MODULE 15A - [Anatomy 1.0] GENERAL ORGANIZATION OF THE NERVOUS SYSTEM

• Excitable cells that are specialized for the reception of stimuli and the conduction of the nerve impulse

NEURON

• Consists essentially of a mass of cytoplasm in which a nucleus is embedded

• Bounded externally by a plasma membrane

  • Surface projects one or more processes called neurites (e.g. dendrites and axons)

CELL BODY

neurites responsible for receiving information

Dendrites

a single, long tubular neurite that conducts impulses away from the cell body

Axons

Dendrites and axons are often referred to as ______ ______

nerve fibers

• Clumps of rough endoplasmic reticulum that are found throughout the cytoplasm of the cell body

• synthesizes proteins within the cell body

Nissl Bodies (Nissl Substance)

Nissl Bodies are absent in _____ and within the _____

Axon Hillock; Axon

• A small conical elevation on the cell body that gives rise to the axon

• Region of the cell body close to the axon

Axon Hillock

• Short processes of the cell body

• Often branch profusely to increase the surface area of the reception of axons from other neurons.

• Cytoplasm resembles that of the cell body

• Function: receive nerve impulse toward the cell body.

DENDRITES

• Longest process of the cell body

• Arises from axon hillock

• branches profusely before their termination

• Function: always conducts impulses away from the cell

  body

  • Except for axons of unipolar neurons which may also carry an impulse toward the body

AXON

• Outer covering of the axon

• Multi-layered phospholipid

• Function: increases the conduction velocity of the nerve impulses along the axon

Myelin Sheath

Enumerate the morphological classification of neurons based on the number of its neurites

• Unipolar

• Bipolar

• Multipolar

• Cell body has a single neurite (or axon) that branches within a short distance from the cell body

• One end is preceding to some peripheral structure and the other end enters the central nervous system (CNS)

• The fine terminal branches at the peripheral end of the axon are often referred to as the dendrites.

• Single neurite divides a short distance from cell body

• Location: Posterior root ganglion

UNIPOLAR NEURONS

• Have an elongated cell body

• From each end emerges a single neurite

• A total of 2 neurites, which are both axons, with the fine terminal branches at the peripheral end of one of the axons, also being referred to as dendrites

• Single neurite emerges from either end of cell body

• Location: Retina, sensory cochlea, and vestibular ganglia

BIPOLAR NEURONS

• Most common kind

• Have several neurites arising from the cell body, which are mostly dendrites and one long axon

• Many dendrites and one long axon

• Location: Fiber tracts of the brain and spinal cord, peripheral nerves, and motor cells of spinal cord

MULTIPOLAR NEURONS

Enumerate the morphological classification of neurons based on the number of its size

• Golgi Type I

• Golgi Type II

• Size: Medium to large

• Arrangement of Neurites: Single long axon

• Location: Fiber tracts of brain and spinal cord, peripheral nerves, and motor cells of spinal cord

Golgi Type I

• Size: Small to Medium

• Arrangement of Neurites: Short axon that often resemble its dendrites

• Location: Cerebral and cerebellar cortex

Golgi Type II

Enumerate the types of Neuroglia in the CNS and PNS

• CNS

  • Ependymal Cells

  • Oligodendrocytes

  • Astrocytes

  • Microglia

• PNS

  • Satelite Cells

  • Schwann Cells

• Line the fluid filled cavities of the brain and the central

  canal of the spinal cord.

• Made up of:

  • Ependymocytes

  • Choroidal epithelial cells

EPENDYMAL CELLS

Assist in the circulation of the cerebrospinal fluid (CSF) within the cavities by the movements of their cilia

Ependymocytes

Involved in the production and secretion of the CSF from the choroid plexuses

Choroidal epithelial cells

• Phagocytes that arise from macrophages

• Aid in removal of damaged neurons and infectious

  agents within the CNS

MICROGLIAL CELLS

• Further divided into 4 cell types

• Two are found within the CNS:

  • Astrocytes and Oligodendrocytes

• The other two are found in the peripheral nervous system (PNS):

  • Schwann cells and Satellite (or capsular) cells

MACROGLIAL CELLS

• Most numerous cells in the CNS

• Have small cell bodies with branching processes

  that extend in all directions.

• Has two types

  • Fibrous

  • Protoplasmic

• Contains Perivascular Feet

• Functions:

  • Serve as a supporting framework for neurons and nerve fibers

  • Serve as “electrical insulators” between neurons → prevent axon terminals from influencing neighboring and unrelated neurons

• Serve as phagocytes by taking up degenerating

  synaptic axon terminals.

Astrocytes

• Expanded processes of astrocytes on blood vessels

• Form an almost complete covering on the external surface of the capillaries

• Important for the blood-brain barrier

Perivascular feet

selectively allow and block the passage of materials from the blood to the CNS.

blood-brain barrier

Mechanisms of how astrocytes serves as electrical insulators between neurons

• Covering the synaptic contacts between neurons; forming barriers

• Taking up neurotransmitter substances

• Controlling the electrolyte balance of the

  CNS

Process where astrocytes fill in the spaces previously occupied by the neurons following the death of neurons due to disease,

replacement gliosis

Forms the myelin sheath of axons of neurons in the CNS

Oligodendrocytes

Provides axons with an insulating coat and greatly increases the speed of nerve conduction

myelin sheath

How many nerve fibers (axons) can 1 oligodendrocyte myelinate

60 nerve fibers (axons)

Produce myelin for the nerves of the

Schwann Cells

How many nerve fibers (axons) can 1 Schwann cell myelinate

1 segment of an axon

Areas of interruption or gaps along the myelin sheath that covers the axons of neurons

• Essential in the speed and timing of delivery of impulses from 1 neuron to another

Nodes of Ranvier

Glial cells that envelope the peripheral and central processes of each neuron from the autonomic ganglia

Satellite Cells (Capsular Cells)

Tumors of Neuroglia are also called?

Gliomas

Tumors of Neuroglia account for _____ to _____ of intracranial tumors and are highly invasive except for _____

40% to 50% ; ependymomas

Most common tumors of neuroglia

Tumors of astrocytes (astrocytomas and glioblastomas)

The brain and spinal cord are surrounded by supporting membranes called _____

Meninges

Enumerate the meninges from the outermost to the innermost membrane

Dura mater → Arachnoid mater → Pia mater

PAD = Padding of the Brains

• Outermost meninx

• A strong fibrous membrane that consists of two layers:

  • Endosteal layer

  • Meningeal layer

DURA MATER

a periosteum surrounding the inner surface of the cranial bones

Endosteal layer (Dura Mater)

Forms 4 folds within the cranium, which are the Falx Cerebri, Falx Cerebelli, Tentorium Cerebelli, and Diaphragma Sellae

Meningeal layer (Dura Mater)

Enumerate the folds of the meningeal layers of the Dura Mater

• Falx Cerebri

• Falx Cerebelli

• Tentorium Cerebelli

• Diaphragma Sellae

Located at the midline between the two cerebral hemispheres

Falx Cerebri

Separates the two cerebellar hemispheres and lies inferior to the tentorium cerebelli

Falx Cerebelli

Forms a roof over the posterior cranial fossa, shielding the superior surface of the cerebellum, and supports the occipital lobes of the cerebral hemispheres

Tentorium Cerebelli

• Small circular fold of dura that forms the roof of the sella turcica, protecting the superior surface of the pituitary gland.

• It has a tiny opening in the middle segment that allows the passage of the stalk of the pituitary gland.

Diaphragma Sellae

• A thin, delicate membrane that loosely surrounds the

  brain and the spinal cord.

• Lies between the dura mater and the pia mater.

ARACHNOID MATER

• A membrane that closely invests the brain, covering

  the gyri and descending into the deepest sulci.

• Highly vascular and contains the cerebral arteries

  entering the substance of the brain and spinal cord.

PIA MATER

Enumerate the Meningeal spaces

• EPIDURAL SPACE

• SUBDURAL SPACE

• SUBARACHNOID SPACE

A potential space located between the bone and the dura mater.

• Potential spaces that may be filled with blood due to traumatic tearing of blood vessels located in these spaces.

EPIDURAL SPACE

The presence of blood inside the epidural space

Epidural Hemorrhage

Potential space located between the dura and the arachnoid.

• Potential spaces that may be filled with blood due to traumatic tearing of blood vessels located in these spaces.

SUBDURAL SPACE

The presence of blood inside the Subdural space

Subdural hemorrhage

• Between the arachnoid and the pia mater

• Contains CSF and communicates with the ventricles of the brain where CSF is formed.

SUBARACHNOID SPACE

The presence of blood inside the subarachnoid space

Subarachnoid hemorrhage

• Consists of the brain and spinal cord

• Main centers for correlation and integration of nervous information

• Covered by meninges and suspended in the CSF

• Protected by the skull and vertebral column

• Interior of the CNS is organized into gray and white

  matter

CENTRAL NERVOUS SYSTEM

Consists of nerve cells (neural body) embedded in neuroglia, thus the gray color

GRAY MATTER

• Consists of nerve fibers (neural axons and dendrites) embedded in neuroglia

• The white color is due to the presence of lipid material in the myelin sheath

WHITE MATTER

• Lies in the cranial cavity and is continuous with the spinal cord through the foramen magnum

• It is conventionally divided into three major divisions

BRAIN

Enumerate the three divisions of the brain

• Forebrain

• Midbrain

• Hindbrain

Enumerate the two parts of the forebrain

• Cerebrum

• Diencephalon

Enumerate the parts of the Hindbrain

• Pons

• Medulla Oblongata

• Cerebellum

Enumerate the parts of the Brainstem (Note this is different from the three major divisions of the brain)

• Midbrain

• Pons

• Medulla Oblongata

• The largest part of the brain

• Consists of two cerebral hemispheres (left and right)

• Each hemisphere extends from the frontal to the occipital bones in the skull, superior to the anterior and middle cranial fossae, and posteriorly it lies above the tentorium cerebelli.

• The two cerebral hemispheres are separated by a deep

  medial longitudinal fissure, into which projects the falx cerebri.

CEREBRUM

The white matter that connects the two hemispheres of the brain

corpus callosum

• Surface layer of the cerebral hemispheres

• Composed of gray matter.

• It has folds called gyri or gyrus

• Several large sulci are used to subdivide the cerebral hemispheres into lobes, which are named from the bones under which they lie.

• Part of the cerebrum

Cortex

• This greatly increases the surface area of the cortex.

• Part of the cerebrum

gyri or gyrus

• The gyri or gyrus are separated by folds called

• Part of the cerebrum

Sulcus or sulci

• Consist of white matter which contains several masses of gray matter, called basal nuclei or ganglia.

• Part of the cerebrum

Inner Core of the Brain

• Fan shaped collection of nerve fibers passing in the

  white matter to and from the cerebral cortex to the brain stem.

• Converges on the basal nuclei

• Part of the cerebrum

Corona Radiata

• Convergence of corona radiata on the basal nuclei which passes in between the basal nuclei

• Part of the cerebrum

Internal Capsule

• Tailed nucleus on the medial side of the internal capsule

• Part of the cerebrum

Caudate Nucleus

• Lens-shaped nucleus on the lateral side of the internal capsule

• Part of the cerebrum

Lentiform Nucleus

• The cavities within each cerebral hemisphere (anterior horn and inferior horn).

• Part of the cerebrum

Lateral Ventricles

Lies below the cerebral hemispheres and consists of a dorsal thalamus and a ventral hypothalamus.

DIENCEPHALON

• A large egg-shaped mass of gray matter that lies on either side of the third ventricle.

• Part of the Diencephalon

Thalamus

• Forms the lower part of the lateral wall and floor of

  the third ventricle.

• Part of the Diencephalon

Hypothalamus

A narrow part of the brain that connects the forebrain to the hindbrain.

MIDBRAIN

• narrow cavity which connects the 3rd and the 4th ventricles.

• Part of the Midbrain

cerebral aqueduct

• Part of the hindbrain

• Situated between the midbrain and the medulla oblongata and anterior to the cerebellum.

• Its name means “bridge”

  • Comes from the large number of transverse fibers that connect the two cerebellar hemispheres on its anterior aspect.

PONS

• Conical in shape

• Connects the pons to the spinal cord

  • Conduit for ascending and descending nerve

    fibers

MEDULLA OBLONGATA

• Lies within the posterior cranial fossa, posterior to the pons and medulla oblongata.

• It consists of two hemispheres

• Also known as the “little brain”

• It also has a cortex composed of gray matter and an inner core of white matter, with several masses of gray matter or nuclei.

CEREBELLUM

The two hemispheres of the cerebellum is connected by a median portion called

vermis

The medulla pons and cerebellum surround the cavity filled with cerebrospinal fluid called the

4th ventricle

• Connected superiorly to the 3rd ventricle through the

  cerebral aqueduct

• Inferiorly, it is continuous with the central canal of the spinal cord.

FOURTH VENTRICLE

Parts of the brain seen in MRI T1 weighted sagittal section of the head

*No Answer*

• Lies below the brain

• Situated within the vertebral canal and is also surrounded by three meninges, the dura, arachnoid, and pia mater.

SPINAL CORD

The Spinal Cord begins superiorly at the _____ below the _____ and terminates inferiorly in the _____ into the _____.

Foramen Magnum; Medulla Oblongata; Lumbar Region; Conus Medullaris

Prolongation of the pia mater that attaches the conus medullaris to the back of the coccyx.

Phylum terminal

Unlike the brain's structure, the spinal cord has an inner core of _____ and an outer covering of _____.

gray matter; white matter

seen as an H-shaped pillar with anterior and posterior gray horns or columns.

GRAY MATTER

• The Anterior and Posterior gray horn of the gray matter of the spinal cord is connected by

• This part also contains the central canal

Gray commissure

• Divided into anterior, lateral, and posterior columns

WHITE MATTER

Along the entire length of the spinal cord are attached _____ of spinal nerves by the anterior roots and posterior roots.

31 pairs

• Efferent/Motor fibers

• Carry nerve impulses away from the CNS

Anterior Roots

• Afferent/Sensory fibers

• Carry nerve impulses toward the CNS

• Has a posterior root ganglion

  • A swelling that contains cell bodies of sensory nerve fibers.

Posterior Roots

Anterior and Posterior roots unite to form a _____ that exits through its respective ____.

spinal nerve; intervertebral foramen