Anatomy &Physiology CLS 221 DR /Noha Elsayed 2014--2015

• Describe the three functions of the nervous system.
• Describe the structure of a neuron.
• Explain how a nerve impulse is conducted along a nerve and across a synapse • Describe the structure of a nerve, and • distinguish between sensory ,motor , and mixed nerves.

• Definition It is defined as the system of cells tissues and organs that regulates the body responses to the external and internal responses.

Sensory input— gathering information
Motor output
To monitor changes occurring inside and outside the body Changes = stimuli
To process and interpret sensory input and decide if action is needed A response to integrated stimuli The response activates muscles or glands

Functions of the Nervous System

Structural Classification of the Nervous System Central nervous system (CNS)
 Brain  Spinal cord
Peripheral nervous system (PNS)
– Nerves outside the brain and spinal cord  Spinal nerves  Cranial nerves

Functional Classification of the Peripheral Nervous System Sensory (afferent) division
Nerve fibers that carry information to the central nervous system
Motor (efferent) division
Nerve fibers that carry impulses away from the central nervous system

Functional Classification of the Peripheral Nervous System Motor (efferent) division (continued) Two subdivisions
• Somatic nervous system = voluntary
Autonomic nervous system = involuntary

Nervous Tissue: Support Cells
Support cells in the CNS are grouped together as “ neuroglia ”
Function
: to support, insulate, and protect neurons

Nervous Tissue: Support Cells •
1-Astrocytes
 Abundant, star-shaped cells  Form barrier between capillaries and neurons  Control the chemical environment of the brain

Nervous Tissue: Support Cells
2-Microglia
 Spiderlike phagocytes  Dispose of debris

Nervous Tissue: Support Cells
3-Ependymal cells
 Line cavities of the brain and spinal cord.
 Circulate cerebrospinal fluid

Nervous Tissue: Support Cells
4-Oligodendrocytes
 Wrap around nerve fibers in the central nervous system.
 Produce myelin sheaths.

Nervous Tissue: Support Cells Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system

Nervous Tissue: Neurons
Neurons = nerve cells:
– Cells specialized to transmit messages
Major regions of neurons 1-Cell body
—nucleus and metabolic center of the cell
2-Processes
—fibers that extend from the cell body

Nervous Tissue: Neurons Cell body  Nucleus.
 Large nucleolus.
Processes outside the cell body
 Dendrites—conduct impulses toward the cell body.
 Axons—conduct impulses away from the cell body.

3-Axons end in axonal terminals
Axonal
terminals
contain vesicles with
neurotransmitters
Axonal terminals are
separated
from the next neuron by a gap
Synaptic cleft
—gap between adjacent neurons
Synapse
—junction between nerves

Myelin sheath
— whitish, fatty material covering axons
Schwann cells
—produce myelin sheaths in jelly roll–like fashion
Nodes of Ranvier
— gaps in myelin sheath along the axon

Interneurons (association neurons)
 Found in neural pathways in the central nervous system  Connect sensory and motor neurons

Multipolar neurons—many extensions from the cell body

Bipolar neurons—one axon and one dendrite

Functional Properties of Neurons
Irritability
Ability to respond to stimuli
Conductivity
Ability to transmit an impulse

Resting neuron
 The plasma membrane at rest is polarized  Fewer positive ions are inside the cell than outside the cell
Depolarization
 A stimulus depolarizes the neuron’s membrane  A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron

Nerve Impulses
Action potential
 If the action potential ( nerve impulse ) starts, it is propagated over the entire axon  Impulses travel faster when fibers have a myelin sheath

Nerve Impulses
Action potential
 If the action potential (nerve impulse) starts, it is propagated over the entire axon  Impulses travel faster when fibers have a myelin sheath

Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve  Neurotransmitter is released from a nerve’s axon terminal  The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter  An action potential is started in the dendrite

A-osteocytes.
B-Osteoclaset.
C-Osseous matrix.
D- Haversian system.