The Nervous System Ch 13 Flashcards
What are the neurons?
- basic functional units of the nervous system
- high requirement for oxygen
- cannot reproduce but can regenerate cell processes if the cell body remains intact
What are neuroglia (glial cells)?
provide structural, functional support and protection to neurons
What is the neuron structure?
central cell body - (soma or perikaryon)
cell processes - dendrites - receive stimuli
- axons - conducts nerve impulses
away
What are dendrites?
- receive stimuli from other neurons and conduct the stimuli to the cell body
- May serve as sensory receptors for heat, cold, touch, pressure, stretch, or other physical changes from inside or outside the body
- short, numerous, multibranched
What are axons?
- conduct nerve impulse away from cell toward another neuron or an effector cell
- single, long process; may be covered with myelin
- white matter: tissue containing myelinated axons
What are myelinated axons?
conduct impulses faster than unmyelinated ones
What is the myelin sheath?
cell membrane of glial cells tightly wrapped around the axon
- Olligodendrocytes in the brain and spinal cord
- schwann cells in the nerves outside the brain and spinal cord
Multiple Schwann cells or the _______ cover the entire length of the axon.
oligodendrocytes
Nodes of Ranvier: gaps between adjacent _____ cells
glial
The organization of nervous system includes?
Anatomical, Direction of impulses
Anatomical includes?
central nervous system (CNS),
Peripheral nervous system (PNS),
The central nervous system includes?
brain and spinal cord - anything surrounded by spinal canal
The peripheral nervous system which extends outward form the central axis toward the periphery of the body includes?
cranial nerves which originate directly from the brain and spinal nerves which emerge from the spinal cord
What are efferent nerves?
conduct impulses away from CNS - also called motor nerves - cause skeletal muscle contraction and movement
What are afferent nerves?
conduct impulses toward CNS - also called sensory nerves - conduct sensations from sensory receptors in the skin and other locations in the body to the CNS
What is autonomic function in the nervous system?
controls and coordinates automatic functions
Ex.: slowing of the heart rate in response to an increased blood pressure
What is somatic function in the nervous system?
actions under conscious, or voluntary, control
Neuron function?
sodium potassium pump; specialized molecule that helps maintain cell resting state
- Pumps (Na+) from inside of neuron to the outside
- pump (K+) from outside of neuron to the inside
What is deplorization - action potential?
during depolarization, inside of the neuron goes from a negatively charged resting membrane potential to a net positive charge due to inflow of sodium ions
- creates large change in electrical charge from negative to positive
Depolarization is?
neuron receives external stimulus
sodium channel opens on neuron cell membrane
sodium ions flow into cell by passive diffusion
Repolarization?
sodium channels close K+ channels open K+ diffuses out of the cell resting state restored - as repolarization ends, sodium-potassium pump moves sodium and potassium ions back to their original sides resting state restored
Threshold stimulus?
stimulus must be sufficient to make the neuron respond and cause complete depolarization
- “all or nothing principle” neuron depolarizes to its maximum strength or not at all
- conduction of the action potential - spreading wave of opening sodium channels in sufficient numbers to allow sodium influx and depolarization - wave of depolarization or nerve cells
What is saltatory conduction?
rapid means of conducting an action potential
depolarization in myelinated axons can only take place at the nodes of Ranvier
Synapse?
junction between two neurons or a neuron and a target cell
Synaptic cleft?
gap between adjacent neurons
Presynaptic neuron?
neuron bringing the depolarization wave to the synapse - releases neurotransmitter
Postsynaptic neuron?
contains receptors for the neurotransmitter
Telodendron?
branched structure on presynaptic neuron
Terminal bouton?
slightly enlarged bulb on each of teledendron (synaptic end bulb, synaptic knob)
Vesicles in the knob contain the neurotransmitter
When _______ wave reaches synaptic knob vesicles fuse with the knob’s cellular membrane and dump neurotransmitter into the synaptic cleft
depolarization
Neurotransmitters diffuse across the ____ ____ toward the postsynaptic membrane
synaptic cleft
_______ on the postsynaptic membrane bind the nerotransmitter
Receptors
What are excitatory neurotransmitters?
usually cause an influx of sodium so that the postsynaptic membrane moves toward threshold
Inhibitory neurotransmitter?
move the charge within the postsynaptic cell farther away from threshold
What are the types of neurotransmitters?
acetylcholine, catecholamines, gamma-aminobutyric acid (GABA) and glycine
Acetylcholine?
can be excitatory or inhibitory depending on its location in the body
Catecholamines?
norepinephrine and epinephrine - associated with “fight or flight” reactions of the sympathetic nervous system
-dopamine - involved with autonomic functions and muscle control
Gamma-aminobutyric acid (GABA) and glycine?
inhibitory
Acetylcholinesterase?
found on postsynaptic membrance; breaks down acetylcholine
Central Nervous System contains?
brain - cerebrum, cerebellum, diencephalon, brain stem
spinal cord
Cerebrum?
gray matter - cerebral cortex; outer layer of the brain
white matter - fibers beneath the cortex and corpus callosum (fibers that connect the two halves of the cerebral cortex)
- area of the brain responsible for higher-order behaviors (learning, intelligence, awareness, etc)
In the cerebrum, gyri (gyrus) is?
folds in cerebral hemispheres
In the cerebrum fissures are?
deep grooves separating the gyri
In the cerebellum, sulci (sulcus) is?
shallow grooves separating the gyri - divides the cerebral hemispheres into lobes
Cerebellum?
located just caudal to the cerebrum
area of the brain responsible for coordinated movement, balance, posture, and complex reflexes
Diencepalon?
-passageway between brain stem and cerebrum
What are the structures associated with the diencephalon?
thalamus, hypothalamus, pituitary
What is the thalamus?
acts as a relay station for regulating sensory inputs to the cerebrum
What is the hypothalamus?
interface between the nervous system and the endocrine system
What is the pituitary?
endocrine “master gland”
What is the brain stem?
connection between the rest of the brain and the spinal cord
- composed of the medulla oblongata, the pons, and the midbrain
- area of the brain responsible for basic support functions of the body
- many of the cranial nerves originate from this area of the brain
What are the meninges?
connective tissue layers that surround brain and spinal cord
- contain blood vessels, fluid, and fat
- supply nutrients and oxygen to the superficial tissues of the brain and spinal cord
- provide some cushioning and distribution of nutrients for the CNS
What are the three layers in the meninges?
dura mater, arachnoid, pia mater
What is the dura mater?
touch, fibrous - most superficial
What is the arachnoid?
delicate, spiderweb-like (lacy)
What is the pia mater?
very thin; lies directly on surface of brain and spinal cord
What is the cerebrospinal fluid?
fluid between layers of the meninges and in canals and ventricles inside the brain and central canal of spinal cord
- provides cushioning function
- may play role in regulation of autonomic functions such as respiration and vomiting
What is blood-brain barrier?
separates the capillaries in the brain from the nervous tissue
- capillary walls in the brain have no fenestrations; covered by cell membranes of glial cells
- prevents many drugs, proteins, ions, and other molecules from readily passing from the blood into the brain
What are the cranial nerves?
12 pairs in PNS that originate directly from the brain in most mammals
- numbered in roman numerals from 1 - 12
- each nerve may contain axons of motor neurons, axons of sensory neurons or combinations of both
The spinal cord consists of?
Medulla, cortex Dorsal and ventral nerve roots, dorsal horns, ventral horns
What is the medulla?
central part of the spinal cord - composed of gray matter
- central canal - center of medulla
What is the cortex?
outer part of the spinal cord
- white matter
- surrounds the gray matter
What does the dorsal and ventral nerve roots do?
emerge from between each pair of adjacent vertebrae
- dorsal nerve roots contain sensory fibers
- ventral nerve roots contain motor fibers
What are dorsal horns?
neurons in gray matter that forward sensory nerve impulses to brain or other parts of spinal cord
What are ventral horns?
neurons in gray matter that forward motor (efferent) nerve impulses to the spinal nerves
What is the autonomic nervous system? What does it include?
controls automatic functions at the subconscious level
sympathetic nervous system and parasympathetic nervous system
What is sympathetic nervous system?
nerves emerge from thoracic and lumbar vertebral regions (thoracolumbar system)
What is parasympathetic nervous system?
nerves emerge from the brain and the sacral vertebral regions (cranial-sacral)
aids in digestive - slows down
What is the primary neurotransmitter of sympathetic nervous system?
noreprinephrine
What is adrenergic neurons?
neurons that release norepinephrine
Epinephrine and norepinephrine are also released from?
adrenal medulla
Primary neurotransmitter of parasympathetic nervous system is?
acetylcholine
What reflexes are in the spinal cord itself and do not require conscious control?
somatic reflexes, autonomic reflexes, contralateral reflex and ipsilateral reflex
What are somatic reflexes?
involve contraction of skeletal muscles
What are autonomic reflexes?
regulate smooth muscle, cardiac muscle, and endocrine glands
What are contralateral reflex?
starts on one side of body and travels to opposite side
What is ipsilateral reflex?
stimulus and response are on the same side of the body
What is reflex arc?
sensory receptor sends an action potential along the sensory neuron to the gray matter of the spinal cord or brain stem
Sensory neuron synapses with other neurons, incoming sensory impulse integrated with other impusles from other sensory neurons
Integrated response of the reflex is sent out by the motor neuron, which ends at the target organ
What is the stretch reflex?
Monosynaptic reflex arc - involves a sensory neuron and only one synapse between them without any interneurons
What is the withdrawal reflex?
also called flexor reflex, several interneuron synapses, results in contraction or flexing of muscles
What is crossed extensor reflex?
contralateral reflex, if withdrawal reflex initiated, afferent sensory neuron synapse with interneurons -causes contraction of opposite extensor muscles
Upper CNS normally produces an _____ ____ on the reflex arcs
inhibitory effect
With injury, intact reflex arcs caudal to the _____ _____ trauma become ______.
spinal cord
hyperreflexive
Trauma where reflex arc enters or leaves the spinal cord, or damage to the sensory nerve or motor nerve of the reflex, results in either _______ or ______ reflex arcs
hyporeflexive
absent
Pupillary light reflex (PLR) is?
normal response to shining light in the eye of an animal is for the iris in both eyes to constrict - shining the light in one eye causes a constriction in both eyes
Palpebral reflex arc is ?
light tap on the medial canthus of the eye produces a blink of the eyelids
What is the refractory period?
time period during which a neutron is insensitive to additional stimuli - cell is still in depolarization and early repolarization
What is the absolute refractory period?
the part of the refractory period during which no stimulus of any intensity can cause a cell to deplorarize again.
What is relative refractory period?
if a stimulus is large enough and comes at the tail end of repolarization, it may be possible to stimulate another deplorization
In the cerebellum, the longitudinal fissure does what?
prominent groove that divides the cerebrum into to right and left cerebral hemispheres
