FUNDAMENTAL OF NERVOUS SYSTEM (N Downloads/A. Handouts...FUNDAMENTAL OF NERVOUS SYSTEM (N.S) ......

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FUNDAMENTAL OF NERVOUS SYSTEM (N.S) Introduction

Organs of N.S.: Brain (cerebrum, cerebellum), spinal cord, peripheral nerves, ganglia

Classification of N.S.: CNS = Brain and spinal cord PNS = Cranial nerves and spinal nerves ANS = Special subdivision (from CNS & PNS) General Functions

− Perception − Integration Maintain homeostasis

− Action Anatomy

Composition of Nervous Tissue = Neuron and neuroglial cells Classification of Neuron: Afferent, efferent, interneuron

Functionally General vs special Somatic vs visceral Structurally: Microscopically: Multipolar, bipolar, unipolar Grossly: Within PNS: Nerve, plexus, ganglion Within CNS: Tract, nuclei Classification of Neuroglial Cells CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells PNS: Schwan cells, satellite cells *Regeneration of peripheral nerves Clinical Application 1. Related to neuron Ischemic cell changes/save the penumbra 2. Related to neuroglial cells Multiple sclerosis Simple nerve pathway Reflexes Physiology

• Polarization • Action potential vs local or graded potential • Nerve impulse and factors affecting conduction • Axonal TP, synapse, NT • Processing of N. impulses: Convergence vs divergence • Synaptic Potential: Excitatory = Hypopolarization due to 8 Na+ permeability Inhibitory = Hyperpolarization due to 8 K+ permeability

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NERVE FIBER CLASSIFICATION

1

General Somatic Afferent Fibers:

Sensory impulses from receptors in the skin and skeletal muscles.

2

General Somatic Efferent Fibers:

Motor impulses to skeletal muscles.

3

General Visceral Afferent Fibers:

Sensory impulses from internal organs and blood vessels.

4

General Visceral Efferent Fibers:

Motor impulses to smooth muscles and glands within internal organs.

5

Special Visceral Afferent Fibers:

Sensory impulses from olfactory and taste receptors.

6

Special Visceral Efferent Fibers:

Motor impulses to special muscles involved in: swallowing, speaking, chewing and facial expression.

7

Special Somatic Afferent Fibers:

Sensory impulses from receptors of sight, hearing and equilibrium.

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INDIVIDUAL HUMAN REFLEXES Introduction 1. Define reflex.

A rapid, automatic response to a stimulus. 2. Describe the nerve pathway of a spinal reflex; of a cranial reflex.

Spinal reflex-sensory neuron to gray of spinal cord, then motor neuron to effector organ, cranial reflex-sensory pathway to brain, then motor pathway to effector organ.

3. How many neurons are normally involved in a reflex pathway.

Spinal - 3; cranial - 4 4. What adaptive advantage is derived from the fact that nerve impulses for many reflexes do not

have to go to the cerebral cortex?

The lesser distance of traveling saves response time prior to interpretation of stimulus 5. Give some examples of reflexes involving the internal organs.

Cardiac acceleration, breathing rate increase, blood vessel constriction, swallowing, coughing, vomiting, sneezing.

Activity The Knee Jerk (Patellar) Reflex

Have the subject sit so that the legs hang free. Locate the patellar tendon just below the knee cap and strike it with the edge of a reflex hammer. The quadriceps femoris muscle should jerk.

Repeat the procedure except have the subject clasp his hands behind his back and pull just prior to the striking of the tendon. Note the difference in the extent of the knee jerk. Greater

Give the subject a column of figures to add, and while he is doing this, tap the patellar tendon. Note the effect that this has on the knee jerk. Greater than first trial; about the same as the second trial. Ankle Jerk (Achilles Reflex)

With the subject=s feet hanging freely, strike the tendon of Achilles with a reflex hammer. The gastrocnemius muscle should contract, resulting in the plantar flexion of the foot.

Repeat the procedure with the subject kneeling on a chair or table. Compare the two results. Physical contact of the ventral surface of the leg and ankle will probably result in the response being slower and not as strong.

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Corneal Reflex

Touch the cornea with a piece of cotton taking care not to touch the eyelids or eyelashes. Give your results. Eyelids close, Same reflex in blind patients. Photopupil Reflex

Have the subject face a bright lamp or sunlighted area and then close his eyes for about two minutes.

When the subject opens his eyes note the difference in the size of the pupil and watch its constriction.

Describe your results. Pupils were large when eyes were first opened and became smaller thereafter until they adjusted to the different intensity of light. The Accommodation Reflex

Have the subject look at a distant object (more than 20 feet) out the window, or in the hallway, or the other end of the room. Do not look into bright light.

Note the size of the pupil. Pupils are dilated

Then have the subject look at a near object such as a pencil or a watch within about 10 inches of their eyes. Have the same conditions of lighting.

Observe the size of the pupil. Pupils are constricted The Convergence Reflex

Have the subject look at a distant object. Note the position of the eyeballs. Visual axes slightly pulled toward midline.

Then have the subject look at a near object (about 10 inches).

Note the change in position of the eyeballs. Visual axes are now considerably closer to midline (nose). Questions 1. Explain the importance of the patellar reflex and the Achilles reflex in the maintenance of posture.

The tendons and muscles that accomplish these two reflexes must be in a stiffened or contracted state in order for a person to stand.

2. Why was the patellar reflex influenced by the clasping of the hands and the adding of a column of

figures? The subject was concentrating on things other than the patellar reflex and thus was not subconsciously resisting its occurrence.

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3. List the kinds of nerve endings that are found in the cornea. Cold, pain and pressure (not touch)

osmoreceptors respond to drying trigger tears.

What sensation brought about the corneal reflex? Pain or drying 4. What is the adaptive advantage of the photopupil reflex?

The amount of light entering the eye is regulated preventing too strong a light from damaging the retina. 5. Give the changes that take place in the following structures during accommodation:

A. Pupil Dilates for far vision; constricts for near vision.

B. Lens Flattens for far vision; increases convexity for near vision.

C. Medial Rectus Ocular Muscle Contracts more strongly for near vision. 6. Give the purpose of the Accommodation Reflex?

Provides for the adjustments which must be made when looking at things of varying distances.

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CNS Introduction

S = Skin C = Connective tissue A = Aponeurosis L = Loose C. T. P = Periosteum

Covering of CNS = Meninges Bone Epidural space Dura mater Subdural space * Meningitis Arachnoid mater Subarachnoid space Pia mater Brain

Development, parts, cavities Anencephaly and Spina bifida CSF: formation, circulation, absorption, pressure and functions and hydrocephalus 3 Major Divisions of the Brain

1. Cerebrum: Gross features (lobes) Cross-section -- gray matter vs. white matter -- corpus striatum -- Basal nuclei -- Internal capsule * Disorders -- Parkinson=s -- Huntington Chorea General functions Functional regions (areas) -- Motor -- Sensory -- Association -- General interpretive

* Hemisphere dominance * Memory Alzheimer=s Disorder * Cerebral injuries

2. Brain Stem -- Diencephalon -- Thalamus

-- Hypothalamus -- Pineal body

-- Midbrain -- Pons -- Medulla oblongata

Reticular Activating System Type of sleep

3. Cerebellum Spinal Cord

Structure and cross section Spinal roots Ascending and descending tracts Functions Injuries to spinal cord

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NERVOUS SYSTEM

Structure

Location

Major Functions Broca=s area

Anterior to primary motor cortex (frontal lobe)

Coordinates speech

Cardiac center

Medulla oblongata

Regulates heart beat

Cerebellar peduncles

Between cerebellum and brain stem

Relays impulses to and from cerebellum

Cerebral peduncles

Midbrain

Provides motor pathways between cerebrum and lower parts

Corpora quadrigemina

Midbrain

Contain visual and auditory reflex centers

Frontal eye fields

Frontal eye field

Controls voluntary movements of eyes and eyelids

Hypothalamus

Diencephalon

Regulates many visceral activities

Limbic system

Diencephalon

Controls emotional feelings

Prefrontal areas

Frontal lobe of cerebrum

Controls emotional behavior

Respiratory center

Medulla oblongata

Regulates rate and depth of breathing

Reticular formation

Brain stem

Activates state of wakefulness

Thalamus

Diencephalon

Relays sensory impulses to cerebral cortex

Vasomotor center

Medulla oblongata

Controls diameter of blood vessels and blood pressure

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PNS PNS Includes 12 pairs cranial nerves and 31 pairs spinal nerves A. Cranial nerves: CN I Olfactory CN VII Facial CN II Optic CN VIII Vestibulocochlear CN III Oculomotor CN IX Glossopharyngeal CN IV Trochlear CN X Vagus CN V Trigeminal CN XI Spinal Accessory CN VI Abducens CN XII Hypoglossal B. Spinal nerves: 8 Cervical C1 – C8 12 Thoracic T1 – T12 5 Lumbar L1 – L5 5 Sacral S1 – S5 1 Coccygeal Co1 Anterior branch Rootlets Roots Spinal nerve Posterior branch .... dermatomes Plexuses I. Cervicobracheal (Ant. Br. C1 T1) Major branch Minor branch 1. phrenic nerve (C3 C4 C5) 1. lat. and med. pectoralis n. 2. musculocutaneous nerve 2. dorsal scapular n. 3. ulnar 3. lower subscapular n. 4. median 4. suprascapular n. 5. radial 5. thoracodorsal n. 6. axillary II. Lumbosacral (Ant. Br. T12 Co1) Major branch Minor branch 1. obturator n. 1. pudendal n. 2. femoral n. 2. inferior gluteal n. 3. sciatic n. 3. superior gluteal n. a. common peroneal b. tibial * Ant. Br. T2 T11 Intercostal Nerves Clinical Application — during childbirth — carpal tunnel syndrome — nerve block — laminectomy

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A MNEMONIC LEARNING DEVICE FOR THE CRANIAL NERVES

No. NAME Poem “A” Poem “B”

I OLFACTORY ON SOME

II OPTIC OLD SAY

III OCULOMOTOR OLYMPUS MARRY

IV TROCHLEAR TOWERING MONEY

V TRIGEMINAL TOP BUT

VI ABDUCENS A MY

VII FACIAL FINN BROTHERS

VIII (ACOUSTIC) VESTIBULOCOCHLEAR

AND SAY

IX GLOSSOPHARYNGEAL GERMAN BAD

X VAGUS VIEWED BUSINESS

XI SPINAL ACCESSORY SOME MARRY

XII HYPOGLOSSAL HOPS MONEY

Poem “A”: The first letter of each word in the poem corresponds to the first letter of the name of

the nerve (with the exception of Cranial Nerves #VIII; these were formerly called Acoustic or Auditory, and are now called Vestibulocochlear.)

Poem “B”: This poem helps you to remember the type of nerve: Sensory, Motor, or Both

(mixed nerves).

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ANS

A special division of the NS consists of nerve fibers that are motor only and part of both CNS and PNS. Controls motor activities that influence involuntary muscles and glands.

Divisions of ANS 1. sympathetic (thoracolumbar) fight and flight 2. parasympathetic (craniosacral) quietude Similarities and differences between the 2 divisions.

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ANATOMICAL, PHYSIOLOGICAL, AND PHARMACOLOGICAL CHARACTERISTICS OF THE SYMPATHETIC AND PARASYMPATHETIC DIVISIONS OF THE

AUTONOMIC NERVOUS SYSTEM

Characteristics Sympathetic Parasympathetic

Higher control Hypothalamus Hypothalamus

Action Prepares body for emergency Conserves and restores energy

Outflow T1-L2 Cranial nerves 3, 7, 9, and 10; spinal nerves S2 through S4

Preganglionic fibers Myelinated Myelinated

Ganglia Paravertebral (sympathetic trunks); prevertebral (e.g., celiac, superior mesenteric, inferior mesenteric)

Small ganglia close to viscera (e.g., otic, ciliary) or ganglion cells in plexuses (e.g., cardiac, pulmonary)

Neurotransmitter within ganglia Acetylcholine Acetylcholine

Ganglion-blocking agents Hexamethonium and tetraethylammonium by competing with acetylcholine

Hexamethonium and tetraethylammonium by competing with acetylcholine

Postganglionic fibers Long, nonmyelinated Short, nonmyelinated

Characteristic activity Widespread due to many postganglionic fibers and liberation of epinephrine and norepinephrine from suprarenal medulla

Discrete action with few postganglionic fibers

Neurotransmitter at postganglionic endings

Norepinephrine at most endings and acetylcholine at a few endings (sweat glands)

Acetylcholine at all endings

Blocking agents on receptors or effector cells

Alpha-adrenergic receptors, phenoxybenzamine, beta-adrenergic receptors, propranolol

Atropine, scopolamine

Agents inhibiting synthesis and storage of neurotransmitter at postganglionic endings

Reserpine

Agents inhibiting hydrolysis of neurotransmitter at site of effector cells

Acetylcholinesterase blockers (e.g., neostigmine)

Drugs mimicking autonomic activity

Sympathomimetic drugs – phenylephrine: alpha receptors; isoproterenol: beta receptors

Parasympathomimetic drugs – pilocarpine, methylcholine

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SOMATIC AND SPECIAL SENSES I. Introduction Exteroceptive Somatic Visceroceptive Proprioceptive General Classification Vision Smell Special Taste Chemoreceptors Hearing Classification of Receptors Nocireceptors Equilibrium Sensitivity to Thermoreceptors Stretch Mechanoreceptors Baroreceptors Photoreceptors Sound waves Definition of sensation, projection, and sensory adaptation. II. Somatic Senses and Their Receptors: A. Touch and Pressure Receptors Merkel’s disks = sensory nerve fibers = course touch (texture) Meissner’s corpuscles = fine touch Pacinian corpuscles = deep pressure B. Temperature Receptors Ruffini’s endings = hear receptors Krause end bulbs = cold receptors C. Pain Receptors = free nerve ending • Cutaneous pain • Visceral pain • Referred pain • Phantom pain • Pain nerve pathway • Regulation of pain impulses • Intractable pain D. Stretch Receptors • Muscle spindle • Golgi tendon organs

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REFERRED PAIN Introduction 1. Referred pain is a common sensory phenomenon in which stimulation in one part of the

body gives rise to sensation that seems localized in a different or remote part of the body.

When pain is aroused by stimulation of afferent endings in the viscera, it is usually referred to some skin area.

Of what diagnostic importance is this?

Pain in a definite area of the skin may indicate the existence of a problem with some particular internal organ.

2. For example, the sensory fibers from the heart terminate in the first through the fourth

thoracic cord segments.

Also the first thoracic segment supplies the inner arm as well as the thorax wall.

Thus sensory information arriving in the gray matter of the spinal cord from either of the previously indicated locations may travel up to the brain over a common nerve pathway.

Explain the role of the cerebral cortex in interpreting this sensory information on its arrival in the brain.

Sensory information arriving in the cerebral cortex from the heart may be interpreted as pain of the inner arm and thorax wall.

Activity

Place some ice in a tray of cold water that is deep enough to cover your elbow.

Immerse your elbow in the ice water and hold it in position long enough for the following progression of sensations: first, a feeling of some discomfort in the region of the elbow; later, pain sensations that are felt in the fingers. Questions 1. Describe the precise location of the referred pain.

The inner side of the hand, the ring finger, the little finger. 2. Explain the occurrence of the referred pain on the basis of a common spinal cord segment

and the idea that a common nerve pathway may transmit messages from different areas up to the brain.

The brain has no way of determining the source of impulses that share a common pathway to the brain - that is, it cannot determine which one, or ones, of the possible sites is actually the place of origin.

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Special Visceral

Dynamic Static

Special Somatic

5 openings connected to the middle ear

III. Special Senses: Smell or olfactory sensation

Taste or gustatory sensation

Hearing or auditory sensation

Balance or equilibrium

Sight or visual sensation Ear = Auditory Apparatus Structure 1. External 2. Middle Oval window Round window Eustachian tube 3. Inner External auditory meatus Mastoid air cells Physiology of: 1. Audition 20-20,000 vibration/sec. / Decibels dB Type of Deafness a. Conductive b. Neuronal 2. Equilibrium Motion Sickness

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Sense of Light/Vision Structure of Organ of Vision Lacrimal gland Eyebrows Eyelashes 1. Accessory Organs Eyelids (palpebrae) Conjunctiva Extrinsic muscle of the eye within the orbit Strabismus Nystagmus 2. Eye Cornea Outer Tunic Sclera Choroid coat Middle Tunic Ciliary bodyy Iris Lens divide the globe into cavities IOP (Intraocular Pressure) Inner Tunic = Retina Physiology of Vision Dim Light Rhodopsin Scotopsin + Retinene/Retinal Nerve Impulse Resynthesized Bright Light Pigment from Protein + Retinal Cone Receptor Rapidly Binocular vision Convex ≈ Converges light waves Refraction of light = Sight Refractive disorders Concave ≈ Diverges light waves

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