O NS O rganization of the Nervous System Joselito B. Diaz, MD, FPNA College of Rehabilitation Sciences

Introduction The Nervous and Endocrine systems together control and coordinate functions of all body systems –Coordinated as an interlocking system termed the Neuroendocrine system –Nervous system performs short term crisis management –Endocrine system regulates long term ongoing metabolic activities

Nervous System CORRELATION COORDINATION MEMORY SENSORY STIMULI AfferentEfferent MUSCLES GLANDS Etc.

Overview of Neural Integration

Functional Organization of the Nervous System

Anatomical Organization of the Nervous System

Terminologies

Nervous Tissue Specialized tissue for rapid conduction of electrical impulses that convey information from one part of the body to another –98% nervous tissue concentrated in brain and spinal cord Neurons = functional units transmit information in the form of electrical current at their cell membranes Neuroglia = “nerve glue” provide physical support for neurons represent 90% of a cells in brain Nerve Cells and Astrocyte (SEM x2,250). Nervous tissue contains two basic cell types

The neuron is the functional unit of the nervous system DendritesDendrites receive information from another cell or receptor and transmit the message to the cell body The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cellscell body The axon conducts messages away from the cell bodyaxon

Central nervous system Consists of the brain located within the skull and the spinal cord located within the vertebral foramen Integration and command center of the body Covered by meninges and surrounded by cerebrospinal fluid

Central nervous system BRAIN Forebrain –Cerebrum –Diencephalon Midbrain Hindbrain –Pons –Medulla –Cerebellum SPINAL CORD Cervical segments Thoracic segments Lumbar segments Sacral segments Coccygeal segments

Central nervous system

Meninges and CSF The meninges are 3 connective tissue membranes that lie external to the brain and the spinal cord –Dura mater, arachnoid mater, pia mater –Cover and protect the CNS –Hold cerebrospinal fluid (CSF) –Prevents harmful substances from entering CSF

Meninges and CSF The CSF is the extracellular fluid found in the ventricles of the brain and subarachnoid space –Surrounds the brain and spinal cord in the subarachnoid space –Cushions and protects the CNS from trauma –Provides mechanical buoyancy and support the brain –Nourishes the CNS and removes metabolites

Meninges

Central nervous system - Brain

Brain

Fissures and gyri

Surface contains gyri and sulci or fissures Longitudinal fissure separates two cerebral hemispheres Central sulcus of Rolando separates the frontal and parietal lobes Lateral Sylvian fissure separates the temporal lobe from the frontal and parietal lobes Line drawn from the parieto-occipital sulcus down to the preoccipital notch delineate the occipital lobe from the temporal and parietal lobes The cerebral cortex

Lobes of the cerebrum

The Cerebral Hemispheres PLAY

White and gray matter

White Matter of the Cerebrum Association fibers –connections from gyrus to gyrus and from lobe to lobe in the same hemisphere –Superior longitudinal fasciculus Commissural fibers –Connections occur between homologous areas of the two hemisperes –Corpus callosum Projection fibers –Connects the cerebral cortex to the subcortical, brainstem and spinal cord nuclei

Subcortical nuclei

Diencephalon and Brainstem

Composed of: Epithalamus Hypothalamus Subthalamus Thalamus Diencephalon

Thalamus Final relay point for ascending sensory information Coordinates the activities of the cerebral cortex, basal nuclei and cerebellum

Hypothalamus Controls somatic motor activities at the subconscious level Controls autonomic function Coordinates activities of the endocrine and nervous systems Secretes hormones Produces emotions and behavioral drives Coordinates voluntary and autonomic functions Regulates body temperature Coordinates circadian cycles of activity

The Hypothalamus in Sagittal Section

Medulla Connects the brain with the spinal cord Contains relay stations reflex centers and cranial nerve nuclei –Olivary nuclei –Cardiovascular and respiratory rhythmicity centers Reticular formation begins in the medulla oblongata and extends into more superior portions of the brainstem

Brainstem - Medulla

Pons Sensory and motor nuclei for four cranial nerves Nuclei that help control respiration Nuclei and tracts linking the cerebellum with the brain stem, cerebrum and spinal cord Ascending, descending and transverse tracts

Brainstem - Pons

Midbrain The tectum (roof) contains the corpora quadrigemina – Superior and inferior colliculi The mesencephalon contains many nuclei and tracts –Red nucleus –Substantia nigra –Cerebral peduncles –RAS headquarters

Brainstem - Midbrain

Adjusts postural muscles and tunes on-going movements Cerebellar divisions –Flocculonodular, anterior and posterior lobes –Vermis and cerebellar hemispheres Superior, middle and inferior cerebellar peduncles link cerebellum with brain stem, diencephalon, cerebrum, and spinal cord Cerebellum

The Cerebellum

Cranial Nerves 12 pairs of cranial nerves –Each attaches to the ventrolateral surface of the brainstem near the associated sensory or motor nuclei

PLAY Cranial Nerves

PLAY Cranial Nerves

Spinal cord The adult spinal cord ends between L 1 and L 2 Locate the: –Shallow posterior median sulcus –Deep anterior median fissure

Spinal cord Enlargements are composed of numerous gray matter dealing with sensory and motor control of the limbs Cervical enlargement - nerves to the shoulder girdles and upper limbs Lumbar enlargement – innervations to the pelvis and lower limbs Conus medularis is the end of the spinal cord

Spinal cord is divided into 31 segments Dorsal root ganglia – contain the cell bodies of sensory neurons Dorsal root – composed of sensory axons which bring sensory information into the spinal cord Ventral roots – axons of motor neurons; control somatic and visceral effectors Sensory and motor roots are bound together into a single spinal nerve (distal to the root ganglion) Spinal nerves are mixed nerves – contain both afferent (sensory) and efferent (motor) fibers Spinal cord

Gross Anatomy of the Adult Spinal Cord

Spinal meninges Membranes surround and protect the spinal cord Provide physical stability and shock absorption Blood vessels branching within these layers deliver oxygen and nutrients to the spinal cord Three layers: –Dura mater –Arachnoid –Pia mater

The Spinal Cord and Spinal Meninges

Sectional anatomy of the spinal cord White matter is composed of myelinated and unmyelinated axons Gray matter dominated by nerve cell bodies and neuroglia Gray matter surrounds the central canal Projections of gray matter called horns

The Sectional Organization of the Spinal Cord

Sectional anatomy of the spinal cord Organization of Gray Matter –Organized into function groups called nuclei –Posterior horns are sensory Posterior gray horn contains somatic and visceral sensory nuclei –Anterior horns are motor Anterior gray horns deal with somatic motor control Lateral gray horns contain visceral motor neurons –Gray commissures join the lateral sides together; axons pass from one side of the spinal cord to the other through the gray commissure

Sectional anatomy of the spinal cord Organization of White Matter –Divided into six columns (funiculi) containing tracts –All axons within a tract relay the same type of information (sensory or motor) in the same direction –Ascending tracts relay information from the spinal cord to the brain –Descending tracts carry information from the brain to the spinal cord Ascending pathways Descending pathways

Peripheral Nervous System The PNS consists of 12 pairs of cranial nerves originate from the brain and 31 pairs of nerves are attached to the spinal cord Sensory (afferent) –all axons carry impulses from sensory receptors via the PNS to the CNS Motor (efferent) –all axons carry impulses via the PNS from CNS Mixed –a mixture of sensory and motor neurons that carry impulses via the PNS to and from CNS – most common type of nerve in the body

Functional Organization of the Nervous System

Sensory division - made of afferent neurons somatic –sensory neurons send information from skin, skeletal muscles, and joints visceral –sensory neurons send information from organs within the abdominal and thoracic cavities Sensory Division of the PNS

Motor Division of the PNS Motor division made of efferent neurons control the action of muscles and glands –somatic motor neurons send APs to voluntary skeletal muscle –visceral motor neurons send APs to involuntary cardiac muscle, smooth muscle and glands –a.k.a. the Autonomic Nervous System (ANS) –2 antagonistic (opposing) divisions Sympathetic Parasympathetic –the two divisions control the same effectors but create opposite responses in the effectors

31 pairs of spinal nerves Nerve sheath consists of: –Epineurium –Perineurium –Endoneurium

Dorsal ramus (sensory and motor innervation to the skin and muscles of the back) Ventral ramus (supplying ventrolateral body surface, body wall and limbs) Rami communicantes –White ramus (myelinated axons) –Gray ramus (unmyelinated axons that innervate glands and smooth muscle) Each pair of nerves monitors one dermatome Spinal nerves

Peripheral Distribution of Spinal Sensory Nerves

Peripheral Distribution of Spinal Motor Nerves

Dermatomes

Complex interwoven network of nerves Four large plexuses –Cervical plexus –Brachial plexus –Lumbar plexus –Sacral plexus Nerve plexus

The Cervical Plexus

The Brachial Plexus

The Lumbar and Sacral Plexuses

Peripheral Nerves and Nerve Plexus

Coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions Two divisions: –Sympathetic division (thoracolumbar, “fight or flight”) Preganglionic fibers leaving the thoracic and lumbar segments –Parasympathetic division (craniosacral, “rest and repose”) Preganglionic fibers leaving the brain and sacral segments Autonomic Nervous System

Preganglionic neurons between segments T1 and L2 Ganglionic neurons in ganglia near vertebral column –Sympathetic chain ganglia (paravertebral ganglia) –Collateral ganglia (prevertebral ganglia) Specialized neurons in adrenal glands Sympathetic division anatomy

Organization of the Sympathetic Division of the ANS

Organization of the Sympathetic Division

Preganglionic neurons in the brainstem and sacral segments of spinal cord –Preganglionic fibers leave the brain as cranial nerves III, VII, IX, X –Sacral neurons form the pelvic nerves Ganglionic neurons in peripheral ganglia located within or near target organs Parasympathetic division

Organization of the Parasympathetic Division of the ANS

Organization of the Parasympathetic Division

Organization of the Nervous System Joselito B. Diaz, MD, FPNA College of Rehabilitation Sciences