Neural Pathways and Muscle Contraction PDF

1\. Corticospinal Tract: The corticospinal tract is a major neural pathway in the central nervous system (CNS) that carries motor commands from the brain's motor cortex to the spinal cord. It is located in the white matter of the brain and spinal cord, specifically the precentral gyrus, and its prim...

1\. Corticospinal Tract: The corticospinal tract is a major neural pathway in the central nervous system (CNS) that carries motor commands from the brain's motor cortex to the spinal cord. It is located in the white matter of the brain and spinal cord, specifically the precentral gyrus, and its primary role is controlling voluntary movements of the limbs and trunk. It controls fine motor movements, especially in the hands and fingers. 2\. Triceps Reflex Movements: The triceps reflex, a monosynaptic reflex, is a stretch reflex triggered by tapping the triceps tendon. It causes the triceps brachii muscle to contract, resulting in extension of the forearm. 3\. Synaptic Knobs: Synaptic knobs are the terminal ends of axons in a neuron. They contain synaptic vesicles filled with neurotransmitters, which are released into the synaptic cleft to transmit signals to the next neuron or target cell. 4\. Consequences of Sensory Nerve Fiber Crossover: When sensory nerve fibers cross over, they result in contralateral (opposite side) sensation. For example, sensory information from the left side of the body is processed in the right hemisphere of the brain. 5\. EPSPs and IPSPs in Action Potential: Excitatory postsynaptic potentials (EPSPs) depolarize the postsynaptic membrane, making it more likely for an action potential to be generated. Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the membrane, making an action potential less likely. 6\. Cerebrospinal Fluid (CSF): CSF is a clear fluid produced by the choroid plexus in the ventricles of the brain. Its functions include cushioning the brain and spinal cord, removing waste, and maintaining the chemical stability of the CNS. It circulates through the ventricles and around the brain and spinal cord. 7\. Adrenergic Fibers: Adrenergic fibers release norepinephrine (noradrenaline) as a neurotransmitter. These fibers are found in the sympathetic nervous system, where they regulate functions such as heart rate and blood pressure. 8\. Transmission of Impulses Between Neurons: The transmission involves the release of neurotransmitters from the presynaptic neuron into the synaptic cleft. These neurotransmitters bind to receptors on the postsynaptic neuron, generating an excitatory or inhibitory signal. 9\. Functional Unit of Muscle Contraction: The functional unit of muscle contraction is the sarcomere, the segment between two Z-lines in a myofibril. It contains actin and myosin filaments, whose interaction is responsible for muscle contraction. 10\. Rigor Mortis: Rigor mortis is the stiffening of muscles after death. It occurs because ATP is no longer available to detach myosin from actin, causing the muscles to remain contracted. 11\. Threshold Stimulus: The threshold stimulus is the minimal stimulus required to cause a neuron to reach its threshold potential and generate an action potential. 12\. Muscle Characteristics: Skeletal Muscle: Striated, voluntary, multinucleated, and attached to bones. Smooth Muscle: Non-striated, involuntary, single-nucleated, found in organs like the intestines and blood vessels. Cardiac Muscle: Striated, involuntary, single or binucleated, found in the heart. 13\. Neurotransmitter Storage: Neurotransmitters are stored in synaptic vesicles located within the synaptic knobs at the ends of axons in presynaptic neurons. 14\. Action Potential Steps: Action potentials occur in the following sequence: Depolarization: Na+ channels open, and Na+ rushes into the cell. Repolarization: K+ channels open, and K+ exits the cell. Saltatory Conduction: In myelinated axons, the action potential "jumps" from node to node (nodes of Ranvier) for faster conduction. 15\. Synapse: A synapse is the junction between two neurons or between a neuron and another cell type (e.g., muscle), where neurotransmitters are released to transmit signals. 16\. Somatic and Autonomic Nervous Systems: Somatic Nervous System (SNS): Controls voluntary muscle movements and connects the CNS to skeletal muscles. Autonomic Nervous System (ANS): Controls involuntary functions like heart rate and digestion, and connects the CNS to smooth muscles, cardiac muscles, and glands. 17\. Striated Skeletal Muscles: Skeletal muscles appear striated due to the arrangement of actin and myosin filaments in sarcomeres, which create visible bands under a microscope. 18\. Events of Muscle Contraction: Excitation: Nerve impulse triggers the release of acetylcholine at the neuromuscular junction. Action Potential Propagation: The impulse travels along the muscle fiber and into the T-tubules. Calcium Release: Calcium ions are released from the sarcoplasmic reticulum. Cross-Bridge Formation: Myosin heads attach to actin, pulling the filaments together and causing contraction. Relaxation: Calcium is reabsorbed, and the muscle relaxes. 19\. Reticular Formation: The reticular formation is involved in regulating wakefulness, sleep cycles, and attention. It also controls some reflexes. 20\. ATP and Creatine Phosphate: Creatine phosphate acts as a quick energy source by donating phosphate to ADP, converting it back to ATP. It helps regenerate ATP during intense muscular activity. 21\. Forebrain Development: The forebrain develops into structures such as the cerebrum, thalamus, and hypothalamus, which are involved in higher brain functions like cognition, emotion, and sensory processing. 22\. Broca's Area: Broca's area is involved in speech production. It is located in the left frontal lobe and helps in forming coherent speech. 23\. Brain Waves: Brain waves record electrical activity in the brain. They vary in frequency and are classified as delta, theta, alpha, and beta waves, each associated with different mental states. 24\. Axon Regeneration Differences: Axons in the PNS can regenerate more effectively than those in the CNS due to the presence of supportive cells like Schwann cells and the absence of inhibitory factors found in the CNS. 25\. Drug Tolerance: Over time, the brain adjusts to neurotransmitter alterations caused by drugs, leading to reduced efficacy of the drug. This is due to receptor desensitization or downregulation. 26\. Myofibrils Composition: Myofibrils are made of repeating units called sarcomeres, composed of actin (thin) and myosin (thick) filaments responsible for muscle contraction. 27\. Bones and Muscles as Mechanical Devices: Bones and muscles function as a lever system in the body, where bones act as levers, joints are pivot points, and muscles provide the force for movement. 28\. Major Parts of the Diencephalon: The diencephalon consists of the thalamus, hypothalamus, epithalamus, and subthalamus. These structures regulate sensory processing, autonomic functions, and emotional responses. 29\. Rapid Conduction in Axons: The most rapid conduction of an impulse occurs in myelinated axons, where the action potential jumps between the nodes of Ranvier. 30\. Meningitis Effects: Meningitis affects the meninges, the protective layers surrounding the brain and spinal cord, causing inflammation and potential damage to the CNS. 31\. Neurons in Neuronal Pools: Interneurons, specifically those involved in processing complex information, organize into neuronal pools to integrate and process signals. 32\. Meningeal Layers: The meninges consist of three layers: Dura Mater: Outermost layer, tough and protective. Arachnoid Mater: Middle layer, contains cerebrospinal fluid. Pia Mater: Innermost layer, adheres closely to the brain and spinal cord. 33\. Partial Sustained Contraction: This is known as tonic contraction, where muscles maintain a steady level of tension, as seen in postural muscles. 34\. Brain Area for Voluntary Movements: The cerebellum coordinates voluntary movements, balance, and fine motor skills. 35\. White and Gray Matter: Gray Matter: Composed of neuron cell bodies, dendrites, and unmyelinated axons, involved in processing and integration. White Matter: Composed of myelinated axons, which transmit signals over long distances. 36\. Dermatome: A dermatome is an area of skin innervated by sensory fibers from a single spinal nerve, helping to localize nerve damage. 37\. Neurotransmitter Release: Presynaptic neurons release neurotransmitters from synaptic vesicles via exocytosis when an action potential reaches the synaptic terminal. 38\. Agonists, Antagonists, and Prime Movers: Agonists: Chemicals that activate receptors to produce a physiological response. Antagonists: Substances that block receptor activity. Prime Movers: Muscles responsible for the primary action in a movement. 39\. When a muscle fiber is exposed to a series of rapid stimuli, individual twitches combine through summation, resulting in a stronger contraction. If the stimuli are frequent enough, this leads to tetanus, a sustained, smooth contraction without relaxation. Here are the answers to the remaining questions: 40\. Reflex Arc Components: Receptor: Detects a stimulus. Sensory Neuron: Sends the signal to the CNS. Integration Center: Processes the information (interneurons in the CNS). Motor Neuron: Sends a response to the effector. Effector: Executes the response, such as a muscle or gland. 41\. Brain Fissures: Longitudinal Fissure: Divides the left and right hemispheres. Central Sulcus: Divides the frontal and parietal lobes. Lateral Fissure (Sylvian Fissure): Separates the temporal lobe from the frontal and parietal lobes. Transverse Fissure: Separates the cerebrum from the cerebellum. 42\. Phrenic Nerve Plexus: The phrenic nerve arises from the cervical plexus (C3-C5) and innervates the diaphragm for breathing. 43\. CNS vs. PNS: CNS: Brain and spinal cord. PNS: Cranial nerves, spinal nerves, and peripheral nerves. 44\. Crossed Extensor Reflex: This reflex complements the withdrawal reflex. For example, if one leg withdraws from a painful stimulus, the other leg extends to maintain balance. 45\. Reflex Functions: Reflexes control involuntary and automatic responses, such as withdrawing from pain, regulating heart rate, and maintaining posture. 46\. Neuron Structure and Function: Dendrites: Receive signals. Cell Body (Soma): Contains the nucleus and processes information. Axon: Conducts impulses to other neurons or effectors. Axon Terminals: Release neurotransmitters. 47\. Muscle Cell Structure and Function: Sarcolemma: Muscle cell membrane. Myofibrils: Contain actin and myosin for contraction. Sarcoplasmic Reticulum: Stores and releases calcium for contraction. 48\. Motor Unit Recruitment: Increasing the number of motor units activated in response to more intense stimulation is called recruitment. 49\. Drugs That Inhibit Monoamine Oxidase: These drugs increase the availability of neurotransmitters like serotonin, norepinephrine, and dopamine, often used to treat depression. 50\. Myelin: What It Is: A lipid-rich sheath surrounding axons. How It's Made: By Schwann cells in the PNS and oligodendrocytes in the CNS. Function: Insulates axons to speed up nerve impulse conduction. 51\. Gray Matter in the Spinal Cord: Gray matter is divided into horns: Anterior Horn: Motor neurons. Posterior Horn: Sensory neurons. Lateral Horn: Autonomic neurons. 52\. Types of Neurons: Bipolar: One axon and one dendrite (e.g., in the retina). Unipolar: Single process splitting into two branches (sensory neurons). Multipolar: Many dendrites, one axon (most CNS neurons). 53\. Acetylcholine Degradation: Acetylcholine is broken down by the enzyme acetylcholinesterase in the synaptic cleft. 54\. Skeletal Muscle and Body Temperature: Skeletal muscles generate heat through contractions, especially during shivering, to maintain body temperature. 55\. Neuron Characteristics: Excitability: Respond to stimuli. Conductivity: Transmit electrical impulses. Secretion: Release neurotransmitters. 56\. Aphasia: Aphasia is a language disorder caused by brain damage, affecting speech, comprehension, or both. Commonly associated with damage to Broca's or Wernicke's areas. 57\. Cerebral Association Areas: These areas integrate sensory input with memory, reasoning, and emotions to enable complex tasks like problem-solving and planning. 58\. Functional Connection Between Neurons: The synapse serves as the functional connection between neurons, allowing transmission of signals via neurotransmitters. 59\. Functions of Neurons: Sensory Neurons: Carry signals to the CNS. Motor Neurons: Carry signals from the CNS to effectors. Interneurons: Integrate information within the CNS. 60\. Muscle Origin and Insertion: Origin: The fixed attachment point. Insertion: The movable attachment point during muscle contraction. 61\. CNS and PNS Cells: CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells. PNS: Schwann cells, satellite cells. 62\. Spinal Nerve Injuries: These can result from trauma, compression (e.g., herniated disc), or inflammation, potentially causing motor or sensory deficits. 63\. Neuromuscular Junction (NMJ): The NMJ is where a motor neuron meets a muscle fiber. Acetylcholine is released here to trigger muscle contraction. 64\. Tendon, Fascia, and Aponeurosis: Tendon: Connects muscle to bone. Fascia: Connective tissue surrounding muscles. Aponeurosis: Flat sheet of connective tissue attaching muscles. 65\. Motor Unit: A motor unit consists of a motor neuron and all the muscle fibers it innervates. 66\. Threshold Stimulus: The minimum stimulus needed to depolarize a membrane and generate an action potential. 67\. Convergence and Divergence: Convergence: Multiple neurons send signals to one neuron, integrating information. Divergence: One neuron sends signals to multiple neurons, amplifying the signal. 68\. Connective Tissue Layers: Muscle Cells: Epimysium (entire muscle), perimysium (fascicles), endomysium (individual fibers). Nerve Cells: Epineurium (entire nerve), perineurium (fascicles), endoneurium (individual fibers). 69\. Steps After Threshold Potential: Sodium channels open (depolarization). Potassium channels open (repolarization). Sodium-potassium pump restores resting potential. 70\. Neuron Cell Bodies in the PNS: Clusters of neuron cell bodies in the PNS are called ganglia. 71\. Basal Ganglia Location and Function: Located in the cerebrum, the basal ganglia control voluntary motor movements, procedural learning, and habits. 72\. Definitions: Cerebral Cortex: The outer layer of gray matter involved in higher brain functions. Hemispheric Dominance: Refers to one hemisphere (usually left) controlling language and analytical tasks. Limbic System: Regulates emotions and memory. 73\. Na+ and K+ in Neurons: During depolarization, Na+ enters the neuron. During repolarization, K+ exits the neuron. The sodium-potassium pump restores ionic balance.