THE NERVOUS SYSTEM

Neuron

is a nerve cell and consist of a cell body with its nucleus, two sets of processes (dendrites and an axon).

Dendrites

are several processes that extend out from the cell body, and carry impulses towards the cell body.

Axon

is a single process extending out from the cell body and may be two or three feet in length. It conveys impulses away from the cell body.

Sensory neuron

is a nerve cell that conducts impulses towards or into the spinal cord, or up the spinal cord to the brain.

Motor neuron

is a nerve cell that carries impulses from the brain down to the spinal cord, or from the cord to muscles or secreting glands, or directly from the brain to muscle or to a gland.

Synapse

is the point of contact of the axon of one nerve with the dendron of another neuron.

Endorgan

is a structure at the free end of an axon or dendron designed to pass on or pick up impulses or sensations.

receptor

is an endorgan at the outer end of a dendron of a sensory neuron that picks up sensations.

effector

is an endorgan at the distal end of an axon of a motor neuron. It may be a plate on a muscle fiber carrying impulses for contraction, or minute delicate branching fibers about the secreting cells of a gland that stimulate secretion.

reflex arc

is a complete circuit consisting of a sensory neuron ending in the spinal cord, a connecting neuron within the cord, and a motor neuron to a muscle.

reflect arc

 A sensory neuron carries a sensation to the spinal cord. A connecting neuron conveys impulses to a motor neuron. This in turn conducts it to a muscle, causing the muscle to contract.

Ganglion

is a group of nerve cell bodies outside of the spinal cord or brain.

Nucleus

is a group of cell bodies within the brain and spinal cord.

center

is a group of nerve cell bodies concerned with some specific function.

Plexus

is a network of cell processes

white matter

consists of nerve, fibers, axons and dendrites and are white in color. They form central parts of the cerebrum, but the outer parts of the spinal cord.

lies inside the cortex and consists of nerve fibers (processes) arising from or ending in the cortical cell bodies.

Gray matter

is made up of the nerve cell bodies and some processes. It appears darker than the white \n matter. It forms the outer part of the cerebrum, and surrounds the white matter here. It forms the central parts of the spinal cord, and is surrounded by the white matter.

Funiculi

are large columns of nerve fibers that pass up and down the spinal cord or brain.

Tracts

are bundles of nerve fibers, and parts of funiculi in close contact with each other that pass up or down the spinal cord.

Conductivity

is the ability to convey impulses, generated by stimuli, along the neurons. The impulse is carried in one direction - from dendrites to cell body - to axon - to synapse.

Irritability

is that property of nerves that renders them responsive to stimuli such as heat, cold, etc. •

communication and control

The function of the nervous system are

Central Nervous System

Peripheral Nervous System

The 2 divisions of the nervous system

Central Nervous System

is the part enclosed by bone. It includes the brain, within the cerebral cranium, and the spinal cord within the vertebral column.

forebrain

midbrain

hindbrain.

The brain is further divided into the

forebrain

is the large expanded mushroom-like upper part of the brain. It occupies the entire cranium except for the posterior cranial fossa. It consists of the cerebrum and diencephalon or interbrain or between brain.

Midbrain

includes two cerebral peduncles, and four small bodies, the corpora quadrigemina or colliculi.

Hindbrain

has a pons, medulla oblongata and cerebellum.

lies below the midbrain and extends down the foramen magnum where it becomes the spinal cord. It occupies the posterior cranial fossa of the skull.

Peripheral Nervous System

is that part outside of the skull and vertebral column. It includes the cranial nerves, spinal nerves and the autonomic nervous system.

brain

It occupies the entire cerebral cranium.

forebrain

large expanded mushroom-like upper part of the brain. It occupies the entire cranium except for the posterior cranial fossa. It consists of the cerebrum and diencephalon or interbrain or between brain.

Cerebrum

forms the visible part of the forebrain and is by far its larger part.

Gyri

are rounded ridges visible on the outer curved surfaces of the cerebrum.

Sulci

are shallow grooves that dip down between adjacent gyri. This arrangement of alternate ridges and grooves increases the surface area of the cerebrum.

Cerebral cortex

outer part of the cerebrum. It is composed of several layers of nerve cell bodies and the gray matter.

White matter

lies inside the cortex and consists of nerve fibers (processes) arising from or ending in the cortical cell bodies

Corpus callosum

is composed of nerve fibers that connect the two halves or hemispheres.

white fibers that pass across the midline from one hemisphere to the other below the longitudinal fissure.

composed of a broad band of white nerve fibers conveys nerve impulses from one cerebral hemisphere across the midline to the other cerebral hemisphere.

Cerebral hemispheres

right and left, are the two lateral halves of the cerebrum separated along the median plane by the longitudinal fissure.

Longitudinal fissure

Transverse fissure

Central sulcus

Lateral sulcus

Parietooccipital sulcus

Fissures and Grooves

Longitudinal fissure

is a deep groove that extends from the front to the back of the cerebrum, along the median line, and under the sagittal suture.

Transverse fissure

passes transversely across the upper limit of the posterior cranial fossa.

Central sulcus

is a deep groove that begins at the longitudinal fissure at about its midpoint.

Lateral sulcus

is a definite groove that begins on the inferior surface of each cerebral hemisphere.

Parietooccipital sulcus

It extends upwards and backwards from the inferior margin of the lateral surface of the hemisphere close to its posterior margin.

Frontal lobe

Parietal lobe

occipital lobe

Temporal lobe

central lobe

Lobes of the Cerebral Hemispheres

central lobe

* insula
* lies deep within each hemisphere, and deep to the lower part of the lateral sulcus.

Temporal lobe

lies adjacent to the temporal bone and below and behind the lateral sulcus. It occupies the middle cranial fossa.

Occipital lobe

lies in contact with the occipital bone posterior to the parietooccipital sulcus, and behind the parietal and temporal bones.

 Parietal lobe 

lies under the parietal bone, and between the central sulcus in front, and the lateral sulcus and parietooccipital sulcus behind.

Frontal lobe

lies adjacent to the frontal bone, and anterior to the central sulcus.

Association fibers

the great white nerve fibers that connects the many gyri and the lobes of one hemisphere of the cerebrum.

conduct nerve impulses from one gyrus to another, or from one lobe to another in the same hemisphere.

Corpus callosum

white fibers that pass across the midline from one hemisphere to the other below the longitudinal fissure.

Projection fibers

a group of fibers that connects the cortex of each hemisphere with parts of the brain below and the spinal cord.

convey impulses from one part of the brain in another part, or to spinal cord.

* Motor area of the cortex
* Centers for hearing and smell - temporal lobe
* Centers for taste - parietal lobe
* Visual center - is in the posterior part of the occipital lobe

Special Areas and Centers of the Cortex

Motor area of the cortex

located in front of the central sulcus in the adjacent gyrus of the frontal lobe. At the upper end of the gyrus are located centers for the muscles of the lower limb, followed by centers for the trunk, the upper limb, with the centers for the head at the lower end of the gyrus.

Diencephalon

the between brain or after brain is located between the cerebrum and the midbrain.

Thalamus

forms the lateral walls of the third ventricle

It has nuclei that are relay stations for sensory impulses from the body and lower brain. It appears to sort out sensations to be transmitted to the cerebrum.

Hypothalamus

forms the floor of the third ventricle.

It appears to have many important functions, such as regulations of secretions of the anterior and posterior lobes of the pituitary gland. It exercises some control over the autonomic nervous system. It helps regulate body temperature, and directs the feeding habits and the quantity of food eaten. It forms the hormone oxytocin and the antidiuretic hormone (vasopressin).

Midbrain

forms a small part of the brain and is less than one inch in length.

Cerebral peduncles

are visible on the ventral surface of the brain as two bulges above the pons. They consist of nerve fibers connecting the cerebrum, hindbrain and cord.

Corpora quadrigemina

cannot be seen in the intact brain as they are located in the dorsal part of the midbrain and are covered by cerebrum. They form relay stations for auditory and visual sensations.

Hindbrain

lies below the midbrain and extends down the foramen magnum where it becomes the spinal cord. It occupies the posterior cranial fossa of the skull

Pons

lies immediately below the midbrain and anteriorly forms a definite prominence with a median groove.

Medulla oblongata

lies below the pons - between it and the spinal cord. It ends at the foramen magnum where the spinal cord begins.

Cerebellum

lies posterior to the pons and upper part of the medulla oblongata. It acts as a coordinator of muscular movements, rendering them smooth and graceful rather than jerky. It is concerned with the maintenance of posture and equilibrium.

brain stem

a term that is occasionally used includes the midbrain, pons and medulla.

right lateral ventricle

left lateral ventricle

third ventricle

fourth ventricle

ventricles of the brain are four cavities that lie within it

lateral ventricles

right and left, are located in the corresponding cerebral hemisphere. Each lies below the corpus collosum, and extends from front to back, corresponding somewhat in shape to that of the hemisphere within which it lies.

Posterior horn

Central part

Anterior horn

Inferior horn

Interventricular foramen

lateral ventricles

Interventricular foramen

* foramen of monroe
* is an opening between the medial margin of a lateral ventricle and the adjacent third ventricle.

Third Ventricle

is a single cavity, lies in the midline of the diencephalon or afterbrain, between the medial margins of the thalami which form the lateral walls.

Cerebral aqueduct

* aqueduct of sylvius
* is a canal that passes between the third and fourth ventricles.

fourth ventricle

a single cavity lies in the hindbrain. The pons and upper medulla lie in front and the cerebellum lies posterior it.

Median aperture

* foremen of magendie
* is an opening between the fourth ventricle and subarachnoid space of the brain in the midline of the roof of the fourth ventricle.

Lateral Apertures

* foramen of luschka
* are the 2 openings between the fourth ventricle and subarachnoid space of the brain in the lateral parts of the roof of the fourth ventricle.

Choroid Plexuses

networks of veins in the wall of each ventricle. Special cells in these areas secrete the CSF into the ventricles

Spinal cord

about 40 to 45 cm (16 to 18 inches) in length lies within the vertebral canal, which is formed by the vertebral foramina of the vertebrae and the ligaments between their arches.

Gray Substance of the cord

composed largely of nerve cell bodies forms the inner part of the cord, an arrangement opposite to that in the cerebrum. It forms an "H" shaped figure.

Anterior horn – anterior half of the limb

Posterior horn – posterior half of the limb

Lateral horn – is a bulge on each limb of gray substance in the thoracic and upper lumbar segments.

Posterior column – contains sensory cells

Anterior column – contains the motor cells

gray substance

White Substance

 is composed of nerve fibers and surrounds the gray substance.

includes dendrites and axons and conducts nerve impulses. They are also named nerve fibers.

Anterior

posterior

2 lateral divisions.

Four large bundles of white substance

Motor tracts

are located in the anterior and lateral funiculi of the cord. Also called descending tracts.

Sensory tracts

are located for the most part in the posterior and lateral funiculi of white matter. Also called ascending tracts.

meninges

are the coverings of the brain and spinal cord.

from three coverings that enclose the brain and spinal cord for protection.

Pia mater

 is the delicate inner membrane. It is closely applied to the outer space of the brain and cord. It dips down into the sulci and fissures, and covers all gyri or convolutions.

Arachnoid

is the middle layer and overlies the pia mater. It does not dip down into the many grooves so that a space is left between it and the pia. 

Subarachnoid space

is the space between the arachnoid and pia mater. The CSF circulates in this space about the brain and around the cord.

Dura Mater

is the tough outer membrane covering the brain ad cord. This membrane consists of two layers that in most areas are adherent to each other. The outer layer forms the periosteum on the inner surface of the cranial bone.

Falx cerebri

 is the fold of dura mater that dips down into the longitudinal fissure between the right and left cerebral hemisphere.

Tentorium cerebelli

is a fold of dura mater that passes transversely across the upper end of the posterior cranial fossa in the transverse fissure. It separates the occipital lobe of the cerebrum from the upper surface of the cerebellum.

Epidural space

in the skull is the interval between the dura mater and cranial bones. In the spine it is the space between the dura mater and the vertebral canal.

Subdural space

is the interval between the arachnoid and dura mater of the brain or the spinal cord.

Arachnoid cisterns

are small cavities where the pia mater and arachnoid are more widely separated from each other than usual.

Cerebrospinal fluid

is a clear colorless fluid that is formed by cells in the choroid plexuses of all of the ventricles, and is secreted into their cavities. It also circulates in the similar space of the spinal cord. It is reabsorbed into the blood through the superior sagittal sinus within the cranium.

forms a fluid cushion that surrounds the brain and cord and provides some protection for these organs from physical trauma.

Arachnoid Granulations

are small knoblike protrusions of the arachnoid into the walls of the superior sagittal sinus. The CSF passes through these granulations into the venous sinus and blood.

Lumbar puncture

is a procedure whereby some CSF is obtained from the spinal cord.

First cranial nerve

* olfactory nerve
* the sensory nerve of smell.

Second cranial nerve

* optic nerve
* the sensory nerve of sight

Third cranial nerve

* oculomotor nerve
* a motor nerve to muscles of the eye.

Fourth cranial nerve

* trochlear nerve
* a motor nerve to superior oblique muscle of the eyeball