Processes that carry impulses from the neuron cell body to another neuron or effector are called

Medical Terminology for Cancer

Functions of the Nervous System
About Neurons
Nerves, Neuroglia, and Ganglia
The Spinal Cord
The Brian
The Sensory Systems
The Autonomic Nervous system [ANS]
Roots, suffixes, and prefixes
Cancer Focus
Related Abbreviations and Acronyms
Further Resources

Functions of the Nervous System

The complex activities of the body are controlled jointly by the Endocrine and the Nervous systems. As opposed to the Endocrine system the Nervous system has a more or less instant effect on the body via a complex network of nerves and control centres. The Central Nervous System [CNS] includes the brain and spinal cord, while Peripheral Nervous System [PNS] includes nerves connected to the spinal cord. The nervous system can be further divided into sub-systems, all of which are composed of neurons and connective tissue:

About Neurons

Neurons are specialised cells of the nervous system, they vary greatly in appearance and length, but contain a similar structure:

Axons are long nerve processes which carry nerve impulses from the Soma to other neurons, they vary in length but can become almost as long as half of the human body.
The soma [body] of the neuron contains the nucleus which acts as the cell's control centre, these contain many small neurofibrils which project from the nucleus into the dendrites.
Dendrites are short, thick processes which branch out of the soma in a tree like manor. They conduct nerve impulses to the soma.

The three categories of neurons:

Afferent [Sensory] Neurons have the dendrites connected to receptors such as the eyes, ears etc. These receptors change the information they receive into electrical impulses that are transmitted to other neurons. In sensory neurons the axons are connected to other neurons.
Efferent [Motor] Neurons have the dendrites connected to other neurons, the axons are connected to effectors. Effectors are either glands or a muscle cell that is the receiving end of the nerve impulse. The nerve, when excited will cause the effector to react [move, contract, or secrete etc].
Internuncial Neurons have both the dendrites and the axons are connected to other neurons. They are sometimes referred to as connector neurons. Internuncial neurons are found throughout the body, but especially in the spinal cord and brain.

Properties and characteristics of Neurons:

Normally the electrical impulses [messages] travel through a neuron in only one direction.
The axon may be surrounded by a 'coat' of lipids [fats] and proteins known as the myelin sheath which acts as an insulator.
Neurons are specialist cells that have lost the ability to reproduce themselves. Once the soma of a neuron has died the entire neuron dies, and can never be replaced.
Repair of damaged neurons only occurs in myelinated neurons.
white matter are coloured by myelin, consisting of many neurons supported by neuroglia.
grey matter is soma and dendrites or bundles of unmyelinated axons and neuralgia.

Nerves, Neuroglia, and Ganglia

A nerve is a bundle of fibres [axons and/or dendrites] outside the CNS.

Neuroglia are cells of the nervous system that help protect and support it.

Ganglia are groups of nerve cell bodies lying outside the CNS.

The Spinal Cord

A spinal tract is a bundle of fibres in the CNS that travel long distances up or down the spinal cord. Ascending tracts carry impulses up the cord to the brain, while descending tracts carry impulses down the cord from the brain. Tracts run along the spinal canal inside the protective spinal column, conveying sensory and motor [movement ] information to and from the brain. Spinal meninges are tough tubes of tissue which protect the cord.

The Brian

The brain is highly complex, it contains about 1000 billion neurons, and weighs about 3 lbs in adults.

There are four main areas of the brain:

The brain stem is at the base of the brain where it joins the spinal chord [contains the medulla, pons, and mid brain]
The diencephalon is above the brain stem [contains the thalamus and hypothalamus]
The cerebrum is above the diencephalon and forms the majority of the brain
The cerebellum is the lower back of the brain

The brain has two hemispheres , there are functional differences, for example the left had side of the brain controls the right hand side of the body and visa versa [lateralisation].

Neurotransmitters are substances which excite or inhibit the neurons of the brain, facilitating communication between brain cells. These include endorphins, neuropeptides.

Cerebrospinal fluid circulates around the brain and spinal tracts to provide protection in addition to that provided by the meninges and protective bones of the spine and skull. A lumbar puncture [spinal tap] is where a needle is placed between the vertebra in the lower back. A sample of cerebrospinal fluid might be taken to see if cancerous cells have entered the CNS, or chemotherapy might be administrated to prevent or combat CNS involvement.

The Sensory Systems

A receptor or sense organ picks up stimulus and converts it into a nerve impulse. This impulse is then conducted along a neural pathway to the brain, where the signal is converted into a sensation. There are various receptors:

Cutaneous [skin] senses. The skin contains specialist receptors for touch, pressure, vibration, hot, cold, and pain.
Proprioceptive [muscle] sensations inform us of the activities and current posture of the muscles.
Integrative sensations are not well defined but include memory, sleep, emotions etc.
Olfactory sensations [smell]. Olfactory neurons have dendrites that are connected to fine hairs in the nose that react to odours.
Gustatory sensations [taste] there are about 2000 taste buds, mostly on the tongue and a few in the throat. Taste buds contain gustatory cells which contain sensitive hair like processes.
Ophthalmic sensations [sight]. The retina of the eye converts light into nerve impulses which are transmitted to the optic nerve. Retinoblastoma is a rare tumour in the cells of the retina.
Auditory senses [hearing]. Sound waves cause fine hairs in the inner ear to vibrate generating nerve impulses.
Equilibrium [sense of balance] the ear also contains receptors that give a sense of static equilibrium [position of the head] and dynamic equilibrium [sudden movements].

The Autonomic Nervous system [ANS]

The nerves of the ANS activate the involuntary smooth muscles, cardiac muscles, and some glands.

Roots, suffixes, and prefixes

Most medical terms are comprised of a root word plus a suffix [word ending] and/or a prefix [beginning of the word]. Here are some examples related to the Nervous System. For more details see Chapter 4: Understanding the Components of Medical Terminology

component	meaning	example
ASTRO-	star	astrocyte = star shaped brain cell
CRANI-	skull	cranial radiation = radiation to the head
CEPHAL-	head	encephal = the brain, en[in] cephal [the head]
MENING-	membrane	meningitis = inflammation of the membranes of the spinal chord
NEUR-	nerve	neuroblast = an immature nerve cell
VENTRICULO-	cavity	ventricles are small cavities in the brain & spinal cord. Ventriculscopy = examination of ventricles
-MALACIA	softening	neuromalacia = morbid softening of the nerves
-GRAM	record	electroencephalogram [EEG] = brain scan

Cancer Focus

Overview of CNS TumoursChildhood CNS TumoursChildhood Brain tumours are the second most common type of childhood cancer. They are however a diverse group of different types of tumours. Classification of brain tumours is based on both histopathology and location in the brain. For example, undifferentiated neuroectodermal tumours of the cerebellum are referred to as medulloblastomas, while tumours with similar histology in the pineal region would be diagnosed as pineoblastomas. Patients may present with headaches, drowsiness, weakness, or vomiting caused by the pressure inside the skull caused by the growing tumour.

Medulloblastoma is nearly always found in children or young adults, 80% are found in children aged under 15. It can spread from the medulla [part of the brain stem] to the spine or to other parts of the body. Prognosis will depend on the child's age, how much of the tumour remains following surgery, and whether the cancer has metastasised.

Cerebellar astrocytoma arise in brain cells called astrocytes. Cerebellar astrocytoma is usually low grade [slow growing and non metastatic cells], while Cerebral astrocytoma can be malignant.

Brainstem gliomas are tumours arising in the mid brain, pons or medulla. They may grow rapidly or slowly, depending on the grade of the tumour, but overall have a less favourable prognosis compared to other tumours such as Cerebellar astrocytoma.

Other brain tumours include: Primitive neuroectodermal tumour [PNET], craniopharyngioma, intracranial germ cell tumour, pineal parenchymal tumour, and optic tract glioma.

Internet Resources for Childhood Brain TumoursAdult CNS Tumours Internet Resources for Brain TumoursCancers of the EyeRetinoblastomaRetinoblastoma is a rare tumour of the eye which develops in the cells of the retina, most patients are under 5 years old. Sometimes only one eye is affected [unilateral-retinoblastoma ], but in about two fifths of patients both eyes have the disease [bilateral-retinoblastoma ]. Some cases are known to be hereditary.

Internet Resources for Retinoblastoma

Intraocular MelanomaIntraocular melanoma is a rare cancer, in which malignant cells are found in the uvea [this is the part of the eye which contains the iris and other tissues]. The uvea contains melanocytes which are cells that contain colour, intraocular melanoma occurs when these cells become cancerous.

Internet Resources for IntraOcular Melanoma

NeuroblastomaNeuroblastoma occurs most often in babies, very young children. It is a disease in which cancer cells are found in certain nerve cells in the body, it originates in the adrenal medulla or other sites of sympathetic nervous system tissue. The most common site is the abdomen, either in the adrenal glands or around the spinal cord. The majority of patients present with metastatic disease. Age and stage are the main prognostic factors. Patients aged under one year at diagnosis have a more favourable prognosis. Stage 4S are a special group of patients aged under one year whose neuroblastoma may undergo spontaneous regression [tumour disappears without treatment]. Also patients aged under one a higher proportion of low stage patients compared to older patients. There is an excess of males compared to females, there are a higher proportion of males in patients with less favourable sites and stage.

Internet Resources for Neuroblastoma

Related Abbreviations and Acronyms

ABTA	American Brain Tumour Association
BAER	Brainstem Auditory Evoked Responce
CNS	Central nervous system - the brain and spine
CSF	Cerebro spinal fluid
EANO	European Association for NeuroOncology
EEG	Electroencephalogram - brain scan
INFA	International Neurofibromatosis Association
INSS	International Neuroblastoma Staging System
LP	Lumbar puncture
NNFF	National Neurofibromatosis Foundation [USA]
NSE	Neuron-Specific Enolase - a neural marker
PNET	Primitive neuroectodermal tumour Context: CNS tumours
PNS	Peripheral nervous system - nervous system outside the brain and spine.

Further Resources [3 links]

Nervous System

SEER, National Cancer Institute
Part of a SEER training module for cancer registry staff.

Nervous System - Self Test questions

WebAnatomy, University of Minnesota
Test your anatomy knowledge with these interactive questions. Includes different question types and answers.

The Nervous System

Paul Andersen
Paul Andersen begins this podcast with a discussion of brain lateralization and gives a brief demonstration of tests that were performed on split-brain individuals. He then discusses the major parts of a neuron and explains how action potentials are generated using voltage-gated ion channels. He explains how neurotransmitters transmit messages across a synapse and how these messages can be either inhibitory or excitatory.

This guide by Simon Cotterill

First created 4th March 1996
Last modified: 1st February 2014

What process carries impulses towards the cell body?

Dendrites are extensions, or processes, of the cytoplasm that carry impulses to the cell body. An extension or process called an axon carries impulses away from the cell body.

What are the neuron processes that normally carry impulses away from the cell body?

Typical neurons have several dendrites - branching processes that conduct impulses toward the cell body, and a single axon - a long straight process that conducts impulses away from the cell body. Axons are often referred to as nerve fibers.

Which part carries impulses from cell body of a neuron to another?

Dendrites are the branched thread-like extensions of a neuron that carry impulses from nearby neurons to the cell body [cyton]. Axons carry impulses away from the cyton.