Nervous Tissue
physiology
Terms
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- neurons
- nerve cells
- axon hillock
- mound from with the axon (nerve fiber) originates
- oligodendrocytes
- kind of neuroglia in CNS that have a bilbous body and armlike processes- each reach out to nerve fiber and spiral around it like electrical tape/ spiral wrapping is called myelin sheath, which insulates nerve fiber and speeds signal conduction
- sympathetic division
- division of autonomic nervous system that tends to arouse the body for actions- ex: accelerate heartbeat and increase airflow, and inhibit digestion
- schwann cells
- type of glial cell in PNS- envelop nerve fiber of PNS- produces myelin sheath and assist in regeneration of damages fibers
- spinal shock
- Any severe injury to the cord first produces a period of sensory and motor paralysis/ causes faccid skeletal muscles, no somatic or visceral reflexes, no sensations relayed via cord
- ganglion
- knotlike swelling in a nerve where the cell bodies of neurons are concentrated
- neuropeptides
- chain of 2-40 amino acids (ex: beta-endorphin,substance P, enkephalins, endorphins), act as lower concentrations and have longer lasting effects than other neurotransmitters, stored in secretory granules, numerous and widespread throughout CNS and PNS, excitatory and inhibitory
- facilitated zone
- part of input neuron that synapses with other neurons in pool, and with fewer synapses on each of them/ can stimulate neurons to fire only with assistance from other input neurons
- terminal arborization
- an extensive complex of fine branches- each branch ends in a synaptic knob and contains synaptic vesicles full of neurotransmitters
- sensory/afferent division
- carries sensory signals from receptors to CNS
- resting membrane potential
- charge difference across the plasma membrane- -70 mV, more negatively charges particles on inside of membrane than outside
- refractory period
- period of resistance to stimulation- divided into two phases: absolute refractory period (no stimulus of any strength will trigger a new AP) and relative refractory period (possible to trigger a new AP but only with unusually strong stimulus)
- dendrites
- primary site for receiving signals from other neurons- the more it has, the more information it can recieve and incorporate into its decision making
- parasympathetic division
- division of autonomic nervous system that tends to have a calming effect, ex: slowing heartbeat and stimulating digestion
- astrocytes
- most abundanat glial cell in CNS and cover entire brain surface and most nonsynaptic regions of neurons in gray matter of CNS- branches have starlike shape- form supportive framework for nervous tissue, have pericascular feet (contact blood capillaries and stimulate them to form a tight seal called blood brain barrier, convert blood glucose to lactate (nourishment), secrete proteins called nerve growth factors that promote neuron growth and synapse formation, communicate electrically, form hardened scar tissue and fill space formerly occupied by neurons (process called astrocytosis or sclerosis)
- anaxonic neurons
- multiple dendrites but no axon- communicate through their dendrites and do not produce action potentials- some found in brain, retina, and adrenal medulla
- electrical potential
- difference in the concentration of charged particles between one point and another- form of potential energy that, under that right circumstances, can produce a current
- initial segment
- short section of nerve fiber between the axon hillock and fist glial cell
- endoneurium
- thin sleeve of fibrous CT along with basil that is external to neurilemma
- visceral sensory division
- carries signals from viscera of thoracic and abdominal cavities
- satellite cells
- type of glial cell in PNS that surround nueron cell body in ganglia of PNS- little is known of function
- neural circuit
- pathways among its neurons/ determine functions of neural pool
- somatic sensory division
- carries signals from receptors in skin, muscles, bones, and joints
- internodes
- myelin covered segments from one gap to the next- .2-1 mm long
- amino acids
- neurotransmitters include glutamate and aspartate (found in CNS, always excitatory, inactivation determines re-uptake (no enzyme), GABA (brain and spinal cord) and glycine (spinal cord)- (inhibitory, open chlorine channels inhibit stimulation
- interneurons
- aka association neurons- lie in CNS and they recieve signals from other neurons and carry out the integrative function->process, store, and retrieve information and make decisions that determines how body responds to stimuli
- monoamines
- neurotransmitter that is synthesized from amino acids (ex: epinephrine, norepinephrin, dopamine, histamine, serotonin)- excitatory or inhibitory, all use second messenger system
- soma
- control center of the neuron, aka cell body or perikaryon
- neurilemma
- thick outermost coil of myelin sheath- bulging of Scwann cell contains nucleus and cytoplasm
- myelin sheath
- insulating layer around nerve fiber- formed from oligodendrocytes in CNS and Schwann cells in PNS- composition of plasma membrane (20% protein, 80% lipid- phospholipids, glycolipids, and cholesterol)
- neuroglia
- supportive cells- aka glial cells- protect neurons and help function- bind neurons together and provide a supportive framework for the nervous tissue
- discharge zone
- part of input neuron when acting alone can make the post synaptic cells fire
- slow axonal transport
- aka axoplasmic flow- .5-10 mm/day and is always anterograde- renews worn out axoplasmic components in mature neurons and supplies new exoplasm for developing or regenerating neurons- case for damaged nerve fibers
- multipolar neurons
- have one axons and multiple dendrites- most common type- includes neurons of brain and spinal cord
- acetylcholine
- neurotransmitter that has low molecular weight, excitatory at NMJ, inhibitory at other synapses (slowing of heart rate), degraded by AChE, nicotinic (blocked by curare)- tends to always be excitatory, muscarinic (blocked by atropine)- tends to be inhibitory but not always
- effectors
- cells and organs that respond to commands from nervous system
- microglia
- kind of nueroglia in CNSsmall macrophages that develop from white blood cells called monocytes- wander through CNS and phagocytize dead nervous tissue and other microorganisms- concentrates in damages areas from infection, trauma, or stroke
- nodes of Ranvier
- gaps between segments of myelin sheath
- Nissl bodies
- dark stained region of rough ER- have microtubules and neurofilaments (bundles of actin) that compartmentalize in it
- fast retrograde transport
- type of fast axonal transport that returns used synaptic vesicles and other materials to soma and informs it of conditions at axon terminal- ex: herpes, rabies, polio and tetanus --> delay between infection and onset of symptoms corresponds to time needed for pathogens to reach somas
- motor/efferent division
- carries signals from CNS to glands and muscle cells
- visceral motor division/ autonomic nervous system
- division of motor division that carries signals to glands, cardiac and smooth muscle (visceral reflexes)
- action potential
- produced by voltage-gates on trigger zone and axon, always begins with depolarization, all or non, irreversible, self propagating (effects a great distance from point of origin), nondecremental (signal maintains same strength regardless of distance)
- somatic reflexes
- involuntary muscle contractions
- unipolar neurons
- one single process leading away from soma- neurons that carry sensory signals to spinal cord- aka pseudounipolar because they start out as bipolar neurons in embryo and two processes fuse as maturation
- axonal transport
- two way passage of proteins, organelles, and other materials along an exon
- sensory/ afferent neurons
- detect stimuli such as light, heat, pressure, and chemicals- transmit info to CNS
- anterograde transport
- movement away from soma down the axon- motor protein called kinesin
- motor/efferent neurons
- send signals to muscle and gland cells
- fast anterograde transport
- type of fast axonal transport that moves organelles and other enzymes and small molecules
- axon
- nerve fiber- cylindrical and unbranched- specialized for rapid conduction of nerve signals to point far from soma
- local potential
- produced by ligand-regulated or mechanically regulated gates on dendrites and soma- may be positive (depolarizing) of negative (hyperpolarizing) voltage change, graded- proportional to stimulus strength, reversible (returns to RMP if stimulation ceases before threshold is reached), local (short distance), decremental (signal grows weaker with distance)
- saltatory conduction
- propagation of a nerve signal that seems to jump from node to node
- bipolar neurons
- one axon and one dendrite- olfactory cells, neurons of retina, and sensory neurons of inner ear
- ependymal cells
- kind of nueoglia in CNS that resemble cubiodal epithelium lining internal cavities of brain and spinal cord- but unlike epithelial cells, no basement membrane and have rootlike processes that penetrate into underlying nervous tissue- these cells produce cerebrospinal fluid (clear liquid that bathes in CNS and fills its internal cavities
- depolarization
- membrane voltage shifts to a less negative value- inflow of sodium
- retrograde transport
- movement up axon toward the soma - motor protein called dynein
- lipofuscin
- brown pigment resulting when lysosomes digest worn-out organelles/ these accumulate with age and push the nucleus to one side of the cell/ these are also called wear and tear granules because they are most abundant in old neurons
- somatic motor division
- division of motor division that carries signals to skeletal muscles
- trigger zone
- axon hillock and initial segment- together initiate a nerve signal
- fast axonal transport
- 20-300 mm/day and can be either anterograde or retrograde