1.Nervous Sys Org - Lecture

8/10/2019 1.Nervous Sys Org - Lecture

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Anatomy and Physiology, Sixth Edi tion

Lecturer: Dr. D. Fisher

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Overview

Of the

Nervous System


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The Nervous System

Components Brain, spinal cord, nerves, sensory receptors

Responsible for

Sensory perceptions, mental activities,stimulating muscle movements, secretions ofmany glands

Subdivisions Central nervous system ( CNS ) Peripheral nervous system ( PNS )


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Central Nervous System

Consists of Brain

Located in cranial vault

of skull Spinal cord

Located in vertebralcanal

Brain and spinal cord Continuous with each

other at foramenmagnum


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Brain and Cranial Nerves

Brain Part of CNS contained in cranial cavity Control center for many of bodys functions Much like a complex computer but more

Parts of the brain Brainstem Cerebellum Diencephalon Cerebrum

Cranial nerves Part of PNS arise directly from brain


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Brainstem

Connects spinal cord to brain Parts

Medulla oblongata Pons

Midbrain


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Brainstem

Medulla oblongata or medulla Regulates: Heart rate, blood vessel diameter,

respiration, swallowing, vomiting, hiccupping,coughing, and sneezing

Pyramids: Decussate

Pons Sleep and respiratory center

Midbrain Integral part of auditory pathways in CNS


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Cerebellum

Involved in control of: balance, posture,locomotion, and finemotor coordination

producing smoothflowing movements


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Diencephalon

Components Thalamus, Subthalamus, Epithalamus, Hypothalamus


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Diencephalon

Thalamus Largest part ofdiencephalon

Most sensory input projectsto here

Influences mood andactions as fear or rage

Subthalamus Involved in controlling

motor functions

Epithalamus Pineal gland may influence

sleep-wake cycle

Hypothalamus Functions

ANS control Endocrine control Muscle control Temperature regulation Regulation of food and

water intake

Emotions Regulation of sleep-

wake cycle


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Cerebrum

Largest portion of brain Divisions

Right

Left Lobes: Frontal, parietal,

occipital, temporal,insula

Cortex: Outer surface Medulla: Center


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Basal Nuclei and Limbic System

Basal nuclei Motor function control

Limbic system Basic survival

functions as memory,

reproduction, nutrition Emotions


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Meninges

Connective tissuemembranes

Dura mater: Superficial Arachnoid mater Pia mater: Bound

tightly to brain

Spaces Subdural: Serous fluid Subarachnoid: CSF


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Meninges

Connective tissuemembranes surroundingspinal cord and brain

Dura mater Arachnoid mater Pia mater

Spaces

Epidural: Anesthesia injected Subdural: Serous fluid Subarachnoid: CSF


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Ventricles

Ventricles: Lateral ventricles (2), third ventricle, fourthventricle

Choroid plexuses produce CSF which fills ventricles andother parts of brain and spinal cord Blood-cerebrospinal fluid barrier: Substances do not pass between

cells but through due to tight junctions of blood endothelial cells


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Cerebrospinal Fluid (CSF)

Similar to serum with most of proteinsremoved

Bathes brain and spinal cord Provides a protective cushion around CNS Provides some nutrients to CNS tissues

Produced by ependymal cells


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Flow of CSF


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Brain Blood Supply

Brain Requires tremendous amount of blood Receives 15-20% of blood pumped by heart Interruption can cause unconsciousness and irreversible

brain damage High metabolic rate and dependence on constant supply

of oxygen and glucose Receives blood through arteries

Blood-Brain barrier Capillary endothelial cells along with astrocytes and

basement membrane To be considered when developing drugs


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Cranial Nerves

Indicated by Romannumerals I-XII fromanterior to posterior

May have one or more of3 functions Sensory (special or general) Somatic motor (skeletal

muscles)

Parasympathetic (regulationof glands, smooth muscles,cardiac muscle)


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Cranial Nerves

Olfactory (I) Optic (II)

Oculomotor (III) Trochlear (IV) Trigeminal (V)

Abducens (VI)

Facial (VII) Vestibulocochlear (VIII)

Glossopharyngeal (IX) Vagus (X) Accessory (XI)

Hypoglossal (XII)


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What are NERVES?

Nerves are distinct peripheral extensionsof the central nervous system (CNS).

Within the CNS (brain and spinal cord)nerve fibers are grouped together to formdistinct tracts (eg spinothalamic tract orthe dorsal lemniscal tract).

Nerve fibers are simply the axons ofvarious neurons.


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Cells of Nervous System

Neurons or nerve cells Receive stimuli and

transmit action potentials

Organization Cell body or soma Dendrites: Input Axons: Output

Neuroglia or glial cells Support and protect

neurons


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Types of Neurons

Functional classification Sensory or afferent: Action potentials toward CNS

Motor or efferent : Action potentials away from CNS Interneurons or association neurons : Within CNS from one

neuron to another

Structural classification Multipolar, bipolar, unipolar


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Morphology of NeuronsAny Neuron can be dividedup into a cell body and a setof neurites (dendrites andaxons).In terms of the position ofthe cell body relative to theneurites neurons can bedivided into three main

groups: (Pseudo)unipolar, bipolar and multipolarneurons.


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Bodian Definitions

That part of the neuron that is specialised toreceive stimuli is called the dendritic zone. That part of the neuron specialized to

conduct the stimuli is called the axoniczone.


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Neuroglia of CNS

Astrocytes Regulate extracellular brain fluid composition Promote tight junctions to form blood-brain barrier

Ependymal Cells Line brain ventricles and spinal cord central canal Help form choroid plexuses that secrete CSF


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Neuroglia of CNS

Microglia Specialized macrophages

Oligodendrocytes Form myelin sheaths if surround axon


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Neuroglia of PNS

Schwann cells or neurolemmocytes Wrap around portion of only one axon to form myelin sheath

Satellite cells Surround neuron cell bodies in ganglia, provide support and nutrients


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Peripheral Nerves

Consist of Axon bundles Schwann cells

Connective tissue Endoneurium Perineurium: Surrounds

axon groups to formfascicles

Epineurium


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Spinal Nerves


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SPINAL NERVES

31 pairs

Named & numberedaccording to region & levelof spinal cord from whichthey emerge

Roots of lower lumbar,sacral, & coccygeal spinal

nerves (i.e. cauda equina)descend at angle to reachrespective intervertebralforamina before emergingfrom vertebral column


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SPINAL NERVES Anterior (ventral) rami, except

thoracic nerves T 2-T12, formnetworks on both right & left sidesof body = called plexuses (named

by general regions they serve or

routes they follow)

Anterior rami of spinal nerves T 2-T12 do not enter into formation of

plexuses

These are calledintercostal/thoracic nerves travel directly to structures theyinnervate in intercostal spaces


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Peripheral Nervous System

Two subcategories Sensory or afferent Motor or efferent

Divisions

Somatic nervoussystem

Autonomic nervoussystem ( ANS )

Sympathetic Parasympathetic Enteric


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Spinal Cord and Spinal Nerves


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Cross Section of Spinal Cord

White matter Myelinated axons

forming nerve tracts Fissure and sulcus Three columns or

funiculi Ventral Dorsal Lateral

Gray matter Neuron cell cell bodies,

dendrites, axons

Horns Posterior (dorsal) Anterior (ventral) Lateral

Commissures Gray: Central canal White


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Cervical Plexus

C1-C4

Phrenic nerve From C3-C5 cervical and

brachial plexus Innervate diaphragm


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Brachial Plexus

C5-T1 Major nerves

Axillary Radial Musculocutaneous Ulnar

Median


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Structure General Innervation Representative Nerves

Cervical Plexus(C1-C4)

Mm and skin of neck &shoulder; diaphragm

phrenic innervatesdiaphragm

Brachial Plexus(C5-T1)

upper extremity Mm &skin

axillary,musculocutaneous,ulnar, median, radial

Lumbar Plexus (L1-L4)

lower extremity Mm &skin, perineal Mm/skin;some abdominal Mm

femoral, obturator,saphenous

Sacral Plexus(L4-S4) lower extremity Mm &skin, perineal Mm/skin sciatic, tibial, fibular,gluteal, pudendal

Intercostal/Thoracic Nerves

Intercostal & AbdominalMm, skin

Intercostal nerve branches (rami)

SPINAL NERVE PLEXUS

SUMMARY


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Nervous System Organization

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1.Nervous Sys Org - Lecture