Organization of the Nervous System PDF

07/04/1446 ORGANIZATION OF THE NERVOUS SYSTEM As a control system: The nervous system (NS) is the higher most body control system. It shares the control function with the endocrine system, but it controls the endocrine syst...

07/04/1446 ORGANIZATION OF THE NERVOUS SYSTEM As a control system: The nervous system (NS) is the higher most body control system. It shares the control function with the endocrine system, but it controls the endocrine system itself. Its functional unit is the neuron which functions in integration and transmission The nervous system is composed of two divisions: Central nervous system (CNS), which includes the brain and the spinal cord, Peripheral nervous system (PNS), which includes sensory receptors, sensory nerves, and ganglia outside the CNS. The CNS and PNS communicate extensively with each other. 1 07/04/1446 The sensory or afferent division brings information into the nervous system, usually beginning with events in sensory receptors in the periphery. These receptors include, visual receptors, auditory receptors, chemoreceptors, and somatosensory (touch) receptors. This afferent information is then transmitted to higher levels of the nervous system and finally to the cerebral cortex. The motor or efferent division carries information out of the nervous system to the periphery. This efferent information results in contraction of skeletal muscle, smooth muscle, and cardiac muscle or secretion by endocrine and exocrine glands. 2 07/04/1446 Afferent pathway Efferent pathway Nervous system Anatomical Functional classification classification Central Somatic Sensory Nervous Brain Nervous Integrative System System (CNS) Spinal (voluntary) Motor Cord Spinal Autonomic Peripheral Sympathetic Nerves Nervous Nervous System System Cranial Para- (ANS) (PNS) Nerves (Involuntary) sympathetic 3 07/04/1446 The CNS includes the brain and spinal cord. The major divisions of the CNS are: 1-Cerebral hemispheres 2-Diencephalon (thalamus and hypothalamus) 3-Brain stem (medulla, pons, and midbrain) 4-Cerebellum 5-The spinal cord 4 07/04/1446 Brain Cerebral cerebellum Brain Stem Others Cortex Midbrain Thalamus Pons Hypo- thalamus Medulla Oblongat Basal a Ganglia 5 07/04/1446 Cerebral Hemispheres The cerebral hemispheres consist of the cerebral cortex, an underlying white matter, and three deep nuclei (basal ganglia, hippocampus, and amygdala). The functions of the cerebral hemispheres are perception, higher motor functions, cognition, memory, and emotion. ♦ Cerebral cortex: is the convoluted surface of the cerebral hemispheres and consists of four lobes: frontal, parietal, temporal, and occipital. The cerebral cortex receives and processes sensory information and integrates motor functions. Thalamus and Hypothalamus Together, the thalamus and hypothalamus form the diencephalon, which means “between brain.” The term refers to the location of the thalamus and hypothalamus between the cerebral hemispheres and the brain stem. The thalamus processes almost all sensory information going to the cerebral cortex and almost all motor information coming from the cerebral cortex to the brain stem and spinal cord. The hypothalamus lies ventral to the thalamus and contains centers that regulate body temperature, food intake, and water balance. The hypothalamus is also an endocrine gland that controls the hormone secretions of the pituitary gland. 6 07/04/1446 Brain Stem The medulla, pons, and midbrain are collectively called the brain stem. The components of the brain stem are as follows: ♦ The medulla is the rostral extension of the spinal cord. It contains autonomic centers that regulate breathing and blood pressure, as well as the centers that coordinate swallowing, coughing, and vomiting reflexes. ♦ The pons is rostral to the medulla and, together with centers in the medulla, participates in balance and maintenance of posture and in regulation of breathing. ♦ The midbrain is rostral to the pons and participates in control of eye movements. It also contains relay nuclei of the auditory and visual systems. Brain stem 7 07/04/1446 Cerebellum The cerebellum is a foliated structure that is attached to the brain stem and lies dorsal to the pons and medulla. The functions of the cerebellum are: Coordination of movement, perform rapidly alternating movements, planning and execution of movement, maintenance of posture, and coordination of head and eye movements. Thus the cerebellum, positioned between the cerebral cortex and the spinal cord, integrates sensory information about position from the spinal cord, motor information from the cerebral cortex. Spinal Cord The spinal cord is the most caudal portion of the CNS. The spinal cord is segmented, with 31 pairs of spinal nerves that contain both sensory (afferent) nerves and motor (efferent) nerves. Sensory nerves carry information to the spinal cord from the skin, joints, muscles, and visceral organs Motor nerves carry information from the spinal cord to the periphery and include both somatic motor nerves, which innervate skeletal muscle, and motor nerves of the autonomic nervous system, which innervate cardiac muscle, smooth muscle, glands, and secretory cells Ascending pathways in the spinal cord carry sensory information from the periphery to higher levels of the CNS. Descending pathways in the spinal cord carry motor information from higher levels of the CNS to the motor nerves that innervate the periphery. 8 07/04/1446 BASIC TASKS Sensory Receptors: Monitor both external and internal environments. Central Nervous System: Analyze the information and often integrate it with stored information. Peripheral Nervous System: If necessary, signal muscles and other effector organs to make an appropriate response. 9 07/04/1446 FUNCTIONAL ORGANIZATION OF THE SENSORY SYSTEM: Sensory receptors: Receive (detect) sensory information, transduce them to electrical energy in the sensory pathway associated with them. Sensory pathways: Transmit the sensory information to areas of perception in the CNS (Sensory cortex). Sensory cortex: Perceives the transmitted sensory information (electrical energy) as modalities of sensations (Touch, pressure, electromagnetic, warm, cold, pain, … etc). FUNCTIONAL ORGANIZATION OF THE MOTOR SYSTEM: Voluntary movements: Orders come from CTX through the descending motor tracts. Muscle tone: This is involuntary activity of skeletal muscles. Coordination of voluntary movement & muscle tone: Is the function of cerebellum & basal ganglia. 10 07/04/1446 CELLS OF THE NERVOUS SYSTEM Neurons, or nerve cells, are specialized for receiving and sending signals. The structure of neurons includes: 1. The cell body (soma) 2. The dendrites; 3. The axon 4. The presynaptic terminals. Glial cells, which greatly outnumber neurons, include astrocytes, oligodendrocytes, and microglial cells; their function, broadly, is to provide support for the neurons. 11 07/04/1446 STRUCTURE OF THE NEURON Cell Body The cell body, or soma, surrounds the nucleus of the neuron and contains the endoplasmic reticulum and Golgi apparatus. It is responsible for the neuron’s synthesis and processing of proteins. Dendrites Dendrites are tapering processes that arise from the cell body. They receive information and thus contain receptors for neurotransmitters that are released from adjacent neurons. 12 07/04/1446 Axon The axon is a projection arising from a specialized region of the cell body called the axon hillock. Whereas dendrites are numerous and short, each neuron has a single axon, which can be quite long (up to 1 meter in length). Axons carry action potentials between the cell body and other neurons or muscle. Axons may be insulated with myelin, which increases conduction velocity; breaks in the myelin sheath occur at the nodes of Ranvier. 13 07/04/1446 Presynaptic Terminals The axon terminates on its target cells (e.g., other neurons) in multiple endings, called presynaptic terminals. When the action potential transmitted down the axon reaches the presynaptic terminal, neurotransmitter is released into the synapse. The transmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane In this way, information is transmitted rapidly from neuron to neuron 14 07/04/1446 SYNAPSE Synapse is the junction between two neurons. It is not an anatomical continuation. But, it is only a physiological continuity between two nerve cells. Synapse is classified by two methods: A. Anatomical classification: 1. Axoaxonic synapse in which axon of presynaptic neuron ends on axon of postsynaptic neuron. 2. Axodendritic synapse in which the axon of presynaptic neuron ends on dendrite of postsynaptic neuron 3. Axosomatic synapse in which axon of presynaptic neuron ends on soma (cell body) of postsynaptic neuron. 15 07/04/1446 B. Functional classification: Based on mode of impulse transmission, synapse is classified into: 1- Electrical synapse: The physiological continuity between the presynaptic and the postsynaptic neurons is provided by gap junction between the two neurons, which allows direct exchange of ions between the two neurons, decreasing the synaptic delay. Example is cardiac muscle fibers, smooth muscle fibers of intestine 16 07/04/1446 2. Chemical synapse: Chemical synapse is the junction between a nerve fiber and a muscle fiber or between two nerve fibers, through which the signals are transmitted by the release of chemical transmitter. Mechanism of impulse transmission in chemical synapse: a. Arrival of impulse (action potential) to the presynaptic neuron, stimulates the release of chemical neurotransmitter in the synaptic cleft (= space between pre- and post- synaptic neurons). b. The neurotransmitter travel through the synaptic cleft to the post- synaptic neuron, where it binds to specific receptors stimulating generation of action potential (=impulse) in the post-synaptic neuron. 17 07/04/1446 18 07/04/1446 19 07/04/1446 Types of Nerve Fibers Nerve fibers are classified according to their conduction velocity, which depends on the size of the fibers and the presence or absence of myelination. The larger the fiber, the higher the conduction velocity. Conduction velocity also is increased by the presence of a myelin sheath around the nerve fiber. Thus large myelinated nerve fibers have the fastest conduction velocities, and small unmyelinated nerve fibers have the slowest conduction velocities. Two classification systems, which are based on differences in conduction velocity, are used. The first system, applies to both sensory (afferent) and motor (efferent) nerve fibers and uses a lettered nomenclature of A, B and C. The second system, applies only to sensory nerve fibers and uses a Roman numeral nomenclature of I, II, III, and IV. 20 07/04/1446 21 07/04/1446 TYPES OF NEURONS IN CNS 22 07/04/1446 GENERAL ORGANIZATION OF THE AUTONOMIC NERVOUS SYSTEM Peripheral Nervous System:  Somatic  Autonomic Divisions Autonomic nervous system is made up of two neurons in series that connect the central nervous system and the effector cells. The first neuron has its cell body in the central nervous system. The synapse between the two neurons is outside the central nervous system in a cell cluster called an autonomic ganglion. The neurons passing between the central nervous system and the ganglia are called preganglionic neurons; those passing between the ganglia and the effector cells are postganglionic neurons. 23 07/04/1446 DIFFERENCE BETWEEN SOMATIC NERVOUS SYSTEM & AUTONOMIC NERVOUS SYSTEM ANATOMICAL ORIGIN OF PARASYMPATHETIC NERVOUS SYSTEM (CRANIO SACCRAL) 24 07/04/1446 Anatomical origin of Sympathetic nervous system (THORACOLUMBAR) NEUROTRANSMITTERS IN ANS 25 07/04/1446 Central Nervous system control of ANS 26 07/04/1446 DEFINITION AND TYPES OF SENSATIONS  Somatosensory system is defined as the sensory system associated with different parts of the body.  Sensations are of two types: 1. Somatic sensations 2. Special sensations 1 07/04/1446 Somatic sensations  Somatic sensations are the sensations arising from skin, muscles, tendons and joints. These sensations have specific receptors, which respond to a particular type of stimulus.  TYPES OF SOMATIC SENSATIONS Generally, somatic sensations are classified into three types: 1. Epicritic sensations 2. Protopathic sensations 3. Deep sensations Epicritic Sensations (Highly Myelinated, Large , Rapid, Fine)  Epicritic sensations are the mild or light sensations.  Such sensations are perceived more accurately. Epicritic sensations are: 1. Fine touch 2. Tactile localization 3. Tactile discrimination 4. Temperature sensation with finer range between 25°C and 40°C. 2 07/04/1446 Protopathic Sensations (Low Myelin, Small > Slow, Coarse and Crude)  Protopathic sensations are the crude sensations. These sensations are primitive type of sensations. Protopathic sensations are: 1. Pressure sensation 2. Pain sensation 3. Temperature sensation with a wider range, i.e. above 40°C and below 25°C. Deep Sensations  Deep sensations are sensations arising from deeper structures beneath the skin and visceral organs. Deep sensations are: i. Sensation of vibration or pallesthesia, which is the combination of touch and pressure sensation ii. Kinesthetic sensation or kinesthesia: Sensation of position and movements of different parts of the body. This sensation arises from the proprioceptors present in muscles, tendons, joints and ligaments.  Proprioceptors are the receptors, which give response during various movements of a joint. 3 07/04/1446  Sensory unit refers to a single sensory axon and all of its peripheral branches.  Receptive field of a sensory unit is the distribution from which a stimulus produces a response in that unit  Tactile localization: refers to the ability of the brain to identify the location of the stimulus accurately.  Tactile discrimination: refers to the ability of the brain to identify the number of the stimuli accurately.  Both , depends on the size of the receptive field of the sensory unit.  The smaller the receptive field of the sensory unit, the greater its Tactile localization and discrimination. 4 07/04/1446 Thermoreceptors  Temperature receptors, or thermoreceptors, are free nerve endings located in: 1. the dermis 2. skeletal muscles 3. the liver 4. the hypothalamus  Thermoreceptors -- Ending of unmyelinated C-fibers -- Spontaneous firing at low-frequency (skin temperature of 34oC) Two Types: 1. Cold receptors – fire when Temp. decreases from 34oC, maximal firing at 25oC 2. Warmth receptors – fire when Temp. increases from 34oC, maximal firing at 45oC Hot sensation – noxious stimulus detected by nociceptors, not thermal receptors Cold receptors are three or four times more numerous than warm receptors. 5 07/04/1446 Pain  Primarily a protective mechanism meant to bring a conscious awareness that tissue damage is occurring or is about to occur  Storage of painful experiences in memory helps us avoid potentially harmful events in future  Sensation of pain is accompanied by motivated behavioral responses and emotional reactions  Subjective perception can be influenced by other past or present experiences  Pain receptors or nociceptors are always free nerve endings on skin & internal organs  Stimulations  Mechanical  Thermal (above 450C)  Chemical (Bradykinin, 5-HT, histamine, K+ ions, proteolytic enzymes, Ach, acids, prostaglandins etc)  Types of pain  Fast (acute) pain – caused by mechanical & thermal stimulus  Slow (chronic) pain – caused mainly by chemical stimulus, but mechanical & thermal stimulus may also cause slow pain 6 07/04/1446 Mechanical sensations  Mechanoreceptors are sensitive to stimuli that distort their cell membranes, which contain mechanically regulated ion channels whose gates open or close in response to: 1. stretching 2. compression 3. twisting  There are three classes of mechanoreceptors: 1. Tactile receptors 2. Baroreceptors 3. Proprioceptors 1- Tactile receptors provide the sensations of touch, pressure, and vibration. 2- Baroreceptors detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts. 3- Proprioceptors monitor the positions of joints and muscles. They are the most structurally and functionally complex of the general sensory receptors. 7 07/04/1446  Fine touch and pressure receptors are extremely sensitive and have a relatively narrow receptive field. They provide detailed information about a source of stimulation, including: 1. its exact location 2. shape 3. size 4. texture  Crude touch and pressure receptors have relatively large receptive fields, provide poor localization, and give little information about the stimulus  Touch and pressure are sensed by four types of mechanoreceptors : 1- Meissner’s corpuscles are dendrites encapsulated in connective tissue and respond to changes in texture and slow vibrations. 2- Merkel cells are expanded dendritic endings, and they respond to sustained pressure and touch. 3- Ruffini corpuscles are enlarged dendritic endings with elongated capsules, and they respond to sustained pressure. 4- Pacinian corpuscles consist of unmyelinated dendritic endings of a sensory nerve fiber, 2 μm in diameter, encapsulated by concentric lamellae 8 07/04/1446 GENERATOR POTENTIALS  When a small amount of pressure is applied to the Pacinian corpuscle, a non-propagated depolarizing potential is recorded. This is called the generator potential or receptor potential  As the pressure is increased, the magnitude of the receptor potential is increased.  The receptor therefore converts mechanical energy into an electrical response, the magnitude of which is proportional to the intensity of the stimulus.  Thus, the responses are described as graded potentials rather than all-or-none as is the case for an action potential 9 07/04/1446 10 07/04/1446 SOMATOSENSORY PATHWAYS  Nervous pathways of sensations are called the sensory pathways. These pathways carry the impulses from receptors in different parts of the body to centers in brain. Sensory pathways are of two types: 1. Pathways of somatosensory system, convey the information from sensory receptors in skin, skeletal muscles and joints. Pathways of this system are constituted by somatic nerve fibers called somatic afferent nerve fibers. 2. Pathways of viscerosensory system, convey the information from receptors of the viscera. Pathways of this system are constituted by visceral or autonomic fibers.  The ascending pathways from sensory receptors to the cortex are different for the various sensations (2 pathways) 1. Ascending sensory pathway that mediates touch, vibratory sense, and proprioception ( dorsal column medial lemniscal pathway ) 2. Ascending sensory pathway that mediates pain and temperature (ventrolateral spinothalamic pathway ). 11 07/04/1446  The posterior column pathway carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception.  This pathway, also known as the dorsal column/medial lemniscus, begins at a peripheral receptor and ends at the primary sensory cortex of the cerebral hemispheres.  The axons of the first-order neurons reach the CNS within the dorsal roots of spinal nerves and the sensory roots of cranial nerves. 12 07/04/1446  The axons ascending within the posterior column are organized according to the region innervated. a. Axons carrying sensations from the inferior half of the body ascend within the fasciculus gracilis and synapse in the nucleus gracilis of the medulla oblongata. b. Axons carrying sensations from the superior half of the trunk, upper limbs, and neck ascend in the fasciculus cuneatus and synapse in the nucleus cuneatus.  Axons of the second-order neurons of the nucleus gracilis and nucleus cuneatus ascend to the thalamus.  As they ascend, these axons cross over to the opposite side of the brain stem. This crossing of an axon is called decussation.  Once on the opposite side of the brain, the axons enter a tract called the medial lemniscus.  As it ascends, the medial lemniscus runs alongside a smaller tract that carries sensory information from the face, relayed from the sensory nuclei of the trigeminal nerve. 13 07/04/1446  The axons in these tracts synapse on third-order neurons in one of the ventral posterior lateral nuclei of the thalamus. These nuclei sort the arriving information according to: 1. the nature of the stimulus 2. the region of the body involved  Processing in the thalamus determines whether you perceive a given sensation as fine touch, as pressure, or vibration.  then from contralateral thalamic ventral posterior lateral (VPL) to then to the primary somatosensory cortex.  Dorsal column pathway : Sensory fibers ascend ipsilaterally via the spinal dorsal columns to medullary gracilus and cuneate nuclei; then cross the midline and ascend in the medial lemniscus to the contralateral thalamic ventral posterior lateral (VPL) and then to the primary somatosensory cortex. 14 07/04/1446 The Dorsal column medial lemniscal system First order neurons – goes through dorsal column – synapse in nucleus of medulla – second order neuron decussate in medulla – goes through medial lemniscus of brain stem – synapse in thalamus – third order neuron projects through internal capsule to somatosensory cortex 15 07/04/1446 The Anterolateral Pathway  The anterolateral pathway provides conscious sensations of poorly localized (“crude”) touch, pressure, pain, and temperature.  In this pathway, the axons of the first-order sensory neurons enter the spinal cord and synapse on second-order neurons within the posterior gray horns.  The axons of these interneurons cross to the opposite side of the spinal cord before ascending.  This pathway includes relatively small tracts that deliver sensations to reflex centers in the brain stem as well as larger tracts that carry sensations destined for the cerebral cortex. 16 07/04/1446  The lateral spinothalamic tracts carry pain and temperature sensations.  These tracts end at third-order neurons in the ventral nucleus group of the thalamus.  After the sensations have been sorted and processed, they are relayed to the primary sensory cortex.  Most somatic sensory information is relayed to the thalamus for processing. A small fraction of the arriving information is projected to the cerebral cortex and reaches our awareness. 17 07/04/1446 The Anterolateral system First order neuron synapse in dorsal horn – second order neuron decussate to lateral or anterior columns – synapse mainly in thalamus or synapse in reticular formation & then goes to thalamus – from thalamus goes to somatosensory cortex through internal capsule Somatosensory area I 18 07/04/1446 Somatosensory area I & II Somatosensory area I is more prominent than somatosensory area II Brodmann’s areas 3, 1 & 2 constitute somatosensory area I, Brodmann’s areas 40 constitute somatosensory area II and areas 5 & 7 constitute somatosensory association area Representation of body in somatosensory area  Somatic senses are represented contralaterally, except for few fibers from face.  Larger areas for lips, thumb, & face, smaller areas for other body parts like trunk & lower parts 19 07/04/1446  Sensory homunculus: This model shows what a man's body would look like if each part grew in proportion to the area of the cortex of the brain concerned with its sensory perception. When damage of somatosensory area occurs  Discrete localization of different sensation is lost. But crude localization is possible with intact brain stem & thalamus.  Loss of judgment for critical degrees of pressure  Stereognosis (ability to judge shapes & forms of objects) is lost  Unable to judge the texture of materials 20 07/04/1446 DESCENDING TRACTS Voluntary movement is the coordinated and purposeful activity of a series of muscles. Proper performance of voluntary movements requires integrity of: 1. Motor areas of cerebral cortex 2. The UMN ( upper motor neuron ) and LMN ( lower motor neuron ) 3. The cerebellum 4. Basal ganglia 1 07/04/1446 Cerebral cortex – Motor cortex Cerebral cortex – Motor cortex Primary motor cortex, The primary motor area is the major control region for initiation of voluntary movements It initiates voluntary fine discrete movement specially of the hands and fingers. It shares premotor area in initiating the gross movements It facilitates the stretch reflex 2 07/04/1446 Premotor cortex, 1. It shares in planning of voluntary movements. 2. It initiates the gross movements 3. It inhibits the stretch reflex and muscle tone 4. It inhibits the grasp reflex 5. It initiates the subconscious automatic movements 6. It contains specialized areas that control specific movements Supplementary motor area In general, this area functions in concert with the premotor area to provide fixation movements of the different segments of the body and positional movements of the head and eyes. It shares in planning and programming of complex voluntary movements supplementary motor area initiates motor learning 3 07/04/1446 Representation of different muscles of the body in the motor cortex and location of other cortical areas responsible for specific types of motor movements Transmission of Signals from the Motor Cortex to the Muscles 4 07/04/1446 CORTICOSPINAL TRACT (PYRAMIDAL TRACT) ORIGIN: motor cortex, as follows: about 30% from the primary motor cortex, 30% from the premotor and supplementary motor areas, 40% from the somatosensory areas posterior to the central sulcus. 5 07/04/1446 Motor signals are transmitted directly from the cortex to the spinal cord through the corticospinal tract and Indirectly through multiple accessory pathways that involve the basal ganglia, cerebellum, and various nuclei of the brain stem. The direct pathways are concerned more with discrete and detailed movements, especially of the distal segments of the limbs, particularly the hands and fingers. Descending pathways Pyramidal pathway 1- Corticospinal pathway Lateral corticospinal Ventral corticospinal 2- Corticobulbar pathway Extrapyramidal pathway 1. Vestibulospinal tract 2. Reticulospinal tract 3. Tectospinal tract 4. Rubrospinal (corticorubrospinal) tract 5. Olivospinal tract 6 07/04/1446 Arises from area 4, area 6, supplemental motor area and somatosensory area, passes to the brain stem through internal capsule, & in the medulla (pyramids) 80% of fibers decussate to form lateral corticospinal tract & end on the LMNs supplying to distal muscles. 20% of fibers from medulla passes to spinal cord without decussating to form ventral corticospinal tract & ends on interneurons which pass impulse to LMNs of both contralateral & ipsilateral side supplying to proximal muscles. 7 07/04/1446 8 07/04/1446 The corticospinal pathway contains three pairs of descending tracts: 1. corticobulbar tracts 2. lateral corticospinal tracts 3. anterior corticospinal tracts These tracts enter the white matter of the internal capsule, descend into the brain stem. Axons in the corticospinal tracts synapse on lower motor neurons in the anterior gray horns of the spinal cord. As they descend, the corticospinal tracts are visible along the ventral surface of the medulla oblongata as a pair of thick bands, the pyramids. Along the length of the pyramids, roughly 85% of the axons cross the midline (decussate) to enter the descending lateral corticospinal tracts on the opposite side of the spinal cord. The other 15% continue uncrossed along the spinal cord as the anterior corticospinal tracts. 9 07/04/1446 10 07/04/1446 Functions of pyramidal tracts 1. Executes voluntary fine discrete movement specially of the hands and fingers. 2. It facilitates the stretch reflex through excitation of the alpha motor neuron 3. Facilitation of superficial reflexes Corticobulbar Tracts Axons of upper neurons run from the primary motor cortex to the corticobulbar tracts in the R. and L. cerebral peduncles of the midbrain The tracts cross and the axons end in the motor nuclei of nine cranial nerves (III, IV,V, VI, VII, IX, X, XI, XII) Extrapyramidal pathways Descending fibers conveying information from nuclei of brain stem like red nucleus, superior colliculus, vestibular nucleus, & motor nuclei of reticular formation. This mainly function for the tone, posture & equilibrium This system includes: 1. the rubrospinal, 2. vestibulospinal, 3. reticulospinal, 4. tectospinal tracts 11 07/04/1446 Functions of extrapyramidal system It controls axial muscles and proximal limb muscles producing gross movements. It produces the subconscious automatic movements. Weak alternative route for performance of fine movements. Adjusts muscle tone and produces postural adjustments for equilibrium and fine movements Controls many autonomic functions Exerts powerful inhibitory effect on the gamma motor neurons and muscle tone 12 07/04/1446 FUNCTIONS AND REFLEXES OF THE SPINAL CORD Spinal cord The major nerve tract of vertebrates, extending from the base of the brain through the canal of the spinal column. It is composed of nerve fibers that mediate reflex actions and that transmit impulses to and from the brain. Like the brain, the spinal cord is covered by three connective-tissue envelopes called the meninges. The space between the outer and middle envelopes is filled with cerebrospinal fluid, a clear, colorless fluid that cushions the spinal cord. 1 07/04/1446 A cross section of the spinal cord reveals white matter arranged around a butterfly-shaped area of gray matter. The white matter consists of myelinated fibers, or axons, that form nerve tracts ascending to and descending from the brain. The gray matter contains cell bodies, unmyelinated motor- neuron fibers, and interneurons connecting the two sides of the cord. Fibres exiting the spinal cord from the dorsal and ventral horns join in paired tracts to form the spinal nerves. Information travels up the ascending tracts of neurons and is sorted by the brain. Responses are induced by nerve impulses traveling down the descending tracts that stimulate motor neurons or that initiate glandular secretion. 2 07/04/1446 The grey matter takes on the shape of a butterfly, with four 'wings' called horns: The horns in the front contain motor neurons; the horns in the back contain sensory neurons which carry sensory information. The spinal cord grey matter is surrounded by a column of white matter, containing axons that allow different parts of the spinal cord to communicate smoothly, with signals passing upwards and downwards conveying sensation and motor signals. Sensory Nerve Fibers enter the Spinal Cord via the Posterior (Dorsal) Root. The cell bodies for these neurons are situated in the Dorsal Root Ganglia. Motor and Preganglionic Autonomic Fibers exit via the Anterior (Ventral) Root. 3 07/04/1446 The spinal cord is the major conduct and reflex center between the peripheral nerves and the brain and transmits motor information from the brain to the muscles, tissues and organs, and sensory information from these areas back to the brain. Its upper end is continuous with the medulla, the transition is defined to occur just above the level of exit of the first pair of cervical nerves. Its tapering lower end, terminates at the level of the L3 vertebra in neonates, and at the level of the L1-2 intervertebral disk in adults. Spinal nerve The term spinal nerve generally refers to a mixed spinal nerve that carries motor, sensory, and autonomic signals between the spinal cord and the body. Humans have 31 left–right pairs of spinal nerves, each roughly corresponding to a segment of the vertebral column. There are eight cervical*, twelve thoracic, five lumbar, five sacral and one coccygeal. The spinal nerves are relatively large nerves that are formed by the merging of two nerve roots: a sensory nerve root and a motor nerve root. Sensory nerve roots emerge from the back of the spinal cord and the motor nerve roots from the front of the spinal cord. As they join, they form the spinal nerves on the sides of the spinal cord. 4 07/04/1446 Spinal Motor neurons Alpha and Gamma motor neurons are both found in the anterior (ventral) horn. Alpha motor neurons are the largest motor neurons in the nervous system and innervate skeletal muscle. Gamma Motor neurons innervate intrafusal muscle fibers of the muscle spindle. 5 07/04/1446 Parts of spinal cord involved in motor functions Anterior motor neurons –α motor neurons – γ motor neurons Interneurons Physiology of Human Reflex Definition: Rapid, predictable and involuntary motor response to stimuli through pathways called reflex arcs. Two systems Autonomic reflexes (unconscious): digestion, sweating etc. Somatic reflexes: activate skeletal muscles. 6 07/04/1446 Neural Reflexes: Classification of Pathways Effector Division Somatic Autonomic Integration site Spinal Brain Neurons in pathway Monosynaptic Polysynaptic 7 07/04/1446 Monosynaptic and polysynaptic somatic motor reflexes Spinal cord reflexes Stretch reflex Inverse stretch reflex (GTO reflex) Withdrawal reflex 8 07/04/1446 Muscle spindle 9 07/04/1446 THE SENSORY RECEPTORS OF THE MUSCLES 1-Muscle Spindles (intrafusal fibers): Located in the muscle belly Include nuclear bag & nuclear chain fibers Detect the change in the muscle length 2-Golgi Tendon Organs: In the tendons of the muscle Detect the change in the muscle tension Intrafusal fibers have : A Central portion (receptor) non-contractile, don not contain actin or myosin. A Peripheral portion contractile portion 10 07/04/1446 Anatomy of the muscle spindle and Golgi tendon organ 11 07/04/1446 Afferent fibers of stretch reflex 1. Muscle spindle Ia fiber II fiber 2. Golgi tendon organ Ib fiber Stretch reflex Sensory receptors Muscle spindle Stimulus muscle length or rate of change of its length 12 07/04/1446 The stretch reflex 13 07/04/1446 Stretch reflex The stretch reflex is the contraction of a muscle that occurs in response to its stretch. It is not controlled by higher functioning center i.e. the brain, and is a monosynaptic response that is transmitted to the spinal cord. Tendon reflex (dynamic stretch reflex) Rapid stretch –immediate, strong reflex contraction Monosynaptic Muscle tonus (static stretch reflex) Slow stretch – weaker, continuous contraction Polysynaptic The stretch reflex was designed as a protective measure for the muscles, in order to prevent tearing that can occur due to vigorous movement. Once the muscle spindle is stretched, the impulse is sent back to the muscle very quickly, and protects it from being pulled forcefully or beyond its normal range of motion. When a reflex takes place, all of the synergistic muscles (those that cause the same movement) also contract while antagonistic muscles are inhibited ( reciprocal inhibition) 14 07/04/1446 The first major function of the stretch reflex is muscle protection. When a muscle length increases, the muscle spindle within that muscle stretches, and its nerve activity will increase. Resulting from this is increased alpha motor neuron activity. These neurons will cause the muscle to contract, and therefore reduce the stretching of the muscle. Neural Input into the Muscle (motor) Extrafusal fibers are input by alpha motor neurons These neurons are large and fast. Intrafusal Fibers are input by gamma motor neurons These neurons are relatively small and slow. They are involved in the control of muscle tone. Gamma efferent system Importance: -strengthening the contraction: alpha-Gamma coactivation -Increase sensitivity to stretch reflex. Functions of stretch reflex 1. Posture and tone 2. Damping and smoothing function 3. Increase power of muscle contraction 15 07/04/1446 Operation of the muscle spindle Tendon reflex Golgi tendon organ Stimulus – tendon tension or rate of change of tension Golgi tendon reflex is entirely inhibitory Provides a negative feedback mechanism that prevents the development of too much tension on the muscle The tendon reflex is ipsilateral and prevents damage to muscles and tendons as a result of stretching It operates as a feedback mechanism to control muscle tension by causing muscle relaxation when muscle force becomes too extreme. Also thought to provide feedback about actual tension generated at times of muscle fatigue 16 07/04/1446 17 07/04/1446 When the stretch receptors fire, the α motor neuron is excited, & the muscle contracts When the golgi tendon organ fire, the α motor neuron is inhibited (via inhibitory interneuron), & the muscle relaxes 18 07/04/1446 19 07/04/1446 SPINAL CORD TRANSECTION AND SPINAL SHOCK Spinal shock is characterized by the temporary reduction or loss of reflexes following a spinal cord injury. When the spinal cord is suddenly transected in the upper neck: essentially all cord functions, including the cord reflexes, immediately become depressed to the point of total silence, this reaction called spinal shock. The reason for this reaction is that normal activity of the cord neurons depends to great extent on continual tonic excitation by the discharge of nerve fibers entering the cord from higher centers, particularly discharge transmitted through the reticulospinaltracts, vestibulospinaltracts, and corticospinaltracts. 20 07/04/1446 Stages of spinal shock. One to two days following the injury: Nerve cells become less responsive to sensory input, resulting in full or partial loss of spinal cord reflexes. This is known as hyporeflexia. One to three days following injury: Initial return of some reflexes. Polysynaptic reflexes — those that require a signal to travel from a sensory neuron to a motor neuron tend to return first. One to four weeks following the injury: Hyperreflexia, a pattern of unusually strong reflexes, occurs. This is the result of new nerve synapse growth, and is normally temporary. One to twelve months following the injury: Hyperreflexia continues, and spasticity may develop. This process is due to changes in the neuronal cell bodies, and takes much longer than the other stages After a few hours to a few weeks the spinal neurons gradually regain their excitability This phenomenon seems to be a natural characteristic of neurons every where in the nervous system; after they lose their source off impulses, they increase their own natural degree of excitability. Some of the spinal functions specifically affected during or after spinal shock are the following: 1.At onset of spinal shock, the arterial blood pressure falls almost instantly and drastically—sometimes to as low as 40mmHg thus ----- demonstrating that sympathetic nervous system activity becomes blocked almost to extinction. The pressure ordinarily returns to normal within a few days. 21 07/04/1446 2.All skeletal muscle reflexes integrated in the spinal cord are blocked during the initial stages of shock. In humans, 2 weeks to several months are sometimes required to return to normal, The first reflexes to return are the stretch reflexes. 3.The sacral reflexes for control of bladder and colon evacuation are suppressed in people for the first few weeks after cord transection, but in most cases they eventually return. 22 07/04/1446 Physiology of Pain Pain 1 07/04/1446 Pain is defined as an unpleasant and emotional experience associated with or without actual tissue damage. Pain sensation is described in many ways like sharp, pricking, electrical, dull ache, shooting, cutting, stabbing. Acute pain is a sharp pain of short duration with easily identified cause. Often it is localized in a small area before spreading to neighboring areas. Chronic pain is the intermittent or constant pain with different intensities. It lasts for longer periods. BENEFITS OF PAIN SENSATION Pain is an important sensory symptom. Though it is an unpleasant sensation, it has protective benefits such as: 1. Pain gives warning signal about the existence of a problem or threat. It also creates awareness of injury. 2. Pain prevents further damage by causing reflex withdrawal of the body from the source of injury 3. Pain forces the person to rest or to minimize the activities thus enabling rapid healing of injured part 4. Pain urges the person to take required treatment to prevent major damage. 2 07/04/1446  Types of pain: A) According to duration 1) Acute pain: 2) Chronic pain: It is a sharp pain of  is the intermittent short duration with or constant pain with easily identified different intensities. cause.  It lasts for longer localized in a small periods. area before spreading  It is somewhat to neighboring areas. difficult to treat and Usually it is treated by it needs professional medications. expert care. Example: Burn  Example: Headache B) According to origin 1) Somatic pain: 2) Visceral pain: Somatic pain is subdivided into: Originates from internal viscera a. Cutaneous pain: originate from the with hollows (i.e., superficial skin layer. stomach, intestine, b. Deep pain: originates from deep tissues ureters, urinary (i.e., joints, ligaments, muscles, tendons, bladder, periosteum..etc) uterus…etc) 3 07/04/1446 Pain sensation has two components: 1. Fast pain 2. Slow pain. Fast pain is the first sensation whenever a pain stimulus is applied. It is experienced as a bright, sharp and localized pain sensation. Fast pain is followed by the slow pain, which is experienced as a dull, diffused and unpleasant pain. Receptors for both the components of pain are same, i.e. the free nerve endings. But, afferent nerve fibers are different. Fast pain sensation is carried by Aδ fibers and slow pain sensation is carried by C type of nerve fibers. FROM SKIN AND DEEPER STRUCTURES Receptors of pain sensation are the free nerve endings, which are distributed throughout the body. First Order Neurons First order neurons are the cells in posterior nerve root ganglia, which receive the impulses of pain sensation from pain receptors through their dendrites. Fast pain fibers Fast pain sensation is carried by Aδ type afferent fibers which synapse with neurons of marginal nucleus in the posterior gray horn. Slow pain fibers Slow pain sensation is carried by C type afferent fibers, which synapse with neurons of substantia gelatinosa of Rolando in the posterior gray horn 4 07/04/1446 Second Order Neurons Neurons of marginal nucleus and substantia gelatinosa of Rolando form the second order neurons. Fibers from these neurons ascend in the form of the lateral spinothalamic tract. Fast pain fibers These fibers form the neospinothalamic fibers in lateral spinothalamic tract. These nerve fibers terminate in ventral posterolateral nucleus of thalamus. Slow pain fibers Fibers of slow pain, which arise from neurons of substantia gelatinosa, cross the midline and run along the fibers of fast pain as paleospinothalamic fibers in lateral spinothalamic tract. One fifth of these fibers terminate in ventral posterolateral nucleus of thalamus. Remaining fibers terminate in any of the following areas: i. Reticular formation in brainstem ii. Midbrain Third Order Neurons Third order neurons of pain pathway are the neurons in: i. Thalamic nucleus ii. Reticular formation iii. Midbrain Axons from these neurons reach the sensory area of cerebral cortex Center for Pain Sensation Center for pain sensation is in postcentral gyrus of parietal cortex. Fibers reaching hypothalamus are concerned with arousal mechanism due to pain stimulus. 5 07/04/1446 FROM VISCERA Pain sensation from thoracic and abdominal viscera is transmitted by sympathetic nerves. Pain from esophagus, trachea and pharynx is carried by vagus and glossopharyngeal nerves. VISCERAL PAIN Pain from viscera is unpleasant. It is poorly localized. CAUSES OF VISCERAL PAIN 1. Ischemia Substances released during ischemic reactions such as bradykinin and proteolytic enzymes stimulate the pain receptors of viscera. 2. Chemical Stimuli Chemical substances like acidic gastric juice, leak from ruptured ulcers into peritoneal cavity and produce pain. 3. Spasm and Overdistention of Hollow Organs Spastic contraction of smooth muscles in gastrointestinal tract and other hollow organs of viscera cause pain by stimulating the free nerve endings. Overdistention of hollow organs also causes pain. Pain pathway and analgesic pathway 6 07/04/1446  Referred Pain Referred pain is the pain that is perceived at a site adjacent to or away from the site of origin. MECHANISM OF REFERRED PAIN: A dermatome includes all the structures or parts of the body, which are innervated by afferent nerve fibers of one dorsal root. Referred pain is felt in the surface somatic structure served by the same dorsal root (= dermatome) as the diseased structure. Derma tomes of the upper and lower limbs 7 07/04/1446  Examples of referred pain: 1. Cardiac pain is felt at inner part of left arm and left shoulder. 2. Pain in ovary is referred to umbilicus 3. Pain in diaphragm is referred to shoulder 5. Pain in gallbladder is referred to epigastric region 6. Renal pain is referred to loin. Analgesia system Body has its own analgesia (= pain control) system in brain, which provides a short term relief from pain (= endogenous analgesic system). Analgesia system has got its own pathway through which it blocks the synaptic transmission of pain sensation in spinal cord and thus attenuates the experience of pain. Analgesic drugs such as opioids act through this system and provide a controlled pain relief. 8 07/04/1446 ANALGESIC PATHWAY Analgesic pathway that interferes with pain transmission Role of Analgesic Pathway in Inhibiting Pain Transmission 1. Fibers of analgesic pathway arise from frontal lobe of cerebral cortex and hypothalamus 2. Fibers from here descend down to brainstem and terminate on: i. Nucleus raphe magnus, situated in the lower pons and upper medulla ii. Nucleus reticularis, situated in medulla 4. Fibers from these reticular nuclei descend through lateral white column of spinal cord and reach the synapses of the neurons in afferent pain pathway Neurotransmitters of Analgesic Pathway Neurotransmitters released by the fibers of analgesic pathway are serotonin and opiate receptor substances namely enkephalin, dynorphin and endorphin. GATE CONTROL THEORY The pain stimuli that transmitted by afferent pain fibers are blocked by gate mechanism located at the posterior gray horn of spinal cord. If the gate is opened, pain is felt. If the gate is closed, pain is suppressed. Mechanism of Gate Control at Spinal Level 1- When pain stimulus is applied on any part of body, besides pain receptors, the receptors of other sensations such as touch are also stimulated. 2- When all these impulses reach the spinal cord through posterior nerve root, the fibers of touch sensation send collaterals to the neurons of pain pathway. 3-. Impulses of touch sensation passing through these collaterals inhibit the release of glutamate and substance P from the pain fibers 4-. This closes the gate and the pain transmission is blocked 9 07/04/1446 Gate control system Role of Brain in Gate Control Mechanism brain also plays some important role in the gate control system of the spinal cord as follows: 1. If the gates in spinal cord are not closed, pain signals reach thalamus through lateral spinothalamic tract 2. These signals are processed in thalamus and sent to sensory cortex 3. Perception of pain occurs in cortical level in context of the person’s emotional status and previous experiences 4. The person responds to the pain, the brain determines the severity and extent of pain. 5. To minimize the severity of pain, brain sends message back to spinal cord to close the gate by releasing pain relievers such as opiate peptides 6. Now the pain stimulus is blocked and the person feels less pain. 10 07/04/1446 Motor Functions Of The Nervous System Motor functions of the nervous system include; 1. Initiation and control of voluntary movements. 2. Coordination of movement. 3. Control of body posture. Movements can be; 1. Involuntary; These are reflex muscle contractions. They are the simplest forms of movements. They can be elicited in an unconscious patient (.e.g. stretch reflex & flexor withdrawal reflex). 2. Voluntary; These are movements which are intended by the individual. 3. Rhythmic movements; These movements are initiated voluntarily and proceed automatically.e.g. walking. How is motor activity done? 1. Idea Generation  from cortical association areas, (i.e., prefrontal cortex, somatosensory association area, auditory & visual association areas) 2. The basal ganglia, premotor cortex, and cerebellum develop motor plan (which muscles should contract, how much they need to contract, and in what order) Feedback 3. The premotor area send plan to primary motor area for generate motor nerve impulses to LMNs spinal cord via corticospinal tracts. 4. LMNs execute plan by transmitting motor orders to skeletal muscle. 5. Stimulated skeletal muscle contract according to ordered pattern result in the preforming the desired movement,. 2 07/04/1446 Cerebellum Cerebral cortex in motor control (Motor Cortex) Site: Precentral gyrus of Frontal lobe. Involved areas: 1. Primary motor area (Area 4) has Body map (Motor Homunculus): Crossed, inverted, depend on motor function: a. Lower parts of body  in medial surface b. Upper parts of the body  in the lateral surface. 2. Premotor area (Area 6). 3. Supplementary motor area. Output (Efferent) Connections of Motor Cortex: a. Corticospinal tracts (anterior and lateral) to spinal cord. b. Corticobulbar tract to brainstem. 3 07/04/1446 Functions of Motor Cortex Areas Function Lesion Premotor 1. Share in planning of voluntary movement Area (Area 2. Postural movements (Control of axial muscles) 6) 3. Inhibit muscle tone. Spastic rigidity 3. Contain special areas: vocalization without whole word 3. a. Broca`s area (in left premotor area) formation. speech center 3.b. Voluntary eye movement area Loss of voluntary eye movement 3.c. Hand skills area Motor apraxia Primary motor 1. Initiation of voluntary discrete (Skilled) 1. Contralateral paralysis (Monoplagia, or Area (area 4) patterns of movements and speech on opposite Hemiplagia), With Some recovery for side. proximal muscle only. 2. Facilitate muscle tone 2. Hypotonia of affected part Supplementary Supplement the premotor area.. motor Cortex Brainstem Nuclei (UMNs) Involved In Voluntary Movement Control A. Midbrain: a. Red Nucleus b. Superior, and inferior Colliculi. B. Pons & Medulla Oblongata: a. Reticular formation b. Vestibular nuclei. c. Inferior Olivary nucleus. 4 07/04/1446 Descending Cortical Motor pathways A. Direct (Pyramidal) motor pathway Extend From the Motor cortex to LMNs Included tracts: 1. Corticobulbar tract. 2. Corticospinal tract: a. Lateral Corticospinal Tracts (decussate in the medulla oblongata). b. Anterior Corticospinal Tracts (decussate in spinal cord). Functions: 1. Control the voluntary movements of the body (nerve impulse originate from cerebral cortex). 2. Facilitate stretch reflex B. Indirect (Extra-Pyramidal) motor pathway Extend from Brainstem nuclei to LMNs Included tracts: 1. Vestibulospinal tracts. 2. Reticulospinal tract. 3. Tectospinal tract. 4. Rubrospinal tract. 5. Olivospinal tract. Functions: They mainly control: a. Muscle tone, b. Posture and equilibrium (nerve impulses originate from the brainstem). c. Rubrospinal tract weak control of skilled movements of upper limb distal muscle. 5 07/04/1446 Allows the colliculus in the LMNs of body to turn A. Superior Eye midbrain Tectospinal skeletal in the muscles of direction of tract the Head sudden visual Ear or auditory and Trunk stimulus. LMNs of skeletal Activate Cerebral fine skilled Nucleus in muscles of midbrain Cortex B. Red Rubrospinal movements the Distal of upper tract parts of the Cerebellum limbs only Upper limb only Inner ear Maintain and Medulla) Nuclei (Pons, C. Vestibular (vestibular posture in apparatus) LMNs of response to Vestibulospinal skeletal changes in tract equilibrium Proprioceptive muscles of the trunk Eye and Excitatory Pontine proximal Regulate D. Reticular formation muscle Ear reticulospinal tract parts of tone the Inhibitory Medullary Cerebellum limbs reticulospinal tract 6 07/04/1446 Basal Ganglia (Basal Nuclei): BG is group of nuclei on each side of the brain, lateral to thalamus gland. Structure of Basal Ganglia: 1. Caudate nucleus 2. Putamen nucleus 3. Globus pallidus nucleus. N.B., Lentiform nucleus= Putamen +Globus pallidus. Neural connections of BG: Basal Ganglia considered the origin of extra-pyramidal tracts. A. cerebral cortex: caudate circuit, Putamen circuits. (Extrapyramidal) B. Brainstem: Globus pallidus send to brainstem nuclei (Reticular formation, vestibular n., red nucleus, and inferior olivary nucleus), which in turn send extrapyramidal tracts to spinal cord AHC. C. Thalamus, subthalamus, and Substantia nigra. 7 07/04/1446 Neurotransmitters in basal ganglia Proper function of BG depends on balance between Excitatory & Inhibitory chemical transmitters: 1- Inhibitory Neurotransmitters: Dopamine and GABA. 2- Excitatory Neurotransmitters: Acetyl-choline & noradrenaline Motor Functions of Basal ganglia 1. CONTROL OF MOTOR ACTIVITY: a. Planning of new patterns, and execution of stored patterns. b. Determine Timing (speed) and scaling (intensity, or range) of movement. Such as rapid writing on paper, and on board. c. Cognitive control (It means subconscious thinking of the brain that precedes the voluntary movements to determine which movement will be done and in what sequence), such as, when a stray dog barks at a man, immediately the person, understands the situation, turns away and starts running. 2. Suppression of unwanted movements during rest. So lesion involuntary movement during rest 3. Regulation of muscle tone: a. Lentiform n. (stronger effect) decrease muscle tone. So lesion of BG Rigidity (i.e. Parkinson`s disease). b. Caudate nucleus  increase muscle tone. So lesion in caudate only hypotonia (i.e. Chorea) 8 07/04/1446 Basal Ganglia lesions Uncontrollable shaking (tremor) and muscle rigidity (stiffness). 1. Parkinson's disease (PD): Pathophysiological disturbance: Degeneration of inhibitory dopamine releasing neuron leading to overactivity of excitatory acetyl choline pathway. Treatment: L- Dopa injection: because dopamine does not cross Blood Brain Barrier. BG Functions BG Lesions Control of motor Akinesia = Difficulty in initiating the activity voluntary movements Suppression of unwanted Rhythmic Static tremor (Rest tremors) movements during rest Regulation of Rigidity (hypertonia) muscle tone 9 07/04/1446 Manifestations of Parkinson`s patient (They appear on the opposite side of the lesion) 1-Akinesia = Difficulty in initiating the voluntary movements & loss of subconscious associated movements that usually associates normal motor activity leading to: a- Loss of facial expression (mask face) b- Loss of swinging the arms during walking. c- Shuffling gait: The patient walks in short steps without lifting his legs from the ground. d- Dysarthria: in the form of slow monotones speech. 2- Rhythmic Static tremor (Rest tremors): - Appear during rest and disappear during voluntary movements. Thumb moves rhythmically over the index and middle fingers (Pill rolling form). - Affects small distal joints. 3- Rigidity (hypertonia) = increased muscle tone all over the body with the following characters: - Affects both flexors more than extensors leading to flexion attitude. - Lead pipe rigidity (continuous stiffness as a pipe of lead) when no tremors or cog wheel when tremors (jerky movements) are present. Others basal ganglia lesions: 2. Chorea: Lesion of caudate nucleus a. Hypotonia b. rapid involuntary purposeless movement at rest. 3. Athetosis: Lesion in globus pallidus a. Hypertonia (rigidity) b. involuntary slow rhythmic and twisting movements, mostly in fingers. 10 07/04/1446 Cerebellum Structural Anatomy 1. Anterior lobe. 2. Posterior lobe 3. Flocculonodular lobe Connections of Cerebellum to brainstem: 1. Superior cerebellar peduncle (Midbrain) 2. Middle cerebellar peduncle (Pons) 3. Inferior cerebellar peduncle (Medulla Oblongata) Functional Anatomy of Cerebellum 1. Corticocerebellum (Neocerebellum) a. Motor Planning b. Facilitate muscle tone (predominant effect) 2. Spinocerebellum (Paleocerebellum) a. Control axial muscle contraction (Control body posture ) b. Control distal muscle contraction (On the same side) c. Inhibit muscle tone 3. Vestibulo-cerebellum Control body posture and equilibrium. 2 07/04/1446 Neural connections of cerebellum Afferent Neural connections Efferent neural connections a) From Cerebral cortex and basal Ganglia a) To Contralateral Monitoring body sensations + intentions Cerebral Cortex. for planned movement. b) From proprioceptors in b) Basal Ganglia joints and muscles  Monitoring actual movement. c) Brain Stem Nuclei Cerebral Cortex Motor and sensory Data Musculo- skeletal Proprioceptive signals 3 07/04/1446 Functions Of The Cerebellum 1- Control of Voluntary movement (Coordination) 2-Control of Postural movements (Background positioning). 3- Function of the cerebellum on the muscle tone. 4-Function of the cerebellum in equilibrium. 1. Cerebellar Control Of Voluntary Movement Co-ordination Before movement start During performance of movement 1. Planning sequence, and timing of 1. Cerebellum Compare motor order Movement Co-ordinated sent to Muscles (motor cortex signals) movement. and muscle response to that order (proprioceptive signals)  if there is mismatch  cerebellum send 2. Predictive function: cerebellum can correcting orders to the motor cortex predict the future position of the (Servo-comparative action). limb and the time needed by the limb to be in that position smooth progression & co-ordination of 2. At end of movement, cerebellum movements. stimulate simultaneous automatic agonist muscle turn off and antagonist muscle turn on. prevent 3. Programming of rapid alternating oscillating (pendular) movement, and sequential movement learning of allow precise movement at intended Ballistic Movement (i.e, Piano point (Damping action=Braking playing, typewriting, cycling..etc). action) 4 07/04/1446 2- Control of postural movement: This function is performed by the paleocerebellum. The cerebellum coordinate involuntary subconscious postural movements, depending on received sensory data (visual, auditory, proprioceptive). 3- Function of the cerebellum on the muscle tone. a. The neocerebellum  Facilitate muscle tone (more strong effect). b. The paleocerebellum  inhibit stretch reflex (muscle tone). 4-Function of the cerebellum in equilibrium.  This function is performed by the Vestibulo-Cerebellum.  It receives impulses from the vestibular system either directly or through the Vestibular nucleus  accordingly, Control axial muscle. Cerebellar Lesions (In unilateral lesion, symptoms are ipsilateral because cerebellum controls the same side of the body) 2. MOTOR 1. HYPOTONIA ATAXIA 5 07/04/1446 1) Hypotonia PENDULAR MOVEMENTS 1. A tap on the 2. Contraction 3. Brisk extension of patellar tendon when of quadriceps leg due to the (knee leg is hanging freely muscle jerk). = Normal Condition 4.a. The leg returns back to resting position immediately. 4.b. The leg swings forwards and backwards several times before coming to rest. = Cerebellar lesion Because hypotonia and loss of cerebellar damping action, the leg oscillate as heavy weight with gravity. 2) Motor Ataxia Unsteadiness& bad coordination of body movement 6 07/04/1446 A. Planning B. Ballistic of complex Movement movement Decomposing of movement: Dys-diadokinesia: Inability to Inability to perform movement make rapid alternating opposite involve movement of more than movement. one joint at same time. Dysarthria: (Stacchato Speech)=difficult speech C. Damping Action 1. Intension tremors (Appear during voluntary movements and disappear during rest. ) 2. Nystagmus: tremor of the eyeballs when try to fixate the eyes on a scene to one side of the head. 3. Rebound Phenomenon: inability to stop movement rapidly (Due to due to the absence of braking action of antagonistic muscle). 7 07/04/1446 E. Servo- G. Coordinate D. Predictive comparative function action Involuntary F. Equilibrium Subconscious Postural Movements Dysmetria= While 1. Wide based unsteady drunken-like gait. reaching for an object, the arm may 2. Lateral deviation of arms overshoot (past when both the arms are pointing= stretched and held in front hypermetria) or it of the body, with closed may fall short of the eyes object (hypometria). Cerebellar lesion 1) Hypotonia: Pendular knee jerk 1) Motor Ataxia: a. Decomposing of movement. b. Nystagmus c. Dysarthria d. Rebound Phenomenon e. Dys-diadokinesia g. Intention tremor f. Dysmetria i. Body deviation movement h. Drunken like gait 8 07/04/1446 Differences Between Rest & Intension Tremors Rest Tremors Intension Tremors (Static Tremors) (Kinetic tremors) Cause Parkinsonism Neocerebellar syndrome Muscle tone Associated with hypertonia Associated with hypotonia. (muscle rigidity) Occur during Occur during rest Occur during voluntary movements Disappear Disappear during voluntary Disappear during rest during movement Sleep & Disappear during sleep and Disappear during sleep and Emotions increased by emotions increased by emotions 9