Central and Peripheral Nervous Systems Flashcards

6.15 Central Nervous System: Brain

• Terminology:

  • Axon: extension of a neuron that transmits signals away from the cell body.

  • Nerve: bundle of axons located in the peripheral nervous system (PNS), facilitating communication between the CNS and the rest of the body.

  • Pathway/Tract/Commissure(left/right brain link): These are bundles of axons located within the central nervous system (CNS), serving as routes for neural communication.

• CNS Pathways:

  • Long Neural Pathways: directly transmit information between the brain and the spinal cord, enabling rapid communication for essential functions.

  • Multisynaptic Pathways: involve complex neural processing through multiple synapses, allowing for intricate integration of information.

  • due to more synapses, multisynaptic pathways perform more complex neural processing

• Information Flow: The flow of information within the nervous system is essential for maintaining homeostasis by coordinating various physiological processes.

• Ganglia vs. Nuclei:

  • Ganglia: clusters of neuron cell bodies located in the peripheral nervous system (PNS), often serving as relay points for nerve signals.

  • Nuclei: clusters of neuron cell bodies located within the central nervous system (CNS), playing key roles in neural processing and integration.

• Brain Development: The brain develops from a neural tube, with the anterior portion differentiating into the forebrain, midbrain, and hindbrain.

• Brain Regions & Subdivisions:

  • Forebrain: The forebrain consists of the cerebrum, responsible for higher-level cognitive functions, and the diencephalon, which includes the thalamus and hypothalamus.

  • Midbrain: The midbrain is a single division involved in motor control, sensory processing, and relaying information between the forebrain and hindbrain.

  • Hindbrain: The hindbrain includes the pons, medulla, and cerebellum, which are responsible for vital functions such as respiration, movement coordination, and balance.

  • Brainstem: The brainstem comprises the pons, medulla, and midbrain, serving as a critical relay center for information between the brain, spinal cord, and peripheral nervous system.

• Table 6.7: Brain Functions Summary

  

• Cerebral Ventricles: four interconnected cavities filled with fluid and provide support for brain

• Cerebrum: largest part of the forebrain; includes the cerebral hemispheres and other structures.

• Cerebral Hemispheres:

  • Cerebral Cortex: outer layer of the cerebrum, composed of gray matter, and is responsible for higher cognitive functions.

    • also contains white matter, which contains myelinated axons that facilitate communication between different brain regions.

    • Subcortical Nuclei: Clusters of gray matter located beneath the cerebral cortex.

    • hypothalamus, thalamus, basal ganglia

• *those 3 above r tracts (bundles of neurons)

• Corpus Callosum: large bundle of axons (commisure) that connects the right and left cerebral hemispheres, enabling communication between them.

Cerebral Cortex

• Lobes: four lobes: frontal, parietal, occipital, and temporal, each associated with specific functions.

• Folding: folding of the cerebral cortex increases its surface area, allowing for more complex neural processing.

• Gyri: Ridges on the surface of the cerebral cortex.

• Sulci: Grooves on the surface of the cerebral cortex.

• Cell Layers: T6 distinct layers, each with unique cellular composition and functions.

• Cell Types:

  • Pyramidal Cells: primary output cells of the cerebral cortex, responsible for transmitting signals to other brain regions.

  • Nonpyramidal Cells: primarily function as inputs to, and for processing of information within, the cortex.

• Specialization: The specialization of different cortical areas allows for increased neuron integration and efficient processing of information.

• Evolution: The complexity of the cerebral cortex parallels the evolutionary development of cognitive abilities.

  • more evolved → more layers

Basal Nuclei

• Subcortical Nuclei: Heterogeneous gray matter groups located beneath the cerebral hemispheres.

  • Basal Nuclei: play a critical role in movement and posture control, as well as influencing behavior.

Limbic System

• Functional System: includes parts of the frontal lobe, temporal lobe, thalamus, and hypothalamus; works together to regulate emotion and memory.

  • fiber pathways connect parts

• Connections: limbic system is interconnected with various parts of the central nervous system (CNS), enabling its diverse functions.

• Functions: The limbic system is involved in learning, emotion, behavior, and visceral/endocrine functions.

Forebrain: The Diencephalon

• Diencephalon: This region of the brain includes the thalamus, hypothalamus, and epithalamus, each with distinct functions.

• Thalamus:

  • relay and integrating center for inputs to the cerebral cortex.

  • It plays a role in arousal and attention, helping to focus cognitive resources.

  • Filters sensory information, prioritizing relevant stimuli.

• Hypothalamus:

  • serves as a command center for coordinating homeostatic regulation.

  • It regulates preservation behaviors, ensuring survival.

  • Pituitary regulation: The hypothalamus controls the release of hormones from the pituitary gland, influencing various bodily functions.

• Epithalamus: The epithalamus contains the pineal gland, which regulates circadian rhythms by secreting melatonin.

Hindbrain: The Cerebellum

• Cerebellum:

  • It has a cerebellar cortex (outer layer) + deeper cell clusters.

  • Coordinates movements, and maintains posture/balance.

  • Receives information from muscles, joints, skin, eyes, viscera, and brain.

  • Involved in learning motor skills.

Brainstem: The Midbrain, Pons, and Medulla Oblongata

• Brainstem:

  • Axons relay signals between the brain and spinal cord.

  • Contains the reticular formation.

• Reticular Formation:

  • Integrates input from ALL regions of CNS.

  • Involved in motor control, cardio/resp control, sleep/wake cycles, and attention.

  • Uses biogenic amine neurotransmitters to modulate brain activity.

  • Regulates arousal and wakefulness.

  • Directs attention to relevant stimuli.

  • Receives spinal cord influence.

  • Interacts with the forebrain, spinal cord, and cerebellum.

  • Brainstem nuclei: Contains centers for cardio, resp, swallowing, and vomiting reflexes.

  • Eye-movement control, and helps maintain body orientation.

• Cranial nerve nuclei (10/12) are located in the brainstem.

6.16 Central Nervous System: Spinal Cord

• Location: The spinal cord is located within the vertebral column, providing protection and support.

• Structure: It is a cylinder of soft tissue that extends from the brainstem to the lumbar region of the vertebral column.

• Gray Matter: butterfly-shaped and contains interneurons, efferent neuron bodies, afferent axons, and glial cells.

  • Dorsal Horns: located at the back of the spinal cord and primarily process sensory information.

  • Ventral Horns: located at the front of the spinal cord and contain motor neurons that control muscle movement.

    

• Dorsal Roots: Afferent (sensory) axons enter the spinal cord via the dorsal roots, with cell bodies located in the spinal ganglia.

• Ventral Roots: Efferent (motor) axons leave the spinal cord via the ventral roots, carrying motor commands to muscles and glands.

• Spinal Nerve: The dorsal and ventral roots combine to form a spinal nerve, which carries both sensory and motor information.

6.17 Peripheral Nervous System

• Function: The peripheral nervous system (PNS) functions to transmit signals between the central nervous system (CNS) and the rest of the body.

• Nerves: Nerves are bundles of axons that transmit signals throughout the body.

• Composition: The PNS consists of 43 nerve pairs: 12 cranial nerves and 31 spinal nerves, which connect with spinal cord.

• Spinal Nerves: These are categorized into cervical, thoracic, lumbar, sacral, and coccygeal nerves, based on their location along the spinal column.

• Cervical Nerves: innervate the neck, shoulders, arms, and hands, controlling movement and sensation in these areas.

• Thoracic Nerves: innervate the chest and upper abdomen, controlling muscles involved in breathing and providing sensory information.

• Lumbar Nerves: innervate the lower abdomen, hips, and legs, controlling movement and sensation in these regions.

• Sacral Nerves: nnervate the genitals and lower digestive tract, controlling sexual function and bowel movements.

• Coccygeal Nerves: Coccygeal nerves primarily innervate the skin around the tailbone.

• All Spinal Nerves: They contain both afferent and efferent fibers, allowing them to transmit sensory information to the CNS and motor commands from the CNS.

• Afferent Neurons: These neurons transmit sensory information from sensory receptors to the CNS.

  • Primary/first-order neurons are the initial sensory neurons in the pathway.

• Efferent Neurons: These neurons transmit signals from the CNS to effector organs.

• Efferent Division: The efferent division of the PNS is divided into the somatic and autonomic nervous systems.

• Somatic Nervous System: The somatic nervous system controls skeletal muscles, enabling voluntary movement.

• Autonomic Nervous System: The autonomic nervous system regulates smooth muscle, cardiac muscle, glands, and GI neurons, controlling involuntary functions.

• Somatic

  • Single neuron: extends from the CNS to skeletal muscle, facilitating rapid and direct control.

  • Innervates skeletal muscle, enabling voluntary movement.

  • Muscle excitation only: Somatic motor neurons trigger muscle contraction.

• Autonomic

  • Two-neuron chain: extends from the CNS to effector organs, with a synapse in an autonomic ganglion.

  • Innervates smooth/cardiac muscle, glands, and GI neurons, controlling involuntary functions.

  • Excitatory or inhibitory: Autonomic neurons can either stimulate or inhibit their target organs.

• Somatic Portion: \ consists of motor neurons that extend from the CNS to skeletal muscle cells.

  • Cell bodies: The cell bodies of somatic motor neurons are located in the brainstem and ventral horn of the spinal cord.

  • Large, myelinated axons: These axons transmit signals rapidly, enabling quick muscle contractions.

  • Acetylcholine neurotransmitter is released at the neuromuscular junction to trigger muscle contraction.

  • Motor neurons: Motor neurons stimulate muscle contraction.

  • Muscle relaxation: Relaxation occurs when motor neuron activity is inhibited, reducing muscle tension.

6.18 Autonomic Nervous System

• Function: provides efferent innervation to organs other than skeletal muscle, regulating involuntary functions.

• Enteric Nervous System: network of neurons within the GI tract that regulates digestive functions independently of the CNS.

• Structure: two neurons in series: a preganglionic neuron and a postganglionic neuron.

• Autonomic Ganglion: This is where the synapse occurs between the preganglionic and postganglionic neurons outside the CNS.

• Preganglionic Neurons: These neurons extend from the CNS to the autonomic ganglia.

• Postganglionic Neurons: These neurons extend from the ganglia to the effector cells in target organs.

• ANS is divided into the sympathetic and parasympathetic divisions, which often have opposing effects on target organs.

• Sympathetic(thoracolumbar) Division: Preganglionic neurons originate from the thoracic and lumbar regions of the spinal cord.

• Parasympathetic(cranial) Division: parasympathetic neurons arise from the brainstem and sacral regions of the spinal cord.

• Ganglia Location:

  • Sympathetic Ganglia: located near the spinal cord, forming the sympathetic chain.

    • form sympathetic trunks

  • Collateral Ganglia: located in the abdominal cavity, innervating digestive organs.

    • celiac superior mesenteric inferior mesenteric ganglia

  • Parasympathetic Ganglia: located near or within the target organs.

• Activation Pattern:

  • Sympathetic: Activation tends to be body-wide, preparing the body for "fight or flight."

  • Parasympathetic: Activation is more specific to individual organs, promoting "rest and digest" functions.

• Neurotransmitters:

  • Acetylcholine: It is the neurotransmitter used by preganglionic neurons in both the sympathetic and parasympathetic divisions.

  • Nicotinic Acetylcholine Receptors: These receptors are found on postganglionic cells in autonomic ganglia.

  • Parasympathetic: Acetylcholine is also used by postganglionic neurons to signal to effector organs.

  • Sympathetic: Norepinephrine is used by most postganglionic neurons to signal to effector organs.

• Nonadrenergic/Noncholinergic Neurons: Some autonomic neurons use nitric oxide or other neurotransmitters.

• Receptors:

  • Nicotinic Receptors: These are located in autonomic ganglia, where preganglionic neurons synapse onto postganglionic neurons.

  • Muscarinic Receptors: These are found on postganglionic targets and mediate the effects of acetylcholine.

• Adrenal Medulla:

  • It is a modified sympathetic ganglion.

  • It releases epinephrine and norepinephrine into the bloodstream.

  • Catecholamines act as hormones, prolonging and amplifying the sympathetic response.

• Dual Innervation: Many organs, such as the heart, glands, and smooth muscles, receive input from both the sympathetic and parasympathetic divisions, allowing for fine-tuned control.

  6.19 Protective Elements Associated with the Brain

• Meninges: protective membranes surrounding the brain and spinal cord, consisting of the dura mater, arachnoid mater, and pia mater.

  • dura mater is thicc

• Subarachnoid Space: filled with cerebrospinal fluid (CSF) and lies between the arachnoid mater and pia mater.

• Functions: These elements protect the brain and spinal cord, provide support, and circulate cerebrospinal fluid (CSF).

• Meningitis: It is an infection of the meninges, leading to inflammation and increased pressure within the skull.

• Choroid Plexus: The choroid plexus produces cerebrospinal fluid (CSF) within the ventricles of the brain.

• CSF Flow: CSF flows through the ventricular system of the brain and into the subarachnoid space, where it cushions and nourishes neural tissue.

• CSF Sampling: CSF can be sampled from the spinal canal below the L2 vertebra for diagnostic purposes.

• Function: The CNS floats in CSF, which cushions and protects the brain from mechanical injury.

• Hydrocephalus: condition which occurs when CSF accumulates in the ventricles, leading to increased intracranial pressure.

• Brain Metabolism:

  • Glucose is the primary substrate metabolized by the brain to meet its energy demands, with most energy from glucose oxidation transferred to ATP.

  • Negligible glycogen stores mean the brain requires a continuous supply of glucose from the blood.

• Stroke: It is the death of neurons due to vascular disease, leading to impaired blood flow and oxygen deprivation.

• Blood Supply:

  • The brain accounts for approximately 2% of body weight but receives 12-15% of the body's blood supply, highlighting its high metabolic demands.

  • Reduced blood flow leads to membrane pump failure, disrupting ion gradients and neuronal function.

• Blood–Brain Barrier:

  • The blood-brain barrier selectively controls the substances that enter the brain, protecting it from harmful compounds.

  • Astrocytes and specialized blood vessel cells form tight junctions that limit permeability.

  • Lipid solubility: Substances with high lipid solubility can rapidly enter the brain.

• Morphine vs Heroin:

  • Heroin is more lipid-soluble than morphine, allowing it to cross the blood-brain barrier more easily and produce a faster, more intense effect.

• Transport Proteins: These facilitate the entry of essential substances into the brain.

• CSF Barrier: The CSF barrier selectively secretes substances into the cerebrospinal fluid, regulating its composition.