chapter 7—the nervous system part 1
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Chapter 7—The Nervous System Part 1. General Functions of the Nervous System. Sensory input – Gathering Information Monitor changes occurring inside and outside the body Changes = stimuli Integration of stimuli To process and interpret sensory input and decide if action is needed - PowerPoint PPT PresentationTRANSCRIPT
Chapter 7—The Nervous SystemPart 1
General Functions of the Nervous System
Sensory input – Gathering Information Monitor changes occurring inside and
outside the body Changes = stimuli
Integration of stimuli To process and interpret sensory input
and decide if action is needed Motor output—Responding to Stimuli
Sending instructions to activate muscles or glands
General Functions of the Nervous System
Central nervous system (CNS) Brain Spinal cord
Peripheral nervous system (PNS) Nerves that extend from the brain and spinal
cord Spinal nerves—carry impulses to & from the
spinal cord Cranial nerves—carry impulses to & from
brain Carry impulses from sensory receptors to CNS &
from CNS to appropriate muscles & glands
Structural Classification of the Nervous System
Figure 7.1
Functional Classification of the Peripheral Nervous System
Sensory (Afferent) Division Nerve fibers that carry information to the
central nervous systemSomatic – fibers from skin, muscles &
jointsVisceral – fibers from internal organs
Figure 7.1
Functional Classification of the Peripheral Nervous System
Motor (efferent) division Nerve fibers that carry impulses away
from the central nervous systemTo effector organs, muscles, glands
Figure 7.1
Functional Classification of the Peripheral Nervous System
Motor (efferent) division Two subdivisions
Somatic nervous system = voluntary (skeletal muscle)
Autonomic nervous system = involuntary (smooth & cardiac muscle, glands)2 parts: sympathetic & parasympathetic
Organization of the Nervous System
Figure 7.2
Nervous tissue made of 2 kinds of cells: Supporting cells = neuroglia (aka glial
cells)Cannot transmit nerve impulsesCan divideMost brain tumors are gliomasFunction – to support, insulate, and protect neurons
Neurons
Nervous Tissue—Structure & Function
Figure 7.3a
Nervous Tissue: Support Cells of CNS
Astrocytes (half of neural tissue) Abundant, star-shaped cells Brace neurons Form barrier
between capillaries and neurons
Control the chemical environment of the brain
Nervous Tissue: Support Cells Microglia
Spider-like phagocytes
Dispose of debris, including bacteria & dead brain cells
Figure 7.3b–c
Nervous Tissue: Support Cells
Ependymal Cells Line cavities of the brain and spinal
cord Circulate cerebrospinal fluid Cushions CNS tissue
Nervous Tissue: Support Cells
Oligodendrocytes Wrap around nerve fibers in the central
nervous system Produce myelin sheath that insulates
nerve fibers
Figure 7.3d
Figure 7.3e
Nervous Tissue: Support Cells of PNS
Satellite Cells Cushion & 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
Cell Body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell bodyNerve fibers covered in whitish, fatty
material = myelin Protects & insulates & increases
transmission rate of nerve impulse
Neuron Anatomy Cell Body
Nissl substanceSpecialized rough endoplasmic
reticulum Neurofibrils
Intermediate cytoskeleton Maintains cell shape
NucleusLarge nucleolus
Figure 7.4a
Neuron AnatomyExtensions outside the cell body (can be 3-4’ long)Dendrites – conduct impulses toward the cell body
Axons – conduct impulses away from the cell body
Neuron has 100’s of dendrites, but only 1 axon
Figure 7.4a
Figure 7.4a–b
Axons and Nerve Impulses
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
Nerve Fiber Coverings
Myelin sheath—whitish, fatty material covering axons
Schwann cells – produce myelin sheaths that form in jelly-roll like fashion around nerve Found in PNS only Neurilemma – cytoplasm on outside
Nodes of Ranvier – gaps in myelin sheath along the axon
Figure 7.5
Neuron
Neuron Cell Body Location Most neuron cell bodies are found in the
central nervous system Gray matter – cell bodies and
unmyelinated fibers Nuclei – clusters of cell bodies within
the gray matter of the central nervous system
White matter – myelinated fibers Ganglia – collections of cell bodies
outside the central nervous system
Functional Classification of Neurons Sensory (Afferent) Neurons
Cell bodies in ganglia of PNS Carry impulses from the sensory
receptors to CNSCutaneous sense organs (skin)Proprioceptors – detect stretch or tension (muscle)
Motor (Efferent) Neurons Cell bodies in CNS Carry impulses from the central
nervous system to viscera, muscles, glands
Functional Classification of Neurons
Free nerve endings (pain & temperature receptors)
Meissner’s Corpuscles (touch receptors
Lamellara Corpuscles (deep pressure receptors)
Golgi Tendon Organ (proprioceptors)
Muscle Spindle (proprioceptor)
Functional Classification of Neurons
Interneurons (Association Neurons)Cell bodies in CNSFound in neural pathways in the central nervous system
Connect sensory and motor neurons
Neuron Complex
Figure 7.6
Structural Classification of Neurons
Multipolar neurons – many extensions from the cell body (all motor & association neurons)
Figure 7.8a
Structural Classification of Neurons
Bipolar neurons – one axon and one dendrite Rare in adults In special sense organs (eye, nose)
Figure 7.8b
Structural Classification of Neurons Unipolar neurons – have a short, single
process leaving the cell body Axon conducts nerve impulses both toward
& away from cell body In PNS ganglia
Figure 7.8c
Functional Properties of Neurons Irritability – ability to respond to stimuli &
convert it into a nerve impulse Conductivity – ability to transmit an
impulse Resting Neuron (Baseline Anatomy):
The plasma membrane (of a neuron) at rest is polarized
Fewer positive ions are inside the cell than outside the cell (K+ inside, Na+ outside)
Starting a Nerve Impulse
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 (aka “nerve impulse”) in the neuron
Figure 7.9a–c
Nerve Impulses
The Action Potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon (all or none)
Impulses travel faster when fibers have a myelin sheath Saltatory conduction – impulse can’t
flow through myelin sheath, so it jumps across from node to node
Nerve Impulses
Repolarization Potassium ions rush out of the neuron
after sodium ions rush in, which repolarizes the membrane Restores electrical conditions at
membrane to polarized or resting state
The sodium-potassium pump restores the original configuration (Na+ outside, K+ inside) This action requires ATP
Nerve Impulses
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 next dendrite
Transmission of a Signal at Synapses
Transmission of a Signal at Synapses
Figure 7.10