Nervous System

The master controlling and communicating system of the body through different electrical impulses.

Electrical impulses are rapid and specific and cause almost immediate responses.

Nervous System

Monitor changes (stimuli sensory input) occurring both inside and outside the body.

Integration – processes and interprets the sensory input and decides what should be done at each moment.

It effects a response by activating muscles or glands (effectors) via motor output.

Roles of the Nervous System

The nervous system does not work alone to regulate and maintain body homeostasis particularly the ENDOCRINE SYSTEM.

NERVOUS SYSTEM – controls through the rapid electrical nerve impulses.

ENDOCRINE SYSTEM – produces hormones that are released into the blood.

Organization of the Nervous System

Nervous System

Structural Classification

Peripheral N.S. Central N.S.

Brain Spinal Cord Spinal Nerves Cranial Nerves

Functional Classification

Peripheral N.S.

Sensory / Afferent Division Motor / Efferent Division

Visceral Sensory Fibers Visceral Afferent

Somatic Sensory Fibers

Somatic N.S. Voluntary N.S.

Autonomic N.S. Involuntary N.S.

Symphathetic Nervous System.

Parasymphathetic Nervous System.

Two principal Types of Cells: 1. Supporting Cells A. Neuroglia / Glia or Glial Cells Astrocytes : protection of neurons. Microglia : disposes debris like dead brain cells and bacteria. Ependymal cells: protective cushion around the CNS Oligoendrocytes: wrap nerve fibers producing fatty insulating

covering called myelin sheath. Schwann Cells : oligodendrocytes Satellite cells : those that protects and cushion cells.

2. Neurons

Nervous Tissue: Structure and Function

Figure 12.12 Glial Cells of the PNS. The PNS has satellite cells and Schwann cells.

Glia

not capable of transmitting nerve impulses.

Never lose their ability to divide.

Forms the brain tumors.

Neurons

Capable of transmitting nerve impulses

Loses their ability to divide.

Brain Cells Characteristics

Neurons

All neurons have a cell body containing the nucleus and processes (fibers) of two types:

AXONS (one per cell) typically generate and conduct impulses away from the cell body and release a neurotransmitter, and

DENDRITES (one to many per cell) typically carry electrical currents toward the cell body.

> Most large fibers are myelinated; myelin increases the rate of nerve impulse transmission.

Anatomy

1. Cell body

> nucleus, cytoplasm, Nissl substance, neurofibrils)

? Centriole

2. Processes (fibers)

> dendrites, axons, axon hillock, collateral brach, axon terminals, synaptic cleft/synapse

> NT

3. Myelin Sheath

> myelin myelin sheath

> neurilemma, nodes of Ranvier

> Schwann cells ( outside CNS) vs.

Oligodendrocytes (within CNS)

Essential Parts of the Neuron

Nuclei : cluster of cell bodies in the CNS

Ganglia : small collection of cell bodies or nuclei.

Tracks : bundles of nerve fibers running in the CNS.

Nerves : bundles of nerve fibers running in the PNS.

Gray Matter : unmyelinated fibers and cell bodies.

White Matter : myelinated fibers/tracks.

Terminologies

Multiple Sclerosis

- Protein in the myelin sheath is attacked by the person’s immune system.

Myelin sheaths around the fibers are gradually destroyed, converted to hardened. sheaths or scleroses

Electrical current is short-circuited along the way down to axon terminals.

Visual and speech disturbance, lose of ability to control muscles.

* No cure but is relieved by Interferon.

Homeostatic Imbalance

Function (direction of impulse transmission)

Sensory (Afferent)

Motor (Efferent)

Association Neurons (Interneurons)

Structure (reveals the number of processes extending from the cell body)

Unipolar

Bipolar

multipolar

Classification of Neurons

Naked nerve endings (pain and temp receptors)

Meissner’s corpuscles (touch receptors)

Pacinian corpuscles (deep pressure receptors)

Golgi tendon organ (proprioreceptors)

Muscle spindle (proprioreceptors)

Types of Sensory Receptors

Two major function of neurons:

Irritability : the ability to respond to a stimulus and convert it into a nerve impulse.

Conductivity : the ability to transmit the impulse to other neurons, muscles or glands.

Neuron Physiology

1. Resting membrane electrical conditions.

2. Stimulus initiates local depolarization.

3. Depolarization and generation of an action potential.

4. Propagation of the action potential.

5. Repolarization.

6. Initial ionic condition restoration.

The Nerve Impulse (Irritability) Electrical Synapse

1 – action potential arrives.

2 – Vesicle fuses with plasma membrane.

3 – NT is released into synaptic cleft.

4 – NT binds to receptor on receiving neuron’s membrane.

5 – ion channel opens

6 – ion channel closes.

The Nerve Impulse (Irritability) Chemical Synapse

A neuron influences other neurons or effector cells by releasing neurotransmitters, chemicals that diffuse across the synaptic cleft and attach to membrane receptors on the postsynaptic cell. The result is opening of specific ion channels and activation or inhibition, depending on the neurotransmitter released and the target cell.

Transmission of the Signal at Synapses

(Conductivity)

A reflex is a rapid, predictable rand involuntary response to stimulus.

There are two types—autonomic and somatic. The minimum number of components of a reflex arc is five:

Sensory receptor, Effector organ, sensory neuron, motor neurons and CNS integration center.

(most, however, have one or more association neurons). Normal reflexes indicate normal nervous system function.

Transmission of the Signal at Synapses - Reflexes

(Conductivity)

Central Nervous system

Embryonic stage : appears as simple tube (neural tube) extending down the dorsal median plane.

4th week AOG: anterior end of the neural tube begins to expand and brain

formation begins.

The rest of the neural tube posterior to the forming brain becomes the spinal cord.

13 weeks: Central canal of the neural tube enlarged in four regions of the

brain to form chambers called ventricles.

CNS Development

About two fistfuls of pinkish gray tissue.

Wrinkled like a walnut and with the texture of cold oatmeal.

Weighs a little over three pounds.

Largest and most complex mass of nervous tissue in the body.

Four main regions:

Cerebral hemisphere / Cerebrum

Diencephalon

Brain stem

cerebellum

Brain

Figure 12.3 Gray Matter and White Matter A brain removed during an autopsy, with a partial section removed, shows white matter surrounded by gray matter. Gray matter makes up the outer cortex of the brain. (credit: modification of work by

“Suseno”/Wikimedia Commons)

The two cerebral hemispheres form the largest part of the brain.

Parts/Three Regions: Gray matter : surface : cortex White matter : interior Basal nuclei ; islands of gray matter situated deep within the

white matter.

Convulated and has GYRI, SULCUS and FISSURE. Involved in: Logical reasoning Moral conduct Emotional responses Sensory interpretation Initiation of voluntary muscle activity

Cerebrum

The frontal lobe contains the olfactory bulb, which processes smells. The frontal lobe also contains the motor cortex, which is important for planning and implementing movement. Areas within the motor cortex map to different muscle groups. Neurons in the frontal lobe also control cognitive functions like maintaining attention, speech, and decision-making. Studies of humans who have damaged their frontal lobes show that parts of this area are involved in personality, socialization, and assessing risk.

The parietal lobe is involved in speech and also reading. Two of the parietal lobe’s main functions are processing somatosensation—touch sensations like pressure, pain, heat, cold—and processing proprioception—the sense of how parts of the body are oriented in space. The parietal lobe contains a somatosensory map of the body similar to the motor cortex.

The occipital lobe is involved in vision—seeing, recognizing, and identifying the visual world.

The temporal lobe is involved in processing and interpreting sounds. It also contains the hippocampus (named from the Greek for “seahorse,” which it resembles in shape) a structure that processes memory formation.

The role of the hippocampus in memory was partially determined by studying one famous epileptic patient, HM, who had both sides of his hippocampus removed in an attempt to cure his epilepsy. His seizures went away, but he could no longer form new memories (although he could remember some facts from before his surgery and could learn new motor tasks).

Broca’s Area : the cortical area involved in our ability to speak.

This is found at the base of the precentral gyrus and damage to this part causes inability to say words.

The basal nuclei, regions of gray matter deep within the white matter of the cerebral hemispheres, modify voluntary motor activity. Parkinson’s disease and Huntington’s disease are disorders of the basal nuclei.

Parkinson’s Disease: a chronic progressive neurological disease chiefly of later life i.e. linked to decreased dopamine production in the substantia nigra marked by tremor of resting muscles, rigidity, slowness of movement, impaired balance and a shuffling gait.

Huntington’s disease: Huntington's disease (HD) is a neurodegenerative genetic disorder that affects muscle coordination, and exhibits abrupt, jerky and almost continuous movements. and leads to cognitive decline and behavioral symptoms.

It is superior to the brain stem and is enclosed by the cerebral hemispheres.

The major structures include the following:

The thalamus

The hypothalamus

Epithalamus

Diencephalon (Interbrain)

Encloses the third ventricle, is the relay station for sensory impulses passing to the sensory cortex for interpretation.

Actual localization and interpretation of the sensation is done by the neurons of the sensory cortex.

Thalamus

Makes up the “floor” of the third ventricle and is the most important regulatory center of the autonomic nervous system (regulates water balance, metabolism, thirst, temperature and the like).

Center for many drives and emotion like the centers for thirst, appetite, sex, pain, and pleasure.

An important component of the LIMBIC SYSTEM.

It regulates the pituitary gland.

Hypothalamus

Includes the pineal body (an endocrine gland) and the choroid plexus of the third ventricle.

The choroid plexus are knots of capillaries within each ventricle and forms the CSF.

Epithalamus

The short region(about a size of the thumb in diameter and approx. 3 inches long) inferior to the hypothalamus that merges with the spinal cord.

Contains many nuclei that forms the cranial nerves and control vital activities such as breathing and BP.

Contains the reticulating system involved in motor control of the visceral organs

A special group of reticular formation neurons, the reticular activating system plays a role in consciousness and the awake/sleep cycle.

The Brain Stem

Regions: Midbrain : the most superior and primarily fiber tracts.

Contains a bulging nuclei i.e. reflex centers for vision and hearing.

Pons: inferior to the midbrain and has fiber tracts and nuclei involved in respiration. Contains a nuclei involved in the control of breathing

Medulla oblongata: the most inferior part of the brain stem. In addition to fiber tracts, it contains autonomic nuclei involved in the regulation of vital life activities (breathing, heart rate, blood pressure, swallowing, vomiting)

The Brain Stem

A large, cauliflower-like part of the brain posterior to the fourth ventricle. It coordinates muscle activity and body balance.

The Cerebellum

Ataxia (?please read on the book)

Homeostatic Imbalance

Protection of the CNS

Bones of the skull and vertebral column are the most external protective structures.

Meninges are three connective tissue membranes:

Dura mater (tough outermost)

Arachnoid mater (middle weblike)

Pia mater (innermost delicate)

Meninges extend beyond the end of the spinal cord.

Cerebrospinal fluid provides a watery cushion around the brain and cord. CSF is formed by the choroid plexuses of the brain. It is found in the subarachnoid space, ventricles, and central canal. CSF is continually formed and drained.

Blood-brain barrier is composed of relatively impermeable capillaries.

Figure 16.21 The cerebral cortex is covered by three layers of meninges: the dura, arachnoid, and pia maters. (credit: modification of work by Gray's Anatomy)

A watery substance similar in its makeup to blood plasma from which it forms. However it contains less protein and more vitamin c and its ion composition is different.

Normal volume : 150 ml.

Lumpar tap.

CSF

Meningitis : inflammation of the meninges 9viral/bacterial cause.

Encephalitis : inflammation of the brain due to nervous tissue infection.

Homeostatic Imbalance

Least permeable capillaries in the whole body.

Allowed to enter: of water-soluble substance, only water, glucose and essential a.a..

Not allowed: metabolic wastes like urea, toxins, protein and most drugs.

This barrier is ineffective for: fats, respiratory gases and other fat-soluble molecule, alcohol, nicotine, anesthetics.

Blood-Brain Barrier

Brain Dysfunctions

Head trauma may cause:

Concussion : reversible damage.

Contussion : nonreversible damage.

When the brain stem is affected, unconsciousness (temporary or permenant) occurs.

Trauma-induced brain injuries may be aggravated by intracranial hemorrhage or cerebral edema, both of which compress brain tissue.

Head Trauma

CVA

Alzheimer’s Dse.

Degenerative Brain Diseases

CVA / Stroke / Brain attack

Result when blood circulation to brain neurons is blocked and brain tissue dies. The result may be visual impairment, paralysis and aphasias.

Cerebrovascular Accident

A degenerative brain disease in which abnormal protein deposits and other structural changes appear.

It results in slow, progressive loss of memory and motor control plus increasing dementia.

Alzheimer’s Disease

EEG

Simple Reflex Tests

Pneumoencephalography

Angiography

CT Scan

PET Scan

MRI Scan

Diagnostic Technique Used in Assessing Brain Dysfunction

A reflex center and conduction pathway.

Found within the vertebral canal, the cord extends from the foramen magnum to L1 to L2.

The cord has a central bat-shaped area of gray matter surrounded by columns of white matter, which carry motor and sensory tracts from and to the brain.

Spinal Cord

A nerve is a bundle of neuron processes wrapped in connective tissue coverings (endoneurium, perineurium and epineurium).

Composed of the 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Peripheral Nervous System

There are four main nerve plexuses in the human body.

The cervical plexus supplies nerves to the posterior head and neck, as well as to the diaphragm.

The brachial plexus supplies nerves to the arm.

The lumbar plexus supplies nerves to the anterior leg.

The sacral plexus supplies nerves to the posterior leg.

Nerve Plexuses of the Body

Peripheral Nervous System

Cranial Nerves

12 pairs of nerves extend from the brain to serve the head and neck region. The exception is the vagus nerve, which extend into the thorax and abdomen.

Spinal Nerves

31 pairs of nerves are formed by the union of the dorsal and ventral roots of the spinal cord on each side.

The spinal nerve proper is very short and splits into dorsal and ventral rami.

Dorsal rami serve the posterior body trunk; ventral rami (except T1 to T12) form plexuses (cervical, brachial, lumbar, sacral) that serve the limbs)

Part of the PNS, composed of neurons that regulate the activity of the smooth and cardiac muscle and glands. This system differs from the somatic nervous system in that there is a chain of two motor neurons from the CNS to the effector.

Two subdivisions serve the same organs with different effects. Parasympathetic division

Sympathetic division

Autonomic Nervous System

The “house-keeping” system and is in control most of the time.

This division maintains homeostasis by seeing that normal digestion and elimination occur and that energy is conserved.

Parasympathetic Division

The fight or flight subdivision which prepares the body to cope with some threat.

Its activation increases heart rate and blood pressure.

Sympathetic Division

Developmental Aspects of the Nervous System

Maternal and environmental factors may impair embryonic brain development. Oxygen deprivation destroys brain cells. Severe congenital brain disease include cerebral palsy, anencephaly, hydrocephalus and spina bifida.

Premature babies have trouble regulating body temperature because the hypothalamus is one of the last brain areas to mature prenatally.

Development of motor control indicates the progressive myelination and maturation of a child’s nervous sytem. Brain growth ends in young adulthood. Neurons die throughout life and are not replaced: thus, brain mass declines with age.

Healthy aged people maintain narly optimal intellectual function. Disease-particularly cardiovascular disease – is the major cause of declining mental function with age.