UNIT 4

corticospinal tracts

*descending tract* •Most neurons from precentral gyrus of cerebral cortex for voluntary motor control of body and limbs •two neuron pathway -upper motor neuron in cerebral cortex lower motor neuron in spinal cord Pathway Precentral gyrus > EPSP > AP > Upper motor neuron (CNS) of corticospinal tract > Synaptic cleft > EPSP > AP > Lower motor neuron (efferent somatic motor spinal nerve) PNS à anterior rootlet > anterior root > intervertebral foramen > spinal nerve > flexors/extensors, etc. in order to move in response to tapping

neuroglial cells

*know all from memory* oligodendrocytes- wrap in myelin sheets astrocyte- really important, stars, function of ependymal-make and move CSF, cuboidal microglia-immune cells, phagocytize foreign invaders schwann- myelin sheet satellite- sheet around soma, and regulate ion environment

variation in neuron structure

*know from memory* •multipolar neuron (CAN RECIEVE A LOTTT OF INFO) -one axon and multiple dendrites -most common -most neurons in the brain and spinal cord •bipolar neuron -one axon and one dendrite -olfactory cells, retina, inner ear •unipolar neuron -single process leading away from soma -sensory from skin and organs to spinal cord •anaxonic neuron -many dendrites but no axon -help in visual processes

Peripheral nervous system (PNS)

-all nervous system except the brain and spinal cord -composed of nerves and ganglia nerve= bundle fo nerve fibers (axons) wrapped in fibrous connective tissue= rogan! ganglion=a knot-like swelling in a nerve where neuron cell bodes are concentrated

tectospinal tract

-arises from neurons in superior colliculus •Sensory info in from eyes and movement out •Orients us with eye movements to objects of interest -reflex turning of head in response to sights and sounds

Nature of Reflexes

-automatic responses to sensory input occur without our intent or often our awareness - 1.reflexes require stimulation •responses to sensory input 2.reflexes are quick •involve few if any interneurons and minimum synaptic delay 3.reflexes are involuntary •occur without intent and difficult to suppress •automatic response 4.reflexes are stereotyped essentially same way every time

brain tumors arise from:

-meninges (protective membranes of CNS) -by metastasis from non-neuronal tumors in other organs -most from glial cells mitotically active throughout life LEAD TO GLIOMAS

Neural Coding

-nervous system converts information to a meaningful pattern of action potentials •qualitative information depends upon which neurons fire •quantitative information - intensity of a stimulus is encoded in two ways: 1.different neurons have different thresholds of excitation •stronger stimuli = more rapid firing rate 2.stronger stimulus = higher frequency •CNS can judge stimulus strength from the firing frequency of afferent neuron

gray matter in spinal cord

-pair of posterior (dorsal) horns -posterior (dorsal) root of spinal nerve carries sensory fibers -pair of thicker anterior (ventral) horns -anterior (ventral) root of spinal nerve carries only motor fibers -gray commissure connects right and left sides •central canal with ependymal cells and filled with CSF -lateral horn - visible from T2 through L1 •contains neurons of sympathetic nervous system

Visceral reflex to High BP

1.Baroreceptors (arterial stretch receptors) detect high blood pressure 2.Glossopharyngeal nerve (IX) carries signal to medulla oblongata 3.Vagus nerve (X) carries signal to heart 4.ACh released causing heart rate to slow reducing blood pressure •homeostatic negative feedback loop •Which division of ANS would this be? What would the reverse system loo The ANS is responsible for the body's visceral reflexes—unconscious, automatic, stereotyped responses to stimulation, much like the somatic reflexes discussed in chapter 13, but involving visceral receptors and effectors and slower responses. Some authorities regard the visceral afferent (sensory) pathways as part of the ANS, but most prefer to limit the term ANS to the efferent (motor) pathways. Regardless of this preference, however, autonomic activity involves a visceral reflex arc that includes receptors (nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli), afferent neurons leading to the CNS, interneurons in the CNS, efferent neurons carrying motor signals away from the CNS, and finally effectors. For example, high blood pressure activates a visceral baroreflex. It stimulates stretch receptors called baroreceptors in the carotid arteries and aorta, and they transmit signals via the glossopharyngeal nerves to the medulla oblongata. The medulla integrates this input with other information and transmits efferent signals back to the heart by way of the vagus nerves. The vagus nerves slow down the heart and reduce blood pressure, thus completing a homeostatic negative feedback loop. A separate autonomic reflex arc accelerates the heart when blood pressure drops below normal—for example, when we move from a reclining to a standing position and gravity draws blood away from the upper body.

flexor and extensor reflexes

1.flexor reflex -contraction of flexor muscles resulting in withdrawal of limb -contraction of flexors and relaxation of extensors in that limb 2.crossed extension reflex - contraction of extensor muscles in limb opposite of one that is withdrawn -maintains balance by extending other leg •

visual projection pathway

1st order > bipolar cells of retina 2nd order > retinal ganglion cells whose axons form optic nerve -two optic nerves combine to form optic chiasm -half fibers cross over to opposite side of brain and chiasm splits to form optic tracts optic tracts pass around hypothalamus with most of axons ending in thalamus 3rd order > thalamus to primary visual cortex of occipital lobe where conscious visual sensation occurs -a few optic nerve fibers project to midbrain and terminate in the superior colliculi and pretectal nuclei superior colliculi controls visual reflexes of extrinsic eye muscles

Somatic vs. Autonomic Pathway

ANS - two neurons from CNS to effectors • presynaptic neuron whose cell body is in CNS • postsynaptic neuron cell body in peripheral ganglion somatic motor pathway a motor neuron from the brainstem or spinal cord issues a myelinated axon that reaches all the way to the skeletal muscle autonomic pathway signal must travel across two neurons to get to the target organ must cross a synapse where these two neurons meet in an autonomic ganglion presynaptic neuron - the first neuron has a soma in the brainstem or spinal cord synapses with a postganglionic neuron whose axon extends the rest of the way to the target cell The ANS has components in both the central and peripheral nervous systems. It includes control nuclei in the hypothalamus and other regions of the brainstem, motor neurons in the spinal cord and peripheral ganglia, and nerve fibers that travel through the cranial and spinal nerves you have already studied. The autonomic motor pathway to a target organ differs significantly from somatic motor pathways. In somatic pathways, a motor neuron in the brainstem or spinal cord issues a myelinated axon that reaches all the way to a skeletal muscle. In autonomic pathways, the signal must travel across two nerve fibers to get to the target organ, and it must cross a synapse where these two neurons meet in an autonomic ganglion. The first fiber, called the preganglionic fiber, leads from a soma in the brainstem or spinal cord to the autonomic ganglion. It synapses there with a neuron that issues a postganglionic fiber to the target cells. In contrast to somatic motor neurons, postganglionic fibers of the ANS do not end by synapsing with a specific target cell, but with a chain of varicosities that diffusely release neurotransmitter into the tissue and stimulate many cells simultaneously. In summary, the autonomic nervous system is a division of the nervous system responsible for homeostasis, acting through the mostly unconscious and involuntary control of glands, smooth muscle, and cardiac muscle. Its target organs are mostly the thoracic and abdominopelvic viscera, but also include some cutaneous and other effectors. It acts through motor pathways that involve two nerve fibers, preganglionic and postganglionic, reaching from CNS to effector. The ANS has two divisions, sympathetic and parasympathetic, that often have cooperative or contrasting effects on the same target organ. Both divisions have excitatory effects on some target cells and inhibitory effects on others.

Language Centers

Broca's area (forming) and Wernicke's area (processing it) Corticospinal output to muscles. Glossopharyngeal Nerve: CN IX (swallowing, salivation, gagging,) Output through Vagus Nerve: CN X (Speech) Accessory Nerve: CN XI (swallowing, head, neck & shoulder movement) Hypoglossal Nerve: CN XII (tongue movements of speech)

Ventricles of Brain

Canals in the brain that contain cerebrospinal fluid. F(x) of CSF, buoyancy, cushion, chemical stability (remove waste and bath brain with nutrients), homeostasis

what two systems maintain internal coordination?

Endocrine and nervous -communicatd by means of hormors -communicated by electical and chemical means to send messages from cell to cell

motor (efferent) neuron

Functional type of neuron -send signals out to muscles and gland cells (the effectors) •motor because most of them lead to muscles •efferent neurons conduct signals away from the CNS

Long-Term Potentiation (long-term memory)

Post-Synaptic Ca++ entry: 1.Activates CaMKII (Ca2+/Calmodulin dependent protein kinase II) 2.CaMKII keeps AMPA receptors open, more Na+ diffuses = more depolarization 3.NO increases glutamate release from presynaptic axon = greater EPSPS 4.Greater pre-synaptic Ca++ entry causes more glutamate release = more EPSP *also what happens with PTSD* fear and memory adrenaline reinforces the same system takes a lot of work of therapy and chemical changes (medications)

Reticular Activating system -Formation

Reticular Activating System (RAS) • Sets level of arousal of cerebral cortex to incoming sensory info • Activity of RAS promotes wakefulness; inhibition of RAS promotes sleep • Includes Medulla, Pons, Midbrain, Thalamus, & Hypothalamus The reticular formation consists of more than 100 small neural networks, with varied functions including the following: 1 Somatic motor control 2 Cardiovascular control 3 Pain modulation 4 Sleep and consciousness 5 Habituation - brain learns to ignore repetitive, meaningless stimuli while remaining sensitive to others. A good example of this is a person who can sleep through loud traffic in a large city, but is awakened promptly due to the sound of an alarm or crying baby. Reticular formation nuclei that modulate activity of the cerebral cortex are part of the ascending reticular activating system

olfactory cells (ethmoid bone, cribriform foramina and plate allow for dendrites to be in mucosa of nasal cavity) -olfactory hairs -binding sites for odorant molecules -in thin layer of mucus -basal end becomes axon -axons collect into small fascicles - leave cranial cavity through cribriform foramina in ethmoid bone -fascicles collectively regarded as Cranial Nerve I

activate G protein and cAMP system opens ion channels for Na+ or Ca2+ depolarizes membrane and creates receptor potential à granule cells inhibit the mitral and tufted cells reason why odors change under different conditions food smells more appetizing when you are hungry women more sensitive to odors than men highly important to social interaction olfactory receptors adapt quickly due to synaptic inhibition in olfactory bulbs some odorants act on nociceptors of the trigeminal nerve ammonia, menthol, chlorine, and capsaicin of hot peppers Human Pheromones human body odors may affect sexual behavior a person's sweat and vaginal secretions affect other people's sexual physiology dormitory effect presence of men seems to influence female ovulation ovulating women's vaginal secretions contain pheromones called copulins, that have been shown to raise men's testosterone level Olfactory tract =bundle of neurons in PNS granule cells, they actually cause more stimulation of the other cells KNOWWW *granule cell, olfactory tract, olfactory nerve fascicle, olfactory cell olfactory hairs, mucus*

descending tracts

carry motor signals down brainstem and spinal cord two neurons --upper motor neuron originate in cerebral cortex or brainstem and terminates on a lower motor neuron - -lower motor neuron in brainstem or spinal cord •axon of lower motor neuron leads to muscle or other target organ

meninges of vertebra and spinal cord

dura mater (dural sheath) arachnoid mater -CSF, runs through spine cushions brain, epididymal cells produce pia mater (adhere to spinal cord/brain) Fat in epidural and subarachnoid space for insulation, stability, support

equilibrium

equilibrium - coordination, balance, and orientation in 3D static equilibrium - perception of orientation of head when body is stationary dynamic equilibrium - perception of motion or acceleration linear acceleration - change in velocity in a straight line (elevator) static equilibrium - when head is tilted, heavy otolithic membrane sags, bending the stereocilia, and stimulating the hair cells dynamic equilibrium - in car, linear acceleration detected as otoliths lag behind, bending the stereocilia, and stimulating the hair cells because the macula sacculi is nearly vertical, it responds to vertical acceleration and deceleration macula sacculi - lies vertically on wall of saccule macula utriculi - lies horizontally on floor of utricle angular acceleration - change in rate of rotation (car turns a corner) equilibrium-rotation as head turns, endolymph lags behind, pushes cupula, stimulates hair cells

Interneurons (association neurons)

functional type of neuron -entirely within CNS -receive signals from many neurons and integrate •process, store, and retrieve information •'make decisions' how the body will respond -90% of all neurons = interneurons -interconnect sensory pathways, and motor pathways of CNS

sensory (afferent) neurons

functional type of neuron -specialized to detect stimuli -transmit information about them to the CNS •begin in almost every organ in the body and end in CNS •afferent - conducting signals toward CNS

vestibular projection pathways

hair cells of macula sacculi, macula utriculi and semicircular ducts synapse on vestibular nerve (part of CN VIII) information sent to five targets: 1. cerebellum - integrates vestibular information into its control of head and eye movements, muscle tone, and posture 2. nuclei of oculomotor, trochlear, and abducens nerves (CN III, IV, and VI) to produce vestibulo-ocular reflex - keeps your vision fixed on distant object while you are walking 3. reticular formation - thought to adjust blood circulation and breathing to postural changes 4. spinal cord - descend through two vestibulospinal tracts of spinal cord and innervate extensor (antigravity) muscles 5. thalamus - thalamic relay to cerebral cortex for awareness of position and motor control of head and body

photoreceptor cells

light absorbing cells rod cells (night vision) cone cells (color, day vision) outer segment tapers to a point

sensory transduction in retina

light energy into action potentials in retina structure of retina -pigment epithelium - most posterior part of retina --absorbs stray light neural components -photoreceptor cells - absorb light and generate a chemical or electrical signal --rods, cones, and certain ganglion cells --only rods and cones produce visual images bipolar cells - synapse with rods and cones and are first-order neurons of visual pathway ganglion cells - largest neurons in retina and second-order neurons of visual pathway

olfaction

smell •olfaction - sense of smell • •olfactory mucosa -2000 to 4000 odors distinguished

components of a reflex arc

somatic receptors -in skin, muscles, or tendons afferent nerve fibers -information from receptors to posterior horn or brainstem integrating center -synaptic contact between neurons in gray matter of spinal cord or brainstem determines whether efferent neurons issue a signal to muscles efferent nerve fibers -carry motor impulses to skeletal muscle skeletal muscles -somatic effectors carry out the response

spinal nerves

spinal cord- cylinder of nervous tissue arises from brainstem at foramen magnum -vertebral canal -ends at ~L1 -31 pair of spinal nerves INTERVERTEBRAL FORAMEN, spinal nerve holes cervical plexus brachial plexus intercostal nerves lumbar plexus sacral plexus cauda equina (horsetail, wispy nerve bundle) cervical nerves c1-c8 thoracic nerves t1-t12 lumbar nerves l1-l5 sacral nerves s1-s5 coccygeal nerve Co1

Sympathetic and Vasomotor Tone

sympathetic division prioritizes blood vessels to skeletal muscles and heart in times of emergency blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise

Neurotramistters and Receptros

sympathetic effects tend to last longer than parasympathetic effect As noted earlier, the divisions of the ANS often have contrasting effects on an organ. The sympathetic division accelerates the heartbeat and the parasympathetic division slows it down, for example. But each division of the ANS also can have contrasting effects on different organs. For example, the parasympathetic division contracts the wall of the urinary bladder but relaxes the internal urethral sphincter; both actions are necessary for the expulsion of urine. It employs acetylcholine for both purposes. Similarly, the sympathetic division constricts most blood vessels but dilates the coronary arteries, and it achieves both effects with norepinephrine. How can different autonomic neurons have such contrasting effects? There are two fundamental reasons: (1) sympathetic and parasympathetic fibers secrete different neurotransmitters, and (2) target cells respond in different ways even to the same neurotransmitter depending on what type of receptors they have for it. All autonomic nerve fibers secrete either acetylcholine or norepinephrine, and each of these neurotransmitters has two major classes of receptors (fig. 15.8).

Gustastion

taste molecules must dissolve in saliva and flood the taste pore taste cells have tuft of apical microvilli (taste hairs) that serve as receptor surface for taste molecules taste pores - pit in which the taste hairs project taste hairs are epithelial cells not neurons synapse with and release neurotransmitters onto sensory neurons at their base basal cells stem cells that replace taste cells every 7 to 10 days two mechanisms of action 1. activate 2nd messenger systems sugars, alkaloids, and glutamate bind to receptors which activates G proteins and second-messenger systems within the cell 2. depolarize cells directly sodium and acids penetrate cells and depolarize it directly either mechanism results in release of neurotransmitters that stimulate dendrites at base of taste cells taste bud consists of a taste pour within the sulcus of the papillae on the tongue taste cells (basal cells replenish) trigger the synaptic vesicles of sensory nerve fibers -2 mechanisms of action 1. g-protein and second messenger system activated (glucose) 2. actually fire and stimulate a depolarization of the sensory nerves (salt, more acidic)

patellar tendon relfex arc

tendon reflex - in response to excessive tension on the tendon inhibits muscle from contracting strongly moderates muscle contraction before it tears a tendon or pulls it loose from the muscle or bone

vision and light

vision (sight) - perception of objects in environment by means of light they emit or reflect light - visible electromagnetic radiation human vision - 400 - 750 nm Light causes photochemical reaction to produce a nerve signal

Alzheimer Disease

•100,000 deaths/year -11% of population over 65; 47% by age 85 •memory loss recent events, moody, combative, lose ability to talk, walk, eat •deficiencies of acetylcholine (ACh) and nerve growth factor (NGF) •diagnosis confirmed at autopsy -atrophy of gyri (folds) in cerebral cortex •genetics implicated •treatment -Give NGF or cholinesterase inhibitors

Acetylcholine (Ach)

•ACh is secreted by all preganglionic neurons in sympathetic and parasympathetic divisions and postganglionic parasympathetic neurons -called cholinergic fibers -any receptor that binds it is called cholinergic receptor - •2 types of cholinergic receptors -muscarinic receptors •all cardiac muscle, smooth muscle, and gland cells have muscarinic receptors •excitatory or inhibitory due to subclasses of muscarinic receptors - nicotinic receptors •on all ANS postganglionic neurons, in the adrenal medulla, and at neuromuscular junctions of skeletal muscle excitatory when ACh binding occurs

Control of Autonomic Function

•ANS regulated by several levels of CNS -cerebral cortex has influence - anger, fear, anxiety •powerful emotions influence ANS because of connections between our limbic system and hypothalamus -hypothalamus - major visceral motor control center •nuclei for primitive functions - hunger, thirst, sex -midbrain, pons, and medulla oblongata contain: •nuclei for cardiac and vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary changes -spinal cord reflexes

PNS terminology

•Collection of cell bodies of neurons = ganglion (pl. ganglia) •Collection/bundle of axons (fibers) = nerve

CNS terminology

•Collection of cell bodies of neurons = nucleus •Collection/bundle of axons (fibers) = tract

Neurotransmitters and Receptors

•How can different autonomic neurons have different effects constricting some vessels but dilating others? - •2 fundamental reasons: • -sympathetic and parasympathetic fibers secrete different neurotransmitters - -target cells respond to same neurotransmitter differently depending upon type of receptor •all autonomic fibers secrete either acetylcholine or norepinephrine •there are 2 classes of receptors for each of these neurotransmitters

Noreprinephrine

•NE is secreted by nearly all sympathetic postganglionic neurons -called adrenergic fibers -receptors for it called adrenergic receptors - •alpha-adrenergic receptors -usually excitatory - •beta-adrenergic receptors -usually inhibitory

Parasympathetic- Cranial Nerve Examples

•Oculomotor nerve (III) -narrows pupil and focuses lens - •Facial nerve (VII) -tear, nasal and salivary glands - •Glossopharyngeal nerve (IX) -parotid salivary gland - •Vagus nerve (X) -viscera as far as proximal half of colon -cardiac, pulmonary, and esophageal plexus Oculomotor nerve (III). The oculomotor nerve carries parasympathetic fibers that control the lens and pupil of the eye. The preganglionic fibers enter the orbit and terminate in the ciliary ganglion behind the eyeball. Postganglionic fibers enter the eyeball and innervate the ciliary muscle, which thickens the lens, and the pupillary constrictor, which narrows the pupil. Facial nerve (VII). The facial nerve carries parasympathetic fibers that regulate the tear glands, salivary glands, and nasal glands. Soon after the facial nerve emerges from the pons, its parasympathetic fibers split away and form two smaller branches. The upper branch ends at the pterygopalatine ganglion near the junction of the maxilla and palatine bone. Postganglionic fibers then continue to the tear glands and glands of the nasal cavity, palate, and other areas of the oral cavity. The lower branch crosses the middle-ear cavity and ends at the submandibular ganglion near the angle of the mandible. Postganglionic fibers from here supply salivary glands in the floor of the mouth. Glossopharyngeal nerve (IX). The glossopharyngeal nerve carries parasympathetic fibers concerned with salivation. The preganglionic fibers leave this nerve soon after its origin and form the tympanic nerve. A continuation of this nerve crosses the middle-ear cavity and ends in the otic10 ganglion near the foramen ovale. The postganglionic fibers then follow the trigeminal nerve to the parotid salivary gland just in front of the earlobe. Vagus nerve (X). The vagus nerve carries about 90% of all parasympathetic preganglionic fibers. It travels down the neck and forms three networks in the mediastinum of the chest—the cardiac plexus, which supplies fibers to the heart; the pulmonary plexus, whose fibers accompany the bronchi and blood vessels into the lungs; and the esophageal plexus, whose fibers regulate swallowing. At the lower end of the esophagus, these plexuses give off anterior and posterior vagal trunks, each of which contains fibers from both the right and left vagus nerves. These trunks penetrate the diaphragm, enter the abdominal cavity, and contribute to the extensive abdominal aortic plexus mentioned earlier. As we have seen, sympathetic fibers synapse here. The parasympathetic fibers, however, pass through the plexus without synapsing. They synapse farther along, in terminal ganglia in or near the liver, pancreas, stomach, small intestine, kidney, ureter, and proximal half of the colon.

anatomy of nerve

•Spinal cord communicates with body by way of spinal nerves • •nerve - organ composed of numerous nerve fibers (axons) bound by connective tissue -thousands of fibers carrying currents in opposite directions - •PNS are ensheathed in Schwann cells -Neurilemma - thin sheath around a nerve axon -Endoneurium - thin sleeve of loose connective tissue -Fascicles - nerve fibers gathered in bundles -Perineurium - wraps fascicles •up to 20 layers of overlapping, squamous , epithelium-like cells -Epineurium - bundles numerous fascicles that constitutes whole nerve •dense irregular connective tissue •protects nerve from stretching and injury • •blood vessels penetrate connective tissue coverings -nerves have high metabolic rate and need plentiful blood supply

Dual Innervation etc.

•antagonistic effects - oppose each other 1.innervation of same effector cells •heart rate decreases (parasympathetic) •heart rate increases (sympathetic) OR • 2.innervation of different cells •pupillary dilator muscle (sympathetic) dilates pupil •constrictor pupillae (parasympathetic) constricts pupil • •cooperative effects - act on different effectors to produce a unified effect (example à eating) -Parasympathetics - increase salivary serous cell secretion -Sympathetics - increase salivary mucous cell secretion

General Properties of ANS

•autonomic nervous system (ANS) - a motor nervous system controls glands, cardiac muscle, and smooth muscle -also called visceral motor system -primary organs of ANS •viscera of thoracic and abdominal cavities •some structures of the body wall -cutaneous blood vessels -sweat glands -piloerector muscles -carries out actions involuntarily -visceral effectors do not depend on ANS to function •only to adjust their activity to body's changing needs The autonomic1 nervous system (ANS) can be defined as a motor nervous system that controls glands, cardiac muscle, and smooth muscle. It is also called the visceral motor system to distinguish it from the somatic motor system that controls the skeletal muscles. The primary target organs of the ANS are viscera of the thoracic and abdominopelvic cavities and some structures of the body wall, including cutaneous blood vessels, sweat glands, and piloerector muscles. The ANS usually carries out its actions involuntarily, without our conscious intent or awareness, in contrast to the voluntary nature of the somatic motor system. This voluntary-involuntary distinction is not, however, as clear-cut as it might seem. Some skeletal muscle responses are quite involuntary, such as the somatic reflexes, and some skeletal muscles are difficult or impossible to control, such as the middle-ear muscles. On the other hand, therapeutic uses of biofeedback have shown that some people can learn to voluntarily control such visceral functions as blood pressure. Visceral effectors do not depend on the autonomic nervous system to function, but only to adjust their activity to the body's changing needs. The heart, for example, goes on beating even if all autonomic nerves to it are severed, but the ANS modulates the heart rate in conditions of rest or exercise. If the somatic nerves to a skeletal muscle are severed, the muscle exhibits flaccid paralysis—it no longer functions. But if the autonomic nerves to cardiac or smooth muscle are severed, the muscle exhibits exaggerated responses (denervation hypersensitivity).

Brain Barrier System

•blood = source of antibodies, macrophages, bacterial toxins, and other harmful agents (environment, metabolic wastes) •brain barrier system - regulates substances from bloodstream into tissue fluid of brain, barrier against harmful substance, neurons are functionally essential to perceive and respond well in the environment •two points of entry must be guarded: -blood capillaries in brain tissue -capillaries of choroid plexus •BBB - protects blood capillaries throughout brain tissue •tight junctions between endothelial cells astrocytes •induce endothelial cells to form tight junctions (seal off gaps between them) •anything leaving blood must pass through cells - not between them •endothelial cells exclude harmful substances from passing to brain tissue while allowing necessary ones to pass

blood supply to brain

•brain receives 15% of blood -750 mL/min •neurons - high demand for ATP, therefore, oxygen and glucose -10 second interruption of blood flow may cause loss of consciousness -1 - 2 minute interruption can cause significant impairment of neural function -4 minutes without blood causes irreversible brain damage capillaries can be leaking b/c lymph, and filtration of kidney, plasma goes out, small substances can go out, big things like protein or red blood cells cannot ASTROCYTES, cover capillaries and entire surface of brain covered with feet, stimulate endothelial (simple squamous) cells of capillaries to have tight junction between them, which seals of gaps

Cross-sectional anatomy of spinal cord

•central area of gray matter shaped like a butterfly •surrounded by white matter in 3 columns •gray matter - neuron cell bodies with little myelin -site of information processing - synaptic integration •white matter - abundantly myelinated axons -carry signals from one part of the CNS to another

anatomy of spinal cord

•cervical, thoracic, lumbar, and sacral regions •cervical enlargement - nerves to upper limb •lumbar enlargement - nerves to pelvic region and lower limbs meduallary cone L1, transition to cauda equina

Spinal Cord

•conduction -bundles of fibers passing information up and down spinal cord -connect different levels of trunk with each other with brain - •locomotion -walking involves repetitive, coordinated actions of several muscle groups -pools of neurons provide control of flexors and extensors causing alternating movements of lower limbs - •reflexes -involuntary, stereotyped responses to stimuli •withdrawal of hand from pain -brain, spinal cord and peripheral nerves

ALS

•destruction of motor neurons and skeletal muscle atrophy from lack of innervation •amyotrophic lateral sclerosis (ALS) - Lou Gehrig disease -destruction of motor neurons and muscular atrophy -sclerosis (scarring) spinal cord -astrocytes fail to reabsorb glutamate from tissue fluid •accumulate to toxic levels -early signs - muscular weakness, difficulty speaking, swallowing, and use of hands -sensory and intellectual functions remain unaffected failure of astrocytes of absorbing glutamate

Dual Innervation

•dual innervation - most viscera receive nerve fibers from both parasympathetic and sympathetic divisions -antagonistic effect - oppose each other -cooperative effects - two divisions act on different effectors to produce a unified overall effect • •both divisions do not normally innervate an organ equally •Digestion à more innervation by parasympathetic •Heart rate à more innervation by the sympathetic Most of the viscera receive nerve fibers from both the sympathetic and parasympathetic divisions and thus are said to have dual innervation. In such cases, the two divisions may have either antagonistic or cooperative effects on the same organ. Antagonistic effects oppose each other. For example, the sympathetic division speeds up the heart and the parasympathetic division slows it down; the sympathetic division inhibits digestion and the parasympathetic division stimulates it; the sympathetic division dilates the pupil and the parasympathetic division constricts it. In some cases, these effects are exerted through dual innervation of the same effector cells, as in the heart, where nerve fibers of both divisions terminate on the same muscle cells. In other cases, antagonistic effects arise because each division innervates different effector cells with opposite effects on organ function. In the iris of the eye, for example, sympathetic fibers innervate the pupillary dilator and parasympathetic fibers innervate the constrictor Cooperative effects are seen when the two divisions act on different effectors to produce a unified overall effect. Salivation is a good example. The parasympathetic division stimulates serous cells of the salivary glands to secrete a watery, enzyme-rich secretion, while the sympathetic division stimulates mucous cells of the same glands to secrete mucus. The enzymes and mucus are both necessary components of the saliva. Even when both divisions innervate a single organ, they do not always innervate it equally or exert equal influence. For example, the parasympathetic division forms an extensive plexus in the wall of the digestive tract and exerts much more influence over it than the sympathetic division does. In the ventricles of the heart, by contrast, there is much less parasympathetic than sympathetic innervation.

universal properties of neurons

•excitability (irritability) -respond stimuli •conductivity -producing electrical signals •secretion -neurotransmitter is secreted that crosses the gap and stimulates next cell

Pathways for taste

•facial nerve à sensory information from taste buds over anterior two-thirds of tongue • •glossopharyngeal nerve à posterior one-third of tongue • •vagus nerve à taste buds of palate, pharynx and epiglottis • •fibers reach medulla oblongata • •signals to two destinations 1.hypothalamus and amygdala control autonomic reflexes - salivation, gagging and vomiting 2.thalamus relays signals to postcentral gyrus of cerebrum for conscious sense of taste •integrated with signals from nose and eyes - form impression of flavor and palatability of food

gliomas

•grow rapidly and highly malignant -blood-brain barrier decreases effectiveness of chemotherapy -treatment consists of radiation or surgery

hearing and equilibrium

•hearing - a response to vibrating air molecules • •equilibrium - sense of motion, body orientation, and balance loudness - the perception of sound energy, intensity, or amplitude of vibration expressed in decibels (dB) pitch - our sense of whether a sound is 'high' or 'low' determined by the frequency - cycles/sec for sounds to carry meaning, we must distinguish between loudness and pitch tectorial membrane hairs (stereocilia) -stimulated hairs open a K+ gate vestibular membrane surrounds cochlear duct that has endolymph within

tumors

•hyperplasia -mature neurons have little or no capacity for mitosis and seldom form tumors

Immediate Memory

•immediate memory - hold something in your thoughts for just a few seconds -essential for reading ability •feel for the flow of events (sense of the present) •our memory of what just happened "echoes" in our minds for a few seconds -reverberating circuits

Divisions of ANS

•innervate same target organs -may have cooperative or contrasting effects - sympathetic division -prepares body for physical activity - exercise, trauma, arousal, competition, anger, or fear •increases heart rate, BP, airflow, blood glucose levels, etc •reduces blood flow to the skin and digestive tract • parasympathetic division -calms many body functions reducing energy expenditure and assists in bodily maintenance •digestion and waste elimination •"resting and digesting" state The ANS has two subsystems: the sympathetic and parasympathetic divisions. These differ in anatomy and function, but they often innervate the same target organs and may have cooperative or contrasting effects on them. The sympathetic division adapts the body in many ways for physical activity—it increases alertness, heart rate, blood pressure, pulmonary airflow, blood glucose concentration, and blood flow to cardiac and skeletal muscle, but at the same time, it reduces blood flow to the skin and digestive tract. Cannon referred to extreme sympathetic responses as the "fight-or-flight" reaction because it comes into play when an animal must attack, defend itself, or flee from danger. In our own lives, this reaction occurs in many situations involving arousal, exercise, competition, stress, danger, trauma, anger, or fear. Ordinarily, however, the sympathetic division has more subtle effects that we notice barely, if at all. The parasympathetic division, by comparison, has a calming effect on many body functions. It is associated with reduced energy expenditure and normal bodily maintenance, including such functions as digestion and waste elimination. This can be thought of as the "resting- and-digesting" state.

Memory and Synaptic Plasticity

•physical basis of memory is a pathway through the brain called a memory trace or engram -synapses were created or existing synapses modified to make transmission easier -synaptic plasticity - ability of synapses to change - strengthen or weaken over time -Often number of receptors -synaptic potentiation - process of making transmission easier •lasting, increased excitability of synapse after high frequency stimulation •kinds of memory -immediate, short- and long-term memory •different modes of synaptic potentiation

nervous system

•receive information - transmits coded messages •brain and spinal cord processes this information - determine appropriate response to circumstances •brain and spinal cord issue commands to muscles and gland cells

Short-term or Working Memory

•short-term memory (STM) - few seconds to several hours -quickly forgotten if distracted -calling a phone number or someone's Snap -reverberating circuits - •facilitation causes memory to last longer -TETANIC STIMULATION - rapid arrival of repetitive signals at a synapse •causes Ca2+ accumulation and postsynaptic cell more likely to fire -releases more neurotransmitters to the synaptic cleft, therefore increasing action potential in postsynaptic cell -post-tetanic potentiation - to jog a memory •Ca2+ level in synaptic knob stay elevated •little stimulation needed to recover memory

Without Dual Innervation

•some effectors receive only sympathetic fibers -adrenal medulla, arrector pili muscles, sweat glands and many blood vessels - •control of blood pressure and routes of blood flow • •sympathetic vasomotor tone - a baseline firing frequency of sympathetics •keeps vessels in state of partial constriction •increase in firing frequency - vasoconstriction •decrease in firing frequency - vasodilation can shift blood flow from one organ to another as needed Dual innervation is not always necessary for the ANS to produce opposite effects on an organ. The adrenal medulla, piloerector muscles, sweat glands, and many blood vessels receive only sympathetic fibers. The most significant example of control without dual innervation is regulation of blood pressure and routes of blood flow. The sympathetic fibers to a blood vessel have a baseline sympathetic tone, which keeps the vessels in a state of partial constriction called vasomotor tone. An increase in firing rate constricts a vessel by increasing smooth muscle contraction. A drop in firing frequency dilates a vessel by allowing the smooth muscle to relax. The blood pressure in the vessel, pushing outward on its wall, then dilates the vessel. Thus, the sympathetic division alone exerts opposite effects on the vessels. Sympathetic control of vasomotor tone can shift blood flow from one organ to another according to the changing needs of the body. In times of emergency, stress, or exercise, the skeletal muscles and heart receive a high priority and the sympathetic division dilates the arteries that supply them. Processes such as digestion, nutrient absorption, and urine formation can wait; thus the sympathetic division constricts arteries to the gastrointestinal tract and kidneys. It also reduces blood flow through the skin, which may help to minimize bleeding in the event that the stress-producing situation leads to injury. Furthermore, since there is not enough blood in the body to supply all the organ systems equally, it is necessary to temporarily divert blood away from some organs in order to supply an adequate amount to the muscular system.

Spina Bifida

•spina bifida - congenital defect, one or more vertebrae fail to form a complete vertebral arch for enclosure of spinal cord -1 in a 1000 -common in lumbosacral region •folic acid (a B vitamin) as part of a healthy diet for all women of childbearing age reduces risk -first four weeks of development, so folic acid supplementation must begin 3 months before conception

the stretch reflex

•stretch (myotatic) reflex - stretched à 'fights back' à contracts maintaining tone à making muscle stiffer -maintain equilibrium and posture •head tips forward as you fall asleep •muscles contract to raise head -stabilize joints by balancing extensors and flexors - •stretch reflex mediated primarily by brain -not strictly a spinal reflex - •tendon reflex - reflexive contraction of a muscle when its tendon is tapped -knee-jerk (patellar) reflex is monosynaptic reflex •one synapse between afferent and efferent neurons -testing somatic reflexes helps diagnose many diseases

Long-term Memory

•types of long-term memory -declarative - retention of events that you can put into words -procedural - retention of motor skills •physical remodeling of synapses -new branching of axons or dendrites •molecular changes = long-term potentiation -changes in receptors (and other features) increases transmission across "experienced" synapses -effect is longer-lasting

white matter in spinal cord

•white matter surrounds gray matter •bundles of axons that course up and down cord -avenues of communication between different levels of CNS •Columns - three pair of these white matter bundles -posterior (dorsal), lateral, and anterior (ventral) columns on each side •tracts (fasciculi) - subdivisions of each column

what are the structures of a neuron?

*draw from memory*

vestibulospinal tract

-begins in brainstem vestibular nuclei -receives impulses for balance from inner ear - vestibulocochlear nerve -controls extensor muscles of limbs for balance control *inner ear*

reticulospinal tract

-controls muscles of upper and lower limbs •especially those for posture and balance *cerebellum (motor info)*

extrinsic eyes muscles

6 muscles innervated by cranial nerves III oculomotor, IV trochlear, and VI abducens 6 muscles inserting on external surface of eyeball 4 rectus muscles move eye up, down, left & right superior & inferior oblique more complicated Innervated by cranial nerves III, IV and VI

histology- layers of retina

8 layers

olfactory projection pathways

•olfactory cells synapse in olfactory bulb • •axons form olfactory tracts -primary olfactory cortex in temporal lobe -secondary destinations - hippocampus, amygdala, hypothalamus, insula, and orbitofrontal cortex •identify odors, integrate smell with taste, perceive flavor, evoke memories and emotional responses, and visceral reactions bypass thalamus which is usually the main information processor and director of signals ***axons form olfactory tracts primary olfactory cortex in temporal lobe secondary destinations - hippocampus, amygdala, hypothalamus, insula, and orbitofrontal cortex identify odors, integrate smell with taste, perceive flavor, evoke memories and emotional responses, and visceral reactions