pinel basics ch02
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Chapter 2The Anatomy of the
Brain
The Systems, Structures, and Cells that Make Up Your Nervous System
Copyright © 2007 by Allyn and Bacon
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General Layout of the Nervous System
• Central Nervous System (CNS)– Brain (in the skull)– Spinal Cord (in the spine)
• Peripheral Nervous System (PNS)– Located outside of the skull and spine– Serves to bring information into the CNS and
carry signals out of the CNS
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General Layout of the Nervous System
• PNS – 2 divisions– Somatic Nervous System
Afferent nerves (sensory) Efferent nerves (motor)
– Autonomic Nervous System Sympathetic and parasympathetic
nerves Both are efferent
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Autonomic Nervous System
• All nerves are efferent• Sympathetic and parasympathetic
nerves generally have opposite effects
• Two-stage neural paths, neuron exiting the CNS synapses on a second-stage neuron before the target organ
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Autonomic Nervous System
• Sympathetic• Thoracolumbar• “fight or flight”• Second stage
neurons are far from the target organ
• Parasympathetic• Craniosacral• “rest and restore”• Second stage
neurons are near the target organ
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Meninges, Ventricles, and CSF
• CNS - encased in bone and covered by three meninges– Dura mater - tough outer membrane– Arachnoid membrane - weblike– Pia mater - sticks to CNS surface
• Cerebrospinal fluid (CSF)– Fluid serves as cushion
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Protecting the Brain
• Chemical protection– The blood-brain barrier – tightly-packed
cells of blood vessel walls prevent entry of many molecules
• Physical protection– Skull – Meninges– Cerebrospinal fluid (CSF)
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Cells of the Nervous System
• Generally two types• Neurons – specialized for reception, conduction,
and transmission• Glial cells – outnumber neurons by 10 to 1.
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Anatomy of Neurons
• Neurons – structural classes– Multipolar– Unipolar– Bipolar– Interneurons
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Anatomy of Neurons• Nuclei – clusters of cell bodies in
the CNS• Ganglia – clusters of cell bodies in
the PNS• Tracts – bundles of axons in the
CNS• Nerves – bundles of axons in the
PNS
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Glial Cells: The Forgotten Majority
• Myelin producers– Oligodendrocytes (CNS)– Schwann cells (PNS)
• Astrocytes – largest, many functions (composed the blood-brain barrier)
• Microglia – smallest, involved in response to injury or disease
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Terminology Note
CNS PNSMyelin-providing glia
Oligodendrocytes Schwann Cells
Clusters of cell bodies
Nuclei (singular nucleus)
Ganglia(singular ganglion)
Bundles of axons
Tracts Nerves
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Some Neuroanatomical Techniques
• Golgi stain – allows for visualization of individual neurons
• Nissl stain – selectively stains cell bodies
• Electron microscopy – provides information about the details of neuronal structure
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Neuroanatomical Directions
• Anterior (rostral) – towards the nose• Posterior (caudal) – towards the tail• Dorsal – towards the surface of the back or
the top of the head• Ventral – towards the surface of the chest or
the bottom of the head
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Neuroanatomical Directions
• Medial – towards the middle• Lateral – towards the side• Proximal – close• Distal – far• Superior – top of the primate head• Inferior – bottom of the primate head
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Sections of the Brain
• Horizontal – a slice parallel to the ground
• Frontal (coronal) – slicing bread or salami
• Sagittal – a midsagittal section separates the left and right halves
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The Spinal Cord
• Gray matter – inner component – primarily cell bodies
• White matter – outer – mainly myelinated axons
• Dorsal – afferent, sensory• Ventral – efferent, motor
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The Five Divisions of the Brain
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The Five Divisions of the Brain
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Major Structures of the Brain
• Myelencephalon = medulla– Composed largely of tracts– Origin of the reticular formation
• Metencephalon– Many tracts– Pons – ventral surface– Cerebellum - coordination
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Major Structures of the Brain
• Mesencephalon – Tectum (dorsal surface)
• Inferior colliculi – audition• Superior colliculi - vision
– Tegmentum (ventral) – 3 ‘colorful’ structures
• Periaqueductal gray – analgesia• Substantia nigra – sensorimotor• Red nucleus– sensorimotor
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Major Structures of the Brain• Diencephalon
– Thalamus – sensory relay nuclei– Hypothalamus
Regulation of motivated behaviors Controls hormone release by the
pituitary• Telencephalon
– Cerebral cortex– Limbic system– Basal ganglia
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Telencephalon – Cerebral Cortex
• Convolutions serve to increase surface area.
• Longitudinal fissure – a groove that separates right and left hemispheres
• Corpus callosum – largest hemisphere-connecting tract
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Consider this..
• Why would evolution have favored fitting more brain into less space, as opposed to the brain simply getting bigger and bigger?
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Telencephalon – Cerebral Cortex
• About 90% of human cerebral cortex is neocortex.– Neocortex consists of 6 distinct
layers
• Two types of cortical neurons– Pyramidal– Stellate
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Limbic System
• Regulation of motivated behaviors
• “a circuit of midline structures that circle the thalamus”
• Consists of– Primitive cortex - hippocampus and
cingulated cortex – Subcortical structures - mammillary
bodies, amygdala, fornix, septum
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Basal Ganglia
• Subcortical structures that play an important role in voluntary movement
• Amygdala, striatum (caudate + putamen), globus pallidus
• Damage to pathway from striatum to midbrain seen in Parkinson’s disease
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