Nervous System

Edison D. Ramos, RMT, MPHAssistant Professor II

College of Medical Technology

Manila Central University

INTRODUCTION

-The nervous system is the body’s control center and communication network.

- It directs the functions of body’s organs and systems.

- It allows us to interpret what is occurring in our external environment and helps us to decide how to react to any environmental changes.

- It shares in the maintenance of homeostasis with endocrine system.

Spinal Cord and Spinal Nerve

Structure FunctionsHave specific perform specific

Enables

includes include

Neurons Transmission and interpretation of sensation, reaction to stimuli

Allow

Neuroglia Protection and support of neuronsAllow

Meninges Allow Protection and nourishment of neural tissue in brain and spinal cord

Spinal cord and spinal

nerves

Allow Sending sensory impulses to brain, integrating reflexes and sending motor

impulses to muscles

ORGANIZATION

2 Major Categories of Nervous System

1. CENTRAL NERVOUS SYSTEM (CNS)

- control center for the whole system

- consists of brain and spinal cord

2. PERIPHERAL NERVOUS SYSTEM (PNS)

- consists of all nerves that connect the brain and spinal cord with sensory receptors, muscles and glands.

a. Afferent Peripheral System- consist of sensory neurons that convey information from receptors in the periphery of the body to the brain and spinal cord

b. Efferent Peripheral System- consists of motor neurons that convey information from the brain and spinal cord to muscles and glands.

b.1. Somatic Nervous System – conducts impulses from the brainand spinal cord to skeletal muscle thereby causing us toreact to changes in environment

b.2. Autonomic Nervous System – conducts impulses from thebrain and spinal cord to smooth and cardiac muscle tissue

b.2.1. Sympathetic Division- stimulate or speeds up activity and thus involves energy expenditures.- uses norepinephrine

b.2.2. Parasympathetic Division- stimulates or speeds up the body’s vegetative activities such as digestion, urination, defecation and slows down other activities- uses acetylcholine

CLASSIFICATION OF NERVE CELLS

- Neurons are nerve cells that transmit nerve impulses in the form of electrochemical changes.

- Neuroglial cells are nerve cells that support and protect neuron.

TYPES DESCRIPTION

Astrocytes Star-shaped cells that function in the blood-brain barrier to prevent toxic substances from entering the brain

Oligodendroglia Provide support and connection

Microglia Involved in the phagocytosis of unwanted substances

Epedymal cells Form the lining of the cavities in the brain and spinal cord

Schwann cells Located only in the PNS and make up the neurilemma and myelin sheath. (also called as NEUROLEMMOCYTES)

Types of Neuroglia

STRUCTURE OF NEURON

DENDRITES – extension of the cell body and are the receptive areas of the neuron.

AXON – single long extension of the cell body that begins as a slight enlargement. The axon may branch but at its end there are many extension called AXON TERMINAL

On large peripheral axons, a SCHWANN CELL produces a fatty MYELIN SHEATH that surrounds and insulates the axon. Narrow gaps in the sheath are called NODES OF RANVIER (also called as Neurofibral Nodes)

STRUCTURAL CLASSIFICATION OF NEURONS

1. Multipolar Neuron

- have several dendrites coming off the cell body and one axon. Most neurons in the brain and spinal cord are multipolar.

2. Bipolar Neuron

- have one dendrite and one axon. They are found in the retina of the eye, inner ear and the olfactory area of the nose.

3. Unipolar Neuron

- have only one process extending from the cell body, which then branches into a central branch that functions as an axon and a peripheral branch functions as dendrite . Most sensory neurons are Unipolar.

FUNCTIONAL CLASSIFICATION OF NEURONS

RECEPTORS detect stimuli in our environment.

SENSORY or AFFERENT NEURONS receive the impulse directly from the receptor site.

INTERNUNCIAL or ASSOCIATION NEURON found in the brain and spinal cord, they transmit the impulse for interpretation and processing.

MOTOR or EFFERENT NEURONS bring about the reaction to the stimulus

SYNAPSE – area where the terminal branches of an axon are close to but not touching the dendrites of another neuron.

- When impulse reaches the axon , it triggers the release of a neurotransmitter into synaptic cleft which allows impulse to travel across the synapse.

Neurotransmitter:

Acetylcholine Epinephrine Norepinephrine Dopamine Endorphins

REFLEX ARC

- Is an involuntary reaction to an external stimulus.

5 Components of Reflex Arc

1. Sensory receptor in the skin

2. Sensory or afferent neuron

3. Association of internuncial neurons in the spinal cord

4. Motor or efferent neuron

5. Effector organ

SPINAL CORD

- continuation of the medulla oblongata

- made up of 31 segments, each give rise to a pair of spinal nerves

- it is protected by SPINAL MENINGES

- the outermost spinal meninx is the dura mater or tough mother, the middle spinal meninx is the spider layer or arachnoid mater and the innermost meninx is the pia mater or delicate mother.

- Between the dura mater and the arachnoid mater is a space called SUBDURAL SPACE which contains serous fluid.

- Between the arachnoid and pia mater is the SUBARACHNOID SPACE in which the CSF circulates.

BRAIN

- it is protected by the cranial bones, cranial meninges and CSF

- the brain is divided into four main parts:

1. BRAINSTEM – medulla oblongata, pons varolii, midbrain

2. DIENCEPHALON – thalamus, hypothalamus

3. CEREBRUM

4. CEREBELLUM

BRAIN

Have specific perform specific

Structure FunctionsEnables

Brain

Cranial meninges

Protects

Brainstem

Diencephalon

Cerebrum

Cerebellum

Consciousness, heartbeat, breathing, visual, auditory

Temperature and pain recognition, homeostasis, thirst center, sleep

patterns

Muscular movements, emotions, intelligence

Coordination of muscular movements, balance

CSF

Include

Shock absorption, circulation of nutrients

Brainstem

Areas of Brain Function

Autonomic Nervous System

Have specific perform specific

Structure Functions

Sympathetic

Parasympathetic

Nose

Tongue

Eye

Ear

Increase of heartbeat and breathing rate, energy expenditure, cope with stress

Restoration of body to non stress state, controls vegetative activities

Sense of smell

Sour, bitter, sour, salty

Sense of sight

Sense of hearing and balance

CRANIAL NERVES

# NAME FUNCTIONS

I Olfactory Sensory: Conveys impulses related to smell

II Optic Sensory: Conveys impulses related to sight

III Oculomotor Motor: Movement of the eyeball, regulation of the size of the pupil

IV Trochlear Motor: Eye movements

V Trigeminal Sensory: Sensations of head and face

Motor: Mastication

Note: Divided into 3 branches – ophthalmic branch, maxillary branch and mandibular branch

VI Abducens Motor: Movement of the eyeball

VII Facial Sensory: Taste

Motor: Facial expression, secretion of saliva

VIII Vestibulocochlear Sensory: Balance, hearing

Note: Divided into 2 branches – vestibular branch responsible for balance and cochlear branch responsible for hearing

IX Glossopharyngeal Sensory: Taste

Motor: Swallowing, secretion of saliva

X Vagus Sensory: Sensation of organs supplied

Motor: Movement of organs supplied

Note: Supplies the head, pharynx, bronchus, esophagus, liver and stomach

XI Accessory Motor: Shoulder movement, turning of head, voice production

XII Hypoglossal Motor: Tongue movements

DISORDERS OF THE NERVOUS SYSTEM

ALZHEIMER’S DISEASE

- results in severe mental retardation, it usually affect older people but may begin in middle life with symptoms of memory loss and behavioral changes. The disease produces a loss of neurons resulting decrease brain size.

CEREBROVASCULAR ACCIDENT (stroke)

- caused by a clot or thrombus in a blood vessel. This situation can result in localized cell death due to lack of blood supply in the tissue.

MENINGITIS

- inflammation of the meninges due to bacterial or viral infections. Severe cases may result in paralysis, coma and death

ENCEPHALITIS

- inflammation of the brain tissue usually caused by a virus transmitted by the bite of a mosquito

TETANUS

- caused by the introduction of bacterium Clostridium tetani into an open wound. The bacteria produces neurotoxin that affects motor neuron in the spinal cord and brainstem

PARKINSON’S DISEASE

- characterized by tremors of the hand when resting and a slow shuffling walk with rigidity of muscular movements

CEREBRAL PALSY

- condition caused by brain damage during brain development or the birth process.

EPILEPSY

- caused by a disorder in the brain where certain parts of it are overactive producing convulsive seizures and possible loss of consciousness.

HEADACHE (cephalalgia)

- can be caused by a variety of factors, from muscle tension and anxiety to swollen sinuses and toothache, can also be caused by inflammation of the meninges, brain tumors and vascular changes in the blood supply to the brain.

END