Nervous System Anatomy Final Study Guide PDF

Structural Divisions of the Nervous System - Central Nervous System: ​ Structurally consists if the brain and spinal cord ​ Integrates and processes nervous information ​ the brain and spinal cord are covered by protective layers called the meninges Peripheral Nervous System: ​ Structura...

Structural Divisions of the Nervous System - Central Nervous System: ​ Structurally consists if the brain and spinal cord ​ Integrates and processes nervous information ​ the brain and spinal cord are covered by protective layers called the meninges Peripheral Nervous System: ​ Structurally consists of all neural tissue found outside of the CNS ​ Carries information from the body to the CNS ​ Receives information from the CNS to cause a response in the body ​ Everything outside of the meninges is part of the PNS Functional Division of the Nervous System - ​ Two functional divisions: Motor & Sensory nervous system– both systems work together to do the following: ​ Collect information (stimuli) about the internal and external environments ​ Process information to determine a response (if needed) ​ Initiate a response based on the collected information Motor (Efferent) Nervous System - ​ Responsible for carrying motor information away from the CNS towards the PNS ​ Carries motor impulses from the brain or spinal cord → through nerves → muscle tissue throughout the body ​ Impulses that contribute to a movement are carried by nerves in the PNS ​ Efferent: causes muscle tissue to contract ​ Carries Somatic and Visceral information Sensory (Afferent) Nervous System - ​ Responsible for collecting sensory information (called stimuli, e.g., pain) because it carries info from peripheral to central NS ​ Receptors sense stimuli, e.g., temperature or pain → stimuli is transmitted to the CNS ​ Initiates different movements (not the actual movement) ​ Afferent: Pain, touch, temperature ​ Carries Somatic and Visceral information Important Definitions - ​ Ganglia: group of neuron cell bodies in the PNS ​ Nerve: Many axons bundled together in the PNS ​ Synapse: junction between a neuron and another cell allowing the transmission of information ​ Sensory (afferent) neurons: Carry signals from the body to the central nervous system, carry afferent fibers ​ Motor (efferent) neurons: Send signals from the central nervous system to muscles or glands to cause movement or other actions, carry efferent fibers ​ Interneurons (also pyramidal): Connect neurons within the central nervous system to process and relay information (multipolar) ​ Afferent Fiber: Carry sensory information from sensory receptors toward the central nervous system (CNS) (brain and spinal cord) ​ Efferent Fiber: Carry motor commands from the CNS to muscles and glands to initiate actions (such as movement) ​ Neuroglia: supporting cells of the nervous system, do not transmit electrical impulses like neurons, but perform their own essential roles Neuroglial Cells in the CNS - Microglial cells: Act as the immune cells of the CNS, removing damaged neurons, infectious agents, and preventing inflammation. They are sensitive to foreign materials and are the first line of defence against pathogens Astrocytes: The most common glial cells in the CNS, they: ​ Contribute to the blood–brain barrier ​ Regulate neurotransmitter levels in the synaptic cleft ​ Maintain the physical structure of the brain by holding neurons in place ​ Store glycogen and provide energy to neurons ​ Regulate the extracellular environment, including ion concentrations ​ Stimulate oligodendrocytes to produce myelin ​ Assist in repairing damaged nerve cells Ependymal cells: Line the brain's ventricles and help produce and circulate cerebrospinal fluid, contributing to the formation of the choroid plexus Oligodendrocytes: Provide support and insulation to axons by forming the myelin sheath. One oligodendrocytes can myelinate multiple axons. They also produce growth-inhibitory proteins that prevent regeneration of damaged axons in the CNS Oligodendrocyte progenitor cells (OPCs): Immature cells that can differentiate into oligodendrocytes, neurons, or astrocytes. They respond to damage in the CNS and play a role in repair Neuroglial Cells in the PNS - Schwann cells (neurolemmocytes): ​ Long, flat cells that wrap around axons in the PNS ​ Form the myelin sheath, which insulates axons and enhances signal transmission  Satellite cells: ​ Flat cells that surround neuron cell bodies in ganglia within the PNS ​ Separate cell bodies from interstitial fluid and regulate the exchange of nutrients and waste between neurons and their environment Type of Neuron Function Tissues/Structures Innervated Somatic Carry motor commands from the - Skeletal muscles (responsible for Efferent CNS to skeletal muscles voluntary movements such as Neurons (voluntary control) walking, talking, etc.) - Control of muscle contraction for movement (e.g., limbs, face, diaphragm) Somatic Afferent Carry sensory information from the - Skin (touch, temperature, Neurons sensory receptors to the CNS pain, pressure) - Muscles (proprioception or body position) - Joints (sensory feedback from joints) - Skeletal structures Visceral Carry motor commands from the CNS - Smooth muscles (e.g., in Efferent to smooth muscle, cardiac muscle, and the walls of blood vessels, Neurons glands (involuntary control) digestive organs) - Cardiac muscle (heart) - Glands (e.g., salivary glands, sweat glands) Visceral Afferent Carry sensory information from - Internal organs (e.g., heart, Neurons internal organs to the CNS lungs, intestines, bladder) - Blood vessels (e.g., stretch receptors in blood vessels) - Viscera (sensory feedback from internal organs) Chemical Synapse: ​ How it works: A chemical synapse involves the release of neurotransmitters (chemicals) from synaptic vesicles in the presynaptic neuron. These neurotransmitters cross the synaptic cleft (the small gap between neurons) and bind to receptors on the postsynaptic cell (another neuron, muscle, or gland). ​ Impulses: The signal is transmitted in one direction: from the presynaptic neuron to the postsynaptic cell. ​ Example: The neuromuscular junction (where a motor neuron connects to a muscle), synapses between neurons, and synapses in the central nervous system. Electrical Synapse: ​ How it works: In an electrical synapse, the presynaptic and postsynaptic cells are directly connected by gap junctions (protein channels). These allow electrical signals (ions) to pass directly from one cell to the next. ​ Impulses: The electrical signal can travel in both directions, allowing for faster and synchronized communication. ​ Example: Electrical synapses are commonly found in smooth muscle, cardiac muscle, and some neurons. They help ensure coordinated contractions, like in the heart or digestive system Q: What is the name of the synapse that occurs between a motor neuron and skeletal muscle? A: Neuromuscular Junction Somatic Nervous System (SNS) - Main Functions ​ Voluntary Control: Regulates skeletal muscle movements. ​ Sensory Input: Relays information about touch, pain, temperature, and position (proprioception) from the body to the central nervous system (CNS). Locations ​ Sensory Pathways: ○​ Found in peripheral nerves, connecting sensory receptors to the CNS (spinal cord and brain). ​ Motor Pathways: ○​ Originate in the CNS (motor cortex or spinal cord) and extend to skeletal muscles. Types of Sensory Receptors: 1.​ Mechanoreceptors: ○​ Detect touch, pressure, vibration, and stretch. ○​ Example: Pacinian corpuscles (pressure) and Meissner’s corpuscles (light touch). 2.​ Thermoreceptors: ○​ Detect changes in temperature. ○​ Example: Free nerve endings. 3.​ Nociceptors: ○​ Detect pain from tissue damage or extreme conditions. ○​ Example: Free nerve endings. 4.​ Proprioceptors: ○​ Detect body position and movement. ○​ Example: Muscle spindles and Golgi tendon organs. Effector Organs - ​ Skeletal Muscles: ○​ Respond to motor commands for voluntary movement Somatic Sensory Pathways - ​ Function: Transmit sensations we are conscious of, such as light touch, proprioception (body position), pain, and temperature. ​ Common Structure: Both pathways involve three sensory neurons: 1.​ 1st-Order Neuron: Starts at the sensory receptor and enters the spinal cord. 2.​ 2nd-Order Neuron: Decussates (crosses to the opposite side) and synapse at thalamus. 3.​ 3rd-Order Neuron: Travels from the thalamus to the primary somatosensory cortex, where the brain interprets the sensory information. Dorsal Column (Medial Lemniscus) Pathway ​ Sensory Information Transmitted: 1.​ Proprioception 2.​ Fine touch  3.​ Pressure ​ Pathway Summary: 1.​ Starts at sensory receptors. 2.​ Decussates and synapses in the medulla oblongata. 3.​ Synapses in the thalamus. 4.​ Ends at the primary somatosensory cortex. ​ Key Point: Provides precise localization of stimuli and detailed sensation. Anterolateral Pathway: ​ Sensory Information Transmitted: ○​ Pain ○​ Temperature ​ Pathway Summary: ○​ Starts at sensory receptors. ○​ Decussates and synapses in the dorsal horn of the spinal cord at the level of entry. ○​ Synapses in the thalamus. ○​ Ends at the primary somatosensory cortex. ​ Tracts: ○​ Anterior Tract: Sensory signals from the upper parts of the body (including the trunk). ○​ Lateral Tract: Sensory signals from the lower half of the body (including the trunk). ***Role of the Thalamus ​ Acts as a relay center for sensory signals. ​ Directs input from ascending tracts (e.g., dorsal column and anterolateral pathways) to specific regions of the primary somatosensory cortex. ​ Helps identify the nature and specific location of stimuli. Sensory vs Motor Pathways - Feature Motor Pathway Sensory Pathway Function Transmits motor signals Transmits sensory signals to muscles from skin and muscles Primary Rami Larger, contains motor Smaller, contains Size axons sensory axons Pathway Involves nerve plexuses Travels horizontally Course (brachial, lumbosacral) from spinal nerve to target Target Structures Skeletal muscles Skin and muscles (sensory input) Example Musculocutaneous nerve Sensation from skin over to biceps brachii erector spinae muscles Dorsal Root Not involved Contains sensory neuron Ganglion cell bodies Grey vs White Matter - Feature Gray Matter White Matter Location Central region of spinal Surrounds gray matter in cord spinal cord Function Processing and Transmitting information integrating information (ascending and descending tracts) Composition Contains nuclei (cell bodies Contains axons (nerve of neurons) fibers) Columns No columns, contains horns Organized into (posterior, lateral, anterior) columns (dorsal, anterior, lateral) Type of Sensory and motor cell Axons of sensory and Neurons bodies motor neurons Key Dorsal horns (sensory Dorsal column (sensory Structures nuclei), lateral tracts), anterior/lateral horns(autonomic columns(motor & sensory neurons), ventral horns tracts), anterior white (motor nuclei) commissure(decussating neurons) Somatic Motor Pathways - General Characteristics: ​ Pyramidal tracts and corticobulbar tracts are responsible for muscle contraction. ​ Both pathways are adjusted by the basal nuclei and cerebellum to fine-tune movement. ​ The pathways involve 2 motor neurons: ○​ Upper motor neuron (UMN): Originates in the primary motor cortex. ○​ Lower motor neuron (LMN): Ends at the skeletal muscle. 1. Lateral Corticospinal Tract (Majority of fibers) ​ Muscles Innervated: ○​ Appendicular muscles (limbs), e.g., arms, legs. ​ Upper Motor Neuron (UMN): ○​ Origin: Primary motor cortex (precentral gyrus). ○​ Decussation: Medulla oblongata (pyramids). ​ Lower Motor Neuron (LMN): ○​ Synapse: Ventral horn of the spinal cord. ○​ Innervation: Appendicular muscles (e.g., muscles of the arms and legs). 2. Ventral (Anterior) Corticospinal Tract (minority of fibers) ​ Muscles Innervated: ○​ Axial muscles (trunk/core), e.g., muscles involved in posture and balance. ​ Upper Motor Neuron (UMN): ○​ Origin: Primary motor cortex. ○​ Decussation: Decussates and synapses at the level of the ventral horn of the spinal cord (does not cross in the medulla like the lateral tract). ​ Lower Motor Neuron (LMN): ○​ Synapse: Ventral horn of the spinal cord. ○​ Innervation: Axial muscles (e.g., muscles of the trunk and posture). Spinal Cord Injuries - ​ Injuries to spinal cord inhibit the passage of electrical impulses in both directions at level of injury Reflex Arcs - Definition: A reflex arc is the basic functional unit of the nervous system, allowing for a quick response to a stimulus without involving the brain Target: Organs or muscles that respond to the motor neuron  1.​ Touch hot object – activates a pain receptor (nociceptor). 2.​ Information travels along a sensory neuron to the spinal cord. 3.​ The sensory neuron enters the spinal cord through the dorsal root. At the Spinal Cord: 1.​ Information splits: ○​ Immediate response: Synapses directly with a motor neuron to quickly pull your hand away. ○​ Slow response: Synapses with interneurons that send the information to the brain for further processing (this happens later). Motor Response: 1.​ The motor neuron exits the spinal cord via the ventral root. 2.​ The motor neuron travels to an effector muscle (e.g., arm muscles). 3.​ The muscle contracts to pull your hand away. 4.​ OUCH! – You feel pain after the action is taken Overview of the Autonomic Nervous System (ANS) ​ The ANS regulates involuntary body functions such as heart rate, blood pressure, digestion, and respiration. ​ It operates below the level of conscious control, working through reflexes and feedback mechanisms. ​ The ANS is divided into three divisions: Sympathetic, Parasympathetic, and Enteric Nervous System. Divisions of the Autonomic Nervous System: 1.​ Sympathetic Division ○​ Main Function: "Fight or flight" response. Prepares the body for stressful or emergency situations. ○​ Key Functions: ​ Increases heart rate and blood pressure. ​ Dilates pupils.  ​ Redirects blood flow to muscles. ​ Stimulates the release of glucose for energy. ​ Inhibits digestive processes. ○​ Sensory Receptors: Located throughout the body, including skin, muscles, and internal organs, particularly for monitoring pain, temperature, and pressure. ○​ Effectors: Smooth muscles, cardiac muscles, and glands (e.g., sweat glands, adrenal glands). 2.​ Parasympathetic Division ○​ Main Function: "Rest and digest" response. Promotes relaxation, energy conservation, and recovery after stress. ○​ Key Functions: ​ Decreases heart rate and blood pressure. ​ Stimulates digestion and nutrient absorption. ​ Promotes the storage of energy (e.g., glycogen storage). ​ Constricts pupils. ○​ Sensory Receptors: Found in organs involved in digestive processes, blood vessels, and other internal organs. ○​ Effectors: Same as the sympathetic division: smooth muscles, cardiac muscles, and glands (e.g., salivary glands, digestive glands). 3.​ Enteric Nervous System ○​ Main Function: Often considered the "third division," it controls the gastrointestinal (GI) tract. ○​ Key Functions: ​ Regulates the movement of food through the digestive tract (motility). ​ Controls the secretion of digestive enzymes. ​ Independently regulates digestive processes, though it communicates with the sympathetic and parasympathetic divisions. ○​ Sensory Receptors: Located within the walls of the GI tract for monitoring the physical state of food, chemical composition, and the condition of the digestive environment. ○​ Effectors: Smooth muscle of the digestive system, digestive glands, and blood vessels supplying the GI tract Sympathetic Ganglia Locations - 1.​ Sympathetic Trunk Ganglia (Paravertebral Ganglia) ○​ Location: 23 pairs along both sides of the vertebral column. ○​ Function: Innervate the head, body wall, thoracic cavity, and limbs 2.​ Collateral Ganglia (Prevertebral Ganglia) ○​ Location: Located in the abdominopelvic cavity. ○​ Function: Sympathetic preganglionic fibers from T1-T5 exit the sympathetic chain and form splanchnic nerves, which synapse with postganglionic neurons in the collateral ganglia. These ganglia include: ​ Celiac ganglia ​ Superior mesenteric ganglia  ​ Inferior mesenteric ganglia ○​ Function: Postganglionic fibers from these ganglia innervate viscera within the abdominopelvic cavity. 3.​ Adrenal Medulla (Modified Sympathetic Ganglion) ○​ Location: Located within the adrenal glands. ○​ Function: Preganglionic fibers originating from T5-T8 synapse in the adrenal medulla, triggering the release of neurotransmitters (e.g., epinephrine (E) and norepinephrine (NE)) into the blood. ○​ Significance: This release of neurotransmitters enhances the body's fight or flight response, increasing heart rate, blood pressure, and energy availability Difference Between Intramural and Terminal Ganglia in the PNS - 1.​ Terminal Ganglia ○​ Location: Near the target organ, typically outside the organ. ○​ Function: Postganglionic neurons synapse here and then travel to innervate the target organ (e.g., heart, digestive organs). ○​ Example: The ganglia of the parasympathetic system that are found near organs such as the heart or lungs. 2.​ Intramural Ganglia ○​ Location: Located within the target organ itself. ○​ Function: Postganglionic neurons synapse directly within the target organ, and their axons extend to the tissues being innervated. ○​ Example: Ganglia found within the walls of organs like the digestive system (e.g., enteric ganglia in the GI tract)  ​ CN III (oculomotor nerve): pupil constriction & lens accommodation ​ CN VII (facial nerve): increase secretion from glands in nose & mouth ​ CN IX (glossopharyngeal nerve): increase secretion from glands in mouth ​ CN X (vagus nerve): heart rate, rate of respiration, secretion of digestive enzymes ​ Lateral grey horn of S2-S4 (pelvic nerves): many abdominopelvic organs, e.g., bladder, sex organs, rectum Sympathetic vs. Parasympathetic Nervous System: Innervation of Key Organs - 1. Heart ​ Sympathetic Nervous System (SNS) ○​ Effect: Increases heart rate (chronotropic effect), increases contractility (ionotropic effect), and raises blood pressure. ○​ Mechanism: Releases norepinephrine, which binds to beta-1 adrenergic receptors. ○​ Role: Prepares for physical activity or stress ("fight or flight"). ​ Parasympathetic Nervous System (PNS) ○​ Effect: Decreases heart rate and lowers blood pressure. ○​ Mechanism: Releases acetylcholine, which binds to muscarinic receptors. ○​ Role: Promotes relaxation and rest ("rest and digest"). 2. Lungs ​ Sympathetic Nervous System (SNS) ○​ Effect: Dilates bronchial airways (bronchodilation) to increase airflow. ○​ Mechanism: Stimulation of beta-2 adrenergic receptors causes smooth muscle relaxation. ○​ Role: Increases oxygen supply during physical activity or stress. ​ Parasympathetic Nervous System (PNS) ○​ Effect: Constricts bronchial airways (bronchoconstriction). ○​ Mechanism: Acetylcholine binds to muscarinic receptors, causing smooth muscle contraction. ○​ Role: Supports normal breathing during rest. 3. Blood Vessels ​ Sympathetic Nervous System (SNS) ○​ Effect: Causes vasoconstriction in most blood vessels to divert blood to essential organs (e.g., muscles, heart). ○​ Mechanism: Stimulation of alpha-1 adrenergic receptors causes blood vessel constriction. ○​ Role: Shunts blood to vital organs during stress ("fight or flight"). ​ Parasympathetic Nervous System (PNS) ○​ Effect: Limited effect on blood vessels, but may cause vasodilation in digestive organs. ○​ Mechanism: Acetylcholine indirectly influences vasodilation. ○​ Role: Promotes blood flow to digestive organs during rest. 4. Gastrointestinal (GI) Tract ​ Sympathetic Nervous System (SNS) ○​ Effect: Inhibits digestion by reducing motility and secretion in the GI tract. ○​ Mechanism: Releases norepinephrine, which decreases peristalsis and digestive enzyme secretion. ○​ Role: Diverts energy from digestion during stress or physical activity. ​ Parasympathetic Nervous System (PNS) ○​ Effect: Stimulates digestion by increasing motility, enzyme secretion, and muscle contractions. ○​ Mechanism: Releases acetylcholine, enhancing peristalsis and digestive enzyme production. ○​ Role: Supports digestion and energy absorption during rest. 5. Urinary System ​ Sympathetic Nervous System (SNS) ○​ Effect: Inhibits urination and contracts bladder sphincter. ○​ Mechanism: Norepinephrine causes bladder sphincter contraction and reduces urine flow. ○​ Role: Reduces urination to conserve energy and fluids during stress. ​ Parasympathetic Nervous System (PNS) ○​ Effect: Promotes urination by stimulating bladder contraction and relaxing the sphincter. ○​ Mechanism: Acetylcholine causes detrusor muscle contraction and sphincter relaxation. ○​ Role: Facilitates normal urination during rest. Comparison of the Somatic and Autonomic Nervous Systems - Characteristic Somatic Nervous Autonomic Nervous System (SNS) System (ANS) Site of CNS (motor cortex, CNS (brainstem, Origination spinal cord) spinal cord) Number of One neuron (direct from Two neurons (pre- Neurons CNS to skeletal muscles) and postganglionic neurons) Effectors Skeletal muscles Smooth muscles, cardiac (voluntary movement) muscles, glands (involuntary functions) Key Voluntary control Involuntary control over Functions over body movement heart rate, digestion, and respiration Control Type Voluntary (conscious Involuntary control) (unconscious control) Function Role of the Hypothalamus Autonomic Regulates heart rate, blood pressure, respiration, and digestion Control through the ANS Endocrine System Controls the pituitary gland, influencing hormone release Coordination that regulates other glands Behavioral Drives Stimulates thirst, hunger, and sexual desire based on internal signals Temperature Regulates body temperature via thermoregulatory Regulation mechanisms (sweating, shivering, etc.) Circadian Coordinates sleep-wake cycles and other daily physiological Rhythms rhythms through the SCN Limbic System Contributes to emotional responses and memory by interacting Interaction with the amygdala and hippocampus