SET 1 - Smith PDF

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SET 1 the nervous system • Master control • Has three overlapping functions • Sensory receptors • monitor inside and outside the body • from PNS to CNS • Processes and interprets sensory input • Makes decisions - integration • Dictates a response by activating effector organs • Response • Muscles • Glands • From CNS to PNS 1. sensory input 2.integration 3. motor output

central nervous system brain (gray matter)and spinal cord (white matter) integrating and command center

gray matter in the spinal cord • H-shaped region - surrounds central cavity • Cell bodies are clustered in the gray matter • Nucleus vs. ganglia

white matter in the spinal cord • External to gray matter • No neuronal cell bodies, but millions of axons • Myelin sheath - white color • Consists of axons running between different parts of the CNS • Tracts - bundles of axons traveling to similar destinations • vs. nerve

neuronal regeneration • Neural injuries may cause permanent dysfunction • If axons alone are destroyed, cells bodies often survive and the axons may regenerate • PNS—macrophages invade and destroy axon distal to the injury • Axon filaments grow peripherally from injured site • Partial recovery is sometimes possible • CNS—neuroglia never form bands to guide regrowing axons and may hinder axon growth with growth-inhibiting chemicals • No effective regeneration after injury to the spinal cord and brain

peripheral nervous system outside the CNS nerves from brain and spinal cord

(cranial nerves, spinal nerves) peripheral nerves link all regions of the body to CNS

sensory input and motor output somatic body region & visceral body region somatic sensory, visceral sensory, somatic motor, and visceral motor

somatic sensory region Monitors skeletal muscles, joints, skin surfaces, and responsible for touch/pressure/pain/temperature sensation

visceral body region internal organs, nerves/neurons

somatic sensory are general senses such as touch, pain, pressure, vibration, temperature and proprioception. Is voluntary because have some control over them and are conscious of them.

visceral sensory Receives sensory info from viscera (internal organs) -hunger, taste

somatic motor (voluntary) - impulses from the CNS that causes contraction of skeletal muscles

visceral motor Carries signals from CNS to internal organs -secretion of pancreas, contraction of bladder, contraction of heart

synapses • Site at which neurons communicate • Signals pass across synapse in one direction • Presynaptic neuron • Conducts signal toward a synapse • Postsynaptic neuron • Transmits electrical activity away from a synapse

signals carried by neurons • Plasma membranes of neurons conduct electrical signals • Resting neuron • membrane is polarized • Inner, cytoplasmic side is negatively charged • Stimulation of the neuron--depolarization

action potentials on axons • Strong stimulus applied to the axon triggers • Nerve impulse or action potential • Membrane becomes negative externally • Impulse travels the length of the axon • Membrane repolarizes itself

synaptic potentials • Excitatory synapses • Leads to an inflow of positive ions • Depolarizes the postsynaptic membrane • Drives the postsynaptic neuron toward impulse

generation • Inhibitory synapses • Inside becomes more negative • Action potential less likely

classifications of neurons • Structural classification • Multipolar - possess more than two processes • Numerous dendrites and one axon • Bipolar - possess two processes • Rare neurons - found in some special sensory organs • Unipolar (pseudounipolar) - possess one short, single process

functional classifications of neurons • According to the direction the nerve impulse travels • Sensory (afferent) neurons -transmit impulses toward the CNS • Virtually all are unipolar neurons • Cell bodies in ganglia outside the CNS

• Motor (efferent) neurons • Carry impulses away from the CNS to effector organs • Most motor neurons are multipolar • Cell bodies are within the CNS • nucleus • Form junctions with effector cells

• Interneurons (association neurons) - most are multipolar • Lie between motor and sensory neurons • Confined to the CNS

supporting cells • Six types of supporting cells • Four in the CNS • Two in the PNS • Provide supportive functions for neurons • Non-excitable • Maintenance • Insulation • Cover nonsynaptic regions of the neurons • Neuroglia • Outnumber neurons 10 to 1 • Make up half the mass of the brain

Astrocytes Glial cells that provide a framework for neurons and supply them with oxygen and nutrition for life

Microglia Act as phagocytes, eating damaged cells and bacteria, act as the brains immune system

Ependymal cells Line ventricles of brain and central canal of spinal cord. Form single layer of cuboidal to columnar cells with cilia and microvilli. Modified epithelial cells.

Oligodendrocytes

A cell that holds nerve fibers together and produces the myelin sheath around axons in the central nervous system

Satellite cells surround neuron cell bodies within ganglia

schwann cells (neurolemmocytes) surround axons in the PNS form myelin sheath around axons of the PNS

myelin sheaths • Segmented structures composed of the lipoprotein myelin • Surround thicker axons • Form an insulating layer • Prevent leakage of electrical current • Increase the speed of impulse conduction

1. A Schwann cell envelops an axon. 2. The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. 3.The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath.

Oligodendrocytes form the myelin sheaths in the CNS • Have multiple processes • Coil around several different axons

multiple sclerosis Immune system attacks the myelin around axons in the CNS Myelin sheaths produced by oligodendrocytes are destroyed.

nerves • Nerves - cordlike organs in the PNS • Consists of numerous axons wrapped in connective tissue • Axon is surrounded by Schwann cells

reflex arch sensory receptor > sensory neuron > integrationcenter > motor neuron > effector

monosynaptic reflex Simplest reflex involving the synapse of a sensory neuron with a motor neuron

polysynaptic reflex reflex that has at least one interneuron placed between the sensory afferent and the motor efferent, thus having a longer delay between stimulus and responseASEE4sae43q

sensory (afferent) division carries impulses from skin, skeletal muscles, and joints to the brain

motor (efferent) division nerve fibers that carry impulses away from the central nervous system

somatic nervous system

Division of the PNS that controls the body's skeletal muscles.

autonomic nervous system Regulates events that are automatic, or involuntary, such as the activity of smooth and cardiac muscles and glands.

sympathetic division A branch of the autonomic nervous system and prepares the body for quick action in emergencies; fight or flight; busiest when frightened, angry, or aroused; increases heart rate, increases breathing rate, enlarges pupils, stops digestion; connects to all internal organs; sudden reaction

parasympathetic division Branch of the autonomic nervous system; it calms and relaxes the body. Chemical substances released by the endocrine glands; they help regulate bodily activities

The visceral motor division of the PNS __________. regulates the contraction of smooth and cardiac muscle and regulates secretion by the body's many glands

A somatic motor neuron carries motor commands to the skeletal musculature.

The peripheral nerve fibers that speed up the movement of the digestive tract are classified as general visceral motor (efferent).

function of synaptic vesicles inside axon terminals store and release neurotransmitters

This is the site of communication between neurons.

synapse

The ________ of a presynaptic neuron associates with the dendrite of a postsynaptic neuron. axon terminal

Chemical signals diffuse between neurons at this location. synapse

This region of the neuron contains a single nucleus surrounded by cytoplasm. cell body

This neuronal region transmits electrical impulses away from the cell body. axon

Which of the following is the correct path an impulse takes across a synapse? axon of presynaptic neuron, synaptic cleft, dendrite of postsynaptic neuron

Action potentials travel along the axon membrane

The chemical substance that is released at axon terminals is called a neurotransmitter

most sensory neurons are unipolar

interneurons Interneurons are multipolar neurons that are confined to the CNS and are linked together in chains that form complex neuronal pathways.

The majority of neurons in the body are multipolar

Interneurons are found only in CNS

What important function could be diminished if the cilia on ependymal cells were absent? circulation of cerebrospinal fluid

Which cells provide the myelin sheath for neurons in the CNS? oligodendrocyctes

These glial cells surround the cell bodies of sensory neurons within ganglia of the PNS. satellite cells

Myelin on axons functions to speed the rate of impulse conduction and insulate neighboring axons from one another.

Nonmyelinated axons conduct impulses more slowly than myelinated axons.

A node of Ranvier (myelin sheath gap) is a bare region of axonal membrane in myelinated axons only.

The difference between myelinated and unmyelinated axons is that Schwann cells wrap around myelinated axons in concentric layers.

Ciliated neuroglial cells that form an epithelium and play an active role in forming and moving cerebrospinal fluid are ependymal cells

perineurium

The entire nerve is surrounded by a tough fibrous sheath called the epineurium.

The covering of a fascicle within a nerve is the perineurium

Which of the following sequences puts the components of a reflex arc in the correct order of their activation? receptor, sensory neuron, CNS integration center, motor neuron, effector

Ganglia represent groups of neuron cell bodies.

Which part or parts of the neuron are found in the white matter of the central nervous system? long axonal processes

How are gray matter and white matter arranged in the CNS? Gray matter is deep to the superficial white matter in the spinal cord.

White matter represents myelinated axons traveling together in the CNS.

In the region of the spinal cord, the cell bodies of most interneurons lie in the dorsal half of the gray matter.

Which structure is responsible for formation of the regeneration tube following injury to an axon? schwann cells

In what instance is axonal regeneration possible? If the cell body of a PNS neuron survives when an axon is damaged, axon filaments can extend peripherally from the injured site toward the original target....