Untitled Quiz

Nervous System Study Guide 7

• The nervous system detects changes, feels sensations, organizes and stores information, and initiates responses to these changes.

Functions of the Nervous System

• Detects changes and feels sensations.
• Organizes and stores information.
• Initiates responses to changes.

Division of the Nervous System

• Central Nervous System (CNS): Brain and Spinal cord
• Peripheral Nervous System (PNS): Cranial Nerves & Spinal Nerves.

Nerve Tissue

• Neurons: the functional units of the nervous system.
  • Cell body: Contains the nucleus and other organelles; regulates neuron function.
  • Nerve cell processes (extensions):
    • Dendrites: Carry impulses toward the cell body.
    • Axon: Carries impulses away from the cell body.

Structure of a Neuron

• Diagram of a neuron with labels for cell body, dendrites, axon, axon hillock, myelin sheath, node of Ranvier, and synaptic end bulbs.

Neuron

• Myelin Sheath: Multilayered lipid and protein covering formed by Schwann cells (PNS) and oligodendrocytes (CNS), surrounding axons of many peripheral and CNS neurons. Allows rapid conduction of impulses.
• Nodes of Ranvier: Spaces between individual Schwann cells or segments of the myelin sheath.

Saltatory Conduction

• Diagram illustrating the process of saltatory conduction. This rapid transmission of nerve impulses occurs along myelinated axons.

Neuroglia (Glial Cells)

• Non-neuronal cells of the CNS.
  • Oligodendrocytes: Produce the myelin sheath to electrically insulate axons of CNS neurons.
  • Microglia: Capable of movement and phagocytosis of pathogens and damaged tissue.
  • Astrocytes: Support neurons, help maintain proper chemical environment, and form the blood-brain barrier.
  • Ependyma: Line the ventricles and central canal of the spinal cord. Involved in cerebrospinal fluid (CSF) circulation.

White & Gray Matter

• White matter: Nerve tissue within the CNS, primarily myelinated axons of neurons.
• Gray matter: Nerve tissue within the CNS, primarily cell bodies of neurons.

Types of Neurons

• Sensory (afferent) neurons: Carry impulses from receptors to the CNS.
• Motor (efferent) neurons: Carry impulses from the CNS to muscles and glands (effectors).

Nerve

• A bundle of neuronal axons and/or dendrites and associated connective tissues located outside the CNS.
  • Sensory nerve: Made only of sensory neurons.
  • Motor nerve: Made only of motor neurons.
  • Mixed nerve: Contains both sensory and motor neurons.

Nerve Tract

• A bundle of nerve axons within the CNS; often referred to as white matter.
  • Ascending tract (sensory): Carries sensory information towards the brain.
  • Descending tract (motor): Carries motor information away from the brain.

Ascending & Descending Pathways

• Diagrams illustrating ascending (sensory) and descending (motor) pathways.

Nerve Impulse (Nerve Action Potential)

• Self-propagating wave of electrical current carrying information along a nerve.
• Stimulus: Any change in the internal or external environment that excites a sensory receptor, neuron, or muscle fiber.

State or Events (Action Potential)

• Polarization: Neuron is not carrying an electrical impulse. Neuron membrane has a positive charge outside and a negative charge inside.
• Depolarization: Generated by a stimulus. Entry of Na+ ions and reversal of charges on either side of the membrane.
• Propagation: Rapid transmission of a nerve impulse from one node of Ranvier (in a myelinated neuron) to the next; characteristic of myelinated neurons.
• Repolarization: Immediately follows depolarization. Exit of K+ ions and restoring of the (+) charge on the outside and (-) charge on the inside of the membrane. Sodium and potassium pumps return Na+ and K+ ions to their original sides.

Synapse

• Point of junction for transmission of nerve impulses; the space between an axon of one neuron and dendrites or cell body of another neuron.
• Neurotransmitters: Chemicals released by an axon that enable a nerve impulse to cross a synaptic junction. (Examples: acetylcholine, norepinephrine, dopamine, and GABA)

Spinal Cord

• Encloses within the vertebral canal; extends from foramen magnum to the intervertebral disc between the first and second lumbar vertebrae.
• Contains:
  • Gray matter: Primarily cell bodies of motor neurons and interneurons.
  • White matter: Primarily myelinated axons of neurons.
  • Central canal: Contains cerebrospinal fluid (CSF).

Functions of the Spinal Cord

• Conducts sensory impulses through ascending tracts to the brain.
• Conducts motor impulses through descending tracts to motor neurons that supply muscles or glands.
• Reflex activities: Simple, rapid, and automatic responses involving few neurons. (Reflex arcs).

Spinal Nerves

• 31 pairs connected to the spinal cord.
• Cauda equina: Lumbar and sacral nerves that extend below the end of the spinal cord.
• Posterior (dorsal) root: Contains sensory neurons carrying impulses into the spinal cord.
  • Posterior (dorsal) root ganglion: Contains the cell bodies of sensory neurons outside the CNS.
• Anterior (ventral) root: Contains motor neurons carrying impulses from the spinal cord to muscles and glands.
• All spinal nerves are mixed nerves.

Distribution of Spinal Nerves

• Plexus: Networks of nerves distributing branches to various body parts.
  • Cervical plexus: Supplies motor and sensory impulses to neck and back of the head. Phrenic nerve arises.
  • Brachial plexus: Supplies nerves to shoulder, arm, forearm, wrist, and hand.
  • Lumbosacral plexus: Supplies nerves to lower extremities. Sciatic nerve is the largest branch.

Reflex Arc

• Diagram illustrating pain receptors stimulating a reflex arc; a pathway connecting receptor and effector in the nervous system..

Brain

• Part of the central nervous system located within the cranial cavity.
  • Main parts of the brain:
    • Cerebrum
    • Diencephalon
    • Brainstem
    • Cerebellum

Main Parts of the Brain

• 1. Cerebrum: Largest part of the brain, divided into right and left hemispheres by the longitudinal fissure.
• 2. Diencephalon: Located between the cerebral hemispheres and the brainstem, includes thalamus, hypothalamus, and pineal gland.
  • Thalamus: Main relay center for sensory impulses.
  • Hypothalamus: Controls the ANS; produces hormones ADH and oxytocin.
  • Pineal gland: Secretes melatonin.
• 3. Brainstem: Connects cerebrum and diencephalon to spinal cord. Includes midbrain, pons, and medulla oblongata.
  • Midbrain: Upper portion of the brain stem.
  • Pons: Connects the midbrain with the medulla; regulates breathing together with the medulla oblongata.
  • Medulla Oblongata: Connects the brain to the spinal cord, regulates respiration, heart rate, and blood vessel diameter; also contains reflex centers for coughing, sneezing, swallowing, and vomiting.
• 4. Cerebellum: Located below the back part of the cerebral hemisphere, connected to the brain stem by pons. Coordinates voluntary muscle movements and aids in balance and muscle tone..

Covering of the Brain and Spinal Cord: Meninges

• Dura mater: Thickest and toughest membrane, lines the skull and vertebral canal.
• Arachnoid mater: Middle membrane, loosely attached to pia mater.
• Pia mater: Thin, innermost membrane containing many blood vessels.

Subarachnoid Space

• Space between arachnoid and pia mater containing CSF (cerebrospinal fluid).
  • CSF functions:
    • Supports neural tissue.
    • Cushions the CNS.
    • Carries nutrients and removes waste products from cells.

Ventricles

• Spaces within the brain that produce and circulate CSF.
  • Choroid plexus: Network of capillaries in each ventricle, filters blood plasma to form CSF.

Four Ventricles

• Lateral ventricles: Largest ventricles in the cerebral hemispheres.
• Interventricular foramen: opening connecting lateral ventricles to 3rd ventricle.
• Third ventricle: Surrounded by the diencephalon.
• Cerebral aqueduct: Tunnel through midbrain allowing CSF flow from the 3rd to 4th ventricle.
• Fourth ventricle: Located at back of the pons and connects with central canal of the spinal cord.
  • CSF circulation: CSF flows throughout system, eventually reabsorbed into the blood plasma through arachnoid granulations in the meninges.

Pathway of CSF Flow

• Diagram illustrating CSF flow from the brain ventricles to venous sinuses..
• Foramina of Luschka and Magendie: Openings that connect the ventricle system to the subarachnoid space.

Hydrocephalus

• Abnormal increase in CSF within brain ventricles.
• Causes: blockages in CSF outflow or problems with reabsorption
• Symptoms: Possible head enlargement in babies. Symptoms vary by age; could involve increased intracranial pressure, causing headache, vomiting, or drowsiness.
• Surgical management: VP shunt or VA shunt diverting CSF to another part of the body.

Surgical Management

• VP shunt or VA shunt are procedures for hydrocephalus; medical devices redirect the flow of cerebrospinal fluid (CSF).

Cerebrum

• Cerebral Cortex: Gray matter on the surface of cerebral hemisphere composed of cell bodies. Receives and analyzes impulses.
• Internal white matter: Composed of myelinated axons. Connects lobes, other parts of cerebrum, and brain.
• Cerebral Cortex Folding: Folded into gyri (elevated parts) and sulci/fissures (grooves). The folding increases the surface area and number of neurons.
• **Important Sulci:**Central sulcus; Lateral sulcus; Longitudinal fissure.
• Corpus Callosum: Band of nerve fibers connecting left and right hemispheres. Used for communication across hemispheres.
• Basal Ganglia: Masses of gray matter deep within the cerebrum. Control subconscious muscle movements (e.g. automatic arm movements)
• Limbic System: Part of the cerebrum concerned with aspects of emotion and behavior and memory storage and retrieval.
• Lobes of Cerebral Hemispheres:
  • Frontal Lobe: Contains the Motor Area & Broca's area, controls voluntary movements and involved in speech.
  • Parietal Lobe: Contains the Sensory Area; responsible for processing sensations from touch, temp, and pain; interprets sensory information.
  • Temporal Lobe: Contains Auditory Area for receiving and interpreting auditory information. Contains Olfactory Area; responsible for sense of smell
  • Occipital Lobe: Contains the Visual Area, for receiving and interpreting visual information.

Important Sulcus

• Central sulcus: Separates frontal and parietal lobes.
• Lateral sulcus: Separates temporal lobe from frontal and parietal lobes.

Cranial Nerves

• 12 pairs of nerves emerging from brain stem and other parts of the brain.
  • Some contain only sensory fibers (CN I, II, and VIII)
  • Others have mostly motor fibers (CNIII, IV, VI, XI and XII)
  • Others are mixed nerves (CN V, VII, IX, and X) and contain both.
• Specific Cranial nerve functions (tables in the original text).

Autonomic Nervous System (ANS)

• Portion of PNS controlling involuntary functions.
  • Visceral motor neurons stimulating smooth muscle, cardiac muscle, and glands.
  • Two-neuron pathway in ganglia:
    • Preganglionic neurons: from CNS to ganglia
    • Postganglionic neurons: from ganglia to effectors
• Two Divisions:
  • Sympathetic: (Thoracolumbar division) dominant in stressful situations.
    • Prepares body for physical demands
    • Nerve fibers originating in the thoracic and lumbar regions of the spinal cord -> reach sympathetic ganglia and synapse with the second set of neurons -> these then extend to glands and involuntary muscles using norepinephrine.
  • Parasympathetic: (Craniosacral division) dominant in relaxed situations.
    • Promotes normal functioning
    • Cell bodies located in the brain stem and sacral part of spinal cord-> axons extending to parasympathetic ganglia generally located close to the target organs themselves -> The postganglionic neurons of this pathway release acetylcholine.

Effects of the Sympathetic and Parasympathetic Nervous System

• Table showing how these systems operate on specific organs to regulate many functions (e.g. iris, heart, lungs, glands, digestive system, etc).