Pinel basics ch02

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


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


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


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


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


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)


Cells of the Nervous System

• Generally two types• Neurons – specialized for reception, conduction,

and transmission• Glial cells – outnumber neurons by 10 to 1.


Anatomy of Neurons

• Neurons – structural classes– Multipolar– Unipolar– Bipolar– Interneurons


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


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


Terminology Note

CNS PNSMyelin-providing glia

Oligodendrocytes Schwann Cells

Clusters of cell bodies

Nuclei (singular nucleus)

Ganglia(singular ganglion)

Bundles of axons

Tracts Nerves


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


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


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


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


The Spinal Cord

• Gray matter – inner component – primarily cell bodies

• White matter – outer – mainly myelinated axons

• Dorsal – afferent, sensory• Ventral – efferent, motor


The Five Divisions of the Brain


Major Structures of the Brain

• Myelencephalon = medulla– Composed largely of tracts– Origin of the reticular formation

• Metencephalon– Many tracts– Pons – ventral surface– Cerebellum - coordination


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


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


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


Consider this..

• Why would evolution have favored fitting more brain into less space, as opposed to the brain simply getting bigger and bigger?


Telencephalon – Cerebral Cortex

• About 90% of human cerebral cortex is neocortex.– Neocortex consists of 6 distinct

layers

• Two types of cortical neurons– Pyramidal– Stellate


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


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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