NCM 116A: Perception and Coordination Lecture 1 PDF

NCM 116A: PERCEPTION AND COORDINATION LECTURE 1: INTRO TO NEUROLOGIC SYSTEM l 2nd Semester l SY: 2024-2025 GANGLIA OR NUCLEI - Nerve cell bodies A ANATOMIC AND PHYSIOLOGIC OVERVIEW occurring in cluster...

NCM 116A: PERCEPTION AND COORDINATION LECTURE 1: INTRO TO NEUROLOGIC SYSTEM l 2nd Semester l SY: 2024-2025 GANGLIA OR NUCLEI - Nerve cell bodies A ANATOMIC AND PHYSIOLOGIC OVERVIEW occurring in cluster CENTER - cluster of cell bodies with the same function (respi fxn) TWO MAJOR PARTS OF NERVOUS SYSTEM 1. Central Nervous System (CNS) NEUROTRANSMITTERS a. Consist of: communicate messages from one neuron ✓ Brain to another or from a neuron to a target cell, ✓ Spinal cord such as muscle or endocrine cells. 2. Peripheral Nervous System (PNS) manufactured and stored in synaptic b. Includes: vesicles. ✓ Cranial nerves released into the synapse when electrical ✓ Spinal nerves action potential moves along the axon and ✓ Autonomic nervous system reaches the nerve terminal. transported across the synapse, binding to FUNCTIONS OF NERVOUS SYSTEM receptors on the postsynaptic cell membrane. Control motor, sensory, autonomic, can either excite or inhibit activity of the cognitive, and behavioral activities. target cell. multiple neurotransmitters work in the neural BRAIN synapse. has > 100 billion cells Many neurologic disorders are due, at least link the motor and sensory pathways in part, to an imbalance in neurotransmitters. monitor the body’s processes ▪ Parkinson’s disease - decreased respond to internal and external environment dopamine maintain homeostasis ▪ myasthenia gravis - impaired direct all psychological, biologic, and acetylcholine binding to muscle cells physical activity through complex chemical Brain functions are modulated through and electrical messages. neurotransmitter receptor site activity, including memory and other cognitive processes B CELLS OF THE NERVOUS SYSTEM SOURCE AND ACTION OF MAJOR NEUROTRANSMITTERS NEURONS basic functional unit of the brain supported, protected, and nourished by glial cells, which are 50 times greater in number than neurons COMPOSED OF: ✓ DENDRITES - branch-type structures for receiving electrochemical messages. ✓ AXON - long projection that carries electrical impulses away from the cell body. with myelinated sheath - increases speed of conduction. BSN 3B l D.E.R Once released, enzymes either destroy the CEREBRAL HEMISPHERES neurotransmitter or reabsorb it into the neuron for In between the cerebral hemispheres is the future use. great longitudinal fissure - separates the cerebrum into the right and left To detect they use hemispheres ✓ PET – dopa, acetyl, serotonin ▪ The two hemispheres are joined at the ✓ Single-photon emission computed lower portion of the fissure by the corpus tomography – dopa (PD) callosum. ▪ The external or outer portion of the C CENTRAL NERVOUS SYSTEM hemispheres (the cerebral cortex) is made up of gray matter consists of the brain and the spinal cord. ❖ Depth: 2 to 5 mm ❖ with billions of neuron cell bodies, giving it a gray appearance. White matter - innermost layer and is composed of myelinated nerve fibers and neuroglia cells that form tracts or pathways connecting various parts of the brain with one another. ▪ These pathways also connect the cortex with lower portions of the brain and spinal cord. LOBES IN CEREBRAL HEMISPHERES I. THE BRAIN the largest lobe, located in 2% of the total-body weight the front of the brain. 1400 g - young adult FUNCTIONS: concentration, 1200 g - older adult abstract thought, information storage or memory, and THREE MAJOR AREAS OF THE BRAIN motor function. FRONTAL 1. CEREBRUM - composed of Contains Broca area, in the ✓ two hemispheres left hemisphere and motor the thalamus control of speech. the hypothalamus Responsible for a person’s ✓ the basal ganglia. affect, judgment, personality, 2. BRAIN STEM - includes the and inhibitions. ✓ Midbrain sensory lobe posterior to the frontal lobe. ✓ Pons analyzes sensory information ✓ Medulla and relays the interpretation 3. CEREBELLUM - located under the cerebrum to other cortical areas and behind the brain stem PARIETAL essential to person’s awareness of body position in 1. CEREBRUM space, size and shape outside surface of the hemispheres discrimination, and right–left has wrinkled appearance due to many orientation. folded layers or convolutions called gyri ▪ GYRI - increase the surface area of located inferior to the frontal the brain, accounting for the high level and parietal lobes of activity carried out by such a small- contains the auditory appearing organ. TEMPORAL receptive areas ▪ SULCUS OR FISSURE - anatomic plays a role in memory of division between each gyrus. sound and understanding of language and music.  located posterior to the ▪ Works with pituitary - maintain fluid OCCIPITAL parietal lobe balance through hormonal release and responsible for visual maintains temperature regulation by interpretation and memory. promoting vasoconstriction or vasodilatation. Site of the hunger center and is involved in appetite control. contains centers that regulate the sleep– wake cycle, blood pressure, aggressive and sexual behavior, and emotional responses (e.g., blushing, rage, depression, panic, fear). controls and regulates the autonomic nervous system. ▪ The OPTIC CHIASM (the point at which the two optic tracts cross) and the MAMMILLARY BODIES (involved in olfactory reflexes and emotional CORPUS CALLOSUM response to odors) are also found in this Thick collection of nerve fibers connecting area. the two hemispheres of the brain BASAL GANGLIA - masses of nuclei Transmit information from one side of the located deep in the cerebral hemispheres brain to the other. responsible for control of fine motor ▪ Information transferred includes movements, including those of the sensation, memory, and learned hands and lower extremities. discrimination. Right-handed people and some left-handed 2. BRAIN STEM people have cerebral dominance on the consists of the midbrain, pons, and medulla left side of the brain for verbal, linguistic, oblongata arithmetic, calculation, and analytic functions. MIDBRAIN ▪ The nondominant hemisphere is responsible for geometric, spatial, connects the pons and the cerebellum visual, pattern, and musical functions. with the cerebral hemispheres Contains sensory and motor pathways Nuclei for cranial nerves I and II are also located in the cerebrum. Center for auditory and visual reflexes. Cranial nerves III and IV originate in the midbrain. THALAMI LOCATION: lie on either side of the third ventricle PONS act as a relay station for all sensation situated in front of the cerebellum between except smell. the midbrain All memory, sensation, and pain impulses contains motor and sensory pathways. pass through thalami. Portions of the pons help regulate respiration. HYPOTHALAMUS Cranial nerves V through VIII originate LOCATION: anterior and inferior to the in the pons. thalamus, and beneath and lateral to the third ventricle. MEDULLA ▪ infundibulum of the hypothalamus bridge between the two halves of the connects it to the posterior pituitary cerebellum, and between the medulla and gland. the midbrain. Role in the endocrine system: Regulates Motor fibers - from the brain to the SC the pituitary secretion of hormones that Sensory fibers - from the SC to the brain influence metabolism, reproduction, stress Most of these fibers cross, or decussate, at response, and urine production. this level.  Cranial nerves IX through XII originate in MIDDLE FOSSA contains the temporal the medulla. lobe Reflex centers for respiration, blood POSTERIOR FOSSA contains the pressure, heart rate, coughing, vomiting, cerebellum and brain swallowing, and sneezing are also located stem in the medulla. The reticular formation, responsible for MENINGES arousal and the sleep–wake cycle, begins in Fibrous connective tissues that cover the the medulla and connects with numerous brain and spinal cord higher structures. Provide protection, support, and nourishment. 3. CEREBELLUM posterior to the midbrain and pons, and below the occipital lobe. integrates sensory information to provide smooth coordinated movement. controls fine movement, balance, and position (postural) sense or proprioception (awareness of position of extremities without looking at them). D STRUCTURES PROTECTING BRAIN LAYERS OF THE MENINGES 1. Dura Mater 2. Arachnoid 3. Pia Mater 1. DURA MATER outermost layer covers the brain and the spinal cord BRAIN tough, thick, inelastic, fibrous, and gray contained in the rigid skull, which protects it from injury. THREE MAJOR EXTENSIONS OF THE DURA i. FALX CEREBRI - folds between the two MAJOR BONES OF THE SKULL hemispheres 1. Frontal ii. TENTORIUM - folds between the occipital 2. Temporal lobe and cerebellum to form a tough, 3. Parietal membranous shelf 4. Occipital iii. FALX CEREBELLI - located between the 5. Sphenoid right and left side of the cerebellum These bones join at the suture lines and form When excess pressure occurs in the cranial cavity, brain tissue may be compressed against the base of the skull. these dural folds or displaced around them, a process called HERNIATION. FOSSAE Indentations in the skull base EPIDURAL SPACE space between the dura and the skull, and ANTERIOR FOSSA contains the frontal between the periosteum and the dura in the lobe vertebral column SUBDURAL SPACE FOUR VENTRICLES exists below the dura i. Right and left lateral Blood or an abscess can accumulate in open into the third ventricle at the these potential spaces. interventricular foramen (also known as the foramen of Monro). 2. ARACHNOID ii. Third and fourth ventricles middle membrane connect via the aqueduct of Sylvius. extremely thin, delicate membrane that The fourth ventricle closely resembles a spider web (name ▪ drains CSF into the subarachnoid arachnoid). space on the surface of the brain w/ CSF in the space below it, known as the and spinal cord, where it is SUBARACHNOID SPACE. absorbed by the arachnoid villi. w/ arachnoid villi - finger-like projections that absorb CSF into the Blockage of the flow of CSF in the ventricular venous system. system produces obstructive hydrocephalus. When blood or bacteria enter the subarachnoid space, the villi become obstructed and F CEREBRAL CIRCULATION communicating hydrocephalus (increased size of ventricles) may result. 3. PIA MATER Innermost thin, transparent layer that hugs the brain closely and extends into every fold of the brain’s surface. E CEREBROSPINAL FLUID Clear and colorless fluid Produced in the choroid plexus of the ventricles and circulates around the surface of the brain and the spinal cord important in immune and metabolic Brain does not store nutrients and requires a functions in the brain. constant supply of oxygen. produced at a rate of about 500 mL/day These needs are met through cerebral the ventricles and subarachnoid space circulation contain approximately 125 to 150 mL of The brain receives approximately 15% of the fluid cardiac output, or 750 mL per minute of The composition of CSF is similar to other blood flow. extracellular fluids (such as blood plasma), but the concentrations of the BRAIN CIRCULATION IS UNIQUE IN SEVERAL various constituents differ. ASPECTS ▪ A laboratory analysis of CSF indicates 1. Arterial and venous vessels are not parallel o color (clear) as in other organs in the body due in part to o specific gravity (normal 1.007) the role the venous system plays in CSF absorption. o protein count 2. Brain has collateral circulation through the o cell count circle of Willis, allowing blood flow to be o glucose redirected on demand. o electrolyte levels 3. Blood vessels in the brain have two rather Normal CSF contains a minimal number of than three layers, which may make them white blood cells and no red blood cells. more prone to rupture when weakened or Tested for immunoglobulins or the presence under pressure. of bacteria. ▪ A CSF sample obtained through a lumbar puncture or intraventricular catheter  ARTERIES This barrier is formed by the endothelial Arterial blood supply to the anterior brain cells of the brain’s capillaries, which form originates from the common carotid artery continuous tight junctions, creating a barrier - the first bifurcation of the aorta. to macromolecules and many compounds. ▪ internal carotid arteries arise at the ▪ All substances entering the CSF must bifurcation of the common carotid. filter through the capillary endothelial cells and astrocytes. Branches of the internal carotid arteries The blood–brain barrier has a protective (the anterior and middle cerebral arteries) function but can be altered by trauma, and their connections (the anterior and posterior communicating arteries) form the cerebral edema, and cerebral hypoxemia. circle of Willis The vertebral arteries branch from the H THE SPINAL CORD subclavian arteries to supply most of the posterior circulation of the brain. At the level of the brain stem, the vertebral arteries join to form the basilar artery - divides to form the two branches of the posterior cerebral arteries. ▪ Functionally, the posterior and anterior portions of the circulation usually remain separate. ▪ However, the circle of Willis can provide collateral circulation through communicating arteries if one of the vessels supplying it becomes occluded continuous with the medulla, extending or is ligated. from the cerebral hemispheres and serving as the connection between the brain and The bifurcations along the circle of the periphery. Willis are frequent sites of aneurysm formation. Approximately 45 cm (18 inches) long and about the thickness of a finger, ▪ Aneurysms - outpouchings of the blood vessel due to vessel wall ▪ extends from the foramen magnum at the weakness. base of the skull to the lower border of the first lumbar vertebra, where it tapers can rupture and cause a hemorrhagic to a fibrous band called the conus stroke. medullaris. Continuing below the second lumbar VEINS space are the nerve roots that extend Venous drainage for the brain does not follow the beyond the conus, which are called the arterial circulation as in other body structures. CAUDA EQUINA as they resemble a The veins reach the brain’s surface, join horse’s tail. larger veins, and then cross the ▪ Meninges surround the spinal cord. subarachnoid space and empty into the In a cross-sectional view, the spinal cord has dural sinuses, which are the vascular an H-shaped central core of nerve cell channels embedded in the dura bodies (gray matter) surrounded by The network of the sinuses carries venous ascending and descending tracts (white outflow from the brain and empties into the matter) internal jugular veins, returning the blood to ▪ The lower portion of the H is broader the heart. than the upper portion and corresponds Cerebral veins are unique as they do not to the anterior horns. have valves to prevent blood from flowing ▪ The anterior horns contain cells with backward and depend on both gravity and fibers that form the anterior (motor) blood pressure for flow. root and for voluntary and reflex activity of the muscles they innervate. G BLOOD–BRAIN BARRIER ▪ The thinner posterior (upper horns) has cells with fibers that enter over the The CNS is inaccessible to many substances posterior (sensory) root and thus serve that circulate in the blood plasma (e.g., dyes, as a relay station in the sensory/reflex medications, antibiotic agents) pathway.  The thoracic region of the spinal cord has a 3 VESTIBULOSPINAL TRACTS projection from each side at the crossbar of ▪ descend uncrossed the H-shaped structure of gray matter called ▪ Involved in some autonomic functions the lateral horn. (sweating, pupil dilation, and circulation) ▪ w/ cells that give rise to the autonomic and involuntary muscle control. fibers of the sympathetic division. CORTICOBULBAR TRACT ▪ The fibers leave the spinal cord through ▪ conducts impulses the anterior roots in the thoracic and ▪ responsible for voluntary head and upper lumbar segments. facial muscle movement ▪ crosses at the level of the brain stem THE SPINAL TRACTS RUBROSPINAL AND RETICULOSPINAL The white matter of the spinal cord is TRACTS composed of myelinated and ▪ conduct impulses involved with unmyelinated nerve fibers. involuntary muscle movement ▪ The fast-conducting myelinated fibers form bundles VERTEBRAL COLUMN ▪ fiber bundles with a common function The bones of the vertebral column surround and are called tracts. protect the spinal cord and consist of ✓ 7 cervical SIX ASCENDING TRACTS ✓ 12 thoracic Two tracts, known as the FASCICULUS ✓ 5 lumbar vertebrae CUNEATUS and GRACILIS OR THE ✓ sacrum (a fused mass of 5 vertebrae) POSTERIOR COLUMNS ✓ coccyx. ▪ conduct sensations of deep touch, pressure, vibration, position, and passive motion from the same side of Nerve roots exit from the vertebral column through the body. the intervertebral foramina (openings) ▪ Before reaching the cerebral cortex, The vertebrae are separated by discs, these fibers cross to the opposite side except for the first and second cervical, in the medulla. the sacral, and the coccygeal vertebrae. The ANTERIOR AND POSTERIOR ▪ has a ventral solid body and a dorsal SPINOCEREBELLAR TRACTS segment or arch, which is posterior to ▪ conduct sensory impulses from the body. muscle spindles, providing necessary ▪ The arch is composed of two pedicles input for coordinated muscle and two laminae supporting seven contraction. processes. ▪ They ascend uncrossed and terminate The vertebral body, arch, pedicles, and in the cerebellum. laminae all encase and protect the spinal cord. The ANTERIOR AND LATERAL SPINOTHALAMIC TRACTS ▪ conduction of pain, temperature, I THE PERIPHERAL NERVOUS SYSTEM proprioception, fine touch, and Includes: vibratory sense from the upper body to ✓ Cranial nerves the brain. ✓ Spinal nerves ▪ They cross to the opposite side of the ✓ Autonomic nervous system cord and then ascend to the brain, terminating in the thalamus I. CRANIAL NERVES EIGHT DESCENDING TRACTS ANTERIOR AND LATERAL CORTICOSPINAL TRACTS ▪ conduct motor impulses to the anterior horn cells from the opposite side of the brain ▪ cross in the medulla ▪ control voluntary muscle activity  Twelve pairs of cranial nerves emerge from SPINAL NERVE the lower surface of the brain and pass through openings in the base of the skull. ▪ 3 CN are sensory (I, II, VIII) ▪ 5 CN are motor (III, IV, VI, XI, and XII) ▪ 4 CN are mixed sensory and motor (V, VII, IX, and X) The CN innervate the head, neck, and special sense structures. The spinal cord is composed of 31 pairs of spinal nerves ✓ 8 cervical ✓ 12 thoracic ✓ 5 lumbar ✓ 5 sacral ✓ 1 coccygeal Each spinal nerve has a ventral root and a dorsal root. ▪ The dorsal roots - sensory and transmit sensory impulses from specific areas of the body known as dermatomes to the dorsal horn ganglia. The sensory fiber may be ▪ Somatic - carrying information about pain, temperature, touch, and position sense (proprioception) from the tendons, joints, and body surfaces ▪ Visceral - carrying information from the internal organs. ▪ The ventral roots - motor and transmit impulses from the SC to the body these fibers are also either somatic or visceral. ▪ Visceral fibers include autonomic fibers that control the cardiac muscles and glandular secretions.  J AUTONOMIC NERVOUS SYSTEM ▪ control of metabolic processes, including fat, carbohydrate, and water metabolism ▪ regulation of body temperature, arterial pressure, and all muscular and glandular activities of the gastrointestinal tract ▪ control of genital functions ▪ sleep cycle The autonomic nervous system is separated into the anatomically and functionally distinct sympathetic and parasympathetic divisions. Most of the tissues and the organs under autonomic control are innervated by both systems. ▪ Parasympathetic division causes contraction (stimulation) of the urinary bladder muscles and a decrease (inhibition) in heart rate ▪ Sympathetic division produces relaxation (inhibition) of the urinary bladder and an increase (stimulation) in Regulates the activities of internal organs the rate and force of the heartbeat. such as the heart, lungs, blood vessels, digestive organs, and glands Maintenance and restoration of internal homeostasis Innervates most body organs ▪ Although usually considered part of the peripheral nervous system, this system is regulated by centers in the spinal cord, brain stem, and hypothalamus. TWO MAJOR DIVISIONS A. Sympathetic nervous system ▪ excitatory responses (i.e., the “fight-or- flight” response) B. Parasympathetic nervous system ▪ controls mostly visceral functions ▪ rest or digest response HYPOTHALAMUS major subcortical center for the regulation of autonomic activities, serving an inhibitory–excitatory role. has connections that link the autonomic system with the thalamus, the cortex, the olfactory apparatus, and the pituitary gland. Located are the mechanisms ▪ control of visceral and somatic reactions for defense or attack and are associated with emotional states (e.g., fear, anger, anxiety)  SYMPATHETIC NERVOUS SYSTEM head and neck, thorax, abdomen, and best known for body’s fight-or-flight pelvis, respectively, having been joined response. in these plexuses by fibers from the ▪ Under stress from either physical or parasympathetic division. emotional causes, sympathetic The adrenal glands, kidneys, liver, spleen, impulses increase greatly. stomach, and duodenum are under the control of the giant celiac plexus, commonly ▪ tbronchioles dilate for easier gas known as the solar plexus. exchange ▪ Receives sympathetic nerve ▪ heart’s contractions are stronger and components in 3 splanchnic nerves, faster composed of preganglionic fibers ▪ arteries to the heart and voluntary from nine segments of the spinal cord muscles dilate, carrying more blood to (T4 to L1), and is joined by the vagus these organs nerve, representing the parasympathetic ▪ peripheral blood vessels constrict, division. skin cool but shunting blood to essential From the celiac plexus, fibers of both organs divisions travel along the course of blood ▪ pupils dilate vessels to their target organs. ▪ liver releases glucose for quick energy ▪ For example, sympathetic storm is a ▪ peristalsis slows syndrome associated with changes in ▪ hair stands on end level of consciousness, altered vital ▪ perspiration increases signs, diaphoresis, and agitation that Norepinephrine (noradrenaline) - main may result from hypothalamic stimulation sympathetic neurotransmitter of the sympathetic nervous system Epinephrine (adrenalin) — A sympathetic following traumatic brain injury discharge releases ▪ the term adrenergic is often used to refer PARASYMPATHETIC NERVOUS SYSTEM to this division. Controller for most visceral functions Acetylcholine - the primary SYMPATHETIC NEURONS neurotransmitter located primarily in the thoracic and lumbar segments of the SC During quiet, nonstressful conditions, impulses Axons/preganglionic fibers from parasympathetic fibers (cholinergic) ○ in anterior nerve roots from the eighth predominate. cervical or first thoracic segment to the second or third lumbar segment. THE FIBERS OF THE PARASYMPATHETIC A short distance from the cord, these fibers SYSTEM ARE LOCATED IN TWO SECTIONS: diverge to join a chain, composed of 22 Brain stem linked ganglia, that extends the entire Spinal segments below L2. length of the spinal column, adjacent to the vertebral bodies on both sides. Some form Because of the location of these fibers, the multiple synapses with nerve cells within the parasympathetic system is referred to as the chain. craniosacral division, as distinct from the ▪ Others traverse the chain without making thoracolumbar (sympathetic) division of the connections or losing continuity to join autonomic nervous system. large “prevertebral” ganglia - thorax, abdomen, or pelvis or one of the The parasympathetic nerves arise from the “terminal” ganglia - bladder or the midbrain and the medulla oblongata. rectum at the end of the colon ▪ Fibers from cells in the midbrain Postganglionic nerve fibers originating in the sympathetic chain rejoin the spinal ▪ travel with the 3RD oculomotor nerve to nerves that supply the extremities and are the ciliary ganglia, where distributed to blood vessels, sweat glands, postganglionic fibers are joined by and smooth muscle tissue in the skin. sympathetic system, creating controlled opposition, with a delicate balance ▪ Postganglionic fibers from the always maintained between the two prevertebral plexuses (e.g., the systems. cardiac, pulmonary, splanchnic, pelvic plexuses) supply structures in the  K MOTOR AND SENSORY PATHWAYS OF THE the spinal cord serve as protective NERVOUS SYSTEM mechanisms. ○ These connections are seen during deep MOTOR PATHWAYS tendon reflex testing. responsible for voluntary, involuntary, and coordination of movement. L UPPER AND LOWER MOTOR NEURONS SENSORY PATHWAYS 2 GROUPS OF NEURONS OF VOLUNTARY receive, integrate, and transmit variety of MOTOR SYSTEM sensations within the CNS. Upper motor neurons Lower motor neurons. MOTOR PATHWAYS UPPER MOTOR NEURONS The corticospinal tract begins in the motor cortex, a vertical band within each frontal Originate in the cerebral cortex, the lobe, and controls voluntary movements of cerebellum, and the brain stem. the body. o Their fibers make up the descending ▪ To initiate movement, these particular motor pathways, are located entirely cells must send the stimulus along within the CNS, and modulate the their fibers. activity of the lower motor neurons. ▪ Stimulation of these cells with an electric The motor pathways from the brain to the current also results in muscle spinal cord, as well as from the cerebrum to contraction. the brain stem, are formed by upper motor neurons. En route to the pons, the motor fibers converge into a tight bundle known as the ▪ They begin in the cortex of one side of internal capsule. the brain, descend through the internal capsule, cross to the opposite side in the ▪ small injury to the internal capsule brain stem, descend through the results in a more severe paralysis than corticospinal tract, and synapse with the does a larger injury to the cortex itself. lower motor neurons in the cord. At the medulla, the corticospinal tracts cross to the opposite side, continuing to the anterior horn of the spinal cord, in LOWER MOTOR NEURONS proximity to a motor nerve cell. located either in the anterior horn of the ▪ Until this point, neurons are known as spinal cord gray matter or within cranial upper motor neurons. nerve nuclei in the brain stem. ▪ As they connect to motor fibers of the Axons of lower motor neurons in both spinal nerves, they become lower motor sites extend through peripheral nerves neurons. and terminate in skeletal muscle. receive the impulse in the located in both the CNS and the posterior part of the cord and run to peripheral nervous system. the myoneural junction located in The lower motor neurons receive the the peripheral muscle. impulse in the posterior part of the cord Involuntary motor activity is also possible and run to the myoneural junction located and is mediated through reflex arcs. in the peripheral muscle. Synaptic connections between anterior horn cells and sensory fibers that have entered adjacent or neighboring segments of UPPER MOTOR NEURON LESIONS connected to that section of the spinal cord Involve the motor cortex, the internal may be regained. capsule, the spinal cord gray matter, and ▪ However, if the anterior horn motor cells other structures of the brain through which are destroyed, the nerves cannot the corticospinal tract descends. regenerate, and the muscles are never If the upper motor neurons are damaged or useful again. destroyed, as frequently occur with stroke Flaccid paralysis and atrophy of the or spinal cord injury, paralysis (loss of affected muscles are the principal signs of voluntary movement) results. lower motor neuron disease. ▪ due the inhibitory influences of intact Lower motor neuron lesions can be the upper motor neurons are impaired, result of trauma, infection (poliomyelitis), reflex (involuntary) movements are toxins, vascular disorders, congenital uninhibited, and hence hyperactive malformations, degenerative processes, deep tendon reflexes, diminished or and neoplasms. absent superficial reflexes, and Compression of nerve roots by herniated pathologic reflexes such as a intervertebral discs is a common cause of Babinski response occur. lower motor neuron dysfunction. ▪ Severe leg spasms can occur due to upper motor neuron lesion COORDINATION OF MOVEMENT the spasms result from the The motor system is complex, and motor preserved reflex arc, which lacks function depends not only on the integrity of inhibition along the spinal cord the corticospinal tracts but also on other below the level of injury. pathways from the basal ganglia and There is little or no muscle atrophy, cerebellum that control and coordinate and muscles remain permanently voluntary motor function. tense, exhibiting spastic ▪ The smoothness, accuracy, and paralysis. strength that characterize the muscular ▪ Paralysis associated with upper motor movements of a normal person are neuron lesions can affect a whole attributable to the influence of the extremity, both extremities, or an entire cerebellum and the basal ganglia. half of the body. Through the action of the cerebellum, the Hemiplegia (paralysis of an arm and contractions of opposing muscle groups are leg on the same side of the body) adjusted in relation to each other to maximal can be the result of an upper motor mechanical advantage; neuron lesion. ▪ muscle contractions is sustained at the ▪ If hemorrhage, an embolus, or a desired tension and without significant thrombus destroys the fibers from the fluctuation, and reciprocal movements motor area in the internal capsule, the can be reproduced at high and constant arm and the leg of the opposite side speed, in stereotyped fashion and with become stiff, weak, or paralyzed, and relatively little effort. the reflexes are hyperactive. The basal ganglia - planning and ▪ If both legs are paralyzed, the condition coordinating motor movements and posture. is called paraplegia. ▪ Complex neural connections link the ▪ If all four extremities are paralyzed, the basal ganglia with the cerebral cortex. condition is called tetraplegia ▪ The major effect of these structures is to (quadriplegia). inhibit unwanted muscular activity. Impaired cerebellar function, which may LOWER MOTOR NEURON LESIONS occur as a result of an intracranial injury or some type of an expanding mass (e.g., a If have lower motor neuron damage if a motor hemorrhage, an abscess, or a tumor), nerve is damaged between the spinal cord results in loss of muscle tone, weakness, and muscle. and fatigue. The result of lower motor neuron damage is Depending on the area of the brain affected, muscle paralysis. the patient has different motor symptoms Reflexes are lost, and the muscle becomes or responses. flaccid (limp) and atrophied from disuse. ▪ abnormal flexion, abnormal If the patient has injured the spinal trunk extension, or flaccid posturing. and it can heal, the use of muscles  ▪ Flaccidity (lack of muscle tone) In the medulla, synaptic connections are preceded by abnormal posturing in a made with cells of the secondary neurons, patient with cerebral injury indicates whose axons cross to the opposite side and severe neurologic impairment, which then proceed to the thalamus. may herald brain death Destruction or dysfunction of the basal INTEGRATING SENSORY IMPULSES ganglia leads not to paralysis but to muscle Thalamus - integrates all sensory impulses rigidity, disturbances of posture, and difficulty except olfaction. initiating or changing movement. ▪ role in the conscious awareness of pain ▪ involuntary movements and the recognition of variation in ▪ tremors in the upper extremities, temperature and touch. particularly in the distal portions ▪ sense of movement and position and ▪ athetosis - movement of a slow, recognize the size, shape, and quality squirming, writhing, twisting type of objects. ▪ chorea - marked by spasmodic, Sensory information is relayed from the purposeless, irregular, uncoordinated thalamus to the parietal lobe for motions of the trunk and the extremities, interpretation. and facial grimacing. SENSORY LOSSES SENSORY SYSTEM FUNCTION Lesions affecting the posterior spinal nerve roots RECEIVING SENSORY IMPULSES ▪ Impair tactile sensation, causing Afferent impulses intermittent severe pain ▪ travel from points of origin to their ▪ Destruction of the spinal cord yields destinations in the cerebral cortex via the complete anesthesia below the level of ascending pathways directly injury. ▪ cross at the level of the SC or in the Selective destruction or degeneration of medulla, depending on the type of the posterior columns of the spinal cord sensation carried. ▪ Loss of position and vibratory sense Sensory impulses in segments distal to the lesion, without ○ convey sensations of heat, cold, and loss of touch, pain, or temperature pain; position; and vibration. perception. Axons Cyst in the center of the spinal cord ○ enter the spinal cord by way of the ▪ causes dissociation of sensation— posterior root, specifically in the loss of pain at the level of the lesion. posterior gray columns of the spinal cord, ▪ dt the fibers carrying pain and where they connect with the cells of temperature cross within the cord secondary neurons. immediately on entering; thus, any lesion Pain and temperature fibers (located in the that divides the cord longitudinally spinothalamic tract) divides these fibers. ○ cross immediately to the opposite side of lesions in the thalamus or parietal lobe the cord and course upward to the ▪ impaired touch, pain, temperature, and thalamus. proprioceptive sensations. Fibers carrying sensations of touch, light pressure, and localization do not connect immediately with the second neuron but ascend the cord for a variable distance before entering the gray matter and completing this connection. The axon of the secondary neuron traverses the cord, crosses in the medulla, and proceeds upward to the thalamus. Position and vibratory sensations are produced by stimuli arising from muscles, joints, and bones. These stimuli are conveyed, uncrossed, all the way to the brain stem by the axon of the primary neuron.