Chapter 7 THE STRUCTURE OF THE NERVOUS SYSTEM

INTRODUCTION  Nervous System  The structure of the nervous system will tell us about brain function  Brain organization General organization and terms used to describe it Examine how the 3D structure of the brain arises through development Cerebral neocortex

GROSS ORGANIZATION OF THE MAMMALIAN NERVOUS SYSTEM  Nervous System of all mammals has two divisions  CNS (central nervous system)  PNS (peripheral nervous system)  Anatomical References

GROSS ORGANIZATION OF THE MAMMALIAN NERVOUS SYSTEM  The Central Nervous System  The parts of the nervous system that are encased in bone  Brain : Cerebrum, cerebellum, brain stem  Spinal cord Relay information among cerebrum, cerebellum, spinal cord The site where vital functions are regulated Breathing, consciousness, temperature Contains as many neurons as both cerebral hemispheres combined Concerned with movements of ipsilateral side of the body Cerebral hemispheres, separated by the deep sagittal fissure Sensations and movements on the contralateral side of the body

GROSS ORGANIZATION OF THE MAMMALIAN NERVOUS SYSTEM  The Central Nervous System  Spinal cord Surrounded by bony vertebral column, attached to the brain stem Conduit of information (brain body)  Skin, joints, muscles Communication with body via the spinal nerves  Dorsal root : into the spinal cord  Ventral root : away from the spinal cord

GROSS ORGANIZATION OF THE MAMMALIAN NERVOUS SYSTEM  The Peripheral Nervous System  Nervous system outside of the brain and spinal cord  Somatic PNS Innervates skin, joints, muscles that are under voluntary control  Visceral PNS = autonomic nervous system (ANS) Innervates internal organs, blood vessels, glands  Afferent and Efferent Axons afferent : sensory axons bringing information into the CNS efferent : axons that emerge from the CNS

GROSS ORGANIZATION OF THE MAMMALIAN NERVOUS SYSTEM  The Cranial Nerves  12 nerves from brain stem  Mostly innervate the head  Axons from CNS, somatic PNS, visceral PNS  The Meninges  Three membranes that surround the brain Dura mater Arachnoid membrane Pia mater  Brain floats in cerebrospinal fluid (CSF)

GROSS ORGANIZATION OF THE MAMMALIAN NERVOUS SYSTEM  The Ventricular System  CSF-filled caverns and canals inside brain  Choroid plexus : specialized tissue in ventricles that secretes CSF  Path : Cerebrum  brain stem core  subarachnoid space  special structures called arachnoid villi absorb CSF  Imaging the Living Brain  Computed Tomography (CT)  Magnetic Resonance Imaging (MRI)  Functional Brain Imaging Positron emission tomography (PET) Functional MRI (fMRI)

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Ventricular System and the CNS  The entire CNS forms from the walls of a fluid-filled tube  The tube ultimately becomes ventricular system  Formation of the Neural Tube  The embryo begins as a flat disk with 3 distinct layers Endoderm : the lining of many of the internal organs Mesoderm : the bones of the skeleton and the muscles Ectoderm : the nervous system – the neural plate

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Formation of the Neural Tube  Neural plate  neural groove  Fusion of neural folds Neural tube (forms CNS neurons) Neural crest (forms PNS neurons) Somites : vertebrae : skeletal muscle Somatic motor nerves Neurulation : the process which the neural plate becomes the neural tube

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Three Primary Brain Vesicles  Differentiation : the process by which structures become more complex and functionally specialized during development  Primary vesicles : the entire brain derives from the three primary vesicles

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Forebrain  The secondary brain vesicles of the forebrain

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Forebrain  Differential of the Telencephalon and Diencephalon Telencephalon : cerebral hemispheres, olfactory bulbs, basal telencephalon Diencephalon : thalamus, hypothalamus Ventricles : lateral ventricles, third ventricle Major white matter systems : Axons extend from developing forebrain to other parts of the NS  Cortical white matter : cerebral cortex  Corpus callosum : two cerebral hemispheres  Internal capsule : brain stem, particularly the thalamus

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Forebrain  Forebrain Structure-Function Relationships Cerebral cortex : Analyze sensory input and command motor output Thalamus : Gateway of the cortex : Carry information from contralateral side of the body Hypothalamus : Control of visceral (autonomic) nervous system

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Midbrain

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Midbrain  Midbrain Structure-Function Relationships Information conduit from spinal cord to forebrain and vice versa : Sensory systems, the control of movements… contralateral side Tectum  Superior colliculus (216p) : receives direct input from the eye, controls eye movements  Inferior colliculus : the ear instead of the eye Tegmentum : Substantia nigra (black substance), red nucleus : Control of voluntary movement

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Hindbrain  Three structures Cerebellum : Movement control : Sensory systems, the control of movements Pons : Switchboard connecting cerebral cortex to cerebellum Medulla  Decussation : Crossing of axons from one side to the other  Neurons that perform many different sensory and motor function

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Differentiation of the Spinal Cord

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Putting the Pieces Together

UNDERSTANDING CNS STRUCTURE THROUGH DEVELOPMENT  Special Features of the Human CNS  Many convolutions on the surface : Sulcus / Gyrus  The lobes of the human cerebrum

A GUIDE TO THE CEREBRAL CORTEX  Common Features of Cerebral Cortex  Cell bodies in layers of sheets  Surface layer separated from pia mater  Apical dendrites form multiple branches

A GUIDE TO THE CEREBRAL CORTEX  Areas of Neocortex  Brodmann construted a cytoarchitectural map : Cortical areas that look different perform different functions

A GUIDE TO THE CEREBRAL CORTEX  Areas of Neocortex  Neocortical Evolution and S-F Relationship  Cortex amount has changed, but not structure  Leah Krubitzer : Primary sensory areas, secondary sensory areas, motor areas  Jon Kaas : Expansion of secondary sensory areas  Association areas : ex) ability to interpret behavior in terms of mental state