Lab 7 notes - The Brain and Cranial Nerves These main...

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The Brain and Cranial Nerves These main divisions of the brain are into the hindbrain , midbrain and forebrain . These are divisions based on the embryological origin of the brain – in the adult the distinction, particularly between the midbrain and the hindbrain, may not seem to make much sense when just looking at the anatomy. Like the spinal cord, the brain is composed of white matter and gray matter. The grey matter is neuron cell bodies, while the white matter is more heavily myelinated and is most likely to be connections between different areas of the brain or between the brain and spinal cord. Most of the grey matter is external, but there are also nuclei (collections of cell bodies within the CNS) deep within some of the areas of the brain. Hindbrain The hindbrain is also called the rhombencephalon . This is the part of the brain that is between the rest of the brain and the spinal cord. The three parts of the hindbrain are the medulla oblongata , the pons and the cerebellum . The medulla oblongata is involved in autonomic innervation of the body and in distributing somatic motor and sensory fibers connecting the brain and spinal cord. The ventral (anterior) surface of the medulla oblongata has two longitudinal ridges called the pyramids , and behind them a round swelling called the olive . The pyramids are motor tracts connecting the brain and the spinal cord (remember the ventral region of the spinal cord is the motor side). The motor information for the left and right sides of the body crosses over at the pyramidal decussation. The pons is a swelling on the ventral surface of the hindbrain, just above the medulla oblongata, containing sensory and motor tracts. The cerebellum is a large ridge covered structure located posterior to the pons and medulla in the posterior cranial fossa- functions in the coordination of movements. The cerebellum is connected to the pons by the midde cerebellar peduncles , to the medulla oblongata by the inferior cerebellar peduncles and to the mesencephalon by the superior cerebellar peduncles . When cut in sagittal section the white matter in the cerebellum has a branching pattern that resembles a tree- this is called the arbor vitae (tree of life). The cerebellum functions in coordinating motor impulses to produce smooth, co-ordinated movements. There is a condition in cats called cerebellar hypoplasia in which the cerebellum fails to form properly. This causes no pain or distress to the animal, but leads to poor coordination, a strange limb posture while walking, and hilarious youtube videos. Midbrain The mesencephalon or midbrain connects the hindbrain to the midbrain- has visual and auditory reflex centers- the superior (visual) and inferior (auditory) colliculi , which are four bumps on the dorsal surface of the midbrain. Visual and auditory reflexes are the
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movements you make when you hear loud noise or see something suddenly and respond to the stimulus by turning your head or ducking without consciously thinking about it. The superior colliculus also contributes to the coordination of eye movements between
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Lab 7 notes - The Brain and Cranial Nerves These main...

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