Nervous System PDF

1 NERVOUS SYSTEM Cytology of Nervous Tissue (Types) 1. Neurons: Specialized for communication (transmitting electrical signals, synaptic transmission). o Structure: Dendrites, cell body (soma), axon hillock, node of Ranvier, axon, myelin shea...

1 NERVOUS SYSTEM Cytology of Nervous Tissue (Types) 1. Neurons: Specialized for communication (transmitting electrical signals, synaptic transmission). o Structure: Dendrites, cell body (soma), axon hillock, node of Ranvier, axon, myelin sheath, axon terminal. o Classification by Shape: Unipolar neuron, bipolar neuron, multipolar neuron.  2 o Classification by Function: ▪ Sensory neuron: Afferent. Sensory neuron from periphery processed and interpreted. ▪ Interneuron: Integration neuron that takes place in the CNS. ▪ Motor neuron: Efferent. Motor branch works with effector organs. 2. Glial Cells: Support and protect neurons. o Astrocytes: Support neurons, form blood-brain barrier. o Oligodendrocytes: Myelinate CNS axons. o Microglia: Immune defense in CNS, remove debris, microbes and damaged nervous tissue. o Ependymal Cells: Line ventricles, produce cerebrospinal fluid and form choroid plexus. o Schwann Cells: Myelinate PNS axons. o Satellite Cells: Surround cell bodies of PNS neurons. 3. Myelination: o CNS Myelination – Oligodendrocytes. o PNS Myelination – Schwann cells. o Functions: Increases conduction speed of nerve impulses. Cranial Meninges 1. Layers of Meninges: o Dura Mater: Outer tough layer. Dense irregular connective tissue. Includes periosteal layer (closest to bone) and meningeal layer (deeper). o Arachnoid Mater: Middle layer with spider-web-like structures. o Pia Mater: Thin, delicate deepest layer closely adhering to the brain. Highly vascularized.  3 2. Meningeal Spaces: o Epidural Space: Between dura mater and skull bones which contains the arteries and veins. Healthy epidural space has no real space. o Subdural Space: Between dura mater and arachnoid mater. o Subarachnoid Space: Between arachnoid mater and pia mater, contains cerebrospinal fluid. 3. Clinical Relevance: o Epidural Hematoma: Space between dura mater and skull bones that may fill with fluid or blood due to trauma or disease. o Subdural Hematoma: Potential space between arachnoid mater and dura mater that can fill with blood or fluid. o Meningitis: Inflammation of the meninges. Can be dangerous and even life-threatening. Cerebrospinal Fluid 1. Functions of CSF: PENB o Protection: Liquid cushion that protects neural structures from movement. o Environmental stability: Exchange nutrients and chemicals between blood and nerve tissue. Remove waste products from the brain. Protect nerve tissue from chemical fluctuations. o Neural signaling: Chemical environment created that facilitates action potentials. o Buoyancy: Brain floats in the CSF. It supports more than 95% of its weight preventing it from sinking. 2. Production and Circulation: o Produced in choroid plexus within ventricles. o CSF circulation: Lateral ventricle – third ventricle – fourth ventricle – subarachnoid space – circulates down the spinal cord and brain.  4 Cerebellum (“Little Brain”) 1. Functions: o Receives a copy of the descending input from the cerebrum to the spinal cord. Compares this sensory feedback input through the medulla and sends output through the midbrain that can correct motor commands for coordination. o Important role in integration of motor output and sensory perception. Diencephalon 1. Thalamus: Gateway to consciousness by filtering what is important, helps with focus, decides what information to send to cerebrum. Sensory impulses go through the thalamus before reaching the cerebral cortex (relay station). 2. Hypothalamus: Bridge between the nervous system and the endocrine system. o Homeostasis – Autonomic functions/ANS (heart rate, blood pressure, digestion, respiration). a) Body temperature regulation. b) Emotional response. c) Regulation of food intake. d) Regulation of water balance and thirst. e) Regulation of sleep/wake cycle. o Controls the endocrine system.  5 3. Epithalamus: Contains the third ventricle, habenular nucleus, and pineal gland (endocrine gland). Secretes melatonin to regulate sleep/wake cycle (circadian rhythm). Brainstem – Medulla Oblongata 1. Functions: o Cardiac centre: Controls heart rate and adjusts myocardial contraction. o Vasomotor centre: Controls the diameter of blood vessels to regulate blood pressure. o Respiratory centre: Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG) control the rate and depth of breathing and with the pneumotaxic centre of the pons, maintain the respiratory rhythm. 2. Anatomy: o Located at the base of the brain, continuous with the spinal cord. o Houses nuclei for cranial nerves (e.g., IX, X, XI, XII).  6 Cranial Nerves – Names and Functions OOO Talk To A FlaVorful GuaVAH o CN I (Olfactory): Smell. o CN II (Optic): Vision. o CN III (Oculomotor): Eye movement, pupil constriction. o CN IV (Trochlear): Eye movement (superior oblique muscle). o CN V (Trigeminal): Sensation from face; motor for chewing. o CN VI (Abducens): Eye movement (lateral rectus muscle). o CN VII (Facial): Facial expression, taste (anterior 2/3 of the tongue). o CN VIII (Vestibulocochlear): Hearing and balance. o CN IX (Glossopharyngeal): Taste (posterior 1/3 of tongue), swallowing. o CN X (Vagus): Parasympathetic control over heart, lungs, and digestive organs. o CN XI (Accessory): Shoulder shrugging, head turning. o CN XII (Hypoglossal): Tongue movement.  7 CN X – Vagus Nerve 1. Function: o Longest cranial nerve. Innervate thoracic and abdominal organs. ▪ Thoracic organs: Increases mucous production, decreases airway diameter, and decreases heart rate and force of contraction. ▪ Abdominal organs: Increases smooth muscle motility and secretory activity in the digestive tract. 2. Parasympathetic Role: o It is a key component of the parasympathetic nervous system, promoting "rest and digest" activities (eg., slowing heart rate, promoting digestion, regulating respiratory rate). Spinal Nerve Formation - Formed when dorsal (posterior) roots + ventral (anterior) roots come together. o Dorsal root – carries afferent information (sensory) from body to spinal cord. o Ventral root – carries efferent information (motor) from spinal cord to muscles and glands. - Play important role in the communication of motor and sensory information between the body and the CNS. - 31 pairs of spinal nerves. Spinal nerve exits in the vertebral canal: 1. Cervical Region: There are 8 cervical spinal nerves (C1–C8). The first seven cervical spinal nerves exit above the corresponding cervical vertebrae (e.g., C1 exits above the first cervical vertebra, C2 exits above C2, and so on). The eighth cervical nerve (C8) exits below the seventh cervical vertebra (since there are only 7 cervical vertebrae). Therefore, C8 is the only spinal nerve that exits below its corresponding vertebra. 2. Thoracic, Lumbar, and Sacral Regions: In the thoracic, lumbar, and sacral regions, the spinal nerves exit through the intervertebral foramina below the corresponding vertebrae (e.g., the T1 nerve exits below the first thoracic vertebra). These nerves continue to exit sequentially, with thoracic nerves T1–T12, lumbar nerves L1– L5, sacral nerves S1–S5, and the coccygeal nerve (Co1).  8 Dermatomes and Referred Pain 1. Dermatomes: o Specific segment of the skin supplied by a single spinal nerve (except C1). 2. Referred Pain: o Pain felt in a region of the body that is not the actual source of the pain, often because of overlapping sensory pathways (e.g., heart attack pain felt in the left arm). o Appendicitis – referred pain to the T10 dermatome at the umbilicus region instead of the abdominopelvic region. Afferent Division vs. Efferent Division FEATURE AFFERENT DIVISION EFFERENT DIVISION PRIMARY FUNCTION Sensory input (brings information to Motor output (sends commands from the CNS) CNS to effectors) NEURONS Sensory neurons (unipolar or bipolar) Motor neurons (multipolar) RECEPTORS/ Sensory receptors (e.g., Effectors: muscles (skeletal, smooth, EFFECTORS thermoreceptors, cardiac) and glands mechanoreceptors) TYPE OF CONTROL No direct control (provides Direct control of muscles and glands information to the CNS) (voluntary/involuntary) EXAMPLE Detecting heat, pressure, pain, and Movement of skeletal muscles, heart proprioception rate regulation, digestion  9 Autonomic Nervous System vs. Somatic Nervous System FEATURE SOMATIC NERVOUS SYSTEM (SNS) AUTONOMIC NERVOUS SYSTEM (ANS) CONTROL Voluntary (conscious control of Involuntary (controls internal organs and skeletal muscles) smooth muscle) NEURONAL Single motor neuron from CNS to Two-neuron chain (preganglionic and PATHWAY skeletal muscle postganglionic neurons) EFFECTORS Skeletal muscles Smooth muscle, cardiac muscle, glands NEUROTRANSMITTER Acetylcholine (ACh) at ACh (preganglionic), NE or ACh neuromuscular junction (postganglionic) FUNCTION Voluntary movement and somatic Regulation of internal processes (e.g., sensation (e.g., touch, pain) heart rate, digestion) DIVISIONS One system (motor and sensory) Sympathetic and parasympathetic  10 Sympathetic and Parasympathetic Systems 1. Sympathetic Nervous System: o Functions: Maintains homeostasis during stress, emergency. "Fight or flight" response, increases heart rate, dilates airways, inhibits digestion. o Anatomy: Originates in thoracolumbar region. ▪ Preganglionic fibers: Short axon, many branches, release acetylcholine. ▪ Ganglia: Closer to spinal cord. Faster signal to trigger action (fight-or-flight response). ▪ Postganglionic fibers: Long axon, release norepinephrine. 2. Parasympathetic Nervous System: o Functions: Maintains homeostasis when resting. "Rest and digest" response, slows heart rate, promotes digestion. o Anatomy: Originates in craniosacral region. ▪ Preganglionic fibers: Long axon, few branches, release acetylcholine. ▪ Ganglia: Close to effector organ (target). More specific, strategic signals since there is no need to alert other organs. ▪ Postganglionic fibers: Short axon, release acetylcholine.  11 Autonomic Plexus Cardiac Plexus: Innervates the heart. o Sympathetic – Increases heart rate and blood pressure. o Parasympathetic – Decreases heart rate. Pulmonary Plexus: Innervates bronchi and lungs. o Sympathetic – Bronchodilation (widen airways) and increases respiratory rate. o Parasympathetic – Bronchoconstriction (narrowed airways) and slows down respiratory rate. Esophageal Plexus: Innervates the esophagus. o Sympathetic – Inhibits peristalsis (movement of food through esophagus). o Parasympathetic – Stimulates peristalsis. Abdominal Aortic Plexus: Innervates abdominal organs (stomach, small intestine, liver, pancreas, kidneys). o Sympathetic – Inhibits digestion, reduces blood flow to digestive organs, and stimulates release of glucose. o Parasympathetic – Stimulates digestion and increases blood flow to digestive organs. Hypogastric Plexus: Innervates reproductive organs, bladder, rectum, and colon. o Sympathetic – Inhibits digestive functions, vasoconstriction of blood vessel in pelvic organs, and stimulates ejaculation in males. o Parasympathetic – Stimulates digestive functions, stimulates urination, stimulates sexual arousal.  12 Neurotransmitters 1. Types of Neurotransmitters: o Acetylcholine (ACh): Primarily used by cholinergic neurons. Released by all preganglionic neurons, parasympathetic postganglionic neurons. o Norepinephrine (NE): Primarily used by adrenergic neurons. Released by most sympathetic postganglionic neurons. Neurotransmitter Neuron Receptors Location Effects Type Acetylcholine Cholinergic Nicotinic Ganglia (synapse Excitatory effect at (ACh) receptors between pre- and ganglia postganglionic neurons) Muscarinic Target organs (heart, Excitatory or Inhibitory receptors smooth muscles, based on organ glands) Norepinephrine Adrenergic Alpha (α1, Smooth muscle Vasoconstriction, pupil (NE) α2) receptors (blood vessels, eyes) dilation, inhibition of & presynaptic norepinephrine release terminals Beta (β1, β2, Heart, smooth Heart rate increase, β3) receptors muscles (lungs, bronchodilation, blood vessels) vasodilation, lipolysis  13 Sensory Nervous System Properties TAR 1. Mechanoreceptors: Detect pressure, touch, vibration. 2. Thermoreceptors: Detect temperature. 3. Nociceptors: Detect pain. 4. Photoreceptors: Detect light (vision). Tactile Receptors - Most numerous Sensory receptors - Mechanoreceptors: react to touch, pressure and vibration - Located in the dermis and subcutaneous layers - Range from simple to complex structures. - Unencapsulated Tactile Receptors: simple in structure, with no connective tissue wrapping them: o Free nerve endings: epidermis, detects primarily temperature and pain o Tactile discs: epidermis, detects light touch o Root hair plexuses: dermis, detects movement of the hair - Encapsulated Tactile Receptors: surrounded by another structure (connective tissue or glial cells) o End bulb: dermis, mucous membranes. Detects light pressure and low-frequency vibration o Lamellated Corpuscle: Dermis, subcutaneous tissue, synovial membranes and some visceras. Detects deep pressure and high-frequency vibration o Bulbous Corpuscle: dermis, subcutaneous and joints capsules. Detects deep pressure and skin distortion o Tactile corpuscle: Dermal papillae (lips, palms, eyelids, nipples and genitals). Detects discriminative textures and shapes, light touch  14 Special Senses 1. Gustation (Taste): The sense of taste – detect the characteristics of what we eat and drink. - Gustatory cells: chemoreceptors located within taste buds on the tongue and soft palate. - Ability to detect taste declines after 50. - Papillae: dorsal surface of the tongue are epithelial and connective tissue elevation. Contain taste buds. o Filiform: anterior two-thirds of the tongue. Assist with texture detection. o Fungiform: tip and sides of the tongue. Contain few taste buds. o Foliate: not well developed in humans. The lateral side of the tongue has few taste buds during infancy and early childhood. o Vallate: least numerous (10-12) but the largest. Inverted V at the posterior surface of the tongue. House most of our taste buds. - Taste buds – Sensory organs, composed of 3 cell types: o Gustatory cells: detect tastants. o Supporting cells: sustain gustatory. o Basal cells: neural stem cells to replace short-lived gustatory cells (7-9 days).  15 2. Vision: - Visual stimuli. Light is focused onto the retina where photoreceptors (rods and cones) detect it. - Visual receptors: Photoreceptors - light, color, movement, detailed visual images. Accessory Structure of the Eye Eye Structure  16 Lens o Strong, deformable, transparent structure, bounded by a dense, fibrous, elastic capsule. o Lens focuses incoming light onto the retina and its shape determines the degree of light refraction o Crystallin- cells filled with crystallin.  17 3. Olfaction (Smell): - Olfactory Receptors: Located in the nasal cavity (chemoreceptors) – Detects airborne chemicals and sends signals to the brain for interpretation. - The sense of smell – volatile molecules (odorants) dissolve in the nasal cavity mucus to be detected. Olfactory Organs Olfactory Discrimination CMMMFS