The Nervous System - Unit 11 Pt 1 and 2 PDF

Part 1 Functions of the Nervous System Detecting sensory stimuli Analyzing and integrating sensory information Responding to internal and external stimuli Regulating organ systems (homeostasis) Reflexes: rapid, unconscious responses to stimuli...

Part 1 Functions of the Nervous System Detecting sensory stimuli Analyzing and integrating sensory information Responding to internal and external stimuli Regulating organ systems (homeostasis) Reflexes: rapid, unconscious responses to stimuli Learning, memory, and emotions Organization two main divisions: Central Nervous System (CNS): composed of the brain and spinal cord, integrates information and decides on a response Peripheral Nervous System (PNS): composed of the nerves that connect the brain or spinal cord with the body's muscles, glands, and sense organs o Somatic Nervous System: voluntary (conscious) control of skeletal muscles o Autonomic Nervous System: involuntary control of smooth and cardiac muscle and glands ▪ Sympathetic (Fight or Flight): stimulated and aroused ▪ Parasympathetic (Rest and Digest): calm and relaxed o Afferent neurons: bring signals from peripheral receptors to the CNS o Efferent neuron: bring signals from the CNS to the skeletal muscle fibers Definitions Neuron: a single nerve cell, the functional unit of the nervous system Nerve: contains thousands of neurons that connect with a specific tissue Glial cells: cells that support the neurons in the CNS and PNS Plexus: a network of nerves that innervate specific tissues, providing redundancy of neurons in case of damage Ganglion: a group of cell bodies in a sensory nerve, e.g. dorsal root ganglion Sensory receptors: detect specific sensory stimuli Neuron Anatomy Structure Function Cell body contains the nucleus and ribosomes Dendrites receive signals, increase cell surface area Axon and transmit electrical activity, starting from axon hillock and moving collaterals toward axon terminals Axon terminal releases neurotransmitters, which connect to other neurons or muscle Structural and functional Classification of Neurons Type Description Motor neurons send information to skeletal or smooth or cardiac muscle (efferent neurons) - Multipolar Sensory send information from receptors to CNS (afferent neurons) neurons - Unipolar - Bipolar found only in ear, retina, and olfactory area of brain Interneurons very short connecting neurons in the CNS Glial Cells of the CNS Type Function Astrocytes - regulate what materials can enter a CNS neuron - regulate external environment - guide neuron growth during embryonic development  - store glycogen - form scar tissue in brain Microglia - phagocytic immune cells - can migrate to infected areas and engulf pathogens and dead cells Ependymal cells - involved with production of cerebral spinal fluid (CSF) in brain ventricles Oligodendrocytes - make up myelin, protect and insulate axons Glial Cells of the PNS Type Function Satellite surround neuron cell bodies in the PNS, regulate ions entering cell cells Schwann surround and form myelin sheaths around the nerve fibers, similar to cells oligodendrocytes in CNS Action Potentials and Graded Potentials Resting membrane potential: approximately -70mV, maintained by the Na+/K+ pump Threshold level: -55mV triggered by stimulus Depolarization: positively charged Na+ ions move into the cell, making it less negative, about +30mV Repolarization: K+ ions leave the cell, restoring the membrane potential to -70mV Hyperpolarization: excess K+ ions leave the cell, causing the membrane charge to be more negative than –70mV, -80mV Graded Potentials: small changes in the electrical potential of a neuron that can vary in magnitude. They are called "graded" because the magnitude of the potential change can vary. A graded potential is a change in the electrical potential of a neuron that can vary in magnitude, allowing for a range of responses to different stimuli. There are two types of graded potentials: Excitatory Post-Synaptic Potential (EPSP): caused by Na+ ions entering the cell, depolarizing the membrane and exciting the neuron.  Inhibitory Post-Synaptic Potential (IPSP): caused by K+ ions leaving the cell and Cl+ ions entering the cell, hyperpolarizing the membrane and inhibiting the neuron. Graded potentials can be summed in two ways: Temporal Summation: many graded potentials in the same location over a period of time. Spatial Summation: many graded potentials affecting multiple areas of the post- synaptic neuron at the same time. If the sum of all EPSPs and IPSPs reaches the Threshold Potential at the axon hillock, an Action Potential occurs. Action Potential vs. Graded Potential Characteristic Action Potential Graded Potential Strength Maintained Decreases (amplitude) Direction Unidirectional Multi-directional Relative Speed Relatively Fast Relatively Slow Location in Neuron Axon Dendrites, soma (cell body), unmyelinated axon Location in Body Mainly PNS Mainly CNS Distance Travelled Long Short Refractory Period Absolute and None Relative Excitatory or Excitatory only Excitatory or Inhibitory Inhibitory Communication Between Neurons and Between Neurons and Muscle Cells The Synapse is the space between the pre-synaptic neuron and the post-synaptic neuron or muscle cell. Neurotransmitters are produced and stored in vehicles at the axon terminal. An action potential in the axon reaches the axon terminal and causes voltage-gated calcium channels to open. Calcium entering the cell binds to vesicles and causes them to bind to the axon terminal membrane and release the neurotransmitters. The neurotransmitter is then released by Exocytosis and diffuses across the Synaptic Cleft to bind to receptor proteins on the post-synaptic membrane, causing EPSPs or IPSPs. Neurotransmitters Acetylcholine (ACh): found in the PNS and CNS, important for learning and memory, and the only neurotransmitter that causes skeletal muscle contraction. Serotonin: related to mood, produces a feeling of contentment, and low levels are associated with depression. Dopamine: helps with concentration, plays a role in the reward pathway, and contributes to addictive behaviors. Amine Neurotransmitters are made from amino acids: Catecholamines: made from Tyrosine (dopamine, norepinephrine, and epinephrine) Tryptophan: serotonin, melatonin Histidine: histamine The enzymes that degrade the biogenic amine neurotransmitters are Monoamine Oxidase (MAO). MAOIs are inhibitors of these neurotransmitters. Part 2 Brain Structure Brain Meninges: The brain and spinal cord are protected by three layers of membranes called meninges. Dura mater (outermost)  Arachnoid mater Pia mater (innermost) Functions: o Cover and protect the CNS o Protect blood vessels and enclose the venous sinuses o Contain cerebrospinal fluid o Form partitions in the skull Meningitis is a serious inflammation of the meninges that can be caused by bacteria or viruses. Cerebrospinal Fluid (CSF): CSF is the extracellular fluid of the CNS Functions: o Cushions and protects the brain and spinal cord. o Provides nutrients to the brain and spinal cord. o Removes waste products from the brain and spinal cord Divisions of the Brain: Diencephalon o Thalamus: Integrating center for sensory input to the cortex. ▪ Part of the reticular activating system (RAS) for arousal and attention o Hypothalamus: Regulates survival behaviors (eating, drinking) and reproductive behaviors ▪ Coordinates neural and endocrine information ▪ Connected to the pituitary gland o Pineal Gland: Regulates biological rhythms ▪ Secretes melatonin to promote sleep Brainstem o Midbrain: Contains neurons for consciousness and sleep-wake cycles (RAS) o Pons: Relays information between the cerebrum and cerebellum (muscle movements). ▪ Contains respiratory centers o Medulla Oblongata: Main respiratory and cardiac centers (breathing and heart rate). ▪ Controls reflexes like coughing, sneezing, and vomiting Cerebellum: Coordinates smooth muscle movements (walking, dancing).  o Involved in learning muscle movements (muscle memory) and fine motor control Cerebrum: o Cerebral Cortex: The outer layer of the cerebrum o Subcortical Region: Contains structures like: ▪ Basal nuclei (muscle movements) ▪ Amygdala (emotions, memory, social interactions) ▪ Caudate nucleus (reward, pleasure, addiction) ▪ Corpus callosum (connects brain hemispheres) o Limbic System: Plays a major role in emotions, learning, memory, and social interactions. ▪ Closely linked to the sense of smell. ▪ Involved in primitive reactions (anger, sadness). ▪ Hippocampus: location of long-term memory o Lobes of the Cerebrum: ▪ Frontal Lobe: Motor cortex, premotor cortex (planning and initiating movements), higher thinking, decision making, self-control. Broca's area (speech production) ▪ Parietal Lobe: Sensory cortex (interprets sensory information), spatial relationships, number and letter recognition ▪ Temporal Lobe: Auditory cortex (interprets sound). Wernicke's area (language comprehension), memory for names and sounds, hippocampus (long-term memories), insula (pain perception) ▪ Occipital Lobe: Visual cortex (interprets visual stimuli), object recognition, motion perception Spinal Cord: Located within the vertebral column (vertebral foramen).  Gray matter (interneurons, cell bodies, dendrites, axons, glia) surrounded by white matter (myelinated axons) Dorsal horns (sensory information) and ventral horns (motor information) Spinal Nerves: 31 pairs of spinal nerves branch from the spinal cord Cauda Equina: Tail-like structure of spinal nerves at the end of the spinal cord Nerve Plexus: A network of nerves that supply specific areas of the body (limbs), providing redundancy and preventing complete paralysis from a single nerve injury Reflexes: Rapid, involuntary responses to stimuli Monosynaptic Reflex: One synapse between sensory and motor neurons (knee- jerk reflex) Polysynaptic Reflex: More than one synapse (withdrawal reflex) Learned Reflexes: Acquired through learning and involve the brain (riding a bike) Autonomic Nervous System (ANS): Involuntary control of smooth muscle, cardiac muscle, and glands Divisions: o Sympathetic NS: "Fight or flight" response o Parasympathetic NS: "Rest and digest" response Neural pathway involves preganglionic and postganglionic neurons (both release ACh). Chronic Pain Treatment: Nerve Blocks: Used to temporarily block pain signals Nerve Ablation: Removal or destruction of a nerve to reduce chronic pain Cranial Nerves: 12 pairs of cranial nerves originate in the brain