Introduction to the Nervous System ch. 12, 13,14 Anat 211 Lab CWI

Sacral Plexus

Forms from the rami of L4-S4 -Superior gluteal nerve - Inferior gluteal nerve - Pendendal nerve - Posterior femor cutaneous nerve - sciatic nerve

Glossopharyngeal Nerve (CN IX)

Glossopharyngeal= throat/swallow/tongue -provides motor axons to the muscles of the pharynx involved in swallowing and sensory fibers from the posterior 1/3 of the tongue for taste sensation.

bipolar neurons

A neuron that has only two projections (one axon/one dendrite) from the cell body

multipolar neuron

A neuron with a single axon and multiple dendrites; the most common type of neuron in the nervous system.

Reflex

An involuntary, predictable motor response to a stimulus. The pathway through which information travels.

Axolemma of axon

Specialized plasma membrane surrounding the axoplasm.

parasympathetic nervous system

the division of the autonomic nervous system that calms the body, conserving its energy

Neurilemma

the thin sheath around a nerve axon (including myelin where this is present).

Reflex Arc

1) Sensory receptor detects the stimulus 2) sensory afferents bring the stimulus to the CNS 3) the CNS Processes and integrates the information. 4) the CNS sends its output via motor efferents to an effector 5) The effector performs the triggered action

steps of action potential

1)The action potential (which occurs as described above) travels along the membrane of the presynaptic cell until it reaches the synapse. The electrical depolarization of the membrane at the synapse causes channels to open that are selectively permeable, meaning they specifically only allow the entry of positive sodium ions (Na+). 2)The ions flow through the presynaptic membrane, rapidly increasing their concentration in the interior. The high concentration activates a set of ion-sensitive proteins attached to vesicles, which are small membrane compartments that contain a neurotransmitter chemical. 3)These proteins change shape, causing the membranes of some "docked" vesicles to fuse with the membrane of the presynaptic cell. This opens the vesicles, which releases their neurotransmitter contents into the synaptic cleft, the narrow space between the membranes of the pre- and postsynaptic cells. 4)The neurotransmitter diffuses within the cleft. Some of it escapes, but the rest of it binds to chemical receptor molecules located on the membrane of the postsynaptic cell. The binding of neurotransmitter causes the receptor molecule to be activated in some way. Several types of activation are possible, depending on what kind of neurotransmitter was released. In any case, this is the key step by which the synaptic process affects the behavior of the postsynaptic cell. 5)Due to thermal shaking, neurotransmitter molecules eventually break loose from the receptors and drift away. The neurotransmitter is either reabsorbed by the presynaptic cell and repackaged for future release, or else it is broken down metabolically.

cranial nerves

12 pairs of nerves that carry messages to and from the brain

Synapse

A junction where information is transmitted from one neuron to the next.

Peripheral Nerve

A nerve that branches from a plexus and supplies sensory and motor functions to many areas of the body.

autonomic nervous system

A subdivision of the peripheral nervous system. Controls involuntary activity of visceral muscles and internal organs and glands.

Axon

A threadlike extension of a neuron that carries nerve impulses away from the cell body.

Abducens Nerve (CN VI)

Abducens = Lateral rectus muscle - a small motor nerve that innervates the final extrinsic eye muscle.

Accessory Nerve (CN XI)

Accessory = move head and neck -the only cranial nerve that has both a cranial component originating from the brain stem and a spinal component originating form the spinal chord. Its motor axons innervate the muscles that move the head and the neck, such as the trapezius and the sternocleidomastoid muscles.

Neuron

a specialized cell transmitting nerve impulses; a nerve cell.

axon hillock

Cone shaped region of an axon where it joins the cell body.

Brachial Plexus

Consist of the anterior rami of c5 -T1. The first structures formed in each ? ? are its large trunk.

Epineurium

Dense connective tissue that surrounds entire nerve including fascicles and blood vessels.

axon terminals (terminal buttons)

Enlarged button like structures at the ends of axon branches

Facial Nerve (CN VII)

Facial = Facial Expression - mixed fibers of the ? ? that innervate many structures and provide for the following: motor muscles of facial expression; taste from the anterior 2/3 of the tongue; motor to the glands that produce the tears (lacrimal glands), mucus and saliva; and sensory from part of the face and mouth.

Nodes of Ranvier

Gaps in the myelin sheath to which voltage-gated sodium channels are confined.

Hypoglossal Nerve (CN XII)

Hypoglossal = tongue/no-taste -a small motor nerve that innervates the muscles that move the tongue. Note that the ypoglossal nerve moves the tongue but does not provide any taste sensation to the tongue.

Optic Nerve (CN II)

Optic= Vision axons emerge from the retina of the eye and meet at the optic chiasma, where the nerves partially exchange axons before diverging to form the optic tracts.

Vagus Nerve (CN X)

Vagus= wanderer/skin/speech/swallowing/spit -the only cranial nerve that "wanders" outside of the head and neck. In the head and neck, it provides some sensory innervation from the skin of the head and the pharynx, motor axons to muscles involved in speech and swallowing, and motor axons to certain salivary glands. Outside the head and the neck it innervates most of the thoracic and abdominal viscera as the main nerve of the parasympathetic nervous system.

Vestibulocochlear Nerve (CN VIII)

Vestibulocochlear- ear/hearing/balance - innervates the structures of the inner ear and provides for the senses of hearing and equilibrium.

myelin sheath

a fatty tissue layer segmentally encasing the axons of some neurons; enables vastly greater transmission speed as neural impulses hop from one node to the next

Effects of neurotransmitter Acetylcholine (Ach)

a) Decreased heart rate, which decreases blood pressure b) dilation of the blood vessels, serving the skin and abdominal viscera, which decreases blood pressure. c) Mild constriction of the bronchioles d) Increased activity of smooth muscle of the digestive tract and secretion from digestive glands. e) Increased urine production. f) Storage of fat and glucose g) constriction of pupils h) Adjustment of the lens for near vision.

Lumbar Plexus

consists of the anterior rami of L1-L4 with a small contribution from T12. Include: - Iliohypogastric & ilioinguinal nerves - Genitofemoral nerve - Femoral nerve - Lateral femoral cutaneous nerve - Obturator nerve

cell body of neuron

contains nucleus and organelles, soma

Nerve Plexus

network of interweaving anterior rami of spinal nerves

satellite cells

surround neuron cell bodies within ganglia

Dendrite

the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body

sympathetic nervous system

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations

Initial Segment (trigger zone)

the first part of the axon; it is where the action potential (nerve impulse) is generated.

Astrocytes

Provide structural and metabolic support for neurons.

Nissl bodies

Rough endoplasmic reticulum in neuron

Telodendria

Series of fine, terminal extensions branching from the axon tip.

neuroglial cells

Specialized cell of the nervous system that produces myelin, communicates between cells, and maintains the ionic environment

Schwann cells (neurolemmocytes)

Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers Similar function as oligodendrocytes Vital to regeneration of damaged peripheral nerve fibers

synaptic vesicles

Tiny pouches or sacs in the axon terminals that contain chemicals called neurotransmitters.

Trigeminal Nerve (CN V)

Trigeminal = chewing - large mixed nerve named for the 3 branches that provide sensory innervation from the face and motor innervation to the muscles of mastication or (chewing)

Trochlear Nerve (CN IV)

Trochlear = superior oblique (eyeball) muscle - small motor nerve that innervates one of the six extrinsic eye muscles that move the eyeball

Oligodendrocytes

Type of glial cell in the CNS that wrap axons in a myelin sheath.

Cervical Plexus

consists of the anterior rami of C1-C4 with small contributions from C5. The branches of each serve the skin of the head and neck and certain neck muscles.

synaptic cleft

The narrow gap that separates the presynaptic neuron from the postsynaptic cell.

Oculomotor Nerve (CNIII)

Oculomotor= eye muscles -Innervates 4 of the 6 eye muscles that move the eyeball, the muscle that opens the eyelid, the muscle that constricts the pupis, and the muscle that changes the shape of the lens for near vision.

Neurotransmitters trigger?

a) increased rate and force of heart contraction, which increases the blood pressure b) constriction of the blood vessels serving the abdominal viscera and the skin, which also increases the blood pressure. c) Dilation of the blood vessels serving the skeletal muscles. d) dilation of the bronchioles (airway passages in the lungs) e) decreased secretion from digestive glands. f) Decreased Urine production g) Increased metabolic rate. h) Increased release of fatty acids and glucose. i) Dilation of the pupils j) The release of epinephrine from the adrenal medulla.

Neurofibrils

bundles of neurofilaments that provide support for dendrites and axon

Perineurium

coarse connective tissue that bundles fibers into fascicles

Fascicle

discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath

pseudounipolar neurons

have only one fused axon that extends from cell body and divides into two processes: one process carries sensory information from sensory receptors to cell body; other process carries sensory information from cell body to spinal cord; sensory neurons that carry information related to pain, touch, and pressure

ependymal cells

line cavities of the brain and spinal cord, circulate cerebrospinal fluid

Endoneurium

loose connective tissue that encloses axons and their myelin sheaths

three-neuron loop

neuronal action potential reaches the axon terminal of neuron 1 -> neurotransmitters are released from axon terminals by exoxytosis -> neurotransmitters diffuse across the synaptic cleft -> neurotransmitters bind to the postsynaptic membrane of neuron 2 and generate an excitatory local potential ->excitatory local potentials summate -> local potentials spread through the plasma membrane to the trigger zone/axon hillock -> axon hillock is a depolarized to threshold ->action potential generated -> voltage gated Na+ channels open, causing depolarization -> voltage gated Na+ channels close, and K+ ion channels open -> K+ ions exit the cytosol, causing repolarization -> K+ ions continue to exit until the membrane in hyperpolarized -> the action potential is propagated along the axon -> the action potential reaches the axon terminals of neuron 2 -> neurotransmitters are released from the axon terminal by exocytosis -> neurotransmitters diffuse across the synaptic cleft -> neurotransmitters cause an excitatory or inhibitory local potential in the postsynaptic membrane of neuron 3

Olfactory (CN I)

olfaction = smell nerve that innervates the olfactory mucosa in the superior nasal cavity where it provides the sense of smell.

internode

space between nodes