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Terms in this set (102)
CNS contains brain and spinal cord. PNS contains cranial and spinal nerves
do not generate or conduct impulses; support, nurture and protect neurons, smaller, more numerous, mitotic
nourish the nerve cells, star shaped, in CNS, maintain K+ balance, link neurons and vessels forming blood-brain barrier that regulated passage into brain
most common, produce myelin sheath around axon in CNS
form from monocytes, phagocytic cells (microbes and debris) in CNS. protect the nerve cells
Line CSF - filled cavities of CNS and filter CSF. circulate cerebral fluid.
produce myelin sheath around axons of PNS neurons
covered by a thin layer of glial plasma membrane (take slower)
have a thick myelin sheath composed of lipid and protein (myelin), acts as insulating layer.Schwann cell membrane wraps around the axon many times; nucleus and cytoplasm form outermost layer or neurolemma which provides regeneration tube. Nodes are uncovered areas between Schwann cells
convert stimuli into nerve impulses (excitability)
cell body with typical plasma membrane and cell organelles
highly branched generally short cytoplasmic processes, receive input.
long thin process, send impulse. originates on axon hillock of soma, initial segment contains trigger zone, with neurofilaments for transport. axon collaterals side brances. terminates in many fine filaments or axon terminals with synaptic knobs containing synaptic vesicles. limited mitosis, new cells form in hippocampus of humans.
one bifurcated process, dendrites and axon are continuous, sensory neurons
two processes, one dendritic and one axonic, special senses neurons
more than two processes, one axon and several dendrites, motor neurons.
Sensory afferent neurons
carry impulses from receptors to the CNS.
Association neuron or interneuron
connects afferent to efferent, excitatory or inhibitory
Motor or efferent neurons
carry impulses from the CNS to effectors (muscles or glands), always excitatory in skeletal muscle
Resting membrane potential
a polarization or electrical difference between the inside and outside of inactive cell caused by concentration differences of certain ions and selective membrane permeability.
propagation of action potential
self propagating change in polarity along an axon
small deviation from the resting membrane potential caused by a stimulus. short distance. Localized no refractory periods. Varies in amplitude and is directly related to the number of voltage-gated NA channels open.
more negative than resting potential
less negative than resting potential. Na+ come into the axon carries positive charges into the axons and decreases potential differences until polarity is reversed
action potential moves in series of small steps along the unmyelinated axon. Slower
action potential jumps from node to node along the myelinated axon, 5-7X faster, uses less ATP energy
myelinated axons conduct faster than unmyelinated axons
larger diameter axons conduct faster than smaller diameter axons
Type A fibers
4-20 micrometer axon diameter, myelinated, 15-120 m/sec
Type B fibers
2-4 micrometer axon diameter, myelinated, 3-15 m/sec
Type C fibers
less than 2 micrometer axon diameter, unmyelinated, 0.5 m/sec
Electrical synapse or Gap junction
action potential passes directly from cell to cell, connection proteins form tunnel that connects cells cytoplasm, 2-way transmission, allows for synchronization of activity, faster than chemical, occurs in smooth and cardiac muscle
action potential produces a chemical signal that crosses the space and produces a new action potential, 1 way, allows for modification. transmission is not jumping of action potential but a complex chemical process permitting grading and modulation (frequency change) of neural activity
neuron sending the impulse. axon of presynaptic neuron terminates on the soma or dendritic region of the postsynaptic neuron. axon ends in terminal branches with synaptic knobs that contain many mitochondria and vesicles of a chemical neurotransmitter. number of knobs per cell varies, (1 -40,000)
space between cells across which an impulse must be transmitted. No direct connection, about 20-50 nm space between presynaptic and postsynaptic
neuron receiving impulse. neurotransmitter produces the action potential. neurotransmitter produces the action potential
is excitatory at skeletal neuromuscular junction, is inhibitory in vagus nerve to the cardiac muscle.
Central Nervous System
comprises the brain and spinal cord
peripheral nervous system
consists of nerves, ganglia, and sensory receptors. These organs constitute the two divisions of the PNS, the somatic system and the autonomic system.
nerve cell bodies mainly in the brain cortex or central spinal cord
myelinated axons in the brain medulla or outer spinal cord
collection of nerve cell bodies inside the CNS but not in the cortex, functinal group
collection of nerve cell bodies outside of the CNS
bundle of afferent & efferent nerve fibers outside of the CNS
network of nerve fibers
bundle of fibers serving a similar function
specialized area of brain for receiving sensory information from specific body regions & transmitting motor impulses to specific body regions
involves skin, skeletal muscle, joints
involves internal organs, blood vessels, glands, smooth & cardiac muscle
Division of brain
Forebrain or prosencephalon, midbrain or mesencephalon, hindbrain or rhombencephalon.
cerebrum, thalamus, hypothalamus, pineal body
small area, only connection between fore & hindbrains
cerebellum, pons, medulla oblongata
rapid automatic repsonse to specific stimuli. predictable with little variability. negative feedback mechanism, often protective
Types of reflexes
innate, acquired, spinal, cranial, somatic, visceral
neural connections from during development, modifiable
complex learned motor patterns, improved by repetition
connections & processing occur in spinal cord
occurs in brain
involuntary control of skeletal muscular system
involuntary control of glands, smooth & cardiac muscle
receptor responds to a stimulus, afferent sensory neuron carries impulse to the CNS. Intergration of information in CNS (involves several synapses). Efferent motor neuron carries impulse from the CNS. Effector is a muscle or gland
function of neurons
is the generation and transmission of nerve impulses
neurons respond to changes in their environment; this is called excitability. If the change, or stimulus, is above a minimum level, then the membrane permeability changes especially for sodium ions. DEPOLARIZATION FOLLOWED BY REPOLARIZATION IS AN ACTION POTENTIAL, OR NERVE IMPULSE
all or none principle
if the graded potential causes a threshold level depolarization, action potentials will be generated in the neuron. The minimal stimulus to initiate depolarization is called a threshold stimulus.
transmission of impulses from cell to cell. transmission occurs across a gap between neurons, called a synapse
a transmission involving neurotransmitters that increase the postsynaptic membrane permeability to sodium ions. This requires a certain volume of neurotransmitters The addition of neurotransmitter molecules tends to lead toward depolarization. Result of chemical-gated Na+ channels opening, lasts about 20 msec.
a transmission that decreases permeability to sodium ions. Result of chemical-gated K+ or Cl- channels
Na-K exchange pump
Returns concentrations of Na+ and K+ to resting state levels
K+ channels open to allow potassiujm ions to move outward, restoring the change on the outside of the membrane to positive.
the spinal cord
a long bundle of nerve tissue extending through the vertebral canal from the base of the brain to the lower back
Protective coverings of the spinal cord
three components protect the cord: the vertebral column, cerebrospinal fluid (CSF), and the meniges.
Layers of the meninges
three layers: the outer dura mater, the middle arachnoid, and the inner pia mater. the meninges of the cord are continuous with those of the brain
Structure of the spinal cord
the cord consist of 31 segments, each containing a pair of spinal nerves. In cross section, it can be observed to contain white matter and gray matter.
contains unmyelinated fibers, neuron cell bodies, and neuroglia. It occupies the center of the cord in the shape of the letter H, and consist of posterior gray horns, the anterior gray horns, and the lateral gray horns, the gray commisure connnecting right and left, and central canal fillled with CSF. The posterior horns are sensory, and the anterior are motors
contains myelinated fibers, and surrounds the gray matter. it contains three regions: the anterior, posterior, and lateral columns. Longitudinal bundles or myelinated fibers extend through the white matter, forming the nerve tracts.
Functions of the spinal cord
conduction pathway and as a reflex center
the spinal cord provides two-way traffic between the brain and peripheral nerves. The ascending tracts carry sensory information to the brain, and the descending tracts carry motor impulses away from the brain.
a spinal reflex is a rapid signal that bypasses the higher brain centers for a reduced responese time. the pathway is called a REFLEX ARC and involves a sensory receptor, sensory neuron, reflex center in the spinal cord or lower brain area, and motor neuron. Somatic reflexes stimulate skeletal muscle, and visceral reflexes stimulate or inhibit visceral organs
is divided into three regions: the forebrain, midbrain, and hindbrain. The forebrain contains the cerebrum and diencephalon, the midbrain is the smallest, and the hindbrain contains the pons, medulla oblongata and cerebellum.
Protective converings of the brain
is protected by cranial bones, CSF, and the three menigeal layers (dura mater, arachnoid, and pia mater)
is produced by filtration through capillary networks in the ventricles, called choroid plexuses. It continual production rate establises a fluid current that pushes CSF through the ventricles, around the subarachnoid space of the spinal cord, to the subarachnoid space around the brain. It is reabsorbed into the bloodstream through arachnoid villi at the top of the brain
Ventricle of the brain
there are four ventricles, or cavities, inside the brain two lateral ventricles, a third ventricle and a fourth ventricle all of which intercommunicate by way of narrow channels.
the largest structure in brain, divided into right and left parts, called hemispheres. Each hemisphere is divided into function lobes: the frontal, parietal, occipital, and temporal.
located below the large cerebrum. It contains two structures: the thalamus and the hypothalamus. the pineal gland and pituitary gland are connected to the diencephalon
the largest part of the diencephalon, it serves as the principal relay station for sensory impulses entering the brain and voluntary motor impulses traveling out.
located below the thalamus; the primary control center for the autonomic nervous system. It regulates food and water intake, and is associated with emotion as part of the limbic system
located between the diencephalon and the pons. It consists of cerebral peduncles on its anterior side, which provide a main connection for motor and sensory pathways; and the colliculi on the posterior side, which contains reflex centers for rapid eye, head, and trunk movements.
located below the midbrain , it bridges the cerebrum and cerebellum
together with the midbrain and pons, makes up the brain stem. The medulla lies below the pons and is continuos with spinal cord. On its posterior side the motor nerves cross, forming a bulge called the pyramids. Sensory nerves also cross in the medulla. The medulla contains numberous visceral reflex centers, such as the cardiac center, the vasomotor center, and the respiratory center.
nerves that originate from the brain. There are 12 pairs, each with a name and Roman numeral. They may be sensory, motor, or mixed in function.
nerves that originate from the spinal cord there are 31 pairs, all of which are mixed in function.
olfactory; sensory- smell
vision; sensory- vision
Oculomotor; motor- extrinsic eye muscles, pupil constriction
trochlear; motor- one extrinsic eye muscle (superior oblique)
trigeminal; Sensory- scalp, most of the face, nasal cavity, nasopharynx, mucous membranes in oral cavity. Motor- muscles of mastication (chewing), soft palate, throat and middle ear.
from receptor to spinal cord or brainstem
from spinal cord or brainstem to thalamus, cross-over occurs
from thalamus to cerebral cortex
Types of reflexes
innate, acquired, spinal, cranial, somatic, visceral
two types of nerve cells
neuroglial cells and neurons