Nervous System A&P-Ruben J. Mora P.2
Major Functions: thinking, movement, internal
processes of physiology.
Divisions of Nervous System
Tissues:
Classifications of Neurons
Brain
Spinal Cord
Action Potential & Nerve Impulse
Cranial Nerves
Spinal Nerves
Neurotransmitters: chemical messengers that convey messages through space. They send electrical impulses from a neuron to another cell. Neurotransmitters are released in response to a nerve impulse
Autonomic NS
Reflex Arc
The Nervous system can be divided into 2 groups
Central Nervous System is the brain and spinal cord. It is responsible for integration of information and decision making
Peripheral Nervous system:Made up of cranial and spinal nerves that connect the CNS to the rest of
the body.Somatic nervous system: controls voluntary skeletal muscles.Autonomic nervous system: controls involuntary effectors.
The main cell types in the nervous system is neurons, cells that communicate via electrical impulses. And Neuroglia, which are cells that support, nourish, and protect neurons
Integrative Function: Coordination of sensory information to CNS. Is responsible for understanding and processing information so you can make decisions.
Motor Function:Nerve impulses are conducted along motor neurons to effectors.
Sensory Function:Is provided by sensory receptors. The information travels from receptors to sensory neurons, which transport info to the CNS
Effectors are muscles or glands that respond to decisions made in the
CNS.
Neuron Structure:
Myelin Sheath:
dendrites conduct impulses toward the cell body, they are long and branching
cell body (soma):contains major organelles including nucleus
axon conducts impulses away from the cell body, arises from a thickening extending from the cell body, called the axon hillock
Larger axons are enclosed by myelin sheaths; they are called myelinated fibers. Narrow gaps in the myelin sheath are called nodes of Ranvier
Unipolar neurons: Have only 1 process extending from the cell outside the cell body, it soon splits into 2 parts that function as one axon, these are sensory neurons.
Bipolar neurons: have 2 processes extending from the cell body, a dendrite, and an axon.
Multipolar neurons: have many dendrites and one axon arising from their cell bodies. Most neurons are multi polar
Motor (efferent) neurons:multipolar neurons that condct impulses from the CNS to peripheral effectors(muscles or glands
Interneurons: multipolar neurons lying within the CNS that form links with other neurons.
Sensory (afferent) neurons: conduct impulses fromperipheral
receptors to the CNS; usually unipolar, although some are bipolar.
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An excitatory stimulus opens chemically-gated Na+ channels;
Na+ ions flow into cell due to concentration gradient, causing inside of neuron to become less negative
Threshold stimulus:potential changes from -70 to -55 mV
Upon reaching threshold potential, voltage-gated Na+ channels open, changing charge to about +30 mV; this is called an action potential.
Types of Impulse conduction
Continuous conduction;Conduct impulses sequentially over the entire length of their membrane.
Saltatory conduction:Impulses “jump” from one Node of Ranvier to the next, since sodium and potassium channels occur only at the nodes.
MUST KNOW:
Norepinephrine:Creates a sense of feeling good; low levels may lead to depression.
Acetylcholine:Stimulates skeletal muscle contraction at neuromuscular junctions
Arachnoid mater:The middle layer of meninges.
Pia mater:The innermost layer of the meninges
Dura Matter:Outermost layer of meninges and is very thick
The meninges consist of the dura mater, arachnoid mater, and pia mater
surrounded by 3 membranes called
meninges that lie between the skull bones
Begins at the base of the brain, the spinal cord consists of 31 segments, each of which connects to a pair of spinal
nerves.
The meninges consist of the dura mater, arachnoid mater, and pia mater
spinal cord are surrounded by 3 membranes called
meninges that lie between the vertebrae and the soft CNS
tissues.
Major function
-transmit impulses to and from the brain, and to house spinal reflexes.
-Ascending tracts carry sensory information to the brain; descending tracts carry motor information from brain to muscles or glands.
Components of a Reflex arc:
-A sensory receptor that detects changes.
-A sensory neuron, that carries the information from a receptor toward the CNS.
-An interneuron in the CNS
-A motor neuron, that carries a command to effectors.
-And an effector that responds to the change
Reflex arcs provide the basis for involuntary actions called reflexes
1)Olfactory, sensory fibers conduct impulses associated with the sense of smell.
2)Optic, sensory, fibers coduct impulses associated with the sense of vision
The first pair arises from the cerebrum, and the second pair from the thalamus, but most arise from the brainstem.The 12 pairs are designated by number and name; the numbers
are in order, from superior to inferior.
6)Abducens, primarilly motor, motor fibers conduct impulses to muscles that move the eyes
Twelve pairs of cranial nerves arise from the underside of the brain.
3)Oculomotot, primaraly motor, motor fibers conduct impulses to muscles that raise euelids, move eyes, adjust the amount of light entering the eyes and focuses the lenses
12)Hypoglossal, primarily motor, motor fibers conduct impulses to muscles that move the tongue
11)Accessory, pribarily motor, divided into the cranial and spinal branch. Motor fibers conuct impulses to muscles of the soft palate, pharync, and larynx. Motor fibers conduxt impulses to muscles of the nexk and back
7)Facial, mixed, sensory fibers conduct impulses associated with taste receptors of the anterior tongue Motor fibers conduct impulses to muscles of facial expression, tear glands, and salivary glands
4)Trochlear, primarily motor, motor fibers conduct impulses to muscles that move the eyes
10)Vagus, miced, somatic motor gibers conduct impulses to muscles associated with speech and swallowing
5)Trigeminal, mixed, has 3 subdivisions.opthamalic division, maxillary division, mandibular division
9)Glossopharyngeal, miced, sensory fibers conduct impulses from the pharync, tonsils, posterior tounge, and carotid artieris
8)Vestbulochlear, sensory, is divided into 2 subdivision, the vestibular branch and the cohlear branch
31 pairs of spinal nerves arise from spinal cord
All except the first pair are mixed nerves
8 pairs of cervical nerves, 12 pairs of thoracic, nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of coccygeal nerves
Cervical Plexuses (C1-C4): lie on either side of the neck; supply muscles andskin of the neck; include the phrenic nerves, which control the diaphragm
The main branches of spinal nerves, except in the thoracic region, form networks called plexuses
Brachial Plexuses (C5 –T1): arise from lower cervical and upper thoracicnerves; supply muscles and skin of arms, forearms, and hands; lead into the upper limbs; include the musculocutaneous, ulnar, median, radial, and axillary nerves
Lumbosacral Plexuses (L1-S4): arise from the lower spinal cord; supplymuscles and skin of the lower abdomen, external genitalia, buttocks, and legs
Portion of the PNS that functions constantly and independently, without conscious effort
Controls visceral motor functions of smooth muscle, cardiac
muscle, and glands
Parasympathetic division: active under normal, restful
conditions
Helps maintain homeostasis, responds to emotional stress, and prepares the body for strenuous activity.
Sympathetic division: active in conditions of stress or
emergency
Nervous tissue coverings:
-Epineurium:outercovering of a nerve
-Endoneurium:covering around individual nertve fibers
-Perineueium:covering arounf fascicles of nerve fibers