Module 3

  1. Internal structure of a cell

    1. Debate in the early 1900s

      1. Golgi

        1. The nervous system is composed of a network of interconnected fibers: a “nerve net”

      2. Cajal

        1. The nervous system is made of discrete cells

        2. Neuron hypothesis

          1. Neurons are the units of brain function

        3. Used the Golgi stain to show the nervous system was made up of discrete cells, thereby supporting the neuron hypothesis

        4. Neuron theory

          1. Neurons are the nervous system's functional units

            1. Now the accepted theory of brain organization

    2. Basic structure of a neuron

      1. Core region called the soma or cell body

        1. Contains nucleus

        2. Integrates info

      2. Dendrites

        1. Branching extensions that collect info from other cells

        2. Gathers info from other neurons

      3. Main root is the single axon, which carries messages to other neurons

        1. A neuron has only one axon, but most have many dendrites

        2. Carries info to be passed on to other cells

  2. The base of information processing

    1. Neurons

      1. Most behaviors are produced by groups of hundreds or thousands of neurons

      2. Functional groups of neurons, or neural networks, connect wide areas of the brain and spinal cord

      3. An ongoing effort aims to map the structural connectivity, the physical wiring or connectome, of the entire human brain

      4. Each neuron's appearance is distinctive, but they are also the essence of plasticity

    2. Structure of neuron

      1. Dendritic spines

        1. Protrusion from a dendrite that greatly increases its surface area and is the usual point of contact with axons of other cells

          1. Ideally need a wide healthy base to build a synapse with an axon so there is a lot of surface area for that communication to occur

        2. All of those protrusions can expand and contact and wither away so that there is no point of contact with those axons

          1. This can happen from any maladaptive experience or injury

            1. Especially stress

        3. Very sensitive

      2. Axon hillock

        1. Juncture of the soma and axon, where the action potential begins

      3. Axon collaterals

        1. Branches of an axon

      4. Telodendria

        1. End branches of an axon

      5. Terminal button

        1. Knob at the tip of an axon that conveys info to other neurons; also called an end foot

          1. Connect to dendritic spines, dendrites, or the soma itself and form a synapse

      6. Synaps

        1. Gap between one neuron and another neuron

        2. This is where that chemical communication occurs

        3. Usually between an end foot of the axon of one neuron and a dendritic spine of another neuron

    3. Function of neurons

      1. Sensory neurons

        1. Carry info from the sensory receptors in or on the body to the spinal cord

        2. Allows us to interpret the world around us

      2. Interneurons (association neurons)

        1. Include association of sensory and motor activity within the CNS

          1. Ex. if someone sees a bee and is allergic to a bee, this information is going to take this sensory information and communicate danger, and the motor output can look vastly different than someone who isn’t allergic

      3. Motor neurons

        1. Send signals from the brain and spinal cord to the muscles

    4. Shape of function of neurons

      1. (A) Sensory neurons of many types detect stimulation or collect info and pass it on to (B) an interneuron. The multibranched interneuron dendrites collect info from varied sources and link to (C) motor neurons, which are distinctively large and pass on commands to muscles to move

      2. Sensory neurons

        1. Bipolar neuron

          1. Contains one axon and one dendrite

          2. Transmits afferent (incoming) sensory information from the retina's light receptors to the neurons that carry info into the brain’s visual centers

        2. Somatosensory neuron

          1. Is a brain cell that brings sensory info from the body into the spinal cord

      3. Interneurons (association cells)

        1. Stellate (star-shaped) cell

          1. Small

          2. Many dendrites that extend around the cell body

          3. Larger brains contain more (behavioral complexity)

        2. Pyramidal cell

          1. Has a long axon, a pyramid-shaped cell body, and two sets of dendrites, apical and basal

          2. Carries info from the cortex to the rest of the brain and spinal cord

        3. Purkinje cell

          1. Distinctively shaped with extremely branched dendrites that form a fan

          2. Carries info from the cerebrum and the spinal cord

      4. Motor neurons

        1. Reside in lower brainstem and spinal cord

        2. These neurons have extensive dendritic networks, large cell bodies, and long axons taht connect to muscles

          1. Our movement is electrical communication

        3. All efferent (outgoing) neural info passes through motor neurons to reach the muscles

      5. Neuronal networks

        1. Sensory neurons collect afferent (incoming) info from the body and connect to interneurons that process the info and pass it on to motor neurons

        2. The motor neurons' efferent connections move muscles and produce behavior

        3. Three organizational aspects of neurons: features of neuronal networks

          1. Input, association, and output

    5. The language of neurons: excitation and inhibition

      1. Each neuron receives thousands of excitatory and inhibitory signals every second

      2. Neurons sum these signals and respond accordingly, becoming active or not

      3. A wide range of behavior possibilities emerge from the simple yes/no language of neurons

  3. Classes of glial cells

    1. Glial cell

      1. Provides insulation, nutrients, and support and that aids in repairing neurons and eliminating waste products

      2. Produced throughout an organism's life, and errors in their replication are a main source of abnormal growths (brain tumors)

      3. Neurons make up 50%-60% of the brain, and glial cells make up the rest

      4. Five classes

        1. Ependymal cells

          1. Small ovoids

          2. Found in the walls of ventricles

          3. Make and secrete cerebrospinal fluid (CSF)

            1. CSF and ventricles supply the brain with a lot of nutrients

            2. CSF helps suspend the brain, and meninges form a protective layer

              1. Important

            3. A lot of development starts occurring from these ventricles and ependymal cells

          4. Hydrocephalus

            1. Buildup of pressure in the brain and swelling of the head caused if the flow of CSF is blocked

            2. Can result in severe intellectual impairment