CHAPTER 7: NERVOUS SYSTEM [PART 1]

Nervous system

This system provides higher mental function and emotional expression, maintains homeostasis, and regulates the activities of muscles and glands.

Electrical and chemical signals

Communication involves a combination of ___ and ____ signals.

Nervous system

It is the master control and communication system of the body.

Electrical impulses

It communicates with body cells using __________ which are rapid and specific and cause almost immediate responses.

Endocrine system

It is the second important regulating system.

1. sensory input

2. integration

3. motor output

The three overlapping functions of the nervous system

Sensory input

Sensory receptors monitor changes occurring in and out of the body (stimuli), and the gathered information is called?

Integration

It processes and interprets the sensory input and decides what should be done at each moment.

Motor output

It then causes a response, or effect, by activating muscles or glands (effectors) via?

Explain the organization of the nervous system

peripheral nervous system

sensory and motor fibers constitute the?

central nervous system and peripheral nervous system

what’re the two structural classification of the nervous system?

central nervous system

• consists of the brain and spinal cord, occupies the dorsal body cavity that act as the integrating and command centers of the NS.

• interprets incoming sensory information and issue instructions based on past experience and current conditions

peripheral nervous system

• includes all parts of the NS outside the CNS

• consists mainly of the nerves that extends from the spinal cord and brain

spinal nerves and cranial nerves

peripheral nervous system is subdivided into?

• these serve as communication lines.

• link all parts of the body by carrying impulses from the sensory receptors to the CNS and from the CNS to the appropriate glands or muscles.

spinal nerves

carry impulses to and from the spinal cord

cranial nerves

carry impulses to and from the brain

functional classification

this classification is concerned only with PNS structures

sensory (afferent) division and motor (efferent) division

functional classification has two principal subdivisions?

sensory (afferent) division

• to go “toward”

• consists of nerves (many indiv. nerve fibers) that convey impulses to the CNS from sensory receptors located in various parts of the body.

• keeps the CNS constantly informed of events going on both inside and outside the body

somatic sensory (afferent) fibers

visceral sensory (afferent) fibers

sensory (afferent) division is classified into?

somatic sensory (afferent) fibers

sensory fibers delivering impulses from the skin, skeletal muscles, and joints

visceral sensory (afferent) fibers

transmitting impulses from the visceral organs are called?

motor (efferent) division

carries impulses from the CNS to effector organs, the muscles and glands, activates them, they effect a motor response.

somatic nervous system and autonomic nervous system

motor division is classified into?

somatic nervous system

• allows us to consciously (voluntarily) control our skeletal muscles

• aka voluntary nervous system

• but not all skeletal muscle activity r controlled voluntarily (ex. skeletal muscle reflexes such as the stretch reflex)

autonomic nervous system

• this regulates events that are automatic (involuntary) such as the activity of smooth muscle, cardiac muscle, and glands.

• aka involuntary nervous system

sympathetic NS

parasympathetic NS

autonomic NS (ANS) is classified into?

supporting cells and neurons

nervous tissue is made up of two principal types of cells?

supporting cells

• in the CNS are “lumped together” as neuroglia, literally “nerve glue”, aka glial cells or glia.

neuroglia

• include many types of cells that support, insulate, and protect the delicate neurons

• each of its types has special functions

Astrocytes

• are abundant star-shaped cells that account for nearly half of neural tissue

• versatile neuroglia

• their swollen ends that cling to neurons anchors them to their nutrient spply lines, the blood capillaries and neurons, help determine capillary permeability, and play a role in making exchanges between the two.

• in this way, they help protect the neurons from harmful substances that might be in the vloodf

• also help control chemical environment in the brain by “mopping up” leaked potassium ions

• and recapturing chemicals released for communication purposes.

microglia

• are spider-like phagocytes that monitor the heath of nearby neurons and dispose of debris, such as dead brain cells and bacteria

ependymal cells

• neuroglia that line the central cavities of the brain and the spinal cord

• the beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective watery cushion around the CNS.

Oligodendrocytes

• neuroglia that wrap their flat extensions (processes) tightly around the nerve fibers, producing fatty insulating coverings called myelin sheaths

true!

true or false?

neuroglia are not able to transmit nerve impulses, a function highly developed in neurons. they also never lose their ability to divide, whereas most neurons do. 

gliomas

most brain tumors are ____, or tumors formed by neuroglia.

Schwann cells and Satellite cells

Supporting cells in the PNS?

Schwann cells

• these form the myelin sheaths around nerve fibers in the PNS

Satellite cells

these cells act as protective, cushioning cells for peripheral neuron cell bodies.

neurons

• aka nerve cells, are highly specialized to transmit messages (nerve impulses) from one part of the body to another.

• all of its types have cell bodies, which contains the nucleus and one or more slender processes extending from the cell body.

cell body

• is the metabolic center of the neuron

• its transparent nucleus contains a large nucleolus

• cytoplasm has the same organelles, but lacks centrioles(confirms the amitotic nature of neurons)

Nissl bodies

rough er in the cell body is called?

neurofibrils

intermediate filaments in the cell body is called? important in maintaining cell shape, abundant in cell body.

processes

• armlike

• aka fibers, vary in length from microscopic to abt 7ft in the tallest humans

• longest reach from the lumbar region of the spine to the great toe

dendrites

neuron processes that convey incoming messages (electrical signals) toward the cell body are called?

may have hundreds of this

axons

generate nerve impulses and typically conduct them away from the cell body are called?

axon hillock

each neuron has only one axon, which arises from a conelike region of the cell body called?

axon terminals

ocassional axons gives off a collateral branch along its length, but all axons branch profusely at their terminal end, forming hundred to thousands of?

neurotransmitters

axon terminals contain hundreds of tiny vesicles, or membranous sacs, that contain chemicals called?

synaptic cleft

each axon terminal is separated from the next neuron by a tiny gap called what?

synapse

such a functional junction (synaptic cleft), where an impulse is transmitted from one neuron to another is called what?

Myelin sheaths

most long nerve fibers are covered with a whitish, fatty material called ____, which has a waxy appearance?

myelin sheath

Schwann cells wrap themselves around the axon in a jelly-roll fashion fashion. initially, the membrane is loose, but the Schwann cell cytoplasm is gradually squeezed from between the membrane layers. when the wrapping process is done, a tight coil of wrapped membranes, the ______, encloses the axon.

Neurilemma

Part of the Schwann cell (cytoplasm), external to the myelin sheath is called?

nodes of Ranvier

gaps between many individual Schwann cells

oligodendrocytes

• in the CNS, with their many flat extensions, they can coil around as many as 60 different fibers at the same time.

• one of this can form many myelin sheaths.

• but lacks a neurilemma

• when a peripheral nerve fiber is damaged, the neurilemma plays an important role in fiber regeneration, an ability that is largely lacking in the CNS.

multiple sclerosis (MS)

• a disease that gradually destroys the myelin sheaths around CNS fibers by converting them to hardened sheaths called scleroses.

• electrical currents may jump to another demyelinated neuron

• nerve signals do not always reach the intended target

• may cause visual and speech disturbances, lose the ability to control muscles, and increasingly disabled.

• is an autoimmune disease

• no cure, but injections of interferons hold the symptoms at bay an provide some relief.

nuclei

• clustered cell bodies found in the CNS

ganglia

small collections of cell bodies found in a few sites in the PNS.

tracts

bundles of nerve fibers (neuron processes) running through the CNS

nerves

bundles of nerve fibers (neuron processes) running through the PNS

white matter

consists of dense collections of myelinated fibers (tracts)

gray matter

contains mostly unmyelinated fibers and cell bodies

sensory neurons or afferent neurons

motor neurons or efferent neurons

interneurons or association neurons

what are the functional classification of neurons?

sensory neurons

• aka afferent neurons

• neurons carrying impulses from sensory neurons to the CNS

• its cell bodies are always found in a ganglion outside the CNS

• its dendrite endings has specialized receptors activated by specific changes occurring nearby

cutaneous sense organs

simpler types of sensory receptors in the skin are?

proprioceptors (muscle spindle or golgi tendon organ)

• sensory receptors in the muscles and tendons

• detect amount of stretch, or tension in skeletal muscles, their tendons, and joints, sending this info to the brain to maintain balance and normal posture.

1. free nerve endings

2. Meissner’s corpuscle

3. Lamellar corpuscle

4. Muscle spindle (proprioceptor)

type of sensory receptors?

free nerve endings

• are pain and temperature receptors

• least specialized of the cutaneous receptors

• most numerous

• strong stimulation is interpreted as pain

Meissner’s corpuscle

are touch receptors

Lamellar corpuscle

Are deep pressure receptors

golgi tendon organs and muscle spindle

Examples of proprioceptors?

motor neurons or efferent neurons

• neurons caryring impulses from the CNS to the viscera and/or muscles and glands

• its cell bodies r usually located in the CNS

interneurons or association neurons

• third category of neurons

• connect the motor and sensory neurons in neural pathways

• cell bodies in CNS

structural classification

this classification of neurons is based on the number of processes, inc. dendrites and axons

multipolar neuron

• several

• all motor and association neurons r multipolar, most common structural type

bipolar neurons

• neurons with two processes—one axon and one dendrite

• are rare in adults, found only in some special sense organs (eye, nose), where they act in sensory processing as receptor cells

Unipolar neurons

• have a single process emerging from the cell body as if the cell body were on a “cul-de-sac” off the “main road” that is the axon

• process is very short and divided almost immediately into proximal (central) and distal (peripheral) processes

• unique in that only the small branches at the end of the peripheral process are dendrites.

• the remainder of the peripheral process and the central process function as the axon; thus, in this case, the axon actually conducts nerve impulses both toward and away from the cell body.

• sensory neurons found in ganglia are unipolar

Axon hillock

• Junction between the cell body and the axon

• Is the main site where action potentials begin

Ganglia

• In the PNS, this serve as relay and processing points for nerve signals

Sensory ganglia and Autonomic ganglia

Ganglia is classified into?

Sensory ganglia

• e.g., dorsal root ganglia

• contain cell bodies of sensory neurons that bring information from the body to the spinal cord

Autonomic ganglia

• e.g., sympathetic and parasympathetic ganglia

• contain cell bodies that help regulate involuntary functions like heart rate, digestion, and gland secretion

ganglion

It is like a “mini processing station” of nerve cells outside the CNS

irritability and conductivity

neurons have two major functional properties?

irritability

the ability to respond to a stimulus and convert it into a nerve impulse

conductivity

the ability to transmit the impulse to other neurons, muscles, or glands.

polarized

• the plasma membrane of a resting or inactive neuron is ____.

• meaning there r fewer positive ions sitting on the inner face of the neuron’s plasma membrane than on the outer face.

• major positive ions inside r polassium

• outside are sodium

• as long as inside remains more negative, the neuron will stay inactive

neurotransmitter

Most neurons in the body are excited by _______ chemicals released by other neurons

depolarization

inward rush of sodium ions changes the polarity of the neuron’s membrane at that site

graded potential

inside is now more positive, outside is less positive, a local electrical situation called ___________.

action potential

if the stimulus is strong enough and the sodium influx is great enough, the local depolarization (graded potential) activates the neuron to initiate and transmit a long distance signal called an _______, also called a nerve impulse in neurons.

all-or-none

the nerve impulse is an ________ response, like starting a car. either propagated over the entire axon or it doesnt happen at all

repolarization

outflow of positive ions from the cell restores the electrical conditions at the membrane to the polarized, or resting, state, an event called ______.

sodium-potassium pump

after repolarization occurs, the ___________ restores the initial concentrations of the sodium and potassium ions inside and outside the neuron, uses ATP to pump

cannot

Until repolarization occurs, a neuron (can/cannot) conduct another impulse.

saltatory conduction

• is the rapid transmission of nerve impulses in myelinated axons, where action potentials occur only at the Nodes of Ranvier.

• Makes the signal “jump” between nodes, greatly increasing speed and efficiency compared to unmyelinated fibers.

70mV

what is the mV of the resting membrane potential?

amount need to be reached in order to generate an action potential. -55mV

what is a threshold and what is the value?