Neurons Chapter 11

anatomy & physiology I

Nervous System

Nervous System

Master control system of the body that utilizes the dorsal cavity brain, spinal cord, nerves

Cells communication

Cells communicate via the electrical and chemical signals

Sensory Input

Information gathered by sensory receptors about internal and external changes

Integration

Processing and interpretation of sensory input

Motor Output

Activation of effector organs (muscle + glands) -> produces a response

Two major parts of the Nervous System

central nervous system and peripheral nervous system

Central Nervous System (CNS)

Brain and Spinal Cord of dorsal body cavity - integration and control center

Interprets sensory input and dictates motor output

Peripheral Nervous System (PNS)

Nervous system outside the brain and spinal cord

Nerves that extend from brain and spinal cord

Peripheral Nervous System has _ functional divisions

2

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 the CNS to effector organs (muscles and glands) - can be sent through either somatic nervous system (controllable) or autonomic nervous system (not controllable)

Somatic Nervous System

Nerve fibers conduct impulses from CNS to skeletal muscle

Voluntary nervous system

Concious control of skeletal muscles

Autonomic Nervous system

Consists of visceral motor nerve fibers

Regulates smooth muscle, cardiac muscle, and glands

Involuntary nervous system

Two subdivisions of the Autonomic Nervous System

sympathetic and parasympathetic (work in opposition to each other)

Nervous tissue consists of two principle cell types

Neuroglia (glial cells): small cells that surround and wrap delicate neurons

Neurons (nerve cells)

excitable cells that transmit electrical signals

Four main neuroglia support CNS neurons

astrocytes, microglial cells, ependymal cells, oligodendrocytes

Astrocyctes (star cells)

Most abundant, versatile, and highly branched of glial cells

Clings to neurons, synaptic endings, and capillaries

Astrocytes functions

Support and brace neurons

Play role in exchanges between capillaries and neurons

Guide migration of young neurons

Control chemical environment around neurons

Respond to nerve impulses and neurotransmitters

Influence neuronal functioning

Participate in information processing in brain

Microglial cells

Small, ovoid cells with thorny processes that touch and monitor neurons

Migrate toward injured neurons

Can transform to phagocytize microorganisms and neuronal debris

Ependymal cells

Range in shape from squamous to columnar

May be ciliated

Cilia beat to circulate CSF

Line the central cavities of the brain and spinal column

Form permeable barrier between cerebrospinal fluid (CSF) in cavities and tissue fluid bathing CNS cells

Oliogondendrocytes

Produce myelin sheath for neurons in the central nervous system

Major Neuoglia seen in PNS

Satellite Cells + Schwann Cells

Satellite Cells

surround neuron cell bodies in PNS

function similar to astrocytes of CNS

Schwann Cells

Supporting cells of the PNS responsible for the formation of myelin.

Vital to regeneration of damaged peripheal nerve fibers

Neurons (nerve cells)

Structural units of nervous system

Extreme longevity (lasts a person's lifetime)

Amitotic, with few exceptions

High Metabolic rate: requires continuous supply of oxygen and glucose

All have CELL BODY and one or more processes

Neuron Cell Body

AKA perikaryon or soma

Biosynthetic center of neuron

Synthesizes proteins, membranes, chemicals

Rough ER (chromatophillic substance, or nisssl bodies)

Contains spherical nucleus with nucleolus

Most Neuron cell bodies are located ______

within the CNS

Nuclei

Clusters of neuron cell bodies in Central Nervous System (CNS)

Ganglia

Clusters of neuron cells bodies in Peripheral Nervous System (PNS)

CNS contain both _____________ and their processes

neuron cell bodies

PNS contains chiefly _______ processes

neuron

Tracts

bundles of neuron processes in CNS

Nerves

bundles of neuron processes in PNS

Two types of processes

Dendrites + Axon

Dendrites of a Motor Neuron

receive information from the CNS and relays it onto the cell body

Axon of Motor Neuron

the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands

Axon functions

Transports molecules and organelels along axons by motor proteins and cytoskeletal elements

Movement occurs in both directions

Anterograde

away from cell body

Examples: mitochondria, cytoskeletal elements, membrane components, enzymes

Retrograde

-toward cell body

-ex: organelles to be degraded, signal molecules, viruses, and bacterial toxins

Myelin sheath

Composed of myelin, a whitish, protein-lipid substance

Myelin Functions

Protect and electrically insulate the axon

Increase speed of nerve impulse transmission

Myelinated fibers

Segmented sheath surrounds most long or large- diameter axons

Nonmyelinated fibers (PNS)

does not contain sheath

Conducts impluses more slowly

Motor Neuron

a neuron that sends an impulse to a muscle or gland, causing the muscle or gland to react

3 types of Neurons

multipolar, bipolar, unipolar

Multipolar

Three or more processes (1 axon, other dendrites)

Bipolar

Two processes (one axon, one dendrite)

Unipolar (pseudounipolar)

one T-like process (two axons)

Peripheral (distal) process: associated with sensory receptor

Proximal (central) process: enters CNS

Interneurons (association neurons)

neurons that carry messages from one neuron to another