BIO TEST #7 - NERVOUS SYSTEM

along with the endocrine system, what does the nervous system do?

coordinates and regulates the functioning of the body’s other systems

in most animals, the nervous system consist of which two major systems (anatomical divisions) that work together

central nervous system (CNS) and peripheral nervous system (PNS)

what does the central nervous system consist of? (CNS)

the brain and spinal cord

what does the peripheral nervous system consist of? (PNS)

consist of nerves that carry sensory messages to the CNS and motor commands from the CNS to the muscles and glands

what two types of cells does the nervous system contain

neurons and neuroglia (neuroglial cells)

what are neurons

cells that transmit nerve impulses between parts of the nervous system

what do neuroglia do

support and nourish neurons, maintain homeostasis, form myelin, and aids in signal transmission

what are the three classes of neurons? (functions best described in relation to the CNS)

sensory neurons, interneurons, and motor neurons

what do sensory neurons do?

takes messages to the CNS and have specialized endings called sensory receptors that detect changes in the environment

what do interneurons do? (they lie entirely within the CNS)

receive input form sensory neurons and from other interneurons in the CNS where they sum up all the messages and communicate with motor neurons

what do motor neurons do?

takes messages away from the CNS to an effector

what are effectors and what do they do?

effectors include organs, muscle fibres, or glands that carry out our responses to environmental changes

neurons vary in appearance, but what three parts do most have?

a cell body, dendrites, and an axon

describe the cell body of a neuron

contains the nucleus and other organelles

describe dendrites of a neuron

extensions leading toward the cell body that receives signals from other neurons and send them on to the cell body

describe what the axon of a neuron does

conducts nerve impulses away from the cell body toward other neurons of effectors

what are some axons covered by?

a protective myelin sheath

in the PNS, what creates a myelin sheath?

a type of neuroglia called Schwann cells which contain the lipid substance myelin in their plasma membrane

how is the myelin sheath made?

Schwann cells wrap around an axon many times and lay down many layers of plasma membrane

each Schwann cell myelinates only a part of an axon, meaning the myelin sheath is interrupted. what is the result of this?

there are gaps where there is no myelin sheath which is called nodes of Ranvier

why might a several hundred or more Schwann cells be required to myelinate a single axon?

each Schwann cell only covers about one millimetre of an axon and a single axon may be a metre or longer

in the PNS, what gives nerve fibres their white, glistening appearance?

the myelin sheath

what does the myelin sheath do in the PNS?

it plays an important role in nerve generation in the PNS because if an axon is severed, the myelin sheath remains and serves as a passageway for new fibre growth

what does the myelin sheath look like in the CNS?

it is produced by oligodendrocytes which is a type of neuroglia. unlike in the PNS, nerve regeneration does not occur to any significant degree in the CNS

what two types of nervous tissue makes up the CNS

grey matter and white matter

why is grey matter grey?

it contains neurons which short, nonmyelinated axons

why is white matter white?

it contains myelinated axons that run together in bundles called tracts

neurons with short axons make up the grey matter in the CNS. however, what do the neurons with long axons and a myelin sheath do in the CNS?

they carry messages from one part of the CNS to another

where is grey matter found in the CNS?

in the surface layer of the brain and the central part of the spinal cord

where is white matter found in the CNS?

deep within the grey matter of the brain and surrounds the grey matter in the spinal cord