Nervous tissue chapter 12

What nervous system is composed of the brain and spinal cord?

Central nervous system (CNS)

What nervous system is composed of nerves and ganglia?

Peripheral nervous state (PNS)

What are the two types of nervous systems?

Central and peripheral nervous systems

What part of the nervous system is a bundle of nerve fibers (axons) wrapped in fibrous connective tissue?

Nerve

What part of the nervous system is a knot-like swelling in a nerve where neuron cell bodies of PNS are concentrated?

Ganglion

What are the two division of the PNS?

sensory and motor division

What PNS division carries signals from receptors to CNS?

Sensory (afferent) division

What sensory division is composed of skin, muscles, bones, and joints?

Somatic

What sensory division signals from the viscera (heart, lungs, stomach, and urinary bladder)?

Visceral

What PNS division carries signals from CNS to effectors (carry out the body’s response)?

Motor (efferent) division

What motor division carries signals to skeletal muscles?

Somatic motor division

What motor division carries signals to glands, cardiac and smooth muscle; no voluntary control?

Visceral motor division (ANS)

What does ANS stand for ?

Autonomic nervous system

What are the divisions of the ANS?

Parasympathetic and sympathetic division

what does SNS stand for?

Somatic nervous system

What are the effectors of the ANS?

smooth muscle, cardiac muscle, glands and adipose tissue?

What are the effectors of SNS?

Skeletal muscle

What are the receptors sensory division?

Special, visceral, and somatic sensory receptors

What are the three functional classes of neurons?

Sensory,motor, and interneurons

What functional classification of neurons detect stimuli and transmit information toward the CNS?

Sensory (afferent) neurons

What functional classification of neurons receive signals from other neurons, processes this information for proper response?

Interneurons

What functional classification of neurons send signals out to muscles and gland cells (the effectors)?

Motor (efferent) neurons

What are the structures of a neuron?

Cell body, axon, and dendrites

What structure of neuron contains nucleus and many organelles?

Cell body

What structure of neuron is long, cylindrical extension; relatively unbranched but may give off axon collaterals?

Axon

What structure of a neuron is the most numerous neurites; primary sites for receiving signals from other neurons

Dendrites

Axon originate at the?

Axon hillock

What is the cytoplasm of axons?

Axoplasm

What is the membrane of axons?

Axolemma

At its end, an axon branches profusely which is?

Terminal arborization

Each branch of arborization ends in a bulbous ———— which forms a synapse with next cell?

Axon terminal

What are the structural classifications of neurons?

Multipolar, bipolar, unipolar, and anaxonic neurons

How are structural classifications determined?

By number of cell processes extending from cell body

What structural classification of a neuron is one axon and multiple dendrites; most motor neurons in CNS?

Multipolar neuron

What structural classifications of a neuron is one axon and one dendrite; examples include olfactory cells, some neurons of retina, sensory neurons of ear?

Bipolar neuron

What structural classifications of a neuron is a single process leading away from cell body, splits into peripheral process and central process; most sensory neurons?

Unipolar neuron

What structural classifications of a neuron has many dendrites but no axon; found in brain, retina, and adrenal gland?

Anaxonic neuron

What type of cell are neuroglia?

Supporting cells

What are the four types of glia that occur in the CNS?

oligodendrocytes, microglia, astrocytes, ependymal cells

What type of glia form myelin sheaths in CNS?

Oligodendrocytes

What type of glia lines internal cavities of brain and spinal cord; secrete and circulate cerebrospinal fluid (CSF)?

Ependymal cells

What type of glia contains macrophages; engulf debris, provide defense against pathogens?

Microglia

What type of glia is the most abundant type; wide variety of functions and Provide framework for nervous tissue; stimulate formation of blood-brain barrier; adjust blood flow; influence synaptic signaling?

Astrocytes

What are the two types of neuroglia in PNS?

Schwann and satellite cells

What neuroglia cell envelops axons of PNS, form myelin sheath, and assist in regeneration of damaged fibers?

Schwann

What neuroglia cell surrounds cell bodies in ganglia of PNS; provide insulation and regulate chemical environment?

Satellite

Brain tumors ride from?

Meninges, metastasis, glial cells, and gliomas

What is the protective membranes of CNS?

Meninges

What from nonneuronal tumors in other organs?

Metastasis

What is mitotically active throughout life?

Glial cells

What are tumors of glial cells; grow rapidly and are highly malignant?

Gliomas

What are spiral layers of insulation around an axon?

Myelin sheath

Myelin sheaths are formed by ———- cells in PNS, —————- in CNS. Sheath consists of the plasma membrane of these cells, 20% protein and 80% lipid

Schwann , oligodendrocytes

What is production of sheaths called ?

myelination

What Aids in conduction speed of axons?

Myelin sheaths

A ———- ——-spirals repeatedly around a small section of a single axon?

Schwann cell

what is the thick, outermost coil in the myelination in PNS?

Neurolemma

What wraps processes around small portions of many axons in immediate vicinity of the myelination in the CNS?

Oligodendrocyte

During ———-, nucleus cannot migrate around the axon like a Schwann cell does.

• Pushes newer layers of myelin under the older ones; myelination spirals inward toward axon

• No neurolemma

Myelination

————- ——- is segmented in CNS and PNS ?

Myelin sheath

What is the gap between segments?

Node of ranvier

What are two diseases of the myelin sheath?

Multiple sclerosis ans Tay-Sachs disease

What disease of the myelin sheath is defined as Oligodendrocytes and myelin sheaths in CNS deteriorate Myelin replaced by hardened scar tissue and Nerve conduction disrupted?

Multiple sclerosis (MS)

What disease of the myelin sheath is a Hereditary disorder mostly in children: usually fatal before age 4 Abnormal accumulation of glycolipid called ganglioside and Nerve conduction disrupted?

Tay-Sachs disease

Many axons in CNS and PNS are ———-?

Unmyelinated

In PNS, ————- ——- hold small unmyelinated axons in surface grooves

Membrane folds once around each axon; does not spiral repeatedly around it

Schwann cells

Regeneration of damaged PNS nerve fiber (axon) can occur if?

nerve cell bodies are intact and at least some neurilemma remains

- Slow regrowth; process may take 2 years - Damaged CNS axons usually unable to regenerate

Regeneration is not fast or always possible

Neural communication is based on ?

electrical potentials and currents

what is the charge difference across plasma membrane?

• Typically −70 millivolts (mV) in an unstimulated, “resting” neuron

Negative value indicates more negatively charged particles on inside of membrane compared to outside

Resting membrane potential (RMP)

what has greatest influence on RMP and is more concentrated in ICF compared to ECF?

Potassium K+

What also influences RMP more concentrated in ECF compared to ICF?

Sodium Na+

what uses ATP to move 3 Na+ out of cell and bring 2 K+ into the cell?

Sodium-potassium pump

Neurons communicate by ?

altering the membrane potential of other neurons

The nerve sending the signal is the?

presynaptic cell.

The impulse is called the ?

action potential

The receiving nerve is called the?

postsynaptic cell.

A connection between 2 nerves is a ?

neural synapse

gap between presynaptic neuron and postsynaptic neuron?

Synaptic cleft

When a nerve —— or ———- is stimulated, regulated gates open and ions rush across membrane.

- Gates may be regulated by light, heat, movement, chemicals, or voltage

Body, dendrite

The type ion that rushes across will dictate whether effector is ?

depolarized (excitatory) or hyperpolarized (inhibitory).

Rapid up-and-down change in voltage produced by the coordinated opening and closing of voltage-gated ion channels

Action potentials

• Voltage at axon hillock must reach threshold— around −55 mV

• Voltage-gated N+ channels open quickly +30

• Voltage-gated K+ channels open more slowly

• Depolarization occurs

• Voltage peaks at +35mV

This describes

Action potential

Voltage-gated K+ fully open,

K+ flows out of cell and membrane becomes more negative again—

Repolarization

Initiated when graded potentials reach a certain ——— (-55 mV)?

Threshold

———— Voltage-sensitive Na+ channels open, Na+ moves into the axon (this reverses the voltage across the membrane, interior becomes +)?

Depolarization

———-Na+ channels close, K+ channels open, K+ moves out of the axon?

Repolarization

——————K+ channels close, the normal activity of the sodium-potassium pump restores resting potential?

Reestablishment of the resting potential

What are Characteristics of action potentials?

All or none law, irreversible, and non decremental

what if threshold reached, neuron fires up to maximum voltage; if threshold not reached, it does not fire?

All-or-none law

what does not get weaker with distance?

Non decremental

what once started, an action potential travels all the way down the axon cannot be stopped?

Irreversible

What period is of resistance to stimulation?

Refractory period

What are two phases of the refractory period?

Absolute and relative refractory period

———-—no stimulus of any strength will trigger another AP • Caused by inactivation of voltage- gated Na+ channels

Absolutely refractory period

————an unusually strong stimulus is needed to trigger a new AP

• During hyperpolarization, a larger depolarization (local potential) is required to reach threshold

Relative refractory period

————— axons have voltage- gated channels along their entire length?

Unmyelinated

Chain-reaction continues down axon

- Like a wave of falling dominoes ?

Continuous conduction

Action potentials generated at the nodes, where voltage-gated ion channels are concentrated

• Electrical signal must spread passively between nodes

• When signal reaches the next node it is still strong enough to depolarize the membrane to threshold

• Action potential seems to “jump” from node to node

This describes?

Saltatory conduction in Myelinated axons

The Process of transmission of impulse from sending (presynaptic neuron) across synaptic cleft to receiving (postsynaptic) target?

Synaptic transmission