brain.
• Tissue arrangement: internal grey matter is surrounded by outer white matter.
• Lower end: the spinal cord ends as the conus medullaris; a fine filament, the filum terminale, arises from it and anchors the cord within the vertebral column.
• Cauda equina: spinal nerves below the second lumbar vertebra are collectively called the cauda equina.