Nervous tissue Flashcards
that are the 3 functions of the nervous system?
- Senses changes in the environment, both internal and external
- Integrates and interprets the sensory input for understanding
- Responds by initiating muscular contractions or glandular secretions
How does the nervous system accomplish its homeostatic role?
through reactions, carried out by electrical messages called nerve impulses (action potentials), allow for second-to-second adjustments in homeostasis
How does the role of the endocrine system compare with that of the nervous system?
The endocrine system, using blood-borne chemical messengers called hormones, controls long-term homeostasis. Rather than making second-to-second adjustments, the endocrine system controls processes over days, weeks, months, and years.
Name the two principal divisions of the nervous system.
central nervous system (CNS)
peripheral nervous system (PNS)
Describe the central nervous system
The CNS consists of the brain and the spinal cord, within which incoming sensory information is processed, thoughts and emotions are generated, and memories are stored. Most nerve impulses that stimulate muscle contraction and glandular secretion originate in the CNS.
describe the peripheral nervous system
The PNS consists of 12 pairs of cranial nerves associated with the brain and 31 pairs of spinal nerves associated with the spinal cord.
what is the relationship between the peripheral and central nervous system
Cranial and spinal nerves of the PNS carry sensory information from the CNS to effectors (muscles and glands) in the periphery.
what are sensory neurones
The input component of the PNS consists of nerve cells called sensory (afferent) neurons that conduct nerve impulses from sensory receptors to the CNS and end within the CNS.
What are motor neurons?
The output component of the PNS consist of nerve cells called motor (efferent) neurons that originate in the CNS and conduct nerve impulses away from the CNS to the effectors.
Somatic nervous system
concerned with sensory information from the skin, skeletal muscles, and special senses, and motor information to the skeletal muscle only.
Autonomic nervous system
carries sensory information from the viscera to the CNS and motor information from the CNS to cardiac muscle, smooth muscles, and glands.
Name the autonomic subdivisions.
The motor portion of the autonomic nervous system is divided into two portions: the sympathetic nervous system and the parasympathetic nervous system.
What are neuroglial cells
Neuroglial cells are the supportive, nurturing, and protective cells for the neurons. They occupy only half of the CNS, are much smaller than neurons and outnumber them. They remain mitotic throughout life and tend to fill in spaces of injured neurons after disease and injury.
Astrocytes
attach blood vessels to neurons,
helping to form the blood-brain barrier. They help maintain the proper balance of K+ for the neurons and participate in the metabolism of neurotransmitters. They are responsible for forming scars in the CNS after injury.
Oligodendrocytes
give support to
neurons of the CNS. They produce the myelin sheath found around axons of the CNS. Each oligodendrocyte uses its processes to wrap several axons.
Microglia
small phagocytic cells that engulf
and destroy microbes and cellular debris in the CNS. They migrate to areas of injured nervous tissue and help to clean the area.
Ependyma
form a continuous epithelial
lining for the ventricles of the brain and the central canal of the spinal cord. They probably assist in the circulation of cerebrospinal fluid, but their role is mostly unknown.
Schwann cells
also known as neuro-
lemmocytes, produce the myelin sheath around the axons of motor neurons and the dendrites of sensory neurons in the PNS.
Satellite cells
support neurons found in
ganglia in the PNS; function is obscure.
What is the myelin sheath?
Most nerve fibers are surrounded by a multilayered lipoprotein produced by the neuroglia (Schwann cells in the PNS and oligodendrocytes in the CNS) called the myelin sheath.
what is the function of the myelin sheath
electrically insulates the nerve fiber, greatly increasing the speed of nerve impulse conduction.
Nerve processes with such a covering are said to be myelinated while those without are unmyelinated. Therefore, there are neurons with different speeds of transmission.
How is the myelin sheath formed in the PNS?
Schwann cells form the myelin sheath around motor axons and sensory dendrites during fetal life and the first postnatal year. In this process, Schwann cells line up along the length of the nerve fiber, attach to it, then begin to spiral around it, leaving behind multiple layers of glial cell membrane.
What is the neurilemma?
As the multiple layers of membrane are formed, the cytoplasm and organelles of the Schwann cells are pushed to the outside. This portion of the Schwann cell is known as the neurilemma. It is found only around neurons of the PNS; oligodendrocytes do not form a neurilemma.
What are the nodes of Ranvier?
At intervals along the length of a nerve process, between the individual Schwann cells (PNS) or pieces of oligodendrocytes (CNS), are gaps in the myelin sheath called the nodes of Ranvier (neurofibral nodes).
What is the function of neurons?
Nerve cells, called neurons, are responsible for conducting impulses from one part of the body to another and are therefore the structural and functional units of the nervous system.
what is the describe the neuron cell body
The cell body (perikaryon, soma) contains
typical cellular organelles surrounded by cytoplasm. There is a large nucleus with a very prominent nucleolus and neurofibrils, elements of the cytoskeleon that give the neuron structure and shape
Nissl substance
Scattered throughout the cytoplasm of the neuron
cell body are structures called Nissl bodies (chromatophilic substance), orderly arrays of rough endoplasmic reticulum used for protein synthesis.
Dendrite
The dendrite is usually a short, tapering, and
highly branched process extending from the cell body; usually unmyelinated (sensory dendrites are the exception). It is ALWAYS a process that carries the nervous message towards the cell body.
Axon
The axon is a single, long, thin, cylindrical projection
from the cell body that moves toward an effector or another neuron. It ALWAYS carries the nervous message away from the cell body.
Axon hillock
The axon hillock, a cone-shaped elevation, is
that region of the neuronal cell body from which the axon arises.
Trigger zone
Just distal to the axon hillock is an area called the trigger zone where nerve impulses arise for propagation along the axon. This area of membrane is rich with voltage-gated sodium channels (to be described later).
Axon collateral
Along the axon’s length, side branches
called axon collaterals may depart from the main axon to innervate other structures.
Telodendrion
At their terminations with effectors, the axon
and axon collaterals end by dividing into many fine processes called axon terminals or telodendria
End bulbs
The tips of the axon terminals swell into bulb-
shaped synaptic end-bulbs that contain synaptic vesicles filled with a chemical known as a neurotransmitter. Neurons utilize a single type of neurotransmitter.
what is a nerve fiber
a general term for any nerve process (sensory dendrite or motor axon).
what is a nerve
a bundle of many nerve fibers, both sensory and motor, that course along the same path in the PNS
what is a tract
a bundle of related nerve fibers in the CNS that connects different areas of the CNS.
Multipola neuron
have several
dendrites and a single axon; most neurons are of this type.