Nervous System

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Nervous System
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Purpose

• Communication
• Control
• Process information
• Gather information

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Neuron

• Cell body
• Contains nucleus and most normal cell functions
• Receives chemical signal from adjacent neuron
• Axon
• Transmits electrical impulse to synaptic
  terminals
• Synaptic terminals
• Transmits chemical signal to cell body of
  adjacent neuron

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Types of Neurons
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Synapse structure and function
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Synapse close-up
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Synapse receptors
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Membrane Potential

• Inside of every cell is negative compared to the
  outside
• Inside
• Anions proteins, amino acids, sulfate and
  phosphate
• Cations potassium (K)
• Outside
• Anions chloride (Cl-)
• Cations sodium (Na)
• Anions and cations cannot pass through the lipid
  bilayer they must pass through selective
  channels

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Action Potential

• Voltage-gated ion channels
• Ions move according to gradient and charge
  attraction
• Potassium (more permeable)
• Sodium (less permeable)
• Sodium/potassium pump
• Requires ATP
• Pumps Na out of cell and K into cell

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Action Potential
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Myelin sheath
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Saltatory Conduction
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Other Cells of the Nervous System

• Support
• Nourishment
• Protection

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Neuroglial Cells

• Non-neuron cells found in the nervous system
• Schwann forms myelin sheath in PNS
• Microglial protect against microbes
• Astrocytes structural and nutritive support
• Oligodendroglial forms myelin sheath in CNS
• Ependymal line CNS cavities and produce
  cerebrospinal fluid

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Three Neuroglial Cell Types
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Nerve structure

• Bundles of myelin covered nerve fibers (axons)
  covered in connective tissue
• Blood vessels

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Organization

• Central nervous system (CNS)
• Brain
• Spinal chord
• Peripheral nervous system (PNS)
• Motor neurons
• Sensory neurons

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Path of Impulses
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Central Nervous System

• Brain
• Spinal chord

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Spinal Chord

• Function
• Transmits signals from brain and other parts of
  the body
• Reflex loop
• Simple motor functions (walking, running)
• Structure
• Gray matter
• Cell bodies of motor neurons
• White matter
• Axons of neurons running up and down spinal chord

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Spinal Chord Structure
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Pain Withdrawal Reflex
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Reflex Loop
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Hindbrain

• Medulla autonomic functions
• Breathing, heart rate, swallowing, blood pressure
• Pons stages of sleep
• Cerebellum coordinates muscles
• Receives info from position and stretch sensors

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Midbrain

• Reticular formation
• Sensory relays
• Sensory filter

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Forebrain

• Thalamus
• Transmits info to and from limbic system, senses,
  cerebrum and cerebellum
• Limbic system
• Basic emotions, drives and behaviors
• Cerebral cortex
• Thinking and information processing

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Cerebrum

• Two hemispheres
• Connected by corpus callosum (white matter)
• Each half divided into 4 lobes
• Frontal, parietal, temporal, occipital lobes
• Cortex
• 3mm layer of gray matter
• Extensive folds to increase surface area

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Cerebrum -- Gross Anatomy
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Functions of Cerebrum Lobes

• Frontal
• Voluntary motor functions, planning, mood, smell
  and social judgement
• Parietal
• Sensory reception integration of sensory
  information
• Occipital
• Visual center of brain
• Temporal
• Hearing, smell, learning, memory and emotional
  behavior

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Sensory Homunculus

• Demonstrates that the area of the cortex
  dedicated to the sensations of various body parts
  is proportional to how sensitive that part of the
  body is.

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Sensory Association Areas

• Association areas interpret sensory information
• Somesthetic association area (parietal lobe)
• Position of limbs, location of touch or pain, and
  shape, weight texture of an object
• Visual association area (occipital lobe)
• Identify the things we see
• Faces are recognized in temporal lobe
• Auditory association area (temporal lobe)
• Remember the name of a piece of music or identify
  a person by his voice

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Motor Control

• Intention to contract a muscle begins in motor
  association (premotor) area of frontal lobes
• Precentral gyrus (primary motor area) processes
  that order by sending signals to the spinal cord
• Motor homunculus is proportional to number of
  muscle motor units in a region (fine control)

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Language

• Includes reading, writing, speaking
  understanding words
• Wernickes area
• Permits recognition of spoken written language
  creates plan of speech
• Angular gyrus processes text into a form we can
  speak
• Brocas area
• Generates motor program for larynx, tongue,
  cheeks lips
• Transmits that to primary motor cortex for action

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Language Centers
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Aphasia

• Any language deficit resulting from lesions in
  same hemisphere as Wernickes Brocas areas
• Lesion to Brocas nonfluent aphasia
• slow speech, difficulty in choosing words
• entire vocabulary may be 2 to 3 words
• Lesion to Wernickes fluent aphasia
• speech normal excessive, but makes little sense
• Anomic aphasia speech understanding are
  normal but text pictures make no sense
• Others understanding only 1st half of words or
  writing only consonants

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Lateralization of Cerebral Functions
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Cerebral Lateralization

• Left hemisphere is categorical hemisphere
• specialized for spoken written language,
  sequential analytical reasoning (math
  science), analyze data in linear way
• Right hemisphere is representational hemisphere
• perceives information more holistically,
  perception of spatial relationships, pattern,
  comparison of special senses, imagination
  insight, music and artistic skill
• Highly correlated with handedness
• 91 of people right-handed with left side is
  categorical
• Lateralization develops with age
• Trauma more problems in males since females have
  more communication between hemisphere (corpus
  callosum is thicker posteriorly)

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EEG and Brain Waves

• Electroencephalogram records voltage changes from
  postsynaptic potentials in cerebral cortex
• Differences in amplitude frequency distinguish
  4 types of brain waves

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Brain Waves Sleep

• States of consciousness can be correlated with
  EEG
• 4 types of brain waves
• Alpha occur when awake resting with eyes closed
• Beta occur with eyes open performing mental tasks
• Theta occur during sleep or emotional stress
• Delta occur during deep sleep
• Sleep is temporary state of unconsciousness
• Coma is state of unconsciousness with no possible
  arousal

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Stages of Sleep

• Non-REM sleep occurs in stages
• 4 stages occurring in first 30 to 45 minutes of
  sleep
• stage 1 is drifting sensation (would claim was
  not sleeping)
• stage 2 still easily aroused
• stage 3 vital signs change -- BP, pulse
  breathing rates drop
• reached in 20 minutes
• stage 4 is deep sleep -- difficult to arouse
• seems to have a restorative effect
• REM sleep occurs about 5 times a night
• rapid eye movements under the eyelids, vital
  signs increase, EEG resembles awake person dreams
• may help sort strengthen information from memory

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Sleep Stages and Brain Waves

• Brain waves change as we pass through 4 stages of
  sleep alpha, to sleep spindles, to theta and
  finally to delta waves during deep sleep

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Cognition

• Cognition is mental processes such as awareness,
  perception, thinking, knowledge memory
• 75 of brain is association areas where
  integration of sensory motor information occurs
• Examples of effects of brain lesions
• temporal lobe -- inability to recognize objects
  or inability to recognize faces
• frontal lobe -- problems with personality

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Memory

• Information management requires learning, memory
  forgetting (eliminating the trivia)
• Abnormalities
• pathological inability to forget have trouble
  with reading comprehension
• can not store new data
• can not remember old data
• Hippocampus - organizes sensory cognitive
  information into a memory
• lesions cause inability to form new memories
• Cerebellum helps learn motor skills
• Amygdala important in emotional memory

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Emotion

• Prefrontal cortex controls how emotions are
  expressed (seat of judgement)
• Emotions form in hypothalamus amygdala
• artificial stimulation produces fear, anger,
  pleasure, love, parental affection, etc.
• electrode in median forebrain bundle in rat or
  human and a foot pedal
• press all day to the exclusion of food (report a
  quiet, relaxed feeling)
• Much of our behavior is learned by rewards and
  punishments or responses of others to them

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Peripheral Nervous System

• Motor neurons
• Sensory neurons

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Organization of Nervous System
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Motor Neurons

• Carry signals from the CNS to muscles and glands
• Somatic voluntary responses
• Skeletal muscles
• Autonomic involuntary responses
• Cell bodies found in ganglia
• Organs
• Glands
• Smooth muscles

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Sensory Neurons

• Mechanoreceptor
• Hearing, pressure, stretch, movement
• Photoreceptor
• Light, vision
• Chemoreceptor
• Olfactory
• Taste
• Pain

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Sensory Receptors

• Where is the stimulus located?
• How strong is the stimulus?
• Stimulus energy
• Sensory receptors transfer signal to other
  neurons
• Specialized cells or modified neurons

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Receiving Sensory Information

• Sensory Transduction
• Converts received signal to action potential
• Amplification
• Signal transmitted contains more energy than
  signal received
• Transmission
• Action potential
• Integration
• Information processing

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Types of Sensory Receptors

• Mechanoreceptor
• Stretch or bending of plasma membrane
• Hearing, pressure, stretch, movement
• Chemoreceptor
• Binding of specific molecules to protein
  receptors in plasma membrane
• Olfactory, taste, pain
• Photoreceptor
• Photons hitting specific proteins in plasma
  membrane
• Vision

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Touch

• Mechanoreceptor

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Parts of the Ear

• Outer ear
• Pinna and auditory canal
• Middle ear
• Tympanic membrane (ear drum)
• Ossicles (malleus, incus, stapes)
• Inner ear
• Cochlea

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Auditory Receptors

• Different pitches vibrate different parts of the
  basilar membrane
• The basilar membrane vibrates against hair cells
  in the cochlear duct
• Shape and thickness of basilar membrane effects
  vibrations

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Pain Receptors

• Chemical receptor
• Detects chemicals released during tissue damage
• Receives chemical on specialized dentrites

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Olfactory Receptors

• Chemical receptor
• Different molecules have different cells with
  unique receptors for that molecule

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Photoreceptors

• Modified neurons containing light absorbing
  pigment
• Rods
• Black and white
• Night vision
• Pigment rhodopsin
• Cones
• Color
• 4 types red, blue and green
• Pigment photopsins

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Photoreceptor Function

• Photoreceptor constantly firing in dark which
  inhibits post synaptic neuron
• Light releases inhibition of postsynaptic neuron

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Retinal Structure

• Rods and cones are not mapped 11 to ganglion
  cells
• More cells per ganglion cell equals lower
  resolution but greater sensitivity
• Dogs have 5x the number of rod cells per ganglion
  cell
• Optic nerve exits through the fovea which creates
  your blind spot