Compendium Notes Chapter 13 – Nervous System

Index:Overview of Nervous SystemThe Central Nervous SystemThe Peripheral Nervous System

13.1 Overview of Nervous System (Mader p. 248 – 253)1. Central Nervous System (CNS)

a. Brain and Spinal Cord.2. Peripheral Nervous System (PNS)

a. Consists of nerves that lie outside the CNS.

Nervous System has 3 Specific Functions:1. Receives sensory input – Sensory receptors in skin and other organs respond to

external and internal stimuli by generating nerve impulses.2. Performs integration – the CNS sums up the input it receives from all over the

body.3. The CNS generates motor output – nerve impulses from the CNS go through PNS

to muscles and glands.

Nervous Tissue-Contains two types of cells: Neurons and Neuroglian.

-Neurons are cells that transmit nerve impulses between parts of the nervous system-Neuroglia support and nourish neurons.

Neuron StructureThree types of Neurons:

1. Sensory Neuron a. Takes nerve impulses from sensory receptor to the CNS. Sensory

receptors are special structures that detect changes in the environment.2. Interneuron

a. Lies entirely within the CNS; they can receive input from sensory neurons and also from other interneurons in the CNS. They sum up all the nerve impulses received from neurons before they communicate with motor neurons.

3. Motor Neuron a. Takes nerve impulses away from the CNS to an effector (muscle fiber or

gland). Effectors carry out our responses to environmental changes (internal and external).

(Mader p. 249).

Three parts to Neurons:1. Cell Body

a. Contains nucleus, as well as other organelles.2. Dendrites

a. Many short extensions that receive signals from sensory receptors or other neurons.

3. Axon a. Portion of a neuron that conducts nerve impulses. Can be quite long, and

when present in nerves, an axon is called a nerve fiber.Myelin Sheath-Many axons are covered by a Myelin sheath. In the PNS, this covering is formed by a type of neuroglia called Schwann Cells.-In CNS, oligodenrocytes perform same function.-Gaps on axons where there is no myelin sheath are called Nodes of Ranvier.

Nerve Impulse-Resting Potential: When the axon is not conducting an impulse, voltmeter records a “membrane potential” of -65 mV.

-Called resting potential because not conducting an impulse.-Correlates with a difference in ion distribution. *Na+ is greater outside the axon than inside, and the concentration of potassium ions (K+) into the axon (due to sodium-potassium pump).

-Action Potential: A rapid change in polarity across an axonal membrane as the nerve impulse occurs.

-One gated channel protein opens to allow Na+ to pass through membrane, and another opens to allow K+ to pass through the membrane.-Sodium Gates Open: When an action potential occurs, the gates of sodium channels open first, and Na+ flows into the axon (changes from -65 to 40+ mV). This is *depolarization.-Potassium Gates Open: Second, the gates of potassium channels open, and K+ flows to outside the axon. As K+ moves to outside the axon, the action potential changes from +40 mV to -65 mV. This is *repolarization.

(Mader p. 251).

The Synapse-Every axon branches into many fine endings (with small swellings) called an axon terminal.-*Each terminal lies close to a dendrite or the cell body of another neuron. This area is called a synapse. *At a synapse, a small gap called the synaptic cleft separates the sending neuron from the receiving neuron.-Transmission across a synapse is carried out by molecules called neurotransmitters.

Events occur like:1. Nerve impulses traveling along an axon reach an axon terminal2. Calcium ions enter the terminal, and they stimulate synaptic cesicles to merge

with the sending membrane.3. Neurotransmitter molecules are released into the synaptic cleft, and they diffuse

across the cleft to the receiving membrane, where they bind with specific receptor proteins.

-In some synapses, the receiving membrane contains enzymes that rapidy inactivate the neurotransmitter.

Types of Neurotransmitters:-100 substances known or suspected to be neurotransmitters are acetylcholine (aCh), norepinephrine (NE), dopamine, serotonin, glutamate, and GABA (gamma aminobutyric acid).

13.2 The Central Nervous System (Mader p. 254 – 259)-Spinal Cord and Brain where sensory information is received and motor control is initiated.

-Both wrapped in membranes known as meninges and filled with fluid called cerebrospinal fluid.

-Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles (interconnecting chambers that produce and serve as a reservoir for fluid).-CNS composed of two types of nervous tissue: Gray matter (contains cell bodies and short, nonmyelinated fibers) and White Matter (contains myelinated axons that run together in bundles called tracts).

*See Mader p. 254 - 259 for parts and roles of the spinal cord and brain.

-Reflex Actions: The spinal cord is the center for thousands of reflex arcs. A stimulus causes sensory receptors to generate nerve impulses that travel in sensory axons to the s pinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract.

-Spinal cord plays role for internal organs: when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve impulses that pass through sensory fiber to the cord and then up an ascending tract to cardio center in the brain.

12.3 The Peripheral Nervous System (Mader p. 262 – 266)-Nerves are designated as Cranial Nerves when they arise from the brain and Spinal Nerves when they arise from the spine.

-All nerves take impulses to and from the CNS.-Humans have 12 pairs of cranial nerves attached to the brain.

-Some are sensory nerves, some are motor nerves, and others are mixed nerves.-Spinals nerves of humans emerge in 31 pairs from either side of the spinal cord.

-The dorsal root of a spinal nerve contains sensory fibers that conduct impulses inward (toward the spinal cord).-Ventral contains motor fibers that conduct impulses outward (away from the cord) to effectors.

-Ganglion: A collection of cell bodies outside the CNS.

Somatic System-Serves the skin, skeletal muscles, and tendons.

The Reflex Arc-See Mader p. 263.

Autonomic System-Located in the PNS.-Regulates the activity of cardiac and smooth muscles and glands.

-Separated into Sympathetic and Parasympathetic

Both:1. They function automatically and usually in an involuntary manner2. They innervate all internal organs3. They utilize two neurons and one ganglion for each impulse.

-The first neuron has a cell body within the CNS and a preganglionic fiber. The second neuron has a cell body within a ganglion and a postganglionic fiber.

Sympathetic:-Most preganglionic fibers of the symp. Division arise from the middle, or thoracolumbar, portion of the spinal cord and almost immediately terminate in ganglia that lie near the cord.

-The pregang fiber is short, but the postgang fiber that makes contact with an organ is long.

-Symp. Is important during fight or take flight.-Accelerates the heartbeat and dilates the bronchi.-Inhibits digestive tract.-Norepinephrine released.

Parasympathetic:-Includes a few cranial nerves as well as fibers that arise from the sacral portion of the spinal cord.-Pregang is long and the postgang is short.-Promots all the internal responses we associate with a relaxed state; for example, causes the pupil of the eye to contract, promotes digestion, and retards heartbeat.

-Neurotransmitter is acetylcholine.

Compendium Notes Chapter 14 – Senses

Index:Sensory ReceptorsSensory Receptors and SensationsSense of Taste and SmellSense of VisionSense of HearingSense of Equilibrium

14.1 Sensory Receptors (Mader p. 274 – 275)-Sensory Receptors: Dendrites specialized to detect certain types of stimuli.

1. Exteroceptors : Receptors that detect stimuli from outside the body.2. Interoceptors : Receive stimuli from inside the body.

Types of Sensory Receptors:1. Chemoreceptors: Respond to chemical substances in the immediate vicinity (i.e.

taste and smell). Also chemo recept.’s monitor blood pH located in carotid and aorta.

2. Pain Receptors: Type of chemoreceptor – naked dendrites that respond to chemical released by damaged tissues.

3. Photoreceptors: Respond to light energy.4. Mechanoreceptors : Stimulated by mechanical forces, which most often result in

pressure of some sort. When we hear, airborne sound waves are converted to fluid-borne pressure waves.

5. Thermoreceptors : Located in the hypothalamus and skin are stimulated by changes in temperature.

14.2 Sensory Receptors and Sensations (Mader p. 276 – 277)

Proprioceptors-Mechanoreceptors involved in reflex actions that maintain muscle tone, and therby the body’s equilibrium and posture. Help us know position of limbs in space.

-Muscle spindles act to increase the degree of muscle contraction, and Golgi tendon organs act to decrease it.

Cutaneous Receptors-Skins is two layers: Epidermis and Dermis.

See Mader p. 277 for list of Cutaneous Receptors.

Pain Receptors-Includes referred pain (i.e. heart attack felt in left arm).-Pain receptors are sensitive to chemicals released by damaged tissue in organs.

14.3 Senses of Taste and Smell (Mader p. 278 – 279)-Called chemical senses because their receptors are sensitive to molecules in the food we eat and the air we breathe.-Approx. 3,000 taste buds are located on the tongue.-Olfactory Cells: Sense of smell depends on these modified neurons. Each cell ends in a tuft of about five olfactory cilia, which bear receptor proteins for odor molecules.

14.4 Sense of Vision (Mader p. 280 – 284)-Estimated a third of cerebral cortex takes part in processing visual information.

-Sclera: Outer layer of eye, except for Cornea which is the transparent collagen fibers (window of eye).-Choroid: Vascular and absorbs stray light rays that photoreceptors have not absorbed.-Iris: Donut shaped behind Cornea, which regulates size of Pupil.-Ciliary Body: Contains ciliary muscle, which controls the shape of the lens for near and far vision.-Lens: Attached to ciliary body by suspensory ligaments.-Aqueous Humor: Anterior compartment in front of lens holds this fluid. This is continually produced each day (blocked with glaucoma from draining).-Retina: Posterior compartment of lens, filled with gelatinous material called vitreous humor.-Fovea Centralis: Cone cells are densely packed here.-Optic Nerve: Sensory fibers turn into this, which leads to the visual cortex.

*See Mader p. 282 – 283 for how Rod and Cone Cells Work

14.5 Sense of Hearing (Mader p. 286 – 290)-Two sensory functions: hearing and balance.

(Mader p. 286).

(Mader p. 290).

14.6 Sense of Equilibrium (Mader p. 291)-Semicircular Canals: Detect rotational and/or angular movement of the head.

-The three canals are set in 3 areas of space.- Detect rotational and/or angular movement of the head.

-The three canals are set in 3 areas of space.-Little hair cells are found within the ampullae (the enlarged opening of each canal).

-Fluid within semicircular canals flow over and displaces a cupula (gelatinous material inside ampullae), and the pattern of impulses is carried by the vestibular nerve to the brain.