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The Nervous System Lecture 6 Chapters 8.

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1 The Nervous System Lecture 6 Chapters 8

2 IX. The Nervous System A. Overall function of the Nervous System
1. Connects to the body via nerves conducting nerve impulses. 2. Sensory input - senses change both within and outside the body 3. Integration – interprets the sensory input (brain and spinal cord). 4. Motor output – causes a response (muscles contract, glands secrete). B. Divisions of the Nervous System 1. Anatomical Classification a. Central Nervous System (CNS) – brain and spinal cord.

3 b. Peripheral Nervous System (PNS).
1.) Sensory (afferent) 2.) Motor (efferent) 2. Functional classification of the PNS. a. Somatic (voluntary) – skeletal muscle. b. Autonomic ( involuntary) – smooth, cardiac muscle, glands. 1.) Sympathetic – “fight or flight” 2.) Parasympathetic – normal activity, “rest and digest”.


5 C. Cells of the Nervous System
1. Neuroglia – most numerous, wrap around, nurture neurons. 2. Neurons – cells that conduct nerve impulses to sensory areas of the brain and from motor brain areas. They compose the brain and spinal cord.

6 a. Structure 1.) Cell body – contains nucleus and typical organelles. 2.) Dendrites – (branches) conduct impulses toward the cell body. 3.) Axons – conduct impulse away from the cell body. 4.) Coverings of neuron cell processes. a.) CNS axons – myelinated (covered by a white fatty sheath from oligodendrocytes. Myelinated = faster conduction. Unmyelinated = slower conduction.

7 Central Nervous System

8 b.) PNS axons – myelinated covered by Schwann
Cells wrapped in concentric rings ( myelin sheath) over the neurilemma (looks white). Unmyelinated lacks the myelin sheath covering the neurilemma.

9 b. Classification of Neurons
1.) Anatomical a.) Unipolar – a single process from the cell body that divides like a T. Are “sensory” neurons. b.) Bipolar – two process (axon & dendrite) from opposite ends of the cell body. Rare, in retina and nose. c.) Multipolar – have three or more processes. 99% of all neurons, major type in the CNS (motor).

10 2.) Functional classification of neurons
a.) Sensory – carries impulses to the CNS from the external and internal (proprioception). b.) Motor – carry impulses from the CNS to muscles and glands for action. somatic division= sk muscle autonomic division=smooth, cardiac glands c.) Association – carry impulses from one neuron to another (interneurons).

11 D. Physiology of Neuron 1. Membrane charges (potentials) – sodium (Na+) and potassium (K+). a. Resting potential -70mV. > Na+ outside, < K+ inside 2. Nerve impulse – “action potential” a. A change in charge on the neurilemma


13 b. Na+ moves in and depolarizes the cell from -70mV to +30mV.
c. The impulse (action potential) will speed to the end of the axon, if to a muscle = contraction, gland = secrete, another neuron = affects the next neuron (stimulate or inhibit) 3. Synapses – junctions between two neurons a. Definition – point of close contact between two neurons or a neuron and an effector cell.

14 b. Excitatory synapse – transmitter substances
neurotransmitters are chemical substances released across the synapse that make the next neuron more permible to Na+ (Cell membrane more +). 1. Acetylcholine (ACh) active in the PNS. 2. Norepinephrine acts in the CNS and PNS. c. Inhibitory synapse – transmitter substances make post synaptic neurons less permible to Na+ (cell membrane more negative) 1. Dopamine acts in the CNS 2. Serotonin acts in the CNS 3. GABA (gamma-aminobutyric acid) active in CNS

15 E. Central Nervous System
1. The brain a. Cerebral hemispheres 1.) Cortex – outer thin layer of gray matter. 2.) Medulla – inner white matter with gray matter.

16 4.) Serves as an area for reasoning, judgments,
moral conduct, emotional responses, sensory interpretation, initiation of muscle activity. 5.) Has the primary motor areas and sensory areas. 6.) Consists of lobes - each with their primary functions. a.) frontal - primary motor for voluntary muscle contraction. b.) parietal - primary sensory areas from the skin. c.) occipital - primary vision area. d.) temporal – primary auditory and gustatory areas.


18 7.) Two of the four ventricles are in the cerebrum.
a.) The lateral ventricles form, contain and circulate cerebrospinal fluid (CSF). b.) CSF is secreted by the vascular choroid plexus found in each ventricle. c.) CSF functions to nourish the brain and spinal cord while protecting them by making them buoyant.


20 b. Diencephalon – (interbrain) area between the cerebral hemispheres and the brainstem.
1.) Thalamus – sensory relay center, encloses the third ventricle. 2.) Hypothalamus – the floor of the third ventricle and the brain’s automatic control center. a.) Regulates water balance – thirst b.) Regulates metabolism – body temperature c.) Regulates pituitary hormones – produces two hormones. c. Brainstem 1.) Midbrain – contains cerebral peduncles “little feet” (white fiber tracts) and corpora quadrigemina involved in eye and ear reflexes.

21 2.) Pons – connecting “bridge” for other brain
divisions. It contains secondary centers that help regulate breathing. 3.) Medulla oblongata – ascending (sensory) from the parietal lobe and descending (motor) pathways from the frontal lobe go through this part. Motor nerve fibers “cross over” to the opposite side (decussation of the pyramids) before entering the spinal cord. a.) Primary control of heart rate. b.) Controls blood vessels, arterioles. c.) Primary control of breathing. d.) Non-vital control centers – sneezing, coughing, vomiting.

22 Descending Tracts= motor Ascending tracts=sensory
Commissural fibers (corpus callosum) Longitudinal fissure Superior Lateral ventricle Association fibers Basal nuclei • Caudate Corona radiata • Putamen • Globus pallidus Fornix Internal capsule Thalamus Gray matter Third ventricle White matter Projection fibers Pons Decussation of pyramids Medulla oblongata (a) Information and motor commands from the right side go to the left side of the body via decussation below medulla

23 d. Cerebellum 1.) Controls coordination of skeletal muscle activity. 2.) Maintains muscle tone. 3.) Helps coordinate balance or equilibrium. 2. The spinal cord – stops at L1 or L2 (in adults) a. Structure 1.) H or butterfly shaped gray matter horns (cell bodies) surrounded by white matter (myelinated fibers). a.) A central canal circulates CSF.

24 2.) Contains ascending posterior (sensory columns)
to the brain and descending anterior (motor columns) or tracts to muscles and organs. 3.) 31 vertebrae segments give rise to 31 pairs of spinal nerves.

25 4.) Covered by 3 meningeal layers (as in the brain)
a.) Outer most dura mater “tough mother” b.) Arachnoid mater with a CSF filled space beneath called the subarachnoid space. c.) Innermost delicate pia mater on the spinal cord surface. 5.) Surrounded by CSF just like the brain. CSF circulates in SubA

26 3. Reflex arcs – structural and functional units of nervous
behavior. Involve cranial (brain) and spinal (spinal cord) nerves. a. A rapid, predictable response to a stimulus. b. typical reflex arcs contain a receptor, sensory neuron, one or more interneurons, a motor neuron, and an effector (muscle or gland).




30 4. Sensory and motor pathways (tracts) in the spinal
cord. a. Nerve processes in the white matter are organized into three columns. The anterior, lateral and posterior white columns. Smaller bundles of fibers in each column are organized into sensory of motor “tracts”. 1.) Sensory tracts conduct impulses up to brain. 2.) Motor tracts conduct impulses down to effector. a.) Descending motor tracts “decussate” in the lower medulla. Left cerebral motor area controls the right side of the body and visa versa.


32 F. Peripheral Nervous System
1. Cranial nerves a. 12 pairs connect brain to organs in the head, neck and shoulders (vagus to thorax and abdomen). b. Names tend to identify functions or general innervations.

33 c. Names and types of cranial nerves. (handout 23B)
1.) I. Olfactory – sensory (smell). 2.) II. Optic – sensory (vision). 3.) III. Oculomotor – motor (controls external eye muscles for movement of the eye). 4.) IV. Trochlear – motor (external eye muscles) 5.) V. Trigeminal – Mixed nerve (motor – chewing) (sensory – sensation from forehead, eyebrows, eyelids, nose, lips, cheeks, gums and teeth). 6.) VI. Abducens – motor (external eye muscles for movement).

34 7.) VII. Facial – mixed (sensory – taste)
(motor – facial expressions, tear glands, salivary glands). 8.) VIII. Vestibulocochlear – sensory (cochlear branch – hearing). (vestibular branch – balance or equilibrium). 10.) X. Vagus – mixed (parasympathetic nerve). motor – organs in the thoracic, sensory abdominal, and pelvic cavities

35 2. Spinal nerves – 31 pairs originate from the spinal cord.
a. Mixed nerves connecting spinal cord to arms, legs, neck and trunk. b. Named by spinal area 1.) C1 - C8 (cervical) 2.) T1 - T (Thoracic) 3.) L1 - L (Lumbar) 4.) S1 - S (Sacral) 5.) C (Coccygeal) c. Nerve Plexuses are 4 areas where spinal nerves from different spinal regions comingle and give rise to nerve trunks to internal organs and muscles of the appendages. The plexuses are: cervical, brachial, lumbar, and sacral. Spinal nerves T2 – T11 do not form plexuses.


37 F. Peripheral Nervous System (PNS)
1. Cranial Nerves a. 12 Pairs connect the brain to parts in the head, neck, shoulders, while the vagus nerve “wanders” into many organs in the thorax and abdomen. b. Names tend to identify their functions or innervations. Know handout 23 B! 2. Spinal Nerves – 31 pairs originate from the spinal cord. a. Spinal nerves are mixed nerves, Why? b. They are named according to the spinal area of their origin. c. Spinal nerves T2 – T11 do not form plexuses. d. Spinal nerves in the neck, shoulder, lumbar, and pelvic area give rise to plexuses.

38 1.) Plexus – means a redistribution of nerve fibers
forming major peripheral nerves. 2.) Cervical plexus – phrenic nerve to diaphragm for breathing. 3.) Brachial plexus – forms nerves to shoulder and arm. a.) Radial nerve – innervates extensors of fingers and wrist. b.) Median nerve – innervates flexors of fingers c.) Ulnar nerve – same as the median.

39 4.) Lumbar plexus – supplies nerves to the lower
abdomen and front of the thigh. a.) Femoral nerve innervates the quadraceps. (Rectus femoris, Vastus medialis, Vastus lateralis). b.) The saphenous nerve innervates the skin of the medial foot and toes. 5.) Sacral plexus – supplies nerves to the back of the thigh and lower leg. a.) Sciatic nerve innervates the hamstrings, (Biceps femoris, Semitendinosus, Semimembranosus). b.) Tibial nerve innervates the calf muscles.



42 6.) Dermatome – is an area of skin innervated by spinal nerves.
7.) Myotome – is an area of muscle innervated by spinal nerves. 3. Covering of Peripheral nerves a. Endoneurium – connective tissue covering surrounding one (each) nerve fiber (axon). b. Perineurium – covers groups of fibers (fascicles). c. Epineurium – tough fibrous sheath covering all fascicles to form the “nerve”.



45 G. Autonomic nervous system , ANS (involuntary control)
1. The autonomic system is a part of the PNS. 2. It functions to maintain homeostasis by controlling the heart, blood vessels and glands. a. The somatic system is one neuron from the brain or spinal cord to skeletal muscles.

46 b. The autonomic system is two neurons (a preganglionic & postganglionic neuron), to smooth, cardiac muscle or glands.

47 3. Two Divisions – sympathetic and parasympathetic
a. Sympathetic – “fight or flight”. 1.) Emerges from thoracic and lumbar spinal cord regions forms the “sympathetic trunk and ganglia” near the spinal column. 2.) The preganglionic neuron is short while the postganglionic neuron is long. 3.) Functions to meet stressful conditions, releases norepinephrine (NE) and epinephrine (E).


49 b. Parasympathetic – “rest and digest”
1.) Emerges from cranial nerves and sacral spinal nerves from the spinal cord. 2.) The preganglionic neuron is long while the postganglionic neuron is short. 3.) Functions in quieter periods to restore energy and is dominant during periods of relaxation. It releases acetylcholine (ACh) neurotransmitter. 4.) *NOTE – ACh excites skeletal muscle, but NOT smooth, cardiac muscle and glands!


51 c. Dual versus single innervation

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