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Nervous System- Chapters 7, 8

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Surgical Papyrus

• Egyptian hieroglyphics.

• 17th Century B.C.

• Oldest known surgical treatise.

• 48 case histories are outlined.

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Organization of the Nervous System

• Consists of two divisions:– Central Nervous System (CNS).

• Brain and spinal cord.

– Peripheral Nervous System (PNS).

• All nervous tissue outside the CNS.

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1) Nervous tissue consists of _________ and ____________.– A) neurons and ganglia– B) neurons and meninges– C) neurons and neuroglia– D) neurons and nerves– E) morons and gangly ganglia

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Nervous System

• Neurology- (neur- gr. nerve) the scientific study of the nervous system.

• Nervous Tissue– Neurons (nerve cells)– Neuroglia

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Neurons

• Neuron- the functional unit of the nervous system.

• Numbers– 100 billion in the brain.– 1 billion in the spinal cord.

• Neurons consist of dendrites, cell bodies, and axons.

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Dendrites

Nucleus

Cell Body

Axon

Synaptic end bulbs

Myelin SheathNodes of Ranvier

Axon terminal

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Functional Classification of Neurons

• Based on the direction the neurons transmit nerve impulses.– Sensory neurons

• Transmit nerve impulses from receptors in the skin, sense organs, muscles, joints, and organs toward the spinal cord and brain.

– Interneurons• Transmit nerve impulses from one neuron to another.

– Motor neurons• Transmit nerve impulses away from the spinal cord to

muscles or glands.

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Types of Neurons

Interneuron

Dorsal-Root Ganglion Sensory

Receptor

Ventral-Root Ganglion

Effector

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Nervous System Functions

• Sensory– Detecting internal and external stimuli.

• Sensory receptors and sensory neurons

• Integrative– Processing sensory information by analyzing,

storing, and making decisions regarding appropriate responses.

• Interneurons

• Motor– Responding to integration decisions.

• Motor neurons

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Neuroglial Cells

• Neuroglia (glia= gr. glue).

• Half the volume of the CNS.

• Smaller than neurons.

• 50X more numerous.

• Functions – Support and protect the neurons.– Maintain homeostasis in the fluid that bathes

neurons.

• 6 types of neuroglia.

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1) Which of the following is not considered a nervous system structure?

A) spinal cord

B) Jeff’s brain

C) ganglia

D) heart

E) enteric plexus

F) sensory receptors

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Nervous System Structures

• Brain– 12 pairs of cranial nerves and their

branches.• Spinal cord

– 31 pairs of spinal nerves and their branches.

• Ganglia- clusters of cell bodies in the peripheral nervous system.

• Enteric plexus- a network of nerves in the GI tract.

• Sensory receptors- parts of neurons or specialized cells that monitor changes in the internal or external environment.

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What is a nerve?

• Nerve- a bundle of long axons outside the central nervous system.

Axon

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Lining the Brain & Spinal Cord= Meninges

• Meninges- 3 layers of protective tissue lining the brain and spinal cord.– Dura Mater– Arachnoid Mater– Pia Mater

• The spaces between the meninges are filled with cerebral spinal fluid.

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Gray and White Matter

• White matter- aggregations of myelinated processes.• Gray matter- nerve fibers with little to no myelin.

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The Brain• One of the largest organs in the body, 3 lbs.• Average length- 7 inches, width- 5.5, height- 4.• Center for registering sensations, correlating them

with one another and with stored information.• Center for intellect, emotions, behavior, and memory.• Chemistry- 78% H2O, 12% lipids, 8% protein, 2%

other.• Consists of four principal parts:

– Cerebrum– Cerebellum– Diencephalon– Brain stem

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MidbrainPons

MedullaOblongata

Thalamus

Hypothalamus

4 Principal Parts of the Brain

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The Cerebrum

• The cerebrum is the largest portion of the human brain.– Communicates with and

coordinates activities of other parts of the brain.

– Divided into left and right cerebral hemispheres.

– The outer layer is termed the cerebral cortex.

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Lobes of CerebrumMotor

Auditory

Visual

Sensory

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True or False1) If you eat right hemispheric sheep brains

biweekly, while watching the movie “The Man With Two Brains”, you will be more creative than someone who eats left hemispheric brains and watches the movie “The Wedding Crashers.”

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Hemispheric Lateralization

VerbalLogicalAnalyticalRational

NonverbalIntuitiveCreative

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Higher Mental Functions• Memory is the ability to hold a thought in the mind

or to recall events from the past.– Short-term- prefrontal lobe.– Long-term- hippocampus.– Amygdala- adds emotional overtones to memories.

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Limbic System- long-term memory

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Brain Stem• Functions

– Acts as a relay station between the cerebrum and the spinal cord and cerebellum.

– Reflex center for visual, auditory, and tactile responses.

MidbrainPons

MedullaOblongata

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Cerebellum• Functions

– Acts as an integration center for sensory input from the eyes, ears, joints, and muscles that relates to body position.

– Sends motor impulses to skeletal muscles that maintain posture and balance.

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Diencephalon• Consists of the hypothalamus and thalamus.• Functions

– Homeostasis for hunger, sleep, temp, water balance.– Receiving center for all sensory input, except smell.– Plays a role in memory and emotions.

Thalamus

Hypothalamus

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Alzheimer’s Disease

• Presence of abnormal neurons in the brain.– Amyloid plaque envelopes

axons.– Tangled axons

(neurofibrillary tangles).• 5% of adults 65-74 years

in age. 50% of those 85 and over.

• Appears to be partly genetic, APOE4.

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Parkinson’s Disease• Characterized by trembling or shaking.• Due to the degeneration of dopamine-releasing neurons

in the brain.• The lack of dopamine results in the sending out of

excess signals to effectors (muscles). • 1% of those over the age of 60.• Treatment is with L-dopa.

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Cranial and Spinal Nerves

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Spinal Cord

• Anatomy– Flattened cylinder, 16-18

inches in length and 3/4 inch diameter.

– In adult ends at L2.• Functions

– Provides communication between the brain and the peripheral nerves.

– Spinal cord reflexes.

33Spinal Nerve

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Peripheral Nervous System (PNS)

• Somatic Nervous System (somat-body)– Neurons that conduct impulses from somatic and special

sense receptors to the CNS.

• Enteric Nervous System (enter-intestines)– Two plexuses that extend the length of the

gastrointestinal tract.

• Autonomic Nervous System (auto-self, nomic-law)– Motor neurons that convey impulses from the CNS to

smooth muscle tissue, to cardiac tissue, and to glands.

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Somatic vs. Autonomic

• The ANS pathway is a 2 neuron pathway, while the SNS is a 1 neuron pathway.

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Divisions of the ANS

• 2 Major Divisions– Sympathetic

• Speeds up the visceral effector.

– Parasympathetic• Slows down the

visceral effector.• Most body organs receive

dual innervation.• Hypothalamus regulates

balance between these two divisions.

Sympathetic Parasympathetic

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Sympathetic Responses

• The sympathetic system dominates during physical or emotional stress conditions. – “E situations”- emergency, embarrassment, excitement, exercise.

• Alarm reaction- flight or fight response.– Dilation of pupils.– Increase of heart rate and blood flow to muscles.– Decrease in blood flow to nonessential organs.– Increase in blood flow to skeletal and cardiac muscles.– Airways dilate and respiratory rate increases.– Blood glucose level increases.– Decrease in intestinal activity and inhibition of urination.– Causes genital erection.

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Parasympathetic Responses

• Rest-and-digest activities.• Mechanisms that help conserve and restore

body energy during times of rest.• SLUDD responses

– Salivation– Lacrimation – Urination– Digestion– Defecation

• 3 “decreases”- decreased– Heart rate, diameter of airways, and diameter of pupils.

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Development of the Nervous System

• Appears around 3-4 weeks.