Lake Michigan College Human Anatomy 205

Nervous System and Links

• Monitor changes inside and outside the body - sensory input
• Integration [interprets sensory input - provides response with effector organs]
• Internal communication is accomplished with both the nervous & endocrine system

• See discussion of Divisions of the Nervous system
• CNS (Central Nervous System is brain & spinal cord)
• PNS (Peripheral Nervous System is 12 cranial & 31 spinal nerves and their branches)
• Sensory and Motor Systems
  • Sensory carries impulses to CNS from sense receptors
  • Motor carries impulses from CNS to effectors (muscle).
• Somatic and Autonomic [sympathetic & parasympathetic] systems
  • See a comparison of Somatic and Autonomic Nervous System
  • Go to Autonomic Nervous System
• Ganglion & nerve (PNS) vs Nucleus & tract (CNS) View illustration

Nervous Tissue 2 classes of cells; Neurons [carry action potential] Neuroglia [supportive]

See Cells of the Nervous System

Neuroglia are support cells of the nervous system
• Neurolemmocytes (Schwann cells) produce myelin sheath in PNS
• Oligodendrocyte produce myelin sheath in CNS
• See animated Myelination
• Astrocytes contact with brain capillaries, forms barrier to large blood molecules
• Microglia are smallest brain glia cell, migratory and phagocytic
Neuron is cell that conducts impulse (action potential)
• Neuron Anatomy [Cell body, nucleus] [axon and dendrite] [neurilemma]
• Myelin sheath on axons and dendrites in PNS produced by neuroglia (neurolemmocytes)
• Neuron Classification by function [Motor] [Sensory] [Interneuron]
• Neuron Classification by structure [Unipolar] [Bipolar] [Multipolar]
Neuron Physiology
• Nerve Impulse
  • Resting potential: axon's membrane is electrically polar. [+ outside (Na⁺); - inside (organic ions)] also K⁺ within axon
  • Stimulus of membrane opens Na⁺ channels then K⁺ channels
  • Action potential - wave of depolartization (Na⁺ in) and repolarization K⁺ out
• See Propagation of Action Potential animation
• Check interactive action potential
• Neuron impulse is "all of none"
• Synapse is a chemical junction between neurons
  • Introduction to presynaptic & postsynaptic neurons (Flash animation)
  • Axon side releases neurotransmitter (NT)
  • Dendrite or cell body side has neurotransmitter (NT) receptors
  • See animated interactive synapse

• Brain has 3 main parts [Cerebrum] [Cerebellum] [Brain Stem]
• Gray matter = cortex or nuclei [unmyelinated neuron cell bodies]
• White matter = tracts [myelinated neuron fibers]
• Links to excellent brain anatomy graphics at university sites
  • The Plastinated Brain at University of Vienna
  • The Whole Brain Atlas at Harvard and Brain Atlas at University of Washington.
  • The Top 100 Brain Structures at Harvard's Whole Brain Atlas
  • Tour the 3D Brain Anatomy at PBS
• Development of CNS
  • Neural plate indents along midline to form neural groove
  • Neural tube then forms from neural groove
  • Anterior end of neural tube forms 3 brain regions [forebrain, midbrain, hindbrain]
  • Forebrain and Hindbrain each divide and this results in 5 brain divisions

  Five brain divisions from neural tube Telencephalon [right and left cerebrum] Forebrain Cavity = lateral ventricles Cerebral nuclei and Cortex Diencephalon Forebrain & brainstem Thalamus and hypothalamus - See Sagittal View Cavity = Ventricle III Pineal and pituitary gland Mesencephalon - See Sagittal View Midbrain & brainstem Coropora quadrigemina [superior and inferior colliculi] Cerebral peduncles Cavity = Cerebral aqueduct connecting ventricles III and IV Metencephalon [ Cerebellum and pons] Cerebellum has three lobes [two hemispheres and medial vermis] Gray matter in convoluted cortex White matter in central branching configuation termed arbor vitae Cerebellum coordinates complex voluntary muscular movement hindbrain & brainstem Cavity = Ventricle IV Myelencephalon [medulla tracts and nuclei] - See Sagittal View hindbrain & brainstem Cavity = Ventricle IV

  Click here to view human brain Click brain above to view closeup of interactive labeled model

• Structure of the Cerebrum
  • Right and left cerebral hemispheres separated by longitudinal fissure
  • Cerebral cortex is convoluted surface layer of gray matter.
    • surface folds are gyri
    • surface grooves are sulci
  • The right & left hemispheres connected by corpus callosum
  • Each hemisphere is subdivided into Lobes [frontal, parietal, temporal, and occipital ]
  • Central sulcus divides frontal from parietal lobes [Pre-and postcentral gyrus]
  • Cerebral nuclei are deep, internal masses of gray matter
    1. Basal nuclei (ganglia) controls voluntary motor activity
       • Corpus striatum = caudate nucleus + putamen + globus pallidus
       • see Corpus Striatum (Cerebral nuclei) on lab model
       • Lentiform nucleus = putamen + globus pallidus
       • Caudate nucleus (Lateral view)
       • Cerebral nuclei motor circuit

         Cerebral cortex 1 →	caudate nucleus + putamen 2 →	globus pallidus + substantia nigra 3 ↓
         	motor cortex of cerebrum5 ←	← thalamus 4 ←

    2. Substantia nigra (located in midbrain) is involved in motor control circuit
    3. Amygdaloid nucleus (amygdala) part of limbic system functions in emotions
  • Voluntary muscle coordination involves complex circuits between frontal cortex, cerebral nuclei, substantia nigra and cerebellum
  • Limbic System makes up emotional nervous system
    • Circuit includes Cingulate gyrus, hypothalamus, fornix, amygdala and hippocampus
    • See image map with pop_up key of components of Limbic Circuit
    • Though to initiate fear and rage
  • White matter is myelinated bundles of neuron fibers termed tracts
  • Olfactory bulb and tract
    • See Brain, Inferior View * See Interactive Closeup Inferior View
    • Olfactory tracts to ANS and limbic system
• Meninges are 3 layers of connective tissue coverings of CNS [ see diagram]
  • Dura mater is thick outer layer [see sheep brain]
  • Arachnoid is the middle layer
  • Subarachoid space contains CSF
  • Pia mater is the inner layer
• Ventricles & Subarachnoid space contain CSF (Cerebrospinal Fluid)
  • see Interactive Lab Model of Ventricles
  • Cast model of ventricles of the brain
  • Lateral ventricles in cerebral hemispheres
  • See lateral venticles in dissected virtual brain
  • Ventricle III in thalamus & ventricle IV in hind brain
  • Cerebral aqueduct connects ventricle III and IV
  • CSF is continuously filtered into ventricles at the choroid plexuses
    • A choroid plexuses is located in the walls of the ventricles
    • CSF enters the subarachnoid space through holes in the roof of the 4th ventricle
    • Moves to the superior, medial border of cerebrum to be absorped into venous blood at arachnoid villi
  • See cerebrospinal fluid circulation tutorial
• Spinal cord
  • Cervical and lumbar enlargments
  • Inferior end [conus medularis, cauda equina, and filum terminale
  • Cross section slide and Cross section diagram [Model with spinal nerves Interactive]
  • Lab model [gray matter - posterior horns; anterior horns] [white matter - tracts]
• Components of the Reflex Arc
  • Receptor generates impulse conducted by sensory neuron
  • Sensory neuron enters CNS through posterior root of spinal cord
  • Interneuron in gray matter of spinal cord communicates between sensory and motor neuron
  • Motor neuron leaves spinal cord via anterior root to muscle
  • Spinal reflex animation see diagram of components of reflex arc

• Nervous System Model [Cranial nerves V & X; rami of spinal nerves]
• PNS [Femoral nerve] [Sciatic nerve] [Cranial nerves I, II, VIII in Cranial cavity]
• Brain Models [Superior View] [Inferior View][Lateral View] [Sagittal View]
• Unlabeled Brain Models [Cerebrum Superior View] [Sagittal View] [Superior half cerebrum removed]
• Close-up of Brain Models [Inferior View region of optic chiasma]
• Interactive Brain Model Close-ups [Ventricles] [Inferior View - olfactory bulb to pons] [ brain stem sagittal section]
• Brain Model Parts [Cerebral nuclei (Corpus Striatum)] [hippocampus]
• Human Brain [Sagittal View]
• Sheep Brain [Dura mater] [Lateral View] [Sagittal View] [Dissection for hippocampus & thalamus]
• Link to a sheep brain dissection video
• Spinal Cord Cross Section Model [Gray & white matter] [with spinal nerves] [Interactive with spinal nerves]
• Lumbar/Sacral Spine Model [Cauda equina]
• PNS Model [Plexuses and peripherial nerves of arm] [Peripherial nerves of leg]

• Nerves [myelinated neuron fibers] and Ganglia [unmyelinated neuron cell bodies]
• Twelve pair of Cranial Nerves and more on cranial nerves
• For each cranial nerve know, number, name and class of neuron fiber it carries
  • I Olfactory, II Optic, III Oculomotor
  • IV Trochlear, V Trigeminal, VI Abducens
  • VII Facial, VIII Vestibulocochlear, [see inner ear model]
  • IX Glossopharyngeal, X Vagus,
  • XI Accessory, XII Hypoglossal
  • Sensory cranial nerves [I, II , VIII]
  • Primarily motor (to muscles) cranial nerves [III, IV, VI, XI, XII]
  • Both sensory and motor cranial nerves [V, VII, IX, X]
• Thirty-one pair of Spinal Nerves [Dorsal and Ventral Roots] [Dorsal and Ventral Rami]
• Nerve Plexuses are formed from unions of ventral rami of spinal nerves.
• There are four plexuses of spinal nerves [Cervical] [Brachial] [Lumbar] [Sacral]
• See the diagram of the components of the reflex arc

• Innervates smooth muscle, cardiac muscle, and exocrine glands
• Two divisions [Sympathetic (SNS) & Parasympathetic (PSNS)] are mostly antagonistic in homeostatic action (sometimes cooperative interaction - sexual activity)
  1. Throracolumbar division (SNS) [Sympathetic] [see diagram]
  2. Craniosacral division (PSNS)[Parasympathetic]
• Transmission of ANS signal over two motor neurons with ganglion between
  • Preganglionic fiber myelinated; postganglionic fiber unmyelinated
  • Compare with anatomy of somatic motor
  • ANS preganglionic fiber from CNS, synapses in ganglion - neurotransmitter (NT) is Acetylcholine (ACh)
  • Autonomic ganglia comparison
    • Sympathetic preganlionic fiber ends at sympathetic ganglia (runs in sympathetic chain - paravertebral ganglia)
    • Some sympathetic preganlion fibers bypass paravertebral ganglia and synapse in collateral ganglia
    • Parasympathetic preganlionic fiber synapse at terminal ganglia located near effector organ.
  • ANS postganglionic fiber axon releases Neurotransmitter (NT) at effector organ (inhibitory or excitatory response dependent on NT receptor)
    • Fiber longer in sympathetic and releases NT, norepinephrine (NE) on organ
    • Fiber shorter in parasympathetic and releases NT, acetylcholine (ACh) on effector organ
• See a comparison of Somatic and Autonomic Nervous System
• Sympathetic effects
  • Sympathetic preganglionic fiber may excite (or inhibit) many postganglionic neurons...sometimes as many as several thousand
  • Mass activation - divergence and convergence cause SNS to be activated as unit
  • Adrenal medulla secrets NE and E when stimulated by SNS preganglionic neuron
• Parasympathetic effects
  • PSNS normally not activated as unit
  • More relaxing effects [muscles, heart rate]
  • See PSNS example: pathway to iris of eye
• NT and receptors
  • NE activated receptors [2 types]
    1. alpha adrenergic receptor [α₁, α₂ subtypes] responds to both NE and epinephrine
    2. beta adrenergic receptor [β₁, β₂, and β₃ subtypes] responds mainly to norepinephrine
  • ACh activated receptors: muscarinic (ANS) and nicotinic (somatic)
• Actions of the ANS
• Hypothalamus sensory input from many interoceptors and motor output to autonomic centers of brain (medulla)
• See list of ANS terms to know]

• Corticospinal (Pyramidal) Pathway
  1. 1st neuron from frontal lobe cortex, crossover in medulla, descends spinal cord to level of exit.
  2. Interneuron from posterior horn to anterior horn
  3. Motor neuron exits via anterior root of spinal cord to muscle
• Spinothalamic Pathway [pain and temperature]
  1. 1st neuron from skin receptor, enters ventral root of spinal cord to posterior horn
  2. 2nd neuron crosses over spinal cord, ascends to thalamus
  3. 3rd neuron trom thalamus to postcentral gyrus of parietal lobe

• Crossword on Introduction to Nervous System * * Brain Structures * * ANS * * Limbic System
• Try WebAnatomy from the University of Minnesota
  • Quizzes [brain 1 ] [brain 2 ] [ spinal nerves ]
  • Games:[ Meninges] [ Spinal cord] [ Brain] [ Cranial nerves] [ Spinal nerves]
• Label parts of the limbic system
• Coronal section quiz [cerebral nuclei, hippocampus, mamillary bodies]
• Cranial Nerve Quizzer

Dynamic Human at McGraw-Hill

Human Anatomy Online

Etymology of Medical Terms

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Revised February 23, 2007
© 1998-2007 Lake Michigan College
Comments to: camelet@lakemichigancollege.edu