Nervous System Flashcards
The Neuron - Name and describe the 4 regions of a neuron.
(1) Dendrites - receptive portion, receive synaptic afferent inputs from upstream neurons (2) Cell body (aka Soma) - integrative portion of neuron, incoming signals from dendrites summed together, contains nucleus/most organelles surrounded by cytoplasm/perikaryon (3) Axon - conductile portion of neuron, efferent signals flow down axon in one direction, toward terminal branches (4) Synaptic terminal - effector portion of neuron, high concentration of vesicles containing neurotransmitters that excite/inhibit next neuron upon release
The Neuron - What determines the type of a neuron? Define the 3 basic types of neuron.
Relative positions of its structural features; (1) Multipolar neuron - multiple dendrites extending from cell body & single axon extending in the opposite direction (2) Bipolar neuron - single dendrite extends from cell body, opposite side from which single axon extends (3) Pseudounipolar neuron - single stem comes off soma & splits into single dendrite & axon
The Neuron - What is an axon hillock?
Conical elevation of cell body from which single axon extends
The Neuron - What is the first step to viewing a neuron under the microscope?
Distinguishing between dendrites and axon(s) (longer and originate from axon hilock)
The Neuron - What is Nissl substance? What is its significance in terms of visualizing neurons?
Equivalent of rough ER in neuron; Makes it easier to distinguish dendrites from axons based on fact that it is found only in soma/dendrites never axon hillock/axon
The Neuron - What are neurofibrils? How are they visualized? What is their importance?
Aggregates of microtubles and neurofilaments that extend from the soma out into the dendrites; Visualized by EM; Mediate slow and fast axonal transport (method by which cytoskeletal elements and membrane-bound organelles move to and from soma)
Nerve Fibers - Whar is a nerve fiber? Where they found? What function do Schwann cells and oligodendrocytes serve? What is the difference between them?
Nerve fiber = neuron’s axon & myelin sheath; Form myelin sheath of axon or associate with axon without forming myelin sheath; Schwann cells - in PNS, myelinates axon of one neuron & Oligodendrocytes - in CNS, each can myelinate multiple neurons;
Nerve Fibers - What are myelin sheaths? What are nodes of Ranvier? What function do they serve?
Electrical insulators that prevent current from leaving axons; Interruptions of myelin sheath = discontinuinity between Schwann cells/Oligodendrocytes along nerve fiber; Current hops between nodes and travel much faster compared to an unmyelinated axon of similar diameter
Nerve Fibers - Define endoneurium, perineurium,& epineurium.
Endoneurium = Delicate connective tissue covering on individual peripheral nerve fibers; Perineurium = More extensive layer of connective tissue that surrounds bundles of nerve fibers; Epineurium = Connective tissue sheath encapsulating entire peripheral nerve trunk
Sensory Nerves - What do sensory nerves do? What type of neurons are sensory neurons? Name and describe the various types of sensory nerve receptors.
Carry impulses to spinal cord; Pseudounipolar; (1) Exteroceptors - carry sensations of pain, temp, touch, & pressure from skin & connective tissue, may be encapsulated or unencapsulated (2) Proprioceptors - carry impulses of stretch & position from muscles, tendons, & joints (3) Visceroceptors - carry stimuli from internal organs & circulatory system
Motor Nerves - What do motor nerves do? What is a motor unit? What is the difference in innervation between muscles for fine control versus less controlled movements? How are motor neurons typically structured?
Innervate one or many muscle fibers to control muscle contraction; Neuron & muscle fibers it supplies; Fine Control = fewer muscle fibers innervated by each neuron, Less Controlled = may have many fibers innervated by one neuron; Typically multipolar with axon that terminates in a nueronmuscular junction on surface of skeletal muscle fibers
Neurons in Spinal Cord - What is ependyma? What does the ventral versus dorsal horn of spinal cord contain? What function do dorsal root ganglia neurons serve and what is their structure? What purpose do satellite cells serve in the DRG?
Epithelial cells that line central canal of spinal cord and produce cerebrospinal fluid; Ventral horn = motor neuron cell bodies & Dorsal horn = cell bodies of ascending secondary sensory neurons; Primary sensory neuron cell bodies, Pseudounipolar (2 branches - 1 to periphery to receive sensory info and 1 to spinal cord to transmit sensory info); Provide structural and metabolic support to sensory neurons
Neurons in the Brain - What is the position of white versus gray matter in the brain?
Reverse of spinal cord = gray matter containing cell bodies is external & white matter containing nerve fibers is internal
Neurons in the Brain - How many layers is the gray matter of cerebral cortext divided into? Name and descirbe the characteristic cell typee of the cortex. What are the 3 layers of cortex?
6; Pyramidal cell - traiangular shape, thick, branching dendrite located at apex and long axon extends toward white matter; (1) Outer molecular layer w/ nerve cell processes (2) Purkinje cell layer (3) Inner granular layer w/ several types of neurons
Neurons in the Brain - What are the defining characteristics of Purkinje cells?
Make up the middle layer of cortex; Very large neurons that possess a tree of branching dendrites that extend the molecular (outer) layer of the cortex
