Regions of the brain

Gray matter holds neuron cell bodies, dendrites and synapses. White matter is mostly myelinated axons, which look white because of the fatty myelin.

• Myelinated axons:
• Correct: Neuron cell bodies, dendrites and synapses:
• Connective tissue:

Inside the CNS a cluster of cell bodies is a nucleus; outside it, a ganglion. A tract is a bundle of axons inside the CNS.

• A ganglion:
• A tract:
• Correct: A nucleus:

The control center compares incoming information with the set point and sends commands to effectors that oppose the change. Sensing is the job of sensory receptors; producing or losing heat is the effectors' job.

• Correct: Compares the sensed temperature with the set point and signals the effectors:
• Produces the heat itself:
• Detects the temperature of the skin:

The occipital lobe is the back of each hemisphere, behind the parieto-occipital sulcus and above the cerebellum. It handles vision.

• Parietal lobe: The parietal lobe lies on top, between the central sulcus and the parieto-occipital sulcus, in front of the pinned lobe.
• Temporal lobe: The temporal lobe lies along the side below the lateral sulcus, not at the back of the hemisphere.
• Correct: Occipital lobe: Correct. The rearmost lobe, sitting above the cerebellum, is the occipital lobe.
• Frontal lobe: The frontal lobe is at the front of the hemisphere, in front of the central sulcus.

The hindbrain (rhombencephalon) splits into the metencephalon, which becomes the pons and cerebellum, and the myelencephalon, which becomes the medulla oblongata.

• Myelencephalon: The myelencephalon is the lower half of the hindbrain; it becomes the medulla oblongata.
• Mesencephalon: The mesencephalon does not split and becomes the midbrain.
• Correct: Metencephalon: Correct. The metencephalon forms the pons and the cerebellum.
• Telencephalon: The telencephalon becomes the cerebrum.

Clumsy, poorly timed movement with normal strength is ataxia, the sign of cerebellar damage. Each side of the cerebellum coordinates the same side of the body, so a clumsy left hand points to the left cerebellum.

• Correct: The left side of the cerebellum: Correct. Ataxia of the left arm comes from the left side of the cerebellum.
• The right side of the cerebellum: The cerebellum coordinates the same side, not the opposite side, so right-sided damage would make the right hand clumsy.
• The left frontal lobe: Damage to the frontal lobe's movement areas causes weakness on the opposite side. Mr. Brandt's strength is normal, and his left side is affected.
• The left occipital lobe: The occipital lobe handles vision; damage there causes loss of vision in part of what you see, not clumsy reaching with normal sight.

The reticular activating system, in the core of the brainstem, sends a steady stream of signals through the thalamus that keeps the cortex awake. Destroy it on both sides and even an undamaged cortex cannot be roused, which is coma.

• The injury destroyed the basal nuclei, which start movement: The basal nuclei lie deep in the cerebrum, not in the brainstem, and their loss affects the selection of movement, not wakefulness.
• The injury cut the corpus callosum, so the hemispheres stopped communicating: The corpus callosum lies in the cerebrum. Cutting it leaves a person fully awake; the hemispheres just share less information.
• The injury destroyed the hypothalamus, which controls body temperature: The hypothalamus is in the diencephalon, not the brainstem core, and loss of temperature control does not by itself prevent waking.
• Correct: The injury destroyed the reticular activating system, which keeps the cortex awake: Correct. Loss of the reticular activating system on both sides causes coma.

The hypothalamus is the control center for temperature, water balance and thirst, and autonomic output such as heart rate. Speech is planned in the frontal cortex, correcting movement is the cerebellum's job, and relaying touch to the cortex is the thalamus's.

• Correct: Body temperature: Yes. Hypothalamic neurons sense blood temperature and drive sweating, skin blood flow and shivering.
• Correct: Thirst and water balance: Yes. The hypothalamus creates thirst and controls a hormone that makes the kidneys keep water.
• Planning the movements of speech: Speech is planned in the frontal lobe of the cerebral cortex, not in the hypothalamus.
• The timing and force of a movement while it is under way: No. Correcting the force and timing of movement is the cerebellum's job.
• Correct: Heart rate, through the autonomic nervous system: Yes. The hypothalamus sends axons to the brainstem and spinal cord neurons of the sympathetic and parasympathetic divisions.
• The relay of touch signals to the cerebral cortex: No. Relaying touch and other body sensations to the cortex is the thalamus's job.

The lowest part of the brainstem is the medulla oblongata, which passes through the foramen magnum. Its nuclei set the basic rhythm of breathing, the heartbeat and blood vessel diameter, so crushing it stops breathing and circulation.

• Loss of the sense of smell: Smell does not depend on the medulla, and losing it is not life-threatening.
• Correct: Loss of the rhythm of breathing and control of the heart: Correct. Compressing the medulla stops breathing and circulation.
• Loss of the ability to form new memories of events: Forming new memories depends on the hippocampus in the temporal lobe, not the medulla.
• Loss of coordination on one side of the body: Coordination depends on the cerebellum. It may be affected too, but losing it is not what kills first.

The internal capsule is the compact band that carries the axons running between the cortex and the brainstem and spinal cord. Movement commands for the left side of the body come from the right hemisphere, so damage to the right internal capsule weakens the left side.

• Clumsy, staggering movement of the right arm and leg: Clumsy staggering movement with normal strength is cerebellar ataxia, and the right side of the body is controlled by the left hemisphere.
• Loss of the sense of smell on the right: Smell does not travel through the internal capsule.
• Correct: Weakness of the left arm and leg: Correct. Motor axons from the right hemisphere pass through the right internal capsule and control the left side.
• Loss of hearing in both ears: Each ear sends signals to both sides of the brain, and hearing does not depend on this band.