Class Notes (1,100,000)
CA (630,000)
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BIOB32H3 (100)
Lecture

BIOB32H3 Lecture Notes - Growth Factor, Cell Adhesion Molecule, Dynorphin


Department
Biological Sciences
Course Code
BIOB32H3
Professor
Kenneth Welch

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Nervous Tissue
Nervous System
The master controlling and communicating system of the body
Functions:
Sensory input monitoring stimuli occurring inside and outside the body
Integration interpretation of sensory input
Motor output response to stimuli by activating effector organs
Organization of the Nervous System
Central nervous system (CNS)
Brain and spinal cord
Integration and command center
Peripheral nervous system (PNS)
Paired spinal and cranial nerves
Carries messages to and from the spinal cord and brain
Peripheral Nervous System (PNS):
Two Functional Divisions
Sensory (afferent) division
Sensory afferent fibers carry impulses from skin, skeletal muscles, and joints to the
brain
Visceral afferent fibers transmit impulses from visceral organs to the brain
Motor (efferent) division
Transmits impulses from the CNS to effector organs
Motor Division: Two Main Parts
Somatic nervous system
Conscious control of skeletal muscles
Autonomic nervous system (ANS)
Regulate smooth muscle, cardiac muscle, and glands
Divisions sympathetic and parasympathetic
Histology of Nerve Tissue
The two principal cell types of the nervous system are:
Neurons excitable cells that transmit electrical signals
Supporting cells cells that surround and wrap neurons
Supporting Cells: Neuroglia
The supporting cells (neuroglia or glia):
Provide a supportive scaffolding for neurons
Segregate and insulate neurons
Guide young neurons to the proper connections
Promote health and growth
Astrocytes
Most abundant, versatile, and highly branched glial cells
They cling to neurons and cover capillaries
Functionally, they:
Support and brace neurons
Anchor neurons to their nutrient supplies
Guide migration of young neurons
Control the chemical environment

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Microglia and Ependymal Cells
Microglia small, ovoid cells with spiny processes
Phagocytes that monitor the health of neurons
Ependymal cells squamous- to columnar-shaped cells
They line the central cavities of the brain and spinal column
Oligodendrocytes, Schwann Cells,
and Satellite Cells
Oligodendrocytes branched cells that wrap CNS nerve fibers
Schwann cells (neurolemmocytes) surround fibers of the PNS
Satellite cells surround neuron cell bodies with ganglia
Neurons (Nerve Cells)
Structural units of the nervous system
Composed of a body, axon, and dendrites
Long-lived, amitotic, and have a high metabolic rate
Their plasma membrane functions in:
Electrical signaling
Cell-to-cell signaling during development
Nerve Cell Body (Perikaryon or Soma)
Contains the nucleus and a nucleolus
Major biosynthetic center
Focal point for the outgrowth of neuronal processes
There are no centrioles (hence its amitotic nature)
Well developed Nissl bodies (rough ER)
Axon hillock cone-shaped area from which axons arise
Processes
Armlike extensions from the soma
Called tracts in the CNS and nerves in the PNS
There are two types: axons and dendrites
Dendrites of Motor Neurons
Short, tapering, and diffusely branched processes
They are the receptive, or input, regions of the neuron
Electrical signals are conveyed as graded potentials (not action potentials)
Axons: Structure
Slender processes of uniform diameter arising from the hillock
Long axons are called nerve fibers
Usually there is only one unbranched axon per neuron
Rare branches, if present, are called axon collaterals
Axonal terminal branched terminus of an axon
Axons: Function
Generate and transmit action potentials
Secrete neurotransmitters from the axonal terminals
Myelin Sheath
Whitish, fatty (protein-lipid), segmented sheath around most long axons
It functions in:
Protection of the axon
Electrically insulating fibers from one another

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Increasing the speed of nerve impulse transmission
Myelin Sheath and Neurilemma: Formation
Formed by Schwann cells in the PNS
A Schwann cell:
Envelopes an axon in a trough
Encloses the axon with its plasma membrane
Concentric layers of membrane make up the myelin sheath
Neurilemma remaining nucleus and cytoplasm of a Schwann cell
Nodes of Ranvier (Neurofibral Nodes)
Gaps in the myelin sheath between adjacent Schwann cells
They are the sites where collaterals can emerge
Unmyelinated Axons
A Schwann cell surrounds nerve fibers but coiling does not take place
Schwann cells partially enclose 15 or more axons
Axons of the CNS
Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma
Regions of the Brain and Spinal Cord
White matter dense collections of myelinated fibers
Gray matter mostly soma and unmyelinated fibers
Neuron Classification
Structural:
Multipolar
Bipolar
Unipolar
Functional:
Sensory (afferent)
Motor (efferent)
Interneurons (association neurons)
Neurophysiology
Neurons are highly irritable
Action potentials, or nerve impulses, are:
Electrical impulses carried along the length of axons
Always the same regardless of stimulus
The underlying functional feature of the nervous system
Electrical Definitions
Voltage measure (mV) of potential energy generated by separated charge
Potential difference voltage measured between two points
Current (I) the flow of electrical charge between two points
Resistance (R) hindrance to charge flow
Insulator substance with high electrical resistance
Conductor substance with low electrical resistance
Electrical Current and the Body
Reflects the flow of ions rather than electrons
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