Nervous System

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Chapter 48

• Nervous System

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Neurons

• Functions
• receive information
• integrate information produce response
• conduct signal
• transmit signal
• Anatomy
• dendrites
• cell body
• axon
• synaptic terminal

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Anatomy of a neuron

• Dendrites branched tendrils extend out from
  cell body
• receive information from other neurons or
  environment
• Cell Body integration center
• receives signal from dendrites
• if enough positive signal is received it emits an
  action potential

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Anatomy of a neuron

• Axon long thin fiber
• conducts the electrical signal
• some are very long (3 feet)
• bundled together in nerves
• wrapped with myelin
• allows for rapid conduction
• Synaptic terminal transmission of signal to
  other cells
• contain neurotransmitters to carry signal to
  other neurons

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How is Neural Activity Produced

• Inactive neurons maintain a constant electrical
  difference
• resting potential
• -40 to 90 mV
• When neuron is stimulated resting potential is
  changed
• if it gains enough positive charge (threshold)
  then an action potential is created

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Ions and Electrical Signals

• How is resting potential generated?
• Cytoplasm and Extracellular environment is very
  different
• Inside K and Org-
• Outside Cl- and Na
• maintained with Na K pumps

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Ions and Electrical Signals

• K can flow out, but Na cannot flow in
• leaving only Org- inside the cell
• When negative charge is enough K stops diffusing

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Ions and Electrical Signals

• Action potential generation
• When appropriate signal is generated Na channels
  open causing influx of Na and a positive charge
  is generated
• This charge travels down the axon to synaptic
  ending

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Neuron Communication

• Occurs at synapses
• postsynaptic potentials (PSPs)
• Tiny gap separates two neurons
• When signal reaches the end of the presynaptic
  neuron it causes release of neurotransmitters
  which bind to postsynaptic neuron

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Different Potentials Created

• Excitatory PSPs (EPSPs)
• make neuron less negative and chances of creating
  an action potential are greater
• Inhibitory PSPs (IPSPs)
• make neuron more negative and chances of creating
  an action potential are less
• When EPSPs and IPSPs are added together, if
  enough positive charge is generated an action
  potential occurs

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Neurotransmitters

• Travel from Presynaptic terminals to postsynaptic
  terminals generating some type of PSP

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Feature of Nervous System

• Information processing
• determine stimulus type
• signal the intensity of the stimulus
• integrate information from many sources
• initiate and direct the response

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Determining Stimulus Type

• All action potentials are the same
• depending on which neurons are stimulated,
  determines what the stimulus type is
• sometimes you get false information
• Optic nerve light
• Olfactory nerve odor

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Determining Stimulus Intensity

• All action potentials carry the same intensity
• intensity is coded by frequency of action
  potentials
• also by the number of neurons that fire

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Processing Information

• Brain and neurons process information through
  convergence
• lots of neurons converge onto smaller neurons
• here the signal is added up and an appropriate
  response is generated

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Divergence of Signal

• Response signal may travel to many neurons
  generating an appropriate response
• one neuron to muscles and glands

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Neuron and Muscle Relationship

• Sensory neurons
• respond to stimulus
• Association neurons
• receive signals from many sources
• send signal to motor neurons
• Motor neurons
• activate muscles or glands
• Effectors
• muscles or glands that perform response directed
  by nervous system

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Reflex

• Simplest behavior in animals
• does not involve conscious portions of the brain

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Types of Nervous Systems

• Diffuse system
• found in jellyfish
• Centralized system
• found in higher animals
• due to cephalization in bilateral organisms

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Human Nervous System

• Divided into two parts
• Central nervous system (CNS)
• brain and spinal cord
• Peripheral nervous system (PNS)
• nerves that connect the CNS to the body

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Peripheral Nervous System

• Axons of neurons carry signals to the CNS
• and signals from CNS to rest of the bod
• Sensory Neurons
• carry signals from sensory organs
• Motor Neurons
• Somatic nervous system
• control voluntary movements
• Autonomic nervous system
• control involuntary movements

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Autonomic Nervous System

• Form synapses on heart, smooth muscle, and glands
• Sympathetic Division
• prepares body for stressful or energetic activity
• redirects blood from digestive system to muscles
  and heart
• pupils widen, air passages in lungs expand

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Autonomic Nervous System cont.

• Parasympathetic Division
• prepares body for rest and digestion
• heart rate slows, blood is redirected to
  digestive system

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Central Nervous System

• Made up of Brain and spinal cord
• Sensory information is received and sorted
• Protection
• Brain cranium
• Spine vertebral column
• Meninges triple layer of connective tissue
• Cerebrospinal fluid cushions CNS and provides
  nutrients
• Blood-brain barrier capillaries in the CNS are
  less permeable than the rest of the body

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Spinal Cord

• Neural cable about 2 cm thick
• Axons from sensory and motor neurons merge here
• Center of spinal cord is made up of grey matter
• surrounded by white matter
• axons that carry signal to the brain and back

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Brain

• Three parts
• Hindbrain
• Medulla breathing, heart rate, blood pressure
• Pons influence transitions between sleep and
  awake
• Cerebellum coordinates movements in the body
  and learning

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Brain

• Midbrain reduced in humans
• auditory relay center
• reflex movements of the eye
• reticular formation receives input from every
  sense
• Forebrain cerebrum
• Thalamus organizes sensory input
• Limbic system produces basic and primitive
  emotions and behaviors
• hypothalamus
• amygdala produce sensations like pleasure,
  punishment, and sexual arousal

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Brain

• Forebrain cont
• limbic system cont
• hippocampus long term memory
• Cerebral cortex
• Cerebral hemispheres communicate via corpus
  callosum
• allows us to think and plan

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How does the brain produce the Mind

• Left and Right Brain specializations
• in right handed people
• Left hemisphere controls speech, reading,
  writing, language, math, and logic
• Right hemisphere controls musical skills,
  artistic ability, facial recognition, emotions
• Gender differences
• females can recover from hemisphere damage faster

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Memory

• Working memory
• short term memory
• as long as axons are stimulated the memory
  remains
• Long term memory
• weak synapses are strengthened adding memory

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Senses - Sound

• Ear
• Outer
• ear and auditory canal
• Middle
• eardrum, hammer anvil and stirrup, and eustachian
  tube
• Inner
• cochlea

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Senses - Light

• Photoreceptors detect light
• Types of eyes
• compound
• mammalian

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Senses - Light
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Vertebrate Eye

• Contains Rods and Cones
• specialized photoreceptors
• Cones detect color
• Rods detect more light (black and white)
• Binocular vision for predators
• eyes are in front of the head
• Peripheral vision for prey
• eyes are on the sides of the head

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Senses - Chemical

• Smell olfaction for airborne chemicals
• Taste for chemicals dissolved in liquid
• Smell
• receptors are hairlike dendrites protruding from
  mucous membranes
• bind certain molecules and send a message to the
  brain

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Senses - Chemical

• Taste
• taste buds contain taste receptors

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Pain

• When cells are damaged the contents of the cell
  stimulate pain receptors