BIO L 105—lab 8B-Nerve Histology-----1
The Nervous System 11/14
Divisions•Central nervous system (CNS)
– Brain and spinal cord (dorsal body cavity)– Integration and command center
• Interprets sensory input and dictates motor output
•Peripheral nervous system (PNS)– Portion of nervous system outside CNS;
brings information from body– Consists mainly of nerves that extend from
brain and spinal cord• Spinal nerves to and from spinal cord• Cranial nerves to and from brain
Lab 8B-BIO 105
BIO L 105—lab 8B-Nerve Histology-----2
Peripheral Nervous System (PNS)
• Two functional divisions– Sensory (afferent) division
• Somatic sensory fibers—convey impulses from skin, skeletal muscles, and joints to CNS
• Visceral sensory fibers—convey impulses from visceral organs to CNS
– Motor (efferent) division • Transmits impulses from CNS to effector organs
– Muscles and glands
• Two divisions– Somatic or Voluntary nervous system– Autonomic nervous system
BIO L 105—lab 8B-Nerve Histology-----3
Motor Division of PNS: Somatic Nervous System
• Voluntary nervous system– Conscious control of skeletal muscles
• Conducts impulses from CNS to skeletal muscle
BIO L 105—lab 8B-Nerve Histology-----4
Motor Division of PNS: Autonomic Nervous System
• Involuntary nervous system– Regulates smooth muscle, cardiac muscle,
and glands– Visceral motor nerve fibers
• Two functional subdivisions which work in opposition to each other
• Sympathetic• Parasympathetic
BIO L 105—lab 8B-Nerve Histology-----5
Histology of Nervous Tissue
• Two principal cell types– Neurons (nerve cells)—excitable cells that
transmit electrical signals– Neuroglia or Glia – small cells that surround,
wrap, and generally support neurons
BIO L 105—lab 8B-Nerve Histology-----6
• Neuroglial cells:– Provide a supportive scaffolding for neurons– Insulate neurons– Guide young neurons so they can make
proper connections– Promote health and growth
BIO L 105—lab 8B-Nerve Histology-----7
Neuroglia
• Astrocytes (CNS)
• Microglial cells (CNS)
• Ependymal cells (CNS)
• Oligodendrocytes (CNS)
• Satellite cells (PNS)
• Schwann cells (PNS)
BIO L 105—lab 8B-Nerve Histology-----8
Astrocytes•Most abundant, highly branched cell•Cling to neurons, synaptic endings, and covers capillaries•Functions include
– Support neurons and help maintain position – Play role in exchanges between capillaries and
neurons; help with nutrient supply – Control chemical environment around neurons
BIO L 105—lab 8B-Nerve Histology-----9
Microglial Cells
•Small cells with processes that monitor neurons
•Migrate toward injured neurons
•Can transform to phagocytize microorganisms and neuronal debris
BIO L 105—lab 8B-Nerve Histology-----10
Ependymal Cells
• May be ciliated– Cilia help CerebroSpinalFluid circulate
throughout CNS• Line central cavities of brain and spinal column
BIO L 105—lab 8B-Nerve Histology-----11
Myelin Sheath• Whitish, protein-lipoid segmented sheath around
most long or large-diameter axons– Myelinated fibers
•Function of myelin– Protects and electrically insulates axon– Increases speed of nerve impulse transmission•Nonmyelinated fibers conduct impulses more slowly
BIO L 105—lab 8B-Nerve Histology-----12
Oligodendrocytes
•Branched cells that wrap CNS nerve fibers and form insulating myelin sheaths•Can wrap up to 60 axons at once•Have Nodes of Ranvier (gaps in myelin)•No neurilemma
BIO L 105—lab 8B-Nerve Histology-----13
Satellite Cells and Schwann Cells: in PNS
•Schwann cells – Surround all peripheral nerve fibers and form
myelin sheaths– Wrap around axon in jelly roll fashion– One cell forms one segment of myelin sheath
• Similar function as oligodendrocytes
– Vital to regeneration of damaged peripheral nerve fibers
BIO L 105—lab 8B-Nerve Histology-----14
• Neurilemma– Outermost layer of Schwann cell containing
nucleus and most of cytoplasm– Essential for axon healing and repair
• Nodes of Ranvier – Myelin sheath gaps between adjacent
Schwann cells
BIO L 105—lab 8B-Nerve Histology-----15
Neurons– Structural units of nervous system--form gray
matter of CNS
– Highly specialized cells that conduct impulses
– Extreme longevity
– High metabolic rate—requires continuous supply of oxygen and glucose
– All have cell body, axon and one or more dendrites
•Plasma membrane functions in:– Electrical signaling
BIO L 105—lab 8B-Nerve Histology-----16
Neuron Cell Body (Perikaryon or Soma)•Contains nucleus and nucleolus•Major biosynthetic center
– Synthesizes proteins, membranes, and other chemicals
– Rough ER is very active; also called nissl bodies • Synthesizes neurotransmitters
•Plasma membrane receives information from other neurons
BIO L 105—lab 8B-Nerve Histology-----17
Dendrites– short, tapering, diffusely branched processes – Increase surface area of cell so can receive
messages
•Receptive (input) region of neuron•Convey incoming electrical signals toward cell body as graded potentials (short distance signals) not action potentials
BIO L 105—lab 8B-Nerve Histology-----18
The Axon •Generates and transmits nerve impulses along axolemma (neuron cell membrane) to axon terminal
– Neurotransmitters released into extracellular space• Either excite or inhibit neurons with which axons are in close
contact
•Carries on many conversations with different neurons at same time
BIO L 105—lab 8B-Nerve Histology-----19
Structural Classification of Neurons•Grouped by number of processes•Three types
– Multipolar – 3 or more processes• 1 axon, other processes dendrites• Most common; major neuron in CNS
– Bipolar – 2 processes• Rare, e.g., Retina and olfactory mucosa
– Unipolar – 1 short process– One process –sensory or afferent receptor – Other process – motor or efferent branch
BIO L 105—lab 8B-Nerve Histology-----20
Functional Classification of Neurons
• Grouped by the direction in which impulse travels in relation to CNS
• Sensory or afferent– Transmit impulses from sensory receptors toward CNS– Almost all are Unipolar
• Motor or efferent– Carry impulses away from CNS to effectors– Multipolar
• Interneurons (association neurons)– Lie between motor and sensory neurons– Shuttle signals through CNS pathways; most are entirely within
CNS
BIO L 105—lab 8B-Nerve Histology-----21
Structure of a Nerve•Bundle of myelinated and non-myelinated axons enclosed by connective tissue•Cell bodies lie in CNS or in ganglia near CNS•Connective tissue coverings include
– Endoneurium—loose connective tissue that encloses axons and their myelin sheaths
– Perineurium—coarse connective tissue that bundles fibers into fascicles
– Epineurium—tough fibrous sheath around a nerve
BIO L 105—lab 8B-Nerve Histology-----22
LABWORK
1.Explain organization of nervous system.
2. Describe neuroglia and process of myelin formation.
3. Describe and identify parts of a neuron and the different classifications of neurons on models and microscope slides.
4. Describe and identify structure of a nerve (microscope slides and models).