nervous

Question 1

neurons also called nerve cells

Answer 1

-are highly specialized to transmit messages (nerve impulses) from one part of the body or another

-although they structurly differ from one another,

they all have a body cell,which contain the nucleou and one or more slender processes exteding from the body

Question 2

Metabolic Center

Answer 2

The cell body is the central part of the neuron where most of its metabolic activities occur, including energy production and biosynthesis.

Question 3

Nucleus:

Answer 3

Transparent and located in the center of the cell body.
Contains a large nucleolus (important for rRNA production).

Question 4

Lack of Centrioles:

Answer 4

The cell body lacks centrioles, which supports the idea that neurons are amitotic (they do not divide after maturing).

Question 5

Organelles:

Answer 5

The cytoplasm contains the usual organelles like mitochondria, but it lacks centrioles.

Question 6

Neuron Processes Length:

Answer 6

Neuron fibers can range in length from microscopic to more than 3 feet long, such as those that extend from the lumbar region of the spine to the great toe.

Question 6

Nissl Bodies:

Answer 6

The rough ER in the cell body forms structures called Nissl bodies.
Nissl bodies are involved in protein synthesis, which is essential for the neuron’s function.

Question 7

Neurofibrils:

Answer 7

Neurofibrils are intermediate filaments found in the cytoplasm.
They help maintain the shape and structure of the neuron.

Question 8

Function: Dendrites

Answer 8

convey incoming messages (electrical signals) toward the cell body.

Question 9

Dendrites Structure

Answer 9

Neurons may have hundreds of branching dendrites, which help receive signals from other neurons.

Question 10

Meaning of “Dendrite”

Answer 10

The word “dendrite” comes from the Greek word for “tree,” reflecting their branching structure.

Question 11

Axons:

Answer 11

Function: Axons generate nerve impulses and conduct them away from the cell body.
Structure: Each neuron has only one axon. It originates from a conelike region of the cell body called the axon hillock.

Question 12

Axon Collaterals:

Answer 12

Occasionally, an axon gives off collateral branches along its length, allowing it to communicate with other neurons or cells.

Question 13

Axon Terminals:

Answer 13

At the terminal end, the axon branches extensively, forming hundreds to thousands of axon terminals.
These axon terminals are responsible for transmitting signals to other cells.

Question 14

Neurotransmitter Vesicles:

Answer 14

The axon terminals contain tiny vesicles, which are membranous sacs.
These vesicles are filled with neurotransmitters (chemicals that transmit signals between neurons or between a neuron and its target cell).

Question 15

Neurotransmitter Release:

Answer 15

When a nerve impulse reaches the axon terminals, it triggers the release of neurotransmitters into the extracellular space.
This space is the gap between neurons (synapse) or between a neuron and its target cell (like a muscle or gland).

Question 16

How Synapse Works:

Answer 16

Functional junction where an impulse is transmitted from one neuron to another.
Separated by the synaptic cleft (tiny gap).
Neurons do not physically touch other neurons or target cells.
Synapse (from Greek “syn” meaning to clasp or join) allows the transfer of impulses.

Question 17

Myelin Sheath:

Answer 17

A whitish, fatty material that covers long nerve fibers.
Protects and insulates nerve fibers, increasing impulse transmission speed.
Works similarly to insulation on electrical wires.
Schwann cells wrap around axons outside the CNS, creating the myelin sheath.
The cytoplasm of Schwann cells is squeezed out, leaving tight coils of membranes.
The outer part of the Schwann cell is the neurilemma (neuron husk).
Nodes of Ranvier are gaps in the myelin sheath, where impulses jump, speeding transmission.

Question 18

Oligodendrocytes

Answer 18

form myelin sheaths in the CNS.

Question 19

Schwann cell

Answer 19

form myelin sheaths in the PNS.

Question 20

PNS

Answer 20

Multiple Schwann cells are needed to myelinate a single axon.

Question 21

CNS:

Answer 21

A single oligodendrocyte can myelinate up to 60 different fibers at once.

Question 22

Myelin sheaths in the cns

Answer 22

in the CNS lack a neurilemma, unlike those in the PNS.

Question 23

The neurilemma

Answer 23

in the PNS helps repair nerve fibers if damaged.

Question 24

Neuron Cell Bodies in the CNS and PNS:

Answer 24

In the CNS, cell bodies are grouped into nuclei. Nuclei are protected within the skull or vertebral column to ensure neuron survival, as they don’t divide after birth. The cell body is responsible for most metabolic functions of a neuron; if damaged, the neuron cannot be replaced. In the PNS, small groups of neuron cell bodies are called ganglia (singular: ganglion).

Question 25

Nerve Fibers in the CNS and PNS:

Answer 25

In the CNS, bundles of nerve fibers are called tracts. In the PNS, bundles of nerve fibers are called nerves. White matter: Contains myelinated fibers (tracts) and appears white due to the myelin. Gray matter: Contains mostly unmyelinated fibers and neuron cell bodies.

Question 26

Sensory Neurons (Afferent Neurons):

Answer 26

Carry impulses from sensory receptors (skin, internal organs) to the CNS. Afferent means "to go toward" the CNS. Cell bodies are located in ganglia outside the CNS. Keep us informed about internal and external body conditions.

Question 27

Dendrite endings of sensory neurons

Answer 27

are linked to specialized receptors activated by specific changes in the environment.

Question 28

Cutaneous sense organs:

Answer 28

Found in the skin, responsible for general sensory perception.

Question 29

Proprioceptors:

Answer 29

Found in muscles and tendons, help with body position awareness.

Question 30

Pain Receptors (Nociceptors)

Answer 30

Least specialized of cutaneous receptors, but the most numerous. Warn us of body damage or potential damage (e.g., heat, cold, pressure).

Question 31

Proprioceptors:

Answer 31

Detect stretch or tension in skeletal muscles, tendons, and joints. Send information to the brain to help maintain balance and normal posture. The term propria means “one’s own,” reflecting how proprioceptors constantly inform the brain of our body’s movements.

Question 32

Motor Neurons (Efferent Neurons):

Answer 32

Carry impulses from the CNS to muscles, glands, and internal organs. Efferent means “to go away from” the CNS. Cell bodies of motor neurons are typically located in the CNS.

Question 33

Interneurons (Association Neurons):

Answer 33

Connect motor and sensory neurons in neural pathways. Cell bodies are typically located in the CNS. Play a key role in processing information within the nervous system.

Question 34

Multipolar Neurons:

Answer 34

Most common type. Have several processes (dendrites and axons). Motor and association neurons are multipolar.

Question 35

Bipolar Neurons:

Answer 35

Have two processes (one axon, one dendrite). Rare in adults, found in special sense organs (eye, nose). Act as receptor cells in sensory processing.

Question 36

Unipolar Neurons:

Answer 36

Have a single process that splits into proximal (central) and distal (peripheral) processes. Only the small branches at the end of the peripheral process are dendrites. Function as axons for transmitting impulses both toward and away from the cell body. Sensory neurons in PNS ganglia are unipolar.