bio l 105—lab 8b-nerve histology-----1 the nervous system 11/14 divisions central nervous system...

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


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


Motor Division of PNS: Somatic Nervous System

• Voluntary nervous system– Conscious control of skeletal muscles

• Conducts impulses from CNS to skeletal muscle


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


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


• Neuroglial cells:– Provide a supportive scaffolding for neurons– Insulate neurons– Guide young neurons so they can make

proper connections– Promote health and growth


Neuroglia

• Astrocytes (CNS)

• Microglial cells (CNS)

• Ependymal cells (CNS)

• Oligodendrocytes (CNS)

• Satellite cells (PNS)

• Schwann cells (PNS)


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


Microglial Cells

•Small cells with processes that monitor neurons

•Migrate toward injured neurons

•Can transform to phagocytize microorganisms and neuronal debris


Ependymal Cells

• May be ciliated– Cilia help CerebroSpinalFluid circulate

throughout CNS• Line central cavities of brain and spinal column


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


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


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


• 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


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


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


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


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


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


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


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


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).

bio l 105—lab 8b-nerve histology-----1 the nervous system 11/14 divisions central nervous system...

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