Ch. 8 Notes - The Nervous System

8.1  NERVOUS SYSTEM

Functions of nervous system1.Sensory input- sensory receptors in skin and organs respond to internal and external stimuli from    nerve signals.2.Integration- CNS interpret data received from sensory input AND signal appropriate nerve response3.Motor output- nerve signals from brain goes to the effectors, muscle, glands, and organs to have    an effect.

Divisions of the Nervous System1.Central Nervous system (CNS)- brain and spinal cord2.Peripheral Nervous System (PNS)- afferent (sensory) and efferent (motor) divisions, includes all cranial and peripheral nerves

Nervous TissuesMade of two principal cell types1.Neurons- the nerve cells which generate and transmit nerve signals2.Neuroglia- nourish and support neurons

Neuron Structure1.Cell body- contains the nucleus and other organelles2.Dendrites- branched extensions that receive signals from sensory receptors or other neurons3.Axon- portion of the neuron that conducts the nerve signals.4.Axon terminal-fine endings, each tipped by a small swelling

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5. Myelin- covering of material that protects nerves and insulatesa.Schwann cells or neurolemmocytes- form myelin sheath in PNSb. Oligodendrocytes- form myelin in CNS

6. Nodes of Ranvier- gaps in the myelin sheath-Axon grouping1.Nerve-bundle of parallel axons in the CNS2.Tract- bundle of parallel axons in CNS

Types of Neurons-Sensory neurons1.Take nerve signals from sensory receptors to CNS2. Unipolar- extension from a cell body divides into one major projection

-Interneurons1.Association neurons that occur in the CNS2.Multipolar- have many dendrites and a single axon3. Convey nerve signals between various parts of CNS

-Motor neurons1.Multipolar neurons that take signals from CNS to muscles, organs, and glands2.Cause contraction, secretion, or organ functions

Nerve Signal Conduction2

-Neurons function to conduct nerve signals and activate the release of neurotransmitters1. Neurotransmitters- chemical messengers that allow neurons to communicate with other cells and transmit information. 2. Action potential- nerve signal conducted by the axon of the neuron

Resting Potential1.Resting potential- the energy a neuron has at rest because the cell membrane is polarized

a. Positively charged outside the cell membrane from excess sodium (Na+) ionsb. Negatively charged on inside of the cell membrane

2.Sodium channels- protein molecules in the cell membrane that control the concentration gradient of      Na+ into the cell3. Potassium channels- protein molecules in the cell membrane that control the concentration     gradient     of potassium (K+) ions out of the cell.4. Inside cell is normally negatively charged due to large negatively charged proteins trapped in the cell. 5. The neuron resting potential is about -70 millivolts (mV) inside the cell6. Sodium-potassium pump- protein carrier molecule in the membrane transport sodium (Na+) out of     the neuron and potassium (K+) into the neuron. (powered by ATP- active transport)

a. Uneven exchange, 3 Na+ are removed from neuron and 2 K+ are returned into the cell b. Potassium diffuses out of cell faster than sodium diffuses inc. Keeps membrane outside positive and inside negative when at rest.

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Action Potential1.Action potential- conduction of the nerve impulse2.Stimulus- energy needed to cause a neuron to respond.3. Voltage-regulated sodium gates- voltage changes cause them to open and to close

a. Not constantly open like sodium channelsb. When open- sodium rushes into the cellc. Causes inside of the axon to become positive compared to outside

4. Threshold- cell’s voltage reaches a certain point that stimulates many sodium gated ion channels    to open a. Cell potential will rise quickly5. Depolarization- rise in cell potential voltage - usually to +35 millivolts

a. When sodium ions rush into the cell6. Voltage-regulated sodium gates will close once depolarization reach 35mV7. Voltage-regulated potassium gates- voltage changes cause them to open and to close

a. Potassium ions rapidly leave the cellb. The inside of the cell becomes negative again

8. Repolarization- drop in cell potential to -70 millivoltsa. When potassium ions rush out of the cell

9. Resting potential is restored by the sodium-potassium pump.

Conducting of Action Potentials

1. Propagation- the transmission of the action potential along the entire length of the neuron.a. Depolarization results in neighboring sodium ions diffuse to more distal sectionsb. These sodium ions will then raise the resting potential to threshold and another action potential will followc. Like dominoes falling- a all-or nothing event

2. Refractory period- time needed to pump sodium outside and potassium inside the cell by the     sodium-potassium pump

a. Brief moment of time the proximal axon cannot conduct an action potentialb. Prevents signal from traveling in reverse

3. Conduction ratea. Unmyelinated neuron- about 1 m/secb. Saltatory conduction- action potential jumps from each node of Ranvier

1) Rate of more than 100 m/sec

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Conduction of an action potential a) unmyelinated b) myelinated

Transmission Across a Synapse1.Synapse- region where an axon terminal and neuron or other cell are located 2.Types of synapse membranes between two neurons

a. Presynaptic- the membrane of the first neuron b. Postsynaptic- membrane of the next neuron

3.Synaptic cleft- gap between two synaptic membranes4.Neurotransmitters- chemical which are stored in vesicles that travel between synapses to send signals5. Synaptic communication

a. Nerve signals from the axon stimulate calcium channels open and release Ca2+ ionsb. Exocytosis- vesicles with neurotransmitters merge with presynaptic membranes empty into the synaptic cleftc. Neurotransmitters diffuse across the cleft to the postsynaptic membraned. Neurotransmitters bind to specific receptor proteins called ligand-regulated gates on postsynaptic membranee. Ligands then open gates to communicate an excitatory or inhibitory response

Graded Potentials and Synaptic Integration1. Neurons can receive either excitatory (start) or inhibitory (stop) a signal2. Graded potential- small signals from a synapse 3. Excitatory neurotransmitter help move the neuron closer to a threshold for an action potential

a. Results in sodium ions (Na+) starting to move into the cell4. Inhibitory neurotransmitter makes it harder for a neuron to have an action potential a. Potassium ions (K+) leave cell and/or chloride ions (Cl-) enter cell5.Integration- summing up the total excitatory and inhibitory responses to either fire or block an action potential.

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Neurotransmitters Function and EffectsName &

TypeFunction Effect of Deficit

(too little)Effect of Surplus

(too much)

Acetylcholine(ACh)

Excitatory

-Stimulates muscle contraction -Memory -Learning

+ Alzheimer’s- memory loss+Botulism poison- paralyze resp. muscles

+ Severe Muscle Spasms+Black widow bite- convulsions

DopamineInhibitory

-Movement -Learning -Attention -Emotion -“Reward” centers in the brain

+ Parkinson’s- decreased mobility

+ Schizophrenia- hallucinations+ Drug Addiction

SerotoninInhibitory

-Mood -Hunger -Sleep and arousal

+ Depression, anxiety+ OCD, insomnia+ Anger control

+Autism +Sluggish

NorepinephrineExcitatory

-Alertness, arousal, sleep - Learning - Increase heart rate, O2, and glucose for “Flight or Fight”

+ Depression + Insomnia

GABA (gamma-aminobutyric acid)

Inhibitory

-Sleep and movement -Inhibits the CNS

+ Seizures, insomnia, epilepsy+ Huntington’s disease+ Anxiety

+ Anxiety, panic attacks

GlutamateExcitatory

-Memory -Most common in CNS (50%) -Too much kills neurons

+ Schizophrenia + Overstimulate brain+ Migraines+ Seizures+ ALS+Avoid MSG

Endorphins Inhibitory

-Pain control -Pleasure -Heroin similar structure

+ Depression+ Chronic aching

+ Slows HR, breathing, and metabolism+ Death or Hibernation

Neurotransmitter Molecules-Over 75 neurotransmitters have been identified- see chart1.Neurotransmitters that have been released and bind to the postsynaptic membrane may be inactivated by enzymes

a.Enzymes like acetylcholinesterase (AChE) break down Acetylcholine2. Other synapses the presynaptic membranes reabsorb the neurotransmitters

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8.2 CENTRAL NERVOUS SYSTEM

Composition of CNS1. Gray matter- contains cell bodies and short, nonmyelinated fibers. 2. White matter- contains myelinated axons that run together in bundles called tracts

Meninges and Cerebrospinal Fluid (CSF)1.Meninges- protective membrane that covers the brain and spinal cord.2.Dura mater- tough, fibrous connective tissue that is next to skull and vertebrae

a. Dural venous sinuses- space inside dura that collects venous blood and cerebrospinal fluid (CSF) and returns to the cardiovascular system3.Arachnoid mater- web-like connective tissue below the dura mater

a.Subarachnoid space- space between arachnoid and pia mater, filled with CSF protects and nourishes the CNS.4.Pia mater- very thin membrane that follows the contour of the brain and spinal cord.5. Cerebrospinal fluid (CSF)

a. Choroid plexus- folds of pia mater lined with capillaries that makes CSF.b. Ventricles- Hollow interconnecting cavities of the brain that make CSF and is filled with it.c. Central canal- cavity that makes and has CSF in it in the spinal cord. d. Drained back into the blood by dural sinuses

6. Hydrocephalus- condition caused by blockage of absorbing CSF and results compression of brain between fluid and skull. Can be corrected surgically.

Head and Neck (coronal) Brain and Meninges (coronal)

The Spinal Cord1.Spinal cord- cylinder of nervous tissue begins at base of skull and goes through opening in skull called foramen magnum. 2. Protected by the vertebrae, each has a intervertebral foramen3.Ends at about the first lumbar vertebra

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The Structure of the Spinal Cord1.Spinal cord is in the center of the vertebral column2.Intervertebral disks- tough fibrocartilage with gelatinous material separate the vertebrae

a.Herniated disk- when a disk is torn open may cause compression of spinal nerves leading to pain and loss of function.

3. Cross section of spinal cord shows central gray matter in shape of “H” surrounded by white mattera. Gray matter houses portions of sensory, motor, and interneurons.

4. Posterior (dorsal) root of a spinal nerve contains sensory fibers entering the gray matter.a. Posterior root ganglions- cell bodies of sensory nerves located here.

5.Anterior (ventral) root of the spinal nerve contains motor fibers exiting the gray matter.6.Roots join together to form a spinal nerve as part of the peripheral nervous system.7. White matter of the spinal cord

a. Ascending tracts- sensory information taken to the spinal cord and brain; posterior matterb. Descending tracts- which takes motor information from the brain; anterior matterc. These tracts cross once enter the brain, so right side of brain controls left side of body and

likewise.

Functions of the Spinal Cord1. Provides communication between the brain and peripheral nervous system2. Sensory information moves upward and motor information moves downward3. Provides reflex arcs – section 8.3

Vertebral column and spinal cord (transverse)

Spinal cord (anterior-posterior)

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The Brain1. The sections of brain are: cerebrum, diencephalon, the cerebellum, and brain stem

Parts of the Brain

2. Ventricles include 2 lateral ventricles, the third ventricle and the fourth ventricle.a. Cerebrum has 2 lateral ventricles, diencephalon with 3rd ventricle, and brain stem and

cerebellum with 4th ventricle.Ventricles of the Brain

The Cerebrum1. Largest portion of the brain in humans2. Carries out integration of information, coordinates activities with other parts of body, and carries out learning, memory and speech.3. Structures of the cerebrum

a. Cerebral hemispheres- two halves called the right and left; longitudinal fissure (deep groove) separates them.

b. Corpus callosum- white matter that connects the two hemispheres.c. Gyri (ridges) are separated by shallow grooves calls sulci (sulcus sing.)d. Divided into various lobes: frontal, parietal, occipital, temporal, and insula

4. Cerebral Cortex- thin, convoluted outer layer of gray matter; accounts for sensation, voluntary movement, and thought processes of consciousness.

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Lobes of the Brain

Motor and Sensory Areas of the Cortex1. Primary motor area

a. Located in the frontal lobe just anterior to the central sulcusb. Responsible for voluntary skeletal muscle movement; each section controls certain part of body

2. Primary somatosensory areaa. Located just posterior to the central sulcus in the parietal lobe.b. Sensory information from skin and muscles arrives here. Each section obtains information

from a certain part of body.

Body Regions Controlled by Primary Motor and Somatosensory Areas

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3. Primary taste area- areas of insula and parietal lobe4. Primary visual area- posterior occipital lobe5. Primary auditory area- temporal lobe

Association Areas1. Association areas- places where integration and memories are stored.2. Premotor area - organizes motor functions for skilled motor activities. (frontal lobe)3. Somatosensory association area- posterior to primary somatosensory area processes and

analyses sensory information.4. Visual association area- in occipital lobe links new visual information to previous images.5. Auditory association area- in temporal lobe links new sounds to previous ones.

Processing Centers1. Areas of brain that perform high level analysis. 2. Prefrontal area- receives information and uses to reason and plan our actions3. Broca’s area or motor speech area- found in left frontal lobe, coordination of respiratory and oral

movements for speech.4. Wernicke’s area or general interpretive area- in temporal lobe of left hemisphere, ability to

interpret written and spoken communication

Central White Matter1. Much of cerebrum below cerebral cortex contains white matter- tracts take information to different

association areas. 2. Descending tracts send from primary motor area communicate with other parts of brain and send

signals to opposite side brainstem and spinal cord.3. Ascending tracts from lower brain centers send sensory information to the primary somatosensory

area.

Basal Nuclei (Basal ganglia)1. Masses of gray matter located deep within the white matter2. Integrate motor control, so muscles are activated or inhibited3. Huntington’s disease and Parkinson’s disease are both to be caused by imbalance of

neurotransmitters in this part of the brain.

The Diencephalon1. A region that encases the third ventricle2. Hypothalamus- integrating center helps maintain homeostasis by regulating hunger, thirst, sleep, body temperature and water balance.

a. Produces the hormones secreted by the posterior pituitary glandb. Secretes hormones that control the anterior pituitary.c. Forms the floor of the third ventricle

3.Thalamus- two gray masses that are located in the sides and roof of third ventricle.a. Sensory relay center for all senses except smellb. Receives and routes information to parts of cerebrumc. Also arousal of cerebrum, memory, and emotions.

4. Pineal gland- located in the posterior diencephalona. Secretes melatonin and regulates our body’s daily rhythms.

The Limbic System1. It is a collection of structures from the cerebrum and diencephalon; connects cerebrum and temporal lobe to the thalamus and hypothalamus2. It causes emotions such as rage, pain, pleasure, and sorrow. 3.Hippocampus- processes short-term memories into long term memories.

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4.Sensory information attached to memories here.5. Amygdala- almond shape gray matter responsible for fear, arousal, and emotional stimulation.

The Cerebellum1. Separated from the brain stem by the fourth ventricle.2. Has two hemispheres, mostly composed of treelike pattern of white matter covered with thin layer of gray matter.3. Receives information from eyes, ears, joints, and muscle about present position of body parts and motor output from cerebrum where should be4. Helps to maintain posture and balance.5. Guides muscles to produce smooth, coordinated voluntary movements.6. Assists in learning new motor skills – like a sport or musical instrument.

The Brain Stem1. Region that joins the upper brain regions to the spinal cord2. Contains three regions: midbrain, pons, and medulla oblongata3. Midbrain- relay station from cerebrum and spinal cord/ cerebellum and reflex centers for vision, hearing and touch.4. Pons- bridge that contains bundles of axons from cerebellum to rest of CNS; head movements in response to visual and auditory stimuli5.Medulla oblongata- reflex centers that control heartbeat, breathing, and vasoconstriction; also reflex centers for vomiting, sneezing, coughing, hiccupping, and swallowing6.Reticular Formation- assist in maintaining muscle tone, help rouse a sleeping person, process sensory stimuli to keep us mentally alert, assist in heart rate , respiration, and blood pressure regulation.

Traumatic Brain Injury (TBI)1.Causes swelling of the brain and meninges which decreases blood flow to the brain.2.Concussion- signs are loss of consciousness, confusion, short-term memory loss.3.Hematoma- bleeding inside the brain or skull; contusion- bruising of the brain both may follow a concussion4.Epidural hematoma- bleeding between the skull and dura mater5. Initial evaluation of a person with a concussion

a. Alert and oriented to person, place or timeb. Pupils react equally and quickly to lightc. Complaints of headache, nausea, and vomitingd. Slow heartbeat, slow breathing, and decreasing consciousness

8.3 PERIPHERAL NERVOUS SYSTEM

1. Nerves- are bundles of axons, both myelinated and unmyelinated, that travel together.2. Ganglia-are swellings associated with nerves that contain a collection of cell bodies.

PNS division1.Afferent or sensory system- carries sensory information to CNS

a. Somatic sensory nerves- signals from skin, special senses, skeletal muscleb. Visceral sensory nerves- signals from body organs

2. Efferent or motor system- carry motor information from CNSa. Somatic motor nerves- signal to skeletal muscle voluntarilyb. Autonomic motor nerves- signals to smooth and cardiac muscle involuntarily

1) Sympathetic- “fight or flight”2) Parasympathetic- “rest and digest”

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Types of Nerves

Cranial Nerves1. Nerves that are attached to the brain; there are 12 of them.2. May be classified as sensory, motor, or both.3. Almost all cranial nerves are concerned with the head, neck and face.

a.Exceptions- Vagus nerve (X) to internal organs, and Spinal accessory nerve (XI) to the neck. 4. See - Cranial Nerve TableNames: Oh. Oh. Oooh. To Touch And Find Very Green Vegetables ... SH!Types: Some Say Money Matters But My Brother Says Big Brains Matters Most

Spinal Nerves1. Have 31 pairs of spinal nerves.2. Spinal nerve C1 emerges between the skull and atlas (first cervical vertebra)3. Rest of spinal nerves named based on intervertebral foramen the go through4. All spinal nerves are mixed, posterior is sensory nerves, and anterior is motor nerves5. Each spinal nerve serves a particular region of the body6. See – Spinal Nerve Table

Table of Cranial Nerves

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Table of Spinal Nerves

Somatic Motor Nervous System and Reflexes1. Most motor activity is voluntary2. Reflexes- automatic involuntary responses to change occurring inside or outside the body; protective mechanism

a. Cranial reflexes- like blinkingb. Spinal reflexes- remove from a painful stimulus

3. Reflex arc- nerve pathway involved in a reflex action a. Pathway: stimulus (affector) sensory neuron interneuron motor neuron

effector (muscle)

A Reflex Arc

4. Diagnostic reflexesa. Knee-jerk reflex- striking the patellar ligament contraction of quadriceps leg

extending.b. Ankle-jerk reflex- tapping the Achilles tendon just above the calcaneus contraction

of the gastrocnemius plantar flexion

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Autonomic Motor Nervous System and Visceral Reflexes1. Both branches of the autonomic nervous system (ANS)

a. Function involuntarily or automaticallyb. All internal organs have one or both divisionsc. Use two motor neurons and one ganglion to transmit an action potential; the preganglionic

and postganglionic axon fibers.2. Visceral reflex actions like blood pressure or breathing rate

a. Sensory nerves send signals from spinal nerves to the CNS.b. Completed when the motor neurons stimulate the smooth or cardiac muscle or a gland

(effectors)

Sympathetic Division: “Fight or Flight”1. Most preganglionic fibers arise from middle or thoracic-lumbar region of the spinal cord. 2. Preganglionic fibers are short and postganglionic fibers (that connect with effectors) are long3. Important in increasing heart rate and dilates bronchi for more air.4. Digestion is inhibited.5. Norepinephrine is the main neurotransmitter found in the sympathetic system

Parasympathetic Division: “Rest and Digest” 1. Most fibers arise from cranial nerves and bottom portion of spinal cord- known as craniosacral portion of ANS. 2. Preganglionic fibers are long and postganglionic fibers (that connect with effectors) are short3. Known as the “housekeeper” – promotes a relaxed state4. Important in pupils to contract, promote digestion of food, slow heart rate, decrease heart contraction.5. Acetylcholine (ACh) is the main neurotransmitter found in the parasympathetic system

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Autonomic System: Structure and Function

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