Anatomy & Physiology I Chapter Summary Notes PDF

Anatomy & Physiology I: Chapter Summary Notes Unit 5: Chapters 12 & 14 Chapter 12: Nervous Tissue An Introduction to the Nervous System Nervous system includes…  The brain and spinal cord  The receptors in complex sense organs  The nerves The organs of the nervous system are made u...

Anatomy & Physiology I: Chapter Summary Notes Unit 5: Chapters 12 & 14 Chapter 12: Nervous Tissue An Introduction to the Nervous System Nervous system includes…  The brain and spinal cord  The receptors in complex sense organs  The nerves The organs of the nervous system are made up of nervous tissue, blood vessels, and connective tissues. There are two types of nervous tissue: neurons and neuroglia. Neurons: basic functional units of the nervous system, which are specialized for intercellular communication. Neuroglia: supporting cells of nervous system, also called glial cells. 12-1 The Nervous System has Anatomical and Functional Divisions The Anatomical Divisions of the Nervous System Anatomically, there are three divisions of the nervous system: the central nervous system (CNS), the peripheral nervous system (PNS), and the enteric nervous system (ENS). The Central Nervous System (CNS): consists of the brain and the spinal cord. The CNS is responsible for integrating, processing, and coordinating sensory data and motor commands.  Sensory data conveys information about conditions inside or outside the body  Motor commands control or adjust peripheral organs, such as skeletal muscles The Peripheral Central Nervous System (PNS): consists of ALL nervous tissue outside the CNS and the ENS. The PNS delivers sensory information to the CNS and carries the motor commands to peripheral tissues and systems, except those if the ENS. The PNS has two functional divisions: the afferent division and the efferent division. The Functional Divisions of the Nervous System The CNS doesn’t have functional divisions like the PNS. Afferent division: the part of the PNS brings sensory information to the CNS from receptors  Receptors: sensory structures that either detect change in the environment (internal or external) or respond to specific stimuli Efferent division: the part of the PNS that carries motor commands from CNS to muscles, glands, and adipose tissue.  Effectors: the target organs which respond by doing something The efferent division has two subdivisions: the somatic nervous system and the autonomic nervous system. Somatic nervous system (SNS): control skeletal muscle contractions.  Voluntary contractions are under conscious control  Involuntary contractions are under subconscious control Reflex: automatic response Ex. If you accidently place your hand on a hot stove, you will withdraw it immediately, usually BEFORE you even notice the pain. Autonomic nervous system (ANS): automatically regulates smooth muscle, cardiac muscle, glandular secretions, and adipose tissue at the subconscious level. The ANS has two subdivisions: the parasympathetic division and the sympathetic division. Parasympathetic: rest and digest. Sympathetic: fight or flight. These divisions usually have antagonistic (opposite) effects. Ex. Parasympathetic activity slows the heart rate, whereas sympathetic activity accelerates heart rate. The Enteric Nervous System (ENS): extensive network of neurons and nerve networks in the walls of the digestive tract. The ENS initiates and coordinates many complex visceral reflexes locally and without instructions from the CNS. *** Please draw figure 12-1, An Overview of the Nervous System. *** 12-2 Neurons are Nerve Cells Specialized for Intercellular Communication Functional Characteristics of Neurons  Generally long-lived and have high metabolic rate  Excitable plasma membrane  Mitochondria in neurons generate the energy needed  Typical CNS neurons cannot divide, cannot be replaced after injury or infection The Structure of Neurons Neurons have a variety of shapes, but each have four major regions: a cell body, dendrites, an axon, and telodendria. Cell body (soma): large body of neuron that has nucleus with a prominent nucleolus. Perikaryon: cytoplasm surrounding nucleus in a neuron. The perikaryon contains organelles that provide energy and synthesize organic materials, especially the neurotransmitters that are important for cell-to-cell communication. Nissl bodies: dense areas of RER and ribosomes that make nervous tissue appear gray (gray matter). Dendrites: slender, sensitive processes that extend and branch out from the cell body. Axon: single, long cytoplasmic process that propagates action potentials. Axolemma: cytoplasm of axon. Initial segment: base of axon. Axon hillock: thick “funnel” region that attaches initial segment to cell body. Collaterals: branches of the axon. Telodendria: fine extensions of distal axon. Axon (synaptic) terminals: tips of telodendria. *** Please draw figure 12-2b, The Anatomy of a Typical Neuron. *** The Classification of Neurons Structural Classification of Neurons Neurons are classified structurally on the basis of the relationship of the dendrites to the cell body and the axon. There are four types of structural classifications of neurons: anaxonic, bipolar, unipolar, and multipolar. Anaxonic neurons  Small  All cell processes look similar  Found in brain and special sense organs Bipolar neurons  Small and rare  One dendrite and one axon  Found in special sense organs Unipolar (pseudounipolar) neurons  Axon and dendrites are fused  Cell body to one side  Found in most sensory neurons of PNS Multipolar neurons  One long axon and two or more dendrites  Found in CNS, VERY COMMON  All motor neurons that control skeletal muscles *** Please draw figure 12-3, Structural Classifications of Neurons. *** Functional Classification of Neurons Neurons are classified functionally by three types: sensory neurons, motor neurons, and interneurons. Sensory (afferent) neurons: processes (afferent fibers) extend from sensory receptors to CNS.  Somatic sensory neurons: monitor external environment.  Visceral sensory neurons: monitor internal environment.  Unipolar  Cell bodies grouped by sensory ganglia Sensory receptors are either the processes of specialized sensory neurons or cells monitored by sensory neurons. There are three types of sensory receptors: interoceptors, exteroceptors, and proprioceptors.  Interoceptors: monitor internal systems. Ex. digestive, urinary, etc. o Internal senses: stretch, deep pressure, pain  Exteroceptors: monitor external environment. Ex. temperature. o Complex senses: sight, smell, hearing  Proprioceptors: monitor position and movement of skeletal muscles and joints. Motor (efferent) neurons: carry instructions from CNS to peripheral effectors via efferent fibers (axons).  Somatic motor neurons: innervate skeletal muscles in SNS.  Visceral motor neurons: innervate all other peripheral effectors. Ex. smooth and cardiac muscle, glands, adipose tissue. Signals from CNS to visceral effectors cross autonomic ganglia that divides axons into…  Preganglionic fibers  Postganglionic fibers Interneurons: located in between sensory and motor neurons, responsible for distribution of sensory information and coordination of motor activity.  Most are in brain and spinal cord o Some in autonomic ganglia  Involved in higher functions. Ex. memory, planning, and learning. *** SAME: S for Sensory, A for Afferent, M for Motor, E for Efferent. Associate S & A together, and M & E together. *** 12-3 CNS and PNS Neuroglia Support and Protect Neurons. Neuroglia: support and protect neurons.   Make up half the volume of the nervous system  Many types in CNS and PNS There are four types of neuroglia in the CNS: astrocytes, ependymal cells, oligodendrocytes, and microglia. Astrocytes: large cell bodies with many processes, star-shaped cells that anchor to capillaries and form BBB.  Maintain blood brain barrier  Create 3-D framework for CNS  Repair damaged nervous tissue  Guide neuron development  Control interstitial environment Ependymal cells: simple cuboidal epithelial cells that line passageways in the brain and spinal cord.  Produce and monitor CSF  Form epithelium that lines central canal pf spinal cord and ventricles of brain  Have cilia that help circulate CSF Oligodendrocytes: small cell bodies with few processes, sheet like cells that wrap around the axon.  Many cooperate to form myelin sheath o Myelin insulates myelinated axons o Increases speed of axons o Makes nerves appear white  Internodes: myelinated segments of axon.  Nodes of Ranvier: lie in between internodes where axons may branch.  White matter: regions of CNS with many myelinated axons.  Gray matter: unmyelinated axons, neuron cell bodies, and dendrites. Microglia: smallest and least numerous neuroglia, phagocytes with many fine-branched processes.  Clean up debris, wastes, and pathogens  Migrate through nervous tissue Myelin: membranous wrapping that acts as electrical insulation and increases the speed at which an action potential travels down the axon. Myelin sheath: oligodendrocytes that form sheath along the length of an axon. Myelinated axons: axon that has a myelin sheath. Unmyelinated axons: axon that doesn’t have a myelin sheath. *** Draw figure 12-4, An Introduction to Neuroglia (Part 1 of 2). *** There two types of neuroglia in the PNS: satellite cells and schwann cells. Satellite cells: surround ganglia and regulate interstitial fluid around neurons. Schwann cells: form myelin sheath or folds of plasma membrane around axons.  Neurolemma: outer surface of schwann cell  A schwann cell sheaths only one axon, many schwann cells will sheath the entire axon *** Draw figure 12-4, An Introduction to Neuroglia (Part 2 of 2). *** Neural Responses to Injuries Wallerian degeneration: the axon distal to injury degenerates, schwann cells form new path for growth and wrap around new axon. Nerve regeneration in CNS is limited by astrocytes, because astrocytes produce scar tissue and release chemicals that block regrowth. 12-4 The Membrane Potential of a Neuron is Determined by Differences in Ion Concentrations and Membrane Permeability. All plasma membranes produce electrical signals by ion movements. Membrane potential is particularly important to neurons. The Resting Membrane Potential Resting membrane potential: membrane potential of a resting cell. Graded potential: temporary, localized change in resting potential caused by stimulus. Action potential: an electrical impulse, produced by graded potential and propagates along surface of axon to synapse. Three important concepts…  The extracellular fluid and intracellular fluid differ greatly in ionic composition o Extracellular fluid contains high concentrations of Na+ and Cl- o Intracellular fluid contains high concentrations of K+ and negatively charged proteins  Cells have selectively permeable membranes  Membrane permeability varies by ion Passive Processes Acting across the Plasma Membrane: The Electrochemical Gradient. Current: movement of charges to eliminate a potential difference. Resistance: how much the membrane restricts ion movement.  If resistance is high, current is small Chemical gradients: concentration gradients of ions (Na+, K+). Electrical gradients: charges are separated by cell membrane.  Intracellular is negative relative to extracellular fluid Electrochemical gradient: sum of chemical and electrical forces acting on an ion across the membrane.  A form of potential energy Equilibrium Potential Equilibrium potential: membrane potential at which there is no net movement of a ion across cell membrane.  K+ = -90 mV  Na+ = +66 mV  Plasma membrane is HIGHLY permeable to K+  o Similarity of equilibrium potential for K+ and resting membrane potential  Resting membrane’s permeability to Na+ is very low o Na+ has a small effect on resting potential Active Processes across the Membrane: The Sodium-Potassium Exchange Pump Sodium-Potassium Exchange Pump  Powered by ATP  Ejects 3 Na+ for every 2 K+ brought in  Stabilizes resting membrane potential (-70 mV) Resting membrane potential exists because…  Intracellular differs from extracellular fluid in chemical and ionic composition.  Plasma membrane is selectively permeable. Membrane potential changes in response to temporary changes in membrane permeability that results from opening or closing of specific membrane channels in response to stimuli. Changes in the Resting Membrane Potential: Membrane Channels Na+ and K+ are the primary determinants of membrane potential and are either active or passive. Passive Ion Channels Passive (leak) ion channels: always open and permeability changes with conditions. Active Ion Channels Active (gated) ion channels: open and close in response to stimuli and at resting membrane potential, most are closed. There are three types of active ion channels: chemically (ligand) gated, voltage-gated, and mechanically gated. Chemically (ligand) gated ion channel: open when they bind to specific chemicals.  Found on cell body and dendrites of neurons Voltage-gated ion channel: respond to changes in membrane potential.  Found in axons of neurons and sarcolemma of skeletal and cardiac muscle cells  Activation gate opens when stimulated  Inactivation gate closes to stop ion movement There are three possible states…  Closed but capable of opening  Open (activated)  Closed and incapable of opening (inactivated) Mechanically gated ion channel: respond to membrane distortion.  Found in sensory receptors that respond to touch, pressure, or vibration Graded Potentials Graded potential: changes in membrane potential.  Cannot spread far from the stimulation  Produced by any stimulus that opens gated channels Depolarization: membrane potential rises. Local current: sodium ions move parallel to plasma membrane, which depolarizes nearby regions of plasma membrane.  Change in potential is proportional to stimulus Repolarization: membrane potential returns to normal, after stimulus is removed. Hyperpolarization: increases the negativity of the resting potential.  Results from opening potassium ion channels o Positive ions move out, not into cell o Opposite effect of opening sodium ion channels Characteristics of Graded Potentials  Membrane potential is most changed at site of stimulation; effect decreases with distance  Effect spreads passively, due to local currents  Graded change in membrane potential may involve depolarization or hyperpolarization  Stronger stimuli produce greater changes in membrane potential and affect a larger area Graded potentials often trigger specific cell functions. Ex. ACh causes graded potential at motor end plate at neuromuscular junction. *** Draw figure 12-12, Depolarization, Repolarization, and Hyperpolarization. *** 12-5 An Action Potential is an All-or-None Electrical Event Used for Long-Distance Communication. Action potential: changes in the membrane potential that affect an entire excitable membrane, also called nerve impulses.  Propagated changes in membrane potential  Begin at initial segment of axon  DON’T diminish as they move away from the source Threshold and the All-or-None Principle Threshold: membrane potential at which an action potential begins.  Threshold for an axon is -60 mV to -55 mV All-or-none principle states that…  any stimulus that changes the membrane potential to threshold will cause an action potential  All action potentials are the same, no matter how large the stimulus  An action potential is either triggered or not Generation of Action Potentials 1. Depolarization to threshold 2. Activation of voltage-gated Na+ channels  Na+ rushes in intracellular fluid  Inner membrane surface changes from negative to positive  Results in rapid depolarization 3. Inactivation of Na+ channels and activation of K+ channels  At +30 mV, inactivation gates of voltage-gated Na+ channels close  Voltage-gated K+ channels open  K+ moves out of intracellular fluid  Repolarization begins 4. Return to resting membrane potential  Voltage-gated K+ channels begin to close o As membrane reaches normal resting potential o K+ continues to leave cell o Membrane is briefly hyperpolarized to -90 mV  After all voltage-gated K+ channels finish closing o Resting membrane potential is restored o Action potential is over The Refractory Period Refractory period: beginning of action potential to return to resting state.  During which the membrane will not respond normally to additional stimuli Absolute refractory period: membrane cannot respond to any further stimulation.  All voltage-gated Na+ channels are already open or inactivated Relative refractory period: begins when Na+ channels regain resting condition and continues until membrane potential stabilizes, and ONLY a strong stimulus can initiate another action potential. Depolarization results from influx of Na+. Repolarization involves loss of K+. The Role of the Sodium-Potassium Exchange Pump  Returns concentrations to prestimulation levels  Maintains concentration gradients of Na+ and K+ over time o Uses one ATP for exchange of two extracellular K+ for three intracellular Na+ Propagation of Action Potentials Propagation: moving an action potential along an axon in a series of steps. Types of Propagation There are two types of propagation: continuous propagation and saltatory propagation. Continuous propagation: affects one segment of an axon at a time, in UNMYELINATED axons. 1. Action potential develops at initial segment. o Depolarizes membrane to +30 mV 2. Local current develops. o Depolarizes second segment to threshold 3. Action potential occurs in second segment. o Initial segment begins repolarization 4. Local current depolarizes next segment 5. Cycle repeats. o Action potential travels in one direction (1 m/sec) Saltatory propagation: local current “jumps” from node to node, occurs in MYELINATED axons.  Faster than continuous propagation, requires less energy  Myelin prevents continuous propagation  Depolarization ONLY occurs at nodes  1. Action potential develops at initial segment. 2. Local current produces a graded depolarization that brings the axolemma at the next node to threshold. 3. An action potential develops at the next node. 4. Cycle repeats. Axon Diameter and Propagation Speed Type A fibers: large diameter, myelinated fibers used to transmit information to and from CNS rapidly. (120 m/sec)  Sensory information such as position and balance  Motor impulses to skeletal muscles Type B fibers: medium diameter, myelinated fibers used to transmit information at medium speed. (18 m/sec) Type C fibers: small diameter, used to transmit information slowly. (1 m/sec)  Mostly sensory information 12-6 Synapses Transmit Signals Among Neurons or Between Neurons and Other Cells. Synapse: specialized site where a neuron communicates with another cell.  Presynaptic neuron: sends the message.  Postsynaptic neuron: receives the message. Types of Synapses There are two types of synapses: electrical and chemical synapse. Electrical synapse: direct physical contact between cells.  Presynaptic and postsynaptic membranes are locked together at gap junctions  Ions pass between cells through pores  Local current affects both cells  Action potentials are propagated quickly  Found in some areas of the brain, eye, and ciliary ganglia Chemical synapse: signal transmitted across a gap by neurotransmitters.  Most common type of synapse between neurons  Only type of synapse between neurons and other cells  Cells are separated by synaptic cleft There are two types of chemical synapses: neuromuscular and neuroglandular junctions. Neuromuscular junction: synapse between neuron and skeletal muscle cell. Neuroglandular junction: synapse between neuron and gland cell. Presynaptic cell: sends the message. Postsynaptic cell: receives the message. Synaptic cleft: a narrow space that separates the two cells. Neurotransmitters: chemical messengers contained within synaptic vesicles in axon terminal of presynaptic cell.  Released into synaptic cleft  Affect receptors of postsynaptic membrane  Broken down by enzymes  Reabsorbed and reassembled by axon terminal Function of Chemical Synapses  Axon terminal releases neurotransmitters that bind to postsynaptic plasma membrane o Produces localized change in permeability and graded potentials  Action potential may or may not be generated in postsynaptic cell, depending on… o Amount of neurotransmitter released o Sensitivity of postsynaptic cell Examples of Chemical Synaptic Function: Cholinergic Synapses Cholinergic synapses: release ACh at…  All neuromuscular junctions involving skeletal muscle fibers  Many synapses in CNS  All neuron-to-neuron synapses in PNS  All neuromuscular and neuroglandular junctions in parasympathetic division of ANS Events at a Cholinergic Synapse An action potential arrives at the presynaptic axon terminal and depolarizes the membrane. Extracellular calcium ions enter the axon terminal, triggering the exocytosis of ACh in synaptic vesicles. ACh binds to receptors on the postsynaptic membrane and depolarizes the membrane. ACh is removed from the synaptic cleft by AChE. Acetylcholinesterase (AChE): an enzyme that breaks down ACh into acetate and choline. Synaptic Delay Synaptic delay: a delay of 0.2-0.5 m/sec that occurs between arrival of action potential at axon terminal and effect on postsynaptic membrane.  Mostly due to time required for calcium ion influx and neurotransmitter release   Fewer synapses lead to faster responses o Some reflexes involve only one synapse Synaptic Fatigue Synaptic fatigue: occurs when neurotransmitter cannot be recycled fast enough to meet demands of intense stimuli.  Response of synapse weakens until ACh is replenished 12-7 The Effects of Neurotransmitters and Neuromodulators Depend on their Receptors. Excitatory neurotransmitters: causes depolarization of postsynaptic membranes.  Promotes action potentials Inhibitory neurotransmitters: causes hyperpolarization of postsynaptic membranes.  Suppresses action potentials Classes of Neurotransmitters and Neuromodulators Biogenic Amines Norepinephrine (NE)  Released by adrenergic synapses  Excitatory and depolarizing effect  Widely distributed in brain and portions of ANS Dopamine  May be excitatory or inhibitory  A CNS neurotransmitter  Involved in Parkinson’s disease and cocaine use Serotonin  A CNS neurotransmitter  Affects attention and emotional states Amino Acids Gamma-Aminobutyric Acid (GABA)  Inhibitory effect  Functions in CNS and is not well understood Neuropeptides Neuromodulators: chemicals released by axon terminals that alter rate of neurotransmitter release or response by postsynaptic cell.  Effects are long term and slow to appear  Affect presynaptic membrane, postsynaptic membrane, or both  Released alone or with a neurotransmitter Opioids: bind to the same receptors as opium and morphine.  There are three main classes of opioids: enkephalins, endorphins, and dynorphins Dissolved Gases Nitric Oxide (NO) Carbon Monoxide (CO) The Functions of Neurotransmitters and Neuromodulators and Their Receptors Direct Effects A direct effect on membrane potential by opening or closing chemically gated ion channels. Ex. ACh, glutamate, aspartate. Indirect Effects by Second Messengers An indirect effect through G proteins. Ex. E, NE, dopamine, serotonin, histamine, GABA. Indirect Effects by Intracellular Enzymes An indirect effect via intracellular enzymes. Ex. lipid-soluble gases (NO,CO). 12-8 Individual Neurons Process Information by Integrating Excitatory and Inhibitory Stimuli. Postsynaptic Potentials Postsynaptic potential: graded potential developed in a postsynaptic cell, in response to neurotransmitters. There are two types of postsynaptic potentials: EPSP and IPSP. Excitatory postsynaptic potential (EPSP): graded depolarization of postsynaptic membrane. Inhibitory postsynaptic potential (IPSP): graded hyperpolarization of postsynaptic membrane.  A neuron that receives many IPSPs is inhibited from producing an action potential because the stimulation needed to reach threshold is increased Integrating Postsynaptic Potentials: Summation Summation: combining EPSPs and IPSPs. There are two types of summation: temporal and spatial summation. Temporal summation: rapid, repeated stimuli at a single synapse. Spatial summation: simultaneous stimuli arrive at multiple synapses. Chapter 14: The Brain and Cranial Nerves An Introduction to the Brain and Cranial Nerves The Brain Develops Four Major Regions: Cerebrum, Cerebellum, Diencephalon, and Brainstem. Major Brain Regions and Landmarks There are four major regions: the cerebrum, cerebellum, diencephalon, and brainstem. Cerebrum Cerebrum: largest part of adult brain.  Controls higher mental functions o Conscious thoughts, intellect, memory, etc.  Divided into left and right cerebral hemispheres Cerebral hemispheres: left and right sides of cerebrum. Cerebral cortex: surface layer of gray matter in the cerebrum. Gyri: rounded elevations that increase surface area. Sulci: shallow depressions. Fissures: deep grooves. Cerebellum Cerebellum: second largest part of brain.  Coordinates repetitive body movements  Divided into left and right cerebellar hemispheres Cerebellar hemispheres: left and right sides of cerebellum. Cerebellar cortex: surface layer of gray matter in the cerebellum. Diencephalon Diencephalon: located under cerebrum and cerebellum.  Thalamus: relays and processes sensory information  Hypothalamus: involved with emotions, autonomic function, and hormone production Infundibulum: a narrow stalk that connects pituitary gland to hypothalamus. Pituitary gland: major endocrine gland that integrates nervous and endocrine systems. Brainstem The brainstem includes the midbrain, pons, and medulla oblongata. Brainstem: relays information between spinal cord and cerebrum or cerebellum. Midbrain: processes sight, sound, and associated reflexes. Pons: connects cerebellum to brainstem.  Contains o Tracts: (collections of CNS axons) o Relay centers o Nuclei for somatic and visceral motor control Medulla oblongata: connects brain to spinal cord.  Inferior portion has a narrow central canal  Relays sensory information  Regulates autonomic functions o Heart rate, blood pressure, and digestion Central canal: narrow inferior portion of medulla oblongata. Ventricles of the Brain Ventricles: chambers within brain, lined with ependymal cells. There are four ventricles in the brain: two lateral ventricles, third ventricle, and fourth ventricle. Lateral ventricles: ventricle in each cerebral hemisphere, separated by septum pellucidum. Third ventricle: in diencephalon, communities with each lateral ventricle via interventricular foramen. Fourth ventricle: extends into medulla oblongata, joins central canal of spinal cord and connects with third ventricle via narrow canal in midbrain called the cerebral aqueduct. 14-2 The Brain is Protected and Supported by the Cranial Meninges, Cerebrospinal Fluid, and the Blood Brain Barrier. Physical Protection of the Brain  Bones of the cranium  Cranial meninges  Cerebrospinal fluid Biochemical Isolation  Blood brain barrier The Cranial Meninges Cranial meninges: three layers that are continuous with spinal meninges. There are three cranial meninges: the dura mater, the arachnoid mater, and the pia mater. Dura Mater and Dural Folds Dura mater: tough outermost layer  Inner fibrous layer (meningeal cranial dura)  Outer fibrous layer (periosteal cranial dura) Dural folds: extensions of meningeal cranial dura into cranial cavity that stabilize and support brain, contains collecting veins called dural venous sinuses. The three largest dural folds: falx cerebri, tentorium cerebelli, and falx cerebelli. Falx cerebri: projects between cerebral hemispheres.  Superior sagittal sinus  Inferior sagittal sinus Tentorium cerebelli: separates cerebrum from cerebellum.  Transverse sinus Falx cerebelli: divides cerebellar hemispheres below the tentorium cerebelli. Subdural space: space between dura mater and arachnoid mater. Arachnoid Mater Arachnoid mater: covers brain and attaches to dura mater.  May be separated by subdural space Subarachnoid space: space between arachnoid mater and pia mater. Pia Mater Pia mater: attached to brain surface by astrocytes. Cerebrospinal Fluid Cerebrospinal fluid (CSF): surrounds all exposed surfaces of CNS. The CSF has several important functions including…  Support brain  Cushion delicate neural structures  Transport nutrients, chemical messengers, and wastes The Formation and Circulation of CSF Choroid plexus: produces CSF.  Specialized ependymal cells surround capillaries   Secretes 500mL of CSF into ventricles each day  Removes waste from CSF  Adjusts composition of CSF CSF Circulation  From choroid plexus  Through ventricles  To central canal of spinal cord  Into subarachnoid space o Via two lateral apertures and one median aperture in roof of fourth ventricle o To surround brain, spinal cord, and cauda equina The Protective Function of the Cranial Meninges and CSF  Dural folds hold the brain in position o Protecting it from damage that would result from contact with cranium  CSF cushions brain against sudden jolts Cranial trauma: head injury resulting from impact with an object. The Blood Supply to the Brain Blood supply to the brain is by internal carotid and vertebral arties. Most blood is removed by dural venous sinuses by internal jugular veins. Cerebrovascular disease: disorders that interfere with blood supply to brain. Cerebrovascular accident (CVA): stops blood flow to a portion of the brain, affected neurons begin to die within minutes, also called a stroke. The Blood Brain Barrier Blood brain barrier (BBB): isolates CNS from general circulation.  Formed by network of tight junctions between capillary endothelial cells in CNS  Generally, only lipid-soluble compounds like O2, CO2, steroids, prostaglandins, and alcohols can diffuse into interstitial fluid of CNS  Astrocytes regulate BBB by releasing chemicals that control permeability of endothelium There are breaks in the BBB…  Portions of the hypothalamus o Allows hypothalamic hormones into circulation  Posterior lobe of pituitary gland o Allows ADH and oxytocin into circulation  Pineal gland o Allows pineal secretions into circulation  Choroid plexus  o Where specialized ependymal cells maintain blood CSF barrier Blood CSF barrier: limits transfer of substances to CSF and allows chemical composition of blood and CSF to differ.  Formed by specialized ependymal cells connected by tight junctions that surround capillaries of choroid plexus 14-3 Brainstem: The Medulla Oblongata Relays Signals between the Rest of the Brain and the Spinal Cord. Medulla oblongata: most inferior part of the brainstem.  Coordinates complex autonomic reflexes  Includes three groups of nuclei o Control visceral functions o Sensory and motor functions of CNS o Relay stations for communication between brain and spinal cord Reflex Centers  Reticular formation: regulates autonomic functions o Gray and white matter with embedded nuclei  Cardiovascular centers: cardiac and vasomotor centers that control blood flow through peripheral tissues  Respiratory rhythmicity centers: set pace for respiratory movements 14-4 Brainstem: The Pons contains Nuclei that Process and Tracts that Relay Sensory and Motor Information. Pons: links the cerebellum with the midbrain, diencephalon, cerebrum, and spinal cord. The pons contains four groups of components…  Sensory and motor nuclei of cranial nerves  Nuclei involved with the control of respiration  Nuclei and tracts that process and relay information sent to or from cerebellum  Ascending, descending, and transverse pontine fibers o Transverse pontine fibers (axons) link nuclei of pons with OPPOSITE cerebellar hemisphere 14-5 Brainstem: The Midbrain Regulates Visual and Auditory Reflexes and Controls Alertness. Structures of the Midbrain Tectum: roof of the midbrain, posterior to the cerebral aqueduct.  Corpora quadrigemina: two pairs of sensory nuclei o Superior colliculi: visual o Inferior colliculi: auditory Tegmentum:  Red nucleus: many blood vessels  Substantia nigra: pigmented gray matter, *** the black stuff *** Cerebral peduncles: nerve fiber bundles on ventrolateral surfaces contain…  Descending fibers to cerebellum  Descending motor command fibers 14-6 The Cerebellum Coordinates Reflexive and Learned Patterns of Muscular Activity at the Subconscious Level. Structures of the Cerebellum Cerebellar cortex: gray matter of highly convoluted surface. Folia: folds in cerebellar cortex. Anterior and posterior lobes  Separated by primary fissure Cerebellar hemispheres Vermis: narrow band of cortex that separates cerebellar hemispheres at midline. Flocculonodular lobe: lies above roof of fourth ventricle. Purkinje cell layer: large, branched neuron cell bodies, in cerebellar cortex that each cell receives input from up to 200,000 synapses. Arbor vitae (tree of life): highly branched, internal white matter of cerebellum.  Cerebellar nuclei: embedded in arbor vitae, relays information to purkinje cells Functions of the cerebellum are to…  Adjust postural muscles  Program and fine-tune conscious and subconscious movements Cerebellar peduncles: tracts that link cerebellum with brainstem, cerebrum, amd spinal cord and leave the cerebellum as…   Superior cerebellar peduncles  Middle cerebellar peduncles  Inferior cerebellar peduncles Disorders of the Cerebellum Ataxia: a disturbance in muscular coordination.  Caused by… o Permanent damage from trauma or stroke o Temporary impairment from intoxication 14-7 The Diencephalon Integrates Sensory Information with Motor Output at the Subconscious Level. Diencephalon Diencephalon integrates sensory information with motor commands. The diencephalon includes the epithalamus, thalamus, and hypothalamus. Epithalamus The pineal gland is in the posterior portion of the epithalamus and secretes melatonin. Thalamus The thalamus filters and relays sensory information from spinal cord and cranial nerves to cerebral cortex.  The third ventricle separates into left and right sides  Interthalamic adhesion: projection of gray matter, extends into third ventricle on each side Hypothalamus Mamillary bodies: control reflex eating movements. Infundibulum: narrow stalk that connects hypothalamus to pituitary gland. Tuber cinereum: produces hormones that affect pituitary gland.  Between infundibulum and mamillary bodies. The hypothalamus has eight major functions…  Secretes ADH and oxytocin  Regulates body temperature  Controls autonomic function  Coordinate voluntary and autonomic functions   Coordinates nervous and endocrine systems  Regulates circadian rhythms  Subconscious control of skeletal muscle  Produces emotions and behavioral drives o Feeding center o Thirst center o Satiety center 14-8 The Limbic System is a Group of Nuclei and Tracts that Functions in Emotion, Motivation, and Memory. Functional grouping that…  Establishes emotional states  Links conscious functions of cerebral cortex with autonomic functions of brainstem  Facilitates memory storage and retrieval Components of the Limbic System  Limbic lobe of cerebral hemisphere  Cingulate gyrus  Dentate gyrus  Parahippocampal gyrus  Hippocampus  Amygdaloid body: acts as interface between the limbic system, cerebrum, and various sensory systems  Fornix: tract of white matter connects hippocampus with hypothalamus  Anterior nuclei of thalamus: relay information from mamillary body to cingulate gyrus  Reticular formation: alertness, excitement lethargy, and sleep 14-9 The Cerebrum Contains Motor, Sensory, and Association Areas, Allowing for Higher Mental Functions. Cerebrum  Largest part of the brain  Controls all conscious thoughts and intellectual functions  Processes somatic sensory and motor information  Gray matter o In cerebral cortex and basal nuclei  White matter o Deep to cerebral cortex, around basal nuclei Structures of the Cerebrum Gyri of cerebral cortex: increase surface area for neurons. Longitudinal cerebral fissure: separates cerebral hemispheres. Lobes: regions of hemisphere. Central sulcus: divides anterior frontal lobe from posterior parietal lobe. Precentral gyrus: in frontal lobe, forms anterior border of central sulcus. Postcentral gyrus: in parietal lobe, forms posterior border of central sulcus. Lateral sulcus: separates frontal lobe from temporal lobe. Insula: lies medial to lateral sulcus, also called island of cortex. Parieto-occipital sulcus separates parietal lobe from occipital lobe. White Matter of the Cerebrum Association fibers: form connections within one hemisphere.  Arcuate fibers: short fibers that connect one gyrus to another.  Longitudinal fasiciculi: longer bundles that connect frontal lobe to other lobes in same hemisphere. Commissural fibers: bands of fibers connecting two hemispheres.  Corpus callosum  Anterior commissure Projection fibers: link cerebral cortex to diencephalon, brainstem, cerebellum, and spinal cord.  Internal capsule: all ascending and descending projection fibers. Basal Nuclei Basal nuclei: masses of gray matter.  Embedded in white matter of cerebrum  Directs subconscious activities Caudate nucleus: large head and slender, curving tail. Lentiform nucleus  Putamen (lateral)  Globus pallidus (medial) Claustrum: thin layer of gray matter close to putamen. Functions of Basal Nuclei   Subconscious control of skeletal muscle tone  Coordination of learned movement patterns (walking, lifting, etc.) Parkinson’s disease  Symptoms are caused by increased activity of basal nuclei Functional Principles of the Cerebrum Cortex of each cerebral hemisphere  Receives somatosensory information from and sends motor commands to the opposite side of the body.  Correspondence between a specific function and a specific area of the cerebral cortex is imprecise. The central sulcus separates motor and sensory areas. Motor Areas  Primary motor cortex: surface of precentral gyrus.  Pyramidal cells: neurons of primary motor cortex Sensory Areas  Primary somatosensory cortex: surface of postcentral gyrus. Special Sensory Cortices  Visual cortex: receives visual information.  Auditory cortex: receives information about hearing.  Olfactory cortex: receives information about smell.  Gustatory cortex: receives information from taste receptors. Association areas: connected to sensory and motor regions of cortex to interpret incoming data or coordinate a motor response. Premotor cortex: coordinates learned movements, also called somatic motor association area. Sensory Association Areas  Somatosensory association cortex: monitors activity in primary somatosensory cortex.  Visual association area: interprets activity in visual cortex.  Auditory association area: monitors auditory cortex. Integrative Centers In the lobes and cortical areas of both cerebral hemispheres that receive information from association areas and directs complex motor activities and perform analytical functions. Wernicke’s area: language comprehension. *** Think brain dictionary ***   Primarily associated with left cerebral hemisphere  Receives information from sensory association areas  Coordinates access to visual and auditory memories Broca’s area: speech production.  Primarily associated with left cerebral hemisphere  Regulates patterns of breathing and vocalization Prefrontal cortex of frontal lobe: coordinates information relayed from all cortical association areas.  Performs abstract intellectual functions. Ex. predicting consequences of actions.  Prefrontal lobotomy o Used to “cure” mental illness in mid 20-th century Hemispheric lateralization: functional differences between left and right cerebral hemispheres.  Each performs certain functions that are not ordinarily performed by the opposite hemisphere o Left cerebral hemisphere  Reading, writing, and math  Speech and language  Decision making o Right cerebral hemisphere  Analyzes sensory information Ex. touch, smell, sight, taste.  Recognition of faces and voice inflections Brain Activity Assessed with electroencephalogram (EEG)  Electrodes are placed on brain or skull and electrical patterns (brain waves) are observed There are four types of typical brain waves: alpha, beta, theta, and delta. Alpha waves: seen in healthy, awake adults at rest with eyes closed. Beta waves: seen in adults who are concentrating or mentally stressed.  Higher-frequency waves Theta waves: seen in children and in intensely frustrated adults. *** Imagination waves ***  May indicate brain disorder in adults Delta waves: seen in sleeping infants and in awake adults with brain damage.  Large-amplitude, low-frequency waves Synchronization of electrical activity between hemispheres is achieved through a “pacemaker” mechanism.  Desynchronization may result from injury or tumor Seizure: a temporary cerebral disorder that are accompanied by changes in electrical activity.  Symptoms depend on region of cortex affected. 14-10 Cranial reflexes are rapid, automatic responses involving sensory and motor fibers of cranial nerves. Cranial nerves: 12 pairs of nerves connected to brain. Classifications of Cranial Nerves  Primarily sensory: carriers of somatic sensory o Touch, pressure, vibration, temperature, and pain  Special sensory: carriers of sensations o Smell, sight, hearing, and balance  Motor: axons of somatic motor neurons  Mixed: sensory and motor fibers Cranial nerves are classified by primary functions and may also have important secondary functions. Olfactory nerve (I): smell (special sensory) Optic nerve (II): vision (special sensory) Oculomotor nerve (III): eye movements (motor) Trochlear nerve (IV): eye movements (motor) Trigeminal nerve (V): face (mixed) Abducens nerve (VI): eye movements (motor) Facial nerve (VII): face (mixed) Vestibulocochlear nerve (VIII): balance and equilibrium, and hearing (special sensory) Glossopharyngeal nerve (IX): head and neck (mixed) Vagus nerve (X): widely distributed in thorax and abdomen (mixed) Accessory nerve (XI): muscles of neck and upper back (motor) Hypoglossal nerve (XII): tongue movements (motor) Cranial Reflexes Cranial reflexes: automatic responses to stimuli that involve the sensory and motor fibers of cranial nerves.  Monosynaptic and polysynaptic reflex arcs that involve sensory and motor fibers of cranial nerves  Clinically useful to check condition of cranial nerves and parts of brain