Nervous System

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Nervous System
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Introduction

• Neurons Nerve cells
• Nerve Impulses transmitted information.
• Nerves are bundles of axons
• Neuroglial cells cells that support the neurons.
• Central Nervous System (CNS) brain and spinal
  cord
• Peripheral Nervous System (PNS) Connects the
  CNS to the rest of the body.

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Anatomy of a Neuron

• 4 Parts
• Cell Body
• Rounded area
• Dendrites
• Receive electrochemical messages
• Axons
• Extensions that send information
• Terminal
• - Contains neurotransmitters

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Functions of the Nervous System

• Receive sensory information from sensory
  receptors.
• Convert environmental information into nerve
  impulses.
• Once received, send messages to effectors, which
  are responsive structures (i.e. muscles)

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Functions of the Nervous System

• 2 types of motor functions
• Somatic Nervous System are consciously
  controlled
• Autonomic Nervous System Involuntary control

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Types of Neuroglial Cells

1. Microglial cells phagocytize bacteria and other
   debris
2. Oligodenmdrocytes provide layers of insulation
   (myelin) around axons of the CNS.

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Types of Neuroglial Cells

• Astrocytes found b/t neurons and blood vessels.
  
• Help regulate concentrations of ions and
  nutrients
• Form scar tissue in the CNS
• 4. Ependymal cells cover specialized parts of
  the brain. (i.e. choroid plexuses)

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Classification of Neurons

• Bipolar Neurons
• 2 processes one from each end. 1 is the axon and
  1 is the dendrite.
• Found in the eyes, nose, and ears.

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Classification of Neurons

• Unipolar Neurons
• 1 single process extending from the cell body.
• Process will divide into 2 shortly after leaving
  the cell body.
• Dendrite branches into the PNS. Axon into the
  CNS.
• Cell bodies can group together to form ganglia
  outside the CNS.

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Classification of Neurons

• Multipolar Neurons
• Have many processes arising from the cell
  bodies.
• Most neurons in the brain and spinal cord.

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Classification of Neurons

• Sensory Neurons
• Carry impulses from the peripheral body parts to
  the brain and spinal cord.
• Either have receptor ends at tips of dendrites or
  they are near receptor cells.
• Most are unipolar, while some are bipolar.

• Neurons also have functional differences.
• Motor Neurons
• Multipolar
• Carry impulses out of brain and spinal cord to
  effectors.
• Stimulate muscles to contract and glands to
  secrete.

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Classification of Neurons
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Classification of Neurons

• Interneurons
• Found in brain and spinal cord.
• Multipolar and link to other neurons.
• Link parts of the brain and spinal cord together
  for processing and interpreting.

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Cell Membrane Potential

• Cell membrane is usually polarized
• Why????
• Distribution of Ions
• Determined by pores or channels in the cell
  membrane.
• Some are always open, while others open and
  close.
• K moves easiest, while Ca is slowest.
• Na is medium

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Cell Membrane Potential

• Resting Potential
• K concentration is usually greater inside the
  cell and Na outside.
• Always have negative ions inside that cannot
  leave.
• Difference in charges b/t the 2 regions is called
  potential difference.
• In a resting cell potential difference is called
  resting potential.
• Na/K pump

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Cell Membrane Potential
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Cell Membrane Potential
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Cell Membrane Potential

• A stimulus will affect the resting potential of a
  neuron by depolarizing the cell (more on the
  inside).
• Changes are graded (proportional to stimuli).
• Once the threshold stimulus has been met. The
  action potential occurs

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Cell Membrane Potential

• Action Potential
• Once depolarization occurs it causes the Na
  channels to open up.
• This causes repolarization.

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Cell Membrane Potential
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Nerve Impulse

• Is caused by a wave of action potentials moving
  down through the axon.

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Impulse Conduction

• Conduction is much faster when the axon is
  myelinated.
• Impulse jumps from schwann cell to schwann cell.
• Action potential is met at the nodes of ranvier.
• All impulses are All-or-None.

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Synaptic Transmission

• Synapse is the junction between communicating
  neurons.
• Terminal releases neurotransmitters across the
  membrane

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Neurotransmitters

• Impulses that increase membrane permeability are
  said to be excitatory.
• If they decrease called inhibitory
• Terminals from many neurons may communicate with
  the dendrites of other neurons.

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Neurotransmitters

• About 50 types.
• Common
• Acetycholine muscles
• Norepinephirne makes you feel good.
• Dopamine feeling good. Low levels assoc. with
  Parkinsons
• Serotonin- leads to sleepiness,mood, emotion, and
  aggression
• Histamine Promotes alertness

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Nerve Pathways

• Reflex Arc Simplest path with few neurons.
• Reflex- Automatic subconscious response to a
  change in stimuli.

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Meningges

• Surround the CNS.
• 3 layers
• Dura mater outermost layer
• Arachnoid layer
• Pia mater layer

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Brain - General

• About 100 billion multipolar neurons
• 3 major portions
• Cerebrum
• Cerebellum
• Brain stem

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Brain - General

• Cerebrum
• Largest
• Centers associated with motor and sensory
  functions and higher mental functions.
• Memory and reasoning
• Diencephalon processes sensory

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Brain - General

• Cerebellum
• Coordinates voluntary muscular movements.
• Brain stem
• Connects parts of the nervous system and
  regulates some visceral activities.

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Structures of the Cerebrum

• Cerebral hemispheres
• Divided by the corpus callosum
• Convolutions (gyri) ridges
• Sulcus grooves
• Fissure deep groove

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Lobes of the Cerebrum

• Frontal
• Parietal
• Temporal
• Occipital
• Cerebral Cortex is the most superficial layer of
  the cerebrum made up of gray matter.
• Where do you find gray matter?

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Functions of the Cerebrum

• Motor areas are found in the frontal lobe
• Motor neurons from one hemisphere cross over to
  other hemisphere at the brainstem
• Controls speech

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Functions of the Cerebrum

• Sensory areas acquire information from
  receptors, produce feelings, and sensations.
• Found in parietal along the central sulcus,
  posterior occipital lobe, temporal lobe, taste is
  along the central sulcus and lateral sulcus.
• Like motor neurons they to cross over.

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Functions of the Cerebrum

• Association areas are neither sensory or motor.
• They connect the two
• Oversee memory, reasoning, verbalizing, judgment,
  and emotion.

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Hemisphere Dominance

• 90 of population the left side is dominant
• Nerve fibers in the corpus callosum connect the
  two hemisphere.

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Ventricles and Cerebral Spinal Fluid

• Ventricle a space in between the cerebral
  hemispheres that contains CSF.
• Choroid Plexus is a ventricle that secretes CSF.
• CSF helps protect and maintain homeostasis.

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Diencephalon

• Located between the cerebral hemispheres and
  above the midbrain.
• Thalamus main center for sensory impulses such
  as pain, touch, and temp.
• Hypothalamus maintains visceral activities, by
  linking the nervous and endocrine systems.

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Diencephalon

• Optic tracts and optic chiasm.
• Pituitary gland
• Pineal gland
• Limbic system thalamus, hypothalamus, and basal
  nuclei.
• Controls emotional experiences

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Brain Stem

• Connects the cerebrum to the spinal cord.
• Composed of the
• Midbrain reflex center for visual and audio.
• Pons rounded bulge underneath brain stem.
• Help cerebrum and cerebellum communicate.

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Brain Stem

• Medulla Oblongata controls cardiac, vasomotor,
  and respiratory.
• Also reflexes such as coughing, sneezing,
  swallowing, and vomiting
• http//www.exploratorium.edu/memory/braindissectio
  n/index.html

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Cerebellum

• Large mass below the occipital lobe.
• Center for integrating sensory motor responses.
• Damage would result in tremors and inaccurate
  movements.

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Peripheral Nervous System

• Nerves that branch out from the Central Nervous
  System.
• 2 Types
• Somatic Nervous System oversees conscious
  activities
• Sensory
• motor
• Autonomic Nervous System Visceral activities
• Parasympathetic
• sympathetic

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Cranial Nerves

1. Olfactory smell
2. Optic sight
3. Oculomotor eye movt
4. Trochlear eyemovt
5. Trigeminal sensation to mouth and face, chewing
6. Abducers eye movt
7. Facial contraction of facial muscles - taste

1. Facial contraction of facial muscles taste
2. Vestibulochoclear balance and hearing.
3. Glosspharyngeal swallowing and taste
4. Vagus Autonomic activity of visceral organs
5. Accessory head, neck,and shoulder movt
6. Hypoglossal tongue movt

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Spinal Cord

• Made up of 31 segments that all give rise to
  spinal nerves.
• Involved with many motor reflexes
• Cervical enlargement gives rise to nerves of
  upper limbs
• Lumbar enlargement gives rise to nerves of lower
  limbs.

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Types of Receptors

• Chemoreceptors
• Pain receptors
• tissue damage
• Thermoreceptors
• Mechanoreceptors
• changes in pressure or movement.
• Photoreceptors

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Somatic Senses

• Touch and Pressure
• Found in epithelial and connective tissue.
• Temperature
• Warm and cold receptors.
• Rapidly adapt.

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Somatic Senses

• Pain
• Receptors every where except the brain.
• Only receptors in the viscera
• Visceral pain may act as referred pain

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Special Senses

• Olfactory Receptors
• Smell
• 12 million receptors
• Gustation (taste)
• 10,000 taste buds
• Tastes
• Sweet
• Sour
• Salty
• bitter

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Special Senseshearing

• Hearing
• External Ear
• Auricle Funnel shaped
• External auditory meatus cannal
• Middle Ear
• Eardrum membrane covered by thin layer of skin
• Auditory ossicles
• Malleus
• Incus
• stapes

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Special Senseshearing

• Eustachian tubes connect the middle ear to the
  throat.
• Inner Ear
• Semicircular canals which provide a sense of
  equalibrium.
• Cochlea functions for hearing.

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Special SensesVision

• Cornea transparent bulge forward where light
  enters
• Sclera white portion of the eye.
• Iris colored portion
• Lens Lies behind Iris
• Pupil opening that allows light to enter.
• Retina contains visual receptors

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Special SensesVision

• Rods photoreceptor that receives black and
  white.
• Cones photoreceptor that receives color.
• Fovea sharpest vision.
• Optic nerve is where your blind spot is.