Transcript Nervous System

Nervous System
Purpose
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Communication
Control
Process information
Gather information
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
Types of Neurons
Synapse structure and function
Synapse close-up
Synapse receptors
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
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
Action
Potential
Myelin sheath
Saltatory Conduction
Other Cells of the Nervous
System
• Support
• Nourishment
• Protection
Neuroglial Cells
• Non-neuron cells found in the nervous
system
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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
Three Neuroglial Cell Types
Nerve structure
• Bundles of myelin covered nerve fibers
(axons) covered in connective tissue
• Blood vessels
Organization
• Central nervous system (CNS)
– Brain
– Spinal chord
• Peripheral nervous system (PNS)
– Motor neurons
– Sensory neurons
Path of Impulses
Central Nervous System
• Brain
• Spinal chord
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
Spinal Chord Structure
Pain Withdrawal Reflex
Reflex Loop
Hindbrain
• Medulla – autonomic functions
– Breathing, heart rate, swallowing, blood
pressure
• Pons – stages of sleep
• Cerebellum – coordinates muscles
– Receives info from position and stretch sensors
Midbrain
• Reticular formation
– Sensory relays
– Sensory filter
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
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
Cerebrum -- Gross Anatomy
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
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.
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
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)
Language
• Includes reading, writing, speaking &
understanding words
• Wernicke’s area
– Permits recognition of spoken & written language &
creates plan of speech
– Angular gyrus processes text into a form we can speak
• Broca’s area
– Generates motor program for larynx, tongue, cheeks &
lips
– Transmits that to primary motor cortex for action
Language Centers
Aphasia
• Any language deficit resulting from lesions in
same hemisphere as Wernicke’s & Broca’s areas
• Lesion to Broca’s = nonfluent aphasia
– slow speech, difficulty in choosing words
– entire vocabulary may be 2 to 3 words
• Lesion to Wernicke’s = 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
Lateralization of Cerebral
Functions
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)
EEG and Brain Waves
• Electroencephalogram records voltage changes from
postsynaptic potentials in cerebral cortex
• Differences in amplitude & frequency distinguish 4
types of brain waves
Brain Waves & Sleep
• States of consciousness can be correlated with EEG
• 4 types of brain waves
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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
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
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
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
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
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
Peripheral Nervous System
• Motor neurons
• Sensory neurons
Organization of Nervous System
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
Sensory Neurons
• Mechanoreceptor
– Hearing, pressure, stretch, movement
• Photoreceptor
– Light, vision
• Chemoreceptor
– Olfactory
– Taste
– Pain
Sensory Receptors
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Where is the stimulus located?
How strong is the stimulus?
Stimulus = energy
Sensory receptors transfer signal to other
neurons
• Specialized cells or modified neurons
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
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
Touch
• Mechanoreceptor
Parts of the Ear
• Outer ear
– Pinna and auditory canal
• Middle ear
– Tympanic membrane (ear drum)
– Ossicles (malleus, incus, stapes)
• Inner ear
– Cochlea
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
Pain Receptors
• Chemical receptor
– Detects chemicals
released during tissue
damage
– Receives chemical on
specialized dentrites
Olfactory Receptors
• Chemical receptor
• Different molecules have different cells
with unique receptors for that molecule
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
Photoreceptor Function
• Photoreceptor
constantly firing
in dark which
inhibits post
synaptic neuron
• Light releases
inhibition of
postsynaptic
neuron
Retinal
Structure
• Rods and cones are
not mapped 1:1 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