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The Nervous system. The nerve cell is the basic unit of communication in the vertebrate nervous system. Three Classes of neurons. The Neural circuit consists of Sensory neurons receptor for stimulus Interneuron integrate signals Motor neuron transfer signal to effector (muscle).

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The Nervous system

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The nervous system l.jpg

The Nervous system

The nerve cell is the basic unit of communication in the vertebrate nervous system


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Three Classes of neurons

  • The Neural circuit consists of

    • Sensory neurons

      • receptor for stimulus

    • Interneuron

      • integrate signals

    • Motor neuron

      • transfer signal to effector (muscle)


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Anatomy of a Neuron

  • Cell body: functional portion

  • Dendrites: short extensions that receive signals

  • Axon: long extension that transmits impulses


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How does a neuron hold and move info?

  • A neuron at rest has a voltage difference across the plasma membrane called a resting voltage potential

  • An action potential is when this charge across the membrane is briefly switched

  • The action potential moves down the membrane at a rapid pace.

  • Ap can move faster over mylenated portions is called saltatory conduction


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How does a signal move from one neuron to another?

  • A synaptic cleft divides 2 neurons

  • The AP will not move across the synaptic cleft

  • Neuro transmitters are released by the signal cell to the receiver cell

  • Move by diffusion


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Types of chemical synapse

  • Acetylcholine: neuromuscular junctions, glands, brain and spinal cord

  • Norepinepherine: affects brain regions concerned with emotions, dreaming


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Signals between the brain and spinal cord move to the body regions by nerves

Sensory nerves move a signal towards the brain and spinal cord

Motor neurons move a signal from the brain or spinal cord to the body

Paths of information flow


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Central nervous system

CNS

Is the brain and spinal cord

Peripheral nervous system

PNS

all nerves that carry signals to and from the CNS

Divisions of the nervous System


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Parts of the PNS

  • Sensory Division carries info to the brain and spinal cord.

  • Motor Division carries info from the brain to the bodies effectors (things that do the work)


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Somatic nerves relay commands to and from skeletal muscle

Voluntary control

Autonomic nerves send signals to and from smooth muscles

Involuntary control

Sympathetic

Parasympathetic

The Motor division of the PNS has 2 divisions


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Parasympathetic

slow down the body activity when the body is not under stress

Rest and digest

Sympathetic

increase overall body activity during times of stress, excitement or danger

fight or flight response

hormone epinephrine

The autonomic divisions


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Sympathetic and Parasympathetic

  • Are Antagonistic

  • Work towards the automatic, subconscious maintenance of homeostasis.


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Spinal cord

31 pair of spinal nerves

Grey matter

White matter

Controls some reflex actions like bladder emptying

Brain parts

Hindbrain

medulla oblongata

cerebellum

pons

Midbrain

Forebrain

cerebrum

thalamus

hypothalamus

Components of the CNS


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Other parts of the CNS

  • The two cerebral hemispheres communicate through the corpus collosum

    • left verbal skills

    • right nonverbal skills such as music math, abstract

  • Brain cavities and Canals

    • cerebrospinal fluid surrounds and fills in cavities in the brain

    • Blood Brain barrier- controls what moves into the brain. Will prevent infections.


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Our state of consciousness

  • The CNS governs sleeping, dozing, daydreaming and full alertness

  • neurons of the reticular activating system control the changing levels of consciousness by releasing serotonin.


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Limbic system

  • Involved in both memory and emotion.

  • Is involved with behavior.

  • Odors pass through this system and may influence or behavior and emotions.


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Association is the linkage of information to structural and chemical changes

short term- few bits lasts a couple of hours

Long term- permanent and limitless

The most important info goes rapidly into long term storage

memory is stored in a form resistant to degradation

Possibly caused by changes in synapses.

Memory


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Tips on studying

  • Concentrate on what you study.

  • Minimize interference.

  • Study takes time.

  • Break material into smaller portions.

  • Rephrase materials in your own words.

  • Test yourself to see what you know.


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Disorders of the nervous system

  • Trauma

  • Infections

  • Transmission and synaptic defects.

  • Abnormal growth


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Sensory Reception

If a tree falls in the woods with no one to listen does it make a sound?


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Receptors

  • Are the actual structures that respond to our environment.

  • Each receptor will respond to a different signal.

  • Essentially translators, they translate an energy into one that can be perceived by the brain.


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Sensory systems consist of

  • Each system has 3 parts

    • 1) sensory receptors.

    • 2) pathway to the brain.

    • 3) region of the brain that recognizes this section.


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Chemoreceptors

Mechanoreceptors

Thermoreceptors

Nociceptors

Photoreceptors

olfaction and taste

touch, stretch, hearing, equilibrium

radiant energy, infared

pain receptors

light

Types of sensory Receptors


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Sensory Pathways

  • If a receptor is stimulated enough it results in an action potential.

  • The action potential reaches the brain.

  • The stronger the stimulus the greater number of action potentials reach the brain.

  • Sensory adaptation is when the action potentials are reduced by a constant stimulus.

  • Certain receptors will not adapt.


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Touch & Pressure

Temperature

Pain

Muscle sense

Mechanoreceptors that respond to changes or constant pressure

Increase in temperature causes and increase in AP

Respond to intense stimulus on other receptors, cannot be ignored

Mechanoreceptors give measurement as to the location of all the muscles and bones in a given moment.

Somatic sensations


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Limb position, length and tension

  • How do we know where we are at?


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Referred pain


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Gustation: Taste

Receptors located on tongue, roof of mouth, throat and palate

Four tastes

sweet

sour

bitter

salty

Olfaction: smell

detect chemicals

olfactory bulbs in brain interpret smell

smell is often combined with emotion

Taste and Smell


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Taste

  • Taste Bud 25 cells

  • Taste hairs project into mouth

  • Hairs contain receptors

  • Categories

    • Sweet

    • Sour

    • Salty

    • bitter


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Hearing

  • Acoustical receptors detect vibrations

  • The ear

  • In the organ of corti loudness is determined by The total number of cells that are stimulated

  • Pitch depends on frequency of vibration


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Vestibular apparatus

Closed system of fluid filled sacs

Contain otoliths that detect changes in orientation as well as acceleration

Overstimulation of the hair cells of the vestibular apparatus results in motion sickness

Balance


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Vestibular apparatus


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The Eye


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Outer sclera (white) (is all the way around)

Cornea (clear)

Pupil (opening to the back)

Lens (transparent)

Retina (back side has photoreceptors and support material)

Fovea has highest concentration of photoreceptors.

Structure of the eye


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Regulating light amount

  • The iris adjusts to amount of light entering the eye.

  • The lens goes through accommodation to adjust lens curvature (as we age the lens cannot buldge enough to focus on a close object)


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Light must reach the sensors by going through neurons.

  • Outermost layer is pigmented to absorb light not absorbed by the sensors

  • Photoreceptors are in middle layer

  • Translucent neurons and ganglions are on top of the photoreceptors.


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Production of Action Potentials by Rods and Cones

  • Within these cells flattened disks contain photopigment

  • When this protein absorbs light it changes conformation, if enough are activated they cause an action potential.

  • Rods contain rhodopsin and are most sensitive to dim light

  • Cones contain different pigments


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Rods and Cones

  • Bright light tends to use more cones, 300x more sensitive

  • Dim light uses Rods and Rhodopsin, it is broken apart by light and must be remade (hence the 5-10 minute wait to see in darker areas)


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Photoreceptors are in the retina

When rods or cones are stimulated they send a signal to the brains visual cortex.

In the brain the final interpretation makes sense of sight

Signaling to visual perception


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Problems with the Eyes

  • Retinal detachment: retina separates form choroid

  • Cataracts: lens becomes opaque

  • Color blindness: Inability to distinguish colors, is a genetic disease, lacks specific types of cones


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The Endocrine system

The oldest method of control is using a signal molecule that moves from one part of the body to the other


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The Endocrine System Regulates

  • Salt and water balance

  • Blood pressure

  • Stress responses

  • Digestion

  • Cellular metabolism

  • Production of RBC’s

  • Growth and development


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Location of Endocrine Glands


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Hormones and other signal molecules

  • Hormones: molecules secreted by glands into the blood that move to a nonadjacent target

  • Neurotransmitters: act on a directly adjacent cell

  • Local signaling molecule: act quickly and degrade quickly

  • Pheromones: secreted by glands and target cells in other organisms


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Signaling Mechanisms

  • Requirements

    • Cells that secrete the signal molecule are either within a gland or nervous tissue

    • The signal molecule

      • Steroid hormone (fat soluble will move through the plasma membrane)

      • Non steroid hormone (peptides and other molecules must bind to a receptor on the cell)

    • Target cell


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Good fit rx occurs

Does not bind,

No reaction

Target cell activities

  • Different hormones activate different cellular response mechanisms

  • No all cells have receptors for all hormones:

Three possible hormones

A cell with a single receptor on it


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Characteristics of the Endocrine system

  • Each hormone acts only on certain cells

  • Cells respond only when they have receptors

  • Is slower than nervous system control

  • Endocrine and nervous system to interact with one another.


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Interaction of Endocrine System and Nervous System


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Negative Control using Hormones


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The pancrease an endocrine and an exocrine gland

  • Glucagon: raises blood sugars, release of stores and AA metabolism

  • Insulin: lowers blood sugars opposes glucagon

  • Somatostatin: inhibits secretion of the above enzymes


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Bracketing using hormones


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Regulation of Blood Calcium concentration

  • Increase Calcium

    • Parathyroid Hormone: removes calcium and phosphate from bone, increase absorption, retention of calcium in kidneys

  • Decrease of Calcium

    • Calcitonin


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Oxytocin and nursing, a cascade of events

  • At the end of pregnancy, Estrogen rise.

  • Uterus produces more oxytocin receptors

  • Fetus produces oxytocin, starts a cycle of material production of oxytocin

  • Oxytocin is a part of the neuroendocrine reflexes and will help in the smooth muscle contractions which cause the release of milk.


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